Prediction of dimensional instability resulting from layer removal of an internally stressed orthotropic composite cylinder

When a layer of cylindrical composite component containing an axisymmetric residual stress state is removed from the inner or outer surface, the dimension of the remaining material changes to balance internal forces. Therefore, in order to machine cylindrical composite components within tolerances, it is important to know dimensional changes caused by residual stress redistribution in the body. In this study, analytical solutions for dimensional changes and the redistribution of residual stresses due to the layer removal from a residually stressed cylindrically orthotropic cylinder were developed. The cylinder was assumed to have axisymmetric radial, tangential and axial residual stresses. The result of this study is useful in cases where the initial residual stress distribution in the component has been measured by a non-destructive technique such as neutron diffraction with no information on the effect of layer removal operation on the dimensional changes.     

Effect of optimum plastic depth on stresses and load-bearing capacity of autofrettaged cylinder

Autofrettage is an effective measure to even distribution of stresses and raise load-bearing capacity for (ultra-)high pressure apparatus. Currently, the research on autofrettage has focused mostly on specific engineering problems, while general theoretical study is rarely done. To discover the general law contained in autofrettage theory, by the aid of the authors’ previous work and according to the third strength theory, theoretical problems about autofrettage are studied including residual stresses and their equivalent stress, total stresses and their equivalent stress, etc. Because of the equation of optimum depth of plastic zone which is presented in the authors’ previous work, the equations for the residual stresses and their equivalent stress as well as the total stress and their equivalent stress are simplified greatly. Thus the law of distribution of the residual stresses and their equivalent stress as well as the total stress and their equivalent stress and the varying tendency of these stresses are discovered. The relation among various parameters are revealed. The safe and optimum load-bearing conditions for cylinders are obtained. According to the results obtained by theoretical analysis, it is shown that if the two parameters, namely ratio of outside to inside radius, k, and depth of plastic zone, kj, meet the equation of optimum depth of plastic zone, when the pressure contained in an autofrettaged cylinder is lower than two times the initial yield pressure of the unautofrettaged cylinder, the equivalent residual stress and the equivalent total stress at the inside surface as well as the elastic-plastic juncture of a cylinder are lower than yield strength. When an autofrettaged cylinder is subjected to just two times the initial yield pressure of the unautofrettaged cylinder, the equivalent total stress within the whole plastic zone is just identically equal to the yield strength, or it is a constant. The proposed research theoretically depicts the stress state of ultra-)high pressure autofrettaged cylinder more accurately and more reasonably and provides the reference for design of (ultra-)high pressure apparatus.     

钻井泵活塞缸套密封系统密封性能流-固耦合分析*

现有的关于钻井泵活塞皮碗受力情况的相关研究,大多忽略了钻井泵工作过程中活塞缸套与钻井液的流-固耦合作用,得出的结论与实际的受力特性有一定的差别。为研究活塞皮碗的受力情况,通过建立活塞缸套的有限元模型,采用流-固耦合方法来模拟活塞缸套受力特性,同时探讨皮碗过盈量以及唇角尺寸对其密封性能的影响。仿真结果表明：缸套与皮碗接触面之间受力变化规律与缸套内压力变化规律相似;在最大工作压力作用下,缸套内表面和垫圈表面与皮碗接触部位等效应力都较大,但相较于缸套和垫圈,皮碗是活塞密封中最易失效的部件;皮碗的应力主要集中在活塞皮碗的唇部及根部与垫圈接触处,而这也是皮碗易发生失效的2个部位;当皮碗过盈量大于1.0 mm,唇角大于15°时,皮碗唇部会产生向心效应,进而影响皮碗的密封性能。     

Transient and residual thermal stresses in quenched cylindrical bodies

To predict residual and thermal stresses which occur during water quenching of solid cylindrical rod and ring cross-sectioned steel tubes, a finite element technique has been used. The variations of residual stresses on different surfaces and cross-sections, e.g. in the radial, axial and tangential directions have been examined, and the effect of internal diameter of tubes on residual stress was investigated. The results show that the residual stresses act as a compressive force along the cooling surface and then by moving away from the surface begin to decrease and reverse their sign, near the centre of the cylinder are subjected to tensile stresses. Because of the reversal of the sign of stress, the effective stress goes to a minimum at some distance from the frontal surface and this may be vital since lower plastic deformation may cause cracking failure. As in solid cylinder, in cylindrical tubes also, the frontal and the upper cooling surface has significant effect on the stress distribution. From the comparison of the residual stress distributions of solid cylinder and cylindrical tubes and using their individual stress maps it was seen that they vary considerably along different cooling surfaces, especially at the frontal surface.     

