| 1. |
- Al-Ramahi, Nawres J., 1980-, et al.
(författare)
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Numerical stress analysis for single-lap adhesive joint under thermo-mechanical load using non-linear material
- 2020
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Ingår i: The 3rd International Conference on Sustainable Engineering Techniques (ICSET20). - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- A comprehensive stress analysis by means of Finite Element Method (FEM) for single-lap joint subjected to thermal and mechanical loads is presented in this paper. Simulation is used to predict the effect of residual thermal stresses (caused by difference of temperature of use and elevated temperature during the assembly of the joint) on stress distribution within adhesive layer. The residual thermal stresses are assigned to joint members as initial condition before the mechanical load is applied. The FEM model employs linear and nonlinear material model and accounts for geometrical nonlinearity. It is confirmed that the difference between the manufacturing and the ambient temperature results in high residual thermal stresses, especially in axial and lateral directions of the joint. The calculation of total stress as superposition of thermal and mechanical stresses works only for linear materials. Moreover, simultaneous application of temperature and mechanical load (applied strain in case of displacement controlled test) in FEM produces inaccurate results, since in real situation the strain is applied to already thermally loaded structure. It is also found that the residual thermal stresses may reduce the peel and shear stress concentration in the adhesive at the ends of overlap and the shear stress within the overlap.
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| 2. |
- Al-Ramahi, Nawres J, 1980-, et al.
(författare)
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Numerical stress analysis in adhesively bonded joints under thermo-mechanical loading
- 2020
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Ingår i: Advances in Mechanical Engineering. - : Sage Publications. - 1687-8132 .- 1687-8140. ; 12:10
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work is to evaluate the effect of residual thermal stresses, arising after assembling a single-lap joint at elevated temperature, on the inelastic thermo-mechanical stress state in the adhesive layer. The numerical analysis (FEM) employing linear and non-linear material models, with geometrical nonlinearity accounted for, is carried out. Simulating the mechanical response, the calculated thermal stresses are assigned as initial conditions to polymeric, composite and metallic joint members to reflect the loading sequence where the mechanical strain is applied to cooled-down structure. It is shown that the sequence of application matters and simulations with simultaneous application of temperature and strain give different result. Two scenarios for adhesive joints with composites are studied: joining by adhesive curing of already cured composite parts (two-step process) and curing the adhesive and the composite simultaneously in one-step (co-curing). Results show that while in-plane stresses in the adhesive are higher, the peaks of out-of-plane shear stress and peel stress (most responsible for the joint failure) at the end of the overlap are reduced due to thermal effects. In joints containing composite parts, the one-step joining scenario is more favorable than the two-step. The ply stacking sequence in the composite has significant effect on stress concentrations as well as on the plateau value of the shear stress in the adhesive.
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| 3. |
- Di Stasio, Luca, 1988-, et al.
(författare)
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Effect of the proximity to the 0°/90° interface on Energy Release Rate of fiber/matrix interface crack growth in the 90°-ply of a cross-ply laminate under tensile loading
- 2020
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Ingår i: Journal of composite materials. - : Sage Publications. - 0021-9983 .- 1530-793X. ; 54:21, s. 3021-3034
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Tidskriftsartikel (refereegranskat)abstract
- Models of Representative Volume Elements (RVEs) of cross-ply laminates with different geometric configurations and damage states are studied. Debond growth is characterized by the estimation of the Mode I and Mode II Energy Release Rate (ERR) using the Virtual Crack Closure Technique (VCCT). It is found that the presence of the 0°/90° interface and the thickness of the 0° layer have no effect, apart from laminates with ultra-thin 90° plies where it is however modest. The present analysis support the claim that debond growth is not affected by the plythickness effect.
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| 4. |
- Kahla, Hiba Ben, et al.
(författare)
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Local Delaminations Induced by Interaction Between Intralaminar Cracking and Specimen Edge in Quasi-Isotropic CF/EP NCF Composites in Fatigue Loadings
- 2020
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Ingår i: Mechanics of composite materials. - : Springer. - 0191-5665 .- 1573-8922. ; 56:3, s. 291-302
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Tidskriftsartikel (refereegranskat)abstract
- Experimental results are presented on the onset and propagation of local delaminations caused by the interaction between specimen edges and intralaminar cracks in fiber bundles of 90 degrees layers in quasi-isotropic [-45/90/45/0](s)CF/EP noncrimp fabric (NCF) laminates subjected to tension-tension fatigue loadings. It is confirmed that the first damage mode is intralaminar cracking in 90 degrees layers, which consists of intrabundle cracks and cracks in the matrix between bundles (often beginning from stitches). This damage mode triggers cracking in off-axis layers and local delaminations in positions where the 90 degrees layer crack meets an adjacent layer. The process of local delamination is significantly enhanced at specimen edges, where the out-of-plane edge stresses contribute to the local delamination. During cyclic loadings, delaminations grow and coalesce along the edge and propagate towards the specimen center. These processes are quantified experimentally at different levels of cyclic load. In a low-stress fatigue, a very high number of cycles is required to detect small edge delaminations, and they stay at the edge. In high-stress cyclic tests, delaminations grow faster inside the composite: about 20% of the interface in the central zone can be delaminated. It is found that the reduction in the axial modulus is proportional to the relative delaminated area, proving that delamination is the major stiffness reduction factor in these laminates.
