表面裂纹弹塑性起裂的V准则

A NEW FRACTURE CRITERION FOR ELASTIC—PLASTIC INITIATION OF THE SURFACE CRACK

本文提出了一个新的断裂准则——裂纹咀张开位移率准则及新的材料断裂韧性参量V(?),并用实验验证了该准则的有效性。该准则特别适用于表面裂纹弹塑性起裂载荷的确定。V(?)可以用单试件法测定,并给出了 V_(1c)与 K_(1(?)),σ_c,J(?)的相互换算关系式。

The elastie-pla(?)stic fracture of pressure vessel steels is a processfrom initiation to stable propagation and to unstable fracture.To study anddesoribe this complex process quantitatively has been one of the importantproblems of engineering fracture mechanics.Surface cracks are the most common flaws in pressure vessels and pipin-gs.The available elastic-pla stic fracture theories and related criteria,such asCOD,J Criterion erc,are only suitable for two dimensional problems.So farthere has not been any mature models for analysing three dimensional cracks.This paper presents a new rarameter V_1,crack mouth opening displace-m ntrate and a new materia(?)l toughness V_1.This new parameter can be usedto estimate the initiation of three dimensional surface cracks and verifiedthrough experiments with a lot of specimens and pressurized cylinders withsurface cracks.Based on the works(1,2),there exists a difinite relationship between thecrack mouth opening displacement and the stress intensity at crack tip forboth embedded and surface cracks.Therefore a new parameter V_1 called ascrack mouth opening displacement rate could be introduced to indicate thedegree of crack tip opening and approaching initiation.Numerous experiments have shown that V_(1c) ison geometry-independentconstant,so it may be used as a new fracture toughness.If V_(1c) is known,the initiation load is easily obtained.V_(?) can be directly measured by the sur-face crack specimens or may be converted from other fracture toughness thr-ough the related equations.In order t(?) expl(?)re the applicati(?)n of V_1 criteria in the prediction of ela-stic-plastic fracture of cracks in pressure vessels or other engineering struc-tures,and to develop a new method of monitoring and estimating the safety ofpressure vessels and piping s on service,a number of tests have been carriedout.The initiation loads ca(?)culated by V_1 criterion are in good agreement withthat obtained from experiments.