缠绕层表面缺陷对CNG-2复合气瓶爆破压力的影响

为了研究复合材料层表面缺陷对于CNG-2复合气瓶爆破压力的影响,通过考察实际的表面缺陷形状,将复合层表面缺陷简化为一定尺寸的矩形槽。对带有2 mm深度矩形槽型缺陷的复合气瓶进行爆破试验,并利用有限元数值计算软件ANSYS计算其爆破压力,以分析2 mm深矩形槽型缺陷对气瓶爆破压力产生的影响及其原因。结果表明,矩形槽型表面缺陷对于气瓶内衬应力的影响并不明显,而对缠绕层应力影响较大,缠绕层矩形槽型缺陷底面的应力超过复合材料抗拉强度保证值,使得复合气瓶爆破压力减小。     

Curing induced residual stresses in laminated cylindrical shells

A viscoelastic finite element analysis is presented to investigate residual stresses occurred in a laminated cylindrical shell during cure. An incremental viscoelastic constitutive equation that can describe stress relaxation during the cure is derived as a recursive formula which can be used conveniently for a numerical analysis. The finite element analysis program is developed on the basis of a 3-D degenerated shell element and the first order shear deformation theory, and is verified by comparing with an one dimensional exact solution. Viscoelastic effect on the residual stresses in the laminated shell during the cure is investigated by performing both the viscoelastic and linear elastic analyses considering thermal deformation and chemical shrinkage simultaneously. The results show that there is big difference between viscoelastic stresses and linear elastic stresses. The effect of cooling rates and cooling paths on the residual stresses is also examined.     

功能梯度压电材料壳体热残余应力

功能梯度压电材料结构成型冷却后会出现热残余现象,影响结构强度.借鉴复合材料层合结构的研究方法,将功能梯度压电材料球壳和圆柱壳沿厚度分为若干层,各层视为均匀材料,根据层间连续条件导出递推关系,得到显式的力—电—热多场耦合热残余解.统一了多层功能梯度压电材料壳体和连续功能梯度压电材料壳体热残余解.对于前者,其解为精确解;对于后者,其解为渐近解,随层数增加而收敛于精确解.其解也适用于功能梯度压电材料涂层.该方法对材料性能的变化方式(函数)没有要求,适应性强.并讨论影响热残余应力和界面强度的因素,球壳因双曲率的影响,热残余应力显著大于柱壳.     

发动机缸盖残余应力的测量及分析

采用盲孔法测量3组发动机铝合金缸盖裂纹附近和敏感部位的残余应力情况,分析缸盖内的残余应力对其裂纹产生的具体影响。考虑到缸盖的复杂结构特点和选择的测点位置,测试选用钻铣床钻盲孔和铣断通油管及其侧板,并在钻盲孔释放残余应力和铣削过程中通过30通道应变仪DRA-30A记录测点的应变时域曲线。对测试结果的分析和研究表明:通油管部分的残余应力以压应力为主,下缸体的上表面以拉应力为主,这种上压下拉的残余应力分布情况是缸盖内产生裂纹的主要原因;测点4处产生裂纹的可能性较大,测点7处通油管对下缸体的局部拉伸作用最为明显;B90组结构设计和加工工艺在3组试样中最为合理。据此测试结果和研究结论改进产品的结构和工艺后,该种缸盖满足设计要求。     

Measurement of residual stress in thick section composite laminates using the deep-hole method

The deep-hole method is a method of measuring residual stress in large metallic components. In this paper, an extension to the deep-hole method is described to allow the residual stresses in thick section composite laminated plates to be evaluated. The method involves first drilling a small hole through the laminate perpendicular to the surface. The material around the hole is then machined away, resulting in a change in diameter of the hole due to the release of residual stress. This change in diameter is measured and used to calculate the residual stress. The calculation requires the evaluation of coefficients that depend on the properties of the composite. In this work, the finite element method is used to evaluate these coefficients. Using this method, the residual stresses in a 22 mm thick carbon/epoxy composite plate are measured and reported.     

