Testing Problems on Non-Metallic Specimens

Abstract

The raw porcelain blanks, the so-called slugs, as long as they are saturated with water, are sufficiently transmissive at frequencies of 0.5 to 2 MHz to be tested in thicknesses of a few 100 mm for larger voids and insufficiently bonded seams. In practice, however, tests are not made on specimens in this state. Dried blanks are no longer transmissive Densely burnt porcelain, as far as transmittance and acoustic velocity are concerned, reaches values close to those for steel Using longitudinal waves of 5 MHz and higher, lengths exceeding 1 m can be penetrated ultrasonically. Other dense ceramics show similar behaviour, e.g. steatite, whose acoustic velocity exceeds even that of steel (see below). Glass likewise has very low attenuation. In practice, however, only insulators of porcelain and steatite have so far been tested during manufacture.