scholarly journals Analytical Modeling of Residual Stress in Selective Laser Melting Considering Volume Conservation in Plastic Deformation

2020 ◽  
Author(s):  
Elham Mirkoohi ◽  
Dongsheng Li ◽  
Hamid Garmestani ◽  
Steven Y. Liang
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Thermal Stress ◽  
Temperature Gradient ◽  
Hydrostatic Stress ◽  
Kinematic Hardening ◽  
The Body ◽  
Heat Of Fusion ◽  
Temperature History ◽  
Volume Conservation

Residual stress (RS) is the most challenging problem in metal additive manufacturing (AM) since the build-up of high tensile RS may influence the fatigue life, corrosion resistance, crack initiation, and failure of the additively manufactured components. While tensile RS is inherent in all the AM processes, fast and accurate prediction of stress state within the part is extremely valuable and would result in optimization of the process parameters in achieving a desired RS and control of the build process. This paper proposes a physics-based analytical model to rapidly and accurately predict the RS within the additively manufactured part. In this model, a transient moving point heat source (HS) is utilized to determine the temperature field. Due to the high temperature gradient within the proximity of the melt pool area, material experience high thermal stress. Thermal stress is calculated by combining three sources of stresses known as stresses due to the body forces, normal tension, and hydrostatic stress in a homogeneous semi-infinite medium. The thermal stress determines the RS state within the part. Consequently, by taking the thermal stress history as an input, both the in-plane and out of plane RS distributions are found from incremental plasticity and kinematic hardening behavior of the metal by considering volume conservation in plastic deformation in coupling with the equilibrium and compatibility conditions. In this modeling, material properties are temperature-sensitive since the steep temperature gradient varies the properties significantly. Moreover, the energy needed for the solid-state phase transition is reflected by modifying the specific heat employing the latent heat of fusion. Furthermore, the multi-layer and multi-scan aspects of metal AM are considered by including the temperature history from previous layers and scans. Results from the analytical RS model presented excellent agreement with XRD measurements employed to determine the RS in the Ti-6Al-4V specimens.

scholarly journals Analytical Modeling of Residual Stress in Laser Powder Bed Fusion Considering Volume Conservation in Plastic Deformation

Modelling ◽  
2020 ◽  
Vol 1 (2) ◽  
pp. 242-259
Author(s):  
Elham Mirkoohi ◽  
Dongsheng Li ◽  
Hamid Garmestani ◽  
Steven Y. Liang
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Thermal Stress ◽  
Temperature Gradient ◽  
Hydrostatic Stress ◽  
Kinematic Hardening ◽  
The Body ◽  
Heat Of Fusion ◽  
Temperature History ◽  
Volume Conservation

Residual stress (RS) is the most challenging problem in metal additive manufacturing (AM) since the build-up of high tensile RS may influence the fatigue life, corrosion resistance, crack initiation, and failure of the additively manufactured components. While tensile RS is inherent in all the AM processes, fast and accurate prediction of the stress state within the part is extremely valuable and results in optimization of the process parameters to achieve a desired RS and control of the build process. This paper proposes a physics-based analytical model to rapidly and accurately predict the RS within the additively manufactured part. In this model, a transient moving point heat source (HS) is utilized to determine the temperature field. Due to the high temperature gradient within the proximity of the melt pool area, the material experiences high thermal stress. Thermal stress is calculated by combining three sources of stresses known as stresses due to the body forces, normal tension, and hydrostatic stress in a homogeneous semi-infinite medium. The thermal stress determines the RS state within the part. Consequently, by taking the thermal stress history as an input, both the in-plane and out of plane RS distributions are found from the incremental plasticity and kinematic hardening behavior of the metal by considering volume conservation in plastic deformation in coupling with the equilibrium and compatibility conditions. In this modeling, material properties are temperature-sensitive since the steep temperature gradient varies the properties significantly. Moreover, the energy needed for the solid-state phase transition is reflected by modifying the specific heat employing the latent heat of fusion. Furthermore, the multi-layer and multi-scan aspects of metal AM are considered by including the temperature history from previous layers and scans. Results from the analytical RS model presented excellent agreement with XRD measurements employed to determine the RS in the Ti-6Al-4V specimens.

