Simpler Estimation of Fracture Toughness during Material Development, Process Optimization and Quality Control of Structural Materials

Abstract

Existing standard International methods to estimate fracture toughness of structural materials as documented in ASTM standard E-1820 are neither appropriate for material development due to the requirement of considerable volume nor suitable for process optimizations like deciding suitable heat treatment or for quality control of tonnage materials at the stage of production due to techno-economic reasons owing to their time-consuming nature. This report overviews several investigations often in their feasibility stage and aims to suggest a common solution to all these problems considering measurement of fracture toughness (KIVM) using chevron notched bend bar specimens with either rectangular cross-section (RC) or circular cross-section (CC). At the outset the theoretical background for obtaining KIVMRC and KIVMCC and the corresponding normalized stress intensity factors are discussed in order to illustrate the relatively simpler principle of estimation of fracture toughness. The usefulness of this technique is next illustrated using a number of examples related to: (a) design of small specimens for fracture toughness determination using this principle (b) optimization of the volume fraction of the constituent phases in dual phase steels, (c) design of heat treatment for cast rolls, (d) optimization of cryotreatment for tool steels and (e) study of the effect of inclusions on toughness characteristics of microalloyed steels. The examples related to (a) is for demonstrating the capability of this technique for material development, that related to (b), (c) and (d) are to illustrate its potential for process optimization and the one related to (e) is to illustrate its potential for quality control of tonnage materials.