三维准静载弹塑性弯曲裂纹塑性区

主要研究准静载荷作用下的三维弹塑性弯曲裂纹尖端的塑性区问题。综合考虑了准静作用应力,三维塑性区域边界上正应力与剪应力,利用二阶摄动方法计算了三维弹塑性弯曲裂纹尖端的塑性区。用数值解法计算出三维弹塑性弯曲裂纹尖端塑性区于裂纹直线部分延长线上的投影长度,作图分析了三维弹塑性弯曲裂纹尖端塑性区尺寸与三维裂纹体几何尺寸之间的变化关系。三维弹塑性弯曲裂纹尖端塑性区随着三维裂纹体厚度的增大而减小,随着三维裂纹体厚度的均匀增大,三维弹塑性弯曲裂纹尖端塑性区尺寸不断减小,减小的幅度越来越小,最终趋于平面应变状态下的弹塑性弯曲裂纹尖端塑性区尺寸。当三维裂纹体几何尺寸相同时,三维弯曲裂纹尖端塑性区尺寸随外载荷的不断增大而逐渐增大。建立了一个计算三维弹塑性弯曲裂纹塑性区尺寸的崭新理论模型。     

三维准静载弹塑性弯曲裂纹张开位移

主要研究准静载荷作用下的三维弹塑性弯曲裂纹尖端的张开位移问题。综合考虑了准静作用应力,三维塑性区域边界上正应力与剪应力,利用二阶摄动方法计算了三维弹塑性弯曲裂纹尖端的张开位移。用数值解法计算出三维弹塑性弯曲裂纹尖端张开位移,作图分析了三维弹塑性弯曲裂纹尖端张开位移与三维裂纹体几何尺寸之间的变化关系。三维弹塑性弯曲裂纹尖端张开位移随着三维裂纹体厚度的增大而减小,随着三维裂纹体厚度的均匀增大,三维弹塑性弯曲裂纹尖端张开位移尺寸不断减小,减小的幅度越来越小,最终趋于平面应变状态下的弹塑性弯曲裂纹尖端张开位移尺寸。当三维裂纹体几何尺寸相同时,三维弯曲裂纹尖端张开位移尺寸随外载荷的不断增大而逐渐增大。建立了一个计算三维弹塑性弯曲裂纹尖端张开位移尺寸的崭新理论模型。     

幂硬化对准静载弹塑性弯曲裂纹塑性区的影响

主要研究准静载荷作用下的硬化材料弹塑性弯曲裂纹尖端的塑性区问题。综合考虑了准静作用应力,塑性区域边界上正应力与剪应力,利用二阶摄动方法计算了硬化材料弹塑性弯曲裂纹尖端的塑性区。用数值解法计算出弹塑性弯曲裂纹尖端硬化塑性区于裂纹直线部分延长线上的投影长度,作图分析了弹塑性弯曲裂纹尖端塑性区尺寸与材料硬化指数之间的变化关系。在幂硬化材料中,弹塑性弯曲裂纹尖端塑性区随着材料硬化指数n的增大而减少,当n等速均匀增加时,弹塑性弯曲裂纹尖端塑性区尺寸加速减少,减少的幅度越来越大。当材料的硬化指数相同时,弯曲裂纹尖端塑性区尺寸随外载荷的不断减小而逐渐减小。建立了一个计算硬化材料弹塑性弯曲裂纹塑性区尺寸的崭新理论模型。     

幂硬化对准静载弹塑性弯曲裂纹张开位移的影响

研究准静载荷作用下的硬化材料弹塑性弯曲裂纹尖端的张开位移问题。综合考虑了准静作用应力,塑性区域边界上正应力与剪应力,利用二阶摄动方法与卡氏定理计算了硬化材料弹塑性弯曲裂纹尖端的张开位移。作图分析了弹塑性弯曲裂纹尖端张开位移尺寸与材料硬化指数之间的变化关系。在幂硬化材料中,弹塑性弯曲裂纹尖端张开位移随着材料硬化指数n的增大而减少,当n等速均匀增加时,弹塑性弯曲裂纹尖端张开位移加速减少,减少的幅度越来越大。当材料的硬化指数相同时,弯曲裂纹尖端张开位移随外载荷的不断减小而逐渐减小。开拓了一个计算硬化材料弹塑性弯曲裂纹张开位移的理论模型的崭新领域。     

