Optimization of spot-welded structures

This paper addresses the optimization problem of a spot-welded structure under fatigue life consideration. The so-called umbrella model of spot welds and the radial stresses around a spot weld were introduced into the optimization process. The idea was to study the optimization problem using the type of analysis which is now considered to be valid for fatigue life prediction. Two formations were considered: one maximizes the stiffness of a structure under fatigue life constraints and the other seeks the maximum fatigue life of the structure. The optimization results show that the optimization process has successfully found the global minimum values of the corresponding objective functions for both the formations.     

半无限体内双圆柱亚表面热波散射问题的研究

本文基于非傅里叶导热定律,采用波函数展开法,研究了含双圆柱缺陷非透明半无限体中热传播问题,给出了基于热传导波动模型的热波散射问题的一般解．温度波由调制光束在材料表面激发,缺陷表面的边界条件为绝热,分析了各物理参数对温度分布的影响,特别是热波波长对温度变化的影响,并给出了温度变化的数值结果。     

铁基非晶稀土合金的结构转变和结构弛豫

通过对铁基非晶稀土合金结构转变和结构弛豫过程特征的研究，讨论了该材料的稳定性；认为稀土成份是影响合金品质和应用前景的关键因素。     

Perturbation of semi-Browder operators and stability of Browder's essential defect and approximate point spectrum

In the present paper we investigate the stability of closed densely defined semi-Browder operators under operator perturbations that belong to a perturbation class related to compact operators. Furthermore, we apply the obtained results to give a characterization and to study the stability of Browder's essential approximate point spectrum and Browder's essential defect spectrum.     

Percolation of the organic phase in hybrid organic–inorganic aerogels

The properties (texture, mechanical behaviour, etc.) of hybrid organic–inorganic silica aerogels change dramatically when the concentration of the organic additive is varied from a given value. It has been known for several years that this critical concentration is around 40% of the total weight of silica present in the sample. We have made use of a new structural model to conclude that this concentration of 40% by weight corresponds to the percolation threshold of the organic phase.     

Structural optimization and experimental analysis of composite material panels for naval use

The purpose of the work is the realization of a composite material with long glass fibers having better characteristic than a fiber random composite, to permit the reduction of weight and costs to shipyards for pleasure craft. Structural optimization is performed by ANSYS for the choice of the layers disposition to obtain the maximum stiffness with minimum material employment, saving weight. The study is centered on the research of the better configurations of plies packing in relation of pure shear stress for four different plies. Unidirectional plies, both symmetric orthotropic and symmetric non-orthotropic ones, are realized successively by the vacuum bag technique. Experimental tests of traction, bending, inter laminar shear and pure shear are executed to characterize the three different type of material. Experimental results are compared to ones obtained numerically to validate the procedures; the comparison with the analytical results permitted to attribute an adequate value to shape factor of the fibers. In all the cases the optimization permitted the construction of much more resistant plies than random ones, with a lower thickness.     

高剂量Ar离子辐照Si缺陷产生及其退火行为EPR研究

112MeVAr离子在50K以下的低温辐照Si到8×10¹⁴/cm²剂量,室温下采用电子顺磁共振技术分析了由辐照引起的缺陷产生及其退火行为,结果表明:Ar离子辐照在Si中引起了中性四空位(Si-P3心)､带正电荷的〈100〉劈裂的双间隙子(Si-P6心)以及连续的非晶层3种缺陷的形成. 在200℃的退火温度,Si-P3心和Si-P6心消失,这时带负电荷的五空位(Si-P1心)开始生长,Si-P1心可以保持到550℃左右的退火温度. 在350℃时,可以明显地观测到另一个含有更多空位的顺磁缺陷心(Si-A11心).连续非晶层的再结晶需要600℃以上的温度,并且在整个退火过程中,非晶顺磁共振线的线型和线宽保持不变. 定性地讨论了结果.     

HIGH ACCURACY ANALYSIS FORINTEGRODIFFERENTIAL EQUATIONS

1.IntroductionLetfibearectangulardomain.WeconsidertheRichardsonextrapolationanddefectcorrectionofthefiniteelementapproximationstothesolutionsofthefollowingsimpleparabolicintegrodifferentialequationsItiswellknownthattheextrapolationmethodsareveryeffectivenumericalmethodsinproducinghigheraccuracyapproximations.Thistechniqueusedforthefiniteelemelltapproximationstothesolutionsofellipticdifferentialequationshasbeenwelldemonstratedin[l--3,5--7,14--18,22and24].Andthistechniquehasalsobeenconsideredfo…     

Nuclear magnetic resonance of Nb in LiNbO3: effect of structural distortions on lineshapes

The expression for the angular dependence of the first moment of the nuclear magnetic resonance central transition (± 1/2 ↔ 1/2) lineshapes of a quadrupolar nuclei with half integer spins in a disordered solid is derived and used for investigation of the structural distortions in LiNbO₃.