含孔复合材料层合板逐渐损伤破坏分析

采用逐渐损伤模型有限元技术对含复合材料层板损伤破坏规律进行了研究，编制了面向对象的后处理软件，为损伤累积，损伤扩展与破坏以及损伤类型与模式的预测和研究提供了先进手段，并针对含孔T30／KH304复合材料层板进行了数值模拟和试验研究，研究表明，采用二维逐渐损伤模型及分析方法，以及所发展的后处理模拟分析软件能够较好地模拟含孔层合板的损伤破坏规律和位移－载荷的响应规律，以豚预测层合板的损伤类型，破坏模式和破坏强度，得到了一些有意义的结论。     

A PROBABILISTIC APPROACH TO THE DEVELOPMENT OF A SIMPLIFIED WORK MEASUREMENT SYSTEM

A probabilistic approach to the development of a simplified work measurement system is presented. As a result of this approach, expected time values and accompanying variances can be calculated for each element under investigation.

General Purpose Date (GPD) and Master Standard Data (MSD), standard data systems which are simplifications of a more detailed predetermined time system, Methods-Time Measurement (MTM), were used to illustrate the applicability of this method.

In order to pursue this probabilistic approach, the various combinations of MTM elements which satisfy each investigated GPD and MSD element have been enumerated. The probability of occurrence of each of these possible combinations has been developed using historical data. Given the time value and the probability of occurrence for each possible combination, the expected time value and accompanying variances were generated for the “simplified” element.     

层间混杂叠层复合材料的最终拉伸破坏(Ⅰ)应力集中分析

Zweben[1]的剪滞假设, 提出一种修正的剪滞分析模型, 研究了层间混杂复合材料低延伸层的断裂、层间界面破坏及高延伸层中部分纤维断裂相互作用所导致的细观应力重分布, 讨论了层间界面破坏对高延伸纤维中的应力集中因子的影响, 为层间混杂叠层复合材料最终拉伸破坏的细观统计分析提供理论依据。      

含预制分层损伤复合材料层合板在压缩载荷下破坏过程和剩余强度的模拟

本文运用一种具有较高精度的高阶位移模式,结合特定的损伤判据和刚度折减方法,建立了一种含损伤有限元模型,并利用其对多个含预制分层损伤的复合材料层合板在压缩载荷下的破坏过程进行了数值模拟,并最终得到这些层合板的剩余强度。与实验结果的对比表明,该数值模拟方法具有较高的精度和有效性。     

层间混杂叠层复合材料的最终拉伸破坏(II)强度的统计分析

采用随机临界核理论, 结合由剪滞模型得出的应力集中分析结果, 对具有层间界面破坏的单向层间混杂叠层复合材料的最终拉伸破坏提出了一种细观统计理论; 导出了计及界面剪切强度效应的强度分布函数和破坏准则; 得到了最终拉伸强度与界面剪切强度的关系。结果表明, 混杂复合材料的最终拉伸强度与界面剪切强度及混杂比存在某种优化匹配关系, 而破坏应变则与现有的实验结果较为接近。      

埋地PVC管纵向断裂失效预测概率模型

针对存在初始裂纹缺陷的埋地PVC管在荷载作用下的纵向断裂失效问题,基于管道环向受力特性和裂纹扩展经验公式建立失效预测模型,并在此基础上运用蒙特卡罗法(MC)对模型和参数的不确定性进行随机模拟,给出管道失效风险率随服役时间变化的规律。计算结果表明:MC数值模拟结果与实测值吻合良好,说明失效预测模型的合理性;裂纹增长是一个由慢到快的过程,初始裂纹越大,失效时间越短;失效风险率在开始的20年内达到最高,随后逐渐减小;所有参数都作为随机变量考虑时与只有初始裂纹为随机变量时相比,失效风险率提高近一倍;管道初始裂纹、内压、残余应力和壁厚是影响管道失效时间的四个重要因素,管道内压和残余应力增加都导致管道失效率变大,准确的给出管道初始裂纹的分布对PVC管纵向断裂失效预测尤为重要。能够减小PVC管初始裂纹缺陷的生产工艺和施工技术可以有效提高管道的使用寿命。     

复合材料层板的拟协调罚单元*

本文在文献提出的多变量拟协调元和罚函数相结合的方法基础上构造了考慮耦合和剪切效应的十五自由度三角形层合板单元。此单元适用于薄和中厚层合板的强度分析,具有收敛和应用范围广的优点。文中以各向同性和复合材料层合板多组数例证明了该单元的有效性,同时还讨论了跨厚比L/h和弹性模量比E₁/E₂与剪切效应的关系,得出了一些有意义的结论。     

