| 1. |
- Gong, Guan, et al.
(författare)
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Development of electrophoretic deposition prototype for continuous production of carbon nanotube-modified carbon fiber fabrics used in high-performance multifunctional composites
- 2018
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Ingår i: Fibers. - : MDPI AG. - 2079-6439. ; 6:4
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Tidskriftsartikel (refereegranskat)abstract
- An electrophoretic deposition (EPD) prototype was developed aiming at the continuous production of carbon nanotube (CNT) deposited carbon fiber fabric. Such multi-scale reinforcement was used to manufacture carbon fiber-reinforced polymer (CFRP) composites. The overall objective was to improve the mechanical performance and functionalities of CFRP composites. In the current study, the design concept and practical limit of the continuous EPD prototype, as well as the flexural strength and interlaminar shear strength, were the focus. Initial mechanical tests showed that the flexural stiffness and strength of composites with the developed reinforcement were significantly reduced with respect to the composites with pristine reinforcement. However, optical microscopy study revealed that geometrical imperfections, such as waviness and misalignment, had been introduced into the reinforcement fibers and/or bundles when being pulled through the EPD bath, collected on a roll, and dried. These defects are likely to partly or completely shadow any enhancement of the mechanical properties due to the CNT deposit. In order to eliminate the effect of the discovered defects, the pristine reinforcement was subjected to the same EPD treatment, but without the addition of CNT in the EPD bath. When compared with such water-treated reinforcement, the CNT-deposited reinforcement clearly showed a positive effect on the flexural properties and interlaminar shear strength of the composites. It was also discovered that CNTs agglomerate with time under the electric field due to the change of ionic density, which is possibly due to the electrolysis of water (for carboxylated CNT aqueous suspension without surfactant) or the deposition of ionic surfactant along with CNT deposition (for non-functionalized CNT aqueous suspension with surfactant). Currently, this sets time limits for the continuous deposition.
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| 2. |
- Gong, Guan, et al.
(författare)
-
SCALING-UP PRODUCTION OF CNT-COATEDFIBRE REINFORCEMENT USING CONTINUOUS EPDFOR HIGH-PERFORMANCE ANDMULTIFUNCTIONAL COMPOSITES
- 2018
-
Konferensbidrag (refereegranskat)abstract
- Itis important within the composite community to improve out-of-plane performance ofcomposites dominated by polymer matrix and properties of matrix-rich regions formed in the gapsbetween the interlaced fibre bundles. These properties are difficult to modify with traditional fibrereinforcement. Various nanoscale materials have been explored for such purpose, among which carbonnanotube (CNT) has been suggested as an ideal candidate because of its outstanding mechanical,electrical and thermal properties (1). Electrophoretic deposition (EPD) is considered as a cost-effectivemethod to deposit CNTs onto substrates with mild working conditions, requiring relatively simpleequipment and being amenable to scaling up (2,3). Due to the shortcoming of existing laboratory setupwhich corresponds to a non-continuous process, EPD has not been used at even a pilot plant scale fornano-coated fibre reinforcement. The current work presents the development of a prototype andmethod for continuous EPD process. Geometric defect of fibre reinforcement introduced during thedeposition, which can shadow the reinforcing effect of CNT deposit, was discovered. Enhancement ofcomposite properties by the CNT deposit was hence shown.
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| 3. |
- Joffe, Roberts, et al.
(författare)
-
Nonlinear behavior of natural fiber/bio-based matrix composites
- 2013
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Ingår i: Challenges in Mechanics of Time-Dependent Materials and Processes in Conventional and Multifunctional Materials. - New York : Encyclopedia of Global Archaeology/Springer Verlag. - 9781461442400 ; , s. 131-137
-
Konferensbidrag (refereegranskat)abstract
- The rising concern about the dependence on synthetic polymers and oil has motivated research on competitive bio-based replacement materials. Some of the often considered bio-based thermoplastics are starch, polylactic acid (PLA) and rather recently, lignin. These bio-plastics in combination with natural fibers (flax, hemp, wood) are used to manufacture whole bio-based composites. Although there are certain direct benefits to use natural fibres in composites, their performance is often very nonlinear. Moreover, properties of these materials are very sensitive to moisture and temperature. The behavior of these composites has to be studied and mechanisms occurring during the loading must be identified. The effect of temperature and relative humidity on mechanical behavior of natural fiber reinforced bio-based matrix composites subjected to the tensile loading was investigated. Time dependent behavior of these materials is analyzed. Testing methodology is suggested to identify sources of nonlinearities observed in stress-strain curves. It was found that microdamage accumulation and stiffness reduction is significant for some of the composites but the major nonlinear phenomena are related to nonlinear viscoelasticity and viscoplasticity. Material models accounting for these effects are proposed and their predictive capability is demonstrated.
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| 4. |
- Kahla, Hiba Ben, et al.
(författare)
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Microcracking in layers of composite laminates in cyclic loading with tensile transverse stress component in layers
- 2015
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Ingår i: ICCM International Conferences on Composite Materials. - : International Committee on Composite Materials.
-
Konferensbidrag (refereegranskat)abstract
- Intralaminar cracking in layers of a quasi-isotropic carbon fiber NCF laminate in tension-tension cyclic loading is studied experimentally. Methodology based on modified Weibull analysis is suggested to combine quasi-static and fatigue testing to identify parameters in the crack density growth model. The validity of the assumptions for the given material is experimentally confirmed. The suggested methodology can lead to significant time and material savings in composites fatigue behaviour characterization.
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| 5. |
- Kahla, Hiba Ben, et al.
(författare)
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Statistical model for initiation governed intralaminar cracking in composite laminates during tensile quasi-static and cyclic tests
- 2018
-
Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 116, s. 1-12
-
Tidskriftsartikel (refereegranskat)abstract
- A simple model for predicting intralaminar cracking in laminates under cyclic loads is proposed and validated. The model is limited to low stresses and low crack density and is based on the assumption that the non-uniformity of the fiber distribution is the main reason for the observed large variation of cracking resistance along the transverse direction of the layer. Hence, the resistance variation in quasi-static and in cyclic loading can be described by the same parameter. At low crack density the failure resistance variation is more significant than the variation of the stress state in the specimen, the latter becoming dominant at high crack density. At low crack density the Weibull distribution for probability of intralaminar cracking is used for crack density growth simulation during cyclic loading. Assuming the non-uniformity of the fiber distribution as the cause for variation of cracking resistance, the Weibull shape parameter in cyclic loading is the same as in quasi-static loading case while the scale parameter is assumed to degrade with the applied number of cycles and this dependence is described by a power function. Thus, the determination of parameters is partially done using quasi-static tests and partially using cyclic tests, significantly reducing the necessary testing time. The predictions of dependency of the cracking on the stress and number of cycles are validated against experimental observations of cracking in the 90-plies of quasi-isotropic non-crimp fabric (NCF) laminates as well as in tape based cross-ply laminates.
