In-Situ Nuclear Magnetic Resonance Investigation of Strain, Temperature, and Strain-Rate Variations of Deformation-Induced Vacancy Concentration in Aluminum

Critical strain to serrated flow in solid solution alloys exhibiting dynamic strain aging (DSA) or Portevin–LeChatelier effect is due to the strain-induced vacancy production. Nuclear magnetic resonance (NMR) techniques can be used to monitor in situ the dynamical behavior of point and line defects in materials during deformation, and these techniques are nondestructive and noninvasive. The new CUT-sequence pulse method allowed an accurate evaluation of the strain-enhanced vacancy diffusion and, thus, the excess vacancy concentration during deformation as a function of strain, strain rate, and temperature. Due to skin effect problems in metals at high frequencies, thin foils of Al were used and experimental results correlated with models based on vacancy production through mechanical work (vs thermal jogs), while in situ annealing of excess vacancies is noted at high temperatures. These correlations made it feasible to obtain explicit dependencies of the strain-induced vacancy concentration on test variables such as the strain, strain rate, and temperature. These studies clearly reveal the power and utility of these NMR techniques in the determination of deformation-induced vacancies in situ in a noninvasive fashion.

Absolute length measurement at high pressure

A length-measurement systcm is described that can make absolute length- change measurements of a meter-long specimen within a pressure vessel (to pressures of 8 kbar) with a fractional error of 3 x 10/sup -8/ even when changes in length of 4 cm occur. Possible uses of such a system for measuring the volume thermal expansivity (at pressure) and the isothermal bulk modulus (at pressure) are described. Moreover, it is noted that, when this system is combined with an ultrasonic velocity measurement system, the adiabatic bulk modulus (at pressure) and Gruneisen parameter as a function of pressure can be directly determined and the absolute pressure itself can be measured. (auth

New absolute high pressure gauge

A new absolute pressure measurement system based on the simultaneous measurement of length and ultrasonic transit times is described. The system was used to determine the transition pressure of pure mercury at 0 deg C at 7571.2 plus or minus 1.6 bars. It is particularly advantageous to use a device for calibrating secondary gauges such as manganin gauges inasmuch as it gives a highly accurate measurement of nonlinearities in such secondary gages. The gage calibrated in the present study reaches a maximum deviation from linearity of 11.6 bars at a pressure midway between atmospheric pressure and the 0 deg C mercury melting pressure. (auth

High pressure calibration with a new absolute pressure gauge

The simultaneous measurement of length and transit time of a specimen under pressure was used to develop a new way of determining absolute high pressure. The mercury freezing point at 0 deg C was deterinined with this new method at 7571.2 plus or minus 1.6 bars. Accurate high-pressure calibration of secondary pressure gages such as manganin gages is possible with this method. The maximum deviation from linearity of the present gage studied is 11.6 plus or minus 1 bars between atmospheric pressure and the mercury freezing point at 0 deg C. (auth