幂硬化对准静载弹塑性弯曲裂纹J积分的影响

主要研究准静载荷作用下的硬化材料弹塑性弯曲裂纹尖端的J积分问题。综合考虑了准静作用应力,塑性区域边界上正应力与剪应力,利用二阶摄动方法与卡氏定理计算了硬化材料弹塑性弯曲裂纹尖端的J积分。作图分析了弹塑性弯曲裂纹尖端J积分大小与材料硬化指数之间的变化关系。在幂硬化材料中,弹塑性弯曲裂纹尖端J积分随着材料硬化指数n的增大而减少,当n等速均匀增加时,弹塑性弯曲裂纹尖端J积分加速减少,减少的幅度越来越大。当材料的硬化指数相同时,弯曲裂纹尖端J积分随外载荷的不断减小而逐渐减小。建立了一个计算硬化材料弹塑性弯曲裂纹J积分的理论模型。     

轧辊修磨技术与修磨制度研究

轧辊在钢铁轧制过程中，因受到制造残余应力、轧制过程中的接触应力、弯曲应力、扭剪应力以及交变热应力的综合作用，轧辊很容易产生热裂纹、疲劳裂纹、不均匀磨损等。这些裂纹和磨损的存在会严重影响轧钢的质量，降低轧辊的使用寿命。为了消除热裂纹、疲劳裂纹、不均匀磨损对轧钢的不利影响，需要定期对轧辊进行修磨，建立合理的轧辊修磨制度。     

Q345C钢板弯曲裂纹原因分析及应对措施

通过对材料成分、材料制造工艺、弯曲工艺、设备等方面的分析,阐述了Q345C钢板弯曲裂纹产生的原因主要是材料的塑性和韧性不够,我们可以通过热处理及对弯曲工艺的优化来避免弯曲裂纹的产生.     

裂纹故障对盘式拉杆组合转子系统应力重组的影响研究

在含裂纹一般整体转子研究中，难以有效反映裂纹尖端奇异效应及其三维形态特征，同时一维方法难以反映复杂组合转子系统的裂纹故障应力影响范围、系统应力重组情况及对系统整体初始形态的影响。针对上述一些问题，以典型三盘拉杆组合转子系统为例，研究了三维裂纹故障对复杂拉杆组合转子系统应力重组及整体弯曲形态的影响，并进行了实验验证。首先，基于三维有限元方法，采用三维等参奇异裂纹有限元建模技术和三维有限软件，建立了三维裂纹子模型及系统有限元模型；然后，采用有限元仿真技术，分析了裂纹及其深度变化对此类组合转子系统的应力分布重组及整体弯曲特性的影响；最后，采用实验方法，验证了裂纹对此类系统整体初始弯曲特性的影响情况。研究结果表明：盘式拉杆组合转子系统裂纹故障的产生会使得裂纹位置区域局部柔性增强，系统的主要界面及系统应力分布发生变化且重组，系统应力分配不均匀，且呈现不对称性，转子整体弯曲形态发生变化；在裂纹深度较浅(0.5 mm)时，裂纹诱发的转子附加弯曲效应并不明显；随着裂纹深度的增加，系统应力分布重组和附加弯曲越趋于严峻，当裂纹深度较深(1.5 mm或2.5 mm)时，裂纹诱发的转子附加弯曲效应较为突出。该...     