scholarly journals Analytical Modeling of Residual Stress in Selective Laser Melting Considering Volume Conservation in Plastic Deformation

2020 ◽  
Author(s):  
Elham Mirkoohi ◽  
Dongsheng Li ◽  
Hamid Garmestani ◽  
and Steven Y. Liang
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Thermal Stress ◽  
Temperature Gradient ◽  
Hydrostatic Stress ◽  
Kinematic Hardening ◽  
The Body ◽  
Heat Of Fusion ◽  
Temperature History ◽  
Volume Conservation

Residual stress (RS) is the most challenging problem in metal additive manufacturing (AM) since the build-up of high tensile RS may influence the fatigue life, corrosion resistance, crack initiation, and failure of the additively manufactured components. While tensile RS is inherent in all the AM processes, fast and accurate prediction of stress state within the part is extremely valuable and would result in optimization of the process parameters in achieving a desired RS and control of the build process. This paper proposes a physics-based analytical model to rapidly and accurately predict the RS within the additively manufactured part. In this model, a transient moving point heat source (HS) is utilized to determine the temperature field. Due to the high temperature gradient within the proximity of the melt pool area, material experience high thermal stress. Thermal stress is calculated by combining three sources of stresses known as stresses due to the body forces, normal tension, and hydrostatic stress in a homogeneous semi-infinite medium. The thermal stress determines the RS state within the part. Consequently, by taking the thermal stress history as an input, both the in-plane and out of plane RS distributions are found from incremental plasticity and kinematic hardening behavior of the metal by considering volume conservation in plastic deformation in coupling with the equilibrium and compatibility conditions. In this modeling, material properties are temperature-sensitive since the steep temperature gradient varies the properties significantly. Moreover, the energy needed for the solid-state phase transition is reflected by modifying the specific heat employing the latent heat of fusion. Furthermore, the multi-layer and multi-scan aspects of metal AM are considered by including the temperature history from previous layers and scans. Results from the analytical RS model presented excellent agreement with XRD measurements employed to determine the RS in the Ti-6Al-4V specimens.

scholarly journals Mechanics Modeling of Residual Stress Considering Effect of Preheating in Laser Powder Bed Fusion

2021 ◽  
Vol 5 (2) ◽  
pp. 46
Author(s):  
Elham Mirkoohi ◽  
Hong-Chuong Tran ◽  
Yu-Lung Lo ◽  
You-Cheng Chang ◽  
Hung-Yu Lin ◽  
...  
Keyword(s):  
Residual Stress ◽  
Thermal Stress ◽  
Temperature Gradient ◽  
Temperature Profile ◽  
Analytical Model ◽  
Kinematic Hardening ◽  
Process Conditions ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed

This study aimed at the investigation of the effect of substrate temperature on residual stress in laser powder bed fusion using a physics-based analytical model. In this study, an analytical model is proposed to predict the residual stress through the calculation of preheating affected temperature profile and thermal stress. The effect of preheating is super-positioned with initial temperature in the modeling of temperature profile using a moving heat source approach; the resultant temperature gradient is then employed to predict the thermal stress from a point body load approach. If the thermal stress exceeds the yield strength of the material, then the residual stress under cyclic heating and cooling will be calculated based on the incremental plasticity and kinematic hardening behavior of metal. IN718 is used as a material example to pursue this investigation. To validate the predicted residual stress, experimental measurements are conducted using X-ray diffraction on IN718 samples manufactured via laser powder bed fusion under different process conditions. Results showed that preheating of the substrate could reduce the residual stress in an additively manufactured part due to the reduction in temperature gradient and resultant shrinkage stresses. However, the excessive preheating could have an opposite impact on residual stress accumulation. Moreover, the results confirm that the proposed model is a valuable tool for the prediction of residual stress, eliminating the costly experiments and time-consuming finite element simulations.

