Weakly-Singular Traction and Displacement Boundary Integral Equations and Their Meshless Local Petrov-Galerkin Approaches

The general meshless local Petrov-Galerkin (MLPG) weak forms of the displacement and traction boundary integral equations (BIEs) are presented for solids undergoing small deformations. Using the directly derived non-hyper-singular integral equations for displacement gradients, simple and straightforward derivations of weakly singular traction BIEs for solids undergoing small deformations are also presented. As a framework for meshless approaches, the MLPG weak forms provide the most general basis for the numerical solution of the non-hyper-singular displacement and traction BIEs. By employing the various types of test functions, several types of MLPG/BIEs are formulated. Numerical examples show that the present methods are very promising, especially for solving the elastic problems in which the singularities in displacements, strains, and stresses are of primary concern.     

基于纳米模压的非晶合金纳米线阵列的形貌与结构演化(英文)

金属纳米线阵列因其优异的催化和传感特性等性能而受到广泛关注.非晶合金纳米模压技术提供了一种廉价便捷的近净成型技术,并可用于制备金属纳米线阵列,但目前对该技术的研究还不够深入.由于金属纳米线阵列的结构和形貌对其性能具有强烈的影响,本文对非晶合金在纳米模压过程中纳米线阵列的结构和形貌演化过程进行了系统的研究.研究发现,纳米线阵列中纳米线的长度随着模压温度、时间和压力的增加而增加,而纳米线长度的增加会促使纳米线阵列的形貌逐渐由分散型转变为聚集型.增加模压温度和时间能促进非晶合金纳米线晶化的发生,而增加模压压力则有助于抑制晶化的发生.通过模压参数的调节可以实现对纳米模压后纳米线阵列结构与形貌的调控,进而实现纳米线阵列性能的调控.     

氢氧化镁/可膨胀石墨/聚丙烯复合材料的热降解过程与燃烧行为

以可膨胀石墨(EG)和氢氧化镁(MH)为无卤阻燃剂，通过熔融共混法制备了无卤阻燃聚丙烯(PP)复合材料(EG/PP、MH/PP和MH/EG/PP)，采用热重法研究了复合材料的热降解过程，以氧指数(LOI)和垂直燃烧(UL-94)评价研究了复合材料的阻燃性能，采用锥形量热仪研究了复合材料的燃烧行为.结果表明:MH和EG间存在显著的协同阻燃作用，在阻燃剂质量分数为60%时，MH与EG质量比为5 : 1的MH/EG/PP材料其氧指数可以达到29.7，与MH/PP复合材料相比提高了11.2%；EG与MH协同具有良好的降低热释放作用，与PP和MH/PP相比，MH/EG/PP复合材料的热释放速率峰值(peak-HRR)分别降低了73.9%和34.2%；EG和MH的协同作用大幅度降低了MH/EG/PP的质量损失速率；结合残炭的形貌结果，揭示了EG和MH协同阻燃机理的关键在于增强了炭层的隔热和隔氧作用.