20 October 2021, Volume 45 Issue 10

    

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  Research Status of Residual Stress Prediction of Dissimilar Metal Weld Joints ofNozzle to Safe-End in Nuclear Power Plant

  GUO Shu, WANG Haitao, HAN Enhou

  Materials For Mechanical Engineering. 2021, 45(10): 1-12. https://doi.org/10.11973/jxgccl202110001

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  The nozzle to safe-end dissimilar metal weld joint is a typical structure in pressurized water reactor power plant connecting the low alloy steel pressure vessel nozzle of the main equipment and the austenitic stainless steel pipe, which is susceptible to primary water stress corrosion cracking. The welding residual tensile stress is one of the primary drivers of this stress corrosion cracking. Thus, accurate estimation of the welding residual stress distribution within the nozzle to safe-end dissimilar metal weld joint is of great significance. Investigating the welding residual stress by finite element modeling aims to ensure the structural integrity of nuclear equipments. The structures, materials and welding process characteristics of the nozzle to safe-end dissimilar metal weld joints are described. The numerical calculation works and typical processes of the residual stress distribution inside the dissimilar metal weld joints predicted by the finite element method, as well as the influence of many factors on finite element modeling residual stresses in dissimilar metal weld joints are reviewed.
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  Research Progress on Preparation Technology of Copper Matrix Composites

  LEI Shasha, LIU Hongjun

  Materials For Mechanical Engineering. 2021, 45(10): 13-21. https://doi.org/10.11973/jxgccl202110002

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  The rapid development of high technology puts forward higher requirements for the development of high-performance copper materials. Copper matrix composites have been widely used because of their high strength and good electrical and thermal conductivity, wear resistance, corrosion resistance and high-temperature stability; their preparation processes are constantly developing, and great progress has been made in recent years. The characteristics and research progress of the main preparation processes of copper matrix composites, including powder metallurgy technique, casting process, mechanical alloying, internal oxidation, in-situ synthesis, melt infiltration, and friction stir processing, are reviewed. The development direction of copper matrix composite preparation technology in the future is prospected.
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  Research Progress on Fracture Toughness Testing Technology of Ductile Cast Iron

  ZHENG Guohua, ZHANG Xinyao, CHEN Pei, SHAN Jianjun, TIAN Qingnian

  Materials For Mechanical Engineering. 2021, 45(10): 22-28. https://doi.org/10.11973/jxgccl202110003

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  Fracture toughness is an important fracture resistance index of materials. The research status of plane strain fracture toughness, elastoplastic fracture toughness, crack tip opening displacement and dynamic fracture toughness testing techniques and their application to ductile cast iron materials are summarized. The influence of the temperature, microstructure and sample size on the fracture toughness of ductile cast iron is described. The problem of crack length testing in the fracture toughness specimen of ductile cast iron is discussed. The test method of fracture toughness of ductile cast iron based on J-Q (J integral-triaxial stress factor) theory is also described. It is believed that the multi-parameter fracture toughness testing based on the J-Q theory is the focus of future research. Furthermore, if the fracture toughness is to be used for engineering safety assessment, the loading mode and environment in actual service must be comprehensively considered during the testing.
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  Fatigue Performance of 2E12-T3 Aluminum Alloy Skin Circumferential Docking Structure

  PENG Hang, QIN Jianbo, ZHANG Yanjun

  Materials For Mechanical Engineering. 2021, 45(10): 29-33,42. https://doi.org/10.11973/jxgccl202110004

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  The fatigue dangerous location of the skin circumferential docking structure was determined by finite element simulation. The theoretical detailed fatigue rating (DFR) of the 2024-T3 aluminum alloy docking structure was calculated. Fatigue tests were conducted on the 2E12-T3 aluminum alloy skin circumferential docking structure, and the fatigue fracture location and fracture morphology were analyzed. The test DFR of the docking structure was calculated, and compared with the theoretical DFR of the 2024-T3 aluminum alloy docking structure. The results show that the fatigue failure occurred at nail holes at the end of the skin circumferential docking structure samples, which was consistent with the structure weak location determined by the finite element analysis. The cracks initiated at the skin hole wall perpendicular to the loading direction at the skin and the strip joint surface. Fatigue bands and a few dimples existed in the crack propagation zone, and dimples and cavities in the instantaneous zone. The DFR of the 2E12-T3 aluminum alloy docking structure was about 13.9% higher than that of 2024-T3 aluminum alloy docking structure.
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  Microstructure and Mechanical Property Evolution of Rare Earth-Containing Al-Mg Alloy During Cold Drawing