scholarly journals Mechanics Modeling of Residual Stress Considering Effect of Preheating in Laser Powder Bed Fusion

2021 ◽  
Author(s):  
Elham Mirkoohi ◽  
Hong-Chuong Tran ◽  
Yu-Lung Lo ◽  
You-Cheng Chang ◽  
Hung-Yu Lin ◽  
...  
Keyword(s):  
Residual Stress ◽  
Thermal Stress ◽  
Temperature Gradient ◽  
Temperature Profile ◽  
Analytical Model ◽  
Kinematic Hardening ◽  
Process Conditions ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed

This study aimed at the investigation of the effect of substrate preheating on residual stress in laser powder bed fusion using a physics-based analytical model. In this study, an analytical model is proposed to predict the residual stress through the calculation of preheating affected temperature profile and thermal stress. The effect of preheating is super-positioned with initial temperature in the modeling of temperature profile using a moving heat source approach; the resultant temperature gradient is then employed to predict the thermal stress from a point body load approach. If the thermal stress exceeds the yield strength of the material, then the residual stress under cyclic heating and cooling will be calculated based on the incremental plasticity and kinematic hardening behavior of metal. IN718 is used as a material example to pursue this investigation. To validate the predicted residual stress, experimental measurements are conducted using X-ray diffraction on IN718 samples manufactured via laser powder bed fusion under different process conditions. Results showed that preheating of the substrate could reduce the residual stress in an additively manufactured part due to the reduction in temperature gradient and resultant shrinkage stresses. However, the excessive preheating could have an opposite impact on residual stress accumulation. Moreover, the results confirm that the proposed model is a valuable tool for the prediction of residual stress- eliminating the costly experiments and time-consuming finite element simulations.

scholarly journals Analytical Modeling of Residual Stress in Laser Powder Bed Fusion Considering Part’s Boundary Condition

Crystals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 337 ◽  
Author(s):  
Elham Mirkoohi ◽  
Hong-Chuong Tran ◽  
Yu-Lung Lo ◽  
You-Cheng Chang ◽  
Hung-Yu Lin ◽  
...  
Keyword(s):  
Residual Stress ◽  
Thermal Stress ◽  
Kinematic Hardening ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Repeated Heating ◽  
Powder Bed ◽  
Heating And Cooling ◽  
Body Load ◽  
Point Body

Rapid and accurate prediction of residual stress in metal additive manufacturing processes is of great importance to guarantee the quality of the fabricated part to be used in a mission-critical application in the aerospace, automotive, and medical industries. Experimentations and numerical modeling of residual stress however are valuable but expensive and time-consuming. Thus, a fully coupled thermomechanical analytical model is proposed to predict residual stress of the additively manufactured parts rapidly and accurately. A moving point heat source approach is used to predict the temperature field by considering the effects of scan strategies, heat loss at part’s boundaries, and energy needed for solid-state phase transformation. Due to the high-temperature gradient in this process, the part experiences a high amount of thermal stress which may exceed the yield strength of the material. The thermal stress is obtained using Green’s function of stresses due to the point body load. The Johnson–Cook flow stress model is used to predict the yield surface of the part under repeated heating and cooling. As a result of the cyclic heating and cooling and the fact that the material is yielded, the residual stress build-up is precited using incremental plasticity and kinematic hardening behavior of the metal according to the property of volume invariance in plastic deformation in coupling with the equilibrium and compatibility conditions. Experimental measurement of residual stress was conducted using X-ray diffraction on the fabricated IN718 built via laser powder bed fusion to validate the proposed model.

