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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
Report Date:
1994-09-01
Pagination or Media Count:
226.0
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 aW-.5.O.9 and SENT aW-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.
Distribution Statement:
APPROVED FOR PUBLIC RELEASE
