路面对悬架螺旋弹簧激励的仿真及载荷谱编制

在MATLAB/Simulink平台下模拟了汽车悬架螺旋弹簧在数种工况下的最大切应力-时间历程,经采用雨流计数方法处理,建立了载荷幅值、均值和相应频次的关系,利用数理统计的方法得到了各工况的分布数学模型,并建立了载荷幅值和均值的联合分布,得出了多工况下悬架圆柱螺旋弹簧的全寿命里程二维疲劳载荷谱。     

基于有限元的多股螺旋弹簧疲劳寿命预测

针对多股螺旋弹簧(多股簧)的疲劳失效问题,以阿联酋某企业使用的特种多股簧为研究对象,通过有限元仿真分析多股簧的应力应变历程并利用子模型技术进行了应力应变的精确计算,通过静态响应试验验证了有限元模型的正确性;进行了钢丝材料试验,结合Manson模型推导出多股簧材料的疲劳性能参数;结合多股簧的应变和疲劳寿命预测模型预测了多...     

多轴随机应变加载下铝合金缺口件有限元分析及寿命预测

在应变控制下对7075-T7451铝合金实心棒带U型环状缺口试件进行拉—扭比例、非比例恒幅和随机加载疲劳试验。查明名义剪切应力最大值与轴向应力最大值的下降规律,并用两者最先开始下降时的循环数比值来评估裂纹萌生寿命。利用弹塑性有限元法分析不同加载条件下试件缺口根部的循环应力、应变响应。基于有限元计算得到的应力、应变结果,采用拉伸型多轴疲劳损伤模型预测随机加载条件下缺口试件的疲劳裂纹萌生寿命,计算结果与试验得到的寿命比较吻合。     

超高强度钢十亿周疲劳研究

利用20kHz压电超声疲劳试验技术，对六种抗拉强度高于1500MPa的低合金钢进行测试。结果表明，这些材料并不存在传统规范中所谓的“疲劳极限”，它们在超过10^7，甚至10^9应力循环后仍然继续发生破坏，而且其S－N曲线表现出“阶梯”型特征。研究还发现，这些材料都存在一个分界应力幅值区间（或应力循环数区间，大约在10^6到10^7的平台内），裂纹萌生由试件表面向其内部转换。实验证明了十亿周级超高周疲劳裂纹由试件内部萌生的机理。     

On the natural frequencies of helical compression springs

The linearized disturbance equations governing the resonant frequencies of a helical spring subjected to a static axial compressive load are solved numerically using the transfer matrix method for clamped ends and circular cross-section to produce frequency design charts. The effect of varying the number of turns of the spring is investigated, and in the limit of large numbers of turns, our results validate earlier work on the vibration of helical compression springs in which the helix was modeled as an elastic beam with rigidities corresponding to those of unclosed circular rings.     

VOLUME DEFECT FATIGUE FAILURE OF CERAMIC BALLS UNDER ROLLING CONDITION

A newly developed pure rolling fatigue test rig with three contact points is used to test the rolling contact fatigue properties of silicon nitride ceramic balls. Ball surfaces are examined after failure with optical microscopy and scanning electron microscopy. The failure cause,fatigue phenomenon and mechanics are analyzed. The research shows that subsurface cracks play a dominant role in the formation of spalling failure. These cracks originated from volume defects of the material and propagate,to form elliptical fatigue spalls under the action of principal tensile stresses. The principal tensile stress increases with increasing contact load,causing spall formation and reduction of rolling contact life. The greater the principal tensile stress is,the more severe the peeling of near surface is. Under the same condition,the closer volume defects are to the surface,the more likely failure occurs,the shorter the rolling contact life is.     

