Literature study report of plasticity induced anisotropic damage modeling for forming processes

A literature study report covering the topics; micromechanics of damage, continuum damage mechanics (gurson model and effective variable concept) and the dependence of damage on strain rate and temperature

Plasticity induced anisotropic damage modeling for forming processes

Stringent carbon emission targets and consumer demands for highly fuel efficient and safe vehicles are driving most of the innovations in the automotive industry. In the present era, the prime technological goal of the automotive industry is to design and manufacture commercially viable lightweight vehicles while maintaining the structural performance of the vehicles at the same time. Development of Advanced High Strength Steels (AHSS) is an important step forward in this context. However, plastic deformation induces damage in AHSS. Damage development during the forming process renders the classical failure prediction techniques ineffective, which poses difficulties in designing the forming process. Therefore damage development in these steels has been studied and incorporated in numerical simulations for accurate failure predictions in forming processes and for determination of the product properties after forming.\ud Damage development is anisotropic by nature and shall be considered anisotropic for accurate failure predictions. In this research, anisotropy in damage has been classified into two categories; Material Induced Anisotropy in Damage (MIAD) and Load Induced Anisotropy in Damage (LIAD). MIAD is related to the anisotropy in distribution and shape of second phase particles or impurities and is governed by void/crack nucleation. LIAD is related to the loading direction of the material. The phenomenon of MIAD was discovered during this research. This is the first research showing the occurrence of MIAD in AHSS.\ud The standard Lemaitre anisotropic damage model was modified to incorporate: lower damage evolution under compression, strain rate dependency in damage and Material Induced Anisotropic Damage (MIAD). Viscoplastic regularization of damage models was revisited. This technique proved to be effective in removing the pathological mesh dependence of local damage models. The damage model parameters for the same grade of DP600 were determined. The Modified Lemaitre’s (ML) anisotropic damage model was validated with experiments

Implementation of an anisotropic damage material model for non-proportional loading

Anisotropic damage for non-proportional loading is incorporated in an implicit finite element code under the framework of continuum damage models, using two different methodologies. Simple simulations are carried out to check the performance of the models. The advantages and drawbacks of both methodologies are discussed briefly

FibreChain: characterization and modeling of thermoplastic composites processing

Thermoplastic composites feature the advantage of melting and shaping. The material properties during processing and the final product properties are to a large extent determined by the thermal history of the material. The approach in the FP7-project FibreChain for process chain modeling of thermoplastic composites is presented

Viscoplastic Regularization of Local Damage Models:A Latent Solution

Local damage models are known to produce pathological mesh dependence in finite element simulations. The solution is to either use a regularization technique or to adopt a non-local damage model. Viscoplasticity is one technique which can regularize the mesh dependence of local damage model by incorporating a physical phenomenon in the constitutive model i.e. rate effects. A detailed numerical study of viscoplastic regularization is carried out in this work. Two case studies were considered i.e. a bar with shear loading and a sheet metal under tensile loading. The influence of hardening / softening parameters, prescribed deformation rate and mesh size on the regularization was studied. It was found that the primary viscoplastic length scale is a function of hardening and softening parameters but does not depend upon the deformation rate. Mesh dependency appeared at higher damage values. This mesh dependence can be reduced by mesh refinement in the localized region and also by increasing the deformation rates. The viscoplastic regularization was successfully used with a local anisotropic damage model to predict failure in a cross die drawing process with the actual physical process parameters

Hot Die Forming - Flat (HDF-F^Al):An innovative hot forming technology for extreme lightweight in aluminum sheet alloys

