Ductile Damage Evolution Research Articles

Prediction of Ductile Damage in Composite Material Used in Type IV Hydrogen Tanks by Artificial Neural Network and Machine Learning with Finite Element Modeling Approach

This study investigates the degradation process of composite materials used in high‐pressure hydrogen storage vessels by employing advanced computational techniques. A recurrent neural network, specifically a bidirectional long short‐term memory (Bi‐LSTM) network, is utilized to predict the temporal evolution of ductile damage. The key degradation features are extracted from finite element modeling (FEM) computations using group method of data handling algorithms and treated as time‐series data. Results demonstrate that the Bi‐LSTM network can accurately undergo both elastic and plastic behaviors of the composite under tensile strength. Additionally, traditional machine learning (ML) algorithms such as extreme gradient boosting and random forest are employed to forecast strain degradation, showing promising results. This hybrid approach combining FEM, ML, and deep learning provides a comprehensive method for predicting the degradation of composite materials, offering significant potential for optimizing the design and durability of hydrogen storage vessels.

Ductile shear damage micromechanisms studied by correlative multiscale nanotomography and SEM/EBSD for a recrystallized aluminum alloy 2198 T8

The damage mechanisms of ductile fracture under shear loading of an aluminum alloy 2198T8R were studied using flat thin-sheet samples. One sample was loaded until 85% of the failure displacement and then unloaded, and another one was loaded up to failure. To overcome the inherent shortcomings of nanotomography concerning the investigation of flat samples, synchrotron nano-laminography was applied to the pre-loaded sample and provided structural information down to the nanometer scale, allowing ductile damage nucleation and evolution to be studied. The damage features, including flat cracks and intermetallic particle-related damage, were visualized in 3D from the highly-deformed shear band region. Using nano-laminography, no nano-voids were found. The damaged shear ligament was also observed after polishing via destructive correlative scanning electron microscope (SEM) and electron back-scatter diffraction (EBSD) which suggests that the detrimental flat cracks were both intergranular and transgranular. The flat cracks were related to highly-deformed bands. No nano-voids could be found using SEM analysis. Fractography on the second broken sample revealed that the flat cracks contained hardly observable nanometer-sized dimples. The final coalescence region was covered by sub-micrometer-sized dimples, inside which dispersoid particles were present. The fact that no nano-void was found for the pre-deformed sample implies that the nucleation, growth and coalescence of these sub-micrometer-sized voids occur at late stages of the loading history.

White etching area damage induced by shear localization in rolling contact fatigue of bearing steel

AbstractWhite etching area (WEA) is a primary damage in rolling contact fatigue (RCF) of bearing steels. In spite of extensive investigations, there is a large discrepancy in the existing mechanisms of WEA formation. We attempt to unify the mechanisms from the perspective of shear localization and plastic damage accumulation based on ductile damage. RCF tests were conducted to generate WEAs with various microstructures and compositions. A thermodynamically consistent model of the ductile damage evolution from an inclusion was established by developing the phase field damage coupled with the crystal elastic‐viscoplastic constitutive relationship under RCF. The model was implemented into the FE framework through a user materials subroutine. The results indicated that the WEA is the shear band resulting from shear localization. The large inhomogeneity and scatter in WEA's microstructure are due to the influence of the crystal orientation. The development and orientation of SBs predicted by the model and the experimental observation of the WEA are in good agreement. The large micro‐shear strain in the WEA provides the driving force for mechanically controlled austenite phase transformation. The shear band center, which has the largest strain and the least stress, is where cracks initiate. This demonstrates that contrary to earlier reports that WEA is induced by previously formed crack faces friction, cracks actually initiate from the interior of the WEA.

