表面裂纹弹塑性断裂参数的估算和测试

On Approximate Calculation of Elastic-Plastic Fracture Mechanics Parameters for Semi-Elliptical Surface Crack Plates

本文提出了一种计算模型,用以估算带半椭圆表面裂纹幂硬化板材的弹塑性断裂参数。用该模型估算的表面裂纹最深点的应力强度因子K值与New-man-Raju 公式计算的K值吻合良好、弹塑性J积分值与Nikishkov-Atluri的三维有限元结果基本相符。用表面裂纹LD10CZ板材测定的表面裂纹嘴张开位移δ_m和J积分值与计算模型估算的δ_m和J值的误差不超过10%。在σ/σ_0> 0.5时,J与a_m有线性关系。

One important task of elastic-plastic fracture mechanics(EPFM) is theealculation of the J-integral and the crack mouth opening displacement(CMOD),etc. In order to make clear the contribution of this paper, it is necessary toreview first past research briefly. Parks[1] and King[2] are of the opinion that the three-dimentionalfinite-element elastic-plastic analysis of surface flaws is too costly in time andmoney to be used in engineering application. Parks[1] first used the nonlinearline-spring model to calculate EPFM parameters of semi-elliptical surface cracks.Next, King[2] as well as Lu et al[3] also used the model to solve the sameproblem for other materials. Although the method is easier than the 3-D finiteelement method, the authors believe that the model still leads to relativelycomplicated theoretical analysis and needs a great deal of calculation, so it isstill not convenient for engineering application. In this paper, in order to make it easy to calculate approximately EPFMparameters of a semi-elliptical surface crack plate subjected to tension, theauthors propose a new calculation model. The model is explained in the firstsection of the paper. The formulas of J-integral and CMOD at the deepest pointof the crack are obtained for surface-cracked plates for materials with power-hardening characteristic by means of the calculating model. The formulas arerelatively convenient to use and only need a relatively small amount ofcalculation. In the opinion of the authors, the method of this paper is relativelysimple compared with that of the nonlinear line-spring model. The model proposed by the authors is partly confirmed by Newman-Raju'sresults[6] which are generally recognized to be reliable. The authors have alsodetermined the elastic-plastic J-integral and CMOD of the surface crack bymeans of experiments. Calculated. and experimental values differ within 10%.