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71.
Deformation behavior and microstructure of an Al-Zn-Mg-Cu-Zr alloy during hot deformation 总被引:1,自引:0,他引:1
The hot deformation behavior and microstructures of Al-7055 commercial alloy were investigated by axisymmetric hot compression at temperatures ranging from 300°C to 450°C and strain rates from 10-2 to 10 s-1,respectively.Microstructures of deformed 7055 alloy were investigated by transmission electron microscopy (TEM).The dependence of peak stress on deformation temperature and strain rate can be expressed by the hyperbolic-sine type equation.The hot deformation activation energy of the alloy is 146 kJ/mol.... 相似文献
72.
Spherical cavity expansion model is often used to study the mechanic characteristics of pressure sensitive mediums. The most important one we do in the paper is that we construct a four-region model with σθ≠0 in damage region,which is different from what Satapathy did before and is more reasonable. By adopting this model,different constitutive equations were constructed by different method-elastic mechanics in elastic region,damage mechanics and fracture mechanics in damage region,and macro-micro mechanics theory in plastic region. Then using Durban's self-similarity assumption,the control differential equations with boundary conditions were established,and the static numerical solution of stress field and displacement field in the three different regions of elastic,damage and plastic area were discussed respectively. Results showed that this four-region model can describe precisely the mechanic characteristics of pressure sensitive mediums under initial pressure. 相似文献
73.
Shape memory alloy ( SMA) torsion actuator is one of the key approaches realizing adaptive wings in airplanes. In this paper,the actuator is made up of SMA wires and a thin-walled tube,in which the SMA wires are twisted and affixed around the surface of the tube at an angle referenced to the center axis of the tube. A thermo-mechanical constitutive model is developed to predict the thermo-mechanical behaviors of the SMA torsion actuator based on the knowledge of solid mechanics. The relationship between the torsion-angle and tem- perature is numerically calculated by using the thermo-mechanical constitutive model coupled with the SMA phase transformation model developed by Zhou and Yoon. The numerical results are compared with the relative experimental results finished by Xiong and Shen. Influences of the twist-angle of SMA wires and geometrical factors on the primary actuation performances of the SMA torsion actuator are also numerically investigated based on the thermo-mechanical constitutive model coupled with the SMA phase transformation model developed by Zhou and Yoon. Results show that the thermo-mechanical constitutive model can well predict the thermo-mechanical behaviors of the SMA torsion actuator. 相似文献
74.
针对长句子引起句法分析性能下降的问题,本文提出了一种基于SVM的句子片段划分方法:先根据语法结构将句子划分为多个片段,识别出每个片段的类别;然后根据片段的类别将句子分割为几个部分,每个部分作为句法分析的基本单元;最后将句法分析之后的各个部分进行合并,形成完整的分析结果.该方法减小了句法分析的复杂度,提高了分析的准确率. 相似文献
75.
为了建立多维应力、应变空间的弹塑性本构关系,将一般加载规律一维全量理论的简单弹塑性模型推广到一般加载规律的多维增量理论,并且给出应力空间的加载函数和应变空间的加载函数以及它们之间的正确的变换关系.在此基础上,在应变空间中建立了推导一般加载规律的多维增量理论的本构关系的一种途径.应用这种途径,从应变空间的加载函数出发,推导了等向强化材料的一般加载规律的弹塑性本构关系.理论和实例表明,这种途径对等向强化材料、随动强化材料、理想弹塑性材料和热弹塑性问题都适用. 相似文献
76.
郭俊 《武汉纺织工学院学报》2009,(6):51-53
以武汉科技学院的办学实践为例,论述了中外合作办学项目发展路径选择上要立足社会需求,充分发挥自身办学特色,做到"人无我有"、"人有我特"。办学过程中,要始终坚持办学质量第一,绝不能为了节约成本降低质量要求。在项目(机构)运行中,要理顺管理体制和运行机制,处理好与学校及相关院系的关系,还要以平等双赢为原则,处理好与外方的关系。 相似文献
77.
To provide a seepage-stress coupling constitutive model that can directly describe the seepage-stress coupling relationship,
a series of one-dimensional seepage-stress coupling tests on two kinds of soft rock (argillaceous siltstone and brown mudstone)
were performed by using an MTS-815.02 tri-axial rock mechanics test system, with which the stress—strain curves according
to the seepage variation were obtained. Based on the experimental results and by employing Hooke’s law, the formulation of
the coefficient of strain-dependent permeability was presented and introduced to establish a coupling model. In addition,
the mathematical expression and the incremental formulation for coupling model were advanced, in which five parameters that
can be respectively determined by using the experimental results were included. The calculated results show that the proposed
coupling model is capable of simulating the stress—strain relationship with considering the seepage-stress coupling in the
nonlinear elastic stage of two kinds of soft rock.
Foundation item: Projects(50378069, 50639090) supported by the National Natural Science Foundation of China; Project(50639090) supported by
the Joint Fund of Yalong River Hydropower Development, China 相似文献
78.
A recently proposed model coupling with the solid-fluid of the saturated sand was utilized to study the deformation band.
Based on the critical state plasticity model by Borja and Andrade, the hydraulic conductivity tensor was naturally treated
as a function of the spatial discretization matrix about the displacement and the stress field, allowing a more realistic
representation of the physical phenomenon. The fully Lagrangian form of the Darcy law was resolved by Piola algorithm, and
then the flow law was gained, leading to the implementation of a modified model of the saturated sand. Then the criterion
for the onset of localization was derived and utilized to detect instability. The constitutive model was implemented in a
finite element program coded by FORTRAN, which was used to predict the formation and development of shear bands in plane strain
compression of saturated sand. At last, the formation mechanism of the shear band was discussed. It is shown that the model
works well, and the simulation sample bifurcates at 1.18% axial strain, which is in a good qualitative agreement with the
experiment. The pore pressure greatly affects the onset and development of the deformation band, and it obviously increases
around the localization-prone regions with the direction toward the outer side of the normal of the shear band, while the
pore stress flows nearly horizontally and is distributed equally far away the shear band region.
Foundation item: Project(2006G007-C) supported by the Foundation of the Science and Technology Section of Ministry of Railway of China; Project(77206)
supported by the Excellent PhD Thesis Innovation Foundation of Central South University, China 相似文献
79.
The experimental tests of tensile for lead-free solder Sn-3.5Ag were performed for the general work temperatures range from
11 to 90 °C and strain rate range from 5×10−5 to 2×10−2 s−1, and its stress—strain curves were compared to those of solder Sn-37Pb. The parameters in Anand model for solder Sn-3.5Ag
were fitted based on experimental data and nonlinear fitting method, and its validity was checked by means of experimental
data. Furthermore, the Anand model was used in the FEM analysis to evaluate solder joint thermal cycle reliability. The results
show that solder Sn-3.5Ag has a better creep resistance than solder Sn-37Pb. The maximum stress is located at the upper right
corner of the outmost solder joint from the symmetric center, and thermal fatigue life is predicted to be 3.796×104 cycles under the calculated conditions.
Foundation item: Project(50376076) supported by the National Natural Science Foundation of China 相似文献
80.