On the ductile damage progression in surface-damaged metallic strands: Towards a damage tolerance analysis

This paper reports a novel and straightforward numerical approach to perform a damage tolerance analysis for metallic strands. This methodology relies on the ductile damage evolution laws experienced by metallic wires and strands under tensile monotonic load. Regarding the wires, this new approach integrates both micromechanics–based and continuum damage mechanics-based approaches. Tensile capacity tests of high strength steel and aluminium alloy wires are simulated using 3-D nonlinear finite element models along with the Gurson-Tvegaard-Needleman constitutive plasticity-damage model (micromechanics–based approach) whose parameters are calibrated iteratively using the disturbed state concept. Numerical simulations reproduce the different phases of the ductile damage process which are then related to an isotropic damage index (continuum damage mechanics-based approach). Results show that the wires develop nonlinear ductile damage evolution laws well captured by the Bonorás model with critical damages ranging from 0.12 to 0.25. The existing gap between wires and strand damage evolutions is then filled by using proper kinematic assumptions for both intact and damaged strands along with a homogenization procedure. The latter have a prescribed number of surface wires, symmetrically and asymmetrically distributed, fully cut to simulate service damage. For validation purposes, strands with 1 × 7 construction typology are analyzed whose diameters range between [9.5–14.3] mm. One approach to assess strands structural integrity and safety conditions is to analyze the stability of damage states as the degradation process occurs. Using this metric for the 1 × 7 strands, reveals that two surface wires cut is the maximum acceptable surface damage which meets the criterion established in different international standards for this strand construction typology. Otherwise, the damage state progresses to either an unstable or inflection state that accelerates the reduction of the capacity of a damaged strand to withstand more damage.

A damage sequence interaction model for predicting the mechanical property of in-service aluminium alloy 6005A-T6

In the long-term service process, materials and structures will bear fatigue, ageing, and other degradation behaviours under environmental factors such as temperature, vibration, and radiation. Service damage makes materials and structures gradually deviate from the original design expectations. In this study, the material is decoupled into a two-phase system consisting of matrix and void phases. The different mechanical behaviours of material by the evolution of the void phase are analysed under the premise of the constitutive uniqueness of the matrix phase. Different characterisation methods of damage are discussed, and a finite element analysis–test combination method is proposed to identify the damage evolution function and the undamaged hardening, avoiding the influence of the necking effect and the accuracy of the test apparatus. A damage interaction model associated with the physical mechanism of microstructure evolution is constructed based on the ductile damage evolution function, discussing the influence of different damage definitions on the sequence interaction. The aluminium alloy 6005A-T6 commonly used in car body structures of rail vehicles is studied. The damage evolution function and undamaged hardening are established by testing undamaged specimens and verified by testing service-damaged specimens that bore a certain service loading. Then the damage interaction mode was determined. The proposed damage sequence interaction model provides an effective non-destructive testing method to obtain the hardening behaviour of in-service engineering materials. It can also extend to various existing constitutive equations.

Corrigendum to ‘Numerical prediction of ductile damage evolution of 40CrNiMo railway axle steel during hot cross wedge rolling’ [Materials Today Communications Volume 33, December 2022, 104942

Corrigendum to ‘Numerical prediction of ductile damage evolution of 40CrNiMo railway axle steel during hot cross wedge rolling’ [Materials Today Communications Volume 33, December 2022, 104942

Analysis of ductile damage evolution and failure mechanisms due to reverse loading conditions for the aluminum alloy EN‐AW 6082‐T6

AbstractThis paper deals with experiments and numerical simulations for reverse uniaxial tension‐compression and shear tests to investigate the ductile damage and fracture behavior of the aluminum alloy EN‐AW 6082‐T6. For this purpose, experiments with different loading sequences and number of loading cycles with uniaxial tensile and new shear specimens have been performed. Furthermore, the digital image correlation (DIC) technique captures the deformations and strain fields during the experimental processes. A modified anisotropic stress‐state‐dependent elastic‐plastic‐damage continuum model is proposed and is validated by experimental strain fields measured by DIC. Moreover, numerically predicted distributions of the principal damage strains are compared with fracture images taken by scanning electron microscopy (SEM).

