薄壁金刚石钻头热压弹性石墨模具设计

根据材料热膨胀特性并结合热压特点,分析了钻头胎体、钢体和石墨模具在热压中的行为,给出了影响热压金刚石钻头胎体结合强度乃至于导致其开裂的主要因素。在此基础上,改进设计了新型石墨模具,推荐了模具设计的二个主要参数。

受内压热超弹性球壳的不稳定性

应用有限变形弹性理论分析了受内压作用的不可压热超弹性球壳发生非对称变形的不稳定性问题.当内压较小时,薄壁球壳发生对称的均匀膨胀变形;当内压大于某一临界值时,产生复杂的非对称变形,其一部分膨胀变形很大,而另一部分仅仅是轻微膨胀,且其形状逐渐远离球形,且此时的变形是不稳定的.厚壁球壳总是发生稳定的均匀膨胀变形.根据球壳的变形曲线,给出了球壳发生不稳定变形的临界厚度.同时,讨论了温度场对球壳变形的影响.

热超弹性圆筒的不稳定性

应用有限变形弹性理论分析了受内压和轴向拉伸作用的不可压热超弹性圆筒发生非均匀变形的不稳定性问题．受内压和轴向拉力作用的薄壁圆筒,当内压较小时,圆筒发生稳定的均匀膨胀变形;当内压大于某一临界值时,圆筒产生复杂的非均匀变形,其一部分膨胀变形很大,形如‘灯泡”状,而另一部分仅仅是轻微膨胀,且此时的变形是不稳定的．但对厚壁圆筒而言,不论压力如何,总是发生稳定的均匀膨胀变形．根据圆筒的变形曲线,给出了圆筒可以发生不稳定变形的临界厚度．同时,讨论了轴向拉伸和温度场对圆筒变形的影响．

热超弹性薄板非对称拉伸的分岔和稳定性

本文应用超弹性材料的有限变形理论分析了在面内等双向拉伸死载荷作用下不可压热超弹性方形薄板发生非对称变形的分岔及其稳定性问题。给出了方板变形的分岔曲线和临界载荷,发现对受面内等双向拉伸载荷作用的均匀方板,当拉伸载荷值较小时,方板双向等伸长变形,发生对称的拉伸变形;但当此载荷值大于某一临界值时,从方板的对称拉伸变形中分岔出非对称的变形,方板在两个方向的变形不再相等。通过变形发生分岔前后的能量比较发现,分岔后的对称变形是不稳定的,而非对称变形是稳定的。同时,给出了板中的应力分布曲线,并由不同温度下变形的分岔曲线和应力分布曲线讨论了温度对方板变形和板中的应力分布的影响。

Fabrication of flatten grooved-sintered wick heat pipe

With the rapid rising of heat flux and reduction of heat dissipating space of microelectronic devises, flattened sintered heat pipe has become an ideal conducting element of use in the electronic cooling field. A manufacturing technology named phase change flattening process is presented to fabricate the flattened grooved-sintered wick heat pipe （GSHP for short）. Deformation geometry of flattened GSHP and the elasto-plastic deformation of flattening process are analyzed theoretically and verified by experiments. The results show that the vapor pressure inside sintered heat pipe during flattening process is determined by the saturated vapor pressure equation; the width and vapor area of flattened heat pipe change greatly as the flattening proceeds; the maximum equivalent strain distributes at the interface between wick and vapor in the fiat section; the buckling phenomenon can be well eliminated when the flattening temperature reaches 480 K; phase change flattening punch load increases with flattening temperature and displacement.

Theoretical Calculations for Structural, Elastic and Thermodynamic Properties of MgB2 under High Pressure

We have investigated the structural and elastic properties of MgB2 under high pressures using the full- potential linearized muffin-tin orbital （FP-LMTO） scheme within the generalized gradient approximation correction （GGA） in the frame of density functional theory. The calculated pressure dependence of the normalized volume is in excellent agreement with the experimental results. At the same time the elastic constants and acoustic anisotropy as a function of applied pressure are presented. Through the quasi-harmonic Debye model, we also investigate the thermodynamic properties of MgB2.

Analytical Solution for Thermo-Electro-Elastic Problems of an Orthotropic Piezoelectric Hollow Cylinder Subjected to Various Loading

An interpolation method was used to solve the Volterra integral equation of the second kind caused by interaction among thermal, electric and mechanical fields. The exact expressions for the transient responses of stresses, electric displacement and electric potential in an orthotropic piezoelectric hollow cylinder were obtained by means of the finite integral transforms. From the sample numerical calculations, it is seen that the present method is suitable for an orthotropic piezoelectric hollow cylinder subjected to arbitrary thermal shock, mechanical load and transient electric excitation. The result can be used as a reference to solve other transient coupled problems of thermo-electro-elasticity.

Elasticity under pressure and thermal property of Mg2La from first-principles calculations

The elastic properties, thermodynamic and electronic structures of Mg_2La were investigated by using first-principles. The calculated results show that pressure affects the elastic constants of C_(11) more than that of C_(12) and C_(44). Specifically, higher pressure leads to greater bulk modulus(B), shear modulus(G), and elastic modulus(E). We predict B/G and anisotropy factor A based on the calculated elastic constants. The Debye temperature also increases with increasing pressure. Based on the quasi-harmonic Debye model, we examined the thermodynamic properties. These properties include the normalized volume(V/V_0), bulk modulus(B), heat capacity(C_v), thermal expansion coefficient(α), and Debye temperature(■). Finally, the electronic structures associated with the density of states(DOS) and Mulliken population are analyzed.

Numerical Simulation of New Friction Welded Joints

In developing the new friction welding technology, the thermal elastic-plastic stress analysis by the finite element method was carried out to seek the suitable welding conditions such as the friction pressure, the friction speed and the upset pressure. The results obtained are as follows： Heat transfer to the specimens and the intermediate material during friction process was made clear; The operational conditions such as the rotation number of the intermediate material and the friction pressure to reach the liquidus in the interface could be estimated; Further, as the overhang length near the interface is well related to the joint efficiency, we tried to obtain the operational conditions by numerical analysis to acquire a certain length of the overhang length near the interface.