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| 6. |
- Leijonmarck, Simon, et al.
(författare)
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Strength of thin solid polymer electrolyte coatings and the coated carbon fibres
- 2015
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Ingår i: ICCM International Conferences on Composite Materials. - : International Committee on Composite Materials. ; 2015
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Konferensbidrag (refereegranskat)abstract
- As a route to increase the efficiency of electric vehicles, weight reductions through composite building materials are constantly being introduced. To further aid this effort focus has been put on structural batteries, where the composite is multifunctional serving both as energy storing as well as load bearing unit. In an attempt to reduce the high ionic resistances solid polymer electrolytes introduces, carbon fibres have been individually coated with polymeric layers ranging from <500 nm to >3 µm in thickness. This study investigates the feasibility of using such coatings in structural applications with respect to mechanical load cycling. The coated fibres were subjected to cyclic load up to approximately 1 % strain for up to 70,000 cycles. The polymer coatings were found not to be visibly affected by the prolonged mechanical fatigue. No cracks were observed in the coatings which makes the coating technique promising for future structural battery applications.
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| 7. |
- Loukil, Mohamed Sahbi, et al.
(författare)
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Thermoelastic constants of symmetric laminates with cracks in 90-layer: application of simple models
- 2013
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Ingår i: Plastics, rubber and composites. - : Taylor & Francis. - 1465-8011 .- 1743-2898. ; 42:4, s. 157-166
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Tidskriftsartikel (refereegranskat)abstract
- The change of thermoelastic properties of cross-ply and quasi-isotropic laminates with intralaminar cracks in layers is analysed. Predictions are performed using previously derived general expressions for stiffness of symmetric damaged laminates as dependent on crack density and crack face opening and sliding. It is shown that the average crack opening displacement can be linked with the average value of axial stress perturbation between two cracks. Using this relationship, analytical shear lag and Hashin’s models, developed for axial modulus, can be applied for calculating thermal expansion coefficients, in-plane moduli and Poisson’s ratios of damaged laminates. The approach is evaluated using finite element method and it is shown that the accuracy is rather similar to that in axial modulus calculation.
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| 8. |
- Pupure, Liva, et al.
(författare)
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An analysis of the nonlinear behavior of lignin-based flax composites
- 2013
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Ingår i: Mechanics of composite materials. - : Springer Science and Business Media LLC. - 0191-5665 .- 1573-8922. ; 49:2, s. 139-154
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Tidskriftsartikel (refereegranskat)abstract
- A lignin composite reinforced with 30% flax fibers at two levels of relative humidity, 34 and 66%, was used in this study. The nonlinearity of the composite was analyzed by studying the degradation of its modulus and the development of viscoelastic and viscoplastic strains. The reduction in the modulus of lignin-based composites in tension starts before the maximum in the stress-strain curve is reached and can be as large as 50%. With increasing relative humidity, these effects are slightly magnified. The time-dependent phenomena in tension were examined in short-term creep and strain recovery tests, demonstrating a rather high viscoplastic strain in lignin composites. Both viscoelastic and viscoplastic strains are larger at a higher relative humidity
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| 9. |
- Pupurs, Andrejs, et al.
(författare)
-
3-D fem modeling of fiber/matrix interface debonding in UD composites including surface effects
- 2012
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Ingår i: 6th EEIGM International Conference Advanced Materials Research. - Bristol : IOP Publishing Ltd.
-
Konferensbidrag (refereegranskat)abstract
- Fiber/matrix interface debond growth is one of the main mechanisms of damage evolution in unidirectional (UD) polymer composites. Because for polymer composites the fiber strain to failure is smaller than for the matrix multiple fiber breaks occur at random positions when high mechanical stress is applied to the composite. The energy released due to each fiber break is usually larger than necessary for the creation of a fiber break therefore a partial debonding of fiber/matrix interface is typically observed. Thus the stiffness reduction of UD composite is contributed both from the fiber breaks and from the interface debonds. The aim of this paper is to analyze the debond growth in carbon fiber/epoxy and glass fiber/epoxy UD composites using fracture mechanics principles by calculation of energy release rate GII. A 3-D FEM model is developed for calculation of energy release rate for fiber/matrix interface debonds at different locations in the composite including the composite surface region where the stress state differs from the one in the bulk composite. In the model individual partially debonded fiber is surrounded by matrix region and embedded in a homogenized composite.
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| 10. |
- Pupurs, Andrejs, et al.
(författare)
-
Analiz rasprostranenia poteri sceplenia v kompozite s odinochnym voloknom pri ciklicheskom nagruzhenii metodom mekhaniki razrushenia
- 2011
-
Ingår i: Mechanika kompozitnych materialov. - 0203-1272. ; 47:1, s. 151-174
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Tidskriftsartikel (refereegranskat)abstract
- A model is developed to analyze fiber/matrix debond growth along the broken fiber interface in a single fiber composite subjected to tension-tension fatigue. Paris law expressed in terms of debond length growth rate and strain energy release rate is used. Analytical solution for Mode II energy release rate GII is obtained for long debonds where the interface crack growth is self-similar. For short debonds the interface crack interacts with the fiber break and therefore FEM modeling in combination with the virtual crack closure technique was performed to calculate the increase of GII. Finally, the calculated GII dependences are summarized in simple expressions that are used to simulate debond growth in fatigue. A parametric study of the effect of Paris law parameters on debond growth is performed.
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| 11. |
- Pupurs, Andrejs, et al.
(författare)
-
Analysis of bending stiffness reduction in laminates due to transverse cracks and delaminations in surface layers
- 2015
-
Ingår i: ICCM International Conferences on Composite Materials. - : International Committee on Composite Materials.
-
Konferensbidrag (refereegranskat)abstract
- In the present work an experimental study of bending stiffness reduction was conducted on carbon/epoxy cross-ply laminates with surface 90° layers with different thicknesses. The initially undamaged laminate samples were statically loaded in 4-point bending by running loading-unloading steps with increasing maximum displacement levels, eventually leading to multiple transverse cracking in the surface 90° layers as well as formation of delaminations at the interface between the surface 90° layer and neighbouring 0° layer. Density of transverse cracks was quantified and presence of delaminations was qualitatively inspected after each loading-unloading step using optical microscopy. Digital image correlation (DIC) system was used to measure the complete displacement distribution of the laminate in the middle region between the load application points ensuring accurate determination of the laminate mid-plane curvature and the bending stiffness. The experimental results of bending stiffness reduction and the mid-plane curvature were compared with 3-D FEM calculation results, where a 4-point bending test of a laminate with parametrically variable transverse crack density and delamination length was simulated. The experimental and numerical results were also compared with analytical model based on Classical Laminate Theory (CLT), where the damaged layer in the laminate is homogenized and replaced by an undamaged layer with effective (reduced) stiffness properties. In the analytical model the effective properties of a damaged layer at any given transverse crack density and delamination length are back-calculated using the in-plane stiffness properties of a representative volume element (RVE) with and without damage. The calculated effective properties of the damaged layer are then used in CLT to predict the reduction of laminate bending stiffness. The predictions of bending stiffness reduction obtained with the analytical CLT based model yield good agreement with experimental and 3-D FEM results for the tested cross-ply laminate configurations.
