The Experts below are selected from a list of 19917 Experts worldwide ranked by ideXlab platform
R Ribacchi - One of the best experts on this subject based on the ideXlab platform.
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Practical Estimate of Deformations and Stress Relief Factors for Deep Tunnels Supported by Shotcrete
Rock Mechanics and Rock Engineering, 2005Co-Authors: Alessandro Graziani, Daniela Boldini, R RibacchiAbstract:Even though ground-support interaction in the vicinity of the tunnel face is a typical 3D problem, tunnel support design is usually based on simplified plane strain models, which are strongly dependent on the assumed degree of ground Stress Relief at the time of lining installation. The paper focuses on tunnels supported by shotcrete close to the face, where the interaction between the loading process and progressive hardening of the green shotcrete makes the problem time-dependent. A constitutive law characterized by the time-dependent stiffness and strength of the shotcrete is employed herein. The results of an extensive parametric study based on 3D axisymmetric models are presented in the form of non-dimensional design charts, which can provide guidance to a preliminary evaluation of convergences and support loadings. Moreover a strategy is proposed to enhance the capability of simplified design methods (2D models, Convergence-Confinement Method). This consists in a “guided estimate” of Stress Relief factors, which again is based on the results of 3D time-dependent analyses. Finally, by way of example, the proposed method is applied to two well-documented case-histories.
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practical estimate of deformations and Stress Relief factors for deep tunnels supported by shotcrete
Rock Mechanics and Rock Engineering, 2005Co-Authors: Alessandro Graziani, Daniela Boldini, R RibacchiAbstract:Even though ground-support interaction in the vicinity of the tunnel face is a typical 3D problem, tunnel support design is usually based on simplified plane strain models, which are strongly dependent on the assumed degree of ground Stress Relief at the time of lining installation. The paper focuses on tunnels supported by shotcrete close to the face, where the interaction between the loading process and progressive hardening of the green shotcrete makes the problem time-dependent. A constitutive law characterized by the time-dependent stiffness and strength of the shotcrete is employed herein. The results of an extensive parametric study based on 3D axisymmetric models are presented in the form of non-dimensional design charts, which can provide guidance to a preliminary evaluation of convergences and support loadings.
Yidu Zhang - One of the best experts on this subject based on the ideXlab platform.
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analysis and homogenization of residual Stress in aerospace ring rolling process of 2219 aluminum alloy using thermal Stress Relief method
International Journal of Mechanical Sciences, 2019Co-Authors: Yidu Zhang, Hanjun Gao, David HuiAbstract:Abstract Substantial amount of material is removed during the manufacturing process of large ring parts, thereby causing the ring parts to become a thin-walled structure with reduced rigidity. The influence of internal and external factors leads to machining deformation, which is ubiquitous in the actual production process in the aerospace industry. Studies showed that the main factor that causes this type of machining deformation is the initial residual Stress inside the blank. The initial residual Stress must be homogenized to solve the machining deformation problem. Large and uneven residual Stress is easily produced during rolling. The research object in this study is a 2219 aluminum-alloy aerospace rolling ring. First, the mechanical model for the rolling process is established to analyze the mechanical behaviors of the diameter and axial directions. The reasonable parameters for the rolling process are determined according to continuous and penetration conditions. Second, a finite element model was established to simulate the rolling process and the Thermal Stress Relief process. This process was conducted to explore and verify the effect of Thermal Stress Relief treatment on the reduction of residual Stress and homogenization of the rolling process. Corresponding rolling and Thermal Stress Relief experiments were conducted to verify the simulation results. The experimental results are highly consistent with the simulation results when the treatment time of Thermal Stress Relief was changed. The Thermal Stress Relief of the rolling ring can effectively reduce and homogenize residual Stress. This study is significant for the reduction and homogenization of large residual Stress.
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fatigue life of 7075 t651 aluminium alloy treated with vibratory Stress Relief
International Journal of Fatigue, 2018Co-Authors: Hanjun Gao, Yidu Zhang, Jing Song, Kai WenAbstract:Abstract As an energy-saving and high-efficient Stress relieving process, vibratory Stress Relief (VSR)’s influence of on fatigue life is still explicit and needs further investigation. Standard specimens are manufactured to study the VSR effects on 7075-T651 aluminium alloy fatigue behaviour. Dynamic Stresses generated during vibration are measured by strain gauge, and the residual Stresses with and without VSR are compared to validate the Stress relieving effects. Eventually, fatigue tests are conducted to obtain the fatigue behaviour of 7075-T651 aluminium alloy treated by VSR with different amplitudes. Experimental results show that when the amplitude is small enough (less than 0.01 mm), the fatigue life is almost unaffected by VSR. Fatigue life increases with the VSR amplitude when the amplitude changes from 0.01 to 0.04 mm. The fatigue limit increases by 11.11% after 0.04 mm amplitude VSR. The fatigue life decreases with the increase of the amplitude when the amplitude changes from 0.05 to 0.1 mm. VSR with 0.1 mm amplitude decreases fatigue life by 11.11%, which should be deliberated in engineering application. It is concluded that low amplitude VSR has positive effects on 7075-T651 aluminium alloy fatigue life, and high amplitude VSR has negative effects.
