ABAQUS User Material Subroutine Research Articles

Modelling and Characterisation of Orthotropic Damage in Aluminium Alloy 2024.

The aim of the work presented in this paper was development of a thermodynamically consistent constitutive model for orthotopic metals and determination of its parameters based on standard characterisation methods used in the aerospace industry. The model was derived with additive decomposition of the strain tensor and consisted of an elastic part, derived from Helmholtz free energy, Hill's thermodynamic potential, which controls evolution of plastic deformation, and damage orthotopic potential, which controls evolution of damage in material. Damage effects were incorporated using the continuum damage mechanics approach, with the effective stress and energy equivalence principle. Material characterisation and derivation of model parameters was conducted with standard specimens with a uniform cross-section, although a number of tests with non-uniform cross-sections were also conducted here. The tests were designed to assess the extent of damage in material over a range of plastic deformation values, where displacement was measured locally using digital image correlation. The new model was implemented as a user material subroutine in Abaqus and verified and validated against the experimental results for aerospace-grade aluminium alloy 2024-T3. Verification was conducted in a series of single element tests, designed to separately validate elasticity, plasticity and damage-related parts of the model. Validation at this stage of the development was based on comparison of the numerical results with experimental data obtained in the quasistatic characterisation tests, which illustrated the ability of the modelling approach to predict experimentally observed behaviour. A validated user material subroutine allows for efficient simulation-led design improvements of aluminium components, such as stiffened panels and the other thin-wall structures used in the aerospace industry.

Analysis on shear band development under large strain torsion of amorphous glassy polymers

Unlike the shear band development of metals generally regarded as the precursor to failure, the shear banding process in amorphous glassy polymers is known to influence both the strengthening and fracturing behaviors. Complementary to the previous experimental work in the literature on the shear band development under torsion under limited cases, the finite element (FE) analysis has been conducted to investigate the general shear banding behaviors in terms of the initiation and propagation in more detail. The FE model has been established by incorporating the Boyce-Parks-Argon (BPA) constitutive model with the full-network modification via a user material subroutine in ABAQUS. A series of nondimensional quantities were used to discuss the mesh sensitivity and the effects of predefined imperfections, specimen geometry, and torsion mode. Besides, by altering the extents of the intrinsic material softening and the strain hardening, the shear banding behaviors of typical materials under typical temperature and strain rate conditions are equivalently investigated. The validity of the simulation has been qualitatively validated by directly comparing with the experimental results from the literature.

Pseudograin decomposition of short fiber-reinforced plastics for two-step homogenization using machine learning approach

Decomposing the representative volume element (RVE) of short fiber-reinforced plastics (SFRPs) into several pseudograins (PGs) is essential for understanding its effective mechanical behavior. However, conventional PG decomposition methodologies are limited by their high computational costs due to iteration-based algorithms. To address this, we propose a machine learning-assisted PG decomposition procedure that utilizes a series–parallel artificial neural network (ANN) system to facilitate the time-consuming decomposition process. To validate the effectiveness of our proposal, we implemented a two-step homogenization framework of SFRP that consists of the series–parallel ANN system, Mori-Tanaka model, and Voigt model into ABAQUS user material subroutine (UMAT). The elastic modulus values predicted by the UMAT are found to be in good agreement with both DIGIMAT-MF and experimental values, while also maintaining low computational time.

UMAT4COMSOL: An Abaqus user material (UMAT) subroutine wrapper for COMSOL

We present a wrapper that allows Abaqus user material subroutines (UMATs) to be used as an External Material library in the software COMSOL Multiphysics. The wrapper, written in C language, transforms COMSOL’s external material subroutine inputs and outputs into Fortran-coded Abaqus UMAT inputs and outputs, by means of a consistent variable transformation. This significantly facilitates conducting coupled, multi-physics studies employing the advanced material models that the solid mechanics community has developed over the past decades. We exemplify the potential of our new framework, UMAT4COMSOL, by conducting numerical experiments in the areas of elastoplasticity, hyperelasticity and crystal plasticity. The source code, detailed documentation and example tutorials are made freely available to download at www.empaneda.com/codes.

