材料裂纹体J～Q断裂准则的工程化方法研究

结合现有材料裂纹体断裂参量的表达式,详细讨论了均匀材料裂纹体的J~Q 双参数准则,并对该准则中各参量的计算方法进行了简化。为了工程应用方便,进一步分析了Q 参量有限元数值解的分布规律,并曲线拟合得到了该参量的工程化计算方法,最后对工程化Q 参量计算方法在断裂参量计算中的有效性进行了讨论。     

拉弯联合载荷下弹塑性J积分估算方法研究

基于计算J积分的等效原场应力方法,利用等效原场应力σeff只有外加载荷意义而不再具有拉伸或者弯曲等载荷类型方面的属性,提出了利用现有含裂纹结构的纯拉伸以及纯弯曲J积分全塑性解直接计算拉弯联合载荷下的J积分简化估算方法。该方法可以直接利用已经存在的J积分纯拉伸和纯弯曲全塑性解来计算拉弯联合载荷下的J积分,简化了拉弯联合载荷下J积分全塑性解的计算;并且可以应用于任意应力-应变材料,包括Ramborg-Osgood关系的材料和任意单调加载非R-O关系材料。计算过程简便。并通过与有限元计算结果对比对之进行验证,说明其工程实用性,为对含裂纹结构进行弹塑性断裂评定奠定基础。     

工程结构化材料疲劳载荷谱实时测定系统的研制

介绍了工程结构化材料疲劳载荷谱的测定方法，设计了以单片机为核心的实时测定系数。对数据采集结果进行了实时压缩处理，实现了数据大量采集和存贮。同时使后续处理方便，快速，实时。数据处理从头到尾一次完成。可用于现场测试，立即显示或打印测量结果，也可用于对构件进行长期连续监测。     

工程结构化材料疲劳载荷谱实时测定系统研制

介绍了工程结构化材料疲劳载荷谱的测定方法,设计了以单片机为核心的实时测定系统.对数据采集结果进行了实时压缩处理,实现了数据大量采集和存贮.同时使后续处理方便、快速、实时.数据处理从头到尾一次完成.可用于现场测试,立即显示或打印测量结果.也可用于对构件进行长期连续监测.     

疲劳载荷下工业纯铁表面与内部裂纹长度的研究初探

疲劳裂纹扩展试验中,采用表面裂纹长度作为疲劳裂纹长度进行疲劳裂纹扩展计算和疲劳裂纹扩展模型建立的过程中,会导致计算的最终结果和模型产生一定的误差。对工业纯铁板材试样进行疲劳裂纹扩展试验,分析疲劳裂纹扩展过程中裂纹长度与裂纹扩展速率的关系,以及对疲劳裂纹扩展断口形貌特征进行观察。结果表明,上述2种方法均可来确定表面裂纹长度和内部裂纹长度之间的关系。     

超声疲劳试验中载荷频率对材料疲劳性能的影响

用超声高频疲劳试验方法获得的40Cr钢和50车轴钢的疲劳性能大于常规低频疲劳试验结果,表明超声加载频率对疲劳性能存在影响,这种影响可归因于应变速率的影响.采用一个超声加载频率修正系数对超声疲劳性能试验中载荷频率对疲劳性能的影响进行修正.超声加载频率修正系数近似等于常规低频疲劳条件下的疲劳强度系数与超声高频疲劳条件下的疲劳强度系数的比值,该修正系数也可通过不同应变速率下材料的断裂强度的比值来近似地确定.     

分布载荷作用下简支功能梯度夹层板的弯曲分析

研究了四边简支具有功能梯度芯材的夹层板在分布载荷作用下的弯曲问题。基于Reissner假设, 根据功能梯度材料的本构方程得出了应力、位移及内力的表达式, 得到功能梯度夹层板的平衡方程; 针对四边简支的边界条件, 通过将挠度 w 与横向剪力 Q_x、Q_y 用双三角级数展开的方法, 求解平衡方程。采用本文方法分别求解了均布载荷作用下、芯材弹性模量线性变化的功能梯度夹层板与芯材为均质各向同性材料的夹层板的弯曲挠度, 并通过与经典解及有限元解进行比较, 证明了本文方法的正确性。     

论几何尺寸因素对大变形时裂纹扩展J积分阻力线变化规律的影响

本文对大塑性变形条件下，裂纹稳定扩展过程的Ｊ积分阻力曲线变化规律进行了全面的分析。给出了不同的约束条件下ｄＪ／ｄａ与试样的载荷因子Ｌ、裂纹尖端张开角ＣＴＯＡ及裂纹扩展时的瞬时旋转中心的系数ｒ＾＊之间的理论表达式。从而论证了不同的约束条件下，试样的几何尺寸因素对其Ｊ阻力曲线变化趋势的影响规律。     

