横向载荷对含表面裂纹对焊接头疲劳裂纹扩展速率影响的研究

研究了双向载荷作用下对焊接头表面裂纹的疲劳扩展规律。采用经精确标定应力强度因子幅值的双向十字形试样,在电液伺服双轴向疲劳试验机上对母材分别为16MnR 和 Q235-B 这两种钢的对焊试板进行了疲劳裂纹扩展试验。同时,将其结果分别与单向应力下对焊接头及母材的疲劳扩展速率进行了比较,为制定我国在役压力容器缺陷评定规范提供了参考数据。     

焊件疲劳裂纹扩展速率的预测

疲劳是工程中最常见的现象之一,焊件的疲劳裂纹扩展速率的研究为进行疲劳寿命预测提供了基础。本文通过对一定存活率下的疲劳裂纹扩展速率的预测回归分析,得到一个既准确又简便的方法求解 Paris 公式。     

高温下12Cr1MoV管材的疲劳裂纹扩展速率

用国产１２ＣｒＭｏＶ管材制作成紧凑拉伸试件，在ＭＴＳ疲劳系统上进行５３０℃高温下的疲劳裂纹扩展速率试验，以得出Ｐａｒｉｓ公式中的ｃ、ｎ材料参数。在ｄａ／ｄＮ及△ｋ双对数坐标图中给出了５３０℃及２０℃两种温度条件下的直线，以供对比。     

07MnCrMoVR钢焊件疲劳裂纹扩展速率

为鉴定０７ＭｎＣｒＭｏＶＲ钢焊件的疲劳性能，通过试验得到了焊接接头以及焊接热影响区的疲劳裂纹扩展速率，同时给出了它们存活率为９７．７３％时的各自疲劳裂纹扩展速率，并对焊接接头与焊接热影响区疲劳裂纹扩展速率进行比较。最后还把结果与“在役含缺陷压力容器安全评定规程”［１］和ＢＳＩＰＤ６４９３［２］推荐结果进行了对比，认为该钢种疲劳裂纹扩展速率在其容许范围内慢于１６ＭｎＲ钢的疲劳裂纹扩展速率     

有机玻璃YB-DM-11的疲劳裂纹扩展特性研究

研究了试样类型、应力比对有机玻璃YB-DM-11疲劳裂纹扩展速率、疲劳裂纹扩展平均寿命的影响。结果表明：试样类型对有机玻璃疲劳裂纹扩展速率影响很小,但紧凑拉伸试样的寿命大于中心裂纹拉伸试样;对于中心裂纹拉伸试样,当应力比为正时,应力比增大,疲劳裂纹扩展速率增加,疲劳裂纹扩展平均寿命减小;应力比为负时,裂纹闭合效应导致裂纹扩展加速;负应力比时的裂纹扩展速率大于正应力比,但疲劳裂纹扩展平均寿命明显小于正应力比。     

高温下12CrlMoV管材的疲劳裂纹扩展速率

用国产１２ＣｒｌＭｏＶ管材制作成紧凑拉伸试件，在ＭＴＳ疲劳系统上进行５３０℃高温下的疲劳裂纹扩展速率试验，以得出Ｐａｒｉｓ公式中的ｃ、ｎ材料参数。在ｄａ／ｄＮ及△ｋ双对数坐标图中绘出了５３０℃及２０℃两种温度条件下的直线，以供对比。     

疲劳裂纹扩展速率的统计分析及疲劳寿命的概率预测

通过对Ｐａｒｉｓ模型的分析,得到ｍ和ｌｏｇＣ的线性关系。试验结果的数据分析表明了ｍ和Ｃ分别符合正态分布及对数正态分布,并运用统计结果对疲劳寿命进行了概率预测。     

水介质中4340钢超高压换热器疲劳裂纹扩展速率

针对超高压换热管常用的ＡＩＳＩ４３４０钢，对表面裂纹的试板采用浸水腐蚀的方法，研究了４３４０钢在水介质中表面裂纹的疲劳扩展速率，并与空气中的扩展速率进行了比较。试验结果表明，腐蚀介质的存在加速厂裂纹扩展，并随裂纹的扩展，其加速作用越来越明显。水中存在的氧是导致腐蚀和加速裂纹扩展的主要原因。     

