Evolution Of Transverse Cracking Research Articles

Transverse crack evolution modeling of cross-ply laminates with a single layer of phantom node intraply elements for identically-oriented ply groups

Discrete damage modeling techniques are superior in predicting failure of composite laminates involving massive delamination. In order to reproduce the influence of transverse crack opening on local stress distribution, identically orientated ply groups are often meshed with multiple layers of elements when applying these techniques to model transverse crack evolution processes of laminates. To save computation costs, researchers also tried to use only a single layer of elements in cracking plies whose accuracy, however, still needs to be improved. In the current study, an improved modeling strategy is proposed where adjacent identically-oriented plies are meshed with a single layer of elements. Herein, a phantom node solid element is adopted for matrix cracking modeling and a phantom node cohesive element is proposed to match the intraply element. Soft interfaces and a Weibull model of transverse strength are introduced in order to reproduce experimental phenomena and a parameter correction method for interface properties is proposed based on a shear lag model to improve predictions. The proposed strategy is verified by modeling crack evolution processes of cross-ply laminates of two different material systems. Besides, influences of model parameters and the applicability of identified parameters to cases of other layups are investigated.

Thermo-mechano-oxidative behavior at the ply’s scale: The effect of oxidation on transverse cracking in carbon–epoxy composites

The use of polymer matrix composites at relatively high temperatures (150–300°C) requires accounting for the oxidation of the polymer and its coupling with mechanical degradation. A vast body of literature investigates these phenomena at very small scales, from the chemistry of the polymer to the mechanical behavior at the fiber’s scale. The aim of this work is to apprehend the effect of oxidation on the transverse composite properties directly at the ply’s scale, and in particular to examine its effect on the evolution of transverse cracking during aging and mechanical loading. Experimental results demonstrated the appearance of a new cracking scenario with respect to unaged composites, and a model based on finite fracture mechanics enabled us to explore the competition between the two different mechanisms. This work is a first step towards a damage mesomodel which incorporates the effects of oxidation aging.

Matrix cracking and delamination evolution in composite cross-ply laminates

AbstractThis study followed numerous simulations of the stress field distribution in damaged composite cross-ply laminates, which were subjected to uni-axial loading. These results led us to elaborate an energy criterion. The related criterion, a linear fracture-based approach, was used to predict and describe the initiation of the different damage mechanisms. Transverse crack damage was generally the first observed damage. The second type of damage was longitudinal cracking and/or delamination. The stress field distribution in the damaged cross-ply laminates was analysed through an approach that used several hypotheses to simplify the damage state. The initiation of transverse cracking and delamination mechanisms was predicted. The proposed results concern the evolution of the strain energy release rate associated to the evolution of transverse cracking and delamination. As in several studies in the literature, to quantify the evolution of the damage mechanisms in the present approach, the laminate is su...

An experimental investigation of the effect of shear-induced diffuse damage on transverse cracking in carbon-fiber reinforced laminates

When subjected to in-plane loading, carbon-fiber laminates experience diffuse damage and transverse cracking, two major mechanisms of degradation. Here, we investigate the effect of pre-existing diffuse damage on the evolution of transverse cracking. We shear-loaded carbon fiber-epoxy pre-preg samples at various load levels to generate controlled configurations of diffuse damage. We then transversely loaded these samples while monitoring the multiplication of cracking by X-ray radiography. We found that diffuse damage has a great effect on the transverse cracking process. We derived a modified effective transverse cracking toughness measure, which enabled a better definition of coupled transverse cracking/diffuse damage in advanced computational models for damage prediction.

A Probabilistic SCG Model for Transverse Cracking in CFRP Cross-ply Laminates under Cyclic Loading

This paper presents a probabilistic fatigue model for transverse cracking in CFRP cross-ply laminates. First, a delayed fracture model for a crack in a brittle material subjected to cyclic loading was established on the basis of the slow crack growth (SCG) concept in conjunction with the Weibull's probabilistic failure model. Second, the above probabilistic delayed fracture model was applied to transverse cracking in cross-ply laminates during cyclic loading. The stress distribution and the length of the unit element were calculated with the aid of a shear lag analysis. The transverse crack density was expressed as a function of maximum stress, stress ratio and number of cycles using the parameters associated with the Paris equation and the Weibull distribution in addition to the mechanical properties. Unknown parameters were determined from experiment data for three kinds of cross-ply laminates to reproduce the transverse crack density against the number of cycles. The parametric studies using the obtained parameters revealed the effects of the Weibull modulus, crack propagation exponent and stress ratio on evolution of transverse cracking under fatigue loading.

