Effect ofαphase morphology on fatigue crack growth behavior of Ti−5Al−5Mo−5V−1Cr−1Fe alloy

Taking a Ti−5Al−5Mo−5V−1Cr−1Fe alloy as exemplary case,the fatigue crack growth sensitivity and fracture features with various tailoredαphase morphologies were thoroughly investigated using fatigue crack growth rate(FCGR)test,optical microscopy(OM)and scanning electron microscopy(SEM).The tailored microstructures by heat treatments include the fine and coarse secondaryαphase,as well as the widmanstatten and basket weave features.The sample with coarse secondaryαphase exhibits better comprehensive properties of good crack propagation resistance(with long Paris regime ranging from 15 to 60 MPa·m1/2),high yield strength(1113 MPa)and ultimate strength(1150 MPa),and good elongation(11.6%).The good crack propagation resistance can be attributed to crack deflection,long secondary crack,and tortuous crack path induced by coarse secondaryαphase.

基于巴西劈裂实验的层状页岩断裂特征试验研究

为揭示层状页岩巴西圆盘试件破坏强度与裂纹特征关系的机理,对圆盘试件进行劈裂试验。利用高速照相机和声发射监测装置分析了试件的破断特征及声发射特征,探讨了试件的破断机理以及破断强度的影响因素。研究表明:1)圆盘试件的裂纹起裂点通常位于试件的中部或加载端处,当层理角度较小时,试件裂纹垂直于或斜交于层理面扩展,随层理角度逐渐增大,裂纹逐渐沿层理方向扩展;2)层理方向会影响试件应力场的分布,当层理角度为0°和90°时,试件中部会产生较大的水平拉应力,试件容易产生拉伸破坏,当层理角度为45°时,试件中部会产生较大的剪应力,试件容易产生剪切破坏;3)由于裂纹表面能密度的差异性,试件的破坏强度分别与总裂纹长度和相对层理裂纹长度成正相关和负相关关系;4)试件的声发射特征与其破断模式密切相关,当试件产生张拉破断时,声发射计数表现为单峰陡增特征,当试件产生剪切+张拉复合破断时,声发射计数表现为多段增长特征。

含尖端相交裂隙岩石的破裂特征

依据相似理论选取与白砂岩性质相似的模拟材料,制作含尖端相交裂隙试样并进行单轴压缩试验,分析2条相交裂隙夹角α和α角的角平分线与水平方向的夹角β对白砂岩破坏模式、力学特性的影响。采用离散元软件PFC3D对试样进行建模,模拟试样在单轴压缩下裂纹的扩展,得到了单轴压缩作用下试样的裂纹扩展特征和起裂应力变化规律。结果表明:1)随着α角的增大,试样峰值强度逐渐降低,预制裂隙内尖端裂纹发育水平逐渐提高;2)随着β角的增大,试样峰值强度逐渐提高,预制裂隙内尖端的裂纹发育水平逐渐降低;3)物理试验与数值模拟结果吻合较好,α角对起裂应力影响较大,随着α角的增大,起裂应力逐渐减小,起裂应力的大小几乎不受β角影响。