A CRACK GROWTH APPROACH TO LIFE PREDICTION OF SPOT-WELDED LAP JOINTS

Fatigue behaviour of spot-welded lap joints is modelled as a single-degree-of-freedom crack growth problem. Although such a model involves simplification of a complicated problem, predictions are in good agreement with experimental results. The model developed here allows a design engineer to analyse the fatigue behaviour of spot-welded steel sheets, which are commonly used in structures, without knowledge of metallurgical and fine geometric details of spot-welds. Only fatigue properties of the sheet metal are needed, so no laboratory facilities are required to generate fatigue data specific to spot-welds or weld metal.     

A NEW MULTIPARAMETER APPROACH TO THE PREDICTION OF FATIGUE CRACK GROWTH

A new multiparameter approach is proposed for the prediction of the combined effects of multiple variables on fatigue crack growth. The method, which is based on multiple linear regression analysis, involves the statistical formulation of mathematical expressions for the crack growth rate, da/dN, as a function of multiple variables, e.g. stress intensity factor range, ΔK, crack closure stress intensity factor, K_cl , and stress ratio, R. A general empirical approach is proposed for the estimation of the fatigue crack growth rate as a function of the above variables. The predictive capability of the empirical approach is then verified by comparing predicted and measured fatigue crack growth and crack growth rate data obtained from tests on a quenched and tempered Q1N (HY80) pressure vessel steel. Error ranges and reliability functions are presented within a probabilistic mechanics framework, and the implications of the results are discussed for the development of generalized fatigue life prediction methods.     

A SIMPLIFIED APPROACH TO CRACK GROWTH PREDICTION IN A CRANKSHAFT

Abstract— Fracture mechanics analyses are carried out on a cracked machine element of complex geometry to predict its fatigue behaviour. Usually, in order to obtain reliable values of stress intensity factors, it is necessary to realize three-dimensional meshes or to utilize the energy approach. An alternative, simplified and approximate approach is proposed here. It is based on the construction of simple two-dimensional models to obtain accurate values of the geometry factors of the component at the deepest point of the crack. Experimental tests show that the relation between the depth and the length of the crack on the free surface is linear. Hence it is possible to reduce the problem to two dimensions with a consequent saving of calculation time. A comparison with experimental data indicates that a satisfactory prediction is obtained by the proposed method.     

纤维增强复合材料迭层圆柱壳的几何非线性分析

本文从非线性弹性理论出发,在小应变、中等小转动的前提下,全面考虑了变形对于平衡方程的影响,导出了和传统理论不同的壳体非线性理论;并用摄动法和伽略金法分别求解了四边不可动固支正交各向异性复合材料迭层园桂壳块以及考虑横向剪切的四边可动简支园桂形扁壳的非线性弯曲问题。计算表明:变形较大时,变形对所有平衡方程的影响都是值得注意的。      

预测复合材料非线性有效介电系数的割线方法

提出了预测复合材料非线性电位移和电场强度关系的一种解析方法,该方法基于各向材料的割线介电常数,将非线性问题转化成一系列线性问题来求解。该方法适用于任意各向异性复合材料和组分材料的非线性性质,而常用的Stroud和Hui的模型只适用于各向同性复合材料和组分材料的弱线性。证明了本文方法具有Ponte Castaneda提出的变分结构。计算结果表明,当基体非线性较小时,本文模型的预测与Stroud和Hui的模型一致,但当基体非线性系数增大时,本文模型能给出合理的预测结果,而Stroud和Hui的模型则会超出基体和夹杂的性能范围。      

带或不带脱层的复合材料层板强度的预报

首先用实验直接测定或从文献中引用单向纤维增强层板的强度的Weibull分布参数α和β.用经典层板理论分析层板中的面内应力;邻层的裂纹引起的应力集中用剪滞法计算;层间应力用简化的平衡方程来确定,层板中单层的当地强度由于邻层的约束作用而提高,假定单层的承载能力直到其裂纹密度饱和时才耗尽;用增强软X光照相技术来监测裂纹密度的发展并测定相应的约束系数,建立最普遍的统计强度准则,结合作用应力的计算和统计强度预报,确定不同层板中各单层的破坏顺序和最终损伤状态.根据最终损伤状态来确定层板的统计强度,并用试验验证.      

