Análise da influência da tensão de cisalhamento de flexão na tenacidade à fratura do aço AISI 8630

Abstract

The toughness response depends on the crack opening modes. Metals present different values of fracture toughness depending on the type of load acting ahead of the crack tip. Although there are 3 different types of loading modes, plus the combined modes, that cracks can be submitted, only mode I of loading (tensile) is standardized. One of the most widely used tests for obtaining the CTOD is the 3-point flexural test, which, even though it’s considered a mode I loading test, is in fact a mixed-mode I/II test since the 3-point bending configuration causes both tensile and shear stress. Several studies have shown that increasing the mode II component in mixed mode loading causes a reduction in the toughness value in steels. There is a worldwide interest in developing a standardized methodology to obtain the CTOD in mixed mode, since under real operating conditions the mechanical components are subjected to loading modes that don’t always corresponds to those performed in laboratory testing, making it necessary to define a scenario that better represents the service conditions. In this context, it is important to understand and quantify the shear effect in the mode I testing procedure already standardized for the development of a mixed mode test methodology. For this purpose, it was proposed to compare the results of CTOD obtained by symmetrical bending test at 3 and 4 points, since the latter only causes tensile load in the midsection of the test specimen, therefore representing a pure mode I testing. The obtained toughness values showed little difference between the tests performed and the reasons for such results were addressed.