Abstract: A method and apparatus for ascertaining internal stresses in a hardened region to be tested for a component made of a predetermined material includes measuring coercive field strength and amplitude of magnetic Barkhausen noise as a function of mechanical stress and hardness in calibration samples of a predetermined material of known hardness and known internal stress. Calibration functions are ascertained from the measured values indicating the dependency of the hardness and the amplitude of the magnetic Barkhausen noise as functions of the hardness and mechanical stress. The coercive field strength and the amplitude of the magnetic Barkhausen noise is measured in a location-dependent manner over the region of the component to be tested. The measured values of the coercive field strength and the amplitude of the magnetic Barkhausen noise are converted in the region to be tested into location-dependent hardness and into location-dependent mechanical stress using the ascertained calibration functions.

Abstract: Method for determining internal stresses in structural members in machine or apparatus manufacturing by machining, around a measuring location provided with strain gages, a circular slot into the surface of the structural member that is to be measured, measuring changes in strain of the core of the measuring location left standing, and calculating the internal stresses from the measured strains and a depth-dependent decay function determined on a calibrating material sample, the improvement therein affording the determination of internal stresses in the structural members at depths greater than about 5 mm, includes the steps of mechanically removing the measuring-location core down to a new surface at the base of the circular slot, securing a strain gage to a new measuring location at the new surface, machining another circular slot around the new measuring location, measuring changes in strain of the core of the new measuring location left standing while measuring changes in strain thereof and repeating the

Abstract: Quartz glass element, such as a diffusion tube useful in the production of semiconductor elements, capable of forming an outer layer of uniformly fine crystalline silica such as cristobalite or tridymite when heated to a temperature at which such crystalline silica forms containing crystallization promoting nuclei having a rate of diffusion in quartz glass less than that of sodium at elevated temperatures. Such nuclei are preferably present in the outer half of the element wall. When the quartz glass element is exposed to elevated temperatures, the nuclei promotes the formation of the outer layer of uniformly fine crystalline silica which imparts thermal dimensional stability for extended periods of use at elevated temperatures.