(Ⅰ+Ⅱ)型载荷下LY12的J积分与COD的关系

应用大应变有限元方法和断裂实验研究了铝合金LY12在（Ⅰ＋Ⅱ）型载荷下弹塑性断裂参量J积分与COD随外载荷变化规律及相互关系，结果表明：1）（Ⅰ＋Ⅱ）型下LY12的J积分和COD关系为：J＝dn·σ0·DⅠ＋ds·T0·DⅡ；J＝d·σ0．2·D．其中dn、ds、d为系数，随复合比而变，σ0、T0为裂尖屈服带上正应力和切应力、DⅠ和DⅡ为COD（D）的Ⅰ型和Ⅱ型分量；2）随Ⅱ型分量增加，LY12的起裂J积分和D值增加     

热交变载荷下10%Cr耐热钢蠕变疲劳裂纹萌生特征

为调节新能源间歇式发电模式所带来的弊端,需要使用火力发电厂调峰稳定电网波动。调峰过程中机组频繁启停,加剧高温部件的疲劳蠕变损伤。通过分析现有寿命模型描述温度交变载荷下汽轮机转子钢性能的不足,提出预载荷实验方案。且以预载荷实验数据为基础,优化现有寿命预测模型。通过模拟交变温度下的临近工况实验,对比应力应变关系和疲劳蠕变寿命,对所优化的寿命模型进行了评估。     

不同时效态3J21合金疲劳行为

在MTS万能实验机上对室温大气环境下欠时效态、峰时效态和过时效态3J21合金的疲劳行为进行研究,并采用扫描电镜(SEM)对宏观断口及微观断口进行分析.结果表明:不同时效态疲劳裂纹均呈穿晶扩展,欠时效态3J21合金疲劳裂纹萌生寿命最长,扩展途径比较曲折,扩展速率最小,表现出最大的疲劳裂纹扩展抗力,疲劳寿命最长.而过时效态3J21合金的疲劳裂纹萌生寿命最短,沿晶扩展的比例增加,扩展途径相对平直,扩展速率最大,裂纹扩展抗力最小,疲劳寿命最低;峰时效态合金介于两者之间.不同时效态的疲劳断口均由疲劳源、疲劳裂纹扩展区和瞬断区组成.在低速扩展区,欠时效态断口呈现小平面,峰时效态和过时效态断口呈现冰糖状花样,在中速扩展区均未看到长的疲劳条纹,仅发现个别细小的疲劳条纹.     

空气和腐蚀环境下双相不锈钢SAF2507的疲劳性能

对超级双相不锈钢SAF2507分别在空气和3.5%NaCl溶液中进行旋转弯曲疲劳实验,研究两种介质下SAF2507不锈钢的疲劳性能。结果表明:宏观上,双相不锈钢SAF2507在3.5%NaCl腐蚀环境中的疲劳强度较空气中的下降幅度小,为空气下的90%。但微观上,空气中疲劳断口表现为韧性断裂,在铁素体和奥氏体相上呈现大量疲劳辉纹;腐蚀环境下,奥氏体为韧性断裂,而铁素体呈现解理断裂模式。两相上疲劳辉纹的宽度和间距随着晶粒位向及二次裂纹的开裂而不同。在奥氏体-铁素体双相不锈钢的疲劳断口中,不能根据疲劳辉纹的间距进行相的鉴别。     

石油钻杆材料G105在不同条件下的疲劳断裂

采用国产PQ-6型旋转弯曲疲劳试验机研究钻杆管体材料G105的弯曲疲劳性能以及H_2S腐蚀和缺口对试样弯曲疲劳性能的影响,利用金相显微镜和扫描电子显微镜对光滑试样断口、缺口试样断口以及H_2S腐蚀后试样断口进行微观形貌分析。结果表明:在光滑试样的疲劳极限载荷作用下,经过H_2S腐蚀后的光滑试样的疲劳寿命和缺口试样的疲劳寿命相当,材料的疲劳寿命都从106降低至104;缺口试样在缺口的高应力集中效应下,加快疲劳裂纹形核过程。H_2S腐蚀对钻杆疲劳性能影响的主要作用在于氢原子在材料内缺陷处聚集引起材料疲劳性能降低,缺口和H_2S腐蚀都会加快疲劳裂纹的扩展。材料疲劳断裂主要是因为试样在交变应力的作用下上产生滑移最后致使位错塞积而导致的。     

Fatigue crack propagation under cyclic thermal stress

Structures used at elevated temperature subject to severe cyclic thermal stress. Therefore, accurate prediction procedures for thermal fatigue crack growth should be applied to rationalise component flaw assessment. Fatigue crack propagation tests under thermal stress were carried out using an modified type 316 stainless steel (316FR), which is a candidate material for the fast reactor in Japan. Thermal stress of the tests was generated by cyclically changed temperature distribution through thickness in a plate by induction heating and air-cooling. Numerical analysis was also carried out to examine the applicability of the J integral under cyclic thermal stress. The J integral under elasto-plastic condition under thermal stress is close to the elastically calculated J integral. Prediction by J integral tends to be conservative for deeper cracks, and modification of the J integral value using crack opening ratio gives good agreement with the experimental crack growth.     

