共查询到19条相似文献,搜索用时 250 毫秒
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本文对高应力集中区中疲劳裂纹扩展进行了研究,对两种材料的中心椭圆孔边裂纹板共6个试件进行了低周疲劳试验。为了减少参量计算引起的误差,首先给出了有限宽板中心椭圆孔边裂纹应力强度因子的计算公式,同时对弹塑性材料引入了大范围塑性区修正方法。为了考证公式和方法的正确性,进行了有限元计算。应力强度因子 K 和大范围塑性区修正形式的 K两者都被用作为相应的参量,结果表明:本文发展的大范围塑性修正形式的代表 J 积分的 K,对高应力区疲劳裂纹扩展是一个合适的参量。 相似文献
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以内压条件下含轴向内表面裂纹的管道为研究对象,通过引入x0参数使J积分全塑性解与蠕变指数无关对Zahoor提出的蠕变断裂参数C*估算方法进行改进;采用改进方法、Zahoor估算公式以及参考应力法中的R6整体解和Kim优化解计算不同蠕变指数和不同裂纹尺寸下的C*值,并与有限元计算结果进行比较.结果表明:参考应力法所得C*值比有限元计算结果大2~8倍,准确度较差;改进方法所得C*值与有限元计算结果的比值在1左右,准确度较高;与Zahoor估算公式相比,改进方法在蠕变指数为3时的计算准确度更高,但随着蠕变指数增大,2种方法的计算准确度趋于相同. 相似文献
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厚钢板焊缝强度匹配对韧度影响的试验方法 总被引:1,自引:0,他引:1
提出了研究厚钢板焊缝强度匹配对韧度影响的试验方法:用“直接测量法”确定焊缝强度匹配系数;用裂纹尖端张开位移(CTOD)断裂韧度作为焊缝材料韧度的指标。用“直接测量法”确定了低合金高强钢S355ML钢板(厚65mm)自动埋弧焊和手工电孤焊的焊缝强度匹配系数,同时将这两项焊接工艺的对接焊缝制成全厚度断裂韧度试样,运用裂纹尖端张开位移试验方法测定其焊缝中心的断裂韧度。结果表明,厚钢板焊态对接焊缝,低匹配焊缝具有较高的韧度,高匹配焊缝的韧度比较低。 相似文献
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力学性能不均匀性对焊接接头三点弯曲试样塑性区发展规律的影响 总被引:3,自引:0,他引:3
利用弹塑性有限元方法对焊接接头试样在三点弯曲试验中塑性区的发展情况进行了计算。分析了不同的裂纹深度、强度组配,焊缝宽度以及不同位置裂纹的焊接接头试样对塑性区形状发展的影响规律。分析结果显示,不同强度组配和几何特征的焊接接头试样对裂纹尖端塑性区的发展规律有较大的影响,由于裂纹尖端拘束程度的不同会造成塑性区的形状和尺寸的改变,因此在做焊接接头试样三点弯曲试验时,可能会得出与均质材料试样不同的驱动力曲线 相似文献
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非匹配焊接接头中裂纹尖端三维拘束状态分析 总被引:6,自引:1,他引:5
应用三维弹塑性有限元方法详细分析了焊接接头中裂纹尖端三维拘束状态的分布特征,结果表明:在试样中面附近围绕Ⅰ型裂纹前缘,应力状态均具有明显的平面应变特征,而应力三轴度(Rσ)仅在韧带附近为最大。匹配参数M、尺寸因素(h/a、B、a/w)及加载方式(CCP、TPB、SEC)均会对试样内部的应力三轴度产生显著影响,其中匹配程度是导强度,平面应变参量β仅表示三维应力状态趋珩平面应变的程度大小,而应力三轴度参量Rσ确实描述了三向拉应力状态的严重程度,对于给定试样形式,裂纹张开位移CTOD相等不能保证三维裂纹端存在相似的三轴应力状态,因而用CTOD参量表征材料断裂行为具有局限性。 相似文献
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裂纹的存在及其扩展严重限制着高温承压部件的使用寿命,而目前对结构三维蠕变裂纹扩展行为的认识及其预测仍比较有限。以典型耐热钢P91为例,在650℃下对其开展了不同应力和不同初始裂纹尺寸的表面裂纹蠕变扩展试验,通过断面观察获得了蠕变裂纹扩展形貌演化,并采用基于多轴蠕变损伤模型的有限元法、基于蠕变裂纹尖端参量C*的有限元法以及英国标准BS7910推荐的简化计算方法进行表面裂纹蠕变扩展分析。结果表明,基于多轴蠕变损伤模型的有限元法能够合理地描述裂纹最终轮廓并准确地预测裂纹扩展时间。相比之下,基于C*的有限元法和BS7910简化计算方法计算的裂纹形貌预测有明显偏差,并且较依赖于紧凑拉伸试样的蠕变裂纹扩展试验数据及其拟合的参数C和q,易导致过于保守的裂纹扩展时间预测。评估了不同计算方法对于表面裂纹蠕变扩展行为的预测能力。 相似文献
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The creep and creep rupture behaviour of two, significantly different, aeroengine materials, namely a nickel-base superalloy at 700°C and a high temperature titanium alloy at 650°C, were studied. Experimental creep tests were conducted on uniaxial specimens and axisymmetric notched bars under constant tensile loads conditions. From the uniaxial creep test results, a creep continuum damage model was established for each of the materials. The skeletal point stress approach was used to obtain the approximate creep rupture stress criterion in the multi-axial generalization of the creep continuum damage models. This approximation was cross-checked using axisymmetric Finite Element (FE) analyses in a trial and error procedure. Multi-axial creep continuum damage models were then used in further FE creep analyses to predict the creep rupture times in specimens subjected to different tensile loads. The FE predictions of the rupture times in these notched specimens were found to be in good agreement with the experimental results for the nickel-base superalloy (Waspaloy) at 700°C and the titanium alloy (IMI834) at 650°C. 相似文献
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TDFAD APPROACH TO HIGH TEMPERATURE DEFECT ASSESSMENT AND ITS ENGINEERING APPLICATION 总被引:3,自引:0,他引:3
Xuan FuzhenTu ShandongWang ZhengdongDepartment of Mechanical Engineering East China University of Scienceand Technology Shanghai China 《机械工程学报(英文版)》2004,17(4):537-542
