摘要：纳米多孔金属因其显著的表面效应和优异的机械性能而获得广泛认可.受限于理论复杂性,以往对纳米多孔金属的研究往往依赖于简化二维模型.然而,这些简化模型无法准确地刻画纳米多孔金属力学性能,也未能充分捕捉表面效应影响,特别是纳米表面曲率依赖性.因此,该研究采用最小能量原理,基于Steigmann-Ogden表面理论,设计了综合考虑纳米多孔材料表面效应的有限元表面单元.利用这种新型表面单元,我们构建不同纳米多孔金属模型,并对其进行单轴拉伸和压缩模拟.研究结果表明,表面弯曲刚度导致材料应变能密度显著增加,从而影响能量吸收率变化趋势.此外,与表面Lamé常数相反,纳米多孔金属杨氏模量受到表面残余应力、表面弯曲模量和加载方向等因素显著影响.所开发的有限元模型为准确预测纳米多孔金属力学性能提供了一种稳健而令人信服的科学方法.

摘要：经典克拉尼图形(Chladni patterns,CP)是特征向量的视觉表示,在振动分析、乐器设计、粒子操纵和分离等领域中具有广泛的应用.均质结构通常会表现出高度规则化的CP,这限制它们的应用场景.因此,实现面向应用来逆向设计结构的CP是非常重要的,而这可以通过使用拓扑优化来实现CP的逆向设计.本研究提出了一种使用基于密度的拓扑优化算法来设计结构CP的方法.优化列式中,给出了描述图形的指标函数,并以最小化特征向量和目标CP之间的误差构建了优化目标.数值结果表明,所提出的方法可以为指定的单阶或多阶CP生成新颖的材料分布.这表明了本文所提出的方法能够实现CP的精确定制设计,进一步为面向应用的需求提供了更多选择.

摘要：本文分别通过双悬臂梁(DCB)实验与数值模拟,研究了不同短纤维插层(包括短纤维种类、短纤维长度与插层面密度)对亚麻纤维增强复合材料I型层间断裂韧性的影响规律.DCB试验结果表明,当插层为5mm长度、25g/m^(2)面密度的短碳纤维插层时,复合材料1型层间断裂韧性达到2.322kJ/m^(2),取得最大提升幅度80.7%,短纤维桥联与亚麻连续纤维多层级破坏为其主要增韧机理。在此基础上,采用五参数控制的三线性内聚力单元,建立了数值仿真模型。实验与数值模拟结果的对比分析揭示了短纤维插层属性与内聚力模型参数之间的定量关系,可为植物纤维增强复合材料短纤维插层增韧设计提供参考依据.

摘要：具有随机孔隙的多孔泡沫在声音管理应用中得到越来越多的利用,其吸声系数通常作为性能评估和设计优化的关键声学参数.根据不同的加工方法,泡沫中的孔隙可以是全开或半开的,并且通常表现为分形分布特征.为了便于工程应用,有必要对这些泡沫的吸声系数进行分析预测.然而,分析预测泡沫的吸声系数是一个挑战.因此,本研究提出了半开孔和全开孔的简化代表结构来微观分析泡沫内部的流动特性,并应用分形理论来描述随机分布的孔隙.引入一个叫“开孔度”的参数来表征孔隙的开放程度,可以解析地获得代表结构的粘性和热特征长度.随后,在经典吸声系数Johnson-Champoux-Allard模型的基础上,建立了一种将代表结构与分形理论统一起来的解析模型,从而可以将吸声系数作为具有全开/半开孔泡沫的关键形态参数的函数进行预测.与已有的实验测量和数值模拟结果相比,本文提出的分析模型可以较好地预测了半开孔和全开孔泡沫的关键流动特性和吸声系数.在0到4500 Hz的频率范围内,半开孔泡沫相对于具有相同孔隙率的全开孔泡沫可以更好地衰减声波.在孔隙率为0.95的条件下,半开孔泡沫的总体吸声系数分别提高了21.2%、57.7%和75.8%,此时开孔度由0.75到0.50降低了0.25.

摘要：Experimental study was carried out on the in-plane bending behavior of glass plates without lateral supports, and the effects of the factors, such as height-to-span ratio, on the stability of glass panels were studied. Results show that the in-plane bending glass plates with both ends simply supported and their upper edge free lose overall stability under loads, which belongs to the limit-point type of instability. It is found that the buckling load increases linearly with the increase of height-to-span ratio of the glass plates. The lateral stress of in-plane bending glass plates without lateral supports increases linearly under loads; while the large-area stress increases nonlinearly and the lateral stress is not the controlling factor of instability. In finite element analysis, the first buckling mode is regarded as the initial imperfection and imposed on the model as 1/1000 of the span of the components. The numerical buckling load according to the theory of large deflection is less than the experiment result, which is more conservative and can provide some reference for design. For the design method, when the in-plane load is imposed on the glass plate, its lateral strength and the deflection should be verified. Considering the stability of the in-plane bending glass plate without reliable lateral support, buckling is another possible failure mode and calls for verification.

