不同损伤参量对橡胶隔振器疲劳寿命预测结果影响的研究

基于橡胶哑铃形试件的疲劳试验结果,分别以最大主工程应变、最大主对数应变、最大主Green-Lagrange应变、八面体切应变、应变能密度、Luo等效应力、Saintier等效应力为损伤参量建立七种橡胶疲劳寿命预测模型。应用此七种模型预测某汽车动力总成橡胶悬置的疲劳寿命,对比不同寿命模型的预测效果。研究结果表明,以最大主工程应变、最大主对数应变、最大主Green-Lagrange应变、八面体切应变、应变能密度为损伤参量建立的寿命模型预测的疲劳寿命均在实测寿命的4倍分散线之内;以Luo应力、Saintiter应力为损伤参量建立的寿命预测模型的预测寿命落在实测寿命的2倍分散线之内。因此,以Luo应力、Saintiter应力为损伤参量建立的寿命预测模型预测效果更好,Luo应力、Saintier应力更适合作为疲劳损伤参量来预测橡胶隔振器的疲劳寿命。     

随机疲劳寿命预测的局部应力应变场强法

在应力场强法研究的基础上，提出了缺口疲劳损伤局部应力应变场强方法，该方法可同时考虑缺口根部局部应力应变梯度对疲劳损伤的影响。通过对缺口件进行随机交变加载下的弹塑性有限元分析，给出一种随机疲劳寿命预测的局部应力应变场强方法，由该法来预测缺口件疲劳裂纹形成寿命，经初步验证，其精度要高于传统的局部应力应变法。     

大型覆盖件应变分布测量与缺陷分析

研究了用网格试验方法对冲压成形后覆盖件的塑性主应变分布进行测量的方法。分析了其原理、网格形式 及其特点、基于单元格均匀变形条件的四边形网格塑性主应变计算的相关理论和方法。以一汽车覆盖件冲压成形 的拉裂缺陷分析为例,采用网格试验法测量计算获得了该零件成形后的塑性应变分布情况,分析了根据测试结果进 行冲压质量诊断和改进冲压工艺的方法。结果表明,该方法为分析和解决覆盖件冲压成形缺陷,优化冲压工艺提供 了一种有效的辅助工具。     

静压支撑单点渐进成形厚向应变分布研究

采用单点渐进成形技术单道次成形复杂形状的薄壁零件时，厚度分布不均匀及过度减薄易于引起板材的断裂和成形失效。将静压支撑引入单点渐进成形中，形成一种静压支撑单点渐进成形工艺；通过促进材料流动和厚向应变分布来提高板材厚度分布的均匀性。选用初始厚度为1 mm的1060铝板，以静压支撑单点渐进成形的圆锥台件为研究对象，通过数值模拟和实验研究分析了静压参数对厚向应变分布和材料流动规律的影响。结果表明：0～0.18 MPa的静压支撑有利于过渡变形区Ⅱ的快速成形，有利于主变形区Ⅲ的厚向应变分布；在有利压力范围内，静压压力越大，由Ⅱ区流向Ⅲ区的材料越多，厚向应变分布越均匀，制件成形性能越好。     

基于网格应变场测量法的橡胶-钢板粘结界面应变分布研究

板式橡胶支座由多层均匀分布的橡胶与钢板粘结而成。本文利用网格法光学测量技术获得橡胶-钢板层合界面的应变场，以宏观剪切负荷-变形同步的形式研究了橡胶与钢板粘结界面间的应变场。观测到应变集中现象，且主应变最大值出现在粘结界面边缘部位。根据其应变集中现象和观测结果说明了橡胶支座内损伤的萌生机理。     

大型宽厚板轧机十字万向节疲劳寿命分析

以国内某大型宽厚板轧机主传动系统十字万向节为研究对象,在材料的应变疲劳寿命特性曲线基础上,利用修正Neuber法的局部应力应变法进行材料的疲劳寿命估算,用数值模拟的方法求得十字万向节的疲劳寿命,并与现场实际使用情况对比,验证计算方法的有效性。     

利用网格技术防止拉伸件裂纹

工件在拉伸过程中,各变形区在径向、切向和法向发生应变,法向应变与其它两向应变相比,可忽略不计。这样,将拉伸件的应变看成平面应变。平面应变可用网格技术来研究工件的生产质量,其中,防止裂纹产生是其重要应用。     

基于DSP的光纤法珀应变仪数据采集技术研究

光纤法珀应变传感是20世纪80年代末发展起来的一种新型应变测量技术。相应的应变测量仪逐渐成为国内外研究的热点。针对现有的应变测量仪，提出了基于DSP的一体化光纤法珀应变仪的思路，对VC33与应变测量仪之间的数据采集进行了探讨，重点介绍了VC33与应变测量仪之间数据采集的硬件和软件设计，并做了采集验证实验。实验结果与理论上传感器的输出结果基本一致，验证了该采集技术的可行性，为后面的数据处理及实现一体化打下了良好的基础。     