  ZHANG Xin, YANG Guangheng, WANG Zehua, ZHOU Zehua, YI Yu, CAI Xin

  Materials For Mechanical Engineering. 2021, 45(10): 34-42. https://doi.org/10.11973/jxgccl202110005

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  Al-3.0Mg-xRE (mass fraction/%, x=0, 0.12, 0.31, RE=La+Ce) alloys containing different-content rare earth were smelted. The evolution of the microstructure, hardness and tensile properties of the alloys were investigated in cold drawing. The results show that during the cold drawing, the grains of the test alloys were elongated; the second phase particles were also elongated and fragmented to small particles, and then gradually aligned on grain boundaries and dendrite boundaries in linearity; the intensity of Copper {112}〈111〉 deforming texture increased. With increasing deformation amount, the strength of the alloys increased linearly, the plasticity decreased and the hardness increased. Proper rare earth addition (0.12%) could improve the microstructure and the mechanical properties of the alloy. However, excessive rare earth addition (0.31%) increased the number and size of the second phases in the alloy, thereby reducing the mechanical properties of the alloy. After cold drawing, the Al-3.0Mg-0.12RE alloy had the smallest and the least second phases, the highest deforming texture intensity and the best mechanical properties.
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  Dynamic Constitutive Relationship and Failure Relationship of GH907 Superalloy Based on J-C Model

  DONG Zemin, CHEN Wei, LIU Lulu, XU Kailong, ZHAO Zhenhua

  Materials For Mechanical Engineering. 2021, 45(10): 43-49. https://doi.org/10.11973/jxgccl202110006

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  The quasi-static mechanical properties at room temperature and dynamic mechanical properties at 20-400 ℃ of the aircraft engine casing material GH907 superalloy were investigated on the universal test machine, Hopkinson tension bar and Hopkinson pressure bar equipments. Based on the test results, the parameters in the Johnson-Cook (J-C) constitutive model and failure model were obtained by fitting, and the dynamic compression process of the test alloy was simulated. The effectiveness of the constitutive model parameters were evaluated. The results show that during tension at room temperature and the strain rates of 0-3 000 s^-1, the test alloy was sensitive to strain rates, but during compression was not. At temperatures of 20-400 ℃, the softening behaviour of the test alloy was obvious. The established J-C models could accurately predict the mechanical behavior of the alloy at different temperatures and strain rates; the relative errors between the simulation and the test results of the sample geometrical size and maximum stress were within 2%.
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  Creep-Fatigue Damage Behavior and Establishment of Creep-Fatigue Damage Constitutive Model of P92 Steel

  CAO Yu, CUI Xin, JI Dongmei

  Materials For Mechanical Engineering. 2021, 45(10): 50-57,65. https://doi.org/10.11973/jxgccl202110007

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  Creep-fatigue tests under stress control and strain control were conducted on P92 steel at 600 ℃. The effects of load level and load holding time on the creep-fatigue damage were analyzed. By combination of stress controlled creep-fatigue test data, introducing the modified Chaboche nonlinear follow-up hardening rate and creep strain under the framework of viscoplastic unified constitutive theory, and considering the damage evolution law, the coupled creep-fatigue damage constitutive model based on Chaboche theory was established. The creep-fatigue cyclic curves of P92 steel were simulated. The results show that P92 steel exhibited cyclic softening characteristics at 600 ℃. Under stress control, the damage of P92 steel at high load holding was positively correlated with the average stress, while the damage at low load holding was negatively correlated with the average stress. Under strain control, P92 steel showed stress relaxation behavior, and the longer the load holding time, the more obvious the stress relaxation. The established creep-fatigue damage constitutive model could simulate the cyclic characteristics of P92 steel well, and the maximum relative error of the stress simulation in creep-fatigue process was 7.30%.
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  Inversion and Finite Element Analysis of Mechanical Properties ofPure Titanium Gradient Material by Ultrasonic Surface Rolling Processing