Effect of overloads on fatigue crack propagation within molded parts of railroad constructions

To determine the regularity of fatigue crack propagation during cyclic loading with tensile overloads, a method of the estimation of the effective stress ratio of loading cycles, which is equivalent to the rate of crack propagation by the diagram of fatigue failure, is proposed. Thereby, the relation between the diagram of the fatigue failure and the phenomenon of crack retardation after tensile loads, which is complicated by its physical nature, is established. The experimental-computational studies were carried out on 20гΦЛ steel of a bogie bolster of a freight car.     

The effects of laser peening and shot peening on fretting fatigue in Ti-6Al-4V coupons

This paper describes testing of Ti-6Al-4V coupons in fretting fatigue and compares the effects of mechanical surface treatments on performance. Fretting fatigue tests were performed using a proving ring for fretting load, bridge-type fretting pads, and applied tension-tension cyclic fatigue stress. As-machined (AM), shot peened (SP), and laser peened (LP) coupons were evaluated, and data generated to compare residual stress, surface condition, lifetime, and fractographic detail encountered for each. Near-surface residual stress in SP and LP coupons was similar. The layer of compressive residual stress was far deeper in LP coupons than in SP coupons and, consequently, subsurface tensile residual stress was significantly greater in LP coupons than in SP coupons. SP coupons exhibited a rough surface and had the greatest volume of fretting-induced wear. LP coupons exhibited a wavy surface and had a small volume of wear localized at wave peaks. SP coupons had the greatest fretting fatigue lifetime, with significant improvement over AM coupons. Lifetimes of LP coupons were similar to those for SP coupons at high fatigue stress, but fell between AM and SP coupons at lower fatigue stress. Fractographic evaluation showed that fractures of AM samples were preceded by initiation of fretting-induced cracks, transition of a lead fretting crack to mode-I fatigue crack growth, and crack growth to failure. SP and LP samples exhibited behavior similar to AM samples at high fatigue stress, but in coupons tested at low stress the lead crack initiated subsurface, near the measured depth of maximum tensile residual stress, despite the presence of fretting-induced cracks. The level of fatigue stress above which lead cracks were initiated by fretting was higher for LP than for SP, and was predicted with good accuracy using an analysis based on linear elastic fracture mechanics, the fatigue crack growth threshold stress intensity factor range, and superposition of measured residual stress and applied fatigue stress.     

铝合金点焊拉剪接头疲劳性能及寿命分析

研究了铝合金AA5754点焊拉剪接头的疲劳性能,获得了不同厚度试件的载荷寿命曲线。研究了铝合金焊点的疲劳失效模式,讨论了焊点疲劳裂纹的扩展形式,并测量了裂纹扩展路径与点焊熔核界面之间的角度。分析了点焊拉剪试件在同时承受I型和II型载荷时,疲劳裂纹的扩展方向,并与测量值进行了比较。利用疲劳破坏后沿铝板厚度方向的实际裂纹长度修正了裂纹尖端的局部应力强度因子,提出了评价焊点寿命的疲劳参量K(i),并对试验数据进行了分析比较。结果证明K(i)可以有效关联试件尺寸效应和焊点疲劳寿命,能够用于预测焊点疲劳寿命。     

球墨铸铁疲劳裂纹扩展的微观机制

研究了在恒幅拉伸循环载荷作用下球铁的疲劳裂纹扩展的微观机制，分析了石墨形态对铸铁疲劳裂纹萌生及扩展行为的影响。结果表明：铸铁的石墨形态对疲劳裂纹的萌生及扩展有很大影响。灰铁由于在共晶团内石墨片相互连接，疲劳裂纹总是沿着与外应力相垂直的石墨片／基体边界扩展。球铁的疲劳裂纹扩展受基体组织及石墨形态所左右，但在石墨球／基体界面产生的滑移带、塑性区及裂纹尖端钝化区决定着疲劳裂纹萌生及扩展的整个过程。球铁的疲劳裂纹扩展规律是：裂纹连续扩展—急速扩展—裂纹尖端钝化—重新诱发裂纹—连续扩展。     