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| 12. |
- Pupurs, Andrejs, et al.
(författare)
-
Bending Stiffness of Damaged Cross-Ply Laminates
- 2021
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Ingår i: Mechanics of composite materials. - : Springer. - 0191-5665 .- 1573-8922. ; 57:1, s. 31-46
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Tidskriftsartikel (refereegranskat)abstract
- The bending stiffness of carbon/epoxy and glass/epoxy cross-ply laminates with intralaminar cracks in the surface 90° plies and local delaminations were studied experimentally using 4-point bending tests. The bending stiffness is defined as the slope of the relation between the applied bending moment and the corresponding midplane curvature. To measure the midplane curvature of laminates with different damage states, the digital image correlation system was used. The reduction in the bending stiffness with increasing density of transverse cracks and delamination length was also analyzed using a 3-D FEM model. The analysis and optical microscopy observations showed that, in the initial stage of damage evolution, local delaminations were small, but with increasing load, the delaminations grew rapidly from the tips of existing and newly created cracks, enhancing the bending stiffness degradation. As an alternative to the 3-D FEM modelling of the test, analytical approaches in conjunction with the classical laminate theory were suggested. The analytical approach was based on the concept of the “effective stiffness of damaged ply,” where the initial stiffness of the damaged ply was replaced by the effective stiffness depending on the damage state. In the present work, two routines were used to determinate the effective stiffness of the damaged ply: a) back-calculation from the difference in the stiffnesses of damaged and undamaged laminates employing the FEM model of the representative volume element; b) simple analytical fitting functions. It is shown that the analytical approach suggested is accurate and convenient for predicting the degradation of bending stiffness of a laminate with an evolving microdamage.
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| 13. |
- Pupurs, Andrejs, et al.
(författare)
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Damage-Caused Residual Curvatures in Symmetric Cross-Ply Laminates
- 2024
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Ingår i: Applied Composite Materials. - : Springer Nature. - 0929-189X .- 1573-4897.
-
Tidskriftsartikel (refereegranskat)abstract
- Thermo-mechanical response of [90n/0m]s carbon/epoxy and glass/epoxy cross-ply laminates in 4-point bending is analyzed experimentally and analytically. Intralaminar cracks in surface 90°-plies and local delaminations introduced in one of the 90°-plies at large deflections reduce the laminate bending stiffness and make the laminate asymmetric due to differences in the damage state in the layers. The latter leads to residual thermal curvature that increases with intralaminar crack density and with growing local delaminations. In the present study optical microscopy was used for crack density quantification. It was also found experimentally that small local delaminations develop in the initial stage of damage evolution and under increasing load they grow rapidly from the existing and newly created crack tips. The effect of damage on residual curvature and the bending stiffness was analyzed using an analytical method, where the concept of the effective stiffness of damaged ply is used in the classical laminate theory. Analytical results were validated with a 3-D FEM simulation of the damaged laminate in a 4-point bending test. In the literature a phenomenon that the microdamage in laminate layers causes redistribution of in-plane thermal stresses is often overlooked. The present paper shows that the used analytical approach gives an accurate description of experimental results regarding two independent sets of data: the residual curvature; and the laminate bending stiffness with evolving micro-damage. The present study also renders a better insight in the mechanics of the phenomena and allows estimation of the extent of local delaminations that is difficult to measure in tests.
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| 14. |
- Pupurs, Andrejs, et al.
(författare)
-
Damage development and stiffness reduction in laminates in out-of-plane loading
- 2014
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Ingår i: 16th European Conference on Composite Materials, ECCM 2014. - : European Conference on Composite Materials, ECCM. - 9780000000002
-
Konferensbidrag (refereegranskat)abstract
- Simple approach based on Classical Laminate Theory (CLT) and effective stiffness of damaged layer is suggested for bending stiffness determination of laminate with intralaminar cracks in surface 90-layers. The effective stiffness of layer with cracks as a function of crack density is back-calculated comparing in-plane stiffness of laminates with and without damage. The accuracy of the CLT and effective stiffness approach is demonstrated comparing with bending stiffness results from FEM simulated 4-point bending test on laminate with damage. Analytical model for damaged laminate stiffness is presented which gives similar values for effective stiffness as FEM calculations for unit cell. Effect of local delaminations initiated from transverse cracks is analyzed.
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| 15. |
- Pupurs, Andrejs, et al.
(författare)
-
Digital Image Correlation (DIC) Validation of Engineering Approaches for Bending Stiffness Determination of Damaged Laminates
- 2022
-
Ingår i: Applied Composite Materials. - : Springer Science and Business Media B.V.. - 0929-189X .- 1573-4897. ; 29, s. 1937-1958
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Tidskriftsartikel (refereegranskat)abstract
- During the last decade new models for bending stiffness prediction of damaged composite laminates have been proposed in the literature advancing the earlier developed engineering approaches in accuracy and in complexity. However, experimental data for validation of complex analytical or engineering models are almost non-existent in the literature. In the present work a detailed experimental study was performed to investigate the bending stiffness reduction of composite cross-ply laminates with evolving micro-damage. Intralaminar cracks and local delaminations in the bottom surface 90-degree layer of carbon/epoxy and glass/epoxy cross-ply laminates were introduced in 4-point bending tests. Digital Image correlation (DIC) technique was used to experimentally determine the midplane curvature. The accuracy of beam theory for bending stiffness determination was assessed. The measured bending stiffness reduction with respect to transverse crack density was also compared with FEM predictions. The results show that the beam theory gives slightly underestimated curvature at low deflections, whereas at large deflections the beam theory overestimates the curvature and the moment–curvature relation becomes nonlinear. Nevertheless, the overall agreement between beam theory and DIC-based results is still very good, which leads to conclude that beam theory based data reduction schemes have sufficient accuracy for predicting bending stiffness even for highly damaged laminates. © 2022, The Author(s)
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| 16. |
- Pupurs, Andrejs, et al.