铸钢焊接接头裂纹扩展行为研究

简要介绍了某深水气田开发项目中出现的高强度铸钢类型,针对该材料的焊接,选用气体保护药芯焊丝开发焊接工艺。测定了焊接接头区域疲劳裂纹扩展速率及疲劳裂纹扩展门槛值,结果表明：整体焊接接头疲劳裂纹扩展性能较好,耐裂纹性能按高低顺序为焊缝>热影响区>铸钢母材。     

静态膨胀剂体积增长率的实验研究

研究了无约束状态下静态膨胀剂反应前后体积增长率随时间变化的规律。采用密度测量法,研究了不同水灰比条件下静态膨胀剂的体积膨胀率和温度在24 h内发生的变化。结果表明：水灰比越大,反应速度越快;反应开始和结束的时间随着水灰比的增大而提前,反应温度最高可达到152℃;在达到最高温度后将持续此温度7～9 h,等反应结束后再降至室温;反应过程中,体积膨胀率随着水灰比的增大而降低。静态膨胀剂反应后的体积能够达到原体积的2.2倍,但考虑到流动性要求,选择水灰比在0.25～0.35之间最合适。     

Time Dependent Crack Growth and Loading Rate Effects on Interfacial and Cohesive Fracture of Adhesive Joints

Double cantilever beam fracture specimens were used to investigate rate dependent failures of model epoxy/steel adhesively bonded systems. Quasi-static tests exhibited time dependent crack growth and the maximum fracture energies consistently decreased with debond length for constant crosshead rate loading. It was also possible to cause debonding to switch between interfacial and cohesive failure modes by simply altering the loading rate. These rate dependent observations were characterized using the concepts of fracture mechanics. The time rate of change of the strain energy release rate, dG/dt, is introduced to model and predict failure properties of different adhesive systems over a range of testing rates. An emphasis is placed on the interfacial failure process and how rate dependent interfacial properties can lead to cohesive failures in the same adhesive system. Specific applications of the resulting model are presented and found to be in good agreement when compared with the experimental data. Finally, a failure envelope is identified which may be useful in predicting whether failures will be interfacial or cohesive depending on the rate of testing for the model adhesive systems.     

Crack Tip Morphology of Slowly Growing Cracks in Glass

We present atomic force microscopy (AFM) observations of crack tips in glass during subcritical propagation. These have been obtained by means of an AFM sample holder which has been specially designed to propagate indentation cracks in glass plates. Crack tips in soda–lime–silica glass are always preceded by a few nanometers deep deformation. In vitreous silica, no other surface deformation than the crack itself could be detected. For both materials, the crack opening is found to largely exceed the elastic solution.     

基于Abaqus的O形橡胶密封圈热应力分析

建立O形橡胶密封圈平面轴对称有限元模型,采用Abaqus有限元软件的Mooney-Rivlin模型,分析O形橡胶密封圈加压后的Von Mises应力分布及温度对应力的影响。结果表明,O形橡胶密封圈应力与温度呈一次线性关系,温度变化对O形橡胶密封圈密封性能有一定影响。     

