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Nanoindentation behavior and creep-induced cracking of long-term crept austenitic steel at 650℃

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Journal of Iron and Steel Research(International) 2024年第2期31卷 464-474页

作者： Zhen Zhang Yu-hang Duan Shuai Wang Jin-shan Chen An-zhe Wang Xiang-yang Mao Yuan-ji Shi Jie Zhang Ming Liu Zheng-fei Hu School of Materials Science and Engineering Nanjing Institute of TechnologyNanjing211167JiangsuChina Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology Nanjing211167JiangsuChina Jiangsu Wind Power Engineering Technology Center Nanjing210023JiangsuChina Nanjing Vocational University of Industry Technology Nanjing210023JiangsuChina Baoshan Iron&Steel Co. Ltd.Shanghai201900China Fujian Provincial Key Laboratory of Terahertz Functional Devices and Intelligent Sensing School of Mechanical Engineering and AutomationFuzhou UniversityFuzhou350116FujianChina School of Materials Science and Engineering Tongji UniversityShanghai201804China

The grain boundary(GB)damage of long-term crept HR3C(25Cr–20Ni–Nb–N)austenitic steel with solid solution state was investigated by nanoindentation test accompanied with in-situ electron back-scattered diffraction.The corresponding microstructure was characterized by scanning electron microscopy and transmission electron microscopy.Results show that the increase in nanoindentation hardness at the GBs and triple grain junctions may be related to the dislocation accumulation and carbide growth during the creep.Coarsened M23C6 and dislocations piling-up at the GB accelerate the nucleation and coalescence of creep cavity along the GB.The nanoindentation hardness in grains varies with orientation of the stress axis.The orientation difference of neighbor grains may induce local high geometrically necessary dislocation densities and strain gradients near the GB,consequently causing stress concentration and subsequent crack growth at specific GBs.

关键词： Austenitic steel creep Nanoindentation Grain orientation creep-induced cracking

A multi-scale framework for life reduction assessment of turbine blade caused by microstructural degradation

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Chinese Journal of Aeronautics 2024年第1期37卷 186-200页

作者： Xiaoguang YANG Menglei WANG Duoqi SHI Zhenlei LI Yongsheng FAN School of Energy and Power Engineering Beihang UniversityBeijing 102206China Research Institute of Aero-Engine Beihang UniversityBeijing 102206China National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics Beihang UniversityBeijing 102206China

The prolonged thermal exposure with centrifugal load results in microstructural degradation,which ultimately leads to a reduction in the fatigue and creep resistance of the turbine blades.The present work proposes a multi-scale framework to estimate the life reduction of turbine blades,which combines a microstructural degradation model,a two-phase constitutive model,and a microstructure-dependent fatigue and creep life reduction model.The framework with multi-scale models is validated by a Single Crystal(SC)Ni-based superalloy at the microstructural length-scale and is then applied to calculate the microstructural degradation and the fatigue and creep life reduction of turbine blades under two specific service conditions.The simulation results and quantitative analysis show that the microstructural degradation and fatigue and creep life reduction of the turbine blade are heavily influenced by the variations in the proportion of the intermediate state,namely,the maximum rotor speed status,in the two specific service conditions.The intermediate state accelerates the microstructural degradation and leads to a reduction of the life,especially the effective fatigue life reserve due to the higher temperature and rotational speed than that of the 93%maximum rotor speed status marked as the reference state.The proposed multi-scale framework provides a capable approach to analyze the reduction of the fatigue and creep life for turbine blade induced by microstructural degradation,which can assist to determine a reasonable Time Between Overhaul(TBO)of the engine.

关键词： creep Fatigue Life reduction Microstructural degradation Multi-scale modeling Turbine blades

Correlating dynamic relaxation and viscoelasticity in metallic glasses

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Science China(Physics,Mechanics & Astronomy) 2024年第5期67卷 81-90页

作者： GuangHui Xing Qi Hao Fan Zhu Yun-Jiang Wang Yong Yang Hidemi Kato Eloi Pineda Si Lan JiChao Qiao School of Mechanics Civil Engineering and ArchitectureNorthwestern Polytechnical UniversityXi'an 710072China State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Science University of Chinese Academy of SciencesBeijing 100049China Department of Mechanical Engineering College of EngineeringCity University of Hong KongHong Kong 999077China Department of Materials Science and Engineering College of EngineeringCity University of Hong KongHong Kong 999077China Institute for Materials Research Tohoku UniversitySendai 980-8577Japan Department of Physics Institute of Energy TechnologiesUniversitat Politècnica de CatalunyaBarceona 9Spain School of Material Science and Engineering Herbert Gleiter Institute of NanoscienceNanjing University of Science and Technology.Nanjing 210094China State Key Laboratory of Clean and Efficient Turbomachinery Power Equipment Northwestern Polytechnical UniversityXi'an 710072China

Relaxation dynamics,essential for the structural evolution of non-equilibrium systems like glassy materials,remain enigmatic.Here,we explore relaxation dynamics and viscoelastic properties in three types of metallic glasses with distinctβrelaxation behavior.In systems with significantβrelaxation,stress relaxation and creep experiments reveal a transition from two-step to one-step relaxation with rising temperature.However,such a phenomenon is absent in systems with weakerβrelaxation.We model the two-step relaxation process using a double Kohlrausch-Williams-Watts equation,and the obtained relaxation times elegantly adhere to the Arrhenius relationship.By combining fitted activation energies with theoretical analysis,we conclusively attribute these relaxation processes toβrelaxation andαrelaxation,respectively.Finally,we analyze the relaxation time spectra of two processes and establish a comprehensive picture linking dynamic relaxation with viscoelasticity.Our study provides new strategies for probing the complex relaxation behaviors of glasses from the perspective of viscoelasticity.