周向裂纹管道在含扭转各种组合变形时的极限载荷分析

到目前为止，还没有文献给中向裂纹管道在非对称弯曲及扭转组合变形时的塑性极限载荷计算公式。文中根据净截面垮塌准则用沙堆比拟法分别求出埋藏裂纹、外表面裂纹、内表面裂纹、穿透裂纹管道发生扭转变形时的塑性极限扭矩；给出含周向裂纹薄壁管道横截面上的剪应力分布规律，其塑性极限扭矩等于一个闭口薄壁截面与一个开口薄壁截面圆环的塑性极限扭矩之和，闭口薄壁截面的壁厚为管道壁厚减裂纹深度；开口薄壁截面的壁厚为裂纹的深度。推导了各种周向裂纹管在内压、轴力、扭矩及非对称弯矩共同作用时的塑性极限载荷关系式，并由此给出其他一些组合变形时的极限载荷计算公式。本文结果可供管道安全评价时参考。     

一种表面裂纹可靠性分析方法

建立受剪应力表面裂纹塑性失稳扩展的可靠性分析模型。采用三维弹塑性模型对其综合变量Ｊ积分进行了计算，分析在不同的无量纲裂纹尺寸和外载应力情况下，裂纹失稳扩展的失效概率分布规律，为工程检测和维修提供指导。     

桥式抓斗卸船机滑轮座底部裂纹的处理及分析

针对650 t/h桥式卸船机滑轮座根部出现的裂纹问题,分析了桥式卸船机滑轮座的工作状态,指出产生裂纹的原因是该处结构承受较大的交变应力和存在焊接缺陷所致。针对原设计的不足,提出通过改变滑轮座的结构形式来改变其应力分布的修复方案。基于Ansys软件的研究结果表明,该方案降低了滑轮座底部应力,使裂纹扩展现象停留在＂裂纹萌生阶段＂,提高了设备的使用寿命。     

Fatigue growth simulation for cracks in notched and unnotched round bars

Fatigue crack growth for various cracks in both unnotched and notched round bars is directly modelled by using an automated numerical technique, which calculates the stress intensity factors at a set of points on the crack front through the three-dimensional finite element method and then applies an appropriate fatigue crack growth law to this set of points to obtain a new crack front. This technique also has the capability of automatic remeshing so that the crack propagation can conveniently be followed. The crack geometries modelled in the present paper include a small internal crack near the free boundary and several initially part-elliptical or irregular surface cracks in a smooth round bar under tension, a surface crack in different semi-circularly notched bars under both tension and bending, a surface crack initiated from the root of a V-notched bar and an initially twin crack configuration within a smooth tension bar. Some fatigue growth characteristics relevant to each type of cracks are also revealed. It is demonstrated that the fatigue growth analyses of various cracks commonly occurring in bars can reliably be made by using the automated finite element technique proposed.     

Crack propagation behavior based on the characteristic of the interaction between two fatigue cracks

Stress interaction fields, which are caused by propagating cracks and other defects, can weaken structures. In this study, crack behavior in the interaction field caused by two different cracks is experimentally studied. In the experiment, the vertical distance between two cracks and the applied stresses are varied to craate different stress interaction fields. In addition, the effect of the plastic zone is used to examine the crack propagation path and rate. Three types of crack propagation in the interaction field were found, and the crack propagating path and rate of two cracks were significantly affected according to different applied stresses as each crack propagates. These results are attributed to the effect of the size and shape of the plastic zone.     

Identification of multiple cracks in beams under bending

The identification of a transverse crack on a beam is the subject of many investigators. Identifying the crack means to find its position and depth. In many cases there are more than one cracks on a beam. Then the solutions, or the combinations of parameters characterising the cracks are more and the problem becomes more complicated particularly when the crack must be identified using one more parameter, the relative each other angular position.In the present paper the dynamic behaviour of a cracked beam with two transverse surface cracks is studied. Each crack is characterised by its depth, position and relative angle. Both cracks are considered to lie in arbitrary angular positions with respect to the longitudinal axis of the beam and at any distance from the left end. A local compliance matrix of two degrees of freedom, bending in the horizontal and the vertical planes is used to model the rotating transverse crack in the shaft and is calculated based on the available expressions of the stress intensity factors and the associated expressions for the strain energy release rates. The compliance matrix is calculated for the first time at any angle of rotation. Thus, the compliance is given as a function of both the crack depth and the angular location. These expressions are usable, due to the stress intensity function limitations, only for limited regions around the zero angular position of the crack and not for every crack angle. For these cases, B-spline curves are used to interpolate the known points and a function in analytical form is given for every crack depth and angle. It is well known that when a crack exists in a structure, such as a beam, then the natural frequency of vibration decreases. This reduction is studied here for six independent parameters namely the depth, the location, and the rotational angle of each crack. By keeping these six parameters constant, the first three flexural eigenmodes can be computed and plotted.Due to its sensitivity in slope or displacement changes the theory of wavelets is used here to identify the locations of the cracks reducing thus the number of independent parameters. As it is well known the existence of a crack on a beam in bending, creates in the elastic line of the beam a slope discontinuity analog generally to the crack depth and additionally here to the angular position. The wavelet transformation of a vibration mode or of the vibration response of the structure under some circumstances could be used to locate the cracks. If the positions are known, then the depths and the respective angles can be determined. Here the diagrams of the first three eigenvalues versus both the crack depth and the rotational angle, are used to identify the remaining unknown parameters for both cracks.     

