Measurement of internal stresses by radiofrequency spectroscopy

The shift with pressure of the Cu63 pure quadrupole resonance frequency in Cu2O has been used to measure the stress developed within a resin due to curing. The method has possibilities for general use in the measurement of internal pressure. It involves the incorporation within a sample of an inert, insulating powder containing nuclei from which a pressure‐sensitive pure quadrupole resonance frequency may be detected. For sample of Epon 828 cured at 80°C for 1½ hr., a stress corresponding to an internal pressure of 2300 ± 400 psi was detected. In addition to the frequency shift of the Cu63 resonance observed in the resin, the absorption was broadened, indicating that a distribution of internal pressures existed.