  SUN Yinsha, JIA Yunfei, YUAN Guangjian, LI Xiao, ZHANG Xiancheng

  Materials For Mechanical Engineering. 2021, 45(10): 58-65. https://doi.org/10.11973/jxgccl202110008

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  Ultrasonic surface rolling processing was conducted on the pure titanium TA2, and the microstructure and residual stress distribution on cross section were studied. The load-indentation depth curves at different distances from surface were measured by nanoindentaion tests, and then the stress-strain curves were obtained by inversion. With the stress-strain relationship as the material property, the load-indentation depth curves were simulated by the finite element method, and were compared with the test curves to verify the inversion method. The influence of the initial yield stress and strain hardening exponent on the load-indentation depth curves was investigated. The results show that a gradient structure with gradually increasing grain size was formed in the sample surface layer, and the residual compressive stress increased and then decreased with increasing distance from surface. The load-indentation depth simulation curves were basically consistent with the test curves, and the relative errors of the maximum indentation depth were within 8%, indicating the inversion method was reliable. With increasing initial yield stress and strain hardening exponent, the loading curvature of the load-indentaion depth curves increased, the plastic work to total work ratio decreased, and the variation of the initial stiffness was not obvious.
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  Numerical Simulation of Quasi-static Axial Compression of Carbon Fiber Composite Winding Aluminum Alloy Tube

  DONG Fan, MA Qihua, GAN Xuehui, ZHOU Tianjun

  Materials For Mechanical Engineering. 2021, 45(10): 66-74. https://doi.org/10.11973/jxgccl202110009

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  With multilayer (10-layer) and few-layer (3-layer) carbon fiber composite winding aluminum alloy tube (Al-CFRP mixed tube) as the research object, the single-layer shell model, multi-layer conventional shell model and multi-layer continuous shell model were established with ABAQUS/Explicit finite element software. The axial compression deformation process of the hybrid tube was simulated with Hashin failure criterion. The simulation accuracy of each model was compared. The simulation relative errors of the initial peak load, specific energy absorption and average compression load and the simulation time were made dimensionless and weighted to evaluate each model comprehensively. The results show that the multi-layer shell model could better predict the damage deformation and energy absorption characteristics of the hybrid tubes under axial compression. For the multilayer winding hybrid tube, the best model was the multi-layer continuous shell model, while for the few-layer winding hybrid tube, the multilayer conventional shell model had the smallest error.
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  Energy Efficiency Analysis and Optimization of Selective Laser Melting Rapid Formation Process

  XIAO Gang, GAO Bin, HAN Yan, WAN Keqian, YANG Qinwen

  Materials For Mechanical Engineering. 2021, 45(10): 75-83. https://doi.org/10.11973/jxgccl202110010

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  The quantitative relationship between system energy consumption, specific energy consumption (indicating energy efficiency) and process parameters was established by analyzing the energy consumption composition and characteristics of selective laser melting (SLM) system. A process parameter optimization strategy for optimizing the energy efficiency was proposed. The results show that the contradiction between the cladding efficiency and the energy consumption should be considered in selecting the laser power. The reasonable increase of laser scanning speed could improve the cladding efficiency and shorten working time of laser cladding under the disadvantage of reducing the cladding channel size, and then reduce energy consumption. Larger powder-bed thickness and scanning speed, as well as smaller transverse overlap rate matching the appropriate laser power, could effectively reduce the specific energy consumption of the SLM system. Choosing a direction with a smaller height for stacking could shorten the interlayer time and reduce the energy consumption of the system.
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  Dynamic Recrystallization Model and Grain Size Numerical Simulation of F45MnVS Non-quenched and Tempered Steel

  WU Xiaodong, WANG Lianjin, XIE Jianfeng, LUO Rui

  Materials For Mechanical Engineering. 2021, 45(10): 84-90. https://doi.org/10.11973/jxgccl202110011

