共查询到19条相似文献,搜索用时 210 毫秒
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本文采用四点弯曲试件考察了常用韧性材料16MnR钢中Ⅰ-Ⅱ复合型裂纹的断裂机理。实验测定了裂纹扩展方向和裂纹尖端位移参量的启裂值;与此同时,采用有限元程序计算了试件中复合型裂纹尖端邻域的应力、应变场,分析了各种控制空洞成核的力学参量的几何分布曲线,结合实验研究和有限元分析表明,Ⅰ-Ⅱ复合型断裂存在两种不同的断裂机理,它们的发生取决于Ⅰ-Ⅱ复合型载荷比的大小,当Ⅱ型载荷分量小于一临界值时、断裂为张开型.裂纹扩展方向与本文的бm峰值线准则一致;而当Ⅱ型载荷分量大于此临界值时,断裂表现为不稳定的剪切型断裂。 相似文献
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Ⅰ-Ⅱ复合型裂纹扩展问题是工程断裂问题中常见的问题,也是断裂力学研究中重要的问题之一。基于复合型裂纹尖端附近等σθεθ线包围区内的体积应变能变化,建立了Ⅰ-Ⅱ复合型裂纹等σθεθ线体积应变能断裂准则,提出了裂纹开裂角公式和断裂扩展条件。应用该断裂准则分别研究了纯Ⅰ型、纯Ⅱ型和Ⅰ-Ⅱ复合型裂纹的开裂角及断裂韧度比随着泊松比的变化规律。此外,给出了复合型裂纹荷载临界比值随裂纹初始角β的变化规律。最后将研究结果与理论预测值和实测值进行了对比,对比结果表明提出的复合型断裂准则物理意义明确,且具有较好的精度。 相似文献
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Ⅰ-Ⅲ复合型裂纹疲劳扩展门槛值 总被引:2,自引:0,他引:2
以垂直于裂纹扩展径向平面上的主应力σ1 及极径r的组合量 2πr·σ1 为主应力强度因子 σ1 ,提出主应力强度因子下的复合型裂纹初始扩展准则及扩展的静态断裂模型 ,在此基础上推导复合型裂纹的门槛值方程和裂纹面扭转角公式及裂纹扩展速率公式 ,定义复合型裂纹的理论门槛值 ,进行Ⅰ Ⅲ复合型裂纹扩展试验。试验表明 ,文中提出的疲劳裂纹扩展门槛值模型是适用的 相似文献
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本文主要在现有的复合型裂纹扩展理论的基础上,针对汽车变速器轴类零件应力应变特点,提出基于塑性区向径应变能的裂纹扩展准则的汽车变速器轴类零件的强度分析。并运用该裂纹扩展准则和对应的分析估算方法,对现有的变速器轴类零件进行分析估算,验证准则及方法的准确性和可行性,并推广应用到汽车变速器轴类零件的设计优化上,以提高汽车变速器轴类零件的设计效率及使用寿命。 相似文献
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采用金相观察和图形分析相结合的方法研究裂尖区域的晶粒变形,可以对试件内部断裂过程区受载后的塑性变形进行直接的定量测试,从而为分析复合型裂纹的破坏机理和断裂过程提供实验依据。本文研究表明,I-Ⅱ复合型裂尖延伸区的破坏以空穴机理为主导,较低的塑性变形即可引起韧窝型起裂;锐化尖角区可以承受很大的累积塑性变形,是集中剪切型断裂的起点。研究结果还表明,拉抻试件的等效塑性变形远低于I-Ⅱ复合型裂纹锐化尖角区的变形,用拉伸试件得到的应力应变曲线不能满足分析复合型裂纹尖端应力应变的需要。 相似文献
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《机械传动》2016,(9):179-183
以渐开线圆柱齿轮为研究对象,在其齿根部存在初始裂纹的前提下,研究齿根疲劳裂纹扩展特性及其寿命;将齿轮啮合过程的动力学计算等效为多个啮合位置的静力分析,得到不同位置的应力强度因子;根据线弹性断裂力学,将裂纹扩展过程线性等效,以K判据分析裂纹是否发生扩展,根据Paris准则计算裂纹扩展量,采用最大周向应力准则确定裂纹扩展角度,得到整个计算周期的应力强度因子、疲劳裂纹扩展路径及疲劳寿命;采用高频试验台对齿轮进行疲劳试验,得到齿轮的疲劳扩展路径,与有限元计算结果进行对比验证;最后分别分析了初始裂纹的尺度、位置和载荷的不同对疲劳裂纹的扩展及疲劳寿命的影响。 相似文献
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E. E. Gdoutos 《International Journal of Mechanical Sciences》1981,23(3):121-128
The fracture characteristic behaviour of a cracked plate subjected to a localised in-plane moment is studied in the framework of the linear theory of fracture. The critical fracture moment and the angle of crack extension are determined using the maximum hoop stress and the minimum strain energy theories. Important results concerning the dependence of the more vulnerable crack tip from which fracture initiates as well as the fracture moment and the crack extension angle on the location of the applied moment are derived. 相似文献
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针对含Ⅰ+Ⅱ应力复合型裂纹的焊接接头,应用弹塑性有限元方法分析了其裂端应力场的分布规律。并对不同组配焊接接头的裂纹张开位移(COD)断裂参量及其复合角进行了数值计算,讨论了加载角度和接头强度组配对焊接接头中应力复合型裂纹的断裂行为及其断裂参量的影响机制。研究结果表明,无论何种强度组配,焊接接头裂纹尖端应力场的分布是不对称的。裂端上部发生锐化现象,而裂端下部发生钝化现象。断裂参量COD值的大小受接头组配的影响,因此,不能简单地采用全母材的性能代替接头进行焊接接头的断裂分析。加载角度对焊接接头中复合型裂纹Ⅰ、Ⅱ型主导性存在很大的影响,而接头强度组配对其影响不明显;而裂纹复合角则会受到加载角度及材料组配因素的影响。因此,在进行含应力复合型裂纹的焊接接头的COD断裂参量的计算时,必须考虑这些因素的综合影响作用。 相似文献
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V.P. Golub 《International Journal of Mechanical Sciences》2005,47(12):1807-1826
A new approach has been suggested for the construction of long-term fracture criteria under creep conditions and multi-axial loading. The method developed overcomes former problems with a view to identifying stresses responsible for failure and material constants, and is based on the equivalent long-term strength diagrams. The criteria are chosen in the form of a mixed invariant relating two stress components, which give rise to brittle and viscous fracture. The values of stress characteristics combined in a mixed invariant take signs of principal stresses into account. The fracture criteria derived have been approved on unified long-term strength diagrams of thin-walled tubular specimens under internal pressure, internal pressure with tension, pure torsion and tension with torsion. 相似文献
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Usik Lee 《Journal of Mechanical Science and Technology》1998,12(2):233-243
