| 1. |
- Andersons, Janis, et al.
(författare)
-
Estimation of laminate stiffness reduction due to cracking of a transverse ply by employing crack initiation- and propagation-based master curves
- 2008
-
Ingår i: Mechanics of composite materials. - : Springer Science and Business Media LLC. - 0191-5665 .- 1573-8922. ; 44:5, s. 441-450
-
Tidskriftsartikel (refereegranskat)abstract
- The applicability range of toughness-and strength-based criteria for progressive cracking of a transverse layer in a cross-ply composite laminate subjected to tensile loading is considered. Using a deterministic cracking model, approximate relations for the crack density as a function of stress are derived for initiation-and propagation-controlled types of cracking. The master-curve approach is applied to progressive cracking in glass/epoxy laminates. The accuracy of estimation of laminate stiffness reduction by using crack density master curves is evaluated.
|
|
| 2. |
- Andersons, J., et al.
(författare)
-
Prediction of crack onset strain in composite laminates at mixed mode cracking
- 2009
-
Ingår i: 5th International EEIGM/AMASE/FORGEMAT Conference on Advanced Materials Research. - Bristol : IOP Publishing Ltd.
-
Konferensbidrag (refereegranskat)abstract
- Failure process of continuous fiber reinforced composite laminates in tension usually starts with appearance of intralaminar cracks. In composite laminates with complex lay-ups and/or under combined loading, intralaminar cracks may develop in plies with different reinforcement directions. A necessary part of mixed mode cracking models is the criterion of failure. For propagation-controlled fracture it is usually formulated in terms of energy release rates and their critical values of the particular composite material. Intralaminar fracture toughness of unidirectionally reinforced glass/epoxy composite was experimentally determined at several mode I and mode II ratios. It is found that the crack propagation criterion, linear in terms of the energy release rates, reasonably well approximates the test results. The determined mixed mode cracking criterion was applied to predict intralaminar crack onset in cross-ply glass/epoxy composite under tensile loading. The predicted crack onset strain values agree with test results at small off-axes angles of the cracking ply (on-axis and 15° off-axis loading), but underestimate crack onset at larger reinforcement angles with respect to the loading direction. The discrepancy is likely to be caused by the deviation of linearity in laminate response before cracking onset in these laminates, related to non-linear shear characteristics of unidirectional plies. The applicability of strength-based fracture criterion for initiation-controlled cracking is discussed.
|
|
| 3. |
- Andersons, Janis, et al.
(författare)
-
Progressive cracking mastercurves of the transverse ply in a laminate
- 2009
-
Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 30:8, s. 1175-1182
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, progressive cracking of a transverse layer in a cross-ply composite laminate subjected to tensile loading is considered. Using the results of a probabilistic cracking model, approximate relations for crack density as a function of stress are derived for initiation-controlled and propagation-controlled cracking. It is shown that the crack density evolution in the transverse ply can be represented by a mastercurve in suitably normalized coordinates. The mastercurve approach is applied to progressive cracking in glass/epoxy laminates.
|
|
| 4. |
- Andersons, Janis, et al.
(författare)
-
Statistical model of the transverse ply cracking in cross-ply laminates by strength and fracture toughness based failure criteria
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:9, s. 2651-2665
-
Tidskriftsartikel (refereegranskat)abstract
- Cross-ply laminate subjected to tensile loading provides a relatively well understood and widely used model system for studying progressive cracking of the transverse ply. This test allows to identify material strength and/or toughness characteristics as well as to establish relation between damage level and the composite stiffness reduction. The transverse ply cracking is an inherently stochastic process due to the random variability of local material properties of the plies. The variability affects both crack initiation (governed by the local strength) and propagation (governed by the local fracture toughness). The primary aim of the present study is elucidation of the relative importance of these phenomena in the fragmentation process at different transverse and longitudinal ply thickness ratios. The effect of the random crack distribution on the mechanical properties reduction of the laminate is also considered. Transverse ply cracking in glass fiber/epoxy cross-ply laminates of the lay-ups [02/902]s, [0/902]s, and [0/904]s is studied. Several specimens of each lay-up were subjected to uniaxial quasistatic tension to obtain crack density as a function of applied strain. Crack spacing distributions at the edge of the specimen also were determined at a predefined applied strain. Statistical model of the cracking process is derived, calibrated using crack density vs. strain data, and verified against the measured crack spacing distributions.
|
|
| 5. |
- Andersons, J., et al.
