新型机加工弹簧静压状态下的应力集中研究

新型机加工弹簧静态拉压时螺旋槽端部应力集中现象十分严重,对弹簧的强度和疲劳寿命有很大的影响.通过Ansys软件分析弹簧基本参数对应力集中的影响,确定机加工弹簧存在应力集中的理论判据;探究切向应力释放孔对压缩变形量和应力集中系数的影响;基于强度理论和曲梁弯曲理论推导了无应力集中下的最大等效应力计算公式.研究表明:中径在15 mm～35 mm之间的机加工弹簧,当螺旋槽宽度与螺距之比小于0.5时存在应力集中现象;螺旋槽端部开切向应力释放孔,控制其孔径接近对应矩形截面高度时可将应力集中基本消除;所推导公式计算的内圈等效应力值与仿真值误差不超过3％,为该弹簧后续的工程设计及应用提供了重要参考.     

材料力学辅导材料

杆的强度计算杆的特点是细长。各横截面形心的联线为杆的轴线。拉伸(或压缩)、扭转和弯曲,是杆变形的基本形式。强度条件的基本形式为:受力不超过抗力。杆的受力程空可用内力和应力表示。抗     

基于有限元的液压铰接接头拧紧力矩计算

针对基于均匀截面应力的铰接接头拧紧力矩工程计算无法充分考虑径向孔等局部结构应力集中效应,计算结果不准确的问题,建立液压铰接接头拧紧过程静强度计算有限元模型,通过在螺纹段定义固定约束,螺母与基体间定义接触约束,施加拧紧力矩及对应的螺纹预紧力载荷,模拟真实受力工况。依据线性强度计算模型下应力结果与施加载荷成正比的关系,确定材料许用应力对应的拧紧力矩,为铰接接头等存在应力集中结构的及接头类产品拧紧力矩确定和结构设计校核提供参考。     

主颚板机械强度理论计算与有限元分析研究

为了确保液压动力钳的上扣质量,针对液压动力钳主颚板的结构特点以及受力情况,利用确定结构危险截面的方法,推导出了主颚板机械强度的理论计算公式,并通过实例应用,分别采用理论计算公式与有限元分析方法进行计算,二者误差仅为3.1%,验证了理论计算公式的正确性。同时针对主颚板存在的应力集中现象,利用有限元法对不同大小的过渡圆角半径进行分析比较,发现最佳过渡圆角半径为R3mm,此时主鄂板的最大应力降低了10%,应力集中现象得以改善。     

基于有限元法的单边裂纹孔板应力强度因子

为了研究板长、圆孔半径对拉伸载荷作用下的有限宽度平板裂纹尖端应力强度因子的影响,运用ABAQUS有限元仿真软件进行数值模拟,给出了有限宽度带孔单边裂纹平板裂纹尖端应力强度因子求解方法。结果表明,板长、板内圆孔半径和裂纹长度对有限宽度裂纹平板的裂纹应力强度因子有着很大的影响。     

齿根出现裂纹与轮齿弯曲失效的标志

前言齿轮轮齿弯曲强度的失效标准是什么?有的认为齿根一出现裂纹就算轮齿失效。这是一个值得商榷的问题。齿面的软硬化的程度、交变载荷值大于、等于、还是小于疲劳极限值、在齿根处产生拉伸压缩应力的不同数值以及不同材质所具有的脉动拉伸压缩强度等等——这些都导致     

闸板T形槽受力分析

通过对闸板T形槽断裂案例分析,说明危险截面上的应力主要来自于双向偏心拉力,提出T形槽强度校核应包括弯曲剪切强度和弯曲拉伸(压缩)强度。     

轴承座装配体的有限元分析

轴承座在机械领域的运用十分广泛,基于ANSYS软件对轴承座装配体进行强度和变形分析。先通过建立模型、选择单元类型、划分网格、施加边界条件等步骤建立轴承座的有限元模型,再对轴承座进行变形和强度分析,找出结构最易破坏的位置。分析结果表明:轴承座产生的变形主要集中螺栓上和轴承座座体以及底板的连接处,最大等效应力也出现在螺栓中间部位,在筋板与轴承座接触区域存在应力集中。     

金属裂纹扩展声发射信号特性研究

机械结构件中的应力集中使得结构极易产生裂纹并逐渐扩展,裂纹扩展时伴有声发射信号,因此有必要对结构件中裂纹扩展时的声发射信号进行特征研究。为研究金属板件中的裂纹声发射源特征行为,通过分析板件中的裂纹声发射源,从理论上推导了裂纹声发射的幅值和频率特征表达式。在裂纹扩展过程中,金属板件的裂纹声发射信号幅值与声发射源的开裂长度和拉伸应力的乘积成正比,频率与裂纹开裂速度成反比,且与裂纹开裂长度成正比。用声发射检测系统对预制有初始裂纹的金属板件进行拉伸状态下的声发射监测,通过对声发射信号求取功率谱密度估计,实现不同声发射信号以功率谱在频域的分布为信号特征的有效区分。实验结果与理论分析相符合,研究结果对金属板件的裂纹声发射检测技术具有重要意义。     