摘要：折板因为结构简单而被广泛加工成吸能构件.输入动能恒定时,不同材料的折板在不同的动力学条件下。最终变形有明显的差异.为了更好地解释这种现象,利用Maple软件对Zhang-Yu吸能器方程编写了通用程序,并首次求得了吸能器的广义坐标(转角9)随时间的变化规律.为了更好地了解吸能器的运动受参数变化的影响,计算了吸能器动力学的相图经过大量数值模拟,我们发现四折板吸能器应当是"质量敏感"型吸能结构.同时,本文建立了低碳钢和6061-T6铝合金两类折板的动态屈曲的有限元模型,并与Caladine-English动态实验和Zhang-Yu刚黏塑性模型进行了比较.结果表明.(1)Zhang-Yu刚黏塑性模型对低碳钢这种应变本敏感型材料更具有指导意义,而折板为6061-T6铝合金这种应变率不敏感材料时误差更大.并且随着初始折角的增大.Zhang-Yu刚黏塑性模型的预测误差进一步扩大.(2)根据有限元模型修正塑性铰的等效塑性长度λ值,可以提高Zhang-Yu刚黏塑性模型的预测伯的精度,我们的研究结果对折板吸能结构的设计与制造有一定的指导意义.

摘要：The response surface method(RSM) is one of the main approaches for analyzing reliability problems with implicit performance *** improved adaptive RSM based on uniform design(UD) and double weighted regression(DWR) was *** the proposed method,the basic principle of the iteratively adaptive response surface method is *** design is used to sample the fitting *** a double weighted regression system considering the distances from the fitting points to the limit state surface and to the estimated design points is set to determine the coefficients of the response surface *** with the conventional approaches,the fitting points selected by UD are more representative,and a better approximation in the key region is also observed with *** examples show that the proposed method has good convergent capability and computational accuracy.

摘要：Remodeled clay and sand rock specimens were prepared by designing lateral confinement and water drainage experiments based on the stress exerted on granular materials in a waste *** in situ test was conducted in an internal waste dump;the physical and mechanical parameters of the remodeled rock mass dumped at different time and depths were *** on statistics,regression analysis was performed with regard to the shearing stress parameters acquired from the two *** factors,such as remodeling pressure(burial depth),remodeling time(amount of time since waste was dumped),and the corresponding functional relationship,were *** indicates that the cohesion of the remodeled clay and its remodeling pressure are correlated by a quadratic function but are not correlated with remodeling time *** situ experimental results indicate that the shear strength of reshaped granular materials in the internal dump is positively correlated with burial depth but poorly correlated with time *** Cand burial depth H follow a quadratic function,specifically for a short time since waste has been *** revealed by both in situ and laboratory experiments,the remodeling strength of granular materials varies in a certain *** consistency of such materials verifies the reliability of the remodeling experimental program.

摘要：The state of the art of the study on the hydraulic conductivity of GCLs is presented in terms of the influence of the effective stress,chemical interactions,freeze-thaw cycles and temperature *** changes of void ratio caused by changes of effective stress have a direct linear effect on the hydraulic conductivity,regardless of the cation concentration or the thickness of the adsorbed *** hydraulic conductivity is related to the relative abundance of monovalent and divalent cation(RMD),and RMD has a great effect on the hydraulic conductivity in weak *** long-term susceptibility of GCLs to increased hydraulic conductivity as a response to repeated freeze-thaw cycling is minimal,which has been proved after 150 freeze-thaw *** potential of desiccation cracking increases with the increasing temperature gradient and is related to the initial subsoil water content,the applied overburden stress,etc.

摘要：本文提出了由之字形单元组成的弹性波超构表面来实现对弯曲波的深亚波长尺度操控.通过遗传算法对单元进行参数优化,可以找到具有全透射率和全相位控制的单元,而其宽度仅为波长的1/5.结合传输模态和Kirchhoff薄板理论,发展了理论模型并解释了这些单元产生优越性能的原因.接着,设计了直线型和曲线型超构表面实现不同位置的弯曲波聚焦,其仿真结果都显示出了优异的性能,进一步加工制作直线型超构表面并进行实验测试,实验结果与仿真结果非常吻合,结果同时表明入射波能量在焦点处提高了6倍以上.本工作提出的超构表面可用于设计紧凑高效的弹性波器件.