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1.
Saralees Nadarajah 《Journal of Mechanical Science and Technology》2008,22(7):1255-1258
It is pointed out that the distribution introduced by Neville [1] (for modeling fracture toughness to failures) is contained
by at least two families of distributions known since the 1940s. Some elementary statistical properties of these families
are discussed. Six data sets on fracture toughness are used to demonstrate that these families are much better models for
fracture toughness than the one introduced by Neville [1]. 相似文献
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Zhang LiZhang YufengHuo LixingSchool of Material Scienceand Engineering Tianjin University Tianjin China 《机械工程学报(英文版)》2004,17(3):346-348
To investigate the effect of dynamic loading on fracture behavior of welded joints of structural steel Q23SB and 16Mn in common use and compare the earthquake resistances of the two kinds of materials, dynamic tension and fracture toughness tests are carried out at room temperature. On the basis of the tests, the stress-strain fields near the crack tip of the compact specimens are analyzed by three-dimensional finite element model. The test results and finite element analysis results show that, the fracture toughness of welds and base metal of 16Mn steel increases with the increment of loading rate. Compared with 16Mn steel, Q235B steel is more sensitive to dynamic loading. The fracture toughness of welds of Q235B is comparatively low under static loading and dynamic loading at room temperature. Compared with the static loading, the fracture toughness of Q235B parent metal under dynamic loading decreases by about four times. Therefore, it can be concluded that compared with 16Mn steel, the earthquake re 相似文献
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提出根据超塑成形-扩散连接(SPF/DB)的工艺技术参数预测扩散连接界面层断裂韧度的计算方法,并对TC4/TA2连接件,开发了相应的界面层断裂韧度的分析和预测软件系统。该计算方法首先在理论分析和试验的基础上,建立扩散连接界面层成长模型,获得扩散连接件界面层厚度的计算公式,确定材料过渡参数m的计算方法;其次对已有的混合型外载的界面断裂准则进行修正,使其适用于扩散连接件界面层断裂时能量释放率曲线的函数模型。计算结果与试验结果吻合良好。分析结果表明:在允许工艺参数范围内,扩散连接件界面断裂韧度随成形温度、成形压力和保压时间的提高而提高。其中,成形压力影响最大,然后依次为保压时间和成形温度。为了提高扩散连接界面层的断裂韧度,必须通过界面层设计来提高其界面裂尖断裂混合度,而上述各工艺技术参数,正与其裂尖断裂混合度的大小密切相关。 相似文献
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从最弱链模型的物理本质出发,探讨了影响焊接热影响区脆性断裂的主要因素。在一定的断裂韧度前提下,随着局部脆性尺寸的增加,焊接热影响区的脆断概率增加。当断裂概率一定时,局部脆性区尺寸增加,焊接热影响区断裂韧度下降。文中讨论了最弱链模型中各参数对断裂概率密度及断裂韧度值分布的影响。. 相似文献
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本工作以玻璃为基质,以金属铝粉为分散相,制备了玻璃/铝复合材料。通过对复合材料断裂韧性的测试及对其断裂表面形貌的分析,提出了金属铝对玻璃的增韧机理。并讨论了影响增韧效果的工艺因素。 相似文献
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在以往的材料断裂韧度测试中,只考虑了对平面应变状态下试件厚度的限制(B≥2.5(KIC/σS)2);而对于非平面应变状态下材料断裂韧度测试中均没有考虑试件厚度的限制。本文从与厚度效应密切相关的应力三轴约束入手,导出了与应力三轴约束TZ相关的裂纹扩展能量释效率G的表达式,进而得出了相应的测试材料断裂韧度的修正R曲线法。最后结合30CrMnSiNi2A钢断裂韧度的实测结果校验了理论分析结果。 相似文献
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Continuous fiber ceramic composites (CFCCs) have advantages over monolithic ceramics: Silicon Nitride composites are not well
used for application because of their low fracture toughness and fracture strength, but CFCCs exhibit increased toughness
for damage tolerance, and relatively high stiffness in spite of low specific weight. Thus it is important to characterize
the fracture resistance and properties of new CFCCs materials. Tensile and flexural tests were carried out for mechanical
properties and the fracture resistance behavior of a SCS6 fiber reinforced Si3N4 matrix CFCC was evaluated. The results indicated that CFCC composite exhibit a rising R curve behavior in flexural test.