基于有限元的连杆运动与静力分析

以某型号汽车连杆作为研究对象,根据其在不同工况下的具体工作情况,分析得出连杆的运动参数及其具体的求解公式;讨论连杆在工作时的主要静载荷——拉伸载荷与压缩载荷,推导并求解出其在工作过程中的受力方程。利用UG建立起连杆的三维模型,导入到ANSYS Workbench中进行静应力的有限元分析,依据其结果可知,拉应力与压应力中压应力对连杆的影响是最大的,也就是说在压缩工况下连杆有最大的应力集中和变形,同时这些的应力集中与变形均发生在连杆的小头部位。     

Uniaxial strength asymmetry in cellular materials: An analytical model

The ability to predict failure of cellular materials depends on the knowledge of microstructural mechanisms that contribute to macroscopic behavior. In this paper, we develop microstructural models to examine the mechanisms responsible for differences in tensile and compressive strength observed in cellular materials. We limit our analyses to those materials that fail by the same mechanism (yielding or microcracking) in tension and compression. Using both a honeycomb and an open-cell foam model, we demonstrate that density-dependent, compression-strong strength asymmetry arises when two conditions are met: the cell wall material has a higher yield strength in compression than in tension, and the cell walls are loaded simultaneously by axial forces and bending moments. Our models predict that strength asymmetry (defined as the ratio of compressive to tensile yield strength of the cellular material) increases with relative density (as observed in real materials such as rigid polyurethane foams and trabecular bone), and that strength asymmetry is more pronounced in anisotropic materials (where oblique struts are more closely aligned with the direction of loading).     

Effect of strength mismatch on fully plastic fields in dissimilar joints under combined loading

Via detailed finite clement limit analyses, plastic limit loads, rotation factors, and crack-tip stress field are investigated for a combined tension and bending of a plance strain single-edge-cracked bimaterial specimen. Limiting bimaterial specimens are considered, consisting of an clastic/perfectly plastic material bonded to an elastic material having the same elastic properties. The limit loads of bimaterial specimens are shown to be very close to those of homogeneous specimens, so that limit load information for homogeneous specimens can be used even for bimaterial specimens. A tractable, approximate elliptical yield locus is proposed, which first the FE. results within 1% for all ranges of tension-to-bending ratios. The plastic rotation factor of bimaterial specimens can be higher than that of homogeneous specimens as much as 25%, when the specimen is subject to small tensile forces. Results from the present analysis is applied to the analysis of typical fracture testing specimens such as compact tension specimens. For both homogeneous and bimaterial specimens, larger tensile forces are associated with substantial loss of crack-tip constrait. Bimaterial specimens have as much as 2 times higher constraint than homogenous specimens, due to plastic strength mismatch. Tractable closed form approximations for crack-tip stresses are proposed in terms of tension-to-bending ratio.     

高速列车车体结构设计及强度分析

根据高速客车车体结构的特点,设计出二等车的拖车车体。为降低车体的重量和提高车体的抗压能力,车体的钢结构采用大型中空挤压铝型材;通过刚度等效法建立车体等效模型,并对其进行有限元分析,详细分析其主要结构的应力;通过对垂向载荷工况、纵向拉伸载荷工况、纵向压缩载荷工况、气动载荷工况的分析计算,得到了车体钢结构满足强度和刚度的要求、强度薄弱部位主要表现为局部应力集中的结论。解决应力集中问题不应通过加大构件断面尺寸,而应采用降低应力集中的结构措施或局部补强,并提出了设计改进意见。     

植物纤维镁合金夹层板的制备和力学性能

以稻壳粉、秸秆粉为主要原料,添加少量玻璃纤维和石膏,以工业水玻璃为粘结剂,在160℃,1.2MPa压力下热压制备了不同配比的植物纤维夹芯,并将其与镁合金板复合制得植物纤维镁合金夹层板,并对其力学性能进行了研究。结果表明:在120℃,1.2MPa条件下可成功制备出轻质、高强度的植物纤维镁合金夹层板;夹层板的压缩性能主要取决于夹芯基料和固化工艺,添加剂的影响较小;添加适量玻璃纤维和石膏可有效提高夹层板的抗弯强度,玻璃纤维和石膏的质量分数分别为8%,5%时制得的夹层板弯曲性能最优。     

某雷达冷板双轴肩搅拌摩擦焊接工艺试验

文中介绍了某雷达MB8镁合金冷板的双轴肩搅拌摩擦焊接试验。双轴肩搅拌摩擦焊接技术对夹具设计以及应用环境的要求较常规搅拌摩擦焊接低。本试验中搅拌头转速设计为1000～1600 r／min,焊接速度设计为100～160 mm／min。通过测量冷板焊接接头处的拉伸强度和硬度,分析了焊接工艺参数对接头力学性能影响的机制。试验结果表明,MB8镁合金冷板双轴肩搅拌摩擦焊接接头处没有出现未焊透、气孔和夹杂等镁合金熔焊常见的缺陷,接头处的拉伸强度为199～211 MPa,平均拉伸强度达到母材强度的91％,接头处布氏硬度为30～39 HBS ,相比母材略有下降。试验结果说明双轴肩搅拌摩擦焊接技术非常适合用于冷板以及其他结构件的焊接。     

