Conference Paper

Progressive Failure Simulation in Laminated Composites under Fatigue Loading by Using Discrete Damage Modeling

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... These damage mechanisms are not isolated and often interact, forming complex damage patterns. Few approaches attempt to model these damage modes and their interaction explicitly in fatigue [1,2]. In [1], both delamination and matrix crack onset are modeled using stress-based criteria and ad-hoc stiffness degradation. ...
... Such an approach is mesh-subjective, limiting its applicability as a predictive tool. In [2], both matrix cracks and delamination are modeled with a fatigue cohesive element approach, rendering an approach that can be mesh-objective. Matrix cracks are represented using the regularized Extended Finite Element Method (rXFEM), and delaminations are represented through interface elements. ...
... Matrix cracks are represented using the regularized Extended Finite Element Method (rXFEM), and delaminations are represented through interface elements. Both damage onset and propagation for matrix cracks and delaminations are modeled through a fatigue cohesive approach [2]. ...
Conference Paper
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A new methodology is proposed to model the onset and propagation of matrix cracks and delaminations in carbon-epoxy composites subject to fatigue loading. An extended interface element, based on the Floating Node Method, is developed to represent delaminations and matrix cracks explicitly in a mesh independent fashion. Crack propagation is determined using an element-based Virtual Crack Closure Technique approach to determine mixed-mode energy release rates, and the Paris-Law relationship to obtain crack growth rate. Crack onset is determined using a stress-based onset criterion coupled with a stress vs. cycle curve and Palmgren-Miner rule to account for fatigue damage accumulation. The approach is implemented in Abaqus/Standard ® via the user subroutine functionality. Verification exercises are performed to assess the accuracy and correct implementation of the approach. Finally, it was demonstrated that this approach captured the differences in failure morphology in fatigue for two laminates of identical stiffness, but with layups containing θ° plies that were either stacked in a single group, or distributed through the laminate thickness.
... The fatigue methodology employed in BSAM is discussed in detail in Ref. [9]. Intralaminar damage initiation is governed by the LaRC04 criteria where the strength as a function of cycles is given by S-N curves for transverse normal and shear loading. ...
... Crack initiation in fatigue analysis was proposed and validated based on Hasin and Rotem failure criterion. A modified version of the Paris Law is used to calculate cohesive zone propagation, Ref. [9]. ...
... For initial validation of Rx-FEM with Strength Tracking Fatigue, open hole tension (OHT) specimens were simulated, as shown in Figure 9. The selected model configuration was chosen based on work performed on the AFRL program "Damage Tolerance Design Principles (DTDP)" (Engelstad [24]; Engelstad and Clay [25]; Clay and Engelstad [26]) for which the authors participated in the program (Hoos et al. [28]; Iarve et al. [27]; Hoos et al. [16]; Iarve et al. [17]). The stacking sequence chosen was [60/0/-60]3S which was previously presented by the authors at AIAA using the previous BSAM fatigue method. ...
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View Video Presentation: https://doi.org/10.2514/6.2022-0107.vid The paper discusses the framework for high-fidelity progressive failure analyses of composite DCB subject to static and fatigue loading using Discrete Damage Modeling (DDM). In addition, the fatigue model is validated against open-hole tension specimens. The model employs a damage model based on the physics-based LaRC04 damage criteria to predict the matrix damage initiation and fiber damage progression. DDM utilizes the Regularized Extended Finite Element Method (Rx-FEM) and cohesive zone modeling to solve the complex damage processes and delamination in laminated composites. The predictive capabilities of DDM are demonstrated using simple DCB setups. Results shown for tape-tape and fabric-fabric models are around the 5% error. This analysis works as the framework of more complicated geometries, including fasteners and combined joint loading sequences. Qualitative comparisons of predicted damage for Open Hole Tension using the Rx-FEM with Strength Tracking method compare favorably with the experimental damage state from X-Ray CT data. They are more accurate to the experiment than the previous method of fatigue.
... Because of lack of experimental data, validation of the crack-length estimates is outstanding and the parameter was only used to show the advantages of QMC over MC. However, we showed that our model was able to accurately predict matrix failure in composites and discrete damage modeling has shown to accurately predict damage processes in composite materials [40,41]. More complex failure modes and stress states, as well as stochastic examination of parameters other than the crack-length is subject to further research. ...