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  The F45MnVS non-quenched and tempered steel was subjected to single-pass compression tests with different deformation amounts (5%-56%) at deformation temperatures of 950-1 050 ℃ and strain rates of 0.01-5 s^-1. The effects of deformation temperature, strain rate and deformation amount on the deformation behavior and grain size of the steel were studied. According to the experimental data, the dynamic recrystallization critical strain model and the average grain size model were established, and the average size of dynamic recrystallization grains was simulated with Deform software embedded with the two models. The results show that with increasing deformation amount or strain rate, or decreasing deformation temperature, the average grain size of the test steel decreased. At relatively high strain rates, the decrease in stress by work softening was not obvious, and the dynamic recrystallization degree was relatively low; the opposite was true at relatively low strain rates. The average recrystallization grain size obtained by the simulation was in good agreement with the experimental results, and the variation of the average grain size with the deformation temperature, strain rate and deformation amount was consistent with the experimental results.
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  Influence of Yield Criterion and Hardening Model on Forming Simulation Accuracy of Automobile Rear Door Inner Panel of DC56D+Z Steel

  E Hongwei, LI Yadong, ZHENG Xuebin, HAN Longshuai

  Materials For Mechanical Engineering. 2021, 45(10): 91-96,103. https://doi.org/10.11973/jxgccl202110012

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  With DC56D+Z ultra-deep drawing steel as the research object, the material performance parameter analysis of the Ludwik, Swift and Hockett-Sherby hardening models was carried out. The hardening model accurately characterizing the mechanical behavior of the steel was determined. The forming of DC56D+Z steel automobile rear door inner panel was simulated by the optimal hardening model with Hill'48, Barlat'89 and BBC-2005 yield criteria, respectively. The simulation of the material inflow, the maximum principal strain and the maximum thinning rate were obtained and compared with the test results to analyze the influence of different yield criteria on the simulation accuracy. The results show that the Hockett-Sherby hardening model had the highest accuracy in describing the mechanical behavior of DC56D+Z steel, and the square of the fitting correlation coefficient was 0.997 9. The simulation model based on the Hockett-Sherby hardening model equipped with the BBC-2005 yield criterion had the highest accuracy in predicting the material inflow, the maximum principal strain and the maximum thinning rate, with the maximum relative errors of 4.9%, 5.6%, 10.1%, respectively. The BBC-2005 yield criterion was more suitable for the forming simulation of DC56D+Z steel sheets.
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  Numerical Simulation of Laser Shock Peening for Superalloy and Fatigue Life Prediction

  GUO Xiaojun, SU Xiao, HU Dianyin

  Materials For Mechanical Engineering. 2021, 45(10): 97-103. https://doi.org/10.11973/jxgccl202110013

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  The macroscopic finite element numerical model and the mesoscopic parametric evolution numerical model of laser shock peening were established. A three-dimensional multi-scale simulation method for laser shock peening was proposed. The distribution law of residual stress, dislocation density and grain size of Inconel 718 superalloy after laser shock peening was analyzed. The Sines fatigue life criterion was modified considering the influence of residual stress and grain refinement caused by laser shock peening on fatigue life, and was verified by tests. The results show that residual compressive stresses no less than 550 MPa within the impact range of the light spot on the sample surface were obtained by simulation; significant dislocation proliferation existed in the surface area, and the local grain size could be refined by about 25%; the simulation was basically consistent with the test results. The fatigue lives predicted by the modified Sines criterion were within 3 times the dispersion band, indicating that the model could predict the fatigue life of Inconel 718 superalloy after laser shock peening.
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  Feature Selection and Prediction of Mechanical Properties of Steel Coils Based on Gradient Boosting Decision Tree

  XIE Shaojie, WANG Wei, HE Fushan

  Materials For Mechanical Engineering. 2021, 45(10): 104-110. https://doi.org/10.11973/jxgccl202110014

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  The basic modeling features of hot-dip galvanized steel coil were selected on the basis of metallurgical mechanism, and then other chemical element features were selected by gradient boosting decision tree algorithm. The model parameters were optimized by combining grid search with cross validation methods, and the effects of different features on yield strength of steel coils were analyzed by the model. The results show that the basic modeling features of mechanical property prediction model of hot-dip galvanized steel coils included process parameter features, specification features and basic chemical element features, and other chemical element features which had great influence on the yield strength of steel coils were nitrogen and aluminum content. After optimizing the model parameters, the root mean squared error of the yield strength measured on the test set was 10.671 MPa, the mean absolute error was 8.244 MPa, and the mean absolute percentage error was 2.641%. The prediction accuracy of the model was significantly higher than that before optimizing the model parameters. When the content of carbon, silicon or manganese or the hot rolling in-rolling temperature changed, the yield strength of steel coils changed greatly.