Fractography, a Powerful Tool for Identifying and Understanding Fatigue in Composite Materials

Abstract

Fractography is a tool widely used in the academic world but a little-known technique in the industrial world. This tool can be useful at most stages of the development of composite parts: prototyping characterization, industrialization, production quality problems,.. Finally when a composite part is broken during service, fractographic analysis is one of the most efficient tools for the determination of the root causes of failure. Fractography is useful for the engineer who has to determine if the failure results of a mechanical overload or of a fatigue phenomenon.The implementation of a fractographic investigation requires to follow a methodology with different steps:The first step is to determine the direction of propagation in the different zones of the rupture by recognition of features on the broken surface. From these results, the initiation area can often be identified. Then a long part of the work consists in seeking features of static or fatigue damage. Fractography also allows to determine what type of mechanical loading has caused the micro-damage in the initiation area. This information can be compared with the expected loading.Sometimes, the fatigue fractographic features are localized just along manufacturing defects. In this case, a specific study is required to establish the harmfulness of these defects. The defect acceptance criteria after manufacturing are then sometimes amended.Article will discuss these aspects through industrial examples.