60Si2Mn螺旋弹簧的压缩应力松弛行为与贮存寿命预测

为评价60Si2Mn螺旋压缩弹簧的室温松弛特性,利用InstronE3000K8953型小吨位电子动静态疲劳试验机,对其在不同温度和初始应力水平条件下进行了高温压缩加速应力松弛试验,研究了环境温度、初始应力水平对松弛行为的影响.基于粘弹性体模型,揭示了应力松弛过程中弹性应变向塑性应变的转化特性与塑性应变随松弛时间的变化规律.在对应力松弛前后弹簧丝材金相和TEM微结构进行对比分析的基础上,探讨了应力松弛的微观机制.结果表明,环境温度与初始应力水平对松弛速率具有显著影响.基于应力松弛过程的热激活特性,建立了60Si2Mn螺旋压缩弹簧的贮存寿命预测方程,并对不同应力水平下弹簧的室温和高温贮存寿命进行了合理预测.     

螺旋压缩弹簧应力松弛特性试验分析及其应用

本文通过应力松弛试验、理论推导及数值模拟研究了高温下螺旋压缩弹簧的应力松弛规律,并利用加速模型对工况下弹簧应力松弛服役寿命做出预测。首先,根据螺旋压缩弹簧的结构特点搭建了弹簧应力松弛连续动态测试装置,该装置不仅避免了传统测试方法存在的缺陷,而且能够保证试验过程中位移载荷恒定,并实时监测载荷变化。本文以某飞机舱门单锁机构中的螺旋压缩弹簧为试验对象进行了不同温度条件下的应力松弛试验,得到其松弛动力学曲线,并基于Arrhenius模型建立了弹簧在工况下的应力松弛服役寿命预测模型;其次,基于应力松弛和蠕变在本质上的一致性,结合金属材料蠕变规律并根据试验弹簧的受力特点,推导出用于描述试验材料松弛行为的蠕变本构方程,由试验结果获得该本构方程的材料常数;最后,通过该本构方程及材料常数,在ANSYS软件中对试验弹簧的松弛过程进行模拟,结果表明,模拟结果与试验结果误差不大于4%。因此,通过本文方法所建立的蠕变方程对弹簧在不同载荷条件下的应力松弛规律进行仿真分析具有一定的可行性与准确性。     

变截面钢板弹簧刚度计算的传递矩阵法

钢板弹簧悬架是商用汽车的关键部件,对整车的平顺性以及操纵稳定性有着重要影响,采用变截面少片簧代替多片簧是整车轻量化的重要趋势。由于变截面钢板弹簧成型的复杂性,传统的设计计算方法存在较大误差。在精确分析梯形梁单元变形特性的基础上,提出了一种新的变截面板簧刚度计算的传递矩阵法。对于广泛应用的各种变截面板簧,一般只需十来个单元即可得到非常逼近于有限元精确分析的结果。最后,通过不同类型板簧和不同方法的对比计算验证了该方法的有效性。     

Influence of Residual Stresses Introduced by Shot Peening Upon the Fatigue Life of Materials

Strain hardening by shot peening is an operation which broadly increases the fatigue resistance of a mechanical part. This increase is particularly due to the compressive residual stresses induced in the surface layers of the material. This article demonstrates the resulting improved fatigue resistance of three types of mechanical parts (helical springs, chain links, and lifting hooks.     

Considerations on the spring analogy

This paper presents an investigation on the spring analogy. The spring analogy serves for deformation in a moving boundary problem. First, two different kinds of springs are discussed: the vertex springs and the segment springs. The vertex spring analogy is originally used for smoothing a mesh after mesh generation or refinement. The segment spring analogy is used for deformation of the mesh in a moving boundary problem. The difference between the two methods lies in the equilibrium length of the springs. By means of an analogy to molecular theory, the two theories are generalized into a single theory that covers both. The usual choice of the stiffness of the spring is clarified by the mathematical analysis of a representative one‐dimensional configuration. The analysis shows that node collision is prevented when the stiffness is chosen as the inverse of the segment length. The observed similarity between elliptic grid generation and the spring analogy is also investigated. This investigation shows that both methods update the grid point position by a weighted average of the surrounding points in an iterative manner. The weighting functions enforce regularity of the mesh. Based on these considerations, several improvements on the spring analogy are developed. The principle of Saint Venant is circumvented by a boundary correction. The prevention of inversion of triangular elements is improved by semi‐torsional springs. The numerical results show the superiority of the segment spring analogy over the vertex one for a small rotation of an NACA0012 mesh. The boundary correction allows for large deformation of the mesh, where the standard spring analogy fails. The final test is performed on a Navier–Stokes mesh. This mesh contains high aspect ratio mesh cells near the boundary. Large deformation of this mesh shows that the semi‐torsional spring improvement is imperative to retain the validity of this mesh. Copyright © 2000 John Wiley & Sons, Ltd.     

