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BAUSCHINGER EFFECT AND DISLOCATION STRUCTURE IN STAINLESS STEEL DURING CYCLIC DEFORMATION

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Acta metallurgica sinica(English Letters) 1989年第1期2卷 1-6页

作者： xia yuebo wang zhongguang DU Xiukui institute of metal research,academia sinica,shenyang,china xia yuebo,associate professor,institute of metal research,academia sinica,shenyang,china

Cyclic deformation in symmetrical push-pull mode was carried out at room temperature in air using a Schenck hydropuls *** total strain amplitude which was kept constant dur- ing the test ranged from ±0.004 to±*** 0.2% offset yield stress σ_(0.2f) in tension and σ_(0.2r) in compression and peak stress σ were measured from the stress-strain hysteresis loop at various *** Bauschinger strenghth differential factor(BSDF)was then calcu- lated from σ_(0.2f) and σ_(0.2r).The energy loss △E of each cycle was determined from hysteresis loop *** parameters,BSDF,σ and △E,appear to have two distinctively different stages. The dislocation structures were observed using TEM in specimens deformed cyclically,for various *** observation shows that the dislocations pile-up mainly against grain boundaries and there exist large amount of deformation *** addition of 0.25 wt-% ni- trogen reduced the stacking fault energy of the alloy ***-slip and climb are therefore rather difficult to occur during the cyclic deformation at room temperature,and well-defined dislocation cells and walls can only be seen at the final stage of fatigue.

关键词： Bausckinger effect cyclic deformation dislocation structure

STRESS RELAXATION BEHAVIOUR OF TITANIUM

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Acta metallurgica sinica(English Letters) 1989年第5期2卷 311-314页

作者： xia yuebo wang zhongguang institute of metal research,academia sinica,shenyang,china associate professor,institute of metal research,academia sinica,shenyang,china

Studies of stress relaxation were carried out on commercially pure *** was found that the stress relaxation behaviour relates closely to the level of *** amount of re- laxed stress (?)σ_R is independent of the amplitude of stress dip in a certain range of ***,it depend on the stress level at which stress relaxation begins in a cer- tain relaxation time t_*** back(critical)stress σ_c and flow stress σ_o vary with the strain in a similar *** effective stress on dislocations σ~* increases with increasing strain under low strains,but keeps constant under higher strains.

关键词： stress relaxation critical stress effective stress relaxed stress

EFFECT OF SLIP ORIENTATION ON STRESS RESPONSE,INTERNAL FRICTION AND ULTRASONIC ATTENUATION DURING CYCLIC DEFORMATION IN Al SINGLE CRYSTALS

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Acta metallurgica sinica(English Letters) 1992年第6期5卷 471-476页

作者： xia yuebo ZHANG Tianyi State Key Laboratory for Fatigue and Fracture of Materials,institute of metal research,academia sinica,shenyang,chinaFEI Guangtao ZHOU Xing Laboratory of Internal Friction and Defects in Solids,institute of Solid State Physics,academia sinica,Hefei,china associate professor,institute of metal research,academia sinica,shenyang 110015,china Inst of metal research Acad Sinica Shenyang China

The variation of cyclic stress,internal friction and ultrasonic attenuation during cyclic deformation and relations among them have been investigated with different slip orientation Al single *** results indicate that the value of cyclic stress σ,internal friction Q^(-1)and ultrasonic attenuation △α depend obviously on the slip *** are large differences in above three parameters for different slip orientation Al *** early stage of fatigue life,σ and △α increase and Q^(-1)decreases with cycles N,and △α reached maxi- mum before σ,while Q^(-1)and σ get the valley and the peak,respectively,at same cycles.

关键词： crystal orientation cyclic deformation stress response internal friction ultrasonic attenuation Al

INFLUENCE OF RESIDUAL STRESS AND SURFACE MORPHOLOGY ON FATIGUE PROPERTIES OF STEEL 60Mn

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Acta metallurgica sinica(English Letters) 1992年第6期5卷 477-483页

作者： KANG Zengqiao GAI Xiuying LI Jiabao wang zhongguang State Key Laboratory for Fatigue and Fracture of Materials institute of metal research,academia sinica,shenyang,china research Assistant,institute of metal research,academia sinica,shenyang 110015,china Inst of metal research Acad Sinica Shenyang China

Influence of residual stress and surface morphology induced by shot-peening on fatigue behav- ior of a medium temperature tempered spring steel 60 Mn has been *** compressive residual stress induced in the near-surface region may improve fatigue limit from 930 to 1010 MPa,and the very high tensile residual stress in the interior may reduce it from 1010 to 940 MPa,whereas the severe surface damage may cause a drop-off of it from 1010 down to 800 *** cracks initiated in such position where the equivalent Mises stress,including residual stress,exceeded the local strength of the *** compressive residual stress, induced by shot-peening,may intensify the effect of crack closure,so as to decrease the crack growth rate.

关键词： shot-peening fatigue limit residual stress surface morphology sleel 60 Mn

MICROFRACTOGRAPHY OF NEAR-THRESHOLD FATIGUE CRACK PROPAGATION IN DUAL-PHASE STEELS

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Acta metallurgica sinica(English Letters) 1992年第5期5卷 385-389页

作者： ZHENG Yesha wang zhongguang AI Suhua State Key Laboratory of Fatigue and Fracture for Materials,institute of metal research,academia sinica,shenyang,110015,china Inst of metal research Acad Sinica Shenyang China

SEM microfractography of near-threshold fatigue crack propagation were carried out in the dual-phase steels of 3 martensite morphologies and 6 volume fractions of martensite (V_m). All of them are featured by cyclic cleavage characteristics in near-threshold region,i.e.,main- ly controlled by mode Ⅱ *** the higher ΔK regions,the fracture surfaces are character- ized by mixed modes including cyclic cleavage facets,two types of secondary cracks and striations,etc..The roughness-induced crack closure of fracture surface is attributed primarily to extreme high fatigue crack growth threshold values.

