Material Degradation Model Research Articles

Dependence of damage modes on the ply-thickness of ultra-thin-ply composites

Transitions between damage modes have been observed in ultra-thin-ply laminates. Numerical methods can be effectively applied to the design and optimization of the microstructure of ultra-thin ply laminates. It is difficult to precisely predict transitions between complex damage modes of composites, such as fiber breakage, matrix cracking, shear failure and delamination. In this paper, a numerical model was developed to comprehensively consider in-plane damage and delamination. The initiation and in-plane propagation of damage was simulated using a material degradation model (MDM), which was implemented by a user subroutine USDFLD in ABAQUS. A cohesive interaction between the surfaces of adjacent layers was used to simulate delamination. The numerical predictions for the transitions between damage modes in cross-ply and Bouligand thin-ply laminates were verified by comparison with experimental results. The novelty of this study is discovering the dependence of damage modes on the ply-thickness under bending load and revealing the influence of damage competition mechanism on the bending properties of thin-ply composite. The research results could help develop a useful tool for improving microstructure design or elucidating the underlying mechanism for the mechanical behavior of thin-ply microstructures.

Framework, method and case study for the calculation of end of life for HWL and parameter sensitivity analysis

Mass construction and operation of hazardous waste landfill infrastructure has greatly improved China’s waste management and environmental safety. However, the deterioration of engineering materials and the failure of landfill may lead to the release of untreated leachate rich in persistent toxic pollutants to the soil and shallow groundwater. Accordingly, we develop the framework and process model to predict landfill life by coupling the landfill hydrological performance model and material degradation model. We found that the decrease rate of the concentration of persistent pollutants in leachate was significantly slower than the deterioration rate of the landfill engineering materials. As a result, when the materials failed, the leachate with high concentrations of persistent pollutants continued to leak, resulting in the pollutants concentration in surrounding groundwater exceeding the acceptable concentration at around 385 a, which is the average life of a landfill. Further simulation indicated that hydrogeological conditions and the initial concentration of leachate will affect landfill lifespan. The correlation coefficients of concentration, the thickness of vadose zone and the thickness of aquifer are − 0.79, 0.99 and 0.72 respectively, so the thickness of vadose zone having the greatest impact on the life of a landfill. The results presented herein indicate hazardous waste landfill infrastructure reinvestment should be directed toward long-term monitoring and maintenance, waste second-disposal, and site restoration.

Free vibration analysis of laminated composite plates during progressive failure

Natural frequencies of laminates during its progressive failure are investigated using finite element method. The finite element formulation is based on seven degrees of freedom displacement field, deduced for an orthotropic material. Free vibration analysis is carried out during ply-by-ply failure for a laminate subjected to uniformly distributed load. The variation of fundamental frequency with material and geometric properties is also presented. This study illustrates the effect of ply failure on the natural frequencies of a laminate. The prediction of failed ply and failure mode is accomplished via. Hashin failure criterion. Ply-discount material degradation model is adopted to modify the elastic constants of the failed ply. The effect of fibre orientation, failure mode and failed-ply on natural frequencies is highlighted in this paper. Jacobi iterative method is used to evaluate the natural frequencies of laminate. For the analysis, a computer code is written using FORTRAN based on the finite element formulation.

Ply-by-ply failure analysis of laminates using finite element method

Ply-by-ply failure analysis of anti-symmetric and symmetric laminated composite plates under uniformly distributed transverse load is carried out in this study. The successive failure analysis includes the determination of ply-by-ply failure load along with the failure mode using different stress-based failure theories. Ply-discount material degradation model is adopted to modify the properties of the failed lamina. The laminate has been modeled using eight noded isoparametric plate bending element having seven degrees of freedom at each node. A computer code is written using FORTRAN based on finite element formulation. The first-ply failure load has been compared with the reported results and a good conformity is found. Further comparison of different failure theories is made based on their ability to predict the failed ply, failure load along with the failure mode. The results are computed for both angle-ply and cross-ply laminates with simply supported and clamped edges. The importance of stacking sequence in terms of strength of the laminate is highlighted in the study.