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Property variations in a structure strongly impact the macroscopic mechanical performance as regions with lower strength will be prone to damage initiation or acceleration. Consideration of the variability in material property is critical for high-resolution simulations of damage initiation and propagation. While the recent progressive damage analyses consider randomness in property fields, accurately quantifying the uncertainty in damage measures remains computationally expensive. Stochastic damage analyses require extensive sampling of random property fields and numerous replications of the underlying non-linear deterministic simulations. This paper demonstrates that a Quasi Monte Carlo (QMC) method, which uses a multi-dimensional low discrepancy Sobol sequence, is a computationally economical way to obtain the mean and standard deviations in cracks evolving in composites. An Extended Finite Element Method (XFEM) method with spatially random strength fields simulates the damage initiation and evolution in a model composite. We compared the number of simulations required for Monte Carlo (MC) and QMC techniques to measure the influence of input variability on the mean crack-length in an open-hole angle-ply tensile test. We conclude that the low discrepancy sampling and QMC technique converges substantially faster than traditional MC methods.
... Xiao et al. [13] performed multiscale fatigue damage predictions for notched composites via a combined continuum and discrete crack modeling. A coupled r-XFEM with a cycle dependent cohesive model has been developed by Hoors et al. [14]. May and Hallett [15,16] developed a combined model for damage initiation and propagation under fatigue loading using cohesive elements allowing modeling of the whole fatigue life in a single, coherent analysis. ...
Preprint
A new 3D damage model is developed to predict the progressive failure and accumulated fatigue damage of woven fabric composite materials. Stress-based failure criteria are used to predict the damage initiation in x-tow, y-tow, and matrix constituent. An S-N based damage accumulation model is implemented to characterize the cycle dependent strength of the x- and y- fiber tows and matrix subjected to axial tension, compression, or in-plane share loading. A curve-fit non-linear shear model is also employed based on the static coupon test data of (+45/-45) woven fabric laminates. A static failure progression module is used to predict the damage and failure at the peak load prior to fatigue cycling. Stiffness degradation, fatigue damage accumulation, and failure mode detection are performed during the fatigue marching process. The developed user-defined material model for Abaqus features: 1) description of initial nonlinear shear before the damage initiation; 2) characterization of failure initiation based on a maximum stress criterion; and 3) performance of fatigue damage accumulation using a phenomenological model based on S-N test data. The predictive capabilities of the developed model are demonstrated using tension-tension fatigue of SYNCOGLAS R420 E-glass woven fabrics.
... Xiao et al. [13] performed multiscale fatigue damage predictions for notched composites via a combined continuum and discrete crack modeling. A coupled r-XFEM with a cycle dependent cohesive model has been developed by Hoors et al. [14]. May and Hallett [15,16] developed a combined model for damage initiation and propagation under fatigue loading using cohesive elements allowing modeling of the whole fatigue life in a single, coherent analysis. ...
Conference Paper
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An efficient two-step progressive damage model has been developed to predict the accumulated damage and fatigue life of woven fabric composite materials. Stress-based failure criterion coupled with a continuum damage approach is employed to predict the damage in fabric material when loaded up to the desired stress level. Upon fatigue cyclic loading, fatigue damage initiation and propagation in the warp and weft tows, in the matrix constituent and their interfaces are evaluated with S-N based accumulation models characterizing the cycle-dependent strengths in the fiber tows and the matrix subject to tension, compression and shear loading. Nonlinear shear behavior of the matrix is characterized by a curve-fit nonlinear shear model from the static coupon test data of (+45/-45) plain weave. The fatigue cycles of each element in the fiber tows, matrix region and their interface are computed via a Newton iteration method and a numerical procedure is performed to effectively estimate the next proceeding cycles based on the element dominated failure mode. A stiffness reduction method is applied once constituent fatigue damage is indicated in each cycle increment, and the stress field is updated accordingly for further loading cycles. The predictive capabilities of the developed fatigue model are demonstrated using tension-tension fatigue of SYNCOGLAS R420 E-glass woven fabrics and T300 5HS/914 dog-bone specimens of different layups.
