An investigation of the yield and postyield behavior and corresponding structure of poly(methyl methacrylate)

The effects of physical aging on the yield and postyield behavior and corresponding evolution in the structural state of glassy polymers are investigated. A systemetic program of uniaxial, isothermal, constant strain-rate rests on poly(methyl methacrylate) specimens of different thermal histories was carried out and positron annihilation lifetime measurements were performed. The results of the mechanical tests show that aging acts to increase both the initial yield stress and the amount of strain softening which occurs subsequently to yield.