Influence of stress triaxiality on hydrogen assisted ductile damage in an X70 pipeline steel

The presence of hydrogen in steel components affects their structural integrity through a phenomenon called hydrogen embrittlement. While it is known that hydrogen affects the mechanical damage development upon loading, the specific mechanisms are still unclear. An experimental study is presented that investigates the plastic anisotropy and ductile fracture behavior of API 5L X70 pipeline steel with and without hydrogen charging at multiple scales. Three different tensile test specimen geometries (smooth and notched axisymmetric) are employed to investigate the influence of stress triaxiality thereon. The macromechanical responses during tensile tests are analyzed, along with micromechanical features of the resulting damage obtained using High-Resolution X-ray Computed Tomography. For all stress triaxialities tested, the presence of hydrogen does not affect the macroscopic plastic anisotropy, but accelerates ductile damage development and fracture, which is in agreement with the plasticity dominated hydrogen embrittlement mechanisms HELP and HESIV. Increasing stress triaxiality leads to a larger susceptibility to hydrogen embrittlement. Hydrogen accelerated void nucleation and enhanced lateral void growth are observed and quantified. The presented results can aid the development of numerical models describing hydrogen embrittlement in high-strength low-alloy steel.

Controlling Damage Evolution in Geometrically Identical Cold Forged Parts by Counterpressure

Abstract It is investigated to what extent the evolution of ductile damage in cold forging can be controlled without changing the geometry of the produced part. Besides the effects of strain hardening and residual stresses, damage, which is the nucleation, growth and coalescence of voids on microscopic level, affects product properties of the manufactured components such as fatigue strength, impact strength, or elastic stiffness. Former investigations have shown that the load path-dependent damage evolution in forward rod extrusion, and thus, the performance of produced parts can be controlled by the process parameters extrusion strain and shoulder opening angle. As these parameters also affect the geometry of extruded parts, design requirements of components might be violated by varying these. Thus, counterpressure is used to superpose purely hydrostatic stresses to forward rod extrusion in order to decrease triaxiality in the forming zone without causing geometric variations in the produced parts. The counterpressure is either introduced by a counterpunch or by modified process routes. The achieved improvements in product performance are in agreement with results obtained by variation of extrusion strain and shoulder opening angle as described in the literature. In addition, it is observed in tensile tests that damage in cold extruded parts does not significantly affect flow stress. All advancements in product performance are realized without affecting the products’ geometries.

Numerical prediction of ductile damage evolution of 40CrNiMo railway axle steel during hot cross wedge rolling

Ductile damage formed by hot forming seriously affects the railway axle fatigue. It is vital to study the damage evolution mechanism of the 40CrNiMo steel during the high-temperature cross wedge rolling for the manufacturing of the high-speed railway axles. In the current study, the ductile damage model was established and verified. The specimens of the 40CrNiMo steel were subjected to the high-temperature tensile test using a Gleeble-3800 thermal simulation testing machine. Three deformation temperatures (1223 K, 1323 K, and 1423 K) and four strain rates (0.5 s -1 , 1.0 s -1 , 5.0 s -1 , and 10 s -1 ) were set. The deformation temperature, the strain rate, and the stress state were quantified by the Z parameter, the stress triaxiality, and Lode parameter, respectively. These were considered in the Bai & Wierzbicki (B&W) fracture strain equation to establish the fracture strain expression for the 40CrNiMo steel, and then the relevant parameters were solved. The secondary development route was used to embed the model into the Deform-3D software to simulate the distribution characteristics of the ductile damage as well as the evolution of the stress state and the Z parameter when the 40CrNiMo steel was rolled into the high-speed rail axle at the high-temperature. The simulation results were studied, and the direction of the process improvement was proposed. The results show that the damage could be decreased by reducing the forming angle, increasing the broadening angle, maintaining the section shrinkage at 35%, machining the hollow axle, and setting the roll speed and the rolling temperature at 8 r/min and 1273–1323 K, respectively.