基于ABAQUS软件二次开发的橡胶疲劳寿命计算结果的可视化

基于ABAQUS有限元分析软件得到橡胶材料单轴拉伸试件的二维模型、圆柱试件的轴对称模型以及哑铃形试件的三维模型的应力-应变结果,将3种试件的应力-应变数据导入二次开发的橡胶疲劳寿命分析程序中,得到各个模型每一节点的对数疲劳寿命和裂纹扩展平面的法向角度。利用Python语言编写程序,运行并生成ABAQUS对应的输出数据库文件。结果表明,二维、轴对称、三维模型的应力分布具有一致性,即试件中部受力大,两端受力小。对于二维及三维的哑铃形试件,疲劳寿命最小值出现在试件中部;对于轴对称的圆柱试件,除试件中部较易破坏外,变形较大的上下端面的边缘位置亦容易发生破坏。3种模型的试件中部产生微裂纹后,裂纹扩展平面的法向角度均为90°,即裂纹沿试件中部且垂直于拉伸方向不断扩展,与试验结果相一致。本研究解决了二维、轴对称、三维模型的二次开发计算结果可视化的问题。     

Observations on Finger-like Crack Growth at a Urethane Acrylate/Glass Interface

Interfacial crack growth behavior along a urethane acrylate/glass interface is characterized by the development of finger-like perturbations along the advancing crack front. The finger-like perturbations grow from a slightly irregular crack front until they reach a steady-state where the velocity of the finger tips equals the velocity of the finger valleys. Once the fingers reached steady-state, the crack velocity was dependent on the applied strain energy release rate via a power law relationship where the exponent was independent of test humidity; however, the multiplicative constant A decreased by an order of magnitude from 80 to 15% RH. The spacing of the fingers was found to be independent of the crack's velocity and the relative humidity of the environment.     

Observations on Finger-like Crack Growth at a Urethane Acrylate/Glass Interface

Interfacial crack growth behavior along a urethane acrylate/glass interface is characterized by the development of finger-like perturbations along the advancing crack front. The finger-like perturbations grow from a slightly irregular crack front until they reach a steady-state where the velocity of the finger tips equals the velocity of the finger valleys. Once the fingers reached steady-state, the crack velocity was dependent on the applied strain energy release rate via a power law relationship where the exponent was independent of test humidity; however, the multiplicative constant A decreased by an order of magnitude from 80 to 15% RH. The spacing of the fingers was found to be independent of the crack′s velocity and the relative humidity of the environment.     

露天、薄壁混凝土结构温度裂缝有限元分析

对环形半下沉式钢筋混凝土结构辅助用房进行裂缝计算和有限元分析,从理论上阐述了露天、薄壁、超长钢筋混凝土结构温度裂缝产生的原因,采用混凝土温度收缩裂缝控制理论,对屋面顶板进行了简化计算。     

天然橡胶/顺丁橡胶复合材料抗裂口增长性能影响因素研究

研究炭黑的种类及用量、硫化体系、硫化条件和天然橡胶(NR)/顺丁橡胶(BR)并用比等因素对NR/BR复合材料抗裂口增长性能的影响。结果表明:当炭黑用量在一定范围内时,炭黑的种类和用量影响NR/BR复合材料的抗裂口增长性能;随着促进剂NS用量的增大或硫化时间的延长,NR/BR复合材料抗裂口增长性能变差;适当提高硫化温度或增大硫黄用量,NR/BR复合材料的抗裂口增长性能提高;NR/BR并用比、炭黑分布或硫化体系不同时,NR/BR复合材料的抗裂口增长性能都有差异性。     

Effect of Atmospheric Humidity on the Fatigue Crack Propagation Behavior of Short Cracks in Silicon Nitride

The effect of the environment on crack-growth processes in silicon nitride was studied by investigating the static and fatigue crack-growth behavior of small surface cracks, as influenced by testing (i) in the ambient environment, (ii) in distilled water, (iii) under vacuum, and (iv) in toluene. A principal finding was that testing under cyclic conditions led to crack-growth rates that were much higher in air than in toluene, whereas testing under static conditions in air or toluene led to minor differences in the rate of static fatigue crack growth. This difference in sensitivity to the environment under static and cyclic loading conditions was attributed, in part, to a much-greater extent of microcracking at the surface ahead of the main crack in air under cyclic conditions, in comparison to that in other environments. This propensity for microcracking at the surface in air under cyclic conditions also was reflected in the aspect ratios of the crack shapes that developed.