The fracture toughness was about 4.8 MPa m1/2 , which resulted in a higher value of the fracture toughness because of fiber bridging. Mechanical properties as like the
elastic modulus, proportional limit and the ultimate strength in a flexural test are greater than those in a tensile test.
Also a numerical modeling of failure process was accomplished for a flexural test. This numerical results provided a good
simulation of the cumulative fracture process of the fiber and matrix in CFCCs. 相似文献
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31Si2MnCrMoVE钢是为符合固体火箭发动机壳体设计需要而专门研制的超高强度钢。随着冶炼技术的进步,31Si2MnCrMoVE钢断裂韧度不断提高,构件采用的板厚也越来越薄。由于较高的断裂韧度和较小的板厚,给钢板表面裂纹断裂韧度测试带来困难,韧带尺寸偏小,难以满足有效性判据。这种情况下,不应该用线弹性断裂力学方法评价材料的断裂韧度,而应采用弹塑性断裂力学测试材料的延性断裂韧度JIC。基于以上原因,在条件断裂韧度不满足有效性判据的情况下,采用试验与有限元分析相结合的方法,通过试验测出裂纹启裂时的条件载荷,用有限元法计算出在条件载荷作用下的延性断裂韧度JIC,再用断裂力学理论转换成表面裂纹断裂韧度KIe。用JIC作为断裂参量,就必须分析J积分的有效性,因此讨论超高强度钢表面裂纹前缘的J守恒和J主导的有效性,从而为固体火箭发动机设计提供依据。 相似文献
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Tribological analysis of fracture conditions in thin surface coatings by 3D FEM modelling and stress simulations 总被引:1,自引:0,他引:1
Kenneth Holmberg Anssi Laukkanen Helena Ronkainen Kim Wallin 《Tribology International》2006,38(11-12):1035
A tribological analysis of deformations and stresses generated and their influence on crack generation and surface fracture in a coated surface loaded by a sliding sphere in dry conditions is presented. A three-dimensional finite element method (3D FEM) model has been developed for calculating the first principal stress distribution in the scratch tester contact of a diamond spherical tip with 200 μm radius sliding with increasing load on a 2 μm thick titanium nitride coated steel surface. The model is comprehensive in that sense that it considers elastic, plastic and fracture behaviour of the surfaces. The hard coating will be stretched and accumulates high tensile stresses. At the same time, it is carrying part of the load and thus reducing the compressional stresses in the substrate under the sliding tip. The first crack is initiated at the top of the coating from bending and pulling actions and it grows down through the coating. The fracture toughness of the coating is calculated by identifying from a scratch test experiment the location of the first cracks and the crack density and using this as input data. 相似文献
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In This study we investigate the dynamic fracture characteristics of a tungsten carbide cobalt (WC-6wt%Co) composite material.
