基于连续介质损伤力学的7075铝合金高温成形极限理论预测与数值仿真

开展7075铝合金高温单向拉伸试验和成形极限试验，获得了不同温度和应变率的应力-应变曲线和成形极限曲线。结果表明，在较高的温度和应变率时7075铝合金的强度减小、成形性提高。为描述7075铝合金高温损伤演化过程，提出一种改进的连续介质损伤模型，并建立了耦合损伤的多轴统一黏塑性本构模型。基于试验结果，运用NSGAII遗传算法标定了模型中的参数，标定后的本构模型可以很好地预测7075铝合金的高温热力行为和极限应变。通过有限元软件Abaqus的用户材料子程序VUMAT，该本构模型被编入到Abaqus软件中进行数值仿真计算。结果表明，仿真获得的成形极限曲线和应变场分布与试验和理论结果吻合度好，进一步证明了所建立的耦合损伤的多轴本构模型的正确性及其在高温成形极限有限元仿真中的适用性。     

一种立方对称晶体结构的唯象连续非线性本构模型及其分析

基于立方对称结构的晶体特点，本文建立一种唯象连续非线性本构模型，推导出一些主要方向如（００１）、（０１１）和（１１１）受单向载荷时的表达式。并对所建模型的适用性进行了分析，指出在较高温度状态时所建模型能较准确地描述Ｎｉ基单晶的非线性变形。     

基于连续介质损伤力学的高强度钢板热成形性数值预测

基于连续介质损伤力学模型,建立耦合损伤的热成形本构方程。将该本构方程引入到自主开发的金属成形有限元软件KMAS中,从而可对高强度钢板在热成形过程中的损伤演化及成形性能进行预测。本构方程中与温度及应变率相关的损伤参数控制着热成形过程中的损伤演化,对成形性数值预测具有重要的意义。为标定本构方程中的损伤参数,进行不同温度及应变率下的等温热拉伸试验,并对拉伸过程进行数值模拟,通过优化对比数值计算和试验所得的力-位移曲线,获得了不同温度及应变率下的损伤参数。随后将损伤参数引入KMAS中,对一款典型汽车B柱在热成形过程的成形性进行数值预测,并与试验结果进行对比,结果证明了所建立耦合损伤本构方程的正确性。     

连续体单孔手术机器人的建模与优化分析

提出了一种新构型的6自由度连续体单孔手术机器人．其形变骨架采用超弹性材料一体化成型加工,具有一系列十字交叉镂空结构的弹性铰链．建立了机器人的运动学模型,分析了机器人的可达工作空间,提出一种手术作业空间的优化搜索方法,获得了作业空间中关键位置的操作灵活性．进而以操作灵活性为目标,以关节形变能力为约束,优化分析连续体机构形变骨架的几何参数,形成提升连续体单孔手术机器人操作灵活性的参数优化方法．最后进行连续体机器人的运动控制实验,经过测试,机器人的末端位置误差为2.23 mm,角度误差为2.06°,验证了模型的准确性．     

An anisotropic damage model for tensile fatigue

Fatigue damage in materials is considered to be the effect of material degradation, and the dispersion in fatigue life is attributed to variability in microstructure. This paper presents a numerical model to simulate fatigue damage evolution using continuum damage mechanics to characterize material degradation. An explicit microstructure topology representation is achieved using Voronoi tessellations. Unlike conventional models which use a scalar approximation for damage, this model treats the damage variable as an anisotropic tensor. The model is used to simulate tensile fatigue failure in thin steel specimen. The fatigue life estimations from the model compares well with published experimental results. The results predict a high variability in fatigue life that is characteristic of metals and alloys, as compared with the existing isotropic damage models available in the literature. The model was also used to study the influence of material inhomogeneity on fatigue life dispersion.     

Goal‐oriented adaptivity for linear elastic micromorphic continua based on primal and adjoint consistency analysis

Microscopic considerations are drawing increasing attention for modern simulation techniques. Micromorphic continuum theories, considering micro degrees of freedom, are usually adopted for simulation of localization effects like shear bands. The increased number of degrees of freedom clearly motivates an application of adaptive methods. In this work, the adaptive FEM is tailored for micromorphic elasticity. The proposed adaptive procedure is driven by a goal‐oriented a posteriori error estimator based on duality techniques. For efficient computation of the dual solution, a patch‐based recovery technique is proposed and compared to a reference approach. In order to theoretically ensure optimal convergence order of the proposed adaptive procedure, adjoint consistency of the FE‐discretized solution for the linear elastic micromorphic continua is shown. For illustration, numerical examples are provided. Copyright © 2017 John Wiley & Sons, Ltd.     