(författare)
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Effective stiffness concept in bending modeling of laminates with damage in surface 90-layers
- 2016
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Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier Ltd. - 1359-835X .- 1878-5840. ; 82, s. 244-252
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Tidskriftsartikel (refereegranskat)abstract
- Simple approach based on Classical Laminate Theory (CLT) and effective stiffness of damaged layer is suggested for bending stiffness determination of laminate with intralaminar cracks in surface 90-layers and delaminations initiated from intralaminar cracks. The effective stiffness of a layer with damage is back-calculated comparing the in-plane stiffness of a symmetric reference cross-ply laminate with and without damage. The in-plane stiffness of the damaged reference cross-ply laminate was calculated in two ways: (1) using FEM model of representative volume element (RVE) and (2) using the analytical GLOB-LOC model. The obtained effective stiffness of a layer at varying crack density and delamination length was used to calculate the A, B and D matrices in the unsymmetrically damaged laminate. The applicability of the effective stiffness in CLT to solve bending problems was validated analyzing bending of the damaged laminate in 4-point bending test which was also simulated with 3-D FEM.
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| 17. |
- Pupurs, Andrejs, et al.
(författare)
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Energy release rate based fiber/matrix debond growth in fatigue : Part I: Self-similar crack growth
- 2013
-
Ingår i: Mechanics of Advanced Materials and Structures. - : Informa UK Limited. - 1537-6494 .- 1537-6532. ; 20:4, s. 276-287
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Tidskriftsartikel (refereegranskat)abstract
- The strain energy release rate related to debond crack growth along the fiber/matrix interface in a unidirectional (UD) composite with a broken fiber is analyzed. The UD composite is represented by a model with axial symmetry consisting of three concentric cylinders: broken and partially debonded fiber in the middle surrounded by matrix, which is embedded in a large block of effective composite. Analytical solution for Mode II energy release rate is found and parametric analysis performed in the self-similar debond crack propagation region. It is shown that many anisotropic elastic constants of the fiber, which are usually not known, have a small effect on .
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| 18. |
- Pupurs, Andrejs, et al.
(författare)
-
Energy Release Rate Based Fiber/Matrix Debond Growth in Fatigue. Part II: Debond Growth Analysis Using Paris Law
- 2013
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Ingår i: Mechanics of Advanced Materials and Structures. - : Informa UK Limited. - 1537-6494 .- 1537-6532. ; 20:4, s. 288-296
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Tidskriftsartikel (refereegranskat)abstract
- The strain energy release rate related to debond crack growth along the fiber/matrix interface in a unidirectional composite with a broken and partially debonded fiber is analyzed. The focus in this paper (Part II) in contrast to the self-similar crack growth analysis in Part I [1] is on growth of short debonds near the fiber break. Since self-similarity condition is not valid for interactive cracks, numerical FEM simulations were used to calculate magnification of previously described coefficients in the strain energy release rate expression. The findings from these studies are used in simulation of the debond growth in tension-tension fatigue using Paris law.
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| 19. |
- Pupurs, Andrejs, et al.
(författare)
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FEM modeling of fiber/matrix debond growth in tension-tension cyclic loading of unidirectional composites
- 2013
-
Ingår i: International journal of damage mechanics. - : SAGE Publications. - 1056-7895 .- 1530-7921. ; 22:8, s. 1144-1160
-
Tidskriftsartikel (refereegranskat)abstract
- The fiber/matrix interface crack (debond) growth from fiber break in unidirectional composite subjected to high stress tension–tension cyclic loading is analyzed. The debond growth is simulated calculating the strain energy release rate GII by FEM in three-dimensional formulation and using power law with respect to the GII change to describe the debond growth rate. Two models were applied. In Model 1 the partially debonded fiber/matrix cylindrical unit with a fiber break is surrounded from all sides by an effective composite phase. In Model 2 the effective composite phase was used around the fiber/matrix unit except the region between the unit and the specimen surface, which contains neat matrix only. Calculations show that the average GII is slightly larger, when the analyzed fiber is closer to the specimen surface. The debond growth was simulated using interface fatigue parameters obtained from single fiber composite specimen tests in the literature. Simulation results show that debonds from fiber breaks close to the specimen surface grow faster than from fiber breaks inside the composite specimen.
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| 20. |
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| 21. |
- Pupurs, Andrejs
(författare)
-
Fiber failure and debonding in composite materials
- 2016
-
Ingår i: Modeling damage, fatigue and failure of composite materials. - Cambridge : Woodhead Publishing Limited. - 9781782422983 ; , s. 173-196
-
Bokkapitel (refereegranskat)abstract
- Fiber–matrix interface debonding initiated from random fiber breaks is known to be one of the key damage mechanisms in unidirectional (UD) composites subjected to quasi-static and cyclic (fatigue) loading. Growth of fiber–matrix interface debonds leads to stiffness reduction and eventually to the final failure of the UD composite through coalescence of multiple debond cracks. This chapter overviews the current state of the art in modeling fiber–matrix interface debonding in UD composites. The methods reviewed in this chapter are based on fracture mechanics principles of the energy release rate. Analytical models for steady-state debond growth are presented. Finite-element method (FEM) based models for analyzing the growth of short debonds and the effects of edges and neighboring fibers are also presented.
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| 22. |
- Pupurs, Andrejs
(författare)
-
Fracture mechanics analysis of damage initiation and evolution in fiber reinforced composites
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When a unidirectional (UD) fiber reinforced polymer composite is loaded in fiber direction in quasi-static or in a high stress cyclic tension-tension regime, many fiber breaks may occur in random positions already during the load increase in the first cycle. This is because fiber strain to failure in UD composites is lower than the polymer matrix strain to failure.In cyclic loading with constant amplitude we usually assume that fibers do not experience fatigue. Therefore the next step in damage evolution with increasing number of cycles may be development of interface cracks (debonds) growing along the fiber/matrix interface.Fracture mechanics concepts are applied and Mode II strain energy release rate GII related to debond crack growth along the fiber/matrix interface is used for damage evolution analysis.In Paper I analytical solution for Mode II energy release rate GII is found and parametric analysis performed in the self-similar debond crack propagation region. For short fiber/matrix debond cracks the self-similarity condition is not valid - due to interaction with fiber crack, GII is magnified. Thus in Paper II, numerical FEM simulations in combination with virtual crack closure technique are used in order to calculate GII for short debond cracks. The findings from GII analysis for self-similar and short debond cracks are summarized in simple expressions and then used in simulations of fiber/matrix interface debond crack growth in tension-tension fatigue using Paris law.In Paper III, debond growth in single fiber (SF) composites subjected to tension-tension fatigue is analyzed. Using the same procedure as for UD composites, first, an analytical solution for Mode II energy release rate GII is obtained for self-similar crack growth region. Then FEM calculations are performed in order to obtain GII magnification profiles for short debond cracks. For SF composites it was additionally found out that equal GII magnification profiles are obtained no matter if purely mechanical, purely thermal or combined mechanical and thermal load is applied to the composite. Thus for SF composites even simpler expressions can be used for simulations of debond growth using Paris law relation.
