Notched multiaxial fatigue of Al7050-T7451: on the need for an equivalent process zone size

M.V.C Sá,J.L.A Ferreira,J.A Araújo,C.R.M Da Silva

doi:10.3221/igf-esis.41.13

Abstract

The aim of this work is to investigate stress gradient effects on the fatigue life estimation of notched Al 7050-T7451 specimens under combined torsion and push-pull loading conditions. Initially, simple push-pull and torsion fatigue tests in plain and notched specimens were independently conducted not only to obtain the material properties necessary to calibrate a standard multiaxial critical plane based model, but also to raise the critical distance versus life curves in tension (L? – Nf) and in torsion (L? – Nf). This latter step also required a Finite Element Elastic Stress Analysis of the notched specimens tested in the medium high-cycle fatigue regime. Then, proportional multiaxial fatigue tests were carried out using this same notched geometry. The combination of a multiaxial model with the theory of critical distance (TCD) was applied to estimate fatigue lives. For this aluminium alloy, neither the use of the L? – Nf nor L? – Nf combined with the predictive multiaxial model was able to estimate lives in an accurate way.

Highlights

A luminium alloys have been used mainly in the aeronautical industry for more than eighty years due to its low density and good mechanical resistance
It has been suggested [11] that a combination of a critical plane based multiaxial model with a simple linear relation between critical distance and life extracted from pushpull data could provide good estimates of life for notched components under multiaxial loading in the MHCF or HCF regime
A methodology available in the literature, which combines a multiaxial critical plane criterion with a critical distance approach was used to estimate the life for the multiaxial tests

Summary

Introduction

A luminium alloys have been used mainly in the aeronautical industry for more than eighty years due to its low density and good mechanical resistance. Carvalho and Voorwald [1] investigated the effect of shotpeening and hard Chromium coating on the fatigue resistance of the Al 7050-T7451 They found out that the deleterious effect of such a coating on the fatigue behavior of the alloy was caused by the presence of high tractive residual stresses and micro-cracks, both generated by the electrodeposition process. In order to do so, the critical distance against life relation will be raised for fully reversed push-pull tests and for alternated torsion Both curves will be combined with a critical plane multiaxial fatigue criterion to estimate life. To validate the analysis multiaxial fatigue tests were conducted on notched Al 7050-T7451 specimens

Objectives

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Conclusion