Hardness and Non-Destructive Testing (NDT) of Ceramic Matrix Composites (CMCs)

Abstract

This article presents a short overview of the most common techniques in non-destructive testing (NDT) of ceramic matrix composites (CMCs), including measurement of hardness. The hardness test is the most commonly used method for determination of basic mechanical property of any material, including composites. It is a simple and fast technique that can also be correlated with some mechanical properties. Concepts of the traditional indenting methods (Brinell, Rockwell, Vickers, Knoop and Berkovich) are shown. Beside macro-indentation techniques, micro- and nanoindentation have become one of the promising techniques in mechanical characterization of composites, since these can provide data on different phases in composites, including fiber/matrix interphases and thin layers. Traditional NDT methods for detecting defects in CMCs are presented: visual and haptic analysis; acoustic emission method; ultrasound analysis; penetration method; thermographic and infrared (IR) analysis; radiography and X-ray computed tomography (CT). Among the simplest approaches in defect detection, penetrant methods have become widespread for all material classes. Radiography is one of the most commonly used methods for non-destructive testing. Radiography images show defects in the material structure but have some drawbacks related to resolution of details below mm scales, as well as in safety aspects. One of the novel technologies, CT imaging, has enabled very precise 3D visualization of the material structure. In CT imaging, 3D volume is visualized by using a series of 2D radiographic images, based on complex algorithms and software image processing. This opened up new directions in material characterization, since it has enabled comprehensive non-destructive testing of materials and components even in dynamic environments and in situ.