Abstract
A novel technique is described for measuring thermal pressure in fluids and for measuring isotropic stress development and reaction kinetics in thermosetting resins during cure and thermal cycling. The method uses a 12.7-mm-diam sealed stainless steel spherical pressure vessel to impose three-dimensional isotropic constraints. The vessel is instrumented with strain gauges and thermocouples. Both isotropic stresses and reaction kinetics during cure at cure temperatures as high as 300 °C can be measured. In addition, measurement of the isotropic stress as a function of temperature yields the thermal pressure coefficient in both the glassy and rubbery (or liquid) states. Experimental results are presented for sucrose benzoate, a pressure-transmitting oil di-2-ethylhexylsebacate and an epoxy resin. The method provides reproducible estimates for the thermal pressure coefficient and the stresses are highly isotropic. A suggestion for improved versions of the device is: thicker walled vessels can be used to increase the upper stress limit (currently at 30 MPa). Also if a lower temperature range is to be studied, then aluminum can be used as a vessel material. Since epoxy resins have better adhesion to aluminum than to stainless steel, there may be an advantage to this.
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