室内模型实验中低强度桩侧应变片粘贴技术与应用

表面粗糙的桩与桩间土共同受力后发生相对位移,在低强度桩侧面有效粘贴应变片以测试轴力传递规律是一个难点.在组合群桩复合地基室内模型试验中,本文结合传统内贴法和外贴法两种贴片方式的优点,提出并采用凹槽法在低强度实心模型桩外侧面贴片,即在桩侧预留凹槽、用环氧树脂对贴片部位进行表层处理,在贴片后密封凹槽,并给出了典型测试结果.分析认为:凹槽法贴片技术有效可行,可供室内含桩地基基础模型试验借鉴.     

轴对称弹性应变梯度理论公式推导及有限元实现

用张量运算推导了弹性应变梯度轴对称问题的基本公式.建立了应变梯度轴对称不协调元的弱连续条件,进一步建立了满足弱连续条件的应变梯度轴对称18-DOF三角形单元(BCIZ+ART9),其中BCIZ满足线性应变C0连续,用于计算应变ε;ART9满足常曲率C1弱连续,用于计算应变梯度η0数值结果表明该单元通过C0-1分片检验并能体现材料的尺度效应.     

渐进密度AESO方法及其在热传导结构拓扑优化中的应用

研究用于结构拓扑优化的基于材料添加策略的进化算法(AESO方法).基于进化算法的思想,利用单元材料相对密度的变化描述材料的添加(从O到1)或删除(从1到O).当某些单元满足进化准则时,单元的相对密度进行O-1交化.研究发现.基于一步变化策略的AESO方法往往不能获得正确的拓扑形式,其原因可能是,进化后的响应量是基于密度为O或很小时的敏度经线性近似获得的,与实际相差很大.这种敏度的计算误差问题在ESO、BESO等硬杀算法中都存在.本文提出将进化过程分成多步,以软杀的思想进行硬杀优化,即使材料密度逐渐由O变化到1,实现材料的逐步添加.基于该策略,提出了渐进密度AESO方法,并比较分析了这种逐步添加的做法对结果的影响.算例验证了该方法的正确性和有效性.渐进密度AESO方法为双向进化算法(BESO)提供了有效的进化(材料添加)策略.     

基于CMDLAC指标和遗传算法的结构损伤定位研究

提出了基于综合多损伤定位保证准则(CMDLAC)指标和遗传算法(GA)的结构损伤定位方法。基于结构损伤标量模型,结合灵敏度分析提出了基于频率和振型变化的CMDLAC指标,将损伤识别问题转化为约束优化问题,最后以CMDLAC指标为优化目标函数应用遗传算法求解实现了结构的损伤定位。在考虑测试自由度不完备和测量噪声等因素影响的情况下,对桁架结构损伤的数值模拟分析表明了方法的有效性,验证了CMDLAC指标定位损伤和抵抗噪声的能力,同时指出其具有较强的实际可操作性。     

考虑自重载荷作用的连续体结构拓扑优化

针对自重载荷作用下连续体结构拓扑优化中常遇到的柔顺度随单元密度变化的非单调性、非有效的材料体积约束和材料低密度区出现的``附属'效应等主要困难,提出了RAMP材料插值模型和平均敏度过滤技术相结合的求解策略,并采用MMA方法进行了优化求解. 研究了惩罚因子的选择对最优拓扑以及材料体积约束的影响. 结果表明,合理增大RAMP材料模型中惩罚因子(例如取值达到20.0), 可使材料体积约束达到有效约束. 此外,通过与Sigmund提出的敏度过滤技术比较表明,当引入平均敏度过滤技术时,结果0/1化程度较Sigmund的敏度技术高,可获得清晰的黑白拓扑.      

基于西原模型的非线性黏弹塑性流变模型

在西原模型的基础上,引入能反映加速蠕变起始点的非线性黏塑性元件和瞬时塑性变形的塑性元件,建立了一个能完整反映蠕变全过程的非线性黏弹塑性流变模型. 在其一维流变模型结构的基础上建立三维的流变模型,推导三维流变方程,接着探讨了在三轴压缩试验中确定三维蠕变参数的方法,并对参数进行了敏感性分析. 用三轴压缩试验结果验证模型的有效性,结果表明模型能很好地模拟蠕变的三阶段,并且在多级偏应力水平下可以采用同一组蠕变参数.     

On The Objective Corotational Rates of Eulerian Strain Measures

In the present paper, some new basis-free expressions for an arbitrary objective corotational rate of the general Eulerian strain measures are provided which are in compact form. Moreover, a complete discussion on the requirements for the continuity of the objective corotational rates are presented.      

Necking of anisotropic micro-films with strain-gradient effects

Necking of stubby micro-films of aluminum is investigated numerically by considering tension of a specimen with an initial imperfection used to onset localisation. Plastic anisotropy is represented by two different yield criteria and strain-gradient effects are accounted for using the visco-plastic finite strain model. Furthermore, the model is extended to isotropic anisotropic hardening （evolving anisotropy）. For isotropic hardening plastic anisotropy affects the predicted overall nominal stress level, while the peak stress remains at an overall logarithmic strain corresponding to the hardening exponent. This holds true for both local and nonlocal materials. Anisotropic hardening delays the point of maximum overall nominal stress.     

Modelling of stresses and strains in bonded concrete overlays subjected to differential volume changes

The differential volume changes between repair material and substrate concrete induces stresses in concrete overlays. These stresses could cause the repair material cracking or the interface delamination, which facilitate the penetration of harmful substances into concrete and hence accelerate the deterioration of concrete overlays. In order to investigate the characteristics of these stresses, an analytical model has been developed based on the plate theory and the assumption of the linear relation between shear stress and slip at the interface. This model is able to calculate the tensile stress in the repair material, shear and normal stresses at the interface and the corresponding strains. With this model, the influence of the interface shear stiffness, the dimension of the concrete overlay, and the elastic moduli of two materials on stresses and strains was studied.