A probabilistic approach for transverse crack evolution in a composite laminate under variable amplitude cyclic loading

Abstract This paper presents a theoretical approach for predicting transverse cracking behavior in a cross-ply laminate with a thick transverse ply under variable amplitude loads for which the cracks grow instantaneously, or very quickly, across the specimen width. The transverse crack density was derived on the basis of the slow crack growth (SCG) concept using the Paris law in conjunction with the Weibull distribution for a brittle material subjected to multi-stage cyclic loading. A fracture criterion obtained was related with the empirical rules by Miner and Broutman & Sahu. Next, the probabilistic SCG model was applied to transverse cracking in a cross-ply laminate under multi-stage cyclic loading. The two-stage fatigue tests with various loading sequences and amplitudes were conducted for carbon fibre reinforced plastic (CFRP) cross-ply laminates in addition to single-stage fatigue tests for various maximum stresses. The experiment results were compared with the predictions to verify the validity of the model.

確率的ＳＣＧモデルとエネルギー解放率を用いたトランスバースクラックに関する疲労破壊クライテリオン

New fatigue fracture criteria for the transverse crack evolution in a composite laminate subjected to cyclic loading were proposed using the probabilistic model and energy release rate. First, a time-dependent fracture model that combines slow crack growth (SCG) with stochastic failure was established for a general brittle material. The fracture probability was obtained as a function of the number of cycles and maximum stress on the basis of the Paris law and Weibull distribution. Next, the above probabilistic SCG model was applied to the fatigue transverse cracking behavior to establish a stress intensity factor criterion. Thirdly, an energy criterion for predicting fatigue transverse crack density was shown through the combination of the energy release rate on the basis of a variational approach by Nairn with the SCG model. The predicted transverse crack density under the static tensile and fatigue loading was compared with the experiment result to verify the reasonability of the above fracture criteria. In addition, the transverse crack density rate versus the number of cycles predicted using the two fracture criteria and the Paris's equation proposed by Nairn was compared with the experimental results. The transverse crack initiation life was also derived from the energy criterion.

Characterization of microscopic damage in composite laminates and real-time monitoring by embedded optical fiber sensors

First, a methodology for observation and modeling of microscopic damage evolution in quasi-isotropic composite laminates is presented. Based on the damage observation using both an optical microscope and a soft X-ray radiography, a damage mechanics analysis is conducted to formulate the stiffness change due to transverse cracking. Then, both energy and stress criteria are combined to provide a valid procedure to predict the transverse crack evolution. The theoretical prediction is found to agree well with the experimental results for the transverse crack density as a function of strain as well as stress–strain curves. Then, another methodology is introduced using two kinds of embedded optical fiber sensors to detect and monitor the transverse crack evolution in composite laminates. One is plastic optical fibers (POF), where the loss in optical power is generated by local deformation of POF due to transverse cracking. The other is fiber Bragg grating (FBG) sensors, where the local strain distribution within the FBG gage length due to transverse cracking alters the power spectrum of the light reflected from the FBG sensors. Embedded optical fiber sensors are found to be a powerful method to detect and monitor the transverse crack evolution in composite laminates.

Experimental characterization of the effects of stacking sequence on the transverse crack behavior in quasi-isotropic interleaved CFRP laminates

Transverse crack behavior in quasi-isotropic interleaved CFRP laminates was observed by an optical microscope and a soft X-ray radiography system. Seven symmetric laminates composed of the same combination of ply orientations were tested to clarify the effect of stacking sequence on transverse crack behavior in 90° plies. The thickness of 90° plies and the modulus of adjacent plies were found to be most influential in their effect on transverse cracking behavior. To model the experimental results, damage mechanics analysis was used. The predictions of transverse crack evolution based on both energy and average stress criteria were compared with the experimental results. The validity of the present analysis was confirmed. The advantage of this analysis was its applicability to general laminate configuration, once the critical values were determined.

Damage Mechanics Analysis of Transverse Cracking Evolution in Delaminated CFRP Laminates

A damage mechanics analysis was applied to predict transverse crack evolution in a laminated composite. The analysis was originally developed to predict thermoelastic properties of a laminate containing transverse cracks. Two criteria based on both critical average ply stress and critical energy release rate were used to discuss the transverse cracking behavior. The effect of delamination was also considered in the present study. The predictions of transverse crack density based on both criteria were successfully compared with experimental results. This analysis can be applied to laminate with arbitrary lay-up configuration.

Evolution of Transverse Cracking in CF/Epoxy Cross-Ply Laminates under Creep Loading

The evolution of transverse cracking in a cross-ply laminate which deforms viscoelastically is investigated. A model predicting the strain under creep loading is established by a combination of the viscoelasticity theory, shear lag analysis and delayed failure concept. The creep strain and transverse crack density of the cross-ply laminates are measured during creep tests. TWo stages of time for transverse cracking are observed in the creep tests. Predicted creep strains using the present model agree well with the experimental ones.

A mechanistic model for fatigue damage evolution in composite laminates

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.

複合材料の設計と評価の最前線 ３．複合材料における損傷の定量評価 横き裂損傷の発達，応力腐食割れの解析を中心に

複合材料の設計と評価の最前線 ３．複合材料における損傷の定量評価 横き裂損傷の発達，応力腐食割れの解析を中心に