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experimental investigation on the fatigue life of ti 6al 4v treated by vibratory Stress Relief
Metals, 2017Co-Authors: Hanjun Gao, Yidu Zhang, Jing SongAbstract:Vibratory Stress Relief (VSR) is a highly efficient and low-energy consumption method to relieve and homogenize residual Stresses in materials. Thus, the effect of VSR on the fatigue life should be determined. Standard fatigue specimens are fabricated to investigate the fatigue life of Ti-6Al-4V titanium alloy treated by VSR. The dynamic Stresses generated under different VSR amplitudes are measured, and then the relationship between the dynamic Stress and vibration amplitude is obtained. Different specimen groups are subjected to VSRs with different amplitudes and annealing treatment with typical process parameters. Residual Stresses are measured to evaluate the Stress relieving effects. Finally, the fatigue behavior under different states is determined by uniaxial tension–compression fatigue experiments. Results show that VSR and annealing treatment have negative effects on the fatigue life of Ti-6Al-4V. The fatigue life is decreased with the increase in VSR amplitude. When the VSR amplitude is less than 0.1 mm, the decrease in fatigue limit is less than 2%. Compared with specimens without VSR or annealing treatment, the fatigue limit of the specimens treated by VSR with 0.2 mm amplitude and annealing treatment decreases by 10.60% and 8.52%, respectively. Although the Stress relieving effect is better, high amplitude VSR will lead to the decrease of Ti-6Al-4V fatigue life due to the defects generated during vibration. Low amplitude VSR can effectively relieve the Stress with little decrease in fatigue life.
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simulation of vibration Stress Relief after welding based on fem
Acta Metallurgica Sinica (english Letters), 2008Co-Authors: Xiaohan Zhao, Yidu Zhang, Huazhao ZhangAbstract:A finite element model is developed for the simulation of vibration Stress Relief (VSR) after welding. For the nonresonant vibration, the reduction in Stress strongly depends on the amplitude of vibration. For the resonant vibration, the vibration frequency is the key for Stress Relief. The vibration frequency should be close to the structure natural frequency for the desired vibration mode. Only small vibration amplitude is required, which will be amplified during vibration. Vibration time does not have a major impact on vibration Stress Relief. When the amplitude of vibration Stress Relief is large, the treatment will be more effective.
Hanjun Gao - One of the best experts on this subject based on the ideXlab platform.
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analysis and homogenization of residual Stress in aerospace ring rolling process of 2219 aluminum alloy using thermal Stress Relief method
International Journal of Mechanical Sciences, 2019Co-Authors: Yidu Zhang, Hanjun Gao, David HuiAbstract:Abstract Substantial amount of material is removed during the manufacturing process of large ring parts, thereby causing the ring parts to become a thin-walled structure with reduced rigidity. The influence of internal and external factors leads to machining deformation, which is ubiquitous in the actual production process in the aerospace industry. Studies showed that the main factor that causes this type of machining deformation is the initial residual Stress inside the blank. The initial residual Stress must be homogenized to solve the machining deformation problem. Large and uneven residual Stress is easily produced during rolling. The research object in this study is a 2219 aluminum-alloy aerospace rolling ring. First, the mechanical model for the rolling process is established to analyze the mechanical behaviors of the diameter and axial directions. The reasonable parameters for the rolling process are determined according to continuous and penetration conditions. Second, a finite element model was established to simulate the rolling process and the Thermal Stress Relief process. This process was conducted to explore and verify the effect of Thermal Stress Relief treatment on the reduction of residual Stress and homogenization of the rolling process. Corresponding rolling and Thermal Stress Relief experiments were conducted to verify the simulation results. The experimental results are highly consistent with the simulation results when the treatment time of Thermal Stress Relief was changed. The Thermal Stress Relief of the rolling ring can effectively reduce and homogenize residual Stress. This study is significant for the reduction and homogenization of large residual Stress.
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fatigue life of 7075 t651 aluminium alloy treated with vibratory Stress Relief
International Journal of Fatigue, 2018Co-Authors: Hanjun Gao, Yidu Zhang, Jing Song, Kai WenAbstract:Abstract As an energy-saving and high-efficient Stress relieving process, vibratory Stress Relief (VSR)’s influence of on fatigue life is still explicit and needs further investigation. Standard specimens are manufactured to study the VSR effects on 7075-T651 aluminium alloy fatigue behaviour. Dynamic Stresses generated during vibration are measured by strain gauge, and the residual Stresses with and without VSR are compared to validate the Stress relieving effects. Eventually, fatigue tests are conducted to obtain the fatigue behaviour of 7075-T651 aluminium alloy treated by VSR with different amplitudes. Experimental results show that when the amplitude is small enough (less than 0.01 mm), the fatigue life is almost unaffected by VSR. Fatigue life increases with the VSR amplitude when the amplitude changes from 0.01 to 0.04 mm. The fatigue limit increases by 11.11% after 0.04 mm amplitude VSR. The fatigue life decreases with the increase of the amplitude when the amplitude changes from 0.05 to 0.1 mm. VSR with 0.1 mm amplitude decreases fatigue life by 11.11%, which should be deliberated in engineering application. It is concluded that low amplitude VSR has positive effects on 7075-T651 aluminium alloy fatigue life, and high amplitude VSR has negative effects.
