Longitudinal Gauges Research Articles

Dynamic high-pressure properties of AlN ceramic as determined by flyer plate impact

The dynamic properties of hot-pressed aluminum nitride ceramics were determined in a series of plate impact experiments using longitudinal and transverse in-material manganin gauges. The Hugoniot curve for hot pressed specimens was determined in the range of 0–190 kbar with a value of 94±2 kbar for the Hugoniot elastic limit (HEL). Using both gauge orientations, the stress deviator in the specimens was determined as the difference between longitudinal and transverse stresses. It was found that the stress deviator remains relatively constant above the HEL, and is about 10% higher than the value at the HEL point. The inferred Hugoniot converges to the extrapolation of the hydrostat. Since the convergence is not due to loss of strength, it may be due to a phase change in the AlN from low-pressure (wurtzite) structure to high-pressure (rocksalt) structure.

Accounting for the crossover phenomenon in the response of longitudinal and transverse piezoresistance gauges in shock wave experiments

The response of a transverse piezoresistance gauge under plane shock wave loading is different than that of a longitudinal piezoresistance gauge. For a given combination of gauge and embedding matrix the response of the transverse gauge can be higher than that of the longitudinal gauge in a certain range of shock stresses, and lower at a different stress range. This ‘‘crossover phenomenon’’ defines a certain stress level (σ*), for which the response of the two gauges is equal. In this paper we analyze this crossover of the gauge’s responses analytically. The analysis accounts for the crossover stress in terms of the yield strength of gauge material and the deviatoric stresses in the embedding matrix. We show that when the yield strength of the gauge is higher than that of the matrix, there is no crossover of the gauge’s response. Experimental results are presented to support the analysis.

Experimental measurements and analysis of the loading and unloading response of longitudinal and lateral manganin gauges shocked to 90 kbar

Experimental results and analysis describing the response of manganin gauges oriented parallel and perpendicular to the shock front and embedded in an aluminum-oxide matrix are presented. Both loading and unloading data to 90 kbar were obtained. An analytic model for piezoresistance response coupled with the electromechanical constants, determined from independent quasistatic experiments, was used to calculate the gauge response. Good agreement was obtained between the experimental results and the analytic model calculations. The analytic model was also used to quantitatively analyze the residual resistance measurements. The results presented here can be used to analyze gauge data during unloading and multiple wave loading.

Shear strength of shock-loaded alumina as determined with longitudinal and transverse manganin gauges

The shear strength of shock-loaded commercial alumina (AD-85 manufactured by Coors) is determined in the 0–140-kbar range of shock stresses. Longitudinal and transverse manganin gauges were used to determine the principal stresses in the shocked specimens. Shear strengths were determined from the difference between the longitudinal and lateral stresses. It was found that the shear strength remains essentially constant at about 27 kbar for shock stresses between 60 kbar (the Hugoniot elastic limit) and the maximum shock amplitude tested in this series (142 kbar). The source for the high shear strength is attributed to the confining pressures that strengthen the comminuted ceramic. Evidence for this interpretation is obtained by considering the release profiles as recorded by the longitudinal gauges when the free-surface rarefactions reach gauge location.

Complex behaviour of a coal sample in a large scalein situ compression test

A large scalein situ compression test of a laminated coal cube is described. The cube was uniformly loaded by a system of hydraulic jacks supplied simultaneously from one pump. At the same time both load and deformations were controlled. Deformations were measured by 60 longitudinal gauges located at the side surface of the cube in the regular net. Due to the heterogeneity of the rock the readings showed scatter. As a first approximation, the scattered data were fitted to the plane using the least square method. Orientations of the planes were analysed and show permanent relative movement between adjacent lamina indicating complex behaviour of the cube under loading. Detailed analysis of this behaviour indicated that the cube was subjected to both bending and twisting.

応力解放法による球面孔底ひずみの測定

The practical system for measuring the strains on a hemi-spherical borehole bottom by the stress relief technique has been presented and its utility has been examined experimentally.The spherical 16-element mold gauge, made of epoxy resin as shown in Fig.3, has beendeveloped to set the 8 latitudinal strain gauges and 8 longitudinal strain gauges at the proposed position on the bottom surface with high accuracy.This mold gauge has been calibrated in the appropriately oriented borehole in the andesite cubic specimens under load, andit is confirmed that the measured strains well agree with the elastic strain distribution analyzed by F.E.M.as shown in Fig.5.The process of in-situ stress relief has been examined by analyzing the strainc hange observed under over-coring.The typical strain change in Fig.8 shows that prior to the stress relief the tension appears in the longitudinal direction.Especially, it is remarkable in the case that the hollow core discing occurs as shownin Fig.9.It has been discussed that such a tension behavior influenced upon the accuracy of strain measurement and it conditioned the limitations and certain disadvantages of this system.