Parameter determination and verification of ZWT viscoelastic dynamic constitutive model of Al/Ep/W material considering strain rate effect

As a new type of energetic structural material, Al/Ep/W(Aluminum/epoxy/tungsten), whether as a fragment or projectile material, should comprehensively consider the impact energy release and structural strength, especially the structural strength is the premise to ensure the material integrity. The dynamic constitutive model of materials is the theoretical basis for describing the strength and dynamic behavior of materials. Therefore, it is great significance to determine the dynamic constitutive model parameters of Al/Ep/W materials considering strain rate effect, and to verify the reliability of the model. In this paper, Al/Ep/W material is prepared, and the stress/strain relationship curve of the material under high strain rate is obtained through Split Hopkinson Pressure Bar (SHPB) test. The ZWT viscoelastic constitutive model is selected based on the composition of the material and the distribution of the internal components, and the simplified ZWT constitutive model with damage under constant strain rate is derived, and the parameters of the constitutive model are fitted by the least square method. By using Kirchhoff stress and Green strain tensor theory, the incremental form of the constitutive model is derived, and the Abaqus user material subroutine is written and embedded in the finite element software. The accuracy of material VUMAT subroutine is verified by comparing the results of SHPB test and numerical simulation under high strain rate. Combined with the verified material model subroutine, the experiment and numerical simulation of Al/Ep/W cylindrical projectile impacting aluminum plate are conducted. The results show that the experimental and numerical simulation results are in good agreement. The proposed model can be used to evaluate the dynamic response characteristics of the new energetic material projectile to the lightweight aluminum armor protective structure.

Progressive pseudograin damage accumulation model for short fiber-reinforced plastics and its application to fatigue life prediction

A progressive pseudograin damage accumulation (PPDA) model is proposed to predict the fatigue life of short fiber-reinforced plastics (SFRPs), combining viscoelastic-viscoplastic (VEVP) two-step homogenization theory with Chaboche fatigue damage model. Each representative volume element (RVE) of SFRPs is decomposed into pseudograins using a two-step homogenization framework. Then, the fatigue life of each pseudograin is predicted using a master S-N curve, which is prepared based on the “normalized fatigue factor” taking into account both the stress ratio and multiaxial stress state. Thereafter, the overall failure of RVE is predicted by a PPDA model, in which each pseudograin fails progressively considering the stress concentration of the living pseudograins, resulting in non-linear fatigue damage evolution. Finally, the PPDA model is successfully implemented into ABAQUS user material subroutine (UMAT), predicting the fatigue lifetime in good agreement with experimental data.

Numerical Simulation of the Taylor Impact Test for Laser Powder Bed Fusion Parts Based on Microstructural Internal State Variables

The response of any engineering design components to stresses should be predictable, While the response of a material to complex loading, such as high strain rates experienced during service, is difficult to represent with simple tests, the Taylor impact test is one of a number of tests devised for high strain rate complex loading. To expedite the acceptance of LPBF Ti6Al4V (ELI) for use in demanding structural applications, there is a need to develop numerical models based on the internal microstructural state variables to predict the performance of the alloy over a wide range of high strain rates using such complex tests. This paper documents the numerical simulation of Taylor impact tests for direct metal laser-sintered and post-processed Ti6Al4V (ELI—Extra Low Interstitial) alloy. A microstructural variable-based constitutive model was used to predict the mechanical properties (stresses and evolution of plastic strains) of the material. The corresponding material parameters of the model were based on the specific microstructure obtained upon post-process heat treatment. The model was first implemented as a user material subroutine in the explicit finite element program ABAQUS using the VUHARD subroutine. Subsequently, the symmetrical Taylor impact tests of Laser Powder Bed Fusion (LPBF) Ti6Al4V (ELI) parts were numerically simulated using the VUHARD subroutine at different impact velocities. The equivalent von Mises stress and plastic strain obtained from numerical simulations were compared with the analytical solutions based on the strain rates obtained. It was shown that the instantaneous and average absolute errors between the numerical and analytical values of the model were generally less than 5%. The mushroom end, commonly observed in a Taylor test specimen, was also seen in the numerical model.

Evaluation of flow liquefaction in Nerlerk berm using collapse surface approach

Numerical investigation of flow liquefaction in Nerlerk underwater berm is done considering field data. The flow failure criterion proposed by Najma and Latifi is used to determine flow initiation and spreading via the Berm structure. This is done using Abaqus user material subroutine (UMAT) for coding Dafalias-Manzari constitutive model. The undrained triaxial tests are used for the calibration and verification of constitutive model coding. Application and performance of flow failure criterion are checked for these models. Then, Nerlerk underwater berm is numerically modeled considering calibration of constitutive model parameters from field investigation data. The performance of the stress ratio criterion is compared to the liquefaction determination method based on plastic modulus. Analyzing flow failure in a 3D numerical model of a real case is done for the first time, adding a constitutive model to commercial software in conjunction with two different flow detection equations defined as solution-dependent variables in developed user material code. This study reveals the ability of developed code in numerical modelling of flow failure initiation and expansion in a real case numerical model, which is the main target of this study.