复合材料中厚板沉头连接结构强度与损伤失效

针对复合材料沉头螺栓连接结构的强度与损伤问题,开展了两种厚度复合材料层合板凸头与沉头螺栓连接结构挤压强度对比试验研究。试验结果表明,增加层合板厚度会引起连接结构挤压强度下降,但沉头连接结构下降比例小于凸头连接结构。通过数值模拟方法对复合材料中厚板沉头连接结构的强度及损伤失效进行分析。提出一种非线性面内连续损伤与三维混合失效模型,模型考虑了复合材料基体剪切非线性特征并改进了纤维损伤失效判据,有效解决了数值模拟中沉头复合材料连接结构难于收敛的问题。对比分析表明:沉头连接结构的数值计算结果与试验结果吻合良好,极限强度最大计算误差8.62%。     

A boundary density evolutionary topology optimization of continuum structures with smooth boundaries

Based on the variable density method, this article proposes a boundary density evolutionary topology optimization method. The method uses a material interpolation model without penalization. Combined with the density grading filtering method, an optimal topology with only 0/1 cells can be obtained. Compared with the solid isotropic microstructures with penalization method (SIMP), no penalty factor is required in the material interpolation model; compared with the evolutionary structural optimization method (ESO), intermediate-density elements are allowed in the optimization process, but the concept of gradually removing the low-utilization materials near the boundary in the ESO method is retained. After the optimal result is obtained, the structural boundary element is processed by the level set of nodal strain energy, and the optimization result with smooth boundaries similar to the level set method (LSM) can be obtained. The proposed method has the superiority of the variable density method, and it also combines the advantages of the evolutionary method and the level set method, so which is named as boundary density evolution (BDE) method. The four static and one dynamic optimization examples illustrate the stability and efficiency of the proposed method.     

A stress-influence-function with adaptive strength feature approach for stress constrained continuum topology optimization via small-loop sequential strategy

Recently, the stress-influence-function (SIF) approach is presented for stress constrained continuum topology optimization. The SIF approach provides an alternative for continuum topology optimization with stress constraints. However, the SIF approach is not good at controlling the maximum stress of the elements compared to the conventional approach. In the study, the stress-influence-function with adaptive strength feature (SIF-ASF) approach via small-loop sequential strategy is proposed to achieve better control on the maximum elemental stress. First, the stress constrained continuum topology optimization formulation is given and the SIF approach is briefly introduced. Then the SIF-ASF approach is proposed for stress constrained continuum topology optimization, in which the strength feature in the stress influence function is adjusted in each iterative step of the optimization process. The adjoint-vector based sensitivity analysis to the design variables is further discussed. Three numerical examples are given to illustrate the applicability and validity of the proposed SIF-ASF approach. It is shown that the proposed SIF-ASF approach can achieve better control on the maximum elemental stress than the SIF approach. Moreover, the proposed SIF-ASF approach may obtain a lighter structure than the conventional approach.     

Modelling Temperature,Body Size,Prey Density,and Stream Gradient Impacts on Longitudinal Patterns of Potential Production of Drift‐Feeding Trout

In this study, we modelled idealized stream reaches using empirical hydrodynamic and bioenergetic parameters to predict how rainbow trout production depends on physical and biological variations across a downstream gradient, and we compared these downstream effects in a low and high‐gradient stream reach. We found that longitudinal production potential (i.e. net rate of energetic intake per 100 m of stream length) generally increased with increasing stream size when stream gradient was low. This was not the case, however, for high‐gradient streams, wherein maximum longitudinal production potential was associated with middle or low stream size (Q_MAD = 2.5 to 25 m³ s^?1). Areal production potential (net rate of energetic intake per m² of wetted stream bed) reached a maximum at low stream size (Q_MAD = 2.5 m³ s^?1) with both high and low gradients. We also showed that high stream temperature and low drift density could potentially cause adult rainbow trout to be excluded from stream reaches with high flow. The models presented here have a stronger mechanistic basis for predicting fish production across heterogeneous stream environments and provide more nuanced predictions in response to variation in environmental features than their physical habitat‐based predecessors. Copyright © 2016 John Wiley & Sons, Ltd.