Stress Sensitivity Of Creep Rate Research Articles

A multiple‐crack model of brittle fracture: 2. Time‐dependent simulations

A numerical multiple‐crack interaction model is developed to simulate the failure process in brittle solids containing significant populations of flaws. The model, which is two dimensional, allows for the growth of microcracks on a regular array of potential crack sites. Individual cracks may be oriented vertically, horizontally, or at 45° to the sample axes. Quasi‐static equilibrium equations are expressed in terms of finite difference approximations and are solved by applying a renormalization group theory approach. In this paper the results presented in the companion paper are extended to include time‐dependent processes. In particular, both subcritical mode I crack growth and stress‐sensitive stable slip on existing crack surfaces are included. Crack growth rate and shear slip rate are defined by the local stress conditions. By including these two simple rules in the crack model, constant stress creep simulations are performed which reproduce the classic creep response, including all three modes of creep. In addition, the model predicts the proper stress sensitivity of creep rate. This result supports the interpretation that room temperature creep in crystalline rock in compression is dominated by the same stress corrosion process that occurs during subcritical crack growth observed in tension experiments. The process of crack localization, characteristic of the tertiary creep phase and culminating in failure, is discussed. The relation between inelastic strain and acoustic emission is also examined.

Creep ductility of cold-worked Zr-2.5 wt% Nb and Zircaloy-2 tubes in-reactor

Deformation of internally pressurized 15 mm diameter tubes of cold-worked Zr-2.5 wt% Nb and Zircaloy-2 has been measured in axial and hoop directions for irradiations up to 24 000 h at 571 K. Specimens have deformed up to 18.1% in the hoop direction, with hoop stresses up to 495 MPa, without rupture. Since the stress sensitivity of creep rate is high (>5) under the test conditions, and is low (≈1) under operating conditions for pressure tubes, creep ductility of pressure tubes should be very high.

Theoretical scatter of creep-relaxation measurements versus the scatter in constant-load creep data

Abstract In a creep-relaxation experiment the specimen is held at constant total (i.e. elastic plus plastic) strain. The stress therefore decreases as the creep strain increases and a theoretical analysis has been made of the associated trend in the scatter of data from replicate specimens. The scatter exhibits a maximum at an intermediate value of residual stress and this offers a method of calculating the stress-sensitivity of creep-rate.