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experimental investigation on the fatigue life of ti 6al 4v treated by vibratory Stress Relief
Metals, 2017Co-Authors: Hanjun Gao, Yidu Zhang, Jing SongAbstract:Vibratory Stress Relief (VSR) is a highly efficient and low-energy consumption method to relieve and homogenize residual Stresses in materials. Thus, the effect of VSR on the fatigue life should be determined. Standard fatigue specimens are fabricated to investigate the fatigue life of Ti-6Al-4V titanium alloy treated by VSR. The dynamic Stresses generated under different VSR amplitudes are measured, and then the relationship between the dynamic Stress and vibration amplitude is obtained. Different specimen groups are subjected to VSRs with different amplitudes and annealing treatment with typical process parameters. Residual Stresses are measured to evaluate the Stress relieving effects. Finally, the fatigue behavior under different states is determined by uniaxial tension–compression fatigue experiments. Results show that VSR and annealing treatment have negative effects on the fatigue life of Ti-6Al-4V. The fatigue life is decreased with the increase in VSR amplitude. When the VSR amplitude is less than 0.1 mm, the decrease in fatigue limit is less than 2%. Compared with specimens without VSR or annealing treatment, the fatigue limit of the specimens treated by VSR with 0.2 mm amplitude and annealing treatment decreases by 10.60% and 8.52%, respectively. Although the Stress relieving effect is better, high amplitude VSR will lead to the decrease of Ti-6Al-4V fatigue life due to the defects generated during vibration. Low amplitude VSR can effectively relieve the Stress with little decrease in fatigue life.
Feng Li - One of the best experts on this subject based on the ideXlab platform.
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an arrhenius equation based model to predict the residual Stress Relief of post weld heat treatment of ti 6al 4v plate
Journal of Manufacturing Processes, 2018Co-Authors: Alexandru Crivoi, Xu Song, Niroj Maharjan, Feng LiAbstract:Abstract Creep models are generally utilized for predicting the residual Stress Relief during post weld heat treatment (PWHT). However, a comprehensive model considering the temperature effect is still lacking. In the present work, a new temperature dependent Arrhenius equation-based model has been developed to predict the residual Stress Relief of PWHT of Ti-6Al-4V. The model was validated by the surface residual Stress measurement of the Ti-6Al-4V plate before and after PWHT using X-ray Diffraction (XRD). The comparative study of modelling results and measurements indicates that the temperature dependent Arrhenius equation-based model developed in this work is accurate and effective for predicting the residual Stress Relief of PWHT of Ti-6Al-4V. Besides, the creep induced strain increment takes the dominant role in residual Stress Relief during the PWHT process of Ti-6Al-4V.
Chunlei Zhang - One of the best experts on this subject based on the ideXlab platform.
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numerical study on Stress Relief and fracture distribution law of floor in short distance coal seams mining a case study
Geotechnical and Geological Engineering, 2021Co-Authors: Chunlei Zhang, Ruimin Feng, Xibin Zhang, Wei ShenAbstract:During the mining process of short distance coal seams group with high gas content, excavation of the protective coal seam will result in Stress Relief and fracture development which provides pathways for gas migration. Gas stored in the lower coal seam moves along the mining-induced fracture to the floor of the upper working face, which may cause the gas over-limit at the upper coal seam. This paper takes the short distance coal seams group in Xinghua coal mine as an example, theoretical analysis, numerical simulation and field monitoring are comprehensively applied to study the floor failure mechanism, pressure Relief law and dynamic evolution of cracks induced by the mining of the second-right working face. The results showed that as the upper coal seam gradually advances, the pressure Relief angle of roof and floor gradually decreases, and the pressure Relief range and floor failure depth gradually increase. After the working face of the upper coal seam is advanced 100 m, the range of the pressure Relief in the surrounding coal and rock masses approaches stable; the cracks in the shallow depth are mainly with small angles or type II shear cracks, and the cracks in the large depth are mainly shear-expansion with lager angles, and the amount of fractures in the floor reduces with the increase of the depth of the floor. It was found that the mining-induced fractures in the floor is distributed in the shape of an “O” ring, and as the working face advances, the range of this “O”-shaped crack circle keeps moving forward but the width of the crack circle is basically unchanged. Finally, the low-level drilling field was used to control the gas from lower coal seams according to the Stress Relief and fracture distribution law, which achieved satisfied application effect and provided guidance for mine gas extraction in similar mining conditions.
