雷电冲击作用下土体的变形特性分析

为研究雷电冲击作用下土体的变形特性,应用冲击波理论描述雷电冲击压力,基于麦克斯韦方程推导雷电在土中产生的电磁力表达式,采用Drucker-Prager弹塑性准则,建立雷电冲击压力和电磁力作用下的土体动态变形特性有限元模型,通过瞬态计算深入探究雷击过程中土体的变形特性,并结合土中应力分布特征对变形进行动力分析,采用正交分析法研究土体力学参数对模型结果的影响以及主次因素排序,分析主要因素和雷电流峰值对模型结果的影响规律。结果表明：一定雷电冲击作用下,土体变形呈先急剧增加而后变形速率逐渐减缓,经过部分回弹后再趋于稳定,在此过程中,土中应力变化动态规律与应力波传播规律类似;土体内摩擦角和弹性模量对土体变形的影响相对较为显著,参数较小时将造成明显的变形增加,且内摩擦角的改变将影响表面土体竖向变形曲线分布规律;此外,随着雷电流峰值的增大,电磁力对土体变形的影响程度显著提升。     

三角形蜂窝的共面冲击动力学

采用有限元方法研究了冲击速度在3-250m／s的条件下,结构参数和冲击速度对三角形蜂窝共面冲击力学性能的影响．三角形蜂窝在不同冲击速度下呈现不同的变形模式,各变形模式间的转换速度随着壁厚边长比和扩展角的增加而增加．当所有结构参数保持恒定时,共面动态峰应力与冲击速度的平方呈线性关系．对于给定的冲击速度,共面动态峰应力与壁厚边长比成幂指数关系,与扩展角的关系可以用一较复杂的数学模型进行拟合．基于有限元计算结果利用最小二乘法拟合得到了共面动态峰应力关于各结构参数和冲击速度的经验关系式．     

金属空心球梯度泡沫结构抗冲击特性仿真与优化

基于有限元方法,研究不同冲击速度下面心立方排布的金属空心球(FCC-MHS)梯度泡沫结构的缓冲吸能特性.以比吸能和远端应力为目标对象,分析梯度排列次序和梯度数对结构抗冲击性能的影响.采用径向基函数方法构建FCC-MHS梯度泡沫冲击代理模型且进行多目标优化.结果显示,在冲击波效应不明显时,梯度排列次序和梯度数对FCC-MHS泡沫抗冲击性能影响有限,FCC-MHS梯度泡沫的抗冲击性能与均质FCC-MHS泡沫接近;在波效应明显的冲击速度下,梯度数多且呈负梯度排列的FCC-MHS泡沫抗冲击性能最优.优化设计能使FCCMHS泡沫的抗冲击性能更优.     

缺陷对金属蜂窝材料面内冲击性能的影响

本文使用动力有限元模型,对缺陷给金属蜂窝材料面内冲击性能造成的影响进行研究,结果表明蜂窝材料面内冲击性能与缺陷尺寸及分布位置密切相关,尤其在中低速情况下敏感性较高,而增加冲击速度能降低缺陷部分不均匀的影响,为金属蜂窝材料的实际应用提供有价值的指导.     

深部条带开采高位关键层离层区周边冲击危险性研究

近年来深部条带开采矿井发生了多起冲击地压事故.事故数据表明,在具有高位关键层的深部条带开采矿井,冲击事件分布具有一定的规律:冲击集中发生在已开采区域周边位置.通过建立关键层离层力学模型,分析了关键层极限跨度与采场尺寸的关系和关键层挠度与关键层下方煤柱压缩量的关系,探讨了高位关键层离层形成条件和离层对周边区域应力分布的影响规律,揭示了深部条带开采关键层离层区周边冲击地压发生机理.研究表明:条带煤柱在两侧采空区传递应力作用下被压缩,导致关键层离层形成应力传递结构.该结构将关键层上方岩层的载荷传递到离层区周边区域,使周边区域应力集中程度明显增加,从而导致该区域冲击地压频繁发生.关键层离层区周边冲击危险性与关键层离层跨度和关键层上方岩层厚度成正相关.研究成果对于类似条件下冲击地压防治具有指导意义.     

冲击的可靠性设计

用能量法求冲击应力和冲击变形.并将应力强度干涉模型运用于冲击问题,讨论了冲击的可靠性设计.     

冲击的可靠性设计

用能量法求冲击应力和冲击变形．并将应力强度干涉模型运用于冲击问题，讨论了冲击的可靠性设计．     

冲击的可靠性设计

用能量法求冲击应力和冲击变形，并将应力强度干涉模型运用于冲击问题，讨论了冲击的可靠性设计。     

弹丸冲击速度对带钢表面鳞层破坏行为影响

为了有效提高抛丸除鳞效率,本文建立了单弹丸除鳞模型。利用有限元数值计算了弹丸冲击速度对鳞层破坏面积、基体塑形凹坑及残余应力的影响行为。结果表明:鳞层在很小的速度(5 m/s)冲击下即可发生破坏,弹丸冲击速度越大除鳞面积越大,同时也会造成基体应力/应变增加。弹丸冲击下鳞层失效区域由两部分构成,分别为弹丸冲击引起的直接失效区域与铁基体形变传递引起的间接失效区域,后者呈星状拓展。基体残留的塑性凹坑深度与冲击速度大致呈一次线性关系。现场实际生产中,应在满足表面粗糙度与残余应力要求的基础上选择较大的冲击速度。     

机械设计中的冲击和冲击失效

介绍了冲击对机器构件的影响,给出了在冲击载荷作用下计算应力和变形量的能量法,并通过计算实例对冲击进行了定量分析。     

多孔泡沫金属抗侵彻能力研究

对泡沫金属材料的动态力学性能及抗侵彻能力的研究成果进行了综述.描述了冲击载荷作用下的变形机理,并分析了影响其抗侵彻能力的主要因素.最后对泡沫金属材料的研究趋势做出展望.     