From the idea of failure of defective structures at high temperature being controlled by two mechanisms: fast fracture due to creep crack growth initiating at the crack tip and creep rupture on the weakened section, a time-dependent failure assessment diagram (TDFAD) is developed on the basis of the time dependent crack tip parameter J integral. According to the proposed TDFAD method, detailed crack initiation and creep crack growth analysis is avoided in safety assessments of high temperature structures by performing simple calculations of stress intensity factor and limit load. To evaluate the creep toughness parameter Kmat, three different expressions are suggested on the basis of experimental load-line displacement, creep crack initiation and growth parameters as well as the isochronous stress-strain curve. The influence of service factors such as temperature and service-time on the proposed TDFAD is discussed by using the properties of 2.25CrlMo steel and an example is also presented to illustrate t 相似文献
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Hye-Jeong Sohn Gunawan Dwi Haryadi Seon-Jin Kim 《Journal of Mechanical Science and Technology》2014,28(10):3957-3962
The statistical aspects of fatigue crack growth life of base metal (BM), weld metal (WM) and heat affected zone (HAZ) in friction stir welded (FSWed) 7075-T651 aluminum alloy has been studied by Weibull statistical analysis. The fatigue crack growth tests were performed at room temperature on ASTM standard CT specimens under three different constant stress intensity factor range controls. The main objective of this paper is to investigate the effects of statistical aspects of fatigue crack growth life on stress intensity factor ranges and material properties, namely BM, WM and HAZ specimens. In this work, the Weibull distribution was employed to estimate the statistical aspects of fatigue crack growth life. The shape parameter of Weibull distribution for fatigue crack growth life was significantly affected by material properties and the stress intensity factor range. The scale parameter of WM specimen exhibited the lowest value at all stress intensity factor ranges. 相似文献
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由SEB( single edged bending)试样变形几何关系,提出断裂韧度测试中用于SEB试样J积分塑性功计算的裂纹嘴张开位移V0与加载点在加载线位移VLL的弹塑性转换公式.对SEB试样进行弹塑性有限元分析表明:试样转动中心位置受材料本构关系的影响微小,仅与裂纹长度α与试样宽度W之比有关,进而提出SEB试样转动半径R(裂纹嘴初始位置到转动中心的距离)的表达式,并对公式的有效性进行验证;应用线弹性柔度公式预测裂纹长度,可以忽略试样转动效应的影响,而刚性转动对SEB试样的J积分计算有一定影响,需采用考虑转动效应的载荷与加载线位移关系曲线来获得真实的J-△α阻力曲线. 相似文献
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研究奥氏体不锈钢0Cr18Ni9在高温(550℃)下的疲劳裂纹扩展规律。测试采用标准CT(compact tension)试样,最大载荷范围为6.5 kN~14 kN,应力比为0.1(室温)和0.05(550℃)。裂纹扩展过程通过QUESTAR长焦距显微镜直接观测,同时采用COD(crack opening displacement)规记录加载线位移。由于在高温条件下,测试终止时试样的裂纹前缘呈明显弧形,故此给出实测表面处裂纹长度有效值的修正方法。对高温疲劳裂纹扩展问题,采用应力强度因子范围ΔK作为裂纹扩展驱动力参数,同时考虑高ΔK和低ΔK值对裂纹扩展规律的影响,得到0Cr18Ni9不锈钢在550℃下的疲劳裂纹扩展规律表征模型,给出裂纹扩展率的上限结果。 相似文献
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The dynamic response of a cracked functionally graded piezoelectric material (FGPM) under transient anti-plane shear mechanical
and in-plane electrical loads is investigated in the present paper. It is assumed that the electroelastic material properties
of the FGPM vary smoothly in the form of an exponential function along the thickness of the strip. The analysis is conducted
on the basis of the unified (or natural) crack boundary condition which is related to the ellipsoidal crack parameters. By
using the Laplace and Fourier transforms, the problem is reduced to the solutions of Fredholm integral equations of the second
kind. Numerical results for the stress intensity factor and crack sliding displacement are presented to show the influences
of the elliptic crack parameters, the electric field, FGPM gradation, crack length, and electromechanical coupling coefficient. 相似文献