含缺陷起重机箱形梁结构断裂分析与有限元仿真

针对起重机箱形梁结构的高发性疲劳裂纹,以线弹性断裂力学理论为基础,结合集装箱门式起重机实际裂纹扩展机理和整机的有限元结果,推算出典型工况下应力强度因子的理论值;利用ANSYS的Shell-Solid子模型技术和参数化设计语言(APDL),建立参数化的裂纹子模型。通过有限元分析,研究箱形梁下盖板从中心裂纹扩展至边裂纹情况下的应力分布情况。再利用KCALC后处理命令得到应力强度因子的有限元值,与理论值比较分析。并深入地研究了裂纹参数、主腹板厚度和下盖板厚度等对应力强度因子的影响。为起重机箱形梁结构设计和安全评定提供依据,具有重要的工程实用价值和理论意义。     

桥式起重机焊接箱形梁疲劳裂纹与剩余寿命的研究

以桥式起重机焊接箱形梁为研究对象,运用断裂力学,对强度因子和疲劳裂纹扩展公式加以修正,研究了在恒幅与随机变幅载荷作用下线弹性裂纹的扩展情况,以及材料在小范围屈服的情况下弹塑性裂纹的扩展情况。该研究与实际情况更加接近,能够相对准确地估算出桥式起重机的剩余寿命,对于减少起重机疲劳破坏事故的发生,指导起重机的设计、制造和特种设备的检验分析具有重要意义。     

基于Ansys的桥式起重机焊接箱形梁疲劳裂纹研究

桥式起重机箱形梁是典型的薄壁结构,由于起重机受载情况及本身结构焊接缺陷等因素,在箱形梁上很容易出现疲劳裂纹。针对桥式起重机箱形梁疲劳裂纹现象,借助Ansys有限元软件,对箱形梁典型工况进行受载分析,判断出裂纹的位置及其产生原因;运用断裂力学和Ansys软件分析模拟出箱形梁疲劳裂纹的应力场、位移场以及应力场区域的大小,对起重机箱形梁进行疲劳裂纹扩展以及剩余寿命的预估都有意义。     

起重机箱型梁疲劳裂纹与寿命预估

起重机疲劳裂纹是起重机破坏的主要形式之一,根据断裂力学与损伤力学,给出了单一裂纹的线弹性与弹塑性的应力强度因子和恒幅载荷与无级变幅载荷下的疲劳裂纹扩展公式,推导出了在无级变幅载荷下多裂纹的应力强度因子公式.运用起重机数据记录仪测得的数据,结合峰值计数法,得出起重机箱形梁的应力谱.结合实例对1台在役起重机箱型梁疲劳裂纹进行分析,实例表明,推导出的疲劳裂纹公式能够正确快捷地求出箱型梁的疲劳寿命;对特种设备检验以及减少起重机疲劳事故的发生具有重要的工程价值.     

起重机焊接箱形梁存在裂纹缺陷的可靠度估算

根据断裂力学及可靠性理论,提出了一种起重机焊接箱形梁存在裂纹缺陷的可靠度计算方法。并根据有关文献给出的试验数据,对试验梁的疲劳可靠度进行了估算,计算结果表明所推荐的计算方法有一定的参考价值。     

起重机焊接箱形梁疲劳可靠度及初始裂纹的蒙特卡罗仿真

断裂力学已被学术界公认是一种估算焊接结构件疲劳寿命最有效的解决方法,但在该方法的应用过程中,还存在着一些混乱现象,尤其对疲劳寿命影响较大的初始裂纹在现有技术难以检测的情况下,不同学者往往给出不同的假设,造成所评估的疲劳寿命相差很大.针对这些状况,分析并澄清在应用断裂力学理论进行焊接结构件疲劳可靠度估算中,应力幅的正确使...     

