Problems and issues in laser beam welding of aluminum–lithium alloys

Aluminum–lithium (Al–Li) alloys are very attractive for potential aerospace applications due to their lower density, higher specific strength and rigidity, better corrosion and fatigue crack growth resistance properties, compared to conventional aluminum alloys. Laser beam welding (LBW), being an advanced joining method, has already been approved for applications involving aluminum alloys. However, there are still a number of problems and issues to be answered and solved in LBW of Al–Li alloys. In this review, the properties of Al–Li alloys and the characteristics of LBW are introduced, the formation and prevention of the main weld defects such as porosity and hot cracking are discussed, and then the weld microstructure and the joint mechanical properties are described in highlight. At the end, an outlook on future trends is presented.     

相控阵双波法缺陷定量与定性

介绍用相控阵超声检测（PAUT）,借助于缺陷衍射回波信号间距和波幅比,改善对缺陷进行定量定性的方法。缺陷快速定性（分类）和准确定量（测高）对在制检测和在用检测很有实用意义。期盼此法迅速推广应用于承压设备检测。     

有限元分析不同形状腐蚀坑水冷壁管的剩余强度

基于ANSYS有限元软件,对含不同形状腐蚀坑水冷壁管剩余强度进行了研究。研究表明,将管壁上腐蚀坑简化为柱状,当腐蚀坑直径和腐蚀深度组合达到?5 mm-80%壁厚、?8 mm-70%壁厚、?12 mm-60%壁厚3种情况时,腐蚀坑直径和腐蚀深度增加则可认为腐蚀区失效;将腐蚀坑简化为球形,当腐蚀坑直径和腐蚀深度达到10H-70%壁厚(H为腐蚀深度)时,腐蚀坑直径或深度增加则可认为腐蚀区域失效;将腐蚀坑简化为矩形,当腐蚀坑尺寸和腐蚀深度达到6H-60%壁厚时,腐蚀深度和尺寸增加会造成腐蚀区域失效。相同尺寸和腐蚀深度的柱形坑、球形坑和矩形坑,球形坑最安全,柱形腐蚀坑最容易失效。     

含预制缺陷PLA蜂窝加筋结构承载力分析

目的 分析不同加筋构型及预制缺陷形式对蜂窝加筋结构抗弯承载能力的影响。方法 以热塑性PLA为基材,通过增材制造技术,制备含预制缺陷蜂窝加筋结构试件,考虑缺陷的长度、数量、深度、方向等因素,采用三点弯曲实验方式,并结合有限元仿真结果进行综合分析。结果 实验得到了结构的位移-荷载关系及破坏情况。线弹性变形阶段,实验与仿真拟合良好,该阶段内,六边构型PLA蜂窝加筋曲板结构承载能力整体优于正六边结构,但后者在后屈曲阶段的残余承载能力更好,且更不易发生断裂。相较于缺陷长度,缺陷深度和缺损肋壁数量对结构承载力的影响更为显著。缺陷方向越趋近宽度方向,结构承载能力越低。结论 实际工程中,应尽可能避免结构中间承载位置处横向加筋肋壁出现缺损,并充分利用正六边与内六边构型蜂窝加筋结构各自的承载优点。     

含缺陷车辆转向桥前梁部件极限承载规律研究

目的 研究车辆转向桥前梁在受损情况下的极限承载规律。方法 对转向桥前梁在破片高速侵彻作用下的破坏结果进行数值模拟研究,确定破片正侵彻转向桥前梁不同部位时的侵彻弹道。对含侵彻缺陷的转向桥前梁承受垂直载荷能力进行数值模拟研究。结果 确定了破片正侵彻转向桥前梁不同部位时的侵彻弹道约为圆形通孔。对于直径为1 cm的圆孔缺陷,当位于非易损区时,前梁达到极限承载时在易损区发生断裂,其极限承载能力约为无缺陷时70%;位于易损区时,前梁达到极限承载时裂纹会经过圆孔,其极限承载能力约为无缺陷时60%。以某典型车辆为例,计算得到前梁易损区圆孔缺陷直径超过1.8 cm时,前梁会在车辆的自重下发生塑性屈服。结论 转向桥前梁部件极限承载能力受缺陷尺寸和位置的影响,缺陷尺寸越大,前梁极限承载能力越小。当缺陷位于易损区时,前梁极限承载能力比同尺寸缺陷位于非易损区时更小。该结果可为转向桥功能失效分析提供参考依据。     

Phenanthrene exposure produces cardiac defects during embryo development of zebrafish (Danio rerio) through activation of MMP-9

Phenanthrene (Phe) is one of the most abundant polycyclic aromatic hydrocarbons in the aquatic environment as a result of human activities. It is widely accepted that Phe has cardiotoxic effects. Even so, knowledge concerning the mechanism(s) of cardiac development toxicity is still limited. In this study, we exposed zebrafish embryos to environmentally relevant concentrations of Phe and then investigated its cardiotoxic effects and the mechanism(s) involved. Some cardiac morphogenetic defects, which was characterized by an abnormally looped and enlarged heart, dilated and thinner ventricular wall, and increased interstitial fibrosis, were observed in the Phe treated groups. The mRNA and protein expression levels of matrix metalloproteinase-9 (MMP-9), as well as the MMP-9 activity, were induced. Moreover, during co-treatment of the zebrafish embryos with MMP-9 inhibitor, the cardiac defects caused by Phe were attenuated. In addition, Phe exposure led to an up-regulation of transforming growth factor β (TGF-β), which plays a crucial role in mediating cardiac fibrosis. Taken together, our data indicated that the exposure to Phe of zebrafish embryos disrupted normal cardiac development, and that the cardiac defects induced by Phe were mediated by the MMP-9, while TGF-β was also involved in these cardiac defects.     

铬暴露导致的秀丽线虫多重毒性的世代间比较

利用模式生物秀丽线虫(Caenorhabditis elegans)对铬(Cr)暴露导致的多重毒性及其在世代间的可传递性进行了研究.发育、生殖、运动行为、行为可塑性与寿命等方面的参数被用于多重毒性的分析.结果表明,Cr能够导致线虫出现多种表型和行为缺陷.低浓度(2.5μmol·L-1)Cr暴露即可导致发育、生殖与寿命上的严重缺陷,而高浓度(75和200μmol·L-1)Cr暴露还可以导致运动行为与行为可塑性上的严重缺陷.而且,大部分高浓度Cr暴露导致的缺陷可以从暴露当代传递到后代,使后代仍然呈现出严重的表型与行为缺陷.在这些后代中,各表型与行为缺陷只能得到有限的恢复,或没有明显的恢复.因此,就秀丽线虫而言,Cr暴露导致的各表型与行为缺陷很大程度上可以从暴露当代传递到后代个体中.