基于应力应变实验的有限元分析结果验证

针对焊接机器人实际工况的复杂性,采用ANSYS对焊接机器人关键部件进行有限元分析,并在此基础上设计了应力应变实验对有限元分析结果进行验证。验证结果显示,实验数值与有限元分析值存在0.47%~29.36%的误差,但曲线的变化趋势是一致的,说明有限元仿真建模在边界条件、网格划分、载荷施加等方面的设置具有合理性,结果也较为可靠。对误差产生的原因进行了分析,为后续焊接机器人结构优化奠定了基础。

基于拓扑优化的变截面铸造式动臂结构设计

研究发现,装载机传统板式动臂存在较大程度的强度和材料冗余现象。这里以某5t装载机为载体,以轻量化为目标,对动臂进行了结构优化。结合结构拓扑优化基本原理,在对原动臂有限元分析和拓扑优化的基础上,提出并设计了一种新型变截面铸造式装载机动臂结构,运用Ansys对优化动臂进行有限元强度验证,并通过应力应变实验验证仿真模型的正确性。仿真和实验结果表明,在满足结构刚度和强度条件下,动臂质量较优化前1035kg减重19.7%,达到了轻量化的目标。

人眼角膜基质生物力学特性研究

目的了解正常人眼角膜基质的生物力学特性,初步获得相对正常角膜组织生物力学相关参数。方法使用全飞秒激光小切口角膜基质透镜取出术术中获取的角膜基质透镜,根据实验需要裁切成角膜基质组织试件,在常温和水浴条件下,分别进行应力-应变实验、蠕变实验和应力松弛实验,初步得到新鲜角膜基质组织的应力-应变曲线、蠕变曲线和应力松弛曲线,以评估人眼角膜基质的生物力学特性。结果低应变区切线模量为(1.32±0.48)MPa,高应变区切线模量为(51.26±8.23)MPa,断裂点应变为(0.52±0.06)mm·mm-1,断裂点应力为(13.00±2.51)MPa。在应力为0.01 MPa、0.02 MPa、0.03 MPa时,角膜基质试件弹性模量分别为(0.89±0.25)MPa、(1.28±0.21)MPa、(1.69±0.18)MPa。在1.00 N恒定载荷下,角膜基质试件形变随时间延长而增大,早期变化较快,后期逐渐变缓,600 s时蠕变率为(4.57±1.67)%。维持角膜基质试件长度至初始长度的1.5倍,应力随着时间的延长逐渐衰减,早期衰减较快,随着时间的延长衰减趋于平缓,1 h时松弛率为(28.49±0.04)%。结论初步得出正常角膜基质组织的生物力学参数,可为进一步深入研究角膜的生物力学特性提供一定的理论参考。

软岩渗流规律研究进展

在前人研究的基础上,介绍了软岩的概念和分类,指出按成因可将软岩分为原生软岩和次生软岩;从流固耦合的角度讨论了软岩渗流的数学模型、实验分析和数值模拟的研究现状;从应力与裂隙的相互作用关系方面分析了软岩和硬岩渗透性差异的理论原因。最后针对软岩渗流的研究工作和实际工程问题提出了一些展望。

温-压耦合作用下深层盐岩盖层封闭能力演化特征

为了研究温-压耦合作用对盐岩盖层封闭能力演化的影响,选择中国金坛盐洞的盐岩样品,利用高温-高压三轴岩石力学测试系统实验装置,设计开展恒温变压、恒压变温以及温-压耦合3组实验,模拟温度、压力条件对盐岩盖层封闭能力演化的影响。研究结果表明:①温-压耦合作用导致盐岩短期强度大幅减弱,塑性大幅增强,缩短了脆-塑性转化时间,其中,由温度引起的盐岩短期强度降低百分比(T_(i))大于35.06%;压力引起的盐岩短期强度降低百分比(p_(i))最大只有38.25%,表明埋藏过程中,盐岩力学性质主要受控于温度。②单一压力作用下,盐岩裂缝具有逐渐减少、愈合的趋势;而温-压耦合作用下,盐岩会出现“裂缝再次发育”现象,其中,低温阶段(温度<90℃),压力占主导地位,高温阶段(温度≥90℃),温度占主导地位,盐岩出现蠕变损伤。③建立“深层盐岩”“脆性—脆-塑性—塑性—蠕变损伤—损伤愈合”演化模式,其中,蠕变损伤阶段对于盐下油气藏的保存极为不利。因此,准确厘定盐岩封闭能力的演化特征可为深层盐下油气藏的富集规律分析提供理论依据。

Changes of Stress-Strain Relationship of Rabbit Femoral Vein after Simulated Weightlessness

Objective: To observe the effect of simulated weightlessness on stress-strain relationship and the structural change of rabbit femoral vein. Methods: After seting up the Head-Down Tilt (-20°) (HDT) model to simulate weightlessness, 24 healthy male New-Zealand Rabbits were randomly divided into HDT-21d group, HDT-10d group and control group, with 8 in each. Femoral venous strips and rings were used to make uniaxial tensile test of the longitudinal and circumferential specimens of the vessels. At last we observed the microstructure of femoral vein wall in 3 groups. Results : With the increasing of load stress, both longitudinal and circumferential strains of vein samples from 3 groups increased significantly (P<0. 01). With the decrease of unload stress, strains decrease obviously (P<0. 01). The unloaded longitudinal and the circumferential strain from 3 groups increased much than those of the loaded. Under the same stress (longitudinal 0-2. 0 g, circumferential 0. 5-1. 0 g) , HDT-21d group and HDT-10d group increased obviously in tlie longitudinal or circumferential strain (load and unload) than control, and HDT-21d increased much than that of HDT-10d. The contents and structures of femoral vein walls of HDT-rabbits changed significantly. Some endotheli-um cells of femoral vein became short, columnar or cubic even fell off. Smooth muscle layers became thinner. Conclusion:The compliance of femoral venous increased significantly after weightlessness-simulation and increased much obviously after 21d-HDT than that of 10 d. The structure of femoral vein wall changed obviously. The changes may be one reason for the increase of femoral vein compliance.

Effect of Engineering Character on Stress-Strain Relationship in Post-Peak Area

Constitutive experiments are the base of all rock mechanics works. The effect of engineering character on constitutive law is a new problem of rock mechanics. The results of series specimens based on the uniaxial and plane strain compression experiments were presented and discussed. It is found that engineering or experiment character has obvious effects on stress-strain relationship and especially on mechanic parameters in post-peak area. And the law of size effect of softening materials was also discussed.

An experimental study on stress-strain behavior and constitutive model of hardfill material

Hardfill is a new type of artificially cemented material for dam construction works,with a wide application prospect.Its mechanical behavior lies between concrete and rockfill materials.A series of large-scale triaxial tests are performed on hardfill specimens at different ages,and the stress-strain behavior of hardfill is further discussed.The strength and stress-strain relationship of hardfill materials show both frictional mechanism and cohesive mechanism.An age-related constitutive model of hardfill is developed,which is a parallel model consisting of two components,rockfill component and cementation component.Moreover,a comparison is made between the simulated and the experimental results,which shows that the parallel model can reflect the mechanical characteristics of both rockfill-like nonlinearity and concrete-like age relativity.In addition,a simplified method for the determination of parameters is proposed.