| 1. |
- Akshantala, Nagendra V., et al.
(författare)
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A mechanistic model for fatigue damage evolution in composite laminates
- 1998
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Ingår i: Mechanics of materials. - 0167-6636 .- 1872-7743. ; 29:2, s. 123-140
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Tidskriftsartikel (refereegranskat)abstract
- We propose a mechanistic model which is capable of describing the evolution of transverse cracking in cross ply laminates subjected to cyclic tension in the longitudinal direction. The key feature of the model is that it incorporates delamination associated with transverse cracks in a manner that induces further formation of transverse cracks as delamination grows in fatigue. A variational approach is taken to estimate the stresses in the region between transverse cracks, and these are found to be accurate away from the crack planes when comparison is made with finite element computations. The evolution of transverse crack density and the associated overall elastic moduli changes predicted by the model are in agreement with experimental results
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| 2. |
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| 3. |
- Bulsara, V.N., et al.
(författare)
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Damage initiation under transverse loading of unidirectional composites with arbitrarily distributed fibers
- 1999
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Ingår i: Composites Science And Technology. - 0266-3538 .- 1879-1050. ; 59:5, s. 673-682
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Tidskriftsartikel (refereegranskat)abstract
- A limiting property governing the thermomechanical behavior of composites is the strength transverse to the fibers. The present study investigates the dependence of this property on the distribution of fibers in the cross-section of a unidirectional composite. The approach taken is to consider actual distributions, which are arbitrary and are not necessarily described by random or periodic distributions. A fundamental issue in studying non-uniform distributions is the size of a representative volume element (RVE). By the use of an actual radial distribution function obtained for a ceramic-matrix composite by quantitative stereology in conjunction with a simulation technique developed in this study, the RVE size is investigated with respect to initiation of debonding and radial matrix cracking - two basic mechanisms governing the transverse strength of composites. Tensile loading transverse to the fibers and residual stresses induced by thermal cooldown are considered separately as loading modes for transverse failure. The results provide some useful insight into the importance of non-uniformity of fiber spatial distribution with regard to the transverse failure of composites. A limiting property governing the thermomechanical behavior of composites is the strength transverse to the fibers. The present study investigates the dependence of this property on the distribution of fibers in the cross-section of a unidirectional composite. The approach taken is to consider actual distributions, which are arbitrary and are not necessarily described by random or periodic distributions. A fundamental issue in studying non-uniform distributions is the size of a representative volume element (RVE). By the use of an actual radial distribution function obtained for a ceramic-matrix composite by quantitative stereology in conjunction with a simulation technique developed in this study, the RVE size is investigated with respect to initiation of debonding and radial matrix cracking - two basic mechanisms governing the transverse strength of composites. Tensile loading transverse to the fibers and residual stresses induced by thermal cooldown are considered separately as loading modes for transverse failure. The results provide some useful insight into the importance of non-uniformity of fiber spatial distribution with regard to the transverse failure composites.
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| 4. |
- Talreja, Ramesh, et al.
(författare)
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An inadequacy in a common micromechanics approach to analysis of damage evolution in composites
- 1998
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Ingår i: International journal of damage mechanics. - : SAGE Publications. - 1056-7895 .- 1530-7921. ; 7:3, s. 238-249
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Tidskriftsartikel (refereegranskat)abstract
- This article examines a commonly used micromechanics approach to evolution of damage in composites. In this approach an initial crack pattern is assumed and on the basis of the local stress fields and a (brittle) fracture criterion, further evolution of the same crack pattern is determined. We question this assumed self-similarity in the damage mode by considering two alternative crack modes, one of which would result in deviation from the assumed crack pattern. Using a simple maximum stress criterion for formation of brittle cracks, it is found that the self-similarity breaks down before saturation of cracking in the assumed crack pattern. This seemingly inherent inadequacy in the damage evolution analysis is discussed.
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| 5. |
- Varna, Janis, et al.
(författare)
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Crack opening displacement and the associated response of laminates with varying constraints
- 1999
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Ingår i: International journal of damage mechanics. - : SAGE Publications. - 1056-7895 .- 1530-7921. ; 8:2, s. 174-193
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports an experimental study of the opening displacement behavior of 90-ply cracks in a class of composite laminates where the constraint to cracking is varied systematically. The study is motivated by a synergistic approach to damage mechanics proposed by Talreja (1996) where the crack opening displacement forms a key micromechanically determined parameter in a continuum damage formulation of the composite response. It is found that although the opening displacement shows scatter from point to point along a crack length, its average over the crack length forms a robust parameter. This parameter, when introduced as the damage influence coefficient in a continuum description of damage, allows satisfactory predictions of the elastic moduli changes due to transverse cracks in the considered class of laminates with varying constraints.
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| 6. |
- Varna, Janis, et al.
(författare)
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Damage in composite laminates with off-axis plies
- 1999
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Ingår i: Composites Science And Technology. - 0266-3538 .- 1879-1050. ; 59:14, s. 2139-2147
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Tidskriftsartikel (refereegranskat)abstract
- Damage in off-axis plies of composite laminates is studied by examining the configuration [0/±θ4/01/2]s with θ=25, 40, 55, 70 and 90 subjected to tensile loading in the axial direction. It is found that for the values of θ, where the stress in the off-axis plies normal to the fibers is tensile, ply cracks lying along fibers initiate and increase in number, while for other θ values the plies do not undergo this damage, as expected. However, the overall laminate elastic moduli are also found to change for the θ values where no ply cracks exist. It is postulated that a shear-induced degradation of the off-axis plies is responsible for the observed laminate moduli changes. The prediction of changes in these moduli by using the ply shear modulus measured on [±θ4]s appears to support this postulate. For the case of moduli changes caused by ply cracks the recently proposed synergistic damage-mechanics approach [1] is applied. The implications of the findings of this work on a class of continuum damage-mechanics formulations proposed in the literature are discussed.
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