A micromorphic approach for gradient-enhanced anisotropic ductile damage

This paper deals with the numerically effective modeling of anisotropic material degradation caused by ductile damage. Although standard local anisotropic damage models are relatively well-developed nowadays, their regularization which is required in order to eliminate their mathematical ill-posedness is far from being straightforward. It bears emphasis that this regularization is not only required from a mathematical point of view, since the aforementioned ill-posedness is known to be the source for the pathological mesh dependence as far as the finite element method is concerned. Within this paper, a general local framework for capturing anisotropic material degradation caused by ductile damage is extended to a non-local model by means of a gradient-enhancement. However, in order to achieve a numerically effective implementation, the gradient-enhancement is not implemented in a direct manner, but by means of a micromorphic approximation. By doing so, the implementation of the underlying local model is almost unaffected. Particularly the inequalities resulting from the yield function can be restricted to the local integration point level. Since a naive micromorphic implementation turns out to be unsuitable for regularizing the underlying local model, a novel adaption of the yield function is proposed. It is shown that the resulting single-surface-model is indeed able to capture anisotropic material degradation caused by ductile damage and, furthermore, that the finite element implementation is mesh objective.

Mooring chain strength tests and ductile failure modeling using micromechanics and phenomenology based failure models

Mooring chains in many offshore floating facilities have failed due to overloading under extreme environmental events. The ductile failure in chains due to overloading has not been addressed in past studies. Therefore, the present study aims to analyze the ductile failure in chain links using micromechanics and phenomenology based numerical models. The material damage model parameters are established using material stress-strain plots obtained from tensile tests on coupons, extracted from a R3 grade steel chain link. The validation of material degradation models is achieved by comparing results from numerical studies and monotonic loading tests on mooring chain links of 76 mm nominal diameter. The material models successfully capture the failure mode and strength of the chain links.

Progressive failure analysis of marine sandwich joints with a modified material degradation model

The progressive failure analysis based on a modified stiffness degradation model was proposed to predict mechanical response of sandwich L-joints for ships. A representative volume element was established for the derivation of the modified material degradation model for two-dimensional orthogonal woven fabric structures based on micromechanical theory. The modified Shokrieh failure criterion and six field variables were applied in ABAQUS user subroutines. Three different coordinate systems were used to assign reasonable material orientation. The predictions of ultimate load, stress distribution, load-displacement curve and failure patterns were compared with experimental results. The good consistence indicates the effectiveness of the proposed stiffness degradation model. The FE results show the edge of the arc bracket is the stress concentration area due to the shear lag effect, and the declined slope of load–displacement curve is caused by delamination failure due to the stiffness difference of laminates and foam core.

Material Degradation Modeling and Failure Prediction Using Microstructure Images

Degradation data, frequently along with low-dimensional covariate information such as scalar-type covariates, are widely used for asset reliability analysis. Recently, many high-dimensional covariates such as functional and image covariates have emerged with advances in sensor technology, containing richer information that can be used for degradation assessment. In this article, motivated by a physical effect that microstructures of dual-phase advanced high strength steel strongly influence steel degradation, we propose a two-stage material degradation model using the material microstructure image as a covariate. In Stage 1, we show that the microstructure image covariate can be reduced to a functional covariate while statistical properties of the image are preserved up to the second order. In Stage 2, a novel functional covariate degradation model is proposed, based on which the time-to-failure distribution in terms of degradation level passages is derived. A penalized least squares estimation method is developed to obtain the closed-form point estimator of model parameters. Analytical inferences on interval estimation of the model parameters, the mean degradation levels, and the distribution of the time-to-failure are also developed. Simulation studies are implemented to validate the developed methods. Physical experiments on dual-phase advanced high strength steel are designed and conducted to demonstrate the proposed model. The results show that a significant improvement is achieved for material failure prediction by using material microstructure images compared with multiple benchmark models.