Microstructure Affected Residual Stress in Direct Metal Deposition

2020 ◽  
Author(s):  
Elham Mirkoohi ◽  
Steven Y. Liang
Keyword(s):  
Residual Stress ◽  
Grain Size ◽  
Thermal Stress ◽  
High Temperature ◽  
Temperature Gradient ◽  
Yield Strength ◽  
Metal Deposition ◽  
Direct Metal Deposition ◽  
Subsequent Recovery ◽  
High Temperature Gradient

Abstract Residual stress build-up in metal additive manufacturing (AM) is a well-known problem that can impede the applicability of the AM parts. Residual stress may cause the part to fail due to the crack or fall out of the specified dimension. Thus, in order for a part to be used in a mission-critical application, it is important to predict the stress state within the AM part accurately and rapidly. During the thermal loading, the grain size is altered at the subsurface through dynamic recrystallization (DRx) and subsequent recovery. The yield strength of the alloys is largely determined by the size of nucleated grains, and it has a substantial influence on residual stress build-up. In this work, a physics-based analytical model is proposed to predict the residual stress considering the microstructure of the additively manufactured part. A moving heat source approach is used to predict the temperature field. Due to the high-temperature gradient in this process, the material properties are considered temperature-sensitive to capture the properties gradient affected thermal distribution. The energy needed for solid-state phase change is also considered by modifying the heat capacity using the latent heat of fusion. Due to the high-temperature gradient, the thermal stress is obtained using Green’s function of stresses due to the point body load. The total stress is the combination of three main sources of stress known as body forces, normal tention, and hydrostatic stress. High thermal stress may exceed the yield strength. The yield surface is obtained by modifying the Johnson-Cook flow stress to incorporate the effect of DRx on grain size using the Hall-Patch equation. The DRx and subsequent recovery affected grain size is predicted using Johnson-Mehl-Avrami-Kolmogorov (JMAK), model. The residual stress is then predicted using incremental plasticity and kinematic hardening behavior of the metal according to the property of volume invariance in plastic deformation and in coupling with equilibrium and compatibility conditions. The predicted residual stress considering microstructure evolution is validated by measuring the residual stress via X-ray diffraction for the In718 parts manufactured via the direct metal deposition process.

Influence of Compressive Stress to the Corrosion Rate of Magnesium

2016 ◽  
Vol 713 ◽  
pp. 284-287 ◽  
Author(s):  
Tetsuya Kawai ◽  
Noriyuki Takano
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Corrosion Rate ◽  
Mechanical Strength ◽  
Compressive Stress ◽  
Shot Peening ◽  
Compressive Residual Stress ◽  
Elastic Stress ◽  
The Body ◽  
The Other

Magnesium has made an attention as implant material. Because it is decomposed and absorbed in the body, and its mechanical strength is stronger than that of polymers. It is, however, reported that the corrosion rate increases under the compressive elastic stress. In the other hand, it decreases in the specimen whose surface is applied to compressive residual stress by laser shot peening. This implies that compressive plastic deformation reduces the corrosion rate. In the present paper, the corrosion rate of magnesium that was plastically deformed by uniform high compressive stress was researched. As the result, the corrosion rate decreased as the compressive stress increased.

Study on Residual Stress Distribution in Surface Grinding

2011 ◽  
Vol 487 ◽  
pp. 49-53 ◽  
Author(s):  
Gui Cheng Wang ◽  
Chong Lue Hua ◽  
Ju Dong Liu ◽  
Hong Jie Pei ◽  
Gang Liu
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Phase Transformation ◽  
Material Properties ◽  
Residual Stress Distribution ◽  
Wheel Speed ◽  
Temperature History ◽  
Good Precision ◽  
Surface Residual Stress ◽  
Key Factor

The grinding process is currently used for most of the parts requiring good precision. However, the apparition of some damage related to this process is still uncontrolled. The major deterioration is from residual stress. In order to investigate the residual stresses caused by mechanical plastic deformation, thermal plastic deformation and phase transformation in ground components, a feasible numerical method was developed to accommodate appropriately thermal stress and phase transformation in a workpiece experiencing critical temperature variation during grinding. The change of the material properties was modeled as function of temperature history. The wheel velocityVsis a key factor in determining the distribution of residual stress; both the surface residual stress and the depth of residual stress are induced with the increase of the wheel speed.

