Calculating the effect of configuration on the response of manganin stress gauges

Abstract
In the “Orthogonal Gauge” technique stress gauges mounted to measure both longitudinal and transverse (or lateral) stresses in a shocked matrix allow the shear strength of the matrix material to be determined. A useful measure of the sensitivity of an orthogonal gauge system to changes in the yield strength of the matrix material is provided by the ratio between the resistance change of gauges of a given cross-sectional shape mounted in transverse and longitudinal orientations, (the T/L Ratio). A low T/L Ratio indicates a more sensitive system. A Eulerian Hydrocode, (Shamrock), has been used to compute the resistance change of manganin wires of rectangular cross section and infinite length embedded in both longitudinal and transverse orientation in steel targets subjected to nominally one-dimensional shocks. Configurations in which the gauges were (a) embedded directly into the steel and (b) mounted within thin strengthless polymer layers were studied. It is shown that in case (a) the T/L Ratio decreases as the aspect ratio of the gauge cross-section increases. When the gauges are embedded in a strengthless polymer layer the T/L Ratio is lower than when the gauges are embedded directly into the matrix but in this case the aspect ratio of the manganin conductor has little influence on the T/L Ratio. The observed resistance changes are explained in terms of the stresses in the gauges. The results give insight into the factors which control resistance change and offer the prospect of improvements to current gauge designs.