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| 23. |
- Pupurs, Andrejs, et al.
(författare)
-
Fracture mechanics analysis of debond growth in a single-fiber composite under cyclic loading
- 2011
-
Ingår i: Mechanics of composite materials. - : Springer Science and Business Media LLC. - 0191-5665 .- 1573-8922. ; 47:1, s. 109-124
-
Tidskriftsartikel (refereegranskat)abstract
- A model is developed to analyze the growth of a fiber/matrix debond along a broken fiber interface in a single-fiber composite subjected to tension-tension fatigue. The Paris law expressed in terms of debond growth and strain energy release rates is used. An analytical solution for the Mode II energy release rate G II is obtained for long debonds, where the interface crack growth is self-similar. For short debonds, the interface crack interacts with the fiber break, and therefore a FEM modeling in combination with the virtual crack closure technique was performed to calculate the increase in G II . Finally, the calculated G II dependences are summarized in simple expressions that are used to simulate the debond growth in fatigue. A parametric study of the effect of Paris law parameters on the debond growth is performed.
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| 24. |
- Pupurs, Andrejs, et al.
(författare)
-
Interface debond crack growth in tension-tension cyclic loading of single fiber polymer composites
- 2013
-
Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 44:1, s. 86-94
-
Tidskriftsartikel (refereegranskat)abstract
- Fiber/matrix interface debond crack growth from a fiber break is defined as one of the key mechanisms of fatigue damage in unidirectional composites. Considering debond as an interface crack its growth in cyclic loading is analyzed utilizing a power law, where the debond growth rate is a power function of the change of the strain energy release rate in the cycle. To obtain values of two parameters in the power law cyclic loading of fragmented single fiber specimen is suggested. Measurements of the debond length increase with the number of load cycles in tension-tension fatigue are performed for glass fiber/epoxy single fiber composites. Analytical method in the steady-state growth region and FEM for short debonds are combined for calculating the strain energy release rate of the growing debond crack. Interface failure parameters in fatigue are determined by fitting the modeling and experimental results. The determined parameters for interface fatigue are validated at different stress levels.
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| 25. |
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| 26. |
- Pupurs, Andrejs
(författare)
-
Micro-crack initiation and propagation in fiber reinforced composites
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Predicting micro-damage initiation and evolution is one of the key challenges for safe design of fiber reinforced polymer composites. Micro-scale damage such as, for example, single fiber break may be unnoticeable and negligible during the initial service life of composite, however, with many loading and unloading cycles this initially micro-scale damage may propagate forming macroscopic scale cracks that can significantly reduce the service lifetime or even lead to unforeseen catastrophic failure of the composite structure. The objective of this Doctoral thesis is to develop methodology for prediction of micro-crack propagation in fiber reinforced polymer composites. Fracture mechanics concepts of strain energy release rate are applied for crack growth analysis. Analytical modeling combined with numerical FEM calculations are used to obtain the values of energy release rate. Parametric analysis is performed to evaluate the significance of the applied load and various material properties on the micro-crack growth rate. Calculation results are implemented into Paris law relation, to predict the crack growth in fatigue loading. In Paper I fiber/matrix interface debond growth starting from single fiber breaks in unidirectional (UD) polymer composites is studied. Analytical solution for Mode II energy release rate GII is found and parametric analysis is performed in the self-similar debond crack propagation region. When the fiber/matrix interface debond crack is short, the self-similarity condition is not valid. Due to interaction with fiber break, GII is magnified. In Paper II, numerical FEM modeling is performed to calculate GII for short debond cracks. The findings from GII analysis for self-similar and short debond cracks are summarized in simple expressions. Simulations of fiber/matrix interface debond crack growth in tension-tension fatigue using Paris law are performed. In Paper III, debond growth in single fiber (SF) composites subjected to tension-tension fatigue is analyzed. Using the same procedure as for UD composites, first, an analytical solution for Mode II energy release rate GII is found for self-similar crack growth region and then FEM modeling is performed to obtain magnification profiles for short debond cracks. In Paper IV modeling methodology described in Paper III is advanced further and the modeling results are compared with experimental data for interface debond crack growth in SF composites subjected to tension-tension fatigue loading. The Paris law constants are extracted from the best fit between the experimental and modeling results. Validation of results prove that Paris law can be implemented to characterize micro-crack growth in fatigue of polymer composites. In Paper V fiber/matrix interface debond growth on the surface of a UD composite subjected to tension-tension fatigue is analyzed. 3-D FEM modeling is performed to account for the non-axisymmetric stress state due to the edge effect. Modeling results for debond growth in fatigue are compared with experimental data available in the literature. Finally, in Paper VI fracture mechanics concepts of energy release rate are used to model micro crack initiation and propagation in a carbon fiber, which, apart from the load bearing function, also serves as an electrode in a novel lithium-ion rechargeable battery. When subjected to lithium ion intercalation, carbon fiber experiences a non-uniform swelling that leads to development of high mechanical stresses. In many cycles of charging-discharging these stresses can introduce damage and reduce the mechanical and electrochemical properties of the battery. FEM modeling using thermal analogy is performed to solve the transient ion diffusion and mechanical stress problem. Different crack initiation and propagation scenarios are compared.
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| 27. |
- Pupurs, Andrejs, et al.
(författare)
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Modeling mechanical fatigue of UD composite: multiple fiberbreaks and debond growth
- 2009
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Ingår i: 5th International EEIGM/AMASE/FORGEMAT Conference on Advanced Materials Research. - Bristol : IOP Publishing Ltd.
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Konferensbidrag (refereegranskat)abstract
- The objective of this paper is to analyze fiber/matrix debond crack growth in unidirectional (UD) composites during high stress cyclic tension-tension loading. High stress loading means that fiber breaks and consecutive fiber/matrix interface debond growth are expected. Fracture mechanics concepts are applied to analyze damage evolution
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| 28. |
- Pupurs, Andrejs, et al.
