复合材料非线性本构关系的机算机模拟

本文对单向连续纤维增强复合材料的弹塑性本构关系进行了数值模拟。首先提出了基于统一弹粘塑性本构理论的有限无法,然后利用微观力学模型研究了弹性纤维增强弹粘塑性基体的复合材料应力——应变关系。      

板壳非线性分析的新理论新方法

提出了板壳非线性分析的新理论新方法。首先建立了下列几个新的本构关系:塑性应变向量增量与总应变向量增量的新关系,热塑性应变向量增量与总应变向量增量及温度应变向量增量的新关系,粘塑性应变向量增量与总应变向量增量的新关系,热粘塑性应变向量增量与总应变向量增量及温度应变向量增量的新关系。这些关系分别称为弹塑性应变增量理论、热弹塑性应变增量理论、弹粘塑性应变增量理论及热弹粘塑性应变增量理论,避开了屈服曲面、加载曲面、流动法则及复杂的非线性应力应变关系。其次建立了非线性样条无网格法,这种方法是以新的本构关系、几何非线性理论、变分原理、广义变分原理、加权残数法及样条离散化为基础建立的,避免了经典本构关系及有限元法带来的巨大困难及缺陷,不仅计算简便,而且精度高,收敛速度很快。建立了板壳非线性分析的统一格式,对板壳的几何非线性分析、材料非线性分析及双重非线性分析都适用。     

沥青砂混合料粘弹塑力学特性研究

在0.1MPa、0.15MPa、0.2MPa、0.25MPa和0.3MPa下进行了沥青砂试样单轴压缩和蠕变实验,分析了其压缩和蠕变性质,根据变形机理提出了粘弹塑本构模型可由粘弹性和粘塑性的两个子模型串联构成,通过对粘塑性子模型中粘性系数进行改进,理论推导了模型蠕变本构方程,确定了模型参数,并求得模型参数与加载应力函数关系。进行模型预测与实验结果对比,结果表明:该模型能够描述沥青砂试样在不同应力下蠕变变形的3个阶段,反映了沥青砂混合料粘弹塑变形特点。     

岩体粘塑性模型参数的反分析

基于弹—粘塑性有限元方法,探讨了通过反分析来确定P.Perzyna粘塑性本构模型中反映岩体粘塑性变形的流动系数和屈服函数的函数的方法,并用实测数据检验了这一反分析方法的可行性。     

复合材料蠕变本构关系及实验测定Ⅰ.本构关系

蠕变是复合材料最重要的力学性能之一,实验表明:复合材料在蠕变条件下的变形可以分为弹性变形、粘弹性变形和粘塑性变形.应用不可逆过程的热力学和广义变量的概念可以分析材料的蠕变变形.本文首先回顾了热力学的基本方程;基于Schapery本构关系的假设和思路推导了蠕变本构关系的一般形式,其中包括弹性变形、粘弹性变形和粘塑性变形;考虑到广义力选取的不唯一性,本文提出了广义力选取的原则以使得到的本构关系尽可能地简单;由此本文给出了复合材料的一维蠕变,各向同性复合材料的二维蠕变和纤维增强复合材料平面内的蠕变的本构关系.     

树脂基三维编织复合材料粘弹性能的数值预报

建立了基于三细胞模型数值预报三维编织复合材料粘弹性能的方法。首先构造了三维编织复合材料的三细胞模型并施加周期性边界条件,随后利用标准线性固体模型模拟树脂基体的粘弹性能,导出基体的松弛模量,再通过有限元计算及Prony级数拟合,得到三种胞元的粘弹性参数。然后根据三种胞元的体积分数和粘弹性参数,利用三个标准线性固体模型并联,模拟得到三维编织复合材料沿编织方向的粘弹性参数和蠕变本构关系。最后,分析了编织角和纤维体积含量对粘弹性能的影响。     

率相关饱和多孔介质动力响应的数值分析

在基于混合物理论的多孔介质模型的基础上,将固体相视为弹粘塑性体,建立了饱和多孔介质的弹粘塑性模型。模型的基本思想是在无粘弹塑性本构关系中引入-时间参数,使固体骨架具备了粘性效应。利用Galerkin加权残值法推导得到了罚有限元格式,并采用Newmark预估校正法求解率相关饱和多孔介质的非线性有限元动力方程,此算法可以很...     

