Accession Number : ADA311401

Title :   Fundamental Studies in Crack Initiation.

Descriptive Note : Final technical rept. Sep 93-Jun 97,

Corporate Author : ILLINOIS UNIV AT CHICAGO CIRCLE DEPT OF CIVIL ENGINEERING MECHANICS AND METALL URGY

Personal Author(s) : Botsis, John

PDF Url : ADA311401

Report Date : JUL 1996

Pagination or Media Count : 52

Abstract : Damage evolution before crack initiation in an amorphous polymer show that damage consists of a core of highly dense crazing and peripheral less dense zone of crazing. Analysis of the kinematics of damage at different times involves comparisons of the inertia moments of damage distributions. The results indicate that damage evolution can be approximated by a linear transformation of the space variables. The crack initiates within a core zone immediately ahead of the notch. The experimental results suggest that damage density within the core is independent of the loading conditions considered herein. An energy release rate is evaluated with the use of a semi-empirical method. Correlation of the elementary movements of the damage zone with the energy release rate shows that damage growth decreases monotonically. Assuming that damage evolution is a stress-temperature driven process, it is shown that a first order reaction equation describes reasonably well damage growth within the core zone. An activation energy for defect nucleation is found twice the enthalpy of activation for secondary chain motions below glass transition. This result indicates that chain motions and chain scission are possible process leading to crack initiation.

Descriptors :   *STRESS ANALYSIS, *CRACK PROPAGATION, *FATIGUE(MECHANICS), KINEMATICS, STRESS STRAIN RELATIONS, LOAD DISTRIBUTION, DEFORMATION, CRACKING(FRACTURING), DAMAGE ASSESSMENT, POLYSTYRENE, ENERGY TRANSFER, AMORPHOUS MATERIALS, NUCLEATION, FRACTURE(MECHANICS), TRANSITION TEMPERATURE, RESIDUAL STRESS, TENSION, ENTHALPY, THERMAL STRESSES, CHAIN REACTIONS, CYCLIC LOADS, NOTCH TOUGHNESS, MOMENT OF INERTIA, DEFECT ANALYSIS, ACTIVATION ENERGY, STRESS CONCENTRATION, CRAZING.

Subject Categories : Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE