层合复合材料冲击损伤破坏过程研究(Ⅰ)——数值分析

基于连续损伤力学,对弹丸冲击复合材料多层板靶的变形-损伤过程给出了必要的基本方程,进行了三维有限元分析.将靶板处理为具有材料各向异性和结构非均匀性;冲击引起的微损伤是各向异性的,造成材料的非线性;冲击造成的局部大变形,构成几何非线性.宏观损伤(包括层内基体开裂、纤维断裂和层间分层)在有限元分析中用节点分裂法处理.钢质弹丸假设是线弹性的,不考虑它在冲击过程中的损伤.计算结果表明,采用本文中提出的方法,能较好地模拟复合材料层合板受弹丸冲击时的损伤、变形过程.     

含界面开裂损伤的复合材料夹层板线性和非线性热—机械力屈性态研究

本文提出基于复合材料层合板的一阶剪切理论和ｚｉｇ－ｚａｇ变形假定的有限元模型，研究了含表板与心体间开裂损伤的复合材料夹层板的线性和非线性热－机械力耦合情况下的屈曲问题，在分析中考虑了材料性质与温度的相关性。通过典型算例分析，讨论了热－机械力耦合效应和损伤面积大小对夹层结构的屈性态的影响关系。     

压缩载荷下复合材料整体加筋板渐进损伤非线性数值分析

建立了考虑脱粘的复合材料整体加筋板渐进损伤有限元分析模型。该模型采用界面单元模拟筋条与壁板之间的连接界面, 连接界面和复合材料层板分别采用Quads准则和Hashin准则作为失效判据, 基于ABAQUS软件, 建立了含连续损伤状态变量的材料刚度退化方案。基于该模型, 采用非线性有限元方法研究了压缩载荷下复合材料整体加筋壁板在考虑初始几何缺陷时的破坏过程, 分析了结构相应失效模式的细观损伤机制; 详细讨论了轴向刚度比对结构承载能力及破坏模式的影响。结果表明: 考虑脱粘损伤的有限元模型能有效模拟加筋板的破坏过程; 在加筋板铺层设计合理的情况下, 增加筋条与壁板刚度比能有效提高加筋板截面单位面积的承载能力。      

层合复合材料冲击损伤破坏过程研究(Ⅰ)——宏观破坏准则

本文对层合复合材料在冲击载荷作用下的细观损伤和宏观损伤(分层、基体开裂、纤维断裂)的破坏机理提出了一种分析模型.该模型假设材料的非线性是由于冲击过程中的细观损伤引起的,在单元本构方程中处理;采用最大应变分量准则,处理材料的宏观损伤,并考虑了相邻层(或单元)材料状态的影响,采用节点分裂的方法模拟上述宏观损伤机理.     

一种等效测量不同湿度条件下离子聚合物金属复合材料弹性模量的方法

离子聚合物金属复合材料的弹性模量与材料内部的含水量紧密相连,材料置于不同湿度环境下因含水量的差异会导致弹性模量不同,由于过程效应、实时性等因素影响,采用拉伸法测量材料的弹性模量不够准确。采用悬臂梁共振的方法测量该材料风干(吸水)过程中不同时刻的共振频率,通过公式转换计算得到不同时刻下弹性模量,然后通过测量材料在风干过程中含水量变化规律以及含水量与环境湿度的对应关系,最终得到该材料在不同湿度条件下的弹性模量,该方法简便可行,解决了测量不同湿度条件下离子聚合物金属复合材料弹性模量的难题。     

含界面脱粘及表板基体开裂损伤的复合材料夹层板非线性稳定性的研究

本文作者基于"zig-zag"模型和Mindlin一阶剪切变形板理论,推导了复合材料夹层板屈曲分析的有限元列式,在该列式中考虑了面板的横向剪切变形和芯体的面内刚度对夹层板力学性能的影响。针对具有面板和芯体间界面脱粘和纤维增强树脂基体微裂纹损伤的夹层板损伤特征,分别提出了分层模型和多标量损伤模型,并推导了多标量形式的损伤本构关系。采用修正的 Newton-Raphson迭代格式求解含损复合材料夹层板的非线性稳定性性状。通过算例研究了脱粘面积、基体的损伤演化、表板的铺设方式及载荷形式对复合材料夹层板屈曲性态的影响。本文作者给出的有限元模型和结论,对复合材料夹层板结构设计的损伤容限的制定具有一定的参考价值。     

复合材料叠层板横向开裂的研究

在Talreja提出的研究复合材料横向开裂的损伤力学方法的基础上,文中引进了一种更合理的计算约束系数的方法,并将其用于研究复合材料叠层板的横向开裂,预估了其弹性模量的变化。经试验结果的验证,其理论的预估结果是正确的。     

三维四向编织CMCs拉伸性能及损伤演化数值预测

发展了一种能够预测三维四向编织陶瓷基复合材料(3D-B-CMCs)拉伸模量与强度以及损伤演化过程的数值计算方法.首先,利用复合圆柱(CCA)和全局载荷分担(GLS)两种模型预测了纤维束的弹性模量和拉伸强度;然后,利用微焦点CT技术建立了能够反映3D-B-CMCs真实编织几何结构的胞元模型;其次,采用Hashin纤维束失效模型以及考虑单元尺寸的各向异性损伤力学本构模型,编制了ABAQUS/UMAT子程序,对3D-B-CMCs材料宏观拉伸的整个过程进行了计算模拟,预测了宏观拉伸应力-应变曲线,并与试验结果相吻合,证明了所建立方法的合理性和UMAT程序的有效性.同时,研究和讨论了拉伸过程中材料内部不同的损伤破坏模式对复合材料整体力学性能的影响,为材料的疲劳和蠕变等力学行为的内部损伤演化提供了依据.     