Full-stress Range Stiffness Characteristics and a New Constitutive Model for Tensile Behaviors of Coated Fabrics under Plane Stresses

The paper investigates the mechanical properties of coated polyester fabrics in biaxial monotonic tensile tests. The nonlinear behaviors of the constitutive parameters within the full-stress range were in detail analyzed, and a new constitutive model based on the specific coupling relationships between the uniaxial and biaxial flexibilities was proposed to describe the complex tensile behaviors of coated fabrics under plane stresses. Finally, the accuracy of the nonlinear model in numerical simulations was verified, and special attention was devoted to the finite element (FE) implementation of the model as an ABAQUS user material (UMAT) subroutine. It was found that the constitutive parameters of the material varied noticeably with the stress level and ratio. The stiffnesses in the larger-stress direction are nearly stress-dominated, and the stress ratios exert a more significant effect on Poisson’s ratios than that on stiffnesses in the lower-stress direction. The proposed constitutive model, considering the material nonlinearities, is validated by the good correlations between the numerical and experimental results. Additionally, the FE simulation results using the UMAT are consistent with the experiments which reveals that the constitutive model proposed and the results obtained in this work are reliable.

Two-temperature thermodynamics and a viscoplasticity model for FCC metals with grain boundary effect

A non-equilibrium thermodynamic route is pursued to model viscoplasticity, including the evolving grain boundary, in face-centered cubic (FCC) metals. The thermodynamic description includes two subsystems: the configurational subsystem describing the relatively slower motion of dislocations and grain boundaries, and a fast-evolving kinetic-vibrational (K-V) subsystem depicting atomic vibrations about equilibrium positions in the lattice. Grain boundary and dislocation densities as well as their interactions are incorporated within the model. The model is initially developed for homogeneous plastic deformation, which is then generalized to the inhomogeneous case via spatial variations in the thermodynamic states over a wide range of strain rate and temperature. The model is implemented as a user material subroutine (VUMAT) in ABAQUS to simulate a problem of industrial interest, viz. deep drawing on an AA 7075 aluminum alloy. Finally, the thermo-viscoplasticity model is used to predict negative strain rate sensitivity in the AA 2219 aluminum alloy at room temperature, for which an experiment is performed at a facility of the VSSC. The predictive quality of the model is demonstrated by a comparison of numerical simulations with the experimental evidence.

Viscoelastic free vibration analysis of in-plane functionally graded orthotropic plates integrated with piezoelectric sensors: Time-dependent 3D analytical solutions

This paper proposes an accurate three-dimensional framework for elastic and viscoelastic free vibration investigation of in-plane functionally graded (IPFG) orthotropic rectangular plates integrated with piezoelectric sensory layers. The developed analytical framework is capable of considering layer-wise unidirectional linear functional gradation in both stiffness and density of the orthotropic composite layers. 3D piezoelasticity-based governing equations of motion are formulated in mixed form by employing Hamilton’s principle, and further solved analytically for Levy-type support conditions using the power-series-based extended Kantorovich method (EKM) jointly with Fourier series. The displacements, stresses, and electrical variables (electric field and electric potential) are solved as the primary variables that ensure the point-wise interlayer continuity and electro-mechanical support conditions. The viscoelastic property of the orthotropic interlayer is defined by employing Biot model, which is similar to the standard linear viscoelastic model. The correctness and efficacy of the present mathematical model are established by comparing the present numerical results with published literature and 3D finite element results, obtained by utilizing user material subroutine in the commercial FE software ABAQUS. An extensive numerical study is performed for various configurations and thickness ratios to investigate the influences of in-plane gradation, viscoelasticity and their coupled effects on the free-vibration response of hybrid laminated plates. It is found that in-plane gradation of stiffness and density remarkably alters the flexural frequencies and corresponding mode shapes of the hybrid intelligent rectangular plates. The flexural frequencies and stresses in the plate can be modified by selecting suitable grading indexes. Another interesting observation is that the in-plane gradation shows a considerably less effect on the electrical response of piezoelectric layers, which can play a vital role in the design of sensors and actuators for dynamic applications. Further, the numerical study demonstrates a potential time-dependent structural behaviour based on the present viscoelastic modelling. The consideration of viscoelasticity could be crucial for analysing the mechanical behaviour of a wide range of polymer composites more realistically and for prospective temporal programming in smart structural systems by exploiting the viscoelastic effect. Although the present analytical solution has been proposed for the free-vibration investigation of smart in-plane functionally graded (IPFG) viscoelastic plates, it can also be utilized directly to analyze the symmetric and asymmetric laminated piezoelectric smart plates with constant properties.