Aluminum is an ideal material for light transport applications. Despite the obvious advantages in weight ratio and corrosion resistance, high strength aluminum alloys have limited formability compared to traditional steels at room temperature conditions. A solution is to combine mechanical loading with thermal component i.e. deformation at elevated temperature. Currently super plastic forming and Quick Plastic Forming (QPF) is used to enhance the formability of Aluminum alloys. However, the cycle time for super plastic forming as well as for QPF is too high for mass production. An innovative and novel forming method called Hot Die Forming (HDF) has been developed to achieve high strains in high strength aluminum alloys (maximum 700 [MPa]) by heating them to Solution Heat Temperature (SHT), while keeping the cycle time suitable for large scale production. To study the feasibility and optimize the process parameters, a digital platform has been developed for simulations of HDF process. The simulation process has been automated, the user can provide tool geometries and input parameters to check the feasibility of HDF process or to optimize the parameters and die shape

Viscoplastic Regularization of Local Damage Models: A Latent Solution

Local damage models are known to produce pathological mesh dependence in finite element simulations. The solution is to either use a regularization technique or to adopt a non-local damage model. Viscoplasticity is one technique which can regularize the mesh dependence of local damage model by incorporating a physical phenomenon in the constitutive model i.e. rate effects. A detailed numerical study of viscoplastic regularization is carried out in this work. Two case studies were considered i.e. a bar with shear loading and a sheet metal under tensile loading. The influence of hardening / softening parameters, prescribed deformation rate and mesh size on the regularization was studied. It was found that the primary viscoplastic length scale is a function of hardening and softening parameters but does not depend upon the deformation rate. Mesh dependency appeared at higher damage values. This mesh dependence can be reduced by mesh refinement in the localized region and also by increasing the deformation rates. The viscoplastic regularization was successfully used with a local anisotropic damage model to predict failure in a cross die drawing process with the actual physical process parameters

A Plasticity Induced Anisotropic Damage Model for Sheet Forming Processes

Plastic deformation induces damage in Advanced High Strength Steels (AHSS). Therefore damage development in these steels shall be studied and incorporated in the simulations for accurate failure predictions in forming processes and for determination of the product properties after forming. An efficient anisotropic damage model suitable for large scale metal forming applications has been developed. The standard Lemaitre anisotropic damage model was modified to incorporate lower damage evolution under compression, strain rate dependency in damage and Material Induced Anisotropic Damage (MIAD). Viscoplastic regularization proved to be effective in removing the pathological mesh dependence of the presented local damage model. Anisotropic damage development was characterized in Dual Phase (DP600) steel. The damage model parameters for DP600 were determined from experiments. The Modified Lemaitre’s (ML) anisotropic damage model was validated with experiments

A field indoor air measurement of SARS-CoV-2 in the patient rooms of the largest hospital in Iran

The coronavirus disease 2019 (COVID-19) emerged in Wuhan city, China, in late 2019 and has rapidly spread throughout the world. The major route of transmission of SARS-CoV-2 is in contention, with the airborne route a likely transmission pathway for carrying the virus within indoor environments. Until now, there has been no evidence for detection of airborne severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and this may have implication for the potential spread of the COVID-19. We investigated the air of patient rooms with confirmed COVID-19 in the largest hospital in Iran, on March 17, 2020. To collect the SARS-CoV-2 particles, ten air samples were collected into the sterile standard midget impingers containing 20 mL DMEM with 100 μg/mL streptomycin, 100 U/mL penicillin and 1 antifoam reagent for 1 h. Besides, indoor particle number concentrations, CO2, relative humidity and temperature were recorded throughout the sampling duration. Viral RNA was extracted from samples taken from the impingers and Reverse-Transcription PCR (RT-PCR) was applied to confirm the positivity of collected samples based on the virus genome sequence. Fortunately, in this study all air samples which were collected 2 to 5 m from the patients' beds with confirmed COVID-19 were negative. Despite we indicated that all air samples were negative, however, we suggest further in vivo experiments should be conducted using actual patient cough, sneeze and breath aerosols in order to show the possibility of generation of the airborne size carrier aerosols and the viability fraction of the embedded virus in those carrier aerosols. © 2020 Elsevier B.V