首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到19条相似文献,搜索用时 171 毫秒
1.
对单晶体以及晶界平行晶粒裂纹和晶界垂直晶粒裂纹的双晶体的断韧性进行了实验研究,设计了三种三点弯曲试件,得到了单晶体和晶界的断裂韧性值,在晶界垂直晶粒裂纹的双晶体试验中,揭示了晶界对晶粒断裂的屏蔽效应;当裂纹距晶界某一特定长度时,断裂韧性值最大,理论分析和晶体滑移有限元数值分析揭示了这种屏蔽效应的机理,双晶晶界处的变表相容性导致了理解纹尖端应国和场的重新分布,并由此产生了晶界屏蔽效应。  相似文献   

2.
通过聚碳酸酯紧凑拉伸试件的疲劳裂纹扩展速率试验和同时进行的光弹性实验,作者发现随着疲劳裂纹的扩展在裂纹尖端附近产生逐渐加强和扩大的残余应力场,揭示出了裂纹尖端附近的闭合效应的存在,它将使应力强度因子降低.因此,疲劳裂纹扩展过程中应力强度因子幅度△K 的理论值应该修正。本文提出了一种简便有效的修正方案.  相似文献   

3.
本文对带环状预裂纹的LD8铝合金缺口试件进行了研究.结果表明:疲劳裂纹扩展速率da/dN与当量J积分范围△J-f的关系不受缺口型式和加载应变范围的影响,用当量J积分来评价铝合金的高温低周疲劳裂纹扩展规律是有效的  相似文献   

4.
李健康  黄义仿 《实验力学》1996,11(2):222-227
本文对35CrMo钢和42CrMo钢带穿透短裂纹(初始裂纹长度a=0.1~0.5mm)的试件进行了弯曲疲劳试验研究,得到了在弯曲疲劳加载下短裂纹扩展速率的计算表达式以及应力比,试件厚度对短裂纹扩展的影响。  相似文献   

5.
随机超载对疲劳裂纹扩展迟滞效应的模拟   总被引:1,自引:0,他引:1  
考虑超载的迟滞效应,对随机超载作用下的疲劳裂纹扩展进行了模拟计算.载荷谱为在基本恒幅循环载荷基础上加入一以泊松流发生的随机超载序列,超载的大小为均匀分布.采用裂纹闭合模型考虑超载的迟滞效应,认为裂纹张开应力在超载引起的塑性区内按线性规律衰减.循环续循环模拟计算出裂纹从初始长度一直到疲劳破坏的扩展曲线.据此,计算了各种超载发生强度和大小下的疲劳裂纹扩展寿命的平均值与标准差。  相似文献   

6.
疲劳裂纹扩展随机模型研究近期进展   总被引:3,自引:0,他引:3  
自1979年Virkler等人发表揭示疲劳裂纹扩展的统计性质的实验结果以来,各国学者相继提出了多个疲劳裂纹扩展的随机模型.本文从数学与物理角度对这些模型作了概括与评述,指出了各个模型之间的关系,并对今后应作的进一步研究提出了我们的看法.  相似文献   

7.
考虑材料循环塑性的疲劳裂纹扩展模拟   总被引:1,自引:1,他引:1  
提出了一种考虑材料循环塑性性能的研究疲劳裂纹扩展与闭合行为的有限元模拟方法.对所选用的循环塑性本构关系进行了基本实验检验.探讨了在疲劳裂纹扩展有限元分析中网格尺寸的影响,给出了网格优化准则.研究了在循环硬化条件下考虑裂纹合效应时裂纹面张开廓形、裂纹尖端应力、应变场和正反向塑性区的演变规律.对于循环硬化和不同循环应力比R等因素对裂纹张开应力水平的影响也作了考察  相似文献   

8.
扩展有限元法在结构件疲劳寿命估算中的应用   总被引:1,自引:0,他引:1  
为了高效、准确估算飞机典型结构件的疲劳扩展寿命,基于通用有限元分析软件ABAQUS的扩展有限元功能计算应力强度因子,采用NASGRO方程计算疲劳裂纹扩展速率。为了避免大量重复提交运算的繁琐过程,应用PYTHON语言开发了在ABAQUS疲劳裂纹扩展分析中反复调用扩展有限元结果和NASGRO方程的子程序,在指定的疲劳裂纹扩展路径上实现了对飞机连接件疲劳裂纹扩展速率与寿命的计算。结果表明,模拟的疲劳裂纹稳定扩展阶段的寿命曲线与实验结果吻合较好,疲劳寿命误差约为10%。  相似文献   