瞬态激励、应变片测量、非线性最优化识别振动系统模态参数

本文提出了用力锤激励、应变片测量响应、用非线最优化方法来识别振动系统模态参数的理论和方法。本文提出了“撼应系数”这一概念。通过撼应系数及柔度系数和刚度系数,找到了应变和位移的关系。文中导出了用应变片测量响应时系统的应变导纳函数公式。采用本文所述方法可识别出振动系数的固有频率、位移振型、应变振型、应力振型、广义阻尼及主刚度和主质量等模态参数。     

改进Logistic蠕变应变预测模型及其有限元实现

提出一种针对蠕变全过程的改进Logistic蠕变应变预测(Logistic creep strain prediction, LCSP)模型，减少模型参数数量并解决初始蠕变应变复数值问题，结合加钒改进型2.25Cr1Mo钢的蠕变变形与断裂寿命数据，利用基于最小二乘法原理的模型参数识别方法，实现对材料的蠕变应变及应变速率的准确预测。综合分析Larson-Miller主曲线方程的寿命预测精度及寿命随应力的变化趋势，确定用于预测蠕变断裂寿命的模型多项式阶数。根据改进LCSP模型的蠕变应变解析公式，推导蠕变应变增量及其对等效应力以及蠕变应变的导数的计算表达式，确保计算收敛性，利用Fortran语言开发了针对改进LCSP模型的usercreep蠕变子程序，通过光滑圆棒试样蠕变有限元分析验证该蠕变子程序的准确性。     

A study on the development of photoelastic experimental hybrid method for colour isochromatics (I)

Isochromatics obtained from photoelastic experiment shows the stress distributions of the full field of a structure under load. Therefore, stress distributions of the structure can be read at a glance through isochromatics. Many experimental data can be obtained from isochromatics which are then used in various photoelastic experimental hybrid methods for stress analysis. Monochromatic light has however, until now been used in the photoelastic experimental hybrid method to produce black and white isochromatics. The use of black and white isochromatics in photoelastic experimental hybrid method for black and white isochromatics requires high fringe orders in order to obtain sufficient experimental data for photoelastic hybrid techniques. Accordingly, this paper develops the photoelastic experimental hybrid method for color isochromatics in which a fringe order of 1 is enough to gather the experimental data of the photoelastic experimental hybrid method. The method was applied to validate stress concentration problems. Experimental results from this study indicated that the photoelastic experimental hybrid method for color isochromatics is more precise than the photoelastic experimental hybrid method for black and white isochromatics. The use of few fringe orders in photoelastic experimental hybrid method for color isochromatics can offer significant advantages in stress analysis of real components using reflective-type photoelastic experimental method.     

Wall slip and hydrodynamics of two-dimensional journal bearing

In the present paper, based on the limiting shear stress model, a multi-linearity finite element algorithm and quadratic programming technique are used to study the influence of wall slip on the hydrodynamic lubrication performance of a two-dimensional journal bearing (finite length journal bearing). It is found that if the lubricated surfaces are designed as homogeneous slip surfaces, the hydrodynamic force will be decreased. If the shaft surface (rotation) is a slippery surface with very low limiting shear stress, almost no fluid load support can be generated. If the sleeve surface is designed as the homogeneous slip surface, a low fluid load support together with a small friction drag can be obtained. However, if the sleeve surface is designed as an optimized slip surface with a slip zone in the inlet region, a high load support and low friction coefficient can be obtained. Optimization of the shape and the size of the slip zone can give the journal bearing many advanced properties.     

A study on the development of photoelastic experimental hybrid method for colour isochromatics (II)

Using the photoelastic experimental hybrid method, we can obtain stress intensity factors and separate the stress components near the crack tip of any material under various loading conditions from only isochromatics. However, monochromatic light has, until now been used in the photoelastic experimental hybrid method to produce black and white isochromatics. The existing photoelastic experimental hybrid method using black and white isochromatics requires high order fringes to obtain sufficient experimental data for photoelastic hybrid techniques. If a photoelastic experimental hybrid method for colour isochromatics is developed, isochromatics with a maximum fringe order of 2 will be adequate for gathering the necessary experimental data for stress analyses using photoelastic hybrid techniques. Therefore, in this work, photoelastic experimental hybrid method for colour isochromatics of a crack problem was developed, and its superiority demonstrated by comparing its results with the results from black and white isochromatics. The use of few fringe orders in photoelastic experimental hybrid method for colour isochromatics is an important feature of this method. Because of this feature, this method, specifically the reflection type photoelastic method where low fringe orders are produced compared to the transmission type photoelastic method, can be widely used in stress analysis of real components.     