桥式起重机箱形梁疲劳裂纹及其剩余寿命

疲劳裂纹是导致桥式起重机箱形梁失效的主要原因,本文以75/20 t×16 m桥式起重机为例,分析其箱形梁疲劳裂纹主要产生位置及产生原因,利用ANSYS得到箱形梁疲劳裂纹在扩展阶段的应力场和位移场,分析其扩展规律,并提出一种结构改进方法,并通过ANSYS验证了这种方法的合理性。采用损伤容限设计法对桥式起重机箱形梁疲劳裂纹的剩余寿命进行计算和分析。     

基于等效裂纹法的桥(门)式起重机箱形梁疲劳寿命估算

针对起重机箱形梁结构及其受力情况复杂的特点,提出了一种以疲劳试验数据为基础的等效裂纹法来估算疲劳寿命。疲劳试验数据能够很好反映结构疲劳危险处的应力集中影响。箱形梁疲劳危险点处的应力集中影响可以大概等效为一未焊接平板上具有一等效裂纹,并用Paris公式计算等效裂纹的扩展寿命。通过将该方法的估算结果与文献中的疲劳试验结果进行对比分析,文中方法对于常幅载荷作用下的疲劳寿命估算是有效可行的,而对于变幅载荷作用下的疲劳寿命估算还有待进一步研究。     

基于ANSYS的焊接箱形梁裂纹断裂分析

以断裂力学理论为基础,推导了焊接箱形梁裂纹尖端应力强度因子计算公式,以ANSYS作为计算工具,模拟焊接箱形梁裂纹扩展,并采用奇异单元计算在不同长度初始裂纹下起重机焊接箱形梁应力强度因子范围。     

基于有限元法对裂纹尖端应力强度因子的计算分析

应力在裂纹尖端会出现无限大的奇异性,但应力强度因子K则为有限值,是表征裂尖应力场强弱的物理参量。采用J积分法,位移外推法和相互作用积分法等3种不同的方法计算断裂模型裂尖的K值,并研究了受力、裂纹长度、含裂纹构件的几何参数等对裂纹尖端应力强度因子的影响。结果表明3种方法模拟出的K值结果一致性较好,与应力强度因子手册值相比都能达到较高精度。对照3种方法,分析出各种方法的优胜劣汰,对应用数值法计算应力强度因子方法的选择具有借鉴和参照作用。     

服役起重机箱型梁结构三维裂纹应力强度因子的有限元模拟

超设计役龄的起重机呈现逐年增长的趋势,大批的服役起重机,由于损伤的累积,钢结构性能退化,形成了极大的安全隐患。因此,对服役起重机箱梁结构的疲劳强度计算具有十分重要的意义。以有限元软件ANSYS为工具,建立在役起重机箱梁结构的三维裂纹模型。通过单元节点耦合的方法,将壳单元与体单元有效连接,保证了计算结果的精确性,并采用奇异单元计算在不同长度初始裂纹下在役起重机焊接箱形梁的应力强度因子,运用Matlab软件对结果值进行曲线拟合,并与实验结果相比较,结果表明该法可获得较好的精度,有利于三维裂纹分析在工程中的推广应用。     

桥式起重机箱形主梁焊缝疲劳寿命研究

以某桥式起重机箱型主梁为研究对象,利用ANSYS软件对其进行静态分析,结果表明该起重机静强度以及静刚度均满足设计要求。依据英国标准BS7608,采用FE-SAFE疲劳软件,对主梁翼缘焊缝疲劳寿命进行分析,得出该起重机主梁下翼缘板与主腹板连接处的翼缘焊缝处疲劳寿命最低。并对该处采用不等边角焊缝模型进行对比分析,结果显示适当增加角焊缝一边的长度,且长边位于翼缘板上时,同一焊缝上两条焊趾处的疲劳寿命均有所提高,有助于改善焊接结构件的抗疲劳性能。     

Crack problems in plane and antiplane elasticity using a singular integral equation

A numerical integration formula for the investigation of the singular integral of loakimidis for classical crack problems in plane and antiplane elasticity is developed. The method is based on a modification of the Gauss-Chebyshev quadrature and the definition of finite part integral having an algebraic sigularity of (−3/2) at the limits of integration. Once developed the procedure is applied to the determination of finite part integrals which have analytical solutions and the results are compared. Finally the integration for mula is applied to an actual crack problem and the stress intonsity factors are computed and presented.     