(författare)
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Modeling mechanical stress and exfoliation damage in carbon fiber electrodes subjected to cyclic intercalation/deintercalation of lithium ions
- 2014
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Ingår i: Composites Part B. - : Elsevier BV. - 1359-8368 .- 1879-1069. ; 65, s. 69-79
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Tidskriftsartikel (refereegranskat)abstract
- Gradients in lithium ion concentration distribution in carbon fiber are accompanied by non-uniform fiber swelling leading to development of mechanical stresses. During lithium deintercalation these stresses may lead to initiation and growth of radial cracks in the fiber. The subsequent cycle of intercalation may result in arc-shaped cracks deviating from the tip of the radial cracks. These phenomena decrease the mechanical properties of fibers if used in structural batteries and reduce the charging properties of the battery by decreased diffusivity of lithium ions and by exfoliating layers on the fiber surface. The crack propagation and possible damage evolution scenarios are analyzed using linear elastic fracture mechanics. The crack geometry dependent ion concentration distributions and the elastic stress distributions were found using finite element software ANSYS.
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| 29. |
- Pupurs, Andrejs, et al.
(författare)
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Modelling mechanical stresses due to intercalation and de-intercalation of lithium-ions in a carbon fiber battery
- 2012
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Ingår i: Proceedings of the 15th European Conference on Composite Materials, Venice, 24-28 June 2012. - Venice. - 9788888785332
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Konferensbidrag (refereegranskat)abstract
- Gradients in Li+ ion concentration distribution in a carbon fiber are accompanied by nonuniform fiber swelling leading to development of mechanical stresses. During lithium deintercalation these stresses may lead to initiation and growth of radial cracks in the fiber. This phenomenon decreases the mechanical properties of fibers if used in structural batteries and reduces the charging properties of the battery by initiating exfoliation of layers on the fiber surface. The radial crack propagation and possible damage evolution scenarios are analyzed using linear elastic fracture mechanics.
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| 30. |
- Pupurs, Andrejs, et al.
(författare)
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Steady-state energy release rate for fiber/matrix interface debond growth in unidirectional composites
- 2017
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Ingår i: International journal of damage mechanics. - : Sage Publications. - 1056-7895 .- 1530-7921. ; 26:4, s. 560-587
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Tidskriftsartikel (refereegranskat)abstract
- Analytical closed form solution is derived for energy release rate due to steady-state debond growth along a broken fiber in unidirectional composite. The problem is represented by a three concentric cylinder model, where the broken and partially debonded fiber is embedded in resin and this unit is surrounded by homogenized effective composite. Parametric analysis shows that parameters in the very simple quadratic expression for energy release rate dependence on temperature change and mechanical strain are rather insensitive with respect to changes in constituent elastic properties and fiber content. The importance to have a large outer radius of the effective composite phase in the concentric cylinder model is demonstrated.
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| 31. |
- Pupurs, Andrejs, et al.
(författare)
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UD composite in mechanical fatigue : modelling multiple fiber breaks and debond growth
- 2009
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Ingår i: ICCM 17, Edinburgh. - London : IOM Communications.
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Konferensbidrag (refereegranskat)abstract
- When unidirectional fiber reinforced polymer composites are loaded in tension-tension fatigue multiple fiber breaks occur in random positions during the first cycle. Assuming that fibers do not experience fatigue, the further damage evolution with increasing number of cycles is in form of debonds growing along the fiber/matrix interface. Fracture mechanics analysis is performed to compare this mechanism with an alternative one where debonds initiate from transverse matrix cracks.
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| 32. |
- Pupurs, Andrejs, et al.
(författare)
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Unidirectional composite in mechanical fatigue : modelling debond growth from fibre breaks
- 2010
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Ingår i: Plastics, rubber and composites. - 1465-8011 .- 1743-2898. ; 39:3-5, s. 128-136
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to analyse fibre/matrix debond crack growth during high stress cyclic tension-tension loading of unidirectional composites. The debond crack evolution analysis is based on fracture mechanics concepts that mode II energy release rate calculations are performed analytically for long debonds, where crack growth is self-similar, and numerically for short debonds by finite element method in combination with virtual crack closure technique. From the calculation results simple expressions are derived for an arbitrary mechanical and thermal loading case. Finally, the obtained expressions are applied in Paris law for debond growth simulations in cyclic tension-tension loading.
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| 33. |
- Rozite, Liva, et al.
(författare)
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Nonlinear behavior of PLA and lignin based flax composites subjected to tensile loading
- 2013
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Ingår i: Journal of Thermoplastic Composite Materials. - : SAGE Publications. - 0892-7057 .- 1530-7980. ; 26:4, s. 476-496
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Tidskriftsartikel (refereegranskat)abstract
- The effect of temperature (T = 22°C, 30°C and 35°C) and relative humidity (RH = 34% and 66%) on mechanical behavior of natural fiber reinforced bio-based matrix composites subjected to tensile loading was investigated. Three composites were studied (a) polylactic acid (PLA) composite with 10% weight fraction of flax fibers; (b) PLA composite containing 5% viscose fibers (filaments of regenerated cellulose); (c) lignin-based composite with 30% of flax fibers. Elastic modulus, the nonlinear tensile stress–strain curves and failure were analyzed showing that all materials are temperature sensitive. The nonlinearity was analyzed studying modulus degradation as well as development of viscoelastic and viscoplastic strains. The modulus reduction in PLA-based composites starts after reaching the stress maximum and is not significant, whereas the modulus reduction in lignin-based composites starts before the maximum and it can reach 50%. With increasing RH these effects are slightly larger. The time-dependent phenomena were analyzed in short-term creep and strain recovery tests demonstrating significantly higher viscoplastic strain in lignin composites. Both viscoelastic and viscoplastic strains are larger at higher RH.
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| 34. |
- Sparnins, Edgars, et al.
(författare)
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The moisture and temperature effect on mechanical performance of flax/starch composites in quasi-static tension
- 2011
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 32:12, s. 2051-2061
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Tidskriftsartikel (refereegranskat)abstract
- The effect of temperature and moisture on mechanical behavior of flax fiber/starch based composites was investigated experimentally. Elastic modulus, the nonlinear tensile loading curves, and failure strain were analyzed. Neat matrix and composites with 20 and 40% weight content of fibers were tested. It was found, performing tests with different amplitudes, that microdamage development with stress is rather limited and the related elastic modulus reduction in this type of compositesis not significant. It was shown that the composite elastic modulus and failure stress are linearly related to the maximum tensile stress in resin. The sensitivity of the maximum stress of the resin with respect to temperature and moisture is the source of composites sensitivity to these parameters. Constant interface stress shear lag model for stress transfer assuming matrix yielding at the fiber/matrix interface has been successfully used to explain the tensile test data. It indicates that the sensitivity of the used composite with respect to the matrix properties change could be significantly reduced by increasing the average fiber length from 0.9 mm to 1.5 mm.
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| 35. |
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| 36. |
- Varna, Janis, et al.
