Micro/nano-scale Characterization and Fatigue Fracture Resistance of Mechanoreceptor with Crack-shaped Slit Arrays in Scorpion

The nocturnal scorpion Heterometrus petersii uses Basitarsal Compound Slit Sensilla (BCSS) as mechanoreceptor to detect mechanical signal (e.g. substrate vibration, cyclic loads caused by walking) without fatigue failure such as initiation of fatigue crack and further propagation of crack-shaped slit. The outstanding perceptive function has been discovered for over half a century. However, it is not yet clear about the microstructure, material composition and micromechanical property which are all important factors that determine the fatigue fracture resistance of the BCSS. Here, the microscopic characteristics of the BCSS were thoroughly studied. The results dicate that anti-fatigue resilin and stiff chitinous cuticle form multilayered composite as the main body of the BCSS. Meanwhile, the pre-existing slit as mechanosensory structure is covered by cuticular membrane which has different mechanical property with the epicuticle. Theoretical analysis shows that the structure-composition-property synergistic relations of composites confer on the BCSS with extreme fatigue fracture tolerance.

Si_(3)N_(4)陶瓷材料高温力学性能和断裂行为定量化实验研究

陶瓷构件常常服役于高温极端环境,易发生脆性断裂破坏。然而,关于陶瓷材料定量化的高温微观断裂研究报道较少。本文基于硅钼棒加热技术开展了Si_(3)N_(4)陶瓷材料高温维氏压痕实验,测试了惰性环境下,材料从室温至1200℃间的维氏硬度和断裂韧性,定量化表征了典型温度下的裂纹偏转和穿沿晶行为。研究表明:Si_(3)N_(4)陶瓷材料的维氏硬度、断裂韧性和杨氏模量在高温下有一定的降低,实验温度下的沿晶裂纹比例远大于穿晶裂纹比例,而裂纹偏转角分布随温度的变化不大。

木基复合材料破坏过程中声发射特性的研究

利用声发射监测系统获取了胶合板和贴面刨花板两种木基复合材料三点弯曲加载状态下断裂损伤的声发射信号。利用累计能量和振铃总计数两项声发射信号特征参量分析了胶合板和贴面刨花板损伤破坏过程及其特点;利用幅值和有效电压(RMS)研究了随挠度增大胶合板和贴面刨花板内部裂纹产生、扩展、宏观裂纹形成至断裂的过程。结果表明:声发射信号的幅值、有效电压、累计能量、振铃总计数等参量可以有效表征木基复合材料内部损伤演化过程;贴面刨花板的断裂损伤发生早于胶合板,且贴面刨花板的损伤演化过程分为线弹性阶段和断裂韧性阶段,胶合板分为线弹性阶段、非线性变形阶段和断裂韧性阶段。

混凝土材料断裂的声发射自相似性识别特征

将对材料声发射的研究，力学过程的研究，同对材料断裂损伤等破坏过程的研究相结合，提出了声发射过程的概念。给出定量考察声发射过程的自相似性特征函数。并在此基础上，根据混凝土试块的三点弯曲试验，确定出了混凝土试块断裂的声发射自相似性识别特征。

基于碳酸钙标记的水泥基材料裂缝自修复表征

为表征微生物自修复水泥基材料裂缝修复深度,提出两种微生物矿化产物碳酸钙的标记方法。一是吸附Cu^(2+)法,通过生物碳酸钙吸附Cu^(2+)在其表面形成碱式碳酸铜进行标记;二是掺杂Eu^(3+)法,通过在生物碳酸钙中掺杂Eu^(3+)形成具有发光性能的CaCO_(3)∶Eu^(3+)进行标记。采用XRD对溶液和水泥基材料中标记前后的生物碳酸钙进行分析,再利用荧光激发和发射光谱对溶液和水泥基材料中掺杂Eu^(3+)的生物碳酸钙进行分析,采用X射线计算机断层成像技术(X-CT)对两种方法标记后的水泥基材料进行表征。结果表明:在Cu^(2+)浓度为12.5 mg/mL,温度为25℃,吸附3 h的条件下,吸附Cu^(2+)标记生物碳酸钙效果最好;在Eu^(3+)掺量为2%,温度为45℃,掺杂48 h的条件下,掺杂Eu^(3+)标记生物碳酸钙效果最好。两种方法对微生物自修复水泥基材料修复深度的评价结果均为3 mm,与热重分析检测结果趋于一致。吸附Cu^(2+)和掺杂Eu^(3+)的方式均能够标定修复产物,且能准确地表征水泥基材料的修复深度。

Improved Fracture Toughness of Cryorolled and Room Temperature Rolled 6082 Al Alloys

In the present work, 6082 Al alloy has been rolled to 40% and 70% thickness reductions at the cryogenic and room temperatures for the improvement in mechanical and fracture toughness properties. All cryorolled samples are subjected to aging at different temperatures, i.e., 140, 160, and 190 ℃ to improve the strength, ductility, and fracture toughness. The microstructures of the cryorolled （CR） and room temperature rolled （RTR） alloy after 40% and 70% thickness reductions are characterized by FE-SEM to reveal the modes of failure. The results show that the starting bulk Al alloy specimen is fractured in total ductile manner, consisting of well-developed dimples over the entire surface. The mechanical properties and fracture toughness of the 70% CR alloy are found better than 70% RTR alloy due to higher dislocations density and formation of sub-grain structures in the CR alloy.

磁电复合材料的力学实验与理论研究进展

磁电复合材料同时具备铁磁、铁电性,并且具有磁电耦合效应,在新型磁电器件、自旋电子器件、高性能信息存储等领域有着广泛的应用前景,已成为目前功能材料领域新的研究热点.论文对磁电复合材料在力电磁多场耦合下的力学行为研究的最新进展进行总结和回顾.着重介绍磁电复合材料的磁电耦合效应实验以及多场耦合微纳米力学实验仪器的研制和表征方法.同时,也阐述了磁电复合材料在多场耦合本构理论、失效断裂理论以及多尺度计算方面的研究进展.最后,总结已有研究存在的不足,就目前有待解决科学问题的进一步研究提出建议.