9.
裂纹闭合效应通常是导致I 型裂纹扩展在高载作用下发生迟滞效应的主要因素之一.本文采用汽车薄板QSTE340TM 材料,针对不同应力比,高载比条件下疲劳裂纹扩展行为进行了实验研究.论文通过断面分析,针对各参数对裂纹闭合效应的具体影响进行了分析讨论,认为裂纹作用区域随裂纹扩展而动态变化,从而提出了一种对有效应力强度因子幅的修正方法.通过在原有模型中引入幂函数形式的动态变量α,表征裂纹闭合效应的作用比例随裂纹长度的动态变化,取得了较好的效果.  相似文献   

10.
通过二元铝锂合金的细观拉伸疲劳实验,动态观察了试样表面金相微观结构组织的变化及微裂纹的萌生及扩展直至断裂的全过程,并分析讨论了晶界及微结构对微裂纹萌生及扩展的影响,微裂纹向短裂纹、长裂纹发展的判据.该实验材料是模型材料,晶界结合强度较弱,裂纹沿晶开裂现象较多.经对实验结果及金相裂纹分析,表明金属材料微结构对裂纹扩展有明显的影响.晶界作为一种物质界面存在于晶粒间,具有一定的物理和力学性质,对微裂纹扩展速率及发展行为有较大影响.  相似文献   

11.
本文应用三点弯曲试样和撕裂模量理论对弹塑性裂纹撕裂扩展的稳定性进行了实验研究,得出了适用于三点弯曲试样的施加撕裂模量T_(app)的计算公式。结果说明了材料硬化和系统柔度等因素对裂纹扩展稳定性的影响。实验中采用多层高柔度组合梁系统,得到了随加载系统柔度增加,裂纹扩展从慢稳定到失稳发展的过程。证明了撕裂模量理论的有效性。实验结果与理论预测相符。  相似文献   

12.
论文针对中密度聚乙烯材料(MDPE),采用平板试样进行了I型疲劳裂纹扩展和单次过载下裂纹扩展试验.发现与金属材料类似,单次拉伸过载对聚乙烯(PE)的疲劳裂纹扩展有明显的迟滞作用,降低了裂纹扩展速率.试验还通过变载荷刻线法获取疲劳裂纹扩展前缘的实际形貌和变化规律,对常规变载荷刻线方法进行了调整和验证,其修正方法对高分子材料的疲劳裂纹扩展前缘刻线具有较好的效果.通过观察发现含楔形塑性区的裂尖钝化是裂纹迟滞的主要原因.过载引入的塑性区内残余应力对裂纹迟滞也起了重要作用.论文利用Dugdale模型计算了塑性区尺寸,使用基于残余应力的Wheeler模型对过载迟滞进行了很好的拟合.  相似文献   

13.
A very simple model of the double cantilever beam (dcb) dynamic crack propagation specimen is studied. The main assumption on which the model is based is that the arms of the dcb specimen deform as shear beams. The particular problem studied is the dynamic growth of a sharp crack from a blunt pre-crack with the ends of the specimen arms held at a fixed separation distance. It is demonstrated that this simple model predicts crack motion which is qualitatively consistent with the results of more detailed numerical analyses of the problem and with experimental results. The analysis employs an energy balance crack propagation criterion and both constant specific fracture energy and a class of crack speed dependent fracture energies are considered. Among the features exhibited by the model is that, for constant specific fracture energy, the crack tip speed is constant from initiation up to arrest. On the other hand, for the same geometry and loading conditions, but a strongly crack speed dependent specific fracture energy, the crack speed decreases gradually between fracture initiation and crack arrest.  相似文献   

14.
A closed form analytical solution of crack propagation in double cantilevered beam specimens opened at a constant rate has been found. Hamilton's principle for non-conservative systems was applied to describe the crack motion, under the assumption of a Bernoulli-Euler beam. The criterion of crack propagation is a critical bending moment at the crack tip. The calculations of beam motion take into account wave effects in the Bernoulli-Euler theory of elastic beams. The beam shape during the crack motion is found with a similarity transformation and expressed by Fresnel integrals. The boundary conditions satisfied are the fixed ones of zero bending moment and constant beam opening rate at the load end of the specimen and the moving ones of zero deflection and zero slope of the deflected beam at the tip of the moving crack. The fracture represents a moving critical bending moment. The analytical results show that the specific fracture surface energy is a unique function of the ratio of the crack length squared to the time subsequent to loading and this is computed from the recorded time-dependence of the crack length.  相似文献   