复合材料蠕变本构关系及实验测定Ⅱ实验测定

在前一部分,本文得到复合材料蠕变的本构关系,在此基础上,本文进一步分析了复合材料蠕变本构关系的具体形式,实验测得了长纤维增强复合材料在蠕变、恢复两个阶段的应变,以用来确定本构关系中的待定参数,考虑到本构关系为复杂的非线性方程,本文提出了用离散变量和最小二乘法联合的方法确定参数,进而拟合蠕变本构关系的理论公式,分离出了蠕变过程中的弹性变形、粘弹性变形和粘塑性变形,对本构关系中的几个参函数,本文根据有限的实验数据拟合了其函数。      

复合材料蠕变本构关系及实验测定 Ⅱ实验测定

在前一部分,本文得到复合材料蠕变的本构关系,在此基础上,本文进一步分析了复合材料蠕变本构关系的具体形式,实验测得了长纤维增强复合材料在蠕变、恢复两个阶段的应变,以用来确定本构关系中的待定参数,考虑到本构关系为复杂的非线性方程,本文提出了用离散变量和最小二乘法联合的方法确定参数,进而拟合蠕变本构关系的理论公式,分离出了蠕变过程中的弹性变形、粘弹性变形和粘塑性变形,对本构关系中的几个参函数,本文根据有限的实验数据拟合了其函数.     

颗粒增强复合材料刚塑性细观损伤本构模型的验证

验证已建立的刚性颗粒增强复合材料刚塑性细观损伤本构理论的合理性和可靠性。将上述本构理论的数值计算结果与SiC颗粒增强的铝基复合材料单轴拉伸实验结果进行比较。结果表明:由此本构模型得到的应力-应变理论曲线与拉伸实验所得的应力-应变曲线基本吻合,从而验证了该本构模型的合理性和可靠性。因此已建立的刚塑性细观损伤本构模型可用于数值计算,在一定程度上可预测颗粒增强复合材料的力学特性。在此基础上对大、小颗粒增强复合材料的延展性、空洞和颗粒体积分数演化规律等作了讨论。      

晶界层电容器晶界势垒的研究

以中间夹层的 Schottky 势垒作为晶界层电容器晶界势垒,从理论上分析、推导了电流电压关系和电容电压关系。利用这些关系式对实验测试数据进行了计算机模拟,并用实验结果和计算机模拟结果检验了该晶界势垒模型的合理性。在此基础上揭示出晶界势垒对晶界层电容器电性能所起的关健作用。     

半流体液料的灌装阀口径的确定

以实验数据为依据,建立了半流体的粘度与温度的关系和粘度与表面张力的关系,以及表面张力与灌装阀口径的关系,以此来确定半流体的灌装阀的口径.     

Compliance crack length relations for the four-point bend specimen

Compliance crack length relations for the four-point bend specimen geometry have not been reported in the literature in spite of this geometry being one of the popularly used specimens for fatigue crack growth studies. An effort has been made in the present work to fill this gap. Accordingly, the finite element technique was employed to simulate loading and calculate displacements at various locations in a four-point bend specimen. The load-displacement data thus obtained were processed to yield compliance crack length relations. These relations were employed to calculate the crack length during fatigue testing of four-point bend specimens in which the crack length was also measured by optical means. A good correlation was observed between the predicted crack length and that measured optically.     

标准化方法和方法标准化

本文分别深入讨论了标准化方法和方法标准化的内涵,剖析了它们的理性形成关系和应用关系,研究了它们在标准化范畴拥有的关系和地位,深入讨论了统一化、互换性、通用化、系列化、模块化等标准化形式形成标准化方法的理论关系,理论上证明了一些标准化形式的标准化属性,详细讨论了方法标准化的方法对象的分类关系、实践关系和范畴,深入研究了标准化方法和方法标准化的相互依赖和对立统一的哲理关系。     

基于技术中介论的交互设计跨情境分析框架

目的 对人与产品的交互关系进行概念化、结构化,并给出交互体验的解释模式,以支持交互设计实践。方法 基于后现象学人—物—世界的“互为塑造论”,分析了一种基于交互关系的跨情境框架。结果 该框架将用户、产品、情境置于一个动态连续体中,区分了具身、解释、他者、背景四类交互关系及其体验特征。结论 本框架从整体上回应了人与产品交互的生成性、体验性、扩展性的特点,不仅使用户体验、交互情境、原型设计的构建和验证变得清晰,而且还着重关注混合物理空间,为物联网和智能产品设计提供了思路。     