金属板材成形应力统一解

为了弄清材料拉压强度不相等时板材成形问题的应力解答和最大截面缩减率,根据统一强度理论,对金属板材成形问题进行分析,得出考虑中间主切应力影响和材料拉压比影响的金属板材成形应力统一解,以及反映最大截面缩减率与拉压比和中间主切应力参与系数之间关系的统一解,给出韧性金属板材成形最大截面缩减率可能的取值域.分析过程中引入一个反映金属板材拉制和压制工艺的系数,将金属板材成形问题的拉制解和压制解统一起来.当材料拉压强度相同时,金属板材成形应力统一强度理论解退化为金属板材成形应力统一屈服准则解,金属板材成形应力的Mises解是金属板材成形应力统一屈服准则解的特例.     

基于ISO 13679 B系试验载荷的特殊螺纹接头密封性能研究

为评估特殊螺纹接头的密封性能,充分考虑螺纹升角对特殊螺纹接头性能的影响,借助ABAQUS有限元软件建立某特殊螺纹接头的三维有限元模型,仿真分析ISO 13679标准B系载荷包络线加载路径下,该特殊螺纹接头密封面上的Von Mises应力及接触压力分布。结果表明:弯曲载荷对接头应力分布及接触压力分布状态影响较大;特殊螺纹接头密封面上的Von Mises应力及接触压力分布趋势一致,均为在受拉一侧Von Mises应力及接触压力数值较小,受压一侧Von Mises应力及接触压力数值较大;接头受拉一侧密封面上的接触压力随着轴向压缩载荷的增大而减小,特殊螺纹接头可能会发生密封失效。     

Unconstrained bending and springback behaviors of aluminum-polymer sandwich sheets

The bending and springback behaviors of sandwich sheets are more complicated than those of monolithic layer metallic sheet due to the extremely large difference in mechanical properties and in the gauges of polymer core and the skin sheet. In the present study, the bending and springback behaviors of aluminum-polymer sandwich sheets were investigated by using analytical method and conducting experiments and numerical simulations. A simplified analytical model was proposed to calculate the bending moments for sandwich sheet in unconstrained bending process through analyzing the strain and stress distributions of skin sheet and core materials. Then, the analytical model was applied to predict the springback of sandwich sheets after bending. Numerical simulations and experiments of unconstrained bending process for aluminum-polymer sandwich sheets were conducted to investigate the influences of mechanical properties of each layer and thickness ratio of two layers on the folding defects, neutral layer location, and springback. The results show that the neutral layer shifts dramatically toward the compression region of the specimen during bending. The folding angle mainly relates to the strength difference between the skin sheet and the core polymer. The springback angle of sandwich sheet is mainly determined by the mechanical properties of skin sheet.     

Fatigue strength depending on position of cracks for weldments

This is a study of fatigue strength of weld deposits with transverse cracks in plate up to 50 mm thick. It is concerned with the fatigue properties of welds already with transverse cracks. A previous study of transverse crack occurrence, location and microstructure in accordance with welding conditions was published in the Welding Journal (Lee et al., 1998). A fatigue crack develops as a result of stress concentration and extends with each load cycle until fatigue occurs, or until the cyclic loads are transferred to redundant members. The fatigue performance of a member is more dependent on the localized state of stress than the static strength of the base metal or the weld metal. Fatigue specimens were machined to have transverse cracks located on the surface and inside the specimen. Evaluation of fatigue strength depending on location of transverse cracks was then performed. When transverse cracks were propagated in a quarter-or half-circle shape, the specimen broke at low cycle in the presence of a surface crack. However, when the crack was inside the specimen, it propagated in a circular or elliptical shape and the specimen showed high fatigue strength, enough to reach the fatigue limit within tolerance of design stresses.     

The stress and strain concentrations of out-of-plane bending plate containing a circular hole

The elastic stress and strain fields of a finite thickness plate containing a circular hole subjected to out-of-plane bending are systematically investigated using the finite element method. It is found that the stress and strain concentration factors of the finite thickness plate are different except at the notch root of the free surface even if the plate is in elasticity state. The through-thickness distributions of strain components are not linear with the distance from the mid-plane in the stress concentration region. The nonlinearity of these distributions is very severe near the free surface especially in thick plate. The Euler-Bernoulli hypothesis and Kane-Mindlin's plate theory may not be reasonable to be used in the stress concentration region especially near the free surface. The maximum stress and strain do not always occur on the free surface and their locations depend on the moment ratio and the plate thickness. The maximum stress and strain concentration factors occur on the free surface only in thin plates of small moment ratio. The differences between the maximum value and surface value of stress concentration factor increase with the plate thickness and the moment ratio. This relation of strain concentration factor is similar to the one of stress concentration factor. But the difference magnitude of stress concentration factor is larger than that of strain concentration factor in same plate.