15.
A novel in situ transmission electron microscopy (TEM) bending method using a nano-cantilever specimen that includes a naturally sharp pre-crack at the interface between a 500 nm-thick SiN layer and a 200 nm-thick Cu layer on a Si substrate is developed in order to precisely characterize the fracture toughness of the interface in nanoscale multilayers. By fabricating a perpendicular nanoscale notch in the SiN layer close to the horizontal Cu/SiN interface, a sharp pre-crack is successfully introduced at the Cu/SiN interface. In addition, by changing the relative position of the notch with respect to the fixed end of the specimen, both the instant and continuous interface crack propagation behaviors could be in situ observed using TEM. Finite element analysis shows that the crack propagation from the sharp pre-crack is dominated by a singular stress field within a region 100 nm from the crack tip under a mixed-mode state in all specimens. On the other hand, the fracture toughness represented by the critical energy release rate for the start of crack propagation along the Cu/SiN interface in all specimens is determined through a compliance method and shows good agreement with an average value of 7.1 J/m2. This indicates the robust reliability and high precision for characterizing the fracture toughness of the interface in nanoscale multilayers.  相似文献   

16.
为研究预制裂纹不同偏移距离时运动裂纹与空孔的相互作用规律,采用动态焦散线实验系统,将预制裂纹的偏移距离设定为唯一变量,对含空孔的有机玻璃(PMMA)试件进行冲击三点弯实验。研究表明,存在两个临界距离:(6 mm (2 R )、9 mm (3 R )),在该偏移距离下,裂纹扩展轨迹、动态断裂特性发生显著改变:(1) 预制裂纹偏移距离不大于3 mm时,裂纹贯穿空孔,发生二次起裂,且二次起裂的速度与应力强度因子显著大于一次起裂,无偏移时裂纹轨迹的分形维数为最小值;(2) 偏移距离增大至6 mm时,裂纹不再贯穿空孔,空孔对裂纹先吸引后排斥,裂纹速度与应力强度因子先减小后增大,裂纹轨迹的分形维数达到最大值;(3) 偏移距离大于6 mm时,空孔对裂纹的吸引作用逐渐减小,大于9 mm后,空孔对裂纹的吸引不再显著,裂纹起裂后即向落锤加载方向扩展直至贯穿试件。  相似文献   

17.
In this paper, the effect of constraint induced by the crack depth on creep crack-tip stress field in compact tension (CT) specimens is examined by finite element analysis, and the effect of creep deformation and damage on the Hutchinson–Rice–Rosengren (HRR) singularity stress field are discussed. The results show the constraint induced by crack depth causes the difference in crack-tip opening stress distributions between the specimens with different crack depth at the same C*. The maximum opening stress appears at a distance from crack tips, and the stress singularity near the crack tips does not exist due to the crack-tip blunting caused by the large creep deformation in the vicinity of the crack tips. The actual stress calculated by the finite element method (FEM) in front of crack tip is significantly lower than that predicted by the HRR field. Based on the reference stress field in the deep crack CT specimen with high constraint, a new constraint parameter R is defined and the constraint effect in the shallow crack specimen is examined at different distances ahead of the crack tip from transient to steady-state creep conditions. During the early stages of creep constraint increases with time, and then approaches a steady state value as time increases. With increasing the distance from crack tips and applied load, the negative R increases and the constraint decreases.  相似文献   

18.
The interaction between piezoelectric screw dislocations and two asymmetrical interfacial cracks emanating from an elliptic hole under combined mechanical and electric load at infinity is dealt with. The closed-form solutions are derived for complex potentials and generalized stress fields. In the limiting cases, some well-known results can be obtained from the present solutions. Moreover, some new exact solutions are shown. The stress intensity factor and the energy release rate at the right tip due to a screw dislocation near the right interfacial crack are also calculated. The results show that the shielding effect of dislocation on crack expanding decreases with the increase in dislocation azimuth angle and the distance between the dislocation and the crack tip, and the repulsion acting on the dislocation from the other half plane demotes crack propagation. The increasing of the length of the other crack promotes crack growth, but the increasing of the minor semi-axis demotes it.  相似文献   

19.
本文应用不同尺寸的三点弯曲试样和带边侧槽试样,用实验方法研究了启裂J积分(J_(1C))和J_R阻力曲线的斜率(dJ/da)受试样尺寸的影响。结果表明,在满足GB2038-80所规定的试样尺寸要求的条件下,J_(1C)值受试样尺寸影响不大,但DJ/da值受试样尺寸影响较大。因此,在应用以J_R曲线理论为基础的裂纹扩展稳定性评定方法时,如撕裂模量理论及EPRI方法,要应用较大尺寸试样或带侧槽试样来测定J_R阻力曲线。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号