含分层损伤的复合材料格栅(AGS)板的非线性热屈曲分析

采用基于复合材料一阶剪切效应理论的有限元法分别研究了含分层损伤的复合材料层合光板、 单向加筋板和格栅加筋(AGS)板的热屈曲性态。在分析中考虑材料热物理性质与温度相关特性, 同时在分层前缘采用了位移约束条件以保证分层区域的各子板的变形相容要求。3种结构的典型算例分析和结果的比较表明, 复合材料格栅(AGS)板具有很强的抗热屈曲的能力, 但是, 分层损伤将使其临界温度降低, 同时还会导致热屈曲的模态发生改变。本文中提出的方法和所得结论对AGS结构的热承载能力预测和损伤容限设计将具有参考价值。      

复合材料圆管构件的等效模型研究

本文针对任意壁厚的复合材料圆管构件的等效弹性模量和剪切模量提出了高阶理论计算方法，它考虑了构件的横向剪切效应以及层合材料的三维本相关系，并且对三种缠绕方式的等效模量进行了预测，预测结果与经典层合报理论和实验的预测结果吻合较好，该方法可用于复合材料杆件结构的设计中。     

Damage Constitutive Equations and its Application to Fiber Reinforced Composites under Transverse Impact

Two continuous field variables, called as continuity tensor and damage variable tensor, are used to describe the anisotropic responses of an elastic-brittle material under transverse impact load. Based on the continuum damage mechanics, anisotropic damage constitutive equations in both full and incremental forms are proposed here. The expressions of effective elastic module tensor, damage variable tensor and damage propagation force tensor are further derived, and the methods for determining the tensors are explained in detail. An example of strain and damage response of a fiber reinforced composite laminated plate under transverse impact load is employed to demonstrate the application of this theory. In the example, the damage variable coupled with geometric large deformation of laminated plate is also considered. The calculating results illustrate the influence of damage on strain field in the impacted laminated plate.     

硬泡沫塑料的力学性能分析:压缩弹性模量分析与计算机摸拟

对包装行业中常用的一类包装材料—硬泡沫塑料的压缩弹性模量的估算方法进行了探讨，发展了以力学模型为基础的随机模拟方法。以PUR发泡硬泡沫塑料为例，将此方法的计算结果与试验数据进行了比较。本方法既反映泡沫塑料的结构的力学性质，又体现了结构参数的随机特征，并且算法简单，编程容易，耗机时小，利于工程应用。     

Mechanical Characterization of KMPR by Nano-Indentation for MEMS Applications

Abstract:  The elastic modulus and hardness of a novel negative photoresist, KMPR, under different heat treatment temperatures, have been characterized in this work using a combination of nanoindentation, uniaxial tension and vibration tests. There are two major conclusions. First, the material exhibits strong anisotropy. The apparent modulus obtained by the indentation method (6.5–7.5 GPa) is higher than that characterized by the uniaxial tensile test (1.07 GPa). The modulus issue is further validated by the subsequent vibration test data. Second, the apparent modulus and the apparent hardness vary with heat treatment temperatures. The room temperature elastic modulus decreased with an increase of the processing temperature but the apparent hardness essentially exhibited an opposite trend. It is suggested that this unusual result was caused by the pile-up effect during the indentation process.     

Damage Development in Gray Cast Iron under Static Deformation

The authors discuss the results of experimental investigation of structural degradation of gray cast iron at various stages of static tensile deformation. Analysis of the deformation process has revealed that damageability of a material under loading can be assessed by both a special strain parameter and scatter of hardness characteristics or a ratio of the modulus deviation to the current value of the elastic modulus. A correlation between these parameters has been established.     

梁结构刚度动态非概率可靠性分析

 为了定量分析在疲劳载荷作用下梁在不同寿命期内刚度的可靠性,建立梁结构物理性能退化的精确公式就十分重要.依据疲劳载荷造成的累积损伤对材料极限应力的影响,基于材料剩余强度模型,利用材料强度与弹性模量之间的关系,推导出结构弹性模量的退化表达式,并在此基础上,提出梁弹性模量退化系数的递推表达式,推导出圆截面梁剩余抗弯刚度的表达式.在对结构可靠性分析时,概率可靠性模型和模糊可靠性模型对于原始数据信息要求较高.为了充分利用结构的不确定性信息弥补原始数据的不足,将梁的初始弹性模量及所受的疲劳载荷等看作区间变量,利用区间模型建立基于刚度退化的梁刚度动态非概率可靠性模型.最后,结合工程实例的计算表明了该方法对梁的刚度退化分析及其刚度动态可靠性分析是可行、有效和合理的.     

