Delamination In Cross-ply Laminates Research Articles

Micro-mechanical analysis of matrix crack-induced delamination in cross-ply laminates in tension

A two-dimensional representative volume element model is developed to study the micro-mechanics of matrix crack-induced delamination in cross-ply laminates under longitudinal tensile loading. Fiber-matrix debonding and matrix cracking are investigated in the 90° ply. The 0° plies are modelled as homogenized, anisotropic elastic solids. A special emphasis is put on the interlaminar region where a thick resin-rich area is explicitly established, and delamination is characterized by a coupled plastic-damage model of the matrix. The process of delamination initiated from the matrix crack tips is accurately revealed by finite element analysis. The impact of different damage mechanisms on the macroscopic mechanical responses is quantitatively captured. A parametric study is done on different cross-ply laminates with various thicknesses of 90° ply to study their effect on the variation of the homogenized longitudinal stiffness and transverse Poisson's responses. It is found that transverse Poisson's response is more sensitive to the damages in the laminate and that degradation of the responses in thicker laminates is severer. In addition, analysis of the influence of thermal residual stress shows that it changes the damage initiation location and evolution path, and affects the transverse Poisson's response more obviously.

Modelling fracture and delamination in composite laminates: Energy release rate and interface stress

This article presents an approach for modelling fracture and delamination, based on the partition of finite elements and on the energy release rate due to crack propagation in cross-ply laminates. The energy release rate is implemented within an Extended Finite Element Method (XFEM) framework. This approach is enabling the prediction of delamination propagation without pre-allocating damage zones. No element deletion techniques were used either. Mesh refinement was not needed for the propagation of cracks. Virtual testing of transverse cracks – eventually triggering delamination in cross-ply laminates – is presented to show the technique efficiency. Thus, a maximum energy release rate of 0.9kJ/m2 is found for a transverse crack within [00,900]s laminate. When maximum energy release rate is reached, delamination in the {00/900} interface is triggered. Furthermore, delamination in a composite double cantilever beam is simulated and presented in some detail. The results were compared with experimental outputs and/or by other numerical means showing an excellent correlation.

Subtle features of delamination in cross-ply laminates due to low speed impact

In cross-ply laminates, the shape of delamination areas, which form due to low velocity impact, have two subtle features, which have been observed consistently in numerous experiments. Those are the pointed delamination tips and the intact zone between the lobes of delamination. However, there have not been any account available in the literature how they can be consistently captured through numerical modelling, and hence these features in published modelling results were often absent. It is the objective of this paper to identify the underlying modelling considerations so that these features can be captured with confidence. A key and unique reason has been identified in each case. Namely, inclusion of intra-laminar damage allows to reproduce the pointed delamination tips, while the gap between the lobes of delamination can be captured by models with sufficiently refined mesh, where friction between the laminas is taken into account. The capability of capturing these subtle features helps to raise the level of fidelity on the simulation of delamination due to impact.

Delamination in cross-ply laminates: Identification of traction–separation relations and cohesive zone modeling

Identification of traction separation relations is at the forefront of damage and fracture mechanics of composite laminates. Such relations are of particular interest in fracture of laminates consisting of layers of different fiber orientations. In this study, an iterative method based on internal strain measurements and parametric numerical modeling is employed to identify a traction-separation relation in quasi-static mode I dominated delamination of a cross-ply carbon fiber epoxy laminate. The results demonstrate that crack propagation is accompanied by a large bridging zone which is smaller than the zone in a uniaxial composite specimen of the same materials and linear dimensions. While the initiation value of the energy release rate (ERR) is the same, the ERR at steady state propagation and the maximum stress in the bridging zone are respectively 1.7 and 3.1 times larger than the corresponding values of the unidirectional specimen. The obtained traction-separation relation is employed in a cohesive zone model to predict the loading response and crack growth. The adopted approach is a step towards a better understanding of delamination in cross-ply composites. (C) 2015 Elsevier Ltd. All rights reserved.

PS14 CFRP薄板のパンチによる穿孔加工

This paper presents experimental characterization of a piercing process of CFRP thin laminates. Recently, application of CFRP is expected to expand to automobiles and mobile electronics. Hence, the present study was carried out to establish a method for a short-time and low-cost piercing process of thin CFRP laminates. A CFRP plate was pierced under various conditions by using a punch drived by a hydraulic testing machine. Surface and internal damages of the CFRP plates were observed by using optical microscopy, stereomicroscope and together with soft X-ray analysis. A damage process was then discussed on the basis of the experimental result. Next, the influence of clearance and shape of a punch on the damage in the specimen was examined to optimize clearance. Especially, the effect of clearance and shape of a punch on delamination in cross-ply laminates was investigated.