An in situ study of microstructural strain localization and damage evolution in an (α+β) Ti-Al-V-Fe-Si-O alloy

Multi-phase titanium (Ti) alloys exhibit highly heterogeneous plastic deformation patterns. Understanding the micro-mechanisms of plastic deformation causing strain heterogeneity is thus of fundamental importance for enhanced manufacturability and in-service performance of Ti alloys. In this study, the critical microstructural factors responsible for microscopic strain localization are systematically investigated in an (α+β) Ti-Al-V-Fe-Si-O alloy by integrating the microstructural insights obtained from in situ microstructure-based digital image correlation (μ-DIC), in situ synchrotron X-ray diffraction (SXRD), and statistical analyses of strain localization incidents. The uniaxial tensile tests along the transverse direction reveal strain localization (i) across favorably oriented adjacent α grains (multi-grain strain localization) and (ii) along grain/phase boundaries (boundary strain localization), both of which suggest the strong influence of local crystallographic orientation on strain heterogeneity. The boundaries shared by soft and hard α grains are observed to be highly susceptible to strain localization, although ductile damage mechanisms are mostly delayed until the later stages of necking. While the majority of the (α+β) microstructure can co-deform to high strain levels without significant ductile damage evolution, micro-void nucleation and growth eventually initiate at the α/β phase interfaces, with work-hardening of the β phase. The insights provided through these in situ experiments highlight the importance of local texture in the strain localization and damage in (α+β) Ti alloys.

Prediction of ductile damage evolution based on experimental data using artificial neural networks

A model for the evolution of ductile damage in the sense of void fractions using artificial neural networks (ANN) is proposed. In contrast to constitutive damage models, the damage prediction is solely based on experimental data and has no underlying assumptions for the damage evolution law. This guarantees that the experimental observations are captured correctly. High resolution experimental void data obtained by scanning electron microscopy with a minimum single void area of 0.02 μm2 are used as training data. The loading state is obtained from finite element simulations. The equivalent plastic strain is used to describe the load amplitude and the triaxiality as well as the normalised Lode angle are utilised to characterise the loading type. Different strategies for the training of the model as well as the prediction are analysed. The model is used to visualise the loading state-dependent damage evolution. Furthermore, it is applied to two different bending processes. It is shown that the prediction quality highly depends on the experimental and numerical data used for training. If the loading states of the application problem are within the domain of the training data, the prediction quality is good and even better than constitutive models used in literature.

Bolt stripping failure and ductility of end plate beam-column connections at ambient and elevated temperatures

PurposeThe effect of bolt stripping failure on the ductility of steel end plate beam-column connections has received relatively little investigation to date. The objective with the present work is to establish a validated numerical model of end plate connections at elevated temperatures, which predicts the mechanical behaviour and failure modes observed in the experimental tests including the bolt stripping failure. Furthermore, the validated FE model was used to investigate the effect of stripping failure on both the rotational and load-bearing capacity of end plate connection.Design/methodology/approachThe analysis was conducted on a validated numerical model of end plate connections at elevated temperatures, which predicts the mechanical behaviour and failure modes observed in the experimental tests including the bolt stripping failure. The material was modelled considering ductile damage initiation and evolution featured in ABAQUS/Standard.FindingsThis study demonstrates that thick end plates can prevent stripping failure which significantly improves the rotational capacity of the connection. This failure mode can develop readily with thin end plates; however the effect is often unrealistically mitigated through idealised experimental tests. The rotational capacity of a connection can be 5.0 times higher if stripping failure is avoided, particularly at elevated temperatures. Eurocode 3 part 1.8 does not consider the possibility of stripping failure when discussing the requirements for plastic analysis. It is concluded in the present study that by allowing for the possibility of bolt stripping, the mode of failure can often shift from end plate failure to bolt stripping, this in turn significantly reduces the connection rotational capacity.Originality/valueThe effect of bolt stripping failure on the ductility of steel end plate beam-column connections has received relatively little investigation to date.