This paper considers smeared continuum damage mechanics based on the equivalent elliptical crack representation of a local
damage. This approach provides a means of utilizing the crack energies derived in fracture mechanics, and of identifying the
local damage state from local stress and strain information. The strain energy equivalence principle is used to derive the
effective continuum elastic properties of a damaged solid in terms of the undamaged elastic properties and a scalar damage
variable. The scalar damage variable is used to develop a consistent damage evolution equation. The combination of representing
local damage as an equivalent elliptical crack, the determination of effective elastic properties using a strain energy equivalence
principle, and a consistent damage evolution equation yields a simple, yet powerful local approach for continuum damage analysis 相似文献
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The impact-induced buckling and delamination of a thin coating was analysed for the purpose of predicting the amount of coating removed when a single particle was launched, at a given velocity, against a coated substrate. A novel post-buckling analysis is presented in which the coating is modelled as a clamped disk prevented from buckling at an arbitrarily set inner radius, due to the presence of the indenting particle. A method for calculating the arrest strain energy release rate and mode mix of interfacial delamination cracks, based on the coupling of the presented buckling analysis with an existing strain energy release rate analysis is then presented. A method to estimate the critical interfacial shear stress at crack initiation is also outlined. An accompanying paper compares experimental results with the results of this analysis, and shows how the results can be used in the context of blast cleaning. 相似文献
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The conventional fracture mechanics parameters KIC and/or JIC are used as fracture toughness criteria necessary for the start of crack propagation under plane strain conditions. These criteria are defined only for small-scale yielding or infinitesimal deformation, though actual fractures involve large plastic deformation. Hence, measurement of fracture resistance during crack propagation is difficult with the conventional parameters.Estimating the mechanical conditions around the propagating crack tip is very useful for reducing damage during accidental fracture. Therefore, establishing a criterion for crack propagation with large-scale yielding is very important for not only science fields but also some industrial fields. For fractures with large-scale yielding, micro- or mesoscale damage processes in the crack tip vicinity have to be considered.In this study, Gurson's constitutive model for void occurrence and growth was introduced into the finite element method to discuss failure behavior in the crack tip vicinity. Fast crack propagation behavior under high-speed deformation was simulated using the moving finite element method based on the Delaunay automatic triangulation. The excellent far-field integral path independence of the T* integral was verified for pure mode I fast crack propagation and non-straight crack propagation under mixed mode conditions. The void growth conditions near the crack propagation path were evaluated. 相似文献
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韧性材料的几种断裂形式及判据讨论 总被引:13,自引:3,他引:13
考察几种韧性材料的复合型断裂试验过程,用传统强度理论思想认定启裂位置与启裂方向,通过对不同物理机制的断裂形式变化规律的研究,判定韧性材料的主要断裂形式有三类,以空穴成核、扩张、聚合为主导机制的正拉断,和以局部剪切带形成、发展为主导机制的两种不同类型的剪切断裂。局部大塑性变形的出现在材料内引起损伤,空穴的聚合或局部剪切带的出现仅发生在载荷达到某一临界值时。导致材料断裂发生的根本因素,是危险点上某应力参数达到了材料的断裂临界值,以此对不同断裂形式的断裂判据进行讨论,提出新的韧性断裂判据。 相似文献
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基于断裂力学理论,推导撕裂能与疲劳裂纹扩展速率间的函数关系式,将复杂的多方向应力转化为单轴等效应力,建立丁腈橡胶疲劳寿命预测模型。选用Mooney-Rivlin本构模型来表征丁腈橡胶超弹性力学行为,在简化DAS组合密封圈结构后建立有限元模型,并通过计算应力分布确定危险单元位置。通过拟合拉伸试验数据得出应力应变关系,采用数值分析方法计算撕裂能变化量,并预测裂纹萌生位置与疲劳寿命。结果表明,DAS组合密封圈的危险单元位置在密封圈接近右侧密封槽倒角处。仿真软件预测的危险单元位置和疲劳寿命与理论计算结果一致,验证理论计算结果的正确性。 相似文献