Accession Number : ADA289113

Title :   Deformation Limits on Two-Parameter Fracture Mechanics in Terms of Higher Order Asymptotics.

Descriptive Note : Final rept. Jan 92-Sep 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 two-parameter 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 Ramberg-Osgood constitutive law. Expansion of the power series over a substantial number of terms yields. only three independent coefficients for low. and medium-hardening materials. The first independent The second and third independent coefficients, K2 and K4 are a function of geometry and loading level. A two-parameter 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 near-tip conditions. Thus two-parameter fracture theory is a valid engineering model only when there is an approximately unique relationship between K2 and K4. We performed elastic-plastic finite element analyses on several geometries and evaluated K2 and K4 as a function of deformation level. A reference,two-parameter 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/W-0.9) lend themselves to a two-parameter characterization. However, the deeply cracked SENT and SENT specimens maintain a high level of constraint to relatively large deformation levels. Thus single-parameter fracture mechanics is fairly robust for these high constraint geometries. but two-parameter 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