Evaluation of Different Methods of Measurement for the Isotropic Stress Development in Curing Thermosets

摘要

We have developed two novel methods for measuring isotropic stress development inrnthermosetting resins during cure and subsequent thermal cycling. The methods involve eitherrnsealed stainless steel spherical pressure vessels or thick-walled tubes to impose threedimensionalrnisotropic constraints. The strain at the outer surface of the vessels is monitored byrnstrain gauges and the temperature of the vessels is measured by thermocouple. The isotropy ofrnthe stresses in tension and compression are examined for both methods. The methods also allowrnus to obtain the thermal pressure coefficient (the product of the thermal expansion coefficientrnand the bulk modulus αK) in both the glassy and rubbery (or liquid) states. The sphericalrnpressure vessel method provides better sensitivity (with detection limit of 2 kPa K~(-1)), but isrnlimited to modest pressures due to yield of the stainless steel. The thick-walled tubes providernbetter constraints and higher internal pressure measurements (with wall yield occurring at arnpressure above 400 MPa). Advantages of both methods over the classical thin-walled tubernmethod are also evaluated.