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| 5. |
- Nunes, Stephanie Goncalves, et al.
(författare)
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On Temperature-Related Shift Factors and Master Curves in Viscoelastic Constitutive Models for Thermoset Polymers
- 2020
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Ingår i: Mechanics of composite materials. - : Springer. - 0191-5665 .- 1573-8922. ; 56:5, s. 573-590
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Tidskriftsartikel (refereegranskat)abstract
- Reliable accelerated testing routines involving tests at enhanced temperatures are of paramount importance in developing viscoelastic models for polymers. The theoretical basis, the time-temperature superposition (TTS) principle, is used to construct master curves and temperature-dependent shift factor, which is the necessary information to simulate the material response in arbitrary temperature and strain regimes. The Dynamic Mechanical and Thermal Analysis (DMTA) TTS mode, being one of the most promising approaches in terms of time efficiency and maturity of the software, is compared in this paper with macrotests at enhanced temperatures in their ability to give reliable master curves. It is shown, comparing simulations with test data for a chosen epoxy polymer, that none of the three DMTA TTS mode-based attempts used (at different temperature steps during frequency scanning) was successful in predicting the epoxy behavior in tests. On the contrary, using one-hour macrotests at enhanced temperatures gives a viscoelastic model with a very good predicting accuracy. Simulations were performed using an incremental formulation of the previously published VisCoR model for linear viscoelastic materials.
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| 6. |
- Pupure, Liva, et al.
(författare)
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Mechanical properties of natural fiber composites produced using dynamic sheet former
- 2020
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis. - 1748-0272 .- 1748-0280. ; 15:2, s. 76-86
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Tidskriftsartikel (refereegranskat)abstract
- Composites formed from wood fibers and man-made cellulosic fibers in PLA (polylactic acid) matrix, manufactured using sheet forming technique and hot pressing, are studied. The composites have very low density (due to high porosity) and rather good elastic modulus and tensile strength. As expected, these properties for the four types of wood fiber composites studied here improve with increasing weight fraction of fibers, even if porosity is also increasing. On the contrary, for man-made cellulosic fiber composites with circular fiber cross-section, the increasing fiber weight fraction (accompanied by increasing void content) has detrimental effect on stiffness and strength. The differences in behavior are discussed attributing them to fiber/ fiber interaction in wood fiber composites which does not happen in man-made fiber composites, and by rather weak fiber/matrix interface for man-made fibers leading to macro-crack formation in large porosity regions.
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| 7. |
- Saseendran, Sibin, 1989-, et al.
(författare)
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Incremental 1D Viscoelastic Model for Residual Stress and Shape Distortion Analysis During Composite Manufacturing Processes
- 2020
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer. - 9783030299859 ; , s. 65-76, s. 65-76
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Konferensbidrag (refereegranskat)abstract
- The present contribution is toward the systematic characterization and development of a one-dimensional incremental viscoelastic (VE) model for thermo-rheologically complex materials (called “VisCoR”) for the prediction of residual stresses and shape distortions in composites. Traditionally, models that have been developed for this purpose within the composites industry are based on incremental linear elastic methods. While these methods are robust, they fall short in predicting exact behaviour of large composite parts and high temperature composites where relaxation effects also play a vital role in the final shape of the part. Moreover, these models also do not consider the dependency of stresses on temperature and degree of cure. Although viscoelastic models have been formulated, they are not in an incremental form (which is suitable for Finite Element (FE) simulations), hence requiring higher computational efforts. The presented model is an incremental form and requires lesser computational cost and characterization efforts and most importantly takes into account the effect of temperature and degree of cure. Preliminary studies indicate that the incremental 1D viscoelastic model can accurately model VE stress relaxation behaviour when compared to exact solutions.
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| 8. |
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| 9. |
- Xu, Johanna, 1989-, et al.
(författare)
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Matrix and interface cracking in cross-ply composite structural battery under combined electrochemical and mechanical loading
- 2020
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Ingår i: Composites Science And Technology. - : Elsevier. - 0266-3538 .- 1879-1050. ; 186
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Tidskriftsartikel (refereegranskat)abstract
- In this paper propagation of matrix cracks and debonds at the coating/matrix interface in the 90°-layer of a cross-ply structural composite battery are studied numerically. The structural composite battery consists of micro-battery units, made of a solid electrolyte coated carbon fiber embedded in an electrochemically active polymer matrix. During charging the fiber swells and the matrix shrinks leading to high stresses on the fiber/matrix scale and to anisotropic free expansion of the composite ply. Two load cases are considered, pure electrochemical load (intercalation) and combined electrochemical and thermomechanical load. Energy release rates (ERR) of radial matrix cracks along two potential propagation paths are calculated using 2-D finite element models of the transverse plane in a cross-ply laminate with a square packing of fibers in the 90°-ply and using homogenized 0°-ply. Results show that the matrix crack growth towards the nearest fiber is unstable, and that the debond crack growth is in mixed mode. For a cross-ply structural battery composite the sequence of macro-scale crack forming events differs from a conventional cross-ply composite, as well as for a UD composite battery laminate. The most likely course of failure events in a cross-ply laminate are: 1) vertical radial matrix crack initiation and unstable growth; 2) debond is initiated at certain length of the matrix crack.
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