THE s-VERSION OF FINITE ELEMENT METHOD FOR LAMINATED COMPOSITES

The s-version of the finite element method is developed for laminated plates and shells. By this technique the global domain is idealized using 2-D Equivalent Single Layer model. The regions where ESL model errs badly in capturing localized phenomena are superimposed by a stack of 3-D elements. Assumed strain formulation and selective polynomial order escalation in the two models, as well as fast iterative procedures, are employed to maintain a high level of computational efficiency.     

金属间化合物基复合材料的界面反应──热力学计算预测

采用热力学基本原理,在已有假设和两个模型基础上,编制了一套通用的计算程序。系统研究了五种金属间化合物:Ti₃Al、TiAl、FeAl、NiAI和NbAl₃,和十种陶瓷材料:B₄C、SiC、TiC;TiB、TiB₂、AlB₁₂;TiN、AlN;SiO₂、Al₂O₃的化学反应性。从而对于上述金属间化合物基体,初步确认了合适的增强剂材料。     

界面性质对颗粒增强复合材料破坏模式影响的数值模拟分析

运用材料破坏过程分析M FPA2D 系统, 对颗粒增强复合材料的变形、损伤及破坏过程进行了数值模拟分析。主要分析了界面性质对破坏模式的影响。模拟结果表明, 增强颗粒与基体的界面对复合材料的宏观性能有很大影响。在理想界面条件下, 破坏模式以界面附近基体的破裂为主, 在非理想界面(且为弱界面) 条件下, 破坏模式以颗粒与基体的脱粘较为明显。      

纤维增强复合材料层合圆柱壳的优化设计

本文从中面内承受轴向压力及从垂直于中面内的横向载荷考虑弯曲挠度和自振频率,综合研究了纤维缠绕层合圆柱壳的优化设计。     

VERIFICATION OF MORPHOLOGICAL TABLE BASED ON PROBABILISTIC ROUGH SETS APPROACH

The objective of this paper is to propose two morphological table verification techniques, both based on the probabilistic rough sets approach. Fundamental aspects of the theories of rough sets and probabilistic approximate classification are discussed which have been adapted for the analysis of a morphological table. These two related theories were used to develop experimental computer programs with the ability to learn from examples, for the analysis of dependencies between variables in a given morphological table. The developed verification programs were used for analysis of two morphological tables of different complexity and development histories. The first test was for a nine-variable table, which has been under development for approximately 15 years and has undergone many changes and corrections. The other test was performed for a 42-variable table developed only recently. The diagrams prepared reveal the learning character of the verification process and the differences between learning based on the theory of rough sets and the probabilistic theory of approximate classification. The results of the first test confirmed the expected comparable importance of individual variables, while in the second test variables were of significantly different importance and many variables could be eliminated. The proposed verification techniques still have an experimental character, but the initial results are promising. These results demonstrate that the proposed verification approach and the developed computer tools are of potential usefulness.     

单向纤维复合材料导热性预测

本文利用均匀化方法预测复合材料导热性。采用这一方法给出了单向纤维复合材料沿纤维方向的导热性表达式;将该方法与有限元技术结合得到了在垂直于纤维方向上复合材料导热性数值形式的预测结果。根据这些结果我们用曲线形式给出了材料导热性同各组分体分比间的关系,分析了体分比、纤维截面形状和分布方式、纤维和基体间的相对导热系数等因素对材料整体导热性影响。注意到纤维分布的随机性,本文还研究了纤维相对位置对材料导热性的影响,指出相对位置的变化可导致材料的各向异性导热性。本文指出基体相导热性对材料整体导热性的影响比纤维相的影响更重要。和已有的理论和实验结果的比较说明,本文提出的方法是很有效的。      

A PROBABILISTIC MODEL FOR PREDICTION OF LCF SURFACE CRACK INITIATION IN PM ALLOYS

The Low Cycle Fatigue (LCF) life of PM Ni-base superalloys is commonly reduced by surface crack initiation at ceramic inclusions. For this reason, a probabilistic model has been developed that predicts the size of surface crack initiation sites from the inclusion size distribution. For the experimental correlation of the model two sets of alloys were examined: a “standard” (i.e. as-received) alloy, and a second material of identical composition to which a known distribution of ceramic inclusions was incorporated (or seeded). Model predictions were found to be in excellent agreement with the results obtained from the seeded materials in which the defect size distribution is larger and better characterized, and were satisfactory for the unseeded material in which two types of surface defects (pores and ceramic inclusions) initiate LCF cracks. The results of these experiments were employed in LCF simulations of both test specimens and full scale components. These indicated that differences exist between the site preference for LCF crack initiation in small test specimens and large scale components due to a scale effect. Such results demonstrate the utility of seeding experiments for generation of LCF test data used in component design.