Energy release rate and stress intensity factors for delaminated composite laminates (original) (raw)
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Composite Structures, 2007
The aim of this paper is the analytical determination of the strain energy release rates in a delaminated laminate by means of a model of plates which provides no singular stresses. The strain energy release rates are expressed as quadratic functions of the interfacial stresses at the crack tip. These expressions and relevant delamination criteria can help predict delamination onset and growth. As an application example, data from edge delamination tests on carbon-epoxy laminates are used for determining a mode III delamination criterion involving the corresponding energy release rate. This criterion yields very accurate predictions and its analytical expression validates from an energy point of view a maximum stress criterion proposed in an earlier paper.
Numerical and analytical study of delamination in composite laminates
2012
A robust numerical method is developed to study delamination in composite beam structures under lateral and axial loads. A tensor symmetrisation technique is used to formulate the beam element based on the Euler beam theory with full geometrical non-linearity to achieve high computational efficiency. Ply interfaces are modelled with high-stiffness springs. It is found that the beam element suffers from membrane locking for non-symmetric laminates. A method is found to overcome it. The model is used to simulate double cantilever composite beam structure tests and end notched flexure tests. Excellent agreement is observed with analytical and existing numerical and experimental data. The model is also used to study the buckling, post-buckling and delamination propagation in moderately thick composite beams. Satisfactory agreement is demonstrated between the present predictions and existing numerical and experimental data. It is noted that the through-thickness shear effect is significant for moderately thick composite laminates.
Buckling and Delamination Growth Analysis of Composite Laminates Containing Embedded Delaminations
Applied Composite Materials, 2010
The objective of this work is to study the post buckling behavior of composite laminates, containing embedded delamination, under uniaxial compression loading. For this purpose, delamination initiation and propagation is modeled using the softening behavior of interface elements. The full layer-wise plate theory is also employed for approximating the displacement field of laminates and the interface elements are considered as a numerical layer between any two adjacent layers which delamination is expected to propagate. A finite element program was developed and the geometric non-linearity in the von karman sense is incorporated to the strain/displacement relations, to obtain the buckling behavior. It will be shown that, the buckling load, delamination growth process and buckling mode of the composite plates depends on the size of delamination and stacking sequence of the laminates.
Loading rate dependency of strain energy release rate in mode I delamination of composite laminates
Theoretical and Applied Fracture Mechanics, 2021
This work aims at studying the loading rate dependency of mode I delamination growth in CFRPs, using typical fracture toughness analysis through both the R-curve and the crack tip opening rate. The average SERR is a method of data reduction based on energy balance which has been previously introduced to characterize delamination growth under different types of loading conditions in a similar manner. In the present research, the application of this method was extended to further analyze the results of delamination experiments at different loading rates. Mode I delamination tests on double cantilever beam specimens were performed at displacement rates varying from standard quasi-static testing up to 400 mm/s. A clear decrease in the propagation fracture toughness as well as in the average SERR was observed at high loading rates. The reduced fracture resistance at elevated rates was physically explained in correlation with fiber bridging, fiber breakage, and matrix cleavage observed in fracture surfaces via scanning electron microscopy.
Physics of delamination onset in unidirectional composite laminates under mixed-mode I/II loading
Engineering Fracture Mechanics, 2019
In order to understand the physics of the delamination onset in laminated composites, an experimental investigation of delamination growth is presented. The main objective of this paper is to demonstrate that delamination onset occurs at lower values than G c defined by the ASTM standards, and that the strain energy release rate level at which the crack growth onset occurs under any mixed mode I/II loading is governed by the critical strain energy density (SED) approach. Quasi-static delamination experiments have been performed under mode I, mode II and mixed mode I/II loadings. The value of the strain energy release rate at the observed crack onset and the angle of the initial crack growth were correlated with the SED theory to test the validity. The acoustic emission was also used to provide more insight into the physics of the delamination growth. The investigation shows that the onset of delamination growth occurs at the strain energy release rate levels predicted by the critical SED approach, and well before reaching the critical strain energy release rate determined via delamination tests following the ASTM standards. Moreover, results indicated that the predicted angle of the initial crack for delamination onset was in a good agreement with the experimental data.
Energy release rates for interlaminar delamination in laminates considering transverse shear effects
Composite Structures, 2009
This paper presents simple and closed-form formulas for calculating mode I and II energy release rates, G I and G II , of a straight interlaminar crack in composite laminates subjected to general loadings. In addition to general combination of geometrical dimensions and material properties, the formulas are also explicitly expressed in terms of generic stress resultants in the cross section at the crack tip. The energy release rates predicted by the present analytical solutions are compared with those in the literatures. The novel formulations are presented and the simple closed-form solutions are obtained in terms of a general material and geometry combination and arbitrary loadings as well as the interface deformations.
Application of a delamination model to laminated composite structures
Composite Structures, 2002
A model for progressive interlaminar delamination is presented for laminated composite structures. Instead of a cumbersome 3D description, a computationally efficient 2D technique is adopted which models the laminated structure as an assembly of sublaminates connected through their interfaces. Constraints between sublaminates are removed to represent the presence of delaminations. The use of laminate theory results in jumps in stress resultants across the delamination tip and this helps to avoid dealing with the singular stress field at the delamination front. A stress-based failure criterion is used to predict delamination initiation. Delamination propagation is analysed by adopting a fracture mechanics approach. The major intralaminar damage mode, matrix cracking, is also included in the present analysis. This is detected by a stress-based failure criterion and a ply discount model is used to account for the effects of material degradation. Finite element analysis has been carried out to assess the deformation and the delamination development in a range of typical structures: a double cantilever beam, a cross-ply laminate and some filament-wound composite pipes. Good agreement has been achieved between the predictions and available experimental data. A study of the effect of mesh size shows that a relatively coarse mesh gives sufficiently accurate results. These examples give a useful indication of the versatility and feasibility of the present approach for real structural applications.
Fatigue <html_ent glyph="@amp;" ascii="&"/> Fracture of Engineering Materials and Structures, 2003
Delamination is one of the most frequent failure modes in laminated composites. Its importance is crucial, because a delamination can occur in the interior of a panel without any noticeable damage on the surface, drastically reducing its strength and stiffness. A study has to be made on critical dimensions of delaminations and their shape, through the calculation of the strain energy release rate (SERR), G. This study was performed numerically, for a given geometry, with varying loads and shapes of delamination, in pure and mixed-mode propagation. All numerical values were obtained with threedimensional finite element (FE) analyses from a commercial package. The use of three-dimensional analyses in simple geometries helps establish the basis for the more complex ones, and the correspondence with the usual analytical or numerical bidimensional plane-strain analysis. The conclusions were (a) G is not constant along the crack tip, even for mode I propagation and straight crack tip; (b) the mean value of G obtained from a three-dimensional analysis equals the value obtained in bi-dimensional plane-strain analysis; (c) in mixed-mode propagation, the method exhibits a good correlation with experimental results and (d) the shape and mode partitioning of the SERR depend not only on the loading, but also on the shape of the crack front.
Mechanical Behavior of Mode I Delamination of a Laminated Composite Material
2019
The objective of our work is to analyze numerically in three dimensions by the finite element method of the effect of a mechanical load on the delamination of unidirectional and multidirectional stratified composites in order to determine the energy release rate G in Mode I and the Von Mises equivalent stress distribution along the damaged area under the influence of several parameters such as applied load and delamination size. The results obtained in this study show that unidirectional composite laminates have better mechanical strength on the loading line than multi-directional composite laminates.