波纹管疲劳寿命可靠性分析

波纹管是典型的低周疲劳部件,用局部应力应变法预测其疲劳萌生寿命可行且精确,考虑到影响疲劳寿命的诸多因素的随机性,将应变寿命曲线表示为概率曲线,并考虑累积损伤的随机性,通过建立近似拟合多项式方法求得各设计寿命下的波纹管的可靠度曲线,该方法是简单有效的波纹管疲劳寿命可靠度计算方法。     

一种采用遗传算法优化Chaboche模型的转子轮盘疲劳寿命预测方法

针对汽轮机一体化联合转子的抗疲劳设计，研究了一种采用遗传算法优化Chaboche模型参数的方法，并结合局部应变法进一步建立起考虑平均应力动态松弛的转子轮盘疲劳寿命预测方法。结合某型转子轮盘的疲劳寿命预测，开展了轮槽材料在应变比R=0下的低周疲劳试验与轮槽构件的疲劳试验。结果表明：经参数优化的Chaboche模型能够较好地模拟轮盘材料在各种应变幅下的滞回环形状和平均应力松弛行为，由此建立的寿命预测方法可显著提高轮槽构件的疲劳寿命预测精度，在研究条件下，预测寿命与试验值位于二倍分散带之内。     

U形波纹管膨胀节强度分析

本文采用细环壳理论推导波纹管的弹性解析解与Anderson,浜田—竹园解极为一致,且与应力电测结果相符。利用曲梁模型,考虑了U形波纹管的应变集中,导出了疲劳寿命预测式,实验证明了其正确性。     

橡胶与塑料材料的疲劳裂纹处理方法

预测疲劳裂纹形成方法认为寿命取决于特定数值的应力或应变历程。疲劳裂纹形成寿命可定义为产生一定尺寸裂纹所需的循环次数。材料疲劳强度试验预测部件疲劳寿命的难点在于所施加的应力和应变本质上通常是多轴的,单轴拉伸疲劳和能量释放速率在这方面的应用价值是有限的。按照研究的目的,可简单地评估不同材料的相对疲劳性能,作为包括长期老化影响在内的总体测试项目的一部分。对于部件寿命预测,在工作环境条件下应尽可能用实际大小或按比例缩小的模型进行。     

抽油机井油管接头有限元分析与寿命预测

对油管接头进行了在循环拉伸载荷作用下的弹塑性接触有限元分析 ,给出油管接头在循环载荷作用下所表现出的力学特性 ,特别是应力应变集中部位 (第 1啮合齿齿根 )的应力应变循环规律以及应力应变幅。采用局部应力应变分析法 ,对油管接头进行疲劳寿命的预测 ,证明J5 5材料、公称锥度上扣 1.5、1.75和 2圈的油管接头在循环拉伸载荷 6 0～ 12 0kN作用下 ,疲劳裂纹萌生期的寿命都达到了 3年以上     

一种压力容器常用钢疲劳及疲劳蠕变寿命预测方法

基于应变能密度理论,并以半寿命等效应变能密度作为控制参量,提出一种新的应力控制寿命预测方法。该方法不仅考虑了疲劳诱导的累积塑性损伤,同时考虑了循环蠕变和静蠕变诱导的延性耗竭损伤。通过三种低合金钢室温及高温、连续疲劳及带保载时间的疲劳蠕变试验验证,预测效果都较好,寿命预测精度基本在±2倍比例因子以内,且能定量反映疲劳、循环蠕变和静蠕变对材料损伤的贡献,此方法适用于应力控制模式不同条件下的疲劳及疲劳蠕变交互作用寿命预测。     

单向Cf/SiC复合材料的弯曲疲劳性能

对单向Cf/SiC复合材料进行了三点弯曲疲劳性能测试,得到了复合材料的应力－寿命曲线（S－N曲线）,并对其进行线性拟合,得到疲劳最大应力与复合材料疲劳寿命的关系;考察了疲劳过程中刚度下降和疲劳裂纹产生情况。结果表明在疲劳过程中复合材料的弯曲模量有3个变化阶段：首先在疲劳加载初期,弯曲模量的下降速度及幅度都较大;其次在弯曲模量下降到原始弯曲模量的85％（133GPa)后,其变化方式没有明显的规律可循,有时甚至可能上升;最后复合材料发生疲劳断裂时,模量将发生突变。显微结构分析表明：基体横向裂纹群的产生是疲劳断裂的独有特征。它的产生是由于基体SiC的断裂应变小于碳纤维的断裂应变,基体首先开裂并导致应力重新分布的结果。     

压力容器焊接接头疲劳裂纹萌生寿命的探讨

对 1 6Mn R焊接接头进行了控制应变幅条件下的疲劳试验 ,获得其疲劳特性参数以及恒应变幅载荷下的疲劳—寿命关系 ,建立了焊接接头低周疲劳寿命曲线方程 ,并将试验结果同局部应力应变法计算的结果进行了比较 ,为该焊接接头应变疲劳研究提供了理论依据     

压力容器焊接接头疲劳裂纹萌生寿命的探讨

本文对16MnR焊接接头进行了控制应变幅条件下的疲劳试验，获得其疲劳特性参数以及恒变变愠载荷下的疲劳－寿命关系，建立了焊接接头低周疲劳寿命曲线方程，并将试验结果同局部应力应变法计算的结晶进行了比较，为该焊接接头应变疲劳提供了理论依据。     

