Paul Zoller

Matrix solidification and the resulting residual thermal stresses in composites

The disparate thermal expansion properties of the fibres and matrices in high-performance composites lead to an inevitable build up of residual thermal stresses during fabrication. We first discuss the thermal expansion behaviour of thermoplastic and thermoset polymers that may be used as high-performance composite matrices. The three classes of polymers considered are epoxies, amorphous thermoplastics, and semicrystalline thermoplastics. The relevant thermal expansion data for prediction of the magnitude of the residual stresses in composites is the zero (atmospheric)-pressure thermal expansion data; these data are plotted for a range of thermoplastics and a typical epoxy. Using the technique of photoelasticity, we have measured the magnitude of the residual stresses in unidirectional graphite composites with an amorphous thermoplastic matrix (polysulfone) and with an epoxy matrix (BP907). The temperature dependence of the residual stress build up and the resulting magnitude of the residual stresses correlate well with the thermal and physical properties of the matrix resin.

Pressure-volume-temperature relationships of solid and molten poly(ethylene terephthalate)

Abstract The pressure-volume-temperature (PVT) properties of poly(ethylene terephthalate) (PET) have been studied experimentally and theoretically in the temperature range 30–342 °C and at pressures to 2000 kg/cm2. In the semicrystalline solid state (ρ = 1.409 g/ cm3 at 20°C), two transitions were resolved. One is the glass transition at Tg = 70°C (P = 0), increasing with pressure according to dTg/dP = 0.025 °C/(kg/cm2). A second transition was observed as a break in the zero-pressure isobar and also as a break in the zero-pressure compressibility versus temperature curve at 160°C. It is interpreted as a premelting (αc) transition. The melt data were fitted successfully to both the empirical Tait equation and the Simha-Somcynsky hole theory (with T∗ = 11710°K, V∗ = 0.7408 cm3/g, and P∗ = 11570 kg/cm2). The Simha-Somcynsky theory was also used to establish a semi-empirical equation of state for amorphous PET in the temperature range Tg < T < Tm and to derive a theoretical pressure dependence of Tg in compl...

Instrumentation for impact testing of plastics

Abstract Instrumentation suitable for a wide variety of impact testers has been developed. Its use on a falling weight tester is described. The falling weight tester has been used to impact samples not only in the Gardner geometry, but also for Charpy and Izod specimens. However, the instrumentation is equally well suited for instrumentating conventional pendulum testers. The instrumentation consists of an accelerometer attached to the impacting mass. The acceleration signal is recorded on a digital oscilloscope and is used to calculate the velocity of the impacting mass, the force on the sample, the deflection of the sample, and the energy transferred from the impacting mass to the sample. The data evaluation and the reporting of the results (in the form of plots and tables) are handled by a dedicated desk-top computer. The capabilities of the instrumentation are illustrated by a series of Gardner tests on polypropylene sheeting.