
Accession Number : ADA289113
Title : Deformation Limits on TwoParameter Fracture Mechanics in Terms of Higher Order Asymptotics.
Descriptive Note : Final rept. Jan 92Sep 94,
Corporate Author : TEXAS A AND M UNIV COLLEGE STATION DEPT OF MECHANICAL ENGINEERING
Personal Author(s) : Crane, D. L. ; Anderson, T. L.
PDF Url : ADA289113
Report Date : SEP 1994
Pagination or Media Count : 226
Abstract : This report addresses the limitations of twoparameter fracture mechanics. We performed an asymptotic analysis of the general power series representation of the crack tip stress potential in an elastic plastic material that obeys a RambergOsgood constitutive law. Expansion of the power series over a substantial number of terms yields. only three independent coefficients for low. and mediumhardening materials. The first independent The second and third independent coefficients, K2 and K4 are a function of geometry and loading level. A twoparameter theory implies that the crack tip stress fields have two degrees of freedom, but the asymptotic analysis implies that three parameters are required to characterize neartip conditions. Thus twoparameter fracture theory is a valid engineering model only when there is an approximately unique relationship between K2 and K4. We performed elasticplastic finite element analyses on several geometries and evaluated K2 and K4 as a function of deformation level. A reference,twoparameter solution (which gives a unique relation between K2 and K4) was provided by the modified boundary layer (MBL) geometry. Results indicate that the near tip stresses in all but the deeply cracked SENT (a/W.5.O.9) and SENT (a/W0.9) lend themselves to a twoparameter characterization. However, the deeply cracked SENT and SENT specimens maintain a high level of constraint to relatively large deformation levels. Thus singleparameter fracture mechanics is fairly robust for these high constraint geometries. but twoparameter theory is of little value when constraint loss eventually occurs. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Descriptors : *STRESS ANALYSIS, *DEFORMATION, *FRACTURE(MECHANICS), STRESS STRAIN RELATIONS, COMPUTER PROGRAMS, MATHEMATICAL MODELS, PARAMETERS, FINITE ELEMENT ANALYSIS, COMPARISON, CRACKS, BOUNDARY LAYER, DEGREES OF FREEDOM, FORTRAN, LIMITATIONS, APPROXIMATION(MATHEMATICS), ASYMPTOTIC SERIES, RUNGE KUTTA METHOD, SURFACE TENSION, ELASTOPLASTICITY, POWER SERIES, BENDING STRESS.
Subject Categories : Mechanics
Numerical Mathematics
Distribution Statement : APPROVED FOR PUBLIC RELEASE