(författare)
-
Stiffness and strength of flax fiber/polymer matrix composites
- 2006
-
Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 27:2, s. 221-229
-
Tidskriftsartikel (refereegranskat)abstract
- Flax fiber composites with thermoset and thermoplastic polymer matrices have been manufactured and tested for stiffness and strength under uniaxial tension. Flax/polypropylene and flax/maleic anhydride grafted polypropylene composites are produced from compound obtained by coextrusion of granulated polypropylene and flax fibers, while flax fiber mat/vinylester and modified acrylic resin composites are manufactured by resin transfer molding. The applicability of rule-of-mixtures and orientational averaging based models, developed for short fiber composites, to flax reinforced polymers is considered.
|
|
| 6. |
- Andersons, Janis, et al.
(författare)
-
Strength distribution of elementary flax fibres
- 2005
-
Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 65:3-4, s. 693-702
-
Tidskriftsartikel (refereegranskat)abstract
- Flax fibres, along with a number of other natural fibres, are being considered as an environmentally friendly alternative of synthetic fibres in fibre-reinforced polymer composites. A common feature of natural fibres is a much higher variability of mechanical properties. This necessitates study of the flax fibre strength distribution and efficient experimental methods for its determination. Elementary flax fibres of different gauge lengths are tested by single fibre tension in order to obtain the stress-strain response and strength and failure strain distributions. The applicability of single fibre fragmentation test for flax fibre failure strain and strength characterization is considered. It is shown that fibre fragmentation test can be used to determine the fibre length effect on mean fibre strength and limit strain.
|
|
| 7. |
|
|
| 8. |
- Andersons, Janis, et al.
(författare)
-
The onset of mixed mode intralaminar cracking in a cross-ply composite laminate
- 2008
-
Ingår i: Mechanics of composite materials. - : Springer Science and Business Media LLC. - 0191-5665 .- 1573-8922. ; 44:6, s. 549-556
-
Tidskriftsartikel (refereegranskat)abstract
- The intralaminar fracture toughness of a unidirectionally reinforced glass/epoxy composite is determined experimentally at several mode I and mode II loading ratios. The crack propagation criterion, expressed as a quadratic form in terms of single-mode stress intensity factors (alternatively, linear in terms of energy release rates), approximates the test results reasonably well. The mixed-mode cracking criterion obtained is used to predict the intralaminar crack on set in a cross-ply glass/epoxy composite under off-axis tensile loading.
|
|
| 9. |
|
|
| 10. |
- Edgren, Fredrik, et al.
(författare)
-
Failure of NCF Composites Subjected to Combined Compression and Shear Loading
- 2006
-
Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 66:15, s. 2865-2877
-
Tidskriftsartikel (refereegranskat)abstract
- Earlier studies have shown that formation of kink bands is the mechanism that is likely to govern failure of compression loaded non-crimp fabric (NCF) composite laminates. Because of this, a failure criterion for prediction of failure caused by kinking under multiaxial (axial compression and shear) loading has been adapted to a NCF composite system. The criterion has been validated for compression tests of quasi-isotropic laminates tested in uniaxial compression. By performing compression tests of the laminate at different off-axis angles, it was possible to vary the ratio of compressive axial stress/shear stress in the specimens. The test results proved that the criterion works well for predictions of kinking governed failure for the present material system. Detailed fractographic studies confirmed that formation of kink bands was the mechanism responsible for specimen failure. Kink bands were also found to develop at loads significantly lower than load at specimen failure.
|
|
