A Photoelastic Dynamometer for Rapidly Varying Forces

A photoelastic dynamometer applicable to rapidly varying forces is described. It consists of a glass slab upon which the force acts, placed between crossed polarizers; the intensity of the transmitted light is a measure of the force. It is indicated by a vacuum photocell working on an amplifier and a cathode-ray oscillograph. The arrangement has been used for recording the variation of pressure over the area of contact in rolling mill research. Compared with piezoelectric methods, it has the advantages of stability and of applicability to moving components without the necessity of using slip-rings.