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QUANTITATIVE RELATIONSHIP BETWEEN YIELD STRESS AND r-VALUE OF Ti SHEET

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Acta Metallurgica Sinica(English Letters) 1992年第3期5卷 188-192页

作者： ZHOU Weixian northwestern polytechnical university,Xi′an,China northwestern polytechnical Univ Xi'an China

Based on the experimental data,it was clarified that the plastic strain ratio R-value is not equal to Hill's r-value for Ti *** the non-quadratic orthotropic yield function pro- posed recently by the author,an optimal expression between yield stress and r-value for Ti sheet was developed on overall *** suitable value of exponent in the function seems to be 6—***,an equation was suggested to estimate strength for the pressure vessel made of Ti sheet.

关键词： Ti sheet yield stress r-value anisotropy

NUMERICAL SIMULATION OF CHANNEL SEGREGATION IN Al-4.5wt-%Cu ALLOY

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Acta Metallurgica Sinica(English Letters) 1991年第8期4卷 108-114页

作者： YU Qiuping ZHOU Yaohe northwestern polytechnical university,Xi’an,China northwestern polytechnical Univ Xi'an China

Equations for numerical simulation of channel segregation based on a model of continuum ap- proach to porous medium were *** order to solve the non-linear computation prob- lem caused by the interactions between unknown variables in the equations,the trial-and-er- ror method is *** computation results showed that the radial back-flow due to natural convection in mushy zone indeed exists in A1-4.5wt-%Cu alloy ingot under the condition of low cooling rate,and that the numerical simulation of channel segregation is applicable due to the coincidence of calculated concentration with the experimental values.

关键词： channel segregation numerical simulation back-flow mushy zone

RECALESCENCES AND SOLIDIFICATION MICROSTRUCTURE OF HIGHLY UNDERCOOLED Ni_(68)B_(21)Si_(11) ALLOY

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Acta Metallurgica Sinica(English Letters) 1993年第2期6卷 111-116页

作者： LI Delin YANG Gencang ZHOU Yaohe northwestern polytechnical university,Xi’an,China Faculty No.403,northwestern polytechnical university,Xi’an 710072,China northwestern polytechnical Univ Xian China

One,two and three recalescence events in the solidification of highly undercooled Ni_68B_21Si_11 alloy melt and the conditions of undercooling together with the effect on solidification morphologies were *** solidification morphologies of the undercooled alloy may be examined in the light of two aspects,i.e,growth of either Ni_3B,Ni_6Si_2B and Ni_2B ternary eutectic or dendrite cluster with Ni_3B as leading *** the degree of undercooling below 200 or over 310 K,the alloy solidifies to accompany one recalescence only, and the crystals grow according to the first mode of *** undercooling at other temperatures,two or three events of recalescence may occur and the dendrite cluster may so- lidify.

关键词： recalescence event undercooling X-ray analysis

CALCULATING RESPONSE SPECTRAL MOMENTS BY COMPLEX MODAL ANALYSIS

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Acta Mechanica Sinica 1989年第2期5卷 159-166页

作者： Fang Tong Zhang Tianshu (northwestern polytechnical university) northwestern polytechnical university China

Response spectral moments are useful for system reliability ***,spectral mo- ments are calculated by the frequency domain *** on the time domain modal analysis of random vibrations,the authors present a new method for calculating response spectral moments through response correlation *** method can be applied to both classical and non-classical damping cases and to three kinds of random excitations,i.e.,white noise,band-limited white noise, and filtered white noise.

关键词： spectral moment random response reliability analysis modal analysis

DENUCLEATION AND HIGH UNDERCOOLING OF Ni-32.5%Sn EUTECTIC ALLOY

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Acta Metallurgica Sinica(English Letters) 1991年第8期4卷 115-120页

作者： WEI Bingbo YANG Gencang ZHOU Yaohe northwestern polytechnical university,Xi’an,China northwestern polytechnical Univ Xi'an China

Undercoolings up to 397 K(0.283 T_E)have been obtained for Ni-32.5% Sn eutectic alloy melted by superheating-cooling cycles and denucleating with inorganic *** predomi- nant dissipation of heat for highly undercooled alloy melt is through *** approxi- mate method is consequently derived to calculate its mean specific heat from measured cooling *** the aid of high speed cinematography,it is revealed that the surface or interface heterogeneous nucleation takes place in preference to homogeneous nucleation even though the undercooling has exceeded 0.2 T_E.