Free vibration/buckling analyses of noncylindrical initially compressed helical composite springs

This article presents the use of the stiffness matrix method based on the first-order shear deformation theory to predict the fundamental natural frequencies and buckling loads of noncylindrical unidirectional composite helical springs subjected to initial static axial force and moment. This theoretical study about such springs with circular/rectangular cross-sections and large pitch angles is performed for the first time in the literature. The validity of the present results is verified by the benchmark studies related with initially compressed isotropic cylindrical springs.     

Modeling and dynamics analysis of helical spring under compression using a curved beam element with consideration on contact between its coils

Helical springs are indispensable elements in mechanical engineering. This paper investigates helical springs subjected to axial loads under different dynamic conditions. The mechanical system, composed of a helical spring and two blocks, is considered and analyzed. Multibody system dynamics theory is applied to model the system, where the spring is modeled by Euler–Bernoulli curved beam elements based on an absolute nodal coordinate formulation. Compared with previous studies, contact between the coils of spring is considered here. A three-dimensional beam-to-beam contact model is presented to describe the interaction between the spring coils. Numerical analysis provides details such as spring stiffness, static and dynamic stress for helical spring under compression. All these results are available in design of helical springs.     

Cyclic deformation of TiNi shape-memory alloy helical spring

The influence of training and shape-memory processing temperature on cyclic deformation of TiNi shapememory alloy helical springs is investigated. The results are summarized as follows. (1) For large strain, significant irrecoverable elongation appears in the early cycles. The appearance of the irrecoverable elongation can be avoided by the training. (2) The recovery force of the spring varies slightly during the thermal cycles, which shows the very stable cyclic characteristics of the force. (3) The cyclic characteristics of deformation in the helical springs depend on the size of the region accompanied by the stress-induced martensitic transformation in the cross section of the wire.Paper was presented at the 1991 SEM Spring Conference on Experimental Mechanics held in Milwaukee, WI on June 10–13.     

The application and extension of Sachs method

In this paper, we present the simplification of Sachs formulas for the measurement and calculation of the residual stresses of the cylinder only with the plane stresses. Furthermore, we present the method for the measurement and calculation of the residual stresses of the cylinder not only with the finite length but with the longitudinal stress. These can be applied to the investigation on the residual stresses of the autofretted gun tube.Communicated by Loo Wen-da     

Two Dimensions Residual Stresses Analysis Through Incremental Groove Machining Combined with Electronic Speckle Pattern Interferometry

In this study a new residual stress determination method in two directions simultaneously is presented. This method is based on stresses relaxation in a groove that is machined incrementally. The residual stresses relaxation occurs simultaneously from both the depth and the length of the groove. Thus, measuring the surface strain field generated by the relaxation enables to determine the stress gradient both along the depth and the length of the groove. To measure the surface strain in a direction perpendicular to the groove, a digital speckle pattern interferometer is used. This method is suitable when the residual stress field in the structure varies in the depth as well as along the surface of the part, like for example in a welded structure. The method is tested here on an aluminium plate in which a central band has been shot peened.     

A combined analytical,numerical, and experimental study of shape-memory-alloy helical springs

In this paper, the pseudoelastic response of shape memory alloy (SMA) helical springs under axial force is studied both analytically and numerically. In the analytical solution two different approximations are considered. In the first approximation, both the curvature and pitch effects are assumed to be negligible. This is the case for helical springs with large ratios of mean coil radius to the cross sectional radius (spring index) and small pitch angles. Using this assumption, analysis of the helical spring is reduced to that of the pure torsion of a straight bar with circular cross section. A three-dimensional phenomenological macroscopic constitutive model for polycrystalline SMAs is reduced to the one-dimensional pure shear case and a closed-form solution for torsional response of SMA bars in loading and unloading is obtained. In the next step, the curvature effect is included and the SMA helical spring is analyzed using the exact solution presented for torsion of curved SMA bars. In this refined solution, the effect of the direct shear force is also considered. In the numerical analyses, the three-dimensional constitutive equations are implemented in a finite element method and using solid elements the loading–unloading of an SMA helical spring is simulated. Analytical and numerical results are compared and it is shown that the solution based on the SMA curved bar torsion gives an accurate stress analysis in the cross section of the helical SMA spring in addition to the global load–deflection response. All the results are compared with experimental data for a Nitinol helical spring. Several case studies are presented using the proposed analytical and numerical solutions and the effect of changing different parameters such as the material properties and temperature on the loading–unloading hysteretic response of SMA helical springs is studied. Finally, some practical recommendations are given for improving the performance of SMA helical springs used as energy dissipating devices, for example for seismic applications.     

Application of a kinematic hardening viscoplasticity model with thresholds to the residual stress relaxation

The life analysis of engine components needs to take into account the residual stress relaxation induced by cyclic service loads. The paper recalls a new class of constitutive equations for cyclic viscoplasticity, using a series of kinematic hardening models with thresholds. The equations are introduced within a recently enlarged thermodynamic framework. Some attention is focused to the relations with multisurface approaches and to a specific determination procedure of the model parameters. The new model is applied to the calculation of the near surface residual stress relaxation after shot peening, when the structure is submitted to cyclic service loads. The simulated stabilized residual stresses are in good accordance with experimental results obtained on an N18 disk alloy at 650°C. In comparison, the classical model without threshold predicts the complete vanishing of the residual stresses, which is not satisfactory.     

