Mechanisms of the Early Fatigue Damage in Metallic Materials

Jaroslav Polak,Martin Petrenec,Jiri Man

doi:10.26552/com.c.2006.4.5-9

Jaroslav Polak, Martin Petrenec + Show 1 more

Open Access

https://doi.org/10.26552/com.c.2006.4.5-9

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Abstract

The early stages of the fatigue damage in f.c.c. and b.c.c. metals are studied using high resolution techniques. The localization of the cyclic plastic strain results in formation persistent slip bands (PSBs) with specific dislocation structure. Characteristic surface relief is formed at locations where PSBs emerge on the surface. It consists of extrusions and intrusions separated by the original flat surface. Atomic force microscopy is used to study the details of the surface relief. The experimental findings are discussed in terms of the point defect model of fatigue crack initiation.

Highlights

The basic facts concerning the surface relief formation in fatigued metals were documented already at the beginning of the 20th century by Ewing and Humfrey [1] by observing the surface of fatigued Swedish iron
The analysis of experimental results on the early fatigue damage in polycrystalline f.cc. and b.c.c. steels and the comparison with physically based models lead to the following conclusions: (i) Localization of the cyclic plastic strain results in the early formation of persistent slip bands (PSBs)
(ii) PSBs have specific dislocation structure consisting of alternating thin dislocation rich walls and wide dislocation free channels

Summary

Introduction

The basic facts concerning the surface relief formation in fatigued metals were documented already at the beginning of the 20th century by Ewing and Humfrey [1] by observing the surface of fatigued Swedish iron. The optical microscope used in these and later studies could not reveal details of the emerging extrusions and intrusions and eventually the early initiation of fatigue cracks. Smooth cylindrical specimens having 8 mm in diameter and 12 mm in gage length were slightly notched to produce surface suitable for surface observations. The area of the notch was mechanically and electrolytically polished to facilitate the observations of the surface relief. The specimens were cycled in computer controlled MTS 880 electrohydraulic machine. Further experimental details concerning the materials and testing procedure can be found elsewhere [3, 4]

Results

Discussion

Conclusion