疲劳研究的历史回顾

本文总结了近一个半世纪以来疲劳研究的主要历程;其中包括裂纹扩展的断裂力学发展的部分。并指出裂纹屏蔽思想是疲劳研究年谱上最新一块里程碑,疲劳研究发展至今,可以说我们刚刚进入控制裂纹扩展的大门。各种新型材料将会不断提出涉及到多种学科相关的更为复杂的疲劳问题。     

Fatigue Performance of Sandwich Beams With Peel Stoppers

Abstract:  This paper concerns a newly developed peel stopper for sandwich structures, which may be embedded as a core insert or an edge stiffener. The major purpose of the peel stopper is to prevent large debonds/delaminations between face sheets and core in sandwich structures in the case of failure. Experimental investigations of conventional sandwich beams and beams furnished with peel stoppers, under static and fatigue loading conditions, and with temperature monitoring, were conducted. The experimental programme included investigation of crack initiation and propagation, as well as of fatigue endurance of conventional and modified sandwich beams. The results showed that although the peel stoppers did not significantly influence the fatigue life of the sandwich beams, they were exceptionally effective in re-routing the crack propagation away from the face–core interface. Moreover, one of the two peel stopper designs presented prevented face–core debonding/delamination and total failure of the sandwich beams.     

Fatigue strength assessment of laser stake‐welded web‐core steel sandwich panels

This paper investigates the fatigue strength assessment of web‐core steel sandwich panels. The production of these structures is made possible by laser stake welding. The investigation in this study considered two series of panels, one being an empty steel structure and the other filled with in situ polyurethane foam in order to increase the panel stiffness. Both series were tested under cyclic bending loading condition (R = 0) until one of the panel joints failed completely. A 3D panel bending response was analysed using finite element method. The J‐integral values at the panel joints were obtained by means of plane strain finite element analysis and by using displacements from 3D panel response. The influence of the weld geometry on the J‐integral value was investigated. It was found that the J‐integral value is similar in the cases of the average and critical geometry. The contact between the joint plates is possible in some cases, but its influence proved to be insignificant for the fatigue strength assessment. The study further shows that by using the average geometry, the J‐integral approach was able to identify the critical panel joints and present the fatigue strength results from both panel series in a narrow scatterband. The fatigue strength at two million cycles obtained for the panels within this study was in agreement with the laser stake welds and other steel joint types from previous studies. However, the slope of the panels fatigue resistance curve was found to be shallower than in the case of joints.     

J‐Integral from Full Field Kinematic Data for Natural Rubber Compounds

The application of the digital image correlation technique to the determination of the J‐integral at fracture initiation for carbon black‐filled natural rubber compounds is discussed. Three different compounds with varying carbon black content were tested, using two different test configurations: pure shear and biaxial tensile test. Digital image correlation was used to measure the displacement field around the crack tip in the tested specimens. From the displacement field, which was interpolated using a finite element scheme, the stresses were evaluated by using Ogden's hyperelastic model, and the J‐integral could be calculated. The results compare well with both theoretical and finite element results.     

二次应力存在时的J积分和断裂准则

本文对二次应力存在时的修正Ｊ积分参量进行了较全面的介绍和总结，用有限元法对各修正Ｊ积分的守恒性及其相互关系进行了比较和讨论，结果表明Ｊ′积分是适用于二次应力存在的具有明确物理意义的最普遍有效断裂参量，并建立了相应的Ｊ积分断裂准则     

菱形加载路径下35CrMoA钢的微动疲劳行为EI北大核心CSCD

采用MTS809拉扭复合疲劳试验机、扫描电镜(SEM)研究了接触应力为150MPa时35CrMoA合金钢在菱形加载路径下微动疲劳性能。结果表明:随着等效应力幅值的增加,材料的软化、硬化效果更加明显;剪应力-剪应变滞后回线的面积增大;裂纹萌生源区的面积减小,瞬断区面积与总断面面积的比例增加,瞬断区的撕裂也越严重。微动磨损使表面塑性枯竭,从而形成疲劳裂纹源。