CRACK GROWTH IN AN ELASTIC-PRIMARY CREEPING MATERIAL (PRIMARY, FRACTURE MECHANICS).

摘要

The asymptotic stress and strain fields near the tip of a slowly growing crack are derived for elastic-primary creeping materials, which deform in tension according to the law (epsilon) = (sigma)/E+B(sigma)('n)(epsilon)('-p). Asymptotic analysis based upon a continuum mechanics model, yields the nature of the near tip singular fields for anti-plane shear (Mode III), plane stress and plane strain (Mode I). The functional dependence of the crack tip singularity changes at n - p = 3. For n - p < 3, an inverse square root stress singularity takes place which is dependent upon the applied loads and the crack history. The steady state crack growth can not occur in an elastic-primary creeping material in this range. For n - p > 3, a new type of singular field is found for both steady state and non-steady state crack growth. The strength of the near tip field is entirely independent of the applied load, crack growth history and geometry of the body. It is specified only by the current crack growth rate and material properties. Although the strain has the same singularity as stress, the dependence of the angular variation of the creep strain upon n and p is much greater than dependence of the angular variation of the stress components.; The problem of a quasi-statically growing crack in an elastic-primary creeping material is then analyzed for the cases of plane strain Mode I and anti-plane shear Mode III under conditions of small scale yielding.; The extension of a macroscopic crack is analyzed based on the crack tip stress field in an elastic-primary creeping material and on models for cavity growth. These studies include the derivation of the cavity growth rate under power-law creep by using the energy method due to Martin and the principle of elastic analogue. The steady state creep crack growth within the confines of small scale yielding was investigated through a combination of a continuum fracture model and a creep damage model. From this, the relation- ship between the rate of crack growth and the stress intensity factor has been established. Below a certain minimum growth rate, no steady state crack growth is possible in the present model. It also shows that the minimum crack growth rate for stable crack propagation will increase with increasing strain-hardening exponent p. (Abstract shortened with permission of author.)