Development of Fatigue Testing System for in-situ Observation by AFM &amp; SEM

Amir Farokh Payam,Oliver Payton,Stacy Moore,Loren Picco,Mahmoud Mostafavi,A.D Warren,Tomas Martin,David Knowles

doi:10.1051/matecconf/201930014002

Abstract

A three-point bend fatigue miniature stage for in-situ observation of fatigue microcrack initiation and growth behaviour by scanning electron microscopy (SEM) and atomic force microscopy (AFM) has been manufactured. Details of the stage design with finite element analysis of the stress profiles on loading are provided. The proposed stage facilitates study of the micro mechanisms of fatigue when used during SEM and AFM scanning of the sample surface. To demonstrate the applicability of the system, fatigue tests have been performed on annealed AISI Type 316 stainless steel. Surface topography images obtained by SEM and HS-AFM (High Speed AFM) are presented for comparison. The data can be used to validate crystal plasticity models which should then directly predict multiaxial behaviour without recourse to deformation rules such as equivalent stress or strain.

Highlights

Fatigue damage evolution in macroscopically defect-free metallic systems requires local cyclic plasticity as a result of the application of repeated stress; this leads to crack initiation [1] and growth
The results are a proof of principle aimed at calibrating CP models which can be tested under biaxial conditions with a future focus on damage evolution
Preparation of the sample surface is critical for quantitative measurement from the HS-atomic force microscopy (AFM) and a suitable surface finish was achieved on the tensile face of the beam following the method outlined by Warren et al [16]

Summary

Introduction

Fatigue damage evolution in macroscopically defect-free metallic systems requires local cyclic plasticity as a result of the application of repeated stress; this leads to crack initiation [1] and growth. While numerous theoretical and computational techniques have been developed to investigate fatigue crack initiation and growth such as [4]–[14], physical evidence and high resolution validation data for fatigue nucleation, initiation and growth relies upon the development of experimental methods and observations. Recent modelling advancement such as crystal plasticity and dislocation dynamics approaches have provided the opportunity to model mesoscale plasticity in considerable detail. The results are a proof of principle aimed at calibrating CP models which can be tested under biaxial conditions with a future focus on damage evolution

Objectives

Methods

Results

Conclusion