An Experimental and Numerical Investigation of Specimen Size Requirements for Cleavage Fracture Toughness.
Final rept. Jan 92-Sep 94,
TEXAS A AND M UNIV COLLEGE STATION
Pagination or Media Count:
Cleavage fracture toughness can be influenced by specimen dimensions. Crack tip constraint can relax in small specimens, resulting in higher apparent toughness. Moreover, there is a statistical sampling effect, where thicker specimens tend to have lower toughness than thin specimens due to an increased sample volume. In deeply notched bend and compact specimens, theoretical modeling, finite element analysis, and experimental data indicate that the results will not be significantly influenced by crack tip constraint as long as the following specimen size requirements are met aW 0.5,B greater than of equal to MJ sub csigma sub y,Bb greater than or equal to 1 where a is the crack length, W is the specimen width, B is the specimen thickness, b is the uncracked ligament, J subc is the critical 3 value, sigma sub y is the effective yield strength and M is a dimensionless constant. These size requirements are conservative if M is set equal to 100 M- 50 appears to be adequate for many materials, but the authors recommend the stricter requirement until fracture validation is performed. When specimens meet the above requirements, fracture toughness should not be influenced by size, provided statistical thickness effects are taken into account.
- Statistics and Probability