Prediction of residual flow and thermoviscoelastic stresses in injection molding

A general model for predicting the total residual stresses generated during filling and cooling stages of injection-molded parts has been developed. The model takes into account the phenomena associated with non-isothermal stress relaxation. The main hypothesis in our approach is to use the kinematics of a generalized Newtonian fluid at the end of the filling stage as the initial state for the calculation of residual flow stresses. These stresses are calculated using a single integral rheological model (Wagner model). The calculation of stresses developed during the cooling stage is based on a thermoviscoelastic model with structural relaxation. Illustrative results emphasizing the effect of both the melt temperature and the flow rate during the filling stage are presented.     

聚合物注塑残余应力的研究进展

综述了聚合物注塑残余应力的研究进展,详细介绍计算残余应力所用的理论模型及其基本概念．注塑制品残余应力由两部分组成,并且有不同的测试方法,这些应力是造成制品翘曲变形的原因．对于残余流动应力,重点分析本构模型的发展和注塑控制方程的建立;对于残余热应力,则讨论了冷却过程中的相交问题,以及热粘弹性模型在应力分析中的应用;最后介绍测量残余应力的几种实验方法．      

Equilibrium equations for 3D critical buckling of helical springs

In most cases,the research on the buckling of a helical spring is based on the column,the spring is equivalent to the column,and the torsion around the axial line is ignored.A three-dimensional(3D) helical spring model is considered in this paper.The equilibrium equations are established by introducing two coordinate systems,the Frenet and the principal axis coordinate systems,to describe the spatial deformation of the center line and the torsion of the cross section of the spring,respectively.By using a small deformation assumption,the variables of the deflection can be expanded into Taylor’s series,and the terms of high orders are ignored.Hence,the equations can be simplified to the functions of the twist angle and the arc length,which can be solved by a numerical method.The reaction loads of the spring caused by the axial load subjected to the center point are also discussed,giving the boundary conditions for the solution to the equilibrium equations.The present work is useful to the research on the behavior of the post-buckling of the compressed helical spring.     

Gravity compensation of parallel kinematics mechanism with revolute joints using torsional springs

Abstract

Passive gravity compensation technologies based on counterweight and torsional springs is rarely discussed due to the unavailability of an exact mathematical manipulation to determine the required spring constants to achieve the static balance. This article proposes using these springs for a parallel kinematics mechanism with revolute joints. Either the spring constants or initial spring displacements are determined by a constrained optimization approach aiming at minimizing the total potential energy of the mechanism or the static reaction in the actuation direction at the actuators, along a prescribed trajectory. This results in reduced actuation forces/ torques and hence reduced power consumption.     

Measuring Inaccessible Residual Stresses Using Multiple Methods and Superposition

The traditional contour method maps a single component of residual stress by cutting a body carefully in two and measuring the contour of the cut surface. The cut also exposes previously inaccessible regions of the body to residual stress measurement using a variety of other techniques, but the stresses have been changed by the relaxation after cutting. In this paper, it is shown that superposition of stresses measured post-cutting with results from the contour method analysis can determine the original (pre-cut) residual stresses. The general superposition theory using Bueckner’s principle is developed and limitations are discussed. The procedure is experimentally demonstrated by determining the triaxial residual stress state on a cross section plane. The 2024-T351 aluminum alloy test specimen was a disk plastically indented to produce multiaxial residual stresses. After cutting the disk in half, the stresses on the cut surface of one half were determined with X-ray diffraction and with hole drilling on the other half. To determine the original residual stresses, the measured surface stresses were superimposed with the change stress calculated by the contour method. Within uncertainty, the results agreed with neutron diffraction measurements taken on an uncut disk.     

Consideration of the masses of helical springs in forced vibrations of damped combined systems

The common point about many systems modeled as Bernoulli-Euler beams with attachments is that the own masses of the helical springs are neglected. Some researchers accounted for the masses of the springs during free vibrations of those systems. Further to these studies, the present study deals with the investigation of the effect of not taking into account the masses of the helical springs in damped combined systems during their forced vibrations. It is shown that the spring mass effect may be important in regions near to the resonance frequencies. Further, this effect influences the phase angles more than the amplitudes.     

Finite element method for the stress analysis of isotropic cylindrical helical spring

This paper presents an efficient two nodes finite element with six degrees of freedom per node, capable to model the total behaviour of a helical spring. The formulation, which includes the shear deformation effects, is based on the assumed forces hybrid approach. The resultant forces approximation verifies exactly the resultant equilibrium equations. The developed model proves its accuracy compared with other elements. This element permits to get the distribution of different stresses along the spring and through the wire surface by only one element.