Interaction of Matrix Cracking and Delamination in Cross-ply Laminates: Simulations with Stochastic Cohesive Zone Elements

Two main damage mechanisms of laminates—matrix cracking and inter-ply delaminationare closely linked together (Joshi and Sun 1). This paper is focussed on interaction between matrix cracking and delamination failure mechanisms in CFRP cross-ply laminates under quasi-static tensile loading. In the first part of the work, a transverse crack is introduced in 90o layers of the cross-ply laminate [01/904/01], and the stresses and strains that arise due to tensile loading are analyzed. In the second part, the cohesive zone modelling approach where the constitutive behaviour of the cohesive elements is governed by traction-displacement relationship is employed to deal with the problem of delamination initiation from the matrix crack introduced in the 90o layers of the laminate specimen. Additionally, the effect of microstructural randomness, exhibited by CFRP laminates on the damage behaviour of these laminates is also accounted for in simulations. This effect is studied in numerical finite-element simulations by introducing stochastic cohesive zone elements. The proposed damage modelling effectively simulated the interaction between the matrix crack and delamination and the variations in the stresses, damage and crack lengths of the laminate specimen due to the microstructural randomness.

Development of Delamination in Cross-Ply Laminates: Effect of Microstructure

Various aspects of the effect of microstructural randomness exhibited by carbon fibre-reinforced cross-ply laminates on the delamination damage mechanism is investigated in this paper. In the first part, the matrix cracks with different spacings measured in experiments are simulated using finite elements in order to obtain the levels of degradation and effective properties for a composite beam loaded in bending. The results show significant levels of degradation of obtained effective properties depicting the importance of accounting for the inherent stochasticity in these laminates. In the second part of the paper, initiation of delamination at an interface between 0° and 90° layers due to stress concentrations at tips matrix cracks is simulated for a beam under tension. Stochastic cohesive zone elements with fracture parameters presented as random fields are used to model this interface in a composite. Different values of the axial stress are obtained for initiation of damage for a number of realisations based on this approach. The results emphasize the need to take into consideration the microstructural randomness in fibre-reinforced laminates for adequate predictions of damage and load carrying capacities.

A decomposition of the strain energy release rate associated with the initiation of transverse cracking, longitudinal cracking and delamination in cross-ply laminates

An energy criterion is proposed to study the damage evolution in a composite cross-ply laminate. This criterion is based on the computation of the partial strain energy release rate associated with each damage mechanism (transverse cracking, longitudinal cracking and delamination) and mode (I, II or III). Several decompositions of the complementary strain energy are put forward. Each component part of this decomposition is related to a specific damage mechanism and loading mode. The related criterion can predict and describe the initiation and propagation of the different damage mechanisms.

A criterion for modelling initiation and propagation of matrix cracking and delamination in cross-ply laminates

A variational approach is used to model the behaviour of composite cross-ply laminates damaged by transverse, longitudinal cracking and delamination. An energetic criterion is proposed. It is based on the strain energy release rate associated with each of the three damage modes. The first part of this paper is concerned with the modelling of the transverse and longitudinal cracking. In the second part, a model for studying delamination damage is presented. The numerical results show that these models provide a consistent level of accuracy for a variety of thin laminate material systems and configurations, with various combinations of delaminations and matrix cracks. In this paper several numerical simulations meant to describe initiation for each damage mode are proposed. The estimation of damage modes contributions is achieved for two thin laminates in order to predict the evolution of damage mode transition.

Transverse cracking and delamination in cross-ply glass-fiber and carbon-fiber reinforced plastic laminates: Static and fatigue loading

A review of developments and understanding of transverse cracking and delamination in cross-ply laminates is presented. First, experimental investigations reported in the literature for analyzing the development of transverse cracking are considered. Next, characteristics of different models for evaluating the stress distribution in the damaged laminates are developed. It is shown how these models associated with the statistical description of strength or energy released in the 90° plies make it possible to describe the development of transverse cracking in monotonic or fatigue loading. According to the nature of cross-ply laminates, transverse cracking is not, however, sufficient for describing the development of transverse cracks in 90° plies in the case of monotonic loading. In this case, the delamination process induced at transverse crack tips is to be considered for describing the experimental results. There are 108 references in this review article.

Statistical analysis of the progression of transverse cracking and delamination in cross-ply laminates

The paper presents a statistical analysis of the transverse cracking and delamination process induced in cross-ply laminates subjected to tensile loading. First, the paper considers the initiation and progression of transverse cracking. This progression is evaluated by an iterative procedure combining a generalized model for evaluating the stress field in a cracked laminate with a statistical distribution of strengths in the 90° layer. Comparisons between the results obtained by this procedure and the experimental results of the literature show that for very low crack densities the progression of transverse cracking is governed by a strength distribution associated with weakness areas resulting from the presence of particular defects in laminates. Next, for higher crack densities the strength distribution in the 90° layer can be described by a pseudo-normal distribution associated with the other defects. Finally, the paper considers the development of delamination which is initiated from the crack tips in the case of some laminates.

A model for transverse cracking and delamination in cross-ply laminates

This paper develops an analytical model to evaluate the stress distibutions in cross-ply laminates subjected to tensile loading and containing transverse cracks and delamination initiated from the transverse crack tips. In the delaminated part the analytical approach is reduced to the usual one-dimensional analysis. In the part without delamination the analytical model is based on a displacement approach which considers that the longitudinal displacement depends on the longitudinal and transverse coordinates in each layer. The stress distributions derived from the analytical model are compared with the results obtained from a finite-element analysis.