Analysis of the fractures of metallic materials using optical coherence tomography

Abstract

Forensic in situ investigations, for example for aviation, maritime, road, or rail accidents would benefit from a method that may allow to distinguish ductile from brittle fractures of metals -as material defects are one of the potential causes of such accidents. Currently, the gold standard in material studies is represented by scanning electron microscopy (SEM). However, SEM are large, lab-based systems, therefore in situ measurements are excluded. In addition, they are expensive and time-consuming. We have approached this problem and propose the use of Optical Coherence Tomography (OCT) in such investigations in order to overcome these disadvantages of SEM. In this respect, we demonstrate the capability to perform such fracture analysis by obtaining the topography of metallic surfaces using OCT. Different materials have been analyzed; in this presentation a sample of low soft carbon steel with the chemical composition of C 0.2%, Mn 1.15%, S 0.04%, P 0.05 % and Fe for the rest has been considered. An in-house developed Swept Source (SS) OCT system has been used, and height profiles have been generated for the sample surface. This profile allowed for concluding that the carbon steel sample was subjected to a ductile fracture. A validation of the OCT images obtained with a 10 microns resolution has been made with SEM images obtained with a 4 nm resolution. Although the OCT resolution is much lower than the one of SEM, we thus demonstrate that it is sufficient in order to obtain clear images of the grains of the metallic materials and thus to distinguish between ductile and brittle fractures. This study analysis opens avenues for a range of applications, including: (i) to determine the causes that have generated pipe ruptures, or structural failures of metallic bridges and buildings, as well as damages of machinery parts; (ii) to optimize the design of various machinery; (iii) to obtain data regarding the structure of metallic alloys); (iv) to improve the manufacturing technologies of metallic parts.

Quantitative matching of forensic evidence fragments utilizing 3D microscopy analysis of fracture surface replicas

“…During the last two decades, new innovative 3D surface topological scanning microscopy has been developed with the potential to improve physical matching. Different 3D acquisition systems, employing 3D laser scanners, optical coherence tomography, stylus scanning instruments, and confocal microscopy, have been utilized for forensic evidence identification applications [19,26,29‐43]. Automated surface acquisition and matching processes utilizing 3D topography data have demonstrated promising improvements in the objectivity of the comparison process [34].…”

Application of fracture mechanics to interfacial ice adhesion and forensic physical match analysis

“…During the last two decades, the transition from 2D imaging to 3D surface topological scanning has provided support for the physical matching examination. Different forensic evidence surfaces including 3D tool marks, firearm, bullets, or fractured/ torn can be acquired for forensic matching applications using 3D laser scan [104,105,108], optical coherence tomography for in situ forensic investigations [113], optical microscopy [114], 3D laser or light microscopy [107,111], stylus scanning instrument [106,110], and confocal microscopy [109,112]. One of the benefits of the 3D representation is that after the 3D surface acquisition process, multiple shared examinations and analyses can be done on the digital data at different laboratories without transporting the forensic evidence [111],…”