Time‐domain hybrid formulations for wave simulations in three‐dimensional PML‐truncated heterogeneous media

We are concerned with the numerical simulation of wave motion in arbitrarily heterogeneous, elastic, perfectly‐matched‐layer‐(PML)‐truncated media. We extend in three dimensions a recently developed two‐dimensional formulation, by treating the PML via an unsplit‐field, but mixed‐field, displacement‐stress formulation, which is then coupled to a standard displacement‐only formulation for the interior domain, thus leading to a computationally cost‐efficient hybrid scheme. The hybrid treatment leads to, at most, third‐order in time semi‐discrete forms. The formulation is flexible enough to accommodate the standard PML, as well as the multi‐axial PML. We discuss several time‐marching schemes, which can be used à la carte, depending on the application: (a) an extended Newmark scheme for third‐order in time, either unsymmetric or fully symmetric semi‐discrete forms; (b) a standard implicit Newmark for the second‐order, unsymmetric semi‐discrete forms; and (c) an explicit Runge–Kutta scheme for a first‐order in time unsymmetric system. The latter is well‐suited for large‐scale problems on parallel architectures, while the second‐order treatment is particularly attractive for ready incorporation in existing codes written originally for finite domains. We compare the schemes and report numerical results demonstrating stability and efficacy of the proposed formulations. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of Pre-heat and Inert Gas Species on Cryogenic Aerosol Cleaning Performance in Semiconductor Manufacturing

Cryogenic aerosol cleaning is a dry cleaning method used in the back end of line (BEOL) semiconductor manufacturing to remove defects from planar hydrophobic surfaces such as SiCOH and SiCxNyHz. Cryogenic aerosol cleaning is preferred over conventional wet cleaning methods as it is a non-contact cleaning method, which uses inert gases to generate sub-micrometer-sized solid aerosol particles that physically remove nanometer-sized contaminants on wafer surfaces. Particle removal mechanism involves detachment of the particles upon impact with aerosol, diffusion, and finally entrainment away from the wafer. In BEOL metal line patterning, particles on the dielectric isolation surfaces translate through the subsequent lithography and copper fill steps in to single or multiple metal line open defects that are yield killers. In this study, we show that the particle removal performance of the standard aerosol cleaning can be enhanced by pre-heating the wafer and use of a higher molecular weight inert gas, namely Ar, for aerosol generation. Both the addition of a Pre-heat step and the use of Ar as the aerosol source showed 47–52% reduction in single and multiple line opens detected through wafer electrical tests during high volume semiconductor manufacturing process.     

Mode I–III Decomposition of the J‐integral from DIC Displacement Data

This paper presents the implementation of the decomposition method on digital image correlation (DIC) obtained displacement fields to obtain J‐integral results (J) and respective stress intensity factors (SIFs). DIC is increasingly used with the J‐integral approach in experimental mechanics to obtain J estimates from complex fracture processes. In this approach, the decomposition method is applied to DIC displacement fields for the first time. Here, displacement fields are separated before stresses and strains are computed, so that subsequent computation of separate J or SIF components may follow the classical full‐field J‐integral approach. The sensitivity of the decomposition method to experimental errors is investigated using synthetically generated errors imposed on crack tip displacement fields (Williams' series), from which improvements to the procedure are proposed. The method is experimentally tested on PMMA Arcan specimens under mode I, II, and III, and mixed‐mode I–III loading. Test results were compared to fracture toughness values obtained from ASTM tests and literature with close agreement.     

