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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

#