Avaliação da tenacidade à fratura: Método teste de torção em entalhe helicoidal

Abstract

The fracture toughness in the plane strain (KIC) has been widely used as a mechanical and structural components project tool. Over the years, several KIC determination methods were developed. However, they have significant limitations, mainly as regards to specimen dimensions. To overcome this problem, Wang and Liu (2003) developed the Spiral Notch Torsion Test (SNTT). Despite being a promising method, the SNTT has not been adopted by the scientific community mainly due to the lack of the test methodology clarity. This work aims the KIC determination using the SNTT method. A SNTT test methodology were described and validated testing the AISI 4340 steel. The results obtained by the SNTT method were compared to those provided by conventional method testing C(T) specimens. The SNTT methodology for KIC determination is efficient. The Analysis of Variance (ANOVA) technique was applied, and it was observed that the KIC values obtained by both methods are statically equals. The systematic error, as the maximum error, associated with the KIC values obtained by SNTT method was of 2.8 %. The repeatability and expanded uncertainty associated with KIC values obtained by the SNTT method were better than those observed for the conventional method. The SNTT method provided KIC values with excellent repeatability, smaller than those observed in the studied literature using conventional method (about 52 % for the worst case). Pre-crack growth was not uniform throughout the whole notch, indicating an “edge effect” on the extremities. This fact denotes that the final stopping angle estimate must be improved.