The dynamic fracture initiation toughness and some of the dynamic fracturing characteristics are evaluated by using the Instrumented
Charpy Impact Testing (ICIT) procedure. The dependence of measured time-to-fracture on the tup impact velocity and the dynamic
fracture toughness for the WC-6wt%Co composite material are obtained by using ICIT. The effect of the loading rate on fracture
initiation toughness is found to be negligible when the time-to-fracture is on the order of 50μsec. At significantly higher
rates of loading it is impossible to determine the apparent dynamic fracture initiation toughness because of the influence
of the inertia force on fracture loading. It is found that the impact velocities affect the time-to-fracture significantly
at lower impact velocities for various engineering materials. It is shown that with the decrease of tup impact velocities
the time-to-fracture is increased and the dynamic fracture initiation toughness converges to static fracture toughness. 相似文献
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Many researchers have made a lot of progress in studying the evaluation of fracture probability of brittle materials. However,
studies of fracture probability for elastic-plasticity have not been made yet. An evaluation method for fracture probability
which is grafted onto a 2-parameter criterion and statistical probability analysis is not only introduced in this study, but
also applied to the simple 2-dimensional model and carbon steel piping to vealuate the effect of statistical variables. 相似文献
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Yonjig Kim 《Journal of Mechanical Science and Technology》2009,23(1):8-13
The fracture properties of commercial carbon fiber reinforced carbon (C/C) composites (CCM190C, CCM191C) that have different
interfacial shear strength were investigated. Postpeak tension-softening phenomena were observed through the fracture mechanics
test for these composites. The failure manner in the fracture process zone was primarily fiber pull-out for CCM190C and fiber
breakage for CCM191C, respectively. It was confirmed that the scale of pseudo strain hardening for CCM190C with low interfacial
shear strength was larger than that of CCM191C. The bridging energy at the postpeak part and the total energy consumed to
produce a unit area of fracture surface were calculated based on the J-based technique. The bridging energy at the postpeak
part accounted for 12.3% of the total energy consumed to produce a unit area of fracture surface for CCM190C. From this result,
it can be deduced that the effect of the postpeak bridging energy on the fracture toughness is large for CCM190C. In contrast,
the contribution of the postpeak bridging energy for the total energy per fracture surface was very small for CCM191C.
This paper was recommended for publication in revised form by Associate Editor Chongdu Cho
Yonjig Kim received B. S. and M. S. degrees in Mechanical Design Engineering and Mechanical Engineering at Chonbuk National University
in 1983 and 1985, respectively. He enlisted in the army as a soldier and leaved the army in 1988, and then got a ph. D. degree
in Mechanical Engineering at Chonbuk National University in 1993. Dr. Kim is currently working as a professor in his alma
mater, Chonbuk National University. His major area of study is materials and fracture mechanics and he is interested mainly
in fracture of fiber reinforced polymer composites. 相似文献
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球墨铸铁断裂韧度的可靠性分析 总被引:1,自引:0,他引:1
通常球墨铸铁与其他铸铁材料一样被认为属于脆性材料,断裂韧度应该用线弹性力学理论进行研究。本文发现由于球墨铸铁中的石墨呈球状,当裂纹通过石墨时,裂纹扩展机理将发生相应的变化,结果显示用弹一塑性理论来研究球墨铸铁的断裂韧度是适应和有效的。对可靠度为95%球墨铸铁断裂韧度的区间估计进行分析,以便对工程中的断裂韧度提供相关的数据。 相似文献
18.
通过双悬臂梁和端部切口弯曲试验分别对平纹编织C/SiC复合材料的Ⅰ型(张开型)和Ⅱ型(滑开型)层间断裂行为进行试验研究,得到该材料以临界能量释放率GⅠC和GⅡC表征的层间断裂韧度值.试验后利用光学显微镜对两组试验的试样断口进行显微观察,以分析其破坏机理.结果表明:Ⅰ型层间断裂韧度值GⅠC和Ⅱ型层间断裂韧度值GⅡC分别为(737.2±57) J/m2和(1082.7±90) J/m2;Ⅰ型开裂为层间SiC基体沿初始裂纹方向的断裂破坏;Ⅱ型开裂与Ⅰ型开裂相似,但裂纹上下表面包裹碳纤维束的SiC基体发生脱落,并且出现碳纤维束中部分碳纤维剪切破坏. 相似文献
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J.G. Cheng J. Zhang C.C. Chu J. Zhe 《The International Journal of Advanced Manufacturing Technology》2005,26(11-12):1222-1230
Fracture toughness is one of the most important mechanical properties for sheet metal in many applications. However not enough attention has been paid to the effects of laser forming conditions on fracture toughness of sheet metal. This paper presents an integrated fracture toughness model to study fracture toughness of sheet metal after laser forming. Microstructure, distribution of residual stresses and geometry of sheet metal specimen are considered in the model. Results of residual stress from microstructure-integrated finite element modelling of laser forming are incorporated in the model. Low carbon steel is used in this paper to validate the model. The results from the fracture toughness study are found to be consistent with microstructure analysis . 相似文献