Explicit cross-link relations between effective elastic modulus and thermal conductivity for fiber composites

Explicit cross-link relations between effective elastic modulus and thermal conductivity for composites with different fiber orientation are derived with help of Mori-Tanaka micromechanical method. Numerical cross-link relations are also established by digital-image-based finite element method, and they compare favorably with the analytical cross-link relations especially for the composite with aligned fibers and planar randomly oriented fibers. Both analytical and numerical cross-link relations agree well with the experimental results available in the literature. For the composite with space randomly oriented fibers, the numerically obtained cross-link relations are insensitive to the fiber’s shape, and the analytical cross-link relations are weakly dependent on fiber’s shape. In sum, the sensitivity of cross-link relations to the fiber’s shape depends on the extent of anisotropic behavior of fiber composites. Such cross-link relations can be potentially applied for predicting the difficult-to-measure elastic modulus from the measured thermal conductivities.     

Causality-imposed (Kramers-Kronig) relationships between attenuation and dispersion

Causality imposes restrictions on both the time-domain and frequency-domain responses of a system. The Kramers-Kronig (K-K) relations relate the real and imaginary parts of the frequency-domain response. In ultrasonics, K-K relations often are used to link attenuation and dispersion. We review both integral and differential forms of the frequency-domain K-K relations that are relevant to theoretical models and laboratory measurements. We consider two methods for implementing integral K-K relations for the case of finite-bandwidth data, namely, extrapolation of data and restriction of integration limits. For the latter approach, we discuss the accuracy of K-K predictions for specific classes of system behavior and how the truncation of the integrals affects this accuracy. We demonstrate the accurate prediction of attenuation and dispersion using several forms of the K-K relations relevant to experimental measurements of media with attenuation coefficients obeying a frequency power law and media consisting of resonant scatterers. We also review the time-causal relations that describe the time-domain consequences of causality in the wave equation. These relations can be thought of as time-domain analogs of the (frequency-domain) K-K relations. Causality-imposed relations, such as the K-K and time-causal relations, provide useful tools for the analysis of measurements and models of acoustic systems.     

论产品造型的科技发展因素

对产品造型和科学技术的发展的关系做了深入的探讨,通过科学技术的发展,工作机理的选择以及工作机理的认知几方面来阐述产品形态的设计.从3个方面论述了他们之间的联系,对目前行业内的产品造型设计只注重形式而忽略科学的根本做了有益的探索和研究.得出了产品造型只有适应科学技术的发展才能满足社会和人类的需要观点.     

Stress/strain/time relations for ice under uniaxial compression

Results of mechanical tests involving uniaxial compression of isotropic ice at ?5°C were analysed and interpreted. Constant load (CL) creep tests were made for applied stresses in the range 0.8 to 3.8 MPa, and “strength” tests under constant displacement rate (CD) were made for applied strain rates in the range 10^?7 to 10^?3 s^?1. Results from CL tests and CD tests corresponded closely, giving much the same information about failure strains, strength, creep rates, time to failure, stress/strain-rate relations, and suchlike. Empirical stress/strain-rate relations were developed for three distinct states of strain: (1) for the initial yield point, where axial strains are typically of the order of 0.1%, (2) for the ductile yield point, where axial strains are typically of the order of 1%, (3) for an axial strain of 10%. Stress/strain-rate relations and stress/strain relations for constant duration of CL loading were examined for load durations up to half an hour. The elapsed time up to the ductile yield point (～1% strain) was related to stress and to strain rate for CL tests and CD tests, and correspondence of the results was demonstrated both for interrelationship between CL and CD tests and for compatibility with the appropriate stress/strain-rate relations. The elapsed time up to the initial yield point was also considered. It was shown that CD stress/strain curves can be constructed from a suitable family of CL creep curves, and vice versa.The characteristics of CL creep curves and CD stress/strain curves were examined in some detail, considering relations between strain rates for certain identifiable points on creep curves, and relations between stresses for certain identifiable parts of stress/strain curves. Effective values for quasi-elastic moduli were considered. The strains for various critical points were compared with each other and with the strains at which rates of acoustic emissions reach maximum values.