关键词： dual-phase steel threshold value fatigue crack growth fractograph near-threshold

FATIGUE BEHAVIOUR OF SiC_p/6061Al COMPOSITE

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Acta metallurgica sinica(English Letters) 1991年第9期4卷 201-205页

作者： YU Weicheng YUAN Jincai wang zhongguang Laboratory of Fatigue and Fracture for Materials,institute of metal research,academia sinica,shenyang,china. Acad sinica Shenyang China

The fatigue of SiC_p/6061Al composite containing 15 v.-% SiC particles has been compared with 6061Al *** structure and microprocess of fatigue crack initiation and propagation in the composite have been investigated by using SEM and *** results in- dicate that the fatigue strength at 10~7 cycles of the composite is 196 MPa,*** 25% higher than matrix *** voids and microcracks initiated at and near the interface be- tween SiC_p and matrix,where has a higher density of dislocations,will propagate and link up to form the fatigue *** is an important evidence to note that the dislocation channels where screw dislocation can travel are formed near interface and corner region of SiC_o in the composite subjected to fatigue stress(σ_(max)=274 MPa N=2.4×10~5 cycles),demonstrating the relationship between fatigue crack initiation and dislocation movement in the SiC particles reinforced 6061 Al alloy composite.

关键词： Al-base composite fatigue SiC particle

CYCLIC DEFORMATION OF COARSE GRAINED POLYCRYSTALLINE PURE Al——Ⅱ.FRACTURE SURFACE MORPHOLOGY

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Acta metallurgica sinica(English Letters) 1992年第5期5卷 330-335页

作者： xia yuebo wang zhongguang State Key Laboratory for Fatigue and Failure of Materials,institute of metal research,academia sinica,shenyang,china

SEM photos for very coarse grained and high ductile polycrystalline pure Al show following characteristics:A few fracture sources are concentrated,the crack propagates in fan-shape near them,and the fatigue striations are cyclic cleavage *** striation consists of a wide cleavage facet and a narrow cleavage *** stages often blunt due to plastic *** fatigue striations are clear and continual,and distribute over whole zone of stage Ⅱ crack *** kinds of fatigue striations form in different levels,are conjoined by a“twisted baked piece of pastry”*** secondary crack along the fatigue striations was observed *** of them have already developed into secondary macrocracks and secondary fatigue striations were found clearly on secondary fracture sur- *** fracture surface can be divided into two parts,initiation and propagation zone of the crack,however,no statical-fracture zone was *** mechanism to form striations was preliminarily discussed.

关键词： fatigue crack Al fatigue striation secondary crack cleavage tongue

CYCLIC DEFORMATION OF COARSE GRAINED POLYCRYSTALLINE PURE Ai——Ⅰ.SLIP CHARACTERISTICS

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Acta metallurgica sinica(English Letters) 1992年第4期5卷 272-277页

作者： xia yuebo wang zhongguang State Key Laboratory for Fatigue and Failure of Materials,institute of metal research,academia sinica,shenyang,china

Comparing with ordinary ploycrystalline materials sized to μm grade,the slip morphology of the coarse grained polycrystalline pure Al is characterized by:(1)several slip domains occur in a grain,and in same domain,several slip systems operate at same time or one after another intensely,a beautiful and neat slip pattern is forming on the specimen surface;(2)for high Σ-value coincident and random grain boundaries,the grain boundary affecting zone (GBAZ),bout 50—120μm wide,is favourable site to form intergranular crack at early fa- tigue life easily,and migration or slide of the boundaries were often *** low Σ-value near-coincident grain boundaries show a higher degree of slip continuity and strain compatibility than high Σ-value *** crack is not easily nucleated at low Σ-value near-coincident boundaries;and(3)due to suppression of grain boundary slip at triple grain boundary node,the high Σ-value and random grain boundary among the three boundaries of tricrystal crack easily during cyclic deformation.

关键词： coincident grain boundary random grain boundary intergranular crack boundary slide serrated grain boundary

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF IN-SITU FORMATION FIBROUS POLYTYPE AlN COMPOSITE-MATERIAL

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Acta metallurgica sinica(English Letters) 1993年第7期6卷 41-45页

作者： LI Zonghuai CHEN Shengqi ZHOU Yanchun xia Fei institute of metal research,academia sinica,shenyang,china professor,institute of metal research,academia sinica,shenyang 110015,china

In-situ formation fibrous polytype AlN composite ceramic materials was prepared from AlN-Y_2O_3-SiO_2 *** comparison with AlN ceramics,both bending strength and fracture toughness of the composite materials are much *** observation revealed that a lot of epitaxial growth fibrous AlN polytype occurred in matrix.Y_2O_3 seems to act as a densifier for in-situ formation materials and as medium for growth of fibrous ***_2 is the growth promoter for fibrous *** occurrnce of fibrous polytype may increase the strength and toughness of AlN ceramic composite mateirals.

关键词： AIN ceramics in-situ formation fibrous polytype