Evaluating the reliability of the cylinder liner of a low-speed marine engine subjected to high-cycle fatigue with high mean stress

Reliability evaluation was performed on the cylinder liner of a low-speed marine engine experiencing high-cycle fatigue with high mean stress. The stress distribution in the cylinder liner under operating condition was estimated through structural analysis, which included thermal boundary conditions and material nonlinearity. Results indicated that the highest stress concentration developed at the round part below the liner collar. Material tests revealed that the Goodman relation can predict the effect of mean stress on fatigue limit. As indicated by the combined results of the structural analysis and experiment, the cylinder liner is reliable under operating condition.     

Residual stresses in a laminated shell during cure

In this paper, a viscoelastic finite element analysis was performed to investigate residual stresses occurred in a laminated shell during cure. A viscoelastic constitutive equation that can describe stress relaxation during the cure was defined as functions of degree of cure and temperature, and derived as a recursive formula used conveniently for numerical analyses. The finite element program was developed on the basis of 3-D degenerated shell element and the first order shear deformation theory, and was verified by comparing with an exact solution of the one dimensional problem. Effects of chemical shrinkage and stacking sequence on the residual stresses in the laminated shell during the cure were investigated. The results showed that there were big differences between viscoelastic stresses and linear elastic stresses calculated by considering thermal deformation and the chemical shrinkage induced by the degree of cure.     

Three dimensional stress analysis of a composite patch using stress functions

A stress function-based analysis is proposed to provide a simple and efficient approximation method of three-dimensional (3D) state of stress that exists near the free edge of bonded composite patches. In order to apply plane strain assumption in a composite patch, a linear superposition of sliced section from a bonded patch is used. In addition, to describe the load transfer mechanism from the substrate to the composite patch, a simple shear lag model is introduced. The 3D stress behavior at the free edge of the composite patch is modeled by Lekhnitskii stress functions, and the governing equations of the given composite patch are obtained by applying the principle of complementary virtual work. After a suitable expansion of the functions, the governing equations are transformed into two coupled ordinary differential equations, and they are solved by a general eigenvalue solution procedure. As the number of base functions increases, the interlaminar stresses converge. The interlaminar stresses reach maximum at the free edge and decrease sharply at the inner part of the patch. The interlaminar stresses are concentrated at the interface between the layers because of the mismatch of material properties and the geometric singularity. Since the proposed method accurately predicts the 3D stresses in a composite patch bonded on the metal substrate, it can be used as a simple and efficient analytical tool for designing such structural components.     

Bending analysis of a laminated composite patch considering the free-edge effect using a stress-based equivalent single-layer composite model

The interlaminar stresses of a laminated composite patch, which is made up of reinforcing fibers (carbon/graphite) and epoxy matrix are analyzed using a stress-based equivalent single-layer model under a bending load. The composite patch is frequently used as reinforcement for a metallic adherend of mechanical/aerospace structures (i.e., aluminum alloy, etc) by attaching the film- or paste-type adhesive (i.e., epoxy, BMI, etc). To calculate the adhesive stresses transferred from the substrate, an interlayer model is introduced. The adhesive stresses are obtained by solving the equilibrium equations. The stress fields of the patch are determined by assuming certain stress functions. To satisfy the equilibrium state of the patch, the stress functions are divided into homogeneous and particular parts. The adhesive stresses act as prescribed stress boundary conditions of the laminated composite patch. The stress functions are substituted into a complementary virtual work principle, and from this, two coupled ordinary differential equations are obtained. General eigenvalue problems are derived to solve the coupled governing equations. To demonstrate the validity and efficiency of the proposed method, cross-ply, angle-ply and quasi-isotropic laminated composite patches are studied. From the observations made, the authors found that the stress function-based approach is suitable for solving the stress prescribed boundary value problem with accuracy and efficiency compared to a displacement-based approach such as the finite element method. The proposed method can be used as an efficient tool in the initial design stage of structural components when it is necessary to consider the free-edge effect.     

