Mechanical properties of prestressed thermoplastics

Abstract

Mechanical tests of prestressed and nonprestressed specimens show that prior stressing often signijicantly changes the stress-strain curve of amorphous and partly crystalline Specimens subjected to a prior mechanical stress show a Jla#er stress-strain curve (even with a "kink") than those not previously stressed. The original properties of prestressed specimens can be restored by tempering (at least in the range of small elongations). Specimens made of ABS react differently: After certain longterm prior stresses, followed by short-term tensile tests, brittle fracture occurs.

Microstructural construction of polymers with improved mechanical properties

“…Different ABS (acrylonitrile±buta-diene±styrene) materials (Novodur from Bayer AG) were investigated with smaller polybutadiene rubber particles (average diameter 130 nm) and larger ones (average diameter about 440 nm) in a bimodal distribution. These materials differ in their reaction on long-time preloading (creep test) [6,7]. As a reference sample, a typical ABS material was chosen showing no alteration in toughness after preloading (called sample 1), whereas sample 2 showed the surprising effect of embrittlement after preloading.…”

“…4. Recently, a surprising effect occurred in the toughness behavior of ABS materials [6]: When creep tests were performed with loads below the actual damage limit and if the specimens were tested afterwards in the tensile mode, samples of certain ABS materials broke, atypically brittle, at a low strain level. There was no visible change on the