发动机橡胶悬置疲劳寿命的研究进展

针对橡胶悬置疲劳寿命预测的研究,综述国内外橡胶材料及橡胶元件疲劳寿命预测方法及其发展。橡胶悬置疲劳寿命的预测方法主要分为裂纹萌生法和裂纹扩展法。裂纹萌生法中,相对于应变和应变能密度,等效应力为损伤参量建立的橡胶疲劳寿命预测模型更适用于橡胶悬置疲劳寿命预测;应用裂纹扩展法建立的橡胶疲劳寿命预测模型能较好地预测橡胶悬置疲劳寿命;与裂纹萌生法相比,裂纹扩展法可预测橡胶悬置的裂纹方向,对工程实际有更好的指导意义。     

桥梁用钢14MnNbq焊接接头的疲劳设计曲线

通过对 14Mn Nbq钢焊接接头的疲劳试验 ,得到了循环应力 -应变方程、应变寿命曲线以及疲劳设计曲线 ,并将 14Mn Nbq钢焊接接头疲劳设计曲线与 ASME、BS5 5 0 0中相应的曲线进行了比较。     

Assessment of the fatigue life of aluminium spot-welded and weld-bonded joints

In modern machinery and automobile structures weight reduction and increased durability are the main issues in design. In these applications, lap welded and/or bonded joints are widely used; therefore, tools are needed to accurately predict their fatigue life. This paper is concerned with the fatigue strength of single lap joints formed with thin plates of 6082-T6 aluminium alloy using a high strength two-component epoxy adhesive (Araldite 420 A/B from Hunstman). Experimental S–N curves were obtained for resistance spot-welded and weld-bonded lap joints. The fatigue lives of weld-bonded joints were significantly higher than those of resistance spot-welding joints. In addition, fatigue lives were predicted with Morrow's modified Manson–Coffin (M/M–C) and the Smith–Watson–Topper (S–W–T) damage equations. Elastic–plastic numerical models were developed, replicating the experimental work, in order to obtain local stress and strain fields. An acceptable agreement was obtained between the numerical predictions and the experimental results. The M/M–C damage equation diverged from experimental results for relatively long fatigue lives, while the S–W–T equation gave good predictions for all fatigue lives.     

A Backface Strain Technique for Detecting Fatigue Crack Initiation in Adhesive Joints

A new backface strain technique was developed to detect fatigue crack initiation in adhesive-bonded lap joints. The technique was based on the special strain distribution in single lap joints and detected the fatigue crack initiation by the switch in the direction of the strain variation. Use of this technique not only permits the determination of fatigue crack initiation life in the joint, but also allows the site of crack initiation to be located. With the assistance of this new backface strain technique, a fatigue crack was found to initiate in the adhesive but to propagate towards the interface to continue its growth on the interface and to cause the final separation of the joint along the interface. Measurements of fatigue crack initiation lives at different stress levels indicate that the adhesive-controlled crack initiation took an increasingly greater proportion of the total fatigue life as the stress decreased, so that the lifetime in the long-life regime was dominated by the resistance of the adhesive to fatigue crack initiation.     

波纹管换热器若干设计问题的分析

通过对波纹管换热器设计过程中遇到的一系列有别于普通列管换热器的技术问题,如管板设计计算、膨胀节的设置分析、折流板间距与厚度、波纹管的稳定性以及技术要求等结构设计计算与使用要求问题进行分析,得到了较为完整的一套波纹管换热器的结构设计方法。     

Fatigue Behaviour of Adhesive Bonded Joints

This paper presents experimental results of the fatigue behaviour of adhesive bonded plastic-to-plastic joints and metal-to-plastic joints under both dynamic and static loading. The fatigue life of the joints was found to be independent of the test frequencies and humidity for the range of values tested, but dependent on the mean stress level and test temperature with greater reduction in fatigue life observed in metal-to-plastic joints at higher temperature. Empirical equations from which the fatigue life of joints could be predicted were obtained by regression analysis.     

Failure behavior of adhesively bonded joints with a rubber modified epoxy adhesive under tensile-shear combined cyclic loading

Rubber-modified epoxy adhesives are used widely as structural adhesive owing to their properties of high fracture toughness. In many cases, these adhesively bonded joints are exposed to cyclic loading. Generally, the rubber modification decreases the static and fatigue strength of bulk adhesive without flaw. Hence, it is necessary to investigate the effect of rubber-modification on the fatigue strength of adhesively bonded joints, where industrial adhesively bonded joints usually have combined stress condition of normal and shear stresses in the adhesive layer. Therefore, it is necessary to investigate the effect of rubber-modification on the fatigue strength under combined cyclic stress conditions. Adhesively bonded butt and scarf joints provide considerably uniform normal and shear stresses in the adhesive layer except in the vicinity of the free end, where normal to shear stress ratio of these joints can cover the stress combination ratio in the adhesive layers of most adhesively bonded joints in industrial applications.

In this study, to investigate the effect of rubber modification on fatigue strength with various combined stress conditions in the adhesive layers, fatigue tests were conducted for adhesively bonded butt and scarf joints bonded with rubber modified and unmodified epoxy adhesives, wherein damage evolution in the adhesive layer was evaluated by monitoring strain the adhesive layer and the stress triaxiality parameter was used for evaluating combined stress conditions in the adhesive layer. The main experimental results are as follows: S–N characteristics of these joints showed that the maximum principal stress at the endurance limit indicated nearly constant values independent of combined stress conditions, furthermore the maximum principal stress at the endurance limit for the unmodified adhesive were nearly equal to that for the rubber modified adhesive. From the damage evolution behavior, it was observed that the initiation of the damage evolution shifted to early stage of the fatigue life with decreasing stress triaxiality in the adhesive layer, and the rubber modification accelerated the damage evolution under low stress triaxiality conditions in the adhesive layer.