填充天然橡胶材料裂纹扩展模型的建模方法

填充天然橡胶材料疲劳裂纹扩模型是指裂纹扩展速率与撕裂能峰值之间的关系,它是用于橡胶减振元件疲劳寿命预测的重要模型。在裂纹扩展试验得到的填充天然橡胶材料裂纹扩展长度与循环次数的数据中,由于橡胶的应力软化现象,试验后期的部分数据不可用。为此,建立了数据处理方法,获得有效的裂纹扩展长度与循环次数数据。基于单轴拉伸载荷下填充天然橡胶材料最大应变能密度与最大应变满足幂函数关系的假设,建立了变幅加载工况下裂纹扩展长度与循环次数的数学模型和识别其模型参数的优化方法。在建立的裂纹扩展长度与循环次数模型的基础上,建立了裂纹扩展速率与撕裂能峰值关系的模型和确定模型中参数的数值方法。利用一组哑铃型试片的疲劳寿命实测数据,对建立的裂纹扩展速率模型进行了验证,证明了所建立模型的正确性。     

圆柱螺旋弹簧的可靠性设计

提出了对圆柱螺旋弹簧的静强度和疲劳强度可靠性设计的公式,并介绍了定力矩扳手的圆柱弹簧在可靠性设计中的应用。     

An efficient numerical method for predicting the natural frequencies of cylindrical helical springs

In this study, the stiffness method is employed for the free vibration problem of cylindrical helical springs. The element stiffness matrix for the helical spring with twelve degrees-of-freedom is obtained exactly by the transfer matrix method. The efficacious numerical algorithm is employed for the computation of the element transfer matrix. The concentrated element mass matrix is used. The subspace iteration method is preferred for the solution of the large-scale eigenvalue problem. The axial and shear deformation and the rotary inertia terms are considered in the formulation. The free vibrational parameters are chosen as the number of coils (n=3–16), the helix pitch angle (α=5–25°), the shape of cross-section (circular, hollow circle and squared) and as the ratio of the diameters of cylinder to wire (D/d=4–16) in a wide range. Solving the miscellaneous problems, the non-dimensional charts are obtained for the cylindrical helical springs fixed at both ends. Using these charts the natural frequencies are expressed in analytical form in a very good approximation (with the maximum absolute relative error of 5%) and presented for the designers.     

氮化硅陶瓷球滚动接触疲劳寿命模型

针对球与圆柱接触模型中的陶瓷球,利用WEIBULL断裂统计方法导出球疲劳失效概率与寿命之间的关系方程,在相关额定寿命与最大接触应力的数值解基础上,基于最大主拉应力,构建氮化硅陶瓷球的滚动接触疲劳寿命与接触应力的数学模型.经与不同接触应力水平下的滚动接触疲劳寿命试验结果验证,表明该拉应力一寿命模型的正确性,从而验证了氮化硅陶瓷球的滚动接触疲劳失效源于最大主拉应力,而非基于最大切应力的设想.通过与L.P切应力一寿命模型预测结果的比较,表明拉应力一寿命模型适合于陶瓷球的接触疲劳寿命预测.     

振动状态下螺旋弹簧运动状态模型

螺旋弹簧受到冲击载荷时,特别是多股螺旋弹簧,由于有质量、惯性,再加上自身的谐振,钢丝材料的弹性变形、多股螺旋弹簧中钢丝与钢丝之间的相对滑移而产生的摩擦阻力等诸多因素,簧圈的运动将变得非常复杂。基于此,建立一套用于检测振动状态下螺旋弹簧任意簧圈的运动状态模型,用于揭示振动状态下螺旋弹簧任意簧圈的位移、速度、加速度随时间的变化规律,特别是用于检测冲击载荷下多股螺旋弹簧的内部变形规律。试验结果表明:螺旋弹簧运动状态分析模型结合非接触多通道检测装置,可以成功地揭示振动状态下螺旋弹簧任意簧圈的运动状态随时间的变化规律,为螺旋弹簧的动态设计理论的建立提供了试验依据。     