基于三剪统一强度准则的厚壁圆筒自增强分析

基于三剪统一强度准则,考虑材料应变强化效应、包辛格效应、拉压异性及中间主应力的影响,采用双线性强化材料模型对厚壁圆筒进行自增强分析,得到了厚壁圆筒加载应力、残余应力和工作应力的解析解,提出了最佳自增强压力的计算方法,探讨了拉压比、强度准则变化参数的影响,比较了自增强处理和非自增强处理及双线性强化模型和理想弹塑性模型厚壁圆筒的应力分布差异。研究结果表明：厚壁圆筒的最佳自增强压力随半径比和强度准则参数的增大而增大;工作时的最大等效应力随半径比和强度理论参数的增大而减小,随拉压比的增大而增大;自增强等效应力的最大值在弹塑性分界面处,且应力沿壁厚的分布较均匀;与理想弹塑性模型相比,双线性强化模型所对应的弹塑性分界面半径和残余应力较小,且随着自增强压力的增大,两种模型的差值越来越大;等效应力随半径比的变化规律可为厚壁圆筒选择合理的壁厚提供一定的参考;自增强技术可改善厚壁圆筒工作时的实际应力分布,提高其极限承载能力。     

薄壁筒焊缝残余应力研究

介绍了薄壁筒焊缝残余应力的实验研究。研究结果表明 ,薄壁筒环焊缝存在残余压应力 ,且垂直于焊缝纵向呈压应力分布 ,同时通过电测实验 ,对电测法测定压力容器残余应力的可靠性及测试精度进行了探讨和评价。     

钢瓶热处理对其残余应力影响的试验研究

对经过不同热处理工艺处理的YSP－15型钢瓶的残余应力进行测定，得出钢瓶残余应力的分布规律，并分析热处理对残余应力的消除效果。     

车用压缩天然气全复合材料气瓶缺陷分析

在对车用压缩天然气全复合材料气瓶进行定期检验过程中,发现气瓶内胆出现鼓包和裂纹等缺陷。为了确定缺陷产生的原因,对复合气瓶内胆材质进行力学性能、微观分析、缠绕层和内胆材料线膨胀系数测试。在此基础上,采用工业CT方法分析了气瓶内压与缺陷产生的关系。分析认为,缠绕层与内胆材料线膨胀系数不同是复合气瓶产生鼓包和裂纹的根本原因,同时,充放气过程中的内压和温度的低周循环也是气瓶产生缺陷的重要因素。     

Al2O3-TiC陶瓷刀具切削铸铁缸套的磨损机理的研究

讨论了Al2O3-TiC复合陶瓷刀具切削HT200缸套的试验过程.缸套为离心铸件,切削性能较差;由扫描电镜对刀具的磨损形态进行观察,分析了刀具磨损特征及磨损机理.试验表明:刀具磨损机理主要为冲击磨损、磨粒磨损、扩散磨损等.     

确定复合材料对称层板层间应力的边界层近似计算法

提出了一种有效的确定复合材料对称层板自由边附近层间应力分布的边界层近似法。所确定的应力场满足０阶边界层控制方程和自由边上的应力边界条件以及层间界面上的应力连续条件。对几种复合材料层板的分析表明，本文提出的方法可以较好地估算工程应用中几层至几十层的复合材料对称层板听层间应力分布。     

Evolution of residual stresses in micro-arc oxidation ceramic coatings on 6061 Al alloy

Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses. However, residual stresses in the surface coatings of structural components have adverse effects on their properties, such as fatigue life, dimensional stability and corrosion resistance, etc. The micro-arc oxidation ceramic coatings are produced on the surfaces of 6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW. A constant current density of 4.4___0.1 A/dm2 and a self-regulated composite electrolyte are used. The micro-arc oxidation treatment period ranges from 10 min to 40 min, and the thickness of the ceramic coatings is more than 20 Bin. Residual stresses attributed to 7-A1203 constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2~u method. The analysis results show that the residual stress in the ceramic coatings is compressive in nature, and it increases first and then decreases with micro-arc oxidation time increase. The maximum stress value is 1 667_＋20 MPa for period of 20 min. Through analyzing the coating thickness, surface morphology and phase composition, it is found that the residual stress in the ceramic coatings is linked closely with the coating growth, the phase composition and the micro cracks formed. It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress. The heat treatment makes the residual compressive stress value decrease 1 378 MPa. The ultrasonic action even alters the nature of the residual stress, making the residual compressive stress change into a residual tensile stress.