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采用显微网格法研究韧性材料平面应力状态下裂尖附近的应变场 总被引:1,自引:0,他引:1
用显微网格数字图象处理方法,测量了韧性材料平面应力条件下I型单边裂纹尖端附近的应变场。实验结果表明:在裂尖两侧存在与裂纹方向夹角约为50°的大变形带。最大应变位于离裂尖一定距离的大变形带上,随着载荷增加,最大应变的位置逐渐靠近裂纹尖端。应变峰值轨迹线在裂纹顶端呈放射状,载荷增加时,应变峰值的轨迹线位置并不改变。 相似文献
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使用焦散线法与光弹法测定三维裂纹混合型应力强度因子 总被引:1,自引:0,他引:1
本文介绍了将焦散线法与应力冻结,“解冻”技术相结合,使焦散线法用于测量三维体内部裂纹前缘应力强度因子的实验方法,并针对复杂应力状态下三维裂纹前缘的不同应变奇异场,合理地综合运用焦散线法与三维光弹法,实际测量与分离了三维裂纹前缘混合型应力强度因子。 相似文献
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研究了应变损伤材料I型动态扩展的裂纹尖端场。假定材料服从J2流动理论,且损伤规律以幂律应变软化的规律给出。对于塑性区引进了应力函数φ,ψ0借助于动力学方程的分析,给出了渐近方程及数值解。结果表明,对于可压缩材料I型平面应变尖端场是完全由塑性区组成,没有弹性卸载区。在裂纹尖端附近,应力和应变分别具有如下的奇异性:σ ̄(lnR/r)^-n/n+1,ε ̄(lnR/r)^1/n+1。 相似文献
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考虑裂纹闭合效应的岩石损伤本构关系 总被引:2,自引:0,他引:2
岩石中的预存裂纹只有在一定的法向压应力即裂纹闭合应力的作用下才可能闭合,其闭合过程与其方位和外加应力场有关,并且,即使对于裂纹已经完全闭合的岩石,如果裂纹闭合应力不同,则岩石的应力应交关系也不相同。本文建立了考虑裂纹闭合效应的岩石细观损伤力学模型,分析了裂纹闭合应力对岩石损伤演化过程和应力应变关系的影响。数值结果表明裂纹闭合应力显著地改变岩石的应力应变关系,表现为随裂纹闭合应力的增加,岩石的轴向应变变化较小,侧向应变和体积应变则大为增加。 相似文献
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平面应力的弹塑性断裂理论的研究一直受到广泛重视,正在深入发展,其中很多工作是通过研究裂纹张开位移和裂纹附近的应变场进行的。用光学方法对裂纹张开位移和裂纹周围的变形进行测量具有显著的优越性,不但测量精度高,而且能够把整个裂纹包括裂纹顶端的张开位移都同时测量出来,并得到裂纹周围的位移全场分布。近年来激光散斑法在实验应力分析中发展很快,已被用来测量裂纹张开位移和裂纹周围的应变场,其 相似文献
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裂纹纹尖弹塑性应力应变场的实验研究和数值分析 总被引:1,自引:0,他引:1
本文分别采用激光和白光DSCM(数字散斑相关测量)方法对聚碳酸脂材料的裂纹尖端弹塑性应力、应变场进行了实验研究,两种方法都取得了较好的结果,有限元计算采用了各向同性多线性随动强化的本构模型,较好地模拟了材料应力、应变曲线,并对裂纹尖端进行了有限元网格的细化,通过对实验结果和有限元计算结果的比较,可以发现两者具有相近的趋势。 相似文献
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刚度微分法计算压电材料平面断裂问题 总被引:4,自引:1,他引:4
把计算应变能释放率的刚度微分法推广到压电材料平面断裂问题.在此基础上,利用压电材料平面断裂问题的有限元数值解作为真实场,用Sosa的平面问题裂端渐近解作为辅助场,由推广的交互M积分法求得了应力强度因子KI,KII和电位移强度因子KIV.算例表明,计算结果与理论解符合得很好 相似文献
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A novel experimental technique for measuring crack tipT-stress, and hence in-plane crack tip constraint, in elastic materials has been developed. The method exploits optimal positioning
of stacked strain gage rosette near a mode I crack tip such that the influence of dominant singular strains is negated in
order to determineT-stress accurately. The method is demonstrated for quasi-static and low-velocity impact loading conditions and two values
of crack length to plate width ratios (a/W). By coupling this new method with the Dally-Sanford single strain gage method for measuring the mode I stress intensity
factorK
I
, the crack tip biaxiality parameter
is also measured experimentally. Complementary small strain, static and dynamic finite element simulations are carried out
under plane stress conditions. Time histories ofK
I
andT-stress are computed by regression analysis of the displacement and stress fields, respectively. The experimental results
are in good agreement with those obtained from numerical simulations. Preliminary data for critical values ofK
I
and β for dynamic experiments involving epoxy specimens are reported. Dynamic crack initiation toughness shows an increasing
trend as β becomes more negative at higher impact velocities. 相似文献
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Xing Ji 《Acta Mechanica Sinica》2016,32(3):491-496