scholarly journals Analytical Modeling of Residual Stress in Laser Powder Bed Fusion

2020 ◽  
Author(s):  
Elham Mirkoohi ◽  
Jinqiang Ning ◽  
Steven Liang
Keyword(s):  
Residual Stress ◽  
Numerical Modeling ◽  
Thermal Stress ◽  
Maraging Steel ◽  
Analytical Modeling ◽  
Kinematic Hardening ◽  
Linear Optimization ◽  
Optimization Techniques ◽  
Repeated Heating ◽  
Heating And Cooling

Rapid and accurate prediction of residual stress in metal additive manufacturing processes is of great importance to guarantee the quality of the fabricated part to be used in a mission-critical application in the aerospace and automotive industries. Experimentation and numerical modeling are valuable tools for measuring and predicting the residual stress; however, to-date conducting experimentation and numerical modeling is expensive and time-consuming. Thus, herein, a physics-based thermomechanical analytical model is proposed to predict the residual stress of the additively manufactured part rapidly and accurately. A moving point heat source approach is used to predict the temperature field by considering the effects of scan strategies, heat loss, and energy needed for solid-state phase transformation. Due to the high temperature gradient in this process, part experiences a high amount of thermal stress following solidification which may exceed the yield strength of the material. The thermal stress is obtained using Green’s function of stresses due to the point body load. The Johnson-Cook flow stress model is used to predict the yield surface of the part under repeated heating and cooling. As a result of the cyclic heating and cooling and the fact that the material is yielded, the residual stress build-up is predicted based on incremental plasticity and kinematic hardening behavior of the metal according to the property of volume invariance in plastic deformation in coupling with the equilibrium and compatibility conditions. The computational methodology is realized with the laser powder fusion of maraging steel 350 as a material of example. The validation of the predictive models has been presented in terms of the comparison of predicted and measured scan-direction and build-direction residual stress distributions along depth of build under various process parameter combinations. Moreover, for the first time, the Jonson-Cook parameters of maraging steel 350 are predicted using analytical modeling of machining forces and non-linear optimization techniques.

Effect of Residual Stress or Plastic Deformation History on Fatigue Life Simulation of Pipeline Dents

2018 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Rick Wang
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Fatigue Life ◽  
Residual Stresses ◽  
Three Dimensional ◽  
Strain History ◽  
Deformation History ◽  
Stress Strain ◽  
Element Analysis ◽  
Fea Model

Mechanical dents often occur in transmission pipelines, and are recognized as one of major threats to pipeline integrity because of the potential fatigue failure due to cyclic pressures. With matured in-line-inspection (ILI) technology, mechanical dents can be identified from the ILI runs. Based on ILI measured dent profiles, finite element analysis (FEA) is commonly used to simulate stresses and strains in a dent, and to predict fatigue life of the dented pipeline. However, the dent profile defined by ILI data is a purely geometric shape without residual stresses nor plastic deformation history, and is different from its actual dent that contains residual stresses/strains due to dent creation and re-rounding. As a result, the FEA results of an ILI dent may not represent those of the actual dent, and may lead to inaccurate or incorrect results. To investigate the effect of residual stress or plastic deformation history on mechanics responses and fatigue life of an actual dent, three dent models are considered in this paper: (a) a true dent with residual stresses and dent formation history, (b) a purely geometric dent having the true dent profile with all stress/strain history removed from it, and (c) a purely geometric dent having an ILI defined dent profile with all stress/strain history removed from it. Using a three-dimensional FEA model, those three dents are simulated in the elastic-plastic conditions. The FEA results showed that the two geometric dents determine significantly different stresses and strains in comparison to those in the true dent, and overpredict the fatigue life or burst pressure of the true dent. On this basis, suggestions are made on how to use the ILI data to predict the dent fatigue life.

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