... However, fatigue damage prediction of composites is known for being several orders more complicated than isotropic materials, which itself is a challenging problem. 1 A range of factors influence the durability prediction of unidirectional composites, notable ones are type of the constituents, laminate stacking sequence, presence of various damage types (such as matrix cracks, delamination, fiber-matrix debonding, fiber buckling etc.) and their interactions, loading conditions, and environmental conditions etc. Numerous models proposed over the years to solve this problem can be found in literature. These models can be broadly classified into three categories 2 : (i) fatigue life modelswhich do not model the mechanical degradation occurring with damage, rather use either S-N curves or Goodman diagrams along with some fatigue failure criterion to predict lifetime, 1 (ii) phenomenological modelswhich use experimental observations for modeling residual stiffness or strength, 3 and (iii) progressive damage modelsthey use one or more damage variables to keep track of different types of measurable damage in the composite, e.g., transverse matrix cracks, delamination, fiber damage etc. [4][5][6] Even though the empirical models have been successful to some degree for specific material systems under simple loading conditions, progressive damage models that capture the physics of the problem using information from different length scales and explicitly model the damage progression with load cycles seem to be best suited to predict the fatigue behavior of any arbitrary composite system under multiaxial loading condition. ...
... Both the cohesive [1][2][3][4] and virtual crack closure technique [5][6][7][8] (VCCT) have been used to perform fatigue damage evaluation of composite structures. The application of the cohesive model has shown its benefit when simulating the damage initiation followed by its propagation without using an initial flaw. ...
... The objective of the progressive fatigue damage simulation exercise was to predict the type and location of damage in test coupons as well as the residual stiffness and strength of the coupons as function of load cycles. Seven teams participated in the study 5,[16][17][18][19][20][21] and from the results it was observed that the progressive fatigue prediction capabilities of the participatory codes were less mature than their static counterparts. ...
Conference Paper
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Fiber-reinforced polymer (FRP) composites are widely used in high-performance aerospace structures, for which fatigue is an important design parameter. Since FRPs exhibit a plethora of damage mechanisms, it is difficult to predict their progressive fatigue behavior based on empirical relationships. Durability prediction in composites demands physics-based methodologies and one such approach based on the kinetic theory of fracture (KTF) was put forward previously to predict fatigue and creep of composites separately. However, fatigue damage accumulation process occurs in tandem with the damage-induced strain, which may affect the fatigue life of the composite. Therefore, an understanding is necessary on how much the damage induced strain affects the fatigue damage progression in FRPs. The KTF based methodology was utilized here to tackle this problem. Progressive fatigue simulations of open-hole tension (OHT) coupons made of unidirectional composite IM7/977-3 and consisting of 3 separate layups were performed with and without accounting for the damage induced strain. The predictions made by the model were benchmarked against the experimental data acquired from the ‘Damage Tolerant Design Principles’ tech scout program of the Air Force Research Lab (AFRL). Predictions from both models (with and without creep relaxation/damage induced strains) matched the stiffness degradation observed in the experiments fairly well. The results indicated that the damage states of the off-axis laminas are significantly different for softer laminates with and without including damage induced strains, which affects the fatigue life of the structure.
... As part of this project, the AFRL tested open-hole composite laminates made of IM7/977-3 for three different layups under cyclic loads for strength and failure progression. The participants in this project reported their predictions and comparison with test results in a series of papers during AIAA SciTech 2016 [26][27][28][29][30][31]. This study presents the stiffness, strength and damage progression predictions as a function of number of load cycles. ...
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An overview of the virtual crack closure technique is presented. The approach used is discussed, the history summarized, and insight into its applications provided. Equations for two-dimensional quadrilateral elements with linear and quadratic shape functions are given. Formulae for applying the technique in conjunction with three- dimensional solid elements as well as plate/shell elements are also provided. Necessary modifications for the use of the method with geometrically nonlinear finite element analysis and corrections required for elements at the crack tip with different lengths and widths are discussed. The problems associated with cracks or delaminations propagating between different materials are mentioned briefly, as well as a strategy to minimize these problems. Due to an increased interest in using a fracture mechanics based approach to assess the damage tolerance of composite structures in the design phase and during certification, the engineering problems selected as examples and given as references focus on the application of the technique to components made of composite materials.