含裂纹传动轴有限元建模及计算

传动轴在工作运行过程中,常在阶梯处出现裂纹导致轴的破坏。为了研究裂纹扩展导致轴的断裂问题,用有限元方法对传动轴阶梯处椭圆裂纹应力强度因子进行了数值计算;在裂纹前沿设置了一系列三维奇异单元来模拟裂纹尖端奇异性,并在阶梯处模拟了过渡圆角单元;通过建立含三维裂纹的子模型和与之相匹配的装配模型,组合成了阶梯处带椭圆裂纹的传动轴断裂力学有限元分析模型;在弯扭组合载荷情况下,分析了不同长度和不同深度裂纹应力强度因子峰值的变化规律。     

LDF型单梁桥式起重机小偏轨箱形主梁的优化设计

对ＬＤＦ型小偏轨单梁起重机主梁进行了优化设计，给出了影响主梁强度、刚度、疲劳强度、稳定性、工艺性能等的约束条件。对１１７种主梁最优化截面规格进行合并，形成了３４种主梁截面规格。归纳总结出了对主梁截面尺寸起主要限制作用的性能参数。     

基于ABAQUS的不同形式裂纹前端建模分析

以带有裂口的3点弯曲试件为研究对象,通过计算得出该模型应力强度因子的理论值.基于ABAQUS软件帮助文档提供的2种不同裂纹前端建模方法,对静载下试件分别进行断裂力学的仿真计算,得到相应的应力强度因子.并将理论计算和2种不同裂纹前端建模方式的模型有限元仿真计算中的应力强度因子进行了比较和分析.     

Creep-fatigue crack growth behavior of a structure with crack like defects at the welds

A study on a creep-fatigue crack growth behavior has been carried out for a cylindrical structure with weldments by using a structural test and an evaluation according to the assessment procedures. The creep-fatigue crack growth behavior following the creep-fatigue crack initiation has been assessed by using the French A16 procedure and the conservatism for the present structural test has been examined. The structural specimen is a welded cylindrical shell made of 316 L stainless steel (SS) for one half of the cylinder and 304 SS for the other half. In the creep-fatigue test, the hold time under a tensile load which produces the primary nominal stress of 45 MPa was one hour at 600°C and creep-fatigue loads of 600 cycles were applied. The evaluation results for the creep-fatigue crack propagation were compared with those of the observed images from the structural test. The assessment results for the creep-fatigue crack behavior according to the French A16 procedure showed that the A16 is overly conservative for the creep-fatigue crack propagation in the present case with a short hold time of one hour.     

Analysis of a radial crack in cross-ply laminates under uniaxial tension

The problem of a radial crack in cross-ply laminates under uniaxial tension is investigated in this paper. The normalized stress intensity factors are obtained by the modified mapping collocation method which is based on analytic complex function theory of complex variables. The present results for an isotropic infinite plate show good agreement with existing solutions. In the range of small crack length, the stress intensity factor for a radial crack in cross-ply laminates under uniaxial tension becomes larger as the percentage of 0° plies increases. However in the range of large crack length, it is insensitive to the percentage of 0° plies.     

Optimisation Method for Determination of Crack Tip Position Based on Gauss-Newton Iterative Technique

In the digital image correlation research of fatigue crack growth rate,the accuracy of the crack tip position determines the accuracy of the calculation of the stress intensity factor,thereby affecting the life prediction.This paper proposes a Gauss-Newton iteration method for solving the crack tip position.The conventional linear fitting method provides an iterative initial solution for this method,and the preconditioned conjugate gradient method is used to solve the ill-conditioned matrix.A noise-added artificial displacement field is used to verify the feasibility of the method,which shows that all parameters can be solved with satisfactory results.The actual stress intensity factor solution case shows that the stress intensity factor value obtained by the method in this paper is very close to the finite element result,and the relative error between the two is only-0.621％;The Williams coefficient obtained by this method can also better define the contour of the plastic zone at the crack tip,and the maximum relative error with the test plastic zone area is-11.29％.The relative error between the contour of the plastic zone defined by the conventional method and the area of the experimental plastic zone reached a maximum of 26.05％.The crack tip coordinates,stress intensity factors,and plastic zone contour changes in the loading and unloading phases are explored.The results show that the crack tip change during the loading process is faster than the change during the unloading process;the stress intensity factor during the unloading process under the same load condition is larger than that during the loading process;under the same load,the theoretical plastic zone during the unloading process is higher than that during the loading process.     

三轴应力状态下复合型裂纹尖端前缘的塑性区分布

利用Ｍｉｓｅｓ屈服准则从理论上分析了Ⅰ－Ⅱ复合型裂纹尖端前缘的塑性区分布。推导出了由三轴应力约束参数Ｔｚ参与表征的裂纹尖端前缘塑性区尺寸ｒｐ的表达式，并绘制出了Ⅰ－Ⅱ复合型裂纹在单轴、双轴载荷作用下裂纹尖端塑性区的分布图。