热氧老化对碳纤维织物增强聚合物基复合材料弯曲性能的影响

为了探索增强体结构对碳纤维增强聚合物基复合材料(CF-PMCs)热氧老化后弯曲性能的影响,对三维四向编织碳纤维/环氧复合材料(简称为三维编织复合材料)和层合平纹碳布/环氧复合材料(简称为层合复合材料)的热氧老化性能进行了研究。利用FTIR、老化失重、弯曲测试和SEM等手段分析了热氧老化前后的试样。结果表明:热氧老化导致基体树脂的氧化断链以及纤维/基体界面结合力的退化是两种复合材料弯曲强度和弯曲模量下降的原因,弯曲强度比弯曲模量更容易受热氧老化的影响。在相同的热氧老化条件下,层合复合材料的热氧老化失重大于三维编织复合材料的,而三维编织复合材料的弯曲强度和弯曲模量保留率均大于层合复合材料的。在140℃下老化1 200h后,层合复合材料的弯曲强度和弯曲模量保留率分别为74.7%和88.3%,而对应的三维编织复合材料的分别为79.4%和91.5%。因此,采用三维编织预制件作为CF-PMCs的增强体是一种有效的提高其热氧稳定性的方法。     

炭黑增强橡胶复合材料的大变形细观力学模型

为考察炭黑对橡胶复合材料超弹性力学行为的影响,首先,利用不同填充体积分数的炭黑增强橡胶复合材料的准静态力学试验数据,对现有的基于均质化方法的"变形放大"细观力学模型的大变形表征能力进行了评估。其次,在此基础上提出了新的"第一不变量放大"关系,并获得了较为合理的预测结果。最后,利用随机序列吸附算法建立了较接近材料真实细观结构的球形颗粒填充数值模型,进行了大变形情况下的三维数值模拟;为考察颗粒聚集效应的影响,还设置了颗粒均匀随机分布和团聚随机分布两种形式。计算结果与试验数据的对照表明:提出的三维细观数值模型已经能在一定程度上预测填充橡胶的大变形宏观力学行为,且颗粒团聚随机分布模型的预测能力更好一些。试验结果验证了该模型的合理性,所建模型为进一步的相关研究提供了参考。     

Numerical investigation on steel fibre reinforced cementitious composite panels subjected to high velocity impact loading

Steel fibre reinforced cementitious composite (SFRCC) panels are numerically investigated for their performances under high velocity impact of short projectiles. Numerical responses are obtained using advanced constitutive material model of Riedel–Hiermaier–Thoma (RHT) for cementitious materials and adopting appropriate modelling techniques. Effects of steel fibre volume and the thickness of panels on the impact performance are mainly highlighted in this paper. Various characteristics phenomenon during impact on cementitious composite panels namely, spalling, cracking, scabbing and perforation, are captured which is a difficult task. Scabbing is likely to occur when tensile stresses at the back face of the panel exceed dynamic tensile strength of the material. Various critical aspects in numerical modelling like boundary conditions, material input parameters, and handling severe distortion of the Lagrangian based finite elements are appropriately explained. Design chart is also developed to determine optimum fibre volume and thickness for an impact energy level up to 2.2 kJ. The numerically predicted impact responses are found to corroborate well with experimental results.     

对流层太赫兹波散射特性研究

基于Mie散射理论分析了球形近似下对流层气溶胶粒子对太赫兹波段的散射特性。通过模拟对比,得出对流层四种粒子在太赫兹波段的散射能力。研究发现,粒子的尺度参数对散射强度的影响比较明显,随着粒子尺度参数的增大,散射相位函数振荡越强,散射强度逐渐变大;散射光逐渐前向集中于更小的角度;曲线越来越尖锐,且出现了更多分叶。仿真给出了波长对散射参数的影响。本文利用Matlab给出了四种粒子太赫兹波段的散射仿真,研究结果对太赫兹技术在气象相关领域的应用具有一定的参考价值。     

SMD石英晶体抗高过载性能的研究

为了研究SMD石英晶体的抗高过载能力,采用自由式霍普金森压杆对7050、6035、5032、3225、3225(一级加固)、3225(二级加固)六种型号SMD石英晶体进行高过载环境下的动态加载测试。结果表明,在高过载条件下,SMD石英晶体的抗高过载性能随尺寸减小而不断提高,并且产品经历高过载环境后电气参数的不良率逐步降低。未经过加固处理的各型号SMD石英晶体(7050、6035、5032、3225)经过高过载试验(50 000~80 000 g)后,电气参数均出现超差,不能满足武器系统的要求。经过加固处理的SMD石英晶体样品(3225一级加固、3225二级加固)经过高过载试验可以正常工作。