SMALL-SIZE FRACTURE TOUGHNESS SPECIMEN WITH HIGH PLASTIC CONSTRAINT GENERATED BY MECHANICAL HETEROGENEITY

This paper develops a new method for a plane-strain fracture toughness test to obtain valid -K1c results according to the ASTM E 399 standard. The idea is based on using the mechanical heterogeneity effect on plastic constraint in the crack-tip region. By inserting two hard zones very near to the crack plane of a very small-size fracture toughness test specimen, the crack-tip plastic constraint was elevated and reached the level specified by the ASTM E399 standard. A parametric survey was done to quantitatively determine the geometrical and mechanical parameters controlling the plastic constraint at the crack-tip region. The distance from the crack tip to the hard zone, the hard zone width and the specimen thickness were the main geometrical parameters considered in this study. The mismatching difference between the base metal and the hard zone was the mechanical parameter investigated. The considered parameters were analyzed using three-dimensional elastic-plastic finite element analysis for a series of single notch bend specimens, SNB. Local approach, using the Weibull stress distribution, was applied to determine the required condition to achieve the plane- strain plastic constraint needed to get valid -K1c results. A valid zone of Weibull stress-CTOD relation was achieved and accordingly, the controlling parameters of the plastic constraint were quantified. In the light of the results a small-size fracture toughness specimen for the material used was proposed. The requirements for this type of specimen to achieve valid -K1c results can be summarised as follows: 1) hard zone strength will be double that for the base metal as a minim ratio 2; 2) distance from hard zone to crack plane should be not greater than 8% of the thickness used and 3) hard zone width can be as large as B/2 or more.

• Supplemental Notes:
  • J Soc Naval Arch Japan, v 178, Dec 1995, p 575 [8 p, 9 ref, 2 tab, 14 fig]
• Authors:
  • El-Shennawy, M
  • Minami, F
• Publication Date: 1995

Language

• English

Subject/Index Terms

• TRT Terms: Finite element method; Fracture properties; Mechanical properties
• Old TRIS Terms: Crack tips
• Subject Areas: Marine Transportation; Materials;

Filing Info

• Accession Number: 00728313
• Record Type: Publication
• Source Agency: British Maritime Technology
• Files: TRIS
• Created Date: Nov 4 1996 12:00AM