基于ANSYS的多股螺旋弹簧有限元分析

简单分析多股螺旋弹簧的基本特性。以三股钢丝的多股螺旋弹簧为例,通过有限单元与接触单元的选取和网格的划分,建立多股螺旋弹簧有限元模型。然后对其进行静态受力分析和动态分析计算,分析冲击载荷质量和速度对多股螺旋弹簧性能的影响。结果表明多股螺旋弹簧在动态系统中具有内部振动波,并可能在中间产生并圈现象,为多股螺旋弹簧设计提供了依据。     

Initiation and propagation of surface cracks in rolling fatigue of high hardness steel

Surface cracks initiating flaking failure observed by Sugino in rolling fatigue were further studied.Surface crack initiation was influenced by either running or material conditions, affecting the residual tensile stress just below the rolling contact surface. The fatigue crack is thought to initiate very near the surface by the stress cycle of small tensile residual stress and large compressive contact stress. The amount and direction of the tensile residual stress due to rolling contact varies with the contact geometry, which probably determines the direction of the surface crack and the appearance of flaking. The transition from the surface crack to flaking failure or complete section fracture is material and running condition dependent and is explained by a fracture mechanics concept.     

高碳铬轴承钢的超长寿命疲劳行为的研究

使用砂漏型试样对高碳铬轴承钢的S-N曲线特性和破坏机理进行了研究。通过旋转弯曲疲劳试验获得的S-N曲线按照破坏模式的不同被划分为裂纹萌生位置不同的两组。一组叫做表面破坏模式的S-N曲线,它发生在高应力幅短寿命区,是由试样表面晶体滑移引起的。另一组叫做内部破坏模式的S-N曲线,它发生在低应力幅长寿命区,是由试样内部的非金属夹杂引起的。由于内部破坏模式的疲劳破坏发生在表面破坏模式的疲劳极限上下很宽的应力幅范围,因此,试验材料的S-N曲线的形状与通常报道的阶梯形状的S-N曲线的形状不同,它具有两条S-N曲线的特性。通过对断口上裂纹萌生位置的详细观察和裂纹萌生位置的初期尺寸参数的计算,阐述了内部破坏模式的破坏机理,提出了基于尺寸参数的超长寿命疲劳极限的推定方法。     

纯滚动状态下氮化硅陶瓷球临界应力分析

氮化硅陶瓷球临界应力在很大程度上决定其滚动接触疲劳和磨损寿命.由于陶瓷材料的抗拉能力较弱,所以设想其滚动接触疲劳失效的临界应力为最大主拉应力.应用弹性接触力学和赫兹理论分析纯滚动条件下陶瓷球表面层接触应力,得到表面层最大主拉应力.针对理论计算值,设计相应的纯滚动接触疲劳实验.分析表明,理论值与实验结果趋于一致,从而证实最大主拉应力为氮化硅陶瓷球滚动接触疲劳失效的临界应力.计算结果为陶瓷球的滚动接触疲劳寿命分析提供理论基础.     

Fatigue crack propagation behavior in STS304 under mixed-mode loading

The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failures occur from cracks subjected to mixed-mode loading. Hence, it is necessary to evaluate the fatigue behavior under mixed-mode loading. Under mixed-mode loading, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. In modified range 0.3≤a/W≤0.5, the stress intensity factors (SIFs) of mode I and mode II for the compact tension shear (CTS) specimen were calculated by using elastic finite element analysis. The propagation behavior of the fatigue cracks of cold rolled stainless steels (STS304) under mixed-mode conditions was evaluated by using K_I and K_II(SIFs of mode I and mode II). The maximum tangential stress (MTS) criterion and stress intensity factor were applied to predict the crack propagation direction and the propagation behavior of fatigue cracks.