(författare)
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Damage and Failure Analysis for Composites
- 2022. - 2
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Ingår i: Comprehensive Structural Integrity. - : Elsevier. - 9780323919456 ; , s. 225-246
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Intralaminar cracking in plies of composite laminates is the first microdamage mode that affects thermo-elastic properties and may trigger local delaminations and final failure of the composite. Intralaminar cracks are like tunnels running along the fiber direction in the ply. The number of cracks increases with the increase of the applied load or with the number of cycles in fatigue loading. In this article, the cracking evolution is analyzed distinguishing two phases in development: initiation and propagation. For laminates with thick plies, the initiation ends with triggering sudden propagation and, therefore, concept of statistical initiation stress distribution in the ply together with Monte Carlo method is used for analysis. For thin-ply laminates, crack initiation does not lead to immediate propagation and the energy release concept is used to analyze crack propagation.
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| 37. |
- Varna, Janis, et al.
(författare)
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Growth and interaction of debonds in local clusters of fibers in unidirectional composites during transverse loading
- 2017
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Ingår i: Key Engineering Materials. - : Trans Tech Publications. - 1013-9826 .- 1662-9795. ; 734, s. 63-66
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Tidskriftsartikel (refereegranskat)abstract
- Fiber/matrix debonding in transverse tensile loading of a unidirectional composite is analyzed calculating energy release rate (ERR) for interface crack propagation. Non-uniform fiber distribution (local hexagonal fiber clustering) is assumed in the model. The matrix region containing the central fiber with the debond and the 6 surrounding fibers is embedded in a large block of homogenized composite which has the same fiber content as the region analyzed explicitly. Some of the fibers surrounding the central fiber may also have a debond. The effect of the local clustering and of the presence of other debonds on magnification of the ERR is analyzed
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| 38. |
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| 39. |
- Varna, Janis, et al.
(författare)
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Non-linear behaviour of PLA based flax composites
- 2012
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Ingår i: Plastics, rubber and composites. - 1465-8011 .- 1743-2898. ; 41:2, s. 49-60
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical behaviour of polylactic acid/flax fibre composite in tension was investigated by analysing elastic properties and loading curves. The observed non-linearity was attributed to microdamage, viscoelastic and viscoplastic response, suggesting Schapery's type of model for viscoelasticilty and Zapas' model for viscoplasticity. It was found that after loading at stress levels below the maximum possible, the elastic modulus is not affected, and therefore, damage does not need to be included in the material model. Viscoplastic and viscoelastic strain development was analysed in creep and strain recovery tests at several high stress levels. The identified and validated material model is non-linear viscoelastic and viscoplastic with slight non-linearity even in the elastic strain term. It appears that there is no region of linear viscoelasticity for this material. Non-linear elasticity, viscoelasticity and viscoplasticity are equally responsible for the observed non-linearity in the tensile tests
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| 40. |
- Varna, Janis, et al.
(författare)
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Steady-State Debond Growth Along Broken Fibers in Unidirectional Composites During Cyclic Loading
- 2013
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Ingår i: 9th International Conference on Composite Science and Technology. - Lancaster : PA Destech Publications Inc.. - 9781605951133 ; , s. 981-983
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Konferensbidrag (refereegranskat)abstract
- Several regions with different governing failure mechanisms may be distinguished analyzing axial tension-tension cyclic loading of unidirectional (UD) composite. At high loads multiple fiber fracture takes place during the first loading cycle. The relative number of broken fibers depends on the maximum stress and can be estimated assuming that the fiber strength is a statistical property following Weibull distribution. Multiple fiber fracture (fragmentation) is possible because the load is transferred into the broken fiber through the interface. In cyclic loading with constant amplitude we usually assume that fibers do not experience fatigue and all fiber breaks occur during the first cycle. During the following cyclic loading debonds start to grow along the fiber/matrix interface and this is the main mode of damage progression analyzed in this paper. The extensive debonding reduces the load borne by the broken fiber causing new fiber breaks and connecting the multiple fiber breaks, finally leading to catastrophic rupture of the UD composite. Hence, understanding of the debond growth process in fatigue is crucial for fatigue life analysis in this load region.
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| 41. |
- Viesturs, Lācis, et al.
(författare)
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Experimental and numerical analysis of heat dissipation in hybrid carbon/glass thin-ply composites for multifunctional applications
- 2022
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Ingår i: ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials. - Lausanne : EPFL Lausanne, Composite Construction Laboratory. - 9782970161400 ; , s. 122-128
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Thermal behavior of hybrid carbon/glass thin-ply laminates with different layer thickness ratios were investigated experimentally. Two different approaches were used for applying thermal loads: in one experiment small-scale external heater was attached on the surface of laminate specimen; in the second approach cyclic mechanical loading with high frequency was applied to generate internal heating within materials. In both experiments transient temperature distribution along the thickness of specimens was measured and recorded using high performance thermal imaging camera. Obtained results demonstrate temperature distribution in reference and hybrid laminate layers during the transient and steady state thermal conditions. Relatively large differences between carbon/epoxy and glass/epoxy layers were found in terms of internal heat generation and heat transfer. Parametric analysis results on reference and various hybrid lay-ups from this study could aid the lay-up design for composites in multifunctional applications with various thermal processes.
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| 42. |
- Xu, Johanna, et al.
(författare)
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Multifunctional composites : Modeling intercalation induced stresses in constituents of micro-battery
- 2016
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Ingår i: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - : European Conference on Composite Materials, ECCM.
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Konferensbidrag (refereegranskat)abstract
- A structural battery that simultaneously carries mechanical loads while storing electrical energy offers the potential of significantly reduced total vehicle weight owing to the multifunctionality. Carbon fiber is employed as negative electrode of the battery and also as a composite reinforcement material. It is coated with a solid polymer electrolyte working as an ion conductor and separator whilst transferring mechanical loads. The coated fiber is surrounded by a conductive positive electrode material. This paper demonstrates a methodology for addressing mechanical stresses arising in a conceptualized micro battery cell during electrochemical cycling, caused by time dependent gradients in lithium ion concentration distribution in the carbon fiber.