关键词： undercooling rapid solidification nucleation eutectic alloy specific

Phenomenological Anisotropic Study of Surface Finish in Pack Rolling

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Journal of Materials Science & Technology 2003年第2期19卷 133-136页

作者： Zhufeng YUEDepartment of Engineering Mechanics, northwestern polytechnical university, Xi’an 710072, China Dept. of Eng. Mech. Northwestern Polytech. Univ. Xi'an 710072 China

A phenomenological anisotropic model has been presented for the surface roughness modeling of pack rolling. The model is an assembly of grains in different orientations and sizes. The grain size is assumed to be in log-normal distribution. To model the macro anisotropic mechanical behavior of the grains induced by the slip deformation, the grains are assumed as isolated anisotropic units. The units have different mechanic behavior, and depend on the crystallographic orientations and the external loading as well as the interaction of the adjunctive grains. In the paper, the material properties of the grains are assumed as uniform distributions. The roughness of the contact surfaces depends on the distribution types and the scatters of the distributions. It is found that the initial roughness of the contact surfaces has a little influence on the surface roughness when the rolling deformation is large. The comparison between the phenomenological model and crystallographic model shows that the phenomenological model can also give out a reasonable result, while it only takes much less CPU time. The agreement between the single sheet model and the pack rolling model shows that in a certain degree the pack rolling model can be replaced by the single sheet model to decrease the CPU time.

关键词： Phenomenological anisotropic model Pack rolling Surface roughness Statistic distribution Initial roughness Single sheet model Crystallographic model

Non-uniform Stress Field and Stress Concentration Induced by Grain Boundary and Triple Junction of Tricrystal

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Journal of Materials Science & Technology 2003年第4期19卷 303-308页

作者： Jiansong WAN and Zhufeng YUEDepartment of Engineering Mechanics, northwestern polytechnical university, Xi’an 710072, China Dept. of Eng. Mech. Northwestern Polytech. Univ. Xi'an 710072 China

The stress characteristics in the anisotropic bicrystal and tricrystal specimens were analyzed using the anisotropic elastic model, orthotropic Hill's model and rate-dependent crystallographic model. The finite element analysis results show that non-uniform stresses are induced by the grain boundary. For bicrystal specimens in different crystallographic orientations, there exist stress concentrations and high stress gradients nearby the boundaries. The activation and slipping of the slip systems are dependent on the crystallographic orientations of the grains and also on the relative crystallographic orientations of the two adjoining grains. For the tricrystal specimens, there is not always any stress concentrations in the triple junction, and the concentration degree depends on the relative crystallographic orientations of the three grains. Different from the bicrystal specimens, there may be or no stress concentration in the vicinity of grain boundaries for the tricrystal specimens, which depends on the relative crystallographic orientations of the three grains. The stress concentration near to the grain boundaries and triple junction can be high enough for the local plastic deformation, damage and voiding or cracking even when the whole specimen is still under the elastic state. It can be further concluded that homogeneous assumption for polycrystalline materials is not suitable to study the detailed meso- or micro-mechanisms for damaging and fracturing.

关键词： Crystallographic plasticity Bicrystal specimens Tricrystal specimens Stress characteristics Hill's modei Anisotropy Finite element analysis

CHARACTERISTICS OF CRITICAL STATE OF TENSILE INSTABILITY

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中国有色金属学会会刊：英文版 1996年第3期6卷 58-62页

作者： Zhou Weixian(Department of Aeronautical Manufacturing Engineering, northwestern polytechnical university, Xi’an 710072) Department of Aeronautical Manufacturing Engineering Northwestern Polytechnical University Xi'an 710072 China

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关键词： tensile instability critical state deformation characteristic

GROWTH BEHAVIOR OF SHORT FATIGUE CRACKS FOR ALUMINUM- LITHIUM ALLOY 8090

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Chinese Journal of Aeronautics 1991年第4期6卷 380-385页

作者： Chen Zheng northwestern polytechnical university

The growth behaviors of short through cracks (0.2 < △a < 2.2mm) and long cracks are compared using CT type specimens in aluminum-lithium alloy 8090 T651. It is found that the short cracks grow much more than long ones and are observed to grow at the stress intensity ranges far below the long crack threshold. The distinction of growth bahavior between short and long cracks is attributed to the difference of their crack closure effect. The growth behavior of short cracks can be rationalized with that of long ones in terms of effective stress intensity ranges. The upper demarcation value of short through cracks for aluminum-lithium alloy 8090 is presented.

关键词： this Figure LITHIUM ALLOY 8090 GROWTH BEHAVIOR OF SHORT FATIGUE CRACKS FOR ALUMINUM