Modeling the Role of Dislocation Substructure during Class M and Exponential Creep
Unified Constitutive Laws of Plastic Deformation
on Lew i Re earch Ce nter Cleveland , Ohi o 44 135 Ilana Seide n Iskovitz Ohi o Aerospace In situte 22800 Cedar Po int Road Cl eveland , Ohi o 44 142 and A .D . F reed Nati onal Aeronautics and Space Admini trati on Lewis Research Center Cleveland . Ohi o 44 135 SUMMARY The different s ubstructure that form in the power-law and ex pone nti al creep reg imes for ingle phase cryta lli ne materials under va ri ou conditi ons of tre , te mperature and train are reviewed. The micro tructure is
... o tructure is correlated both qualitati vely and qu antitati vely with power-law a nd ex ponenti al creep a we ll as with steady tate and no n-steady state deformati on behavior. These ob ervati on sugge t that creep i influenced by a co mplex interacti o n between everal elements of the mi crostru cture, such as di s loca ti o ns, cell s and ubgra in . The stability of the creep substructure is examined in both of the e creep regimes during tre and temperature change ex perime nts. T he e ob ervations are rationali zed on the ba i of a phenomenolog ica l model, where noml al primary creep is interpreted as a series of constant structure ex pone nti al creep rate-tre re lati on hips. The implica ti on of this viewpoint on the magnitude of the tress exponent and steady-state behav ior are di c u ed . A theory is developed to predi ct the macroscopic creep behav ior of a sin gle phase material u in g qua ntitati ve mi crostructural data. In thi s technique the thermall y ac ti vated deform ati on mechani sm proposed by di locati on phys ics are interlinked with a prev iously developed mul tiphase, three-dimensional, di slocati on substructure creep model. Th is proced ure leads to several co upled diffe rential equ ati ons interrelating macroscopi c c reep pI a ticity with microstructural evoluti on.