纳米压入法的柔度效应及其校正

根据亚微压入仪的柔度测定，考察了仪器柔度对纳主入法测试材料表层硬度和弹性模量的影响，指出柔度因子主要影响卸载线的斜率，用单测点法弹性模量和硬度分布时修正测试结果。     

纤维缠绕复合材料纤维束形态的细观分析及弹性模量预测

在对纤维缠绕复合材料缠绕图案分析的基础上, 考虑到纤维束的交叠与波动, 提出一种用于计算纤维缠绕复合材料弹性模量的方法。该方法是在纤维缠绕图案中提取一代表单元, 将代表单元分成层板区域和纤维束波动区域。层板区域用经典层板理论计算弹性模量; 纤维束波动区域根据纤维波动的细观图形及走势计算弹性模量。根据层板区域和纤维束波动区域在代表单元中所占的比例, 组合2 个区域的弹性模量以获得代表单元的总体弹性模量。通过测试炭纤维/ 环氧树脂缠绕管在轴向拉伸载荷下的轴向弹性模量及泊松比, 验证了理论计算结果,表明该计算方法能较准确地计算纤维缠绕复合材料的弹性模量, 因此可为这类材料的设计计算提供有益的理论依据。      

Comparison of Dynamic Young’s Modulus of Thin Concrete Disks to Stress Wave–Based Nondestructive Evaluation Findings

Stress wave–based nondestructive evaluation (NDE) techniques are frequently used for in-situ evaluation of concrete. Stress wave velocity in a material is related to Young’s modulus of elasticity. Cores for in-situ compressive strength are subject to a minimum length-to-diameter ratio requirement that enforce large specimen sizes. Thin circular disks sawn from cylinders or cores are widely used in measurement of chloride or air permeability of concrete. While these methods provide useful information on concrete properties with depth, the capability of measuring changes in mechanical properties such as elastic Young’s modulus in small depth increments is of value to both researchers and consulting engineers conducting condition assessment or NDE, particularly when damage gradients exist. Changes in properties over relatively small depths may be undetected otherwise due to limitations of test method, equipment, or imposed specimen size. This study presents applications of Young’s modulus of thin concrete disks to structural assessment projects involving damage and damage gradients. In-situ nondestructive ultrasonic pulse velocity (UPV) testing was used in identification of affected areas. Young’s modulus of thin concrete disks was used in interpretation of the NDE results and provided an improved understanding of the extent of damage that was indicated using NDE. Two different case studies are discussed: exposure to fire and exposure to thermal shock and cryogenic temperatures. The use of thin disks enabled determination of mechanical properties of relatively thin layers of concrete and, therefore, provided a means to quantitatively assess the extent of damage gradients. Confirmation of NDE results using modulus data and analytical modeling using the relationship between Young’s modulus and pulse velocity provided improved understanding of NDE findings reducing uncertainty in engineering analysis and improving repair recommendations.     

Kinetics of scattered fracture in structural metals under elastoplastic deformation

The paper presents a procedure whereby the damage accumulation kinetics in structural materials, such as steel 45, stainless steel 12Kh18N10T, aluminum alloy D16T, and titanium alloy VT22, under elastoplastic deformation is studied based on variation parameters of elastic modulus and resistivity. For complex stress conditions, a continuum model for damage accumulation is proposed which relates the damage parameter to the intensity of accumulated plastic strains. The data calculated by the proposed continuum model are compared to the experimental findings of the investigation of the damage accumulation kinetics for some structural metals. __________ Translated from Problemy Prochnosti, No. 3, pp. 23–34, May–June, 2007.     

竹塑模压异型板包装材料工艺

目的 传统塑料包装透气性较差,不利于环保,为解决这些缺陷,研发一种塑料-细竹丝模压异型板件的新型外固定用包装材料,并通过实验方法确定其性能.方法 首先,介绍塑料-细竹丝模压异型板件新型包装材料的特点与成型工艺;其次,通过实验对塑料-细竹丝模压异型板件包装材料制造时最佳竹塑比进行确定;最后,利用概率设计理论求解出异型板件包装材料主方向的弹性模量,并通过实验对其理论公式进行验证.结果 当竹塑比值为0.150时,异型板件包装材料的各项性能较好,上异型板件包装材料单位质量的最大抗压力平均值达到4.33 kN/kg,下异型板件包装材料单位质量的最大抗压力平均值达到5.26 kN/kg.力学实验结果显示,所建立异型板件包装材料的弹性模量理论求解公式正确,且细竹丝的加入提高了原有包装材料的力学性能.结论 新型包装材料具有较好的稳定性和透气性,更加环保,是传统塑料包装材料的理想换代产品.文中研究将推进我国异型板件包装材料工业化的发展,并为异型板件包装材料产业化加工设备的设计制造提供理论和实验依据.