A ductile damage evolution model for the simulation of machining processes in materials with limited ductility

A damage evolution model with Lode dependence is presented, based on fracture and damage mechanics, with regard to recent evidence supporting the theory of critical strain to fracture. The damage evolution is partitioned into two variables, DE and Dσ, which depend on the stress tensor evolution during plastic straining. The model is based on the definition of fracture as the disruption of plastic flow caused by a critical strain, considering the damage evolution as a function of fracture energy and the loading mode. The model successfully predicts the fractographic features present in ductile fractured tensile and compressive specimens and numerically predicts chip morphology in metal cutting, considering the complexity of the strain paths of which the material is subjected in the process. The influence of thermal coupling is left out of the present formulation on purpose, to stress the effect of the damage variables.

Coupling Between Ductile Damage Evolution and Phase Transition in Single Crystal Niobium Subjected to High Strain Rate Loading

Coupling Between Ductile Damage Evolution and Phase Transition in Single Crystal Niobium Subjected to High Strain Rate Loading

A crystal plasticity-based constitutive model for near-[formula omitted] titanium alloys under extreme loading conditions: Application to the Ti17 alloy

A crystal plasticity-based constitutive model is proposed to describe the thermo-mechanical behavior of the Ti17 titanium alloy subjected to extreme loading conditions. The model explicitly incorporates the effect of the crystallographic orientation of the hcp α and bcc β phases. The constitutive equations are built in the context of continuum thermodynamics with internal variables. The general framework of continuum damage mechanics is used to consider the impact of ductile damage on the mechanical behavior. The proposed model is implemented in a finite element method solver. The material parameters are identified from an extensive experimental dataset with an inverse method. According to the results, the impact of the strain rate and the temperature on the mechanical behavior is correctly depicted. The model is then used to evaluate the impact of temperature on strain localization. The role of the local texture on the development of ductile damage is also discussed for different specimen geometries. Finally, the impact of heat exchanges on the mechanical behavior at low and high temperatures is investigated.

Effect of non-linear tension-compression loading reversal on the hardening behavior and initiation fracture strain of a cold-rolled TRIP780 steel sheet

This work examines the influences of non-linear pre-forming paths on the ductile behavior and damage evolution of a cold-rolled transformation-induced plasticity (TRIP) steel. Two non-linear pre-forming paths, i.e. tension followed by compression (TC) and compression followed by tension (CT), were designed to reveal the Bauschinger effect and fracture ductility. The experimental results demonstrated that the fracture strain was strongly affected by the loading path and magnitude of pre-forming. A single-surface plasticity model accounting for a non-associated Hill’ 48 plastic flow potential was developed by combining a Voce-Swift isotropic hardening law and a mixed non-linear kinematic (NLK) hardening rule. The experimental strain-stress curves of pre-formed specimens were utilized to calibrate the model parameters. The proposed model well predicted the hardening anisotropy, Bauschinger effect, permanent softening and transient behavior of specimens undergoing TC and CT pre-forming strategies. In addition, the influence of non-linear TC and CT pre-forming loading paths on the initiation fracture strain were modeled and investigated through a Hosford-Coulomb fracture criterion. The results showed that the proposed non-associated and mixed hardening model can describe the hardening behavior under TC and CT non-linear deformation. It is also found that the Hosford-Coulomb fracture model is capable to provide reasonable prediction on the fracture strain under different non-linear pre-forming loading paths even though a larger scatter for the TC deformation. These results also confirm that the ductility of the TRIP780 increases under a TC or CT non-linear pre-forming.