A bi-material property based FE modelling method for progressive damage analyses of composite double-lap bolted joints

Abstract A bi-material property method was proposed to describe mechanical properties of the unidirectional composite lamina. It divided the lamina into the fiber layer and the resin layer, which have different material properties and are responsible for the intra-laminar and inter-laminar properties, respectively. Furthermore, a finite element modelling method with the composite lamina simulated by the bi-material property method was presented. Combined with a Hashin-type failure criterion and a micromechanics-based material degradation model, a novel progressive damage model (PDM) was constructed for typical double-lap bolted joints. To validate the novel PDM, four double-lap, single-bolt joints with various width-to-hole-diameter ratios were designed and quasi-static tensile tests of the joints were performed. Numerical results of the novel PDM show better agreements with the experimental outcomes than the traditional PDMs. Besides, the novel PDM can describe the inter-laminar damage more precisely via a more reasonable simulation for the inter-laminar property of the lamina, and can also obtain more accurate deformation of the hole along the thickness direction of the laminate. Furthermore, influences of the width-to-hole-diameter ratio W/D on failure behaviours of the double-lap, single-bolt joint were revealed, and an optimal width-to-hole-diameter ratio was recommended for engineering practice. Combined with our previous study on effects of the end-distance-to-hole-diameter ratio E/D, a failure mode map with varying W/D and E/D was determined for the double-lap bolted joint. It is helpful for designers to seek safer designs of composite bolted joints because the W/D and E/D are key geometrical parameters that significantly affect failure behaviours of the joints.

Energy based collocation method to predict progressive damage behavior of imperfect composite plates under compression

Abstract A new collocation methodology is presented to predict failure and progressive damage behavior of composite plates in this paper. The present work deals with composite plates containing initial geometric imperfections and different boundary conditions under uniaxial in-plane compressive load. In the present study, the domain is discretized with Legendre-Gauss-Lobatto nodes and the approximation of displacement fields is performed by Legendre Basis Functions (LBFs). The onset of damage and damage evolution are predicted by Hashin’s failure criteria and by proposed material degradation models. Three geometric degradation models are also assumed to estimate the degradation zone around the failure location which are named complete, region and node degradation models.

Mixed-Order Finite-Element Modeling of Magnetic Material Degradation Due to Cutting

As a part of manufacturing of electrical machines, electrical sheets are cut to the desired shape by various cutting techniques, such as punching and laser cutting. This cutting process degrades the magnetic material near the cut edge, which should be included in the finite-element modeling of electrical machines. However, due to the nature of the cutting effects, the existing finite-element modeling of the cutting effect results in computationally heavy simulations. This paper investigates the application of mixed-order elements to model the cutting effect. The second-order nodal triangular elements are used near the cut edge, whereas transition/first-order elements are applied in the remaining solution domain. Furthermore, the accuracy of the presented method is analyzed with the traditional method. According to the simulations, the mixed-order elements returned accurate results significantly faster than the traditional finite-element-based approaches. Furthermore, the effect of the cutting on the machine performance is also studied by comparing its results briefly.

A progressive failure analysis of all-C/SiC composite multi-bolt joints

A progressive damage model (PDM) was proposed to analyse the failure of plain-weave carbon fibre-reinforced silicon carbide (C/SiC) composite joints with C/SiC bolts, which were manufactured by the chemical vapour infiltration (CVI) technique. A bilinear constitutive model was established to describe the pseudo-plasticity of the C/SiC composites. Several failure criteria, including the maximum stress failure criterion, Tsai-Wu failure criterion, and Hashin-type criterion, and several material degradation models were compared. Moreover, the deposition models accounting for the deposition effects of CVI in the all-C/SiC composite joints were discussed. A series of comparative failure analyses of a C/SiC open-hole composite laminate with available experimental data in the literature was conducted to determine the most suitable combination of the Hashin-type criterion and the combined material degradation model was filtered for C/SiC composite structures. Based on the PDM, the failure strength and failure pattern of an all-C/SiC composite single-lap, three-bolt joint were predicted. Static tension experiments testing the all-C/SiC composite single-lap, three-bolt joints fabricated by the CVI technique were also conducted. Good consistency between the numerical failure predictions and the experimental outcomes was obtained, indicating the effectiveness of the proposed PDM for failure analyses of all-C/SiC composite multi-bolt joints.