Research on Crack Propagation of Deep Geologic Mass Disturbed by Excavation Based on Phase Field Method

In recent years, the phase field fracture model has been widely studied and applied. It has good convergence in crack propagation simulation. Comparing with other methods, the phase field method has advantages in simulating crack intersection, bifurcation, and three-dimensional propagation. Based on the phase field method, the influence of excavation disturbance on crack initiation of rock mass is realized in this paper. The phase field fracture variational model is built by using user-defined element interface (UEL) and user material subroutine (UMAT) in ABAQUS. Firstly, the prefabricated crack propagation simulation is carried out to verify the algorithm. The fracture initiates in a butterfly shape and then expands along the horizontal direction. The results show that the maximum support reaction decreases with the gradual increase of l , which is compared with the results obtained by Miehe et al. The result proved the correctness and reliability of the algorithm. In this paper, the phase field fracture model of a flat plate with a reserved small hole under the upper tension is established. The results show that the crack finally produces a crack in the lower left and upper right directions of the square hole and continues to extend to the model boundary, which proves the feasibility of crack independent initiation and propagation by the phase field method. The stress formed a butterfly region until the fracture occurs. And the butterfly stress distribution was still present at the end of crack propagation. The maximum vertical stress was 1.7 × 103 MPa. Based on the South-to-North Water Transfer Project, the simulation of tunnel crack propagation under excavation disturbance is realized for the first time, which is based on the phase field method. The results show that the influence area of excavation disturbance will increase after considering crack development. Comparing the simulation results without considering crack propagation with the simulation results considering crack propagation, it is found that the stress level in the excavation disturbance area around the tunnel is greatly affected by cracks. When the crack is not considered, the maximum vertical stress is 2.16 × 105 Pa, and the maximum horizontal stress is 9.35 × 105 Pa, which occurs at the waist of the tunnel on the horizontal axis. When the crack is considered, the maximum vertical stress is 2.53 × 105 Pa, and the maximum horizontal stress is 1.10 × 106 Pa. It shows that the stress at the dome increases greatly. The vertical stress reaches 3.68 × 105 Pa, and the horizontal stress is up to 3.07 × 103 Pa. For the rock mass far away from the excavation disturbance area, because part of the elastic strain energy is absorbed by the surface crack, the stress level considering the crack is lower than that without the crack. But it is basically similar, indicating the accuracy of the phase field fracture model. This paper realizes the simulation of crack propagation under excavation disturbance and provides a way for the application of phase field fracture model in rock mechanics. This paper proves that phase field method has broad prospects in simulating rock crack propagation and provides the possibility for the popularization of phase field method.

Fatigue damage evaluation of welded joints in steel bridge based on meso-damage mechanics

Welding is a rapid and flexible connection that facilitates the use of a broad range of steel bridge. However, fatigue cracks initiating from various welded connection details are common problems in steel bridges. Therefore, it is vital to accurately evaluate the fatigue damage evolution and fatigue life of welded joints in steel bridge. In this study, a fatigue damage evolution model based on the meso-damage mechanics was proposed to evaluate the fatigue damage of welded joints in steel bridge. The number density of micro-cracks was adopted as the damage variable in the fatigue evolution model. Finite element modelling and user material subroutine (UMAT) in ABAQUS were combined to simulate fatigue damage evolution of welded joints in steel bridge. The fatigue damage evolution model was embedded in UMAT while the UMAT was coupled with the finite element model of the welded joints under cyclic loading. Then, the proposed model was validated by fatigue tests. The fatigue damage evolution model was also used to investigate the fatigue damage evolution process, and fatigue life prediction of the typical welded joints specimens in orthotropic steel decks (OSDs) of steel bridge. The results indicate that the fatigue strengths of nominal stress method were estimated to be 65.7 MPa for typical welded joints. The fatigue cracks mainly initiating at the weld toe and propagating along the weld toe line. The simulation results indicate that the fatigue damage evolution model provides superior ability in evaluating fatigue damage process and fatigue life of welded joints in steel bridge.