A contribution to numerical prediction of surface damage and residual stresses on die-sinking EDM of Ti6Al4V

A numerical simulation under plane-strain assumption of residual stresses and damage on titanium alloy Ti6Al4V in die-sinking electrical discharge machining (EDM) process is presented using Johnson–Cook (J–C) model and dynamic explicit temperature-displacement algorithm. A special attention is given to model the damaged thermo-mechanical behavior of EDMed Ti6Al4V alloy while considering the ductile damage evolution via a fully uncoupled damage formulation. A rigorous selection method including analytical and finite-element (FE) computations of tensile fracture behavior with thermal effect is proposed for suitable selection of J–C model parameters for the grade of Ti6Al4V alloy under investigation. The relationships between the machining parameters and both the heat flux density and the available sparking radius are considered for defining sparking analysis input. For a selected set of machining settings, the residual stresses and surface damage profiles were retrieved at the end of a cooling analysis. It has been concluded that J–C constitutive model can be used to describe material damaged thermo-plastic behavior under die-sinking EDM process conditions and thereby forecast temperature distribution, crater cavity shape, thermally induced residual stresses, white layer thickness and EDM thermal cracks formation. Unusually, an approach including damage criterion was proposed for assessment of both the geometry of crater cavity and the thickness of white layer and compared to based-on temperature criterion classical approach. Thus, numerical simulation of damage in die-sinking EDM offers a new insight into the mechanism of surface damage creation and helps to find out such phenomenon very precociously, which is otherwise difficult to access by experiment, such as surface crack formation due to damage mechanism as triggered in sparking phase and which was re-established in cooling. The numerical model yields reliable results for residual stresses profiles when compared with titanium alloy Ti6Al4V experimental results available in literature in the same machining conditions.

On Ductile Damage Modelling of Heterogeneous Material Using Second-Order Homogenization Approach

The paper deals with the numerical modelling of ductile damage responses in heterogeneous materials using the classical second-order homogenization approach. The scale transition methodology in the multiscale framework is described. The structure at the macrolevel is discretized by the triangular C1 finite elements obeying nonlocal continuum theory, while the discretization of microstructural volume element at the microscale is conducted by means of the mixed type quadrilateral finite element with the nonlocal equivalent plastic strain as an additional nodal variable. The ductile damage evolution at the microlevel is modelled by using the gradient enhanced elastoplasticity. The macrolevel softening is governed by two criterions expressed by the increase in homogenized damage variable and the threshold of the local equivalent strain. The softening at each material point at the macrolevel is detected by the critical value of the homogenized damage, where homogenization of the damage variable is performed only within softening area. Due to the nonlocal continuum theory applied, a realistic softening behaviour is demonstrated after the damage initiation, compared to the widely used first-order homogenization approach. All algorithms derived have been embedded into the finite element code ABAQUS by means of the user subroutines and verified on the standard benchmark problems. The damage evolution at both microlevel and macrolevel has been demonstrated.

Multiscale damage plasticity modeling and inverse characterization for particulate composites

In this paper, we propose a multiscale damage plasticity model for particulate composites within an incremental Mori-Tanaka (MT) micromechanics framework and present numerical and experimental verification. J2 plasticity and Lemaitre-Chaboche ductile damage models account for damage in the matrix and a linear spring model accounts for interface damage between the matrix and inclusions. Local and global strain concentration tensors are iteratively updated by minimizing errors caused by the constantly changing algorithmic tangent operator of the ductile damage matrix. Finite element (FE)-based direct numerical simulation (DNS) models are used as baseline models for verification. Properties of the ductile damage matrix and interface damage variables are inversely identified from experimental data. FE-MT multiscale damage plasticity model with the identified properties are experimentally verified with uniaxial tensile test results of glass bead/epoxy composites. Ductile damage evolution and patterns from the proposed model are verified with digital image correlation (DIC) test results. Increasing porosity within the matrix and interface damage from micro-computed tomography (CT) and microscope, respectively, prove the importance of damage modeling in the prediction of structural response by the model.