The complex stress intensity factor K governing the stress field of an interface crack tip may be split into two parts, i.e.,■ and s~(-iε), so that K = ■ s~(-iε), s is a characteristic length and ε is the oscillatory index. ■ has the same dimension as the classical stress intensity factor and characterizes the interface crack tip field. That means a criterion for interface cracks may be formulated directly with■, as Irwin(ASME J. Appl. Mech. 24:361–364, 1957) did in 1957 for the classical fracture mechanics. Then, for an interface crack,it is demonstrated that the quasi Mode I and Mode II tip fields can be defined and distinguished from the coupled mode tip fields. Built upon SIF-based fracture criteria for quasi Mode I and Mode II, the stress intensity factor(SIF)-based fracture criterion for mixed mode interface cracks is proposed and validated against existing experimental results. 相似文献
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本文将数字梯度敏感方法用于航空透明件断裂力学问题研究。首先,基于透明材料的弹性-光学效应,建立了透明件应力状态与光线穿过透明件后的偏转角之间的关系。在平面应力假设下,利用最小二乘拟合建立了I型裂纹尖端应力强度因子与光学偏转角的关系。其次,通过数字梯度敏感方法搭建非接触光学测试平台,开展了带单边裂纹的航空有机玻璃试件三点弯曲实验,应用数字梯度敏感方法提取了I型裂纹尖端应力强度因子。最后,通过选择不同计算子区域和步长大小,分析了数字梯度敏感方法中的子区域和步长选择对计算结果的影响。研究结果表明,数字梯度敏感方法实验所得应力强度因子与经验公式计算所得结果偏差小于10%,通过增加最小二乘拟合项数以及合理的子区域和步长选择可以减小数字梯度敏感方法计算应力强度因子误差。 相似文献
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有限厚度板穿透裂纹前缘附近三维弹性应力场分析 总被引:7,自引:1,他引:7
通过三维有限元计算来研究有限宽度、有限厚度含有穿透裂纹板的裂纹前缘应力场,从中找出应力强度因子与板的厚度、裂纹长度之间的关系,同时还分析了裂尖的三维约束程度和三维约束区的大小。分析结果表明:应力强度因子沿厚度的分布是不均匀的,应力强度因子的最大值及其位置与厚度有关;有限厚度板中面应力强度因子(KI)m-p及最大应力强度因子(KI)max均大于平面应力或平面应变的应力强度因子。对有限厚度裂纹问题,按平面应力或平面应变来考虑是不安全的;板中面的应力强度因子(KI)m-p及最大应力强度因子(KI)max是厚度B/a的函数;板的中面离面约束系数Tx最大,自由面(z=B)Tx=0。沿厚度方向裂尖附近的离面约束系数Tx也是z/B和B/a的函数,随着厚度的增加离面约束系数Tx增大,离中面越近离面约束系数Tx越大。Tx随着x的增大急剧减小,三维约束影响区域大小大约为板厚的一半,且裂纹长度a/W对应力强度因子沿厚度变化规律及Tx影响区域大小影响较小。 相似文献
19.
The strain gradient effect becomes significant when the size of fracture process zone around a crack tip is comparable to
the intrinsic material lengthl, typically of the order of microns. Using the new strain gradient deformation theory given by Chen and Wang, the asymptotic
fields near a crack tip in an elastic-plastic material with strain gradient effects are investigated. It is established that
the dominant strain field is irrotational. For mode I plane stress crack tip asymptotic field, the stress asymptotic field
and the couple stress asymptotic field can not exist simultaneously. In the stress dominated asymptotic field, the angular
distributions of stresses are consistent with the classical plane stress HRR field; In the couple stress dominated asymptotic
field, the angular distributions of couple stresses are consistent with that obtained by Huang et al. For mode II plane stress
and plane strain crack tip asymptotic fields, only the stress-dominated asymptotic fields exist. The couple stress asymptotic
field is less singular than the stress asymptotic fields. The stress asymptotic fields are the same as mode II plane stress
and plane strain HRR fields, respectively. The increase in stresses is not observed in strain gradient plasticity for mode
I and mode II, because the present theory is based only on the rotational gradient of deformation and the crack tip asymptotic
fields are irrotational and dominated by the stretching gradient.
The project supported by the National Natural Science Foundation of China (19704100), National Natural Science Foundation
of Chinese Academy of Sciences (KJ951-1-20), CAS K.C. Wong Post-doctoral Research Award Fund and Post-doctoral Science Fund
of China 相似文献
20.
Three-dimensional elliptic crack under impact loading 总被引:4,自引:0,他引:4
The dynamic stress intensity factor of a three-dimensional elliptic crack under impact loading is determined with the finite
element method. The computation results can take into account the influence of time and the ratio of the wave speeds on the
stress intensity factor. The present method is suitable not only for three-dimensional dynamic crack, but also for three-dimensional
dynamic contact.
Project supported by the National Natural Science Foundation of China (No. K19672007). 相似文献