•A modified Lemaitre model suitable for negative stress triaxiality was proposed.•A rolling composite model considering the hardening layer was constructed.•The cold rolling composite mechanism was ...validated through experiments and FEM.
Exploring the bonding mechanisms within bimetallic composite plates throughout the cold rolling process poses a considerable challenge, especially in simulating the bonding between different metals. A novel finite element model for rolling, grounded in Lemaitre continuum damage theory, was developed using copper/aluminium composite plates as a case study to characterize the dynamic bonding process in cold rolling precisely. The model replicates the dynamics of crack formation at the metal interface, the subsequent flow of the matrix metal through these fissures, and the ensuing contact. Considering the intricate stress conditions at the interface during rolling and the influence of compression on damage accumulation, the damage evolution constant in the original Lemaitre model has been revised. This modification aims to improve the model's performance in dominant shear forces and low-stress triaxiality scenarios. The damage constant has been transformed into a variable correlating with the Lode parameter and the degree of stress triaxiality to achieve this. The model parameters were calibrated using force-displacement data derived from shear and tensile experiments. The rolling model is ingeniously designed, employing hardened layer elements as barriers to segregate the fresh metal. Experimental rolling trials and corresponding simulation analyses were performed on copper/aluminium composite plates with varying initial thickness ratios, specifically 1:2, 1.5:1.5, and 2:1. The outcomes demonstrated a high degree of agreement between the experimental and simulated profiles, including the post-rolling thickness ratios, with a maximum discrepancy of 6.1 %. The finite element model effectively captured the deformation behaviour of the bimetallic material throughout the rolling process and elucidated the micromechanical processes underlying the interfacial bonding between the dissimilar metals.
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Mechanical damage induced failure within protective coatings is one of the main reasons for loss of coating integrity. Thus, for applicability of any coating and sealing technology it is mandatory to ...know the stress/strain levels at which mechanical component failure will occur and it is important to understand which physical entities drive damage initiation and propagation. Within this work a model has been developed which allows correlating and study the effect of brittle porous coatings on the stress-strain curve evolution of plasma electrolytic oxidation (PEO) coated extruded Mg substrates. This is a great benefit as deriving material laws might be challenging since measured stress-strain relationships are a convolution of substrate and coating material contribution. The approach is based on a damage model which allows distinguishing between the substrate contribution model as a bulk body described by dedicated material laws, and the brittle coating contribution mathematically modelled as a boundary condition. The effect of coating thickness, the resulting steady state crack spacing and the contribution of coating porosity on the stress-strain curve is shown. The approach allows direct estimation of PEO coating barrier properties from slow-strain rate tensile testing.
•New macroscopic FEM model describes damage effect of PEO coating on cpMg.•PEO layer porosity, thickness and steady state crack spacing are correlated to specimen's stress-strain response.•Local stress distribution is simulated in PEO fragments at steady state crack spacing.
•The Lemaitre CDM is modified by damage parameter coupled with local hardness ratio.•The modified CDM for FZ and HAZ fracture prediction is verified by notch tensile and flaring tests.•A constitutive ...law in the welds is established with the rule of mixture based on local hardness ratio.•A regression function of hardness distribution to local hardening or softening in the welds is proposed.
A continuum damage model (CDM) based on local hardness in welds is developed to predict fracture of welded tubes. A regression function of hardness distribution in the welds is proposed to establish hardness continuously through hardness mapping method in the finite element model. A constitutive model of the weld zone is determined by the rule of mixture, which estimates the flow stress of the welds from the hardness ratio. Coefficients of the flow stress model in the welds are validated by comparing finite element analysis (FEA) solution and experimental load - displacement data of tensile specimens. Softening after necking is considered by Lemaitre CDM. A damage parameter is newly given as a function of hardness ratio varying with angular position. Coefficients of damage parameter are obtained by the inverse FEA of tensile and flaring tests. The proposed method finely predicts the ductile fracture of welded tubes by considering local plastic properties and damage evolution.
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The geometric size effects (GSEs) of Lemaitre damage model parameters (the critical damage value at rupture, Dc, the strain at the damage threshold, ɛD, and the strain at rupture, ɛR) of a rolled ...CuAl5 alloy were evaluated using uniaxial tensile experiments and the finite element method. The results indicated the presence of size effect on the damage model parameters of the rolled CuAl5 alloy. With an increase in reduction ratio (Rr) at a constant thickness (t), Dc increased; with an increase in t at a constant Rr, Dc decreased and then increased. Both ɛD and ɛR decreased with increasing Rr and decreasing t. New models of the relationship between the damage model parameters and t were established for the three Rr values. The predicted results of the models agreed with the experimental ones. These results help to accurately predict the fracture behavior of microparts during plastic forming.
We investigated the impact of heat treatment on preform deduction during the hot forging of In718 turbine disks. Proposed preform design method leverages a Convolutional Neural Network (CNN) to aim ...for minimized damage and uniform grain size in the final forged products. For damage calculation, we employ the Lemaitre damage model, while the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model is utilized for grain size calculation. The CNN, trained on datasets of NURBS-generated preform shapes and final forged disks from them, showed superior performance in terms of damage and grain size of forged disk compared with other existing approaches. Moreover, the results indicate that preforms deduced with heat treatment considerations can lead to significant improvements in forging results, including up to a 17% reduction in average grain size and a 16% decrease in standard deviation compared to preforms without heat treatment consideration. These results underscore the importance of considering heat treatment in preform design, offering valuable insights for industries where the integrity of forged products, like aerospace, is critical.
