Subsurface Defect Detection in Ceramic Materials Using Optical Gating Techniques

Components made from advanced ceramics materials, because of their thermomechanical and chemical properties, have several advantages over traditional steel parts, making them well suited for use in severe operating environments. In particular, silicon nitride (Si3N4) ceramics, because of their stiffness and resistance to corrosion, are being considered for use in rolling contact elements such as bearings and contact races. In addition, when combined with rare-earth oxide sintering aids such as yttria (Y2O3), silicon nitride ceramics have high-temperature strength which makes them excellent candidates for components such as rotors and blades in advanced turbine engines

Depth-Resolved Subsurface Defect Detection in Ceramics Using Optical Gating Techniques

Components made from advanced ceramics materials find widespread use in many industrial and military applications. However, the presence of defects in the bulk and on the surface of the ceramic parts can alter their operation and lead to a reduced lifetime or a catastrophic failure. These defects may include various inclusions, inherent powder defects, poorly distributed second phase material, as well as voids and cracks. They can be introduced at each stage of the manufacturing process. Near-surface defects are particularly critical in many applications since the stresses in this region of the ceramic component are greatest during the operation. These flaws may be intrinsic to the bulk material or can be introduced in the final stages of fabrication (e.g. machining, grinding and polishing). Additionally, in composite ceramics defects can appear as a delamination of internal layers. Because the potential market for ceramic components is so large, a considerable effort has been put into developing non-destructive evaluation (NDE) techniques to detect flaws at various stages of the manufacturing process [1–5]

Phase Modulation at 125 kHz in a Michelson Interferometer Using an Inexpensive Piezoelectric Stack Driven at Resonance

Fast phase modulation has been achieved in a Michelson interferometer by attaching a lightweight reference mirror to a piezoelectric stack and driving the stack at a resonance frequency of about 125 kHz. The electrical behavior of the piezo stack and the mechanical properties of the piezo-mirror arrangement are described. A displacement amplitude at resonance of about 350 nm was achieved using a standard function generator. Phase drift in the interferometer and piezo wobble were readily circumvented. This approach to phase modulation is less expensive by a factor of roughly 50 than one based on an electro-optic effect

Depth-Resolved Subsurface Defect Detection in Ceramics Using Optical Gating Techniques

Components made from advanced ceramics materials find widespread use in many industrial and military applications. However, the presence of defects in the bulk and on the surface of the ceramic parts can alter their operation and lead to a reduced lifetime or a catastrophic failure. These defects may include various inclusions, inherent powder defects, poorly distributed second phase material, as well as voids and cracks. They can be introduced at each stage of the manufacturing process. Near-surface defects are particularly critical in many applications since the stresses in this region of the ceramic component are greatest during the operation. These flaws may be intrinsic to the bulk material or can be introduced in the final stages of fabrication (e.g. machining, grinding and polishing). Additionally, in composite ceramics defects can appear as a delamination of internal layers. Because the potential market for ceramic components is so large, a considerable effort has been put into developing non-destructive evaluation (NDE) techniques to detect flaws at various stages of the manufacturing process [1–5].</p