关键词： creep relaxation glasses

A bounding surface visco-plasticity model considering generalized spacing ratio of soils

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第5期16卷 1832-1846页

作者： Xiaosen Kang Hongjian Liao Qiangbing Huang Jianbing Peng Department of Geological Engineering Chang’an UniversityXi’an710054China Department of Civil Engineering Xi’an Jiaotong UniversityXi’an710049China

The non-unique critical state of soils with time-dependent behaviors is a significant issue in geotechnical engineering problems.However,previous bounding surface plasticity models cannot predict accurately the non-unique critical state of soils,because the distance between the compression line and critical state line charged by strain-rate effect is basically neglected.To fill this gap,a generalized spacing ratio of soils is defined in the elasto-viscoplastic framework,and a bounding surface visco-plasticity model is formulated and verified,which can consider the generalized spacing ratio.Specifically,the generalized spacing ratio of soils reflects the distance between the compression line and the critical state line of soils with time-dependent behaviors.Then,the generalized spacing ratio is introduced into an improved anisotropic bounding surface.A new expression of the visco-plastic multiplier is derived by solving the consistency equation of an anisotropic bounding surface.In the expression,a strain rate index is proposed to account for the strain-rate effect on visco-plastic strain increment,and a visco-plastic hardening modulus is derived to predict the visco-plastic response of soils in overconsolidation conditions.The model is then verified through constant strain rate tests and creep tests.Notably,it can capture the non-unique critical states of soils with time-dependent behaviors due to the generalized spacing ratio and the creep rupture of soils due to the visco-plastic multiplier that considers the stress ratio and visco-plastic strain rate.

关键词： Soil Constitutive model Visco-plastic behavior Strain rate creep Anisotropic

creep behavior and permeability evolution of coal pillar dam for underground water reservoir

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International Journal of Coal Science & Technology 2023年第1期10卷 136-141页

作者： Yulong Chen Xianjie Hao Dongjie Xue Zhe Li Xiaoran Ma State Key Laboratory of Water Resource Protection andUtilization in Coal Mining BeijingChina China University of Mining and Technology BeijingBeijingChina

Using goof as water storage space plays a vital role in the ecological environment and economic development of arid mining areas,while the rock strength and the stability of coal pillars in underground water reservoirs are closely related to creep process.In this work,triaxial creep-seepage tests were conducted for coal samples to develop new insights into the creep behavior and permeability evolution.The results showed that the creep deformation and permeability evolution of coal samples exhibit three stages,namely,the compaction hardening stage before the stress threshold,volumetric compaction stage,and volumetric dilatancy stage.The coal permeability decreases first and then increases with the creep strain and it is well correlated with the variation of volumetric strain.

关键词： Coal creep Permeability Volumetric strain

creep life assessment of aero-engine recuperator based on continuum damage mechanics approach

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Frontiers of Mechanical Engineering 2022年第4期17卷 273-284页

作者： Pengpeng LIAO Yucai ZHANG Guoyan ZHOU Xiancheng ZHANG Wenchun JIANG Shantung TU Key Laboratory of Pressurized System and Safety MOESchool of Mechanical and Power EngineeringEast China University of Science and TechnologyShanghai 200237China State Key Laboratory of Heavy Oil Processing College of Chemical EngineeringChina University of Petroleum(East China)Qingdao 266555China

The creep life of an aeroengine recuperator is investigated in terms of continuum damage mechanics by using finite element simulations.The effects of the manifold wall thickness and creep properties of brazing filler metal on the operating life of the recuperator are analyzed.Results show that the crack initiates from the brazing filler metal located on the outer surface of the manifold with the wall thickness of 2 mm and propagates throughout the whole region of the brazing filler metal when the creep time reaches 34900 h.The creep life of the recuperator meets the requirement of 40000 h continuous operation when the wall thickness increases to 3.5 mm,but its total weight increases by 15%.Decreasing the minimum creep strain rate with the enhancement of the creep strength of the brazing filler metal presents an obvious effect on the creep life of the recuperator.At the same stress level,the creep rupture time of the recuperator is enhanced by 13 times if the mismatch between the minimum creep rate of the filler and base metal is reduced by 20%.