During the metal forming process, the avoidance of ductile fracture has been of great interest to the scientific and engineering communities over the past decades. Hence, ductile damage prediction ...remains a key issue for achieving defect-free products. In this paper, the elastoplastic damage behaviour of DC04 steel has been studied and simulated to predict the fracture during the deep drawing process and reduce the industrial trial cost. In this context, a fully coupled elastoplastic damage model has been developed and implemented in the Abaqus explicit code using the VUMAT subroutine, knowing that the used elastoplastic and the damage parameters were identified by experimental tests. Numerical simulations have been performed to validate this model, followed by comparisons with the experimental results. These comparisons show a good correlation between the experimental and simulation results and good agreement with the empirical observations. Thus, the initiation of damage and its evolution leading to ductile fracture can be predicted using this model.
The computational homogenization technique is employed to investigate the effect of pre-existing microstructural voids on the failure response of a ceramic fiber reinforced aluminum composite ...subjected to loads in transverse to the fiber direction. Automated numerical simulations are carried out using a hierarchical interface-enriched finite element method (HIFEM), which enables the use of simple structured meshes for creating the discretized model. The HIFEM is integrated with a new microstructure quantification algorithm relying on the Random Sequential Adsorption (RSA) and Non-Uniform Rational B-Splines (NURBS) to create realistic periodic unit cells of the composite based on imaging data. A strain-driven homogenization problem is then solved at the microscale to simulate the damage evolution in the aluminum matrix using the Lemaitre elasto-plastic damage model. Six virtual models of the composite microstructure with varying volume fractions and spatial distributions of pre-existing voids are analyzed to determine their failure responses subject to macroscopic normal and shear strains. The outcomes of this study indicate that although for the latter type of loading the impact of small volume fractions of voids on the failure response is negligible, their presence significantly deteriorates the composite mechanical strength subject to uniaxial and equi-biaxial macroscopic normal strains.
Selecting an appropriate material behavior is considered to be one of the most important parts of simulating mechanical tests in dual phase (DP) steels. In this study, Lemaitre damage model besides ...combined isotropic/kinematic hardening is used for finite element modelling of DP600 steel in uniaxial tensile loading. Plane strain analysis was performed on a representative volume element selected from the scanning electron microscopy (SEM) picture which was captured from surface of the specimen. Calibration of material parameters for ferrite phase obtained good results in stress-strain diagram and damage distribution in simulation which verified with experimental results. Simulation and also SEM analysis showed that almost all damaged regions were in ferrite/martensite boundary and especially between two martensite islands that are close to each other; these regions are in main shear bands areas. At the end, a parametric study was done to determine the effect of morphology and distribution of martesite phase on DP steel behavior under tensile loading. The results showed that regular morphology of martensite phase gave better results in terms of energy required for fracture and damage distribution than irregular morphology.
Predicting the die and tool replacement time in the blanking process is very important in terms of product quality and cost efficiency. In order to predict tool life, tool wear must be observed ...constantly and the product defect rate must be analyzed. In this study, a procedure to predict tool life during the blanking process is proposed. Tool wear is represented with the modified Archard wear model and the Lemaitre damage model for ductile fracture. These models express abrasive and fatigue wear, respectively. The surface geometry of a tool is updated based on the computed amount of wear to describe the phenomenon of realistic wear. Through the blanking process, the amount of wear that is measured and calculated is compared. The difference was found to be 7.2%. Using the calculated wear result, the tool replacement time was predicted and the wear prediction procedure was validated by performing a series of procedures using other process conditions.
•Abrasive and fatigue type of wear meachanisms are assumed in a blanking process.•The modified Archard and the Lemaitre models were utilized to estimate tool wear.•The side surface and corner wears are employed to predict the tool replacement time.•The worn amount is subtracted from the tool surface to update the tool geometry.•To examine the tool prediction model, another type of blanking process was performed.
The research presented in this paper deals with the development of an integrated numerical model for the estimation of the incremental surface wear and damage accumulation in linear slide rails. The ...target is the estimation of the progressive increment of the end-point deflection of the last member of the slide rail during the operational lifetime. The surface abrasion is accounted for by utilizing a modified Archard equation with the aim of estimating the amount of wear along the vertical direction of the slide rails members. In addition to that, the Lemaitre damage model is utilized for the estimation rolling contact fatigue (pitting), considering the total strain and not only the plastic strain. Experiments have been carried out on a small-scale slide rail testing machine in order to define the wear increment on the slide rail inner groove for increasing number of cycles and, accordingly, estimate the modified Archard model constants. In addition to that, the wear parameters for the Lemaitre damage model have been inversely calibrated from the results of tensile tests. A numerical model has been implemented in ABAQUS/Explicit and an external geometry-update subroutine has been employed to update the geometry of the slide rail groove for increasing number of cycles as a consequence of wear and roll contact fatigue. The comparison between numerical and experimental results on real rails have shown a maximum deviation equal to 12.9%, supporting the reliability of the proposed approach.
•Modified Archard wear model to estimate the vertical wear.•Modified Lemeitre damage model to include the elastic strain contribution.•Numerical model to estimate the rail members deflection due to wear and RCF.•Reduction of the computational time due to external program.•Reliable experimental-numerical approach for the slide rail lifetime prediction.
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