压弯组合应力下高强钢焊接板表面裂纹疲劳寿命计算

潜艇上浮下潜运动使得其耐压壳承受交变的外压载荷。潜艇耐压壳的疲劳热点为锥一柱过渡结构连接焊缝焊趾处，该处所受的应力特征为压弯组合应力。压弯组合应力下表面裂纹应力强度因子及其疲劳寿命的计算尚无报道。弄清楚压弯组合应力作用下带表面裂纹焊接板试件的疲劳特性对潜艇等结构的疲劳研究是必要的。文中提出用成一定角度的对接焊板试件和轴向加载获得压弯组合应力来模拟潜艇耐压壳锥一柱焊接结合区的应力特征的实验方法。用980高强钢作试件，研究焊趾处预制表面裂缝，并在压弯组合应力为特征的疲劳载荷作用下表面裂纹的疲劳行为。给出高强钢焊趾表面裂纹在压弯组合应力下应力强度因子及其疲劳寿命计算式。该结果可供海洋平台、压力容器及管道的某些受力特征为压弯组合应力的重要结构的疲劳设计时参考。     

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.     

热疲劳裂纹网的屏蔽规律及主裂纹应力强度因子的计算方法

热疲劳裂纹网中主裂纹的应力强度因子可反映构件的损伤程度,然而由于裂纹间的屏蔽效应,直接计算裂纹网中主裂纹的应力强度因子是困难的。根据热疲劳试验提出假设：① 主裂纹不会位于裂纹网的边缘;② 裂纹网中的裂纹互相平行,且垂直于约束方向。定义主裂纹的屏蔽剩余百分数s,裂纹的比间距n,裂纹长度比f。分别研究两条长度相等裂纹、两任意长度裂纹、三条裂纹和多条裂纹屏蔽效应的规律。发现s-f-n有确定的关系,这一关系由裂纹网的结构确定,而与边界条件、裂纹尺寸等因素无关。利用屏蔽效应的规律可由单条裂纹时的应力强度因子推算裂纹网中屏蔽效应发生时主裂纹的应力强度因子。算例表明此方法精确、简便、快捷。     

The equivalent elastic compliances of an elastic solid with interface cracks

A periodic array of interface cracks was considered earlier as a simple model to study the effect of crack interaction on the elastic fields of a solid composed of two dissimilar isotropic elastic materials. This paper focuses on the perturbation of the elastic compliances of the solid due to the interacting interface cracks. The problem is formulated using Betti's reciprocal theorem. The analysis provides the equivalent elastic compliances in terms of the geometric parameters of the interface cracks for various levels of loadings and material combinations. The results show that the interaction between cracks is significant only when the crack spacing is less than four times the crack length. Also, contact between crack faces introduces coupling between applied shear stress and normal displacement, but it is significant only when the ratio of the magnitudes of the shear and normal stresses exceeds two.     

复合结构圆柱钱币裂纹的应力强度因子

利用裂纹张开能量释放率建立一个求解复合圆柱钱币裂纹应力强度因子的方法。给出G^*-积分在三维裂纹裂尖边缘近场的应力强度因子表征，G^*-积分与载荷、几何参量以及力学性能参数的关系，进而得到复合圆柱钱币裂纹的应力强度因子。研究表明该积分法用于分析计算有限边界三维裂纹问题，过程极为简单。