A thermodynamically consistent continuum damage model for time-dependent failure of thermoplastic polymers

In this study, a thermodynamically consistent damage model is presented to predict failure in glassy polymers. This model is based on the Eindhoven Glassy Polymer (EGP) multimode model, and it considers the effects of plastic deformation and hydrostatic stress on damage evolution. The model is implemented as an ABAQUS user material (UMAT) subroutine. Three experiments are simulated to show the model’s abilities. First, the model is used to predict failure in a T-fitting burst pressure test to investigate the model’s capabilities in predicting damage evolution and failure. This test shows two failure locations one dominated by the plastic deformation and the other by the hydrostatic stress and provides the possibility to investigate the model capabilities in capturing these contributions to the failure. Through comparison with experimental results, it is demonstrated that the model can effectively take into account the influence of hydrostatic stress and plastic deformation on failure. Second, the D-split test of notched pipe rings is simulated to show the time-dependent behavior of the model. Third, the cyclic behavior of a polycarbonate specimen under compression is investigated.

A methodology for predicting processing induced thermal residual stress in thermoplastic composite at the microscale

A computational finite element (FE) model of thermal residual stress was developed for carbon fiber/thermoplastic composites at the microscale and implemented via user material subroutine (UMAT) in ABAQUS. This model accounts for cooling-rate effects on crystallinity and stress-free temperature, temperature-dependent elastic modulus, temperature-dependent coefficient of thermal expansion (CTE) of the matrix, and the temperature-independent transversely isotropic properties of the carbon fiber. Results are generated for a model composite, consisting of a single carbon fiber embedded in a polypropylene thin film. Single filaments are pre-tensioned in the polymer melt to induce different levels of residual axial strain as well as maintain straight fibers during cool-down. Three different preload conditions (1g, 4g, and 8g) were experimentally fabricated and modeled. The residual strain along the length of the fiber is quantified and validated including the shear lag region that develops at the free edge of the sample. Experimentally measured residual strain shows a good correlation with the FE predictions for the applied fiber preloading conditions.

Understanding the deformation gradient in Abaqus and key guidelines for anisotropic hyperelastic user material subroutines (UMATs)

This tutorial paper provides a step-by-step guide to developing a comprehensive understanding of the different forms of the deformation gradient used in Abaqus, and outlines a number of key issues that must be considered when developing an Abaqus user defined material subroutine (UMAT) in which the Cauchy stress is computed from the deformation gradient. Firstly, we examine the “classical” forms of global and local deformation gradients. We then show that Abaqus/Standard does not use the classical form of the local deformation gradient when continuum elements are used, and we highlight the important implications for UMAT development. We outline the key steps that must be implemented in developing an anisotropic fibre-reinforced hyperelastic UMAT for use with continuum elements and local orientation systems. We also demonstrate that a classical local deformation gradient is provided by Abaqus/Standard if structural (shell and membrane) elements are used, and by Abaqus/Explicit for all element types. We emphasise, however, that the majority of biomechanical simulations rely on the use of continuum elements with a local coordinate system in Abaqus/Standard, and therefore the development of a hyperelastic UMAT requires an in-depth and precise understanding of the form of the non-classical deformation gradient provided as input by Abaqus. Several worked examples and case studies are provided for each section, so that the details and implications of the form of the deformation gradient can be fully understood. For each worked example in this tutorial paper the source files and code (Abaqus input files, UMATs, and Matlab script files) are provided, allowing the reader to efficiently explore the implications of the form of the deformation gradient in the development of a UMAT.

Predicting the mechanical properties of biopolymer gels using neural networks trained on discrete fiber network data

Biopolymer gels, such as those made out of fibrin or collagen, are widely used in tissue engineering applications and biomedical research. Moreover, fibrin naturally assembles into gels in vivo during wound healing and thrombus formation. The macroscale properties of fibrin and other biopolymer gels are dictated by the response of a microscale fiber network. Hence, accurate description of biopolymer gels can be achieved using representative volume elements (RVE) that explicitly model the discrete fiber networks of the microscale. These RVE models, however, cannot be efficiently used to model the macroscale due to the challenges and computational demands of multiscale coupling. Here, we propose the use of an artificial, fully connected neural network (FCNN) to efficiently capture the behavior of the RVE models. The FCNN was trained on 1100 fiber networks subjected to 121 biaxial deformations. The stress data from the RVE, together with the total energy on the fibers and the condition of incompressibility of the surrounding matrix, were used to determine the derivatives of an unknown strain energy function with respect to the deformation invariants. During training, the loss function was modified to ensure convexity of the strain energy function and symmetry of its Hessian. A general FCNN model was coded into a user material subroutine (UMAT) in the software Abaqus. The UMAT implementation takes in the structure and parameters of an arbitrary FCNN as material parameters from the input file. The inputs to the FCNN include the first two isochoric invariants of the deformation. The FCNN outputs the derivatives of the strain energy with respect to the isochoric invariants. In this work, the FCNN trained on the discrete fiber network data was used in finite element simulations of biopolymer gels using our UMAT. We anticipate that this work will enable further integration of machine learning tools with computational mechanics. It will also improve computational modeling of biological materials characterized by a multiscale structure.