A progressive fatigue damage model for composite structures in hygrothermal environments

An improved progressive fatigue damage model (PFDM) involving hygrothermal effects was proposed to predict fatigue failure of composite structures in hygrothermal environments. In the improved PFDM, a unified model was established to evaluate the variation of composite material properties caused by hygrothermal environments. The hygrothermal-induced material properties were utilized in the stress analysis model, material degradation models and fatigue failure criterion. The hygrothermal strains were introduced into the constitution equation to account for the hygrothermal effects. A residual-strain-based gradual material degradation model and a micromechanics-based sudden material degradation model were enhanced to describe the damage of composite materials in hygrothermal environments. Besides, fatigue tests and progressive fatigue damage analyses of an open-hole laminate were performed in hygrothermal environments. The good consistency between the numerical and experimental results validated the improved PFDM. Both the experimental and numerical outcomes indicate that the effective moisture equilibrium considerably reduces the compressive strength and compressive fatigue life of the open-hole laminate made of T800 carbon/epoxy composites.

A novel material degradation model for unidirectional CFRP composites

Abstract A novel material degradation model (MDM), which is an essential component of progressive damage models for failure analysis of composite structures, is proposed based on the representative volume element (RVE) method. In this model, a material degradation rule accounting for seven failure modes in a modified Hashin-type failure criterion is proposed. This rule determines the mechanical parameters that are degraded when a failure occurs. The degradation factors of these parameters are calculated from the RVE models for perfect and damaged materials corresponding to the seven failure modes, which are based on the fundamental properties of transverse isotropic fibers and isotropic matrix. To verify the proposed method, the calculated MDMs are used in the progressive failure analyses of open-hole laminates made of three types of CFRP composites under tensile and compressive loadings. Furthermore, the failure analyses of four kinds of double-lap single-bolted joint structures with various layups and geometry dimensions are also conducted under tensile loading. The numerical predictions of failure loads, failure patterns and load-displacement curves are compared to the experimental results. Good agreement between the model predictions and the experimental results demonstrates the effectiveness of the proposed MDM for the progressive damage analyses of open-hole laminates and composite bolted joints.

Progressive failure analysis of fiber-reinforced laminated composites containing a hole

The present work aims to obtain failure loads for open-hole unidirectional composite plates under tensile loading. For this purpose, a user-defined material model in the finite element analysis package, ABAQUS, was developed to predict the failure load of the open-hole composite laminates using progressive failure analysis. Hashin and modified Yamanda-Sun’s failure criteria with complete and Camanho’s material degradation model are studied. In order to achieve the most accurate predictions, the influence of failure criteria and property degradation rules are investigated and failure loads and failure modes of the composites are compared with the same experimental test results from literature. A good agreement between experimental results and numerical predictions was observed.

A residual strain model for progressive fatigue damage analysis of composite structures

A residual strain model was presented based on the fatigue-accumulated damage mechanisms of composite materials. By combining the proposed residual strain model with a residual stiffness model, the gradually degraded material properties due to the damage in fatigue cycles were characterized. Accompanying the residual strain based gradual material degradation model with a micromechanics-based sudden material degradation rule for describing the stiffness degradation in one fatigue cycle and an extended maximum strain criterion for evaluating failure of materials, a progressive fatigue damage model (PFDM) of a typical double-lap three-bolt joint made of T800 carbon/epoxy composites was developed. Compared with the residual strength model in a traditional PFDM, the residual strain model has consistent parameters with those in the residual stiffness model, which could be determined by nondestructive experiments. Fatigue tests of the double-lap three-bolt joint specimens under a stress ratio R=−0.2 and three-level load ratios q=0.7, 0.8, 0.9 were performed. Good consistency between the experimental results and numerical predictions of the PFDM validates the efficiency of the proposed residual strain model and PFDM in accurately predicting the residual strength and fatigue life of composite structures.

