Instrumented thick-walled tube method for measuring thermal pressure in fluids and isotropic stresses in thermosetting resins

Abstract

We have developed a method for measuring the thermal pressure coefficient and cure-induced and thermally induced stresses based on an instrumented thick-walled tube vessel. The device has been demonstrated at pressures up to 330 MPa and temperatures to 300 °C. The method uses a sealed stainless steel thick-walled tube to impose three-dimensional isotropic constraints. The tube is instrumented with strain gauges in hoop and in axial directions and can be used in open or closed configurations. By making measurements of the isotropic stresses as a function of temperature, the method allows determination of the thermal pressure coefficient in both the glassy and rubbery (or liquid) states. The method also can be used to measure isotropic stress development in thermosetting resins during cure and subsequent thermal cycling. Experimental results are presented for sucrose benzoate, di-2-ethylhexylsebacate, and an epoxy resin. The current report shows that the method provides reliable estimates for the thermal pressure coefficient. The thermal pressure coefficient is determined with resolution on the order of 10kPa∕K. Among advantages of the method is that the tubes are reusable, even when measurements are made for cure response of thermosetting resins.

Viscoelastic properties and residual stresses in polyhedral oligomeric silsesquioxane‐reinforced epoxy matrices

“…10 Recently, a novel technique was developed in our laboratories to measure the thermal pressure coefficient of thermosetting resins during cure and thermal cycling using an instrumented pressure vessel. [11][12][13] In that work, we found that the thermal pressure coefficient of the liquid monomer was higher than that of the glassy polymer 13 but we did not measure the property as a function of temperature or resin structure.…”

Direct Measurement of Cure‐Induced Stress in Thermosetting Materials by Means of a Dynamic Mechanical Analyzer

“…Several methods have been developed to measure the cure stress buildup for thermosetting polymers. These include beam‐bending technique,7,8 steel ring method,9 thin‐walled tube,10–11 thick‐walled tube,12 instrumented sphere method,13 etc. However, the above methods cannot measure the cure stresses directly, and cure stresses have to be computed on the basis of measured strain or deflection value.…”

Investigation of cure stresses in non-conductive adhesive interconnects

“…Several methods have been developed to measure the build-up of cure stress for thermosetting polymers. These include beam-bending technique [69][70], steel ring method [102], thin-walled tube [66,72], thick-walled tube [103], instrumented sphere method [104], etc. However, the above methods cannot measure the cure stresses directly and cure stresses have to be computed based on the measured strain or deflection value.…”