Progressive Fatigue Failure Analysis of a Filament Wound Ring Specimen with a Hole

A progressive FEA mechanical fatigue degradation model for composites was developed and implemented using a UMAT user material subroutine in Abaqus. Numerical results were compared to experimental strain field data from high frequency digital image correlation (DIC) of split disk fatigue testing of pressure vessel cut outs with holes. The model correctly predicted the onset and evolution of damage in the matrix as well as the onset of fiber failure. The model uses progressive failure analysis based on the maximum strain failure criterion, the cycle jump method, and Miner’s sum damage accumulation rule. A parameter study on matrix properties was needed to capture the scatter in strain fields observed experimentally by DIC. S-N curve for the matrix material had to be lowered by 0% to 60% to capture the experimental scatter. The onset of local fiber failure had to be described by local S-N curves measured by DIC having 2.5 times greater strain than that of S-N curves found from standard coupon testing.

بررسی اثر شدت تکسچر بر رفتار تغییر شکل آلیاژ Mg-0.8wt%Y اکسترود شده تحت بارگذاری کشش و فشار با استفاده از روش المان محدود کریستال پلاستیسیته

Magnesium alloys due to their compact hexagonal structure (HCP) usually have a yield asymmetry in tensile and compressive loadings. This is due to various active plastic deformation mechanisms under tensile and compressive loadings. Therefore, it is necessary to study the deformation behavior of magnesium alloys on the grain scale. This study focuses on the 3D Representative Volume Element (RVE) simulations of extruded magnesium alloy to investigate the effect of basal texture intensity on tensile–compressive yield asymmetry of Mg-0.8wt% Y. Polycrystalline aggregate models are built based on the theory of Voronoi diagram; then, the Slip-based crystal plasticity formulation is applied as a User Material Subroutine in ABAQUS (UMAT) to study the relationship of microstructures and stress-strain responses in Mg-0.8wt% Y alloy during tension and compression test and the results are presented. The results show that when the orientation of the grains is considered random (zero texture intensity), the activities of different deformation modes are almost the same and minimum tensile-compressive yield asymmetry happens. Also, the results reveal when all the grains are oriented in a certain direction (texture intensity 1), maximum tensile–compressive yield asymmetry occurs. Indeed, according to the Relative Activity (RA) results, in agreement with Schmid Factor (SF) results, in a strong basal texture with the intensity of 1, maximum contribution of accumulated plastic deformation is related to tensile twinning while in compressive loading, prismatic slip and contraction twinning are responsible for major plastic deformation. Therefore, due to the activation of various deformation modes in strong basal texture, the highest amount of tensile–compressive yield asymmetry occurs. The S-shape strain hardening curve which is the main characteristic of twin-dominated deformation shows a strong dependency on texture in the extruded material so that during loading at the weaker texture, s-shape hardening is no longer present due to the dominated non-basal slips in weaker texture.

Life prediction of wind turbine blades using multi-scale damage model

Wind turbine blade life prediction is the most important parameter to estimate the power generation cost. Due to the price and importance of wind blade, many experimental and theoretical methods were developed to estimate damages and blade life. A novel multiaxial fatigue damage model is suggested for the life prediction of a wind turbine blade. Fatigue reduction of fiber and interfiber characteristics are separately treated and simulated in this research. Damage behavior is considered in lamina level and then extended to laminate; hence, this model can be used for multidirectional laminated composites. The procedure of fatigue-induced degradation is implemented in an ABAQUS user material subroutine. By applying the fatigue damage model, life is estimated by the satisfaction of lamina fracture criteria. This model provides a comprehensive idea about how damage happens in wind blades regarding a multi-axis fatigue loading condition.