Embrittlement failure assessment
Introduction
Fractography is the study of the fracture surfaces of materials. Fractographic methods are routinely used to determine the cause of failure in engineering structures, especially in forensic engineering or in failure analysis. In research in the field of materials science, fractography is used to develop and evaluate the theoretical behavior of crack growth models.
One of the objectives of fractographic examination is to determine the causes of material failure by studying the characteristics of a fractured surface. Different types of crack growth (e.g. due to fatigue, stress corrosion, or hydrogen embrittlement) produce characteristic features on the surface, which can be used to help identify the failure mode. However, the overall pattern of cracking can be more important than a single crack, especially for brittle materials such as ceramics and glass.
Applications
Fractography is a technique widely used in forensic engineering, forensic materials engineering, and fracture mechanics to understand the causes of material failure and also to verify theoretical predictions with observed real-life behavior. It is useful in forensic science to analyze fractured items that have been used as weapons, such as broken bottles. Therefore, a defendant could claim that a bottle was defective and accidentally broke when it struck the victim of an assault. Fractography could show that the allegation is false and that considerable force was required to break the bottle before using the broken end as a weapon to deliberately attack the victim. Bullet holes in windshield or window glass can also indicate the direction of impact and the energy of the projectile. In these cases, the overall cracking pattern is vital to reconstructing the sequence of events, rather than the specific characteristics of a single crack. Fractography can determine whether the cause of a train derailment was a faulty rail, or whether an airplane wing had fatigue cracks before the crash.
Fractography is also used in materials research, as fracture properties can be correlated with other properties and the structure of materials.
Types of fracture
The analysis, generally visual (with the naked eye and microscopic) of the fractographic figures, makes it possible to identify the properties of the material (ductility, fragility), exfoliation planes "Exfoliation (mineralogy)") or its homogeneity. In certain cases, such as iron casting, the distinction between materials is based on the appearance of the fracture surface (gray, white, or mottled cast iron).