Failure analysis of wear of main clutch separating ring of heavy vehicles

The severe wear of separating ring is considered to be a main reason which leads to the improper declutch of the main clutch of heavy vehicles. The wear mechanism of the separating ring is not well understood. Scanning electron microscopy and transmission electron microscopy were employed to analyze the surface features and dislocation characteristics of the separating ring. The typical features of furrows and rolled tongue-like metal were found on the surface of separating ring by scanning electron microscopy observation, which can be considered as a major indi cation of the grain-abrasion. A zone of high density dislocation was noted on the subsurface of the separating ring by transmission electron microscopy observation, which implies the contribution of the severe impact on the surface of the separating ring in the wear process. The influences of the structure of the separating ring, the service condition and the in-service stress distribution on the wear behavior, were also analyzed. The results show that the failure of separating ring results from the impact wear and grain-abrasion together with the plastic deformation.     

大跨越输电塔电梯井道在静风载荷下的受力分析

以某大跨越工程为背景,利用ANSYS有限元分析软件对大跨越输电塔及其电梯井道进行了受力分析,得到电梯井道在承受风载荷情况下的受力及变形情况,结果验证了此大跨越塔的设计符合规范的要求.     

Deformation division of metal flow behavior during extrusion process of 7075 aluminum alloy

To reduce defects caused by non-homogeneous metal flow in conventional extrusion, a die with guiding angle was designed to improve the metal flow behavior. The characteristic quantities such as the second invariant of the deviator stress J ₂ and Lode’s coefficient μ were employed for the division of deformation area. The results show that when the metal is extruded with the guiding angle, no metal flow interface forms at the container’s bottom, the dead zone completely disappears, the deformation types of the metal in the plastic deformation area change from three types to one type of tension, and the homogeneity of the deformation as well as metal flow are greatly improved. The non-homogeneous metal flow at the final stage of extrusion is improved, reducing the shrinkage hole at the axis end. The radial stress of the furthest point from the axis is transformed from tensile stress to compressive stress and the axial stress, and decreased from 70.8 to 34.8 MPa. Therefore, the surface cracks caused by additional stress are greatly reduced.     

Failure analysis of wear of main clutch separating ring of heavy vehicles

The severe wear of separating ring is considered to be a main reason which leads to the improper declutch of the main clutch of heavy vehicles. The wear mechanism of the separating ring is not well understood. Scanning electron microscopy and transmission electron microscopy were employed to analyze the surface features and dislocation characteristics of the separating ring. The typical features of furrows and rolled tongue-like metal were found on the surface of separating ring by scanning electron microscopy observation, which can be considered as a major indication of the grain-abrasion. A zone of high density dislocation was noted on the subsurface of the separating ring by transmission electron microscopy observation, which implies the contribution of the severe impact on the surface of the separating ring in the wear process. The influences of the structure of the separating ring, the service condition and the in-service stress distribution on the wear behavior, were also analyzed. The results show that the failure of separating ring results from the impact wear and grain-abrasion together with the plastic deformation. Foundation item: Project(41327040101) supported by the Pre-research Fund of General Armament Department; project(51489010104QT0101) supported by the Fund of State Key Laboratory of Re-manufacture Technology     

Experimental investigation on the yield behavior of metal foam under shear-compression combined loading

Metal foams are typically subjected to quasi-static or dynamic shear-compression combined loading in applications such as energy absorbers and structure protectors. The yield behavior of a metal foam under dynamic and quasi-static shear-compression combined loadings is investigated in this study. First, quasi-static and dynamic compression-shear combined tests at different loading angles are conducted using a universal testing machine and a rotatable Hopkinson bar system, respectively. Shear deformation reduces the plateau stress as the loading angle increases. Subsequently, the yield modes of the metal foam under combined loadings are investigated. Only one yield band occurs under a combined loading with large loading angles(mode I),whereas several yield bands occur under a combined loading with small loading angles(mode II). Finally, the yield surface plot of metal foam indicates significant enhancement in terms of normal stress and shear stress under dynamic loading. Quasi-static and dynamic phenomenological yield criteria for a shear-normal stress space are established to provide a brief and precise prediction of the behavior of metal foam under quasi-static and dynamic combined loadings.     

非轴对称零件挤压过程的上限元分析

推证矩形截面齿形零件及梯形截面齿形零件挤压的体积不变方程和速度场方程。并运用上限元法模拟金属成形过程和两种非轴对称挤压零件成形过程的变形力及金属流动;分析各种工艺参数对成形过程的影响,探讨工艺参数优化设计问题。模拟结果与实验进行了比较,两者表现出良好的一致性。     

芳纶层压复合材料靶板的点冲击破坏模式

利用Hopkinson压杆技术研究了层压复合材料靶板的动态点冲击响应行为 ,完整地检测了整个冲击过程 ,考察了冲击力和冲击点速度随时间变化的规律 ,研究了靶板变形与破坏模式。     

机车轮对加装扣环方案的有限元分析

利用ANSYS软件，对机车轮对进行了应力、变形的非线性分析，并对轮箍加装扣环前后其配合面内的接触应力分布进行比较；详细讨论了直线持续牵引工况中，轴重、牵引力、水平侧向力等对机车轮对应力分布的影响，模拟分析了在加载作用下，加装扣环前后轮对配合面的应力分布情况。通过分析计算，确定了机车轮对轮箍加装扣环方案对轮对的强度的影响。