A micromechanics-based degradation model for composite progressive damage analysis

A new material degradation model only with fundamental material properties required is proposed for composite progressive damage analysis based on micromechanics. For different failure modes, the effects of fiber and/or matrix damage on the composite material properties are explored, from which the material degradation factors for these failure modes are deduced. The material degradation model is then implemented for progressive damage analyses, using user subroutines in the commercial code ABAQUS®, accompanying with a modified Hashin type failure criterion and finite element models for six commonly used double-lap composite bolted joints with various layups, geometry dimensions, and fasteners. The numerical predictions of failure loads, failure patterns, and load–displacement curves are compared with results obtained from static tests and further ultrasonic C-scan detection. Good agreements between numerical failure predictions and experimental outcomes indicate the effectiveness and suitability of the proposed model for progressive damage analyses of composite bolted joints.

Anisotropic continuum damage model for prediction of failure in flax/polypropylene fabric composites

An anisotropic continuum damage modeling approach was applied to model failure of a composite of unidirectional flax in a polypropylene matrix under quasi-static tensile loading. Tensile, compressive and shear stiffness, and strength values of the composite were characterized according to ASTM standards, and the damage was quantified by optical microscopy. Based on the experimental strength and damage values, an anisotropic strain-dependent material damage model was developed and implemented in the finite element program ABAQUS. This was combined with geometric models of the fabric composites incorporating the yarn geometry. Good agreement was observed between the experimental and numerical stress–strain curves, and the failure strength prediction by the model was within 3.1% of the experimental value. This study shows that combining a geometric model closely incorporating the actual geometry of a fabric composite with an experimentally determined material degradation model can yield good predictions of the mechanical behaviour of the composite. POLYM. COMPOS., 37:2588–2597, 2016. © 2015 Society of Plastics Engineers

Tensile Strength Prediction of Out-of-Plane Composite Joints for Integrated Composite Cabins

The failure of an adhesive-bonded and bolted composite joint under axial tensile loading is investigated. A progressive damage model consisting of a three dimensional FEM accompanying with a three dimensional maximum stress failure criterion and corresponding material degradation model is established to predict the failure behavior of the joint. The predicted failure load and load-displacement curve are validated by the experimental results is obtained. Moreover, the result shows that the discontinuity between two L-shaped laminates is the weak spot and required to be strengthened.

Durability Modeling of Environmental Barrier Coating (EBC) Using Finite Element Based Progressive Failure Analysis

The necessity for a protecting guard for the popular ceramic matrix composites (CMCs) is getting a lot of attention from engine manufacturers and aerospace companies. The CMC has a weight advantage over standard metallic materials and more performance benefits. However, these materials undergo degradation that typically includes coating interface oxidation as opposed to moisture induced matrix which is generally seen at a higher temperature. Additionally, other factors such as residual stresses, coating process related flaws, and casting conditions may influence the degradation of their mechanical properties. These durability considerations are being addressed by introducing highly specialized form of environmental barrier coating (EBC) that is being developed and explored in particular for high temperature applications greater than 1100°C. As a result, a novel computational simulation approach is presented to predict life for EBC/CMC specimen using the finite element method augmented with progressive failure analysis (PFA) that included durability, damage tracking, and material degradation model. The life assessment is carried out using both micromechanics and macromechanics properties. The macromechanics properties yielded a more conservative life for the CMC specimen as compared to that obtained from the micromechanics with fiber and matrix properties as input.