On a New Method to Determine the Yield Stress in Lubricating Grease

An experimental study using both a controlled stress and a controlled strain rheometer has been undertaken to characterize lubricating grease in shear, creep, stress relaxation, and oscillatory flow, with a main focus on determining the yield stress. The yield stress was examined using a cone–plate and parallel-plate system with smooth and rough surfaces. Clear discrepancies were observed in the yield stress values obtained using different techniques where oscillatory strain sweep measurements seem to be the best choice. This technique is less sensitive to wall slip, shows good reproducibility, and is relatively easy to perform. The method also shows that the yield stress is a function of the imposed frequency and therefore of the time domain. At lower values of shear—that is, in the linear viscoelastic regime—there is no structural breakdown and the rheology of the grease can be described by the Maxwell model where the stress and the strain are almost proportional to each other. Based on this observation, a novel method to determine the yield stress is proposed: “The yield stress can be determined from the point where this linearity no longer applies.” This method is compared to those that are commonly used. The yield stress was found to depend exponentially on temperature and linearly on frequency.     

A study of the development of the stress optic law of photoelastic experiment considering residual stress

Photoelastic experiment has two significant problems. The first problem is manufacturing a model specimen for complicated shapes of structures. The second problem is residual stress contained in the photoelastic model material. In this paper, the stress optic law that can be effecitvely used on photoelastic model materials with residual stress is developed. By using the stress optic law as developed in this research, we can obtain good results in photoelastic experiments using model material in which residual stress is contained. It is assured that the stress optic law developed in this research is useful. Therefore, it is suggested that the stress optic law considering residual stress can be applied to the photoelastic experiment for the stress analysis of the composite materials or bi-materials in which the residual stress is easily contained.     

卡瓦式套管头可靠性分析

卡瓦悬挂系统是套管头的核心,卡瓦能否安全可靠地悬挂套管是其关键。对卡瓦悬挂套管进行了力学分析,并采用有限元法进行了模拟,结果表明,当壳体内部受液态压力时,应力随厚度的减小而不断增大,最大应力为220MPa;卡瓦的最大应力在齿的根部,为366MPa,悬挂体主要承受卡瓦的挤压载荷,其最大载荷为200MPa。经过校核,壳体、卡瓦和悬挂均符合设计要求,同时也指出了危险应力位置,以期为后续套管头的设计提供理论依据。     

Evaluating lifetime performance of limited slip differentials

Extensive research has been performed regarding wet clutch function and performance. Although wet clutches are used in both automatic transmissions and limited slip differentials in cars, most research has been performed for wet clutches incorporated in automatic transmissions. The operating conditions of wet clutches in automatic transmissions differ from the operating conditions of the wet clutches used in limited slip differentials. Therefore, a method and a test bench to use in the investigation of the degradation of limited slip differentials were developed in this work. The typical operating conditions of the limited slip differential and the differences compared with wet clutches incorporated in automatic transmissions were also addressed. Tests performed showed that the developed test bench and method can be used to address differences in frictional response over time for different types of operating conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

钢筋与混凝土粘结性能的试验研究

钢筋与混凝土之间的粘结性能是连续配筋混凝土路面重要的设计参数,而粘结性能可以用粘结应力与相对滑移来表示。基于连续配筋混凝土路面结构形式,设计了钢筋混凝土粘结试件,测试了连续配筋混凝土路面钢筋与混凝土粘结应力与相对滑移。通过对这两个参数测试结果进行分析,确立了连续配筋混凝土路面钢筋混凝土粘结应力与相对滑移的近似分段线性关系。     

斜刃剪切机机架应力分析

在分析研究剪切机架应力分布和强度时,采用模型实验应力分析和实测机架动应力相结合的方法。在模型实验应力分析中采用脆性涂料法确定模型机架最大主应力部位和主应力方向,采用电阻应变测量法确定模型机架的主应力水平。据此选定最大主应力的测点进行实际剪切过程中动态应力和相应剪切力的测定,确定并分析机架强度。     

Numerical investigation of the combined effects of slip and texture on tribological performance of bearing

Slider bearings are used in many applications. An increase in the load support may allow for saving of energy. In this work, in order to enhance the load support and decrease the friction force, a combined textured surface bearing using boundary slip is discussed. A modified Reynolds equation with slip is adopted. With the main goal of evaluating the effects of slip and texture, a parametric analysis is performed. For the given operating conditions, texturing features as well as slip pattern are analysed in detail. The numerical analysis is undertaken under the condition of different gap ratio values and the slip-textured area. The results show that combined techniques of slip and texture have a significant effect on the improvement of the tribological performance of bearing, that is, a high load support but low friction force. The gap ratio of the bearing is shown to have a significant effect on the lubrication behaviour. It is found that even with a smallest gap ratio (parallel gap), a high load support can be produced. However, it is also shown that the gap ratio appears to contribute to the generated friction force and the volume flow rate more than the boundary slip. Further analysis indicates that the optimum slip-text zones for certain gap ratio are highlighted. These findings may provide references for designing hydrodynamic-textured slider bearing considering boundary slip.