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| 43. |
- Xu, Johanna, 1989-
(författare)
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Structural Composite Lithium-Ion Battery : Effect of Intercalation induced volumetric changes on micro-damage
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The quest for lighter materials and structures to reduce climate impacts in the automotive industry has paved the way for multifunctional solutions. Mass saving on a system level can be achieved by materials or structures having more than one primary function, thus reducing the number of components used. Structural batteries are composite materials that simultaneously carry mechanical loads while delivering electrical energy. While carbon fiber is a commonly used reinforcing material in high-performance composite materials, it also possesses excellent lithium intercalation properties.Therefore,it is possible to use carbon fiber to develop structural batteries based onlithium-ion battery technology.Among several proposed solutions,the micro-battery employs the carbon fiber asa negative electrodeof the battery and also as a composite reinforcement material. The fiber is coated with a solid polymer electrolyte which works as an ion conductor and separator whilst transferring mechanical loads. The coated fiber is surrounded by additional matrix material acting asapositive electrode, composed of conductive additives, active electrode material and electrolyte. This assembly of materials allows thenecessary electrochemical processes to occur simultaneously, including electrochemical reactions at the surface of the active electrode material, mass transport within active electrode material by diffusion, mass transport in electrolyte by diffusion and migration, and electronic conduction.During electrochemical cycling the electrodes undergo volume changes as a result of lithium transport. The work in this thesis addresses the effects of volume changes on internal mechanical stress state in the structural battery. A physics-based mathematical model employing a number of coupled nonlinear differential equations has been set-up and solved numerically to investigate performance in the structural battery material. The resulting transient lithium ionconcentration distributions were used in combination with linear elastic analysis in order to assess the mechanical stresses in the fiber, coating and matrix caused by non-uniform swelling and shrinking of the micro-battery. Stress analysis shows that high hoop stress in the matrix during charging may initiate radial matrix cracks at the coating/matrix interface. Linear elastic fracture mechanics hasbeen used to analyze radial matrix crack propagation and debonding at coating/matrix interface in both unidirectional (UD) and cross-ply laminate, under electrochemical load only and combined electrochemical and thermomechanical load. Results show that for cross-ply structural battery composite the sequence of macro-scale crack forming events differs from a conventional cross-plied composite, as well as froma UD composite battery laminate. The most likely course of failure events in a cross-ply laminate were found to be: 1) radial matrix crack initiation and unstable growth; 2)matrix/coatingdebond when the matrix crack hasacertain length.
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| 44. |
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| 45. |
- Zhuang, Linqi, et al.
(författare)
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Effect of fiber clustering on debond growth energy release rate in UD composites with hexagonal packing
- 2016
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Ingår i: Engineering Fracture Mechanics. - : Elsevier Ltd. - 0013-7944 .- 1873-7315. ; 161, s. 76-88
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Tidskriftsartikel (refereegranskat)abstract
- Steady-state energy release rate (ERR) for fiber/matrix interface debond growth originated from fiber break in unidirectional composite is calculated using 3-D FEM models with hexagonal fiber arrangement. In the model the debonded fiber is central in the hexagonal unit which is surrounded by effective composite. The effect of neighboring fibers focusing on local fiber clustering on the ERR is analyzed by varying the distance between fibers in the unit. The steady-state ERR is calculated from potential energy difference between a unit in the bonded region far ahead of the debond front and a unit in the debonded region far behind the debond front. The ERR for different modes of crack propagation is obtained from a FEM model containing a long debond by analyzing the stress at the debond front.Results show that in mechanical axial tensile loading fracture Mode II is dominating, it has strong angular dependence (effect of closest fibers) but the average ERR is not sensitive to the local fiber clustering. In thermal loading the Mode III is dominating and the average ERR is highly dependent on the distance to neighboring fibers. However, for realistic loads the thermal ERR is much smaller than the mechanical. © 2016 Elsevier Ltd.
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| 46. |
- Zhuang, Linqi, et al.
(författare)
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Effect of neighboring fibers on energy release rate during fiber/matrix debond growth
- 2014
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Ingår i: 16th European Conference on Composite Materials, ECCM 2014. - : European Conference on Composite Materials, ECCM. - 9780000000002
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Konferensbidrag (refereegranskat)abstract
- In this paper fiber/matrix interface debond growth in unidirectional composites subjected to mechanical tensile loading is analyzed using fracture mechanics principles of energy release rate (ERR). The objective of the present study is to analyze the effect of neighboring fibers on the ERR. 5-cylinder axisymmetric FEM models with adjustable inter-fiber distance were used for ERR calculations. The results show that the ERR slightly increases with the inter-fiber distance in the case of long debonds. For short debonds, however, because the stress-state is more complex, it was found that the debond propagates in a mixed Mode I and Mode II and contribution of each mode to the ERR depends on the actual debond length. It was found that for very small debond lengths ERR significantly increases with the inter-fiber distance.
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| 47. |
- Zhuang, Linqi, et al.
(författare)
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Effects of inter-fiber spacing on fiber-matrix debond crack growth in unidirectional composites under transverse loading
- 2018
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Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 109, s. 463-471
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Tidskriftsartikel (refereegranskat)abstract
- The energy release rate (ERR) of a fiber–matrix debond crack in a unidirectional composite subjected to transverse tension is studied numerically. The focus of the study is the effect of the proximity of the neighboring fibers on the ERR. For this, a hexagonal pattern of fibers in the composite cross-section is considered. Assuming one fiber to be debonded at certain initial debond arc-length, the effect of the closeness of the surrounding six fibers on the ERR of the crack is studied with the inter-fiber distance as a parameter. Using an embedded cell consisting of discrete fibers in a matrix surrounded by the homogenized composite, a finite element model and the virtual crack closure technique are used to calculate the ERR. Results show that the presence of the local fiber cluster accelerates the crack growth up to a certain initial crack angle, beyond which the opposite effect occurs. It is also found that the residual stress due to thermal cooldown reduces the ERR. However, the thermal cooldown is found to enhance the debond growth in plies within a cross-ply laminate.
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| 48. |
- Zhuang, L., et al.
(författare)
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Fiber/matrix debond growth from fiber break in unidirectional composite with local hexagonal fiber clustering
- 2016
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Ingår i: Composites Part B. - : Elsevier Ltd. - 1359-8368 .- 1879-1069. ; 101, s. 124-131
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Tidskriftsartikel (refereegranskat)abstract
- Energy release rate (ERR) for fiber/matrix debonding in composite with local fiber clustering, subjected to axial tension, has been investigated numerically by a 3-D finite element (FE) model. In the model, broken fiber is central in a hexagonal unit which is embedded in an effective composite. Fiber/matrix debond with circular front is assumed to be originated from the fiber break. The effect of the local fiber clustering on ERR is studied by varying distance between the broken fiber and the neighboring fibers. For very short debonds as well as for long debonds (almost steady-state growth) the ERR was calculated by both the J integral and the Virtual Crack Closure Technique (VCCT). Results show that the debond growth is Mode II dominated and that the ERR strongly depends on the angular coordinate. The local fiber clustering has larger effect on the angular variation for shorter debonds and the effect increases with larger local fiber volume fraction. The results obtained from the 3-D hexagonal model are compared with those obtained previously using 5-cylinder axisymmetric model developed by the same authors. The ERR values from 5-cylinder axisymmetric model could be considered as upper bound for the 3-D hexagonal model.
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