关键词： creep life assessment brazed joint continuum damage mechanics aeroengine recuperator

Influence of recycled carbon fiber addition on the microstructure and creep response of extruded AZ91 magnesium alloy

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镁合金学报(英文) 2023年第7期11卷 2518-2529页

作者： Sinan Kandemir Jan Bohlen Hajo Dieringa Department of Mechanical Engineering Izmir Institute of TechnologyGülbahçeUrlaIzmir 35430Türkiye Helmholtz-Zentrum Hereon Institute of Material and Process DesignMax-Planck-Straße 1Geesthacht 21502Germany

In this study,the recycled short carbon fiber(CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion.The objective was to investigate the impact of CF content(2.5 and 5.0 wt.%)and fiber length(100 and 500μm)on the microstructure,mechanical properties,and creep behavior of AZ91 alloy matrix.The microstructural analysis revealed that the CFs aligned in the extrusion direction resulted in grain and intermetallic refinement within the alloy.In comparison to the unreinforced AZ91 alloy,the composites with 2.5 wt.%CF exhibited an increase in hardness by 16-20%and yield strength by 5-15%,depending on the fiber length,while experiencing a reduction in ductility.When the reinforcement content was increased from 2.5 to 5.0 wt.%,strength values exhibited fluctuations and decline,accompanied by decreased ductility.These divergent outcomes were discussed in relation to fiber length,clustering tendency due to higher reinforcement content,and the presence of interfacial products with micro-cracks at the CF-matrix interface.Tensile creep tests indicated that CFs did not enhance the creep resistance of extruded AZ91 alloy,suggesting that grain boundary sliding is likely the dominant deformation mechanism during creep.

关键词： Metal matrix composites Magnesium alloys Recycled carbon fiber Extrusion,Microstructure Mechanical properties creep

Comprehensive insights into the thermal and mechanical effects of metallic glasses via creep

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Journal of Materials Science & Technology 2022年第4期99卷 39-47页

作者： Z.R.Xu J.C.Qiao J.Wang E.Pineda D.Crespo School of Mechanics Civil Engineering and ArchitectureNorthwestern PolytechnicalUniversityXi’an 710072China State Key Laboratory of Solidification Processing Northwestern PolytechnicalUniversityXi’an 710072China Department of Physics Barcelona Research Center in Multiscale Science and TechnologyInstitute of Energy TechnologiesUniversitat Politècnica de CatalunyaBarcelona 08019Spain

Evolution of deformation and relaxation behaviors of a prototypical Cu_(46)Zr_(46)A_(l8)metallic glass was explored by extensive creep tests under both physical aging and cyclic loading.Deep insights into the microstructure-induced dynamic heterogeneity which accommodates creep deformation were successively revealed via experimental measurements and spectral analyses.An annihilation of local defects within metallic glass with increasing annealing time and cyclic numbers was observed through the reduction of amplitude in both activation energy spectra and relaxation-time spectra,which were also accompanied by an ascending value of β_(KWW).It is further found that the corresponding deformation units within the metallic glass do not disappear permanently,but are recoverable over the course of cyclic loading.The apparent suppressed relaxation process can be gradually alleviated with increasing resuming time between two consecutive cycles,behaving differently from physical aging,which indicates a notable discrepancy between thermal treatment and mechanical treatment.

关键词： Metallic glasses creep Physical aging Cyclic loading Relaxation-time spectrum

Quantitative Characterization of the Elasticity,Net creep,and Swelling of the Intervertebral Disc:An In Vitro Experiment

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Journal of Bionic Engineering 2022年第4期19卷 1077-1086页

作者： Mengying Yang Yangyang Cui Yu Zhang Huakai Wu Beibei Hu Song Wang Weiqiang Liu Department of Mechanical Engineering Tsinghua UniversityBeijing 100084China Tsinghua Shenzhen International Graduate School Tsinghua UniversityShenzhen 518055China Biomechanics and Biotechnology Lab Research Institute of Tsinghua University in ShenzhenShenzhen 518057China ACQTEC Instruments Technology(Shanghai)Limited Shanghai 201706China

During the in vitro creep of intervertebral discs,both applied loads and osmosis of solution influence their biomechanical behaviors.More specifically,the total displacement can be attributed to three parts:the elastic response during the loading period that results from instant tissue deformation;the nonlinear displacement during the creep period that is due to the poro-elastic fluid flow and visco-elastic deformation;and the swelling of discs that are affected by the osmolality.However,their respective contributions to the total displacement are unknown.To this end,this study aims to discern contributions of the above three parts in ex vivo experiments quantitively.Specimens were compressed for 4 h after 0.5 h preload.Displacement and strain were recorded and curve-fitted.The instant elastic displacement was positively related to the applied load,and its proportion rose from 18.09 to 21.46% as the load elevated.While the contribution of the net creep was inversely related to the applied load,dropping from 74.49 to 60.16%.An increase of 0.74 MPa of the osmolality induced a rise in displacement by 7.42-18.38%.Moreover,with the help of the non-contact measurement,researchers are able to know the contribution of each part quantitatively,which is of importance in understanding the creep mechanisms and developing biomaterials with mechanical mimicry of natural discs.

关键词： Intervertebral disc In vitro creep Compression Non-contact measurement