Geometry factor determination of round specimens using fracture mechanic approaches in Al 2024‐T3

Abstract

Purpose

The purpose of the paper is to characterize the fatigue behavior, such as fatigue strength, and stress intensity factor values of aluminum alloy type 2024‐T3, using only a round specimen. The aim in this study is to interrelate the fatigue behavior directly with the microstructure, as an attempt to reduce other parameters that might be associated in using different specimen geometries.

Design/methodology/approach

For this purpose, round specimens were machined from 2024‐T3, and the fatigue behavior was studied with various heat treatments. Two different temperatures were selected; 160 and 200°C, at different times. From stress‐number of cycles diagram, the fatigue strength is determined for the selected specimens. Moreover, the linear elastic fracture mechanic approach was used to determine threshold stress intensity factor, crack growth rate, and fracture toughness. A replica method is used for following and calculating the crack depth in round specimens. Moreover, theoretical equations and approaches have been carried out to evaluate the effect of specimen geometry (correction factor) on the results.

Findings

The results showed that the specimen aged at 160°C for five h develops greatest values of fatigue limit, ultimate strength, yield strength, and hardness. Moreover, the specimen aged at 200°C for 15 h develops greatest threshold stress intensity factor and fracture toughness.

Practical implications

The heat treatment does not have a strong influence on crack growth rate. Generally, the specimens, which develop greatest values of strength values, and HB, had lowest K_th, and K_IC values and vice versa.

Originality/value

The LEFM approaches can be used even on round specimens to follow the crack growth rate instead of plates. A specific equation as a correction factor of geometry effect has been determined for round specimen.

Citation

Khoshnaw, F.M. and Hussain, N.A. (2007), "Geometry factor determination of round specimens using fracture mechanic approaches in Al 2024‐T3", Aircraft Engineering and Aerospace Technology, Vol. 79 No. 5, pp. 469-474. https://doi.org/10.1108/00022660710780597