Prediction of Delayed Fracture from Crack Coalescence — Alumina

A model for delayed fracture, based on microscopic cracks and their interaction and coalescence, is proposed as opposed to the conventional single-worst flaw model. It is found that an assembly of microscopic cracks, which may not be observable, may be worse than a single macroscopic crack in delayed fracture and that the coalescence of the microscopic cracks may occur in a very short time without being identified because the critical amount of slow crack growth from the individual inherent flaws can be very small. It is demonstrated that the existing concepts give nonconservative prediction of time-to-failure; but the nonconservative prediction is partially or sometimes excessively compensated by conservative estimation of the initial crack size.

[1]  J. M. Ragosta,et al.  Crack Growth from Small Flaws in Larger Grains in Alumina , 1980 .

[2]  Sheldon M. Wiederhorn,et al.  Subcritical Crack Growth in Ceramics , 1974 .

[3]  T. Sōma,et al.  Applicability of Crack Propagation Data to Failure Prediction in Porcelain , 1980 .

[4]  A. Evans.  A Dimensional Analysis of the Grain‐Size Dependence of Strength , 1980 .

[5]  Anthony G. Evans,et al.  A method for evaluating the time-dependent failure characteristics of brittle materials — and its application to polycrystalline alumina , 1972 .

[6]  B. Lawn.  Physics of Fracture , 1983 .

[7]  P. Popper,et al.  Special ceramics 7 , 1981 .

[8]  T. Yokobori,et al.  Non-linear interaction between main crack and near-by slip band , 1975 .

[9]  D. Rooke,et al.  The compendium of stress intensity factors , 1978, International Journal of Fracture.

[10]  A. Virkar,et al.  Strength‐Grain Size Relations in Polycrystalline Ceramics , 1979 .

[11]  A. Evans,et al.  Fracture Mechanics of Ceramics , 1986 .

[12]  R. Bradt,et al.  (K-V) Diagrams for Ceramic Materials , 1975 .

[13]  D. J. Green,et al.  Crack Origins and Microcracking in Delayed Fracture of Alumina , 1982 .

[14]  U. F. Zackay.  High-strength Materials , 1965 .

[15]  Roy W. Rice,et al.  The Dependence of Strength‐Controlling Fracture Energy on the Flaw‐Size to Grain‐Size Ratio , 1980 .

[16]  T. Okada,et al.  Flaws Responsible for Slow Cracking in the Delayed Fracture of Alumina , 1983 .

[17]  J. Petrovic,et al.  Slow Crack Growth from Controlled Surface Flaws in Hot-Pressed Si3N4 , 1978 .

[18]  J. D. Embury,et al.  A Treatment of Inelastic Deformation Around a Crack Tip due to Microcracking , 1980 .

[19]  M. Mendiratta,et al.  Lifetime prediction of brittle materials having spatial variations in fracture properties KIC and v versus K1 , 1977 .

[20]  G. Sines.  Rationalized Crack Growth and Time‐to‐Fracture of Brittle Materials , 1976 .