Size and Deformation Limits to Maintain Constraint in KiC and Jc Testing of Bend Specimens
Abstract
The ASTM Standard Test Method for Plane-Strain Fracture Toughness of Metallic Materials (E399-83) restricts test specimen dimensions to insure the measurement of highly constrained fracture toughness values (K sub Ic). These requirements insure small-scale yielding conditions at fracture, and thereby the validity of linear elastic fracture mechanics. When these conditions are satisfied, the diameter of the plastic zone is nearly twenty five times smaller than all specimen dimensions. The need for this degree of plastic zone confinement, set by the factor 2.5 in a, b, B greater than or equal to 2.5(K sub q/omega sub ys)squared was based on K sub Ic data for many different alloys. These data show that all specimens satisfying the size requirements of E399 produce highly constrained fracture toughness values. However, the required multiplier ranges from 1.0 for certain steel alloys to 2.5 for titanium alloy 6- 6-2 in the aged condition. To maintain a standard test method applicable to all materials, the more restrictive 2.5 value has been retained by ASTM Committee E08. Recently, Dodds and Anderson have proposed a less restrictive size requirement for cleavage fracture toughness measured in terms of the J-integral (J sub c). Dodds and Anderson performed finite element analyses to calculate the ratio of J in the finite-sized specimen (J sub SE(B)) to J under small-scale yielding (J sub SSY) needed to produce equivalent stresses ahead of both crack tips, and thereby equivalent conditions for cleavage fracture. Fracture toughness, Specimen size requirements, Experimental validation, J-integral.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1994
- Accession Number
- ADA284363
Entities
People
- Kyle C. Koppenhoefer
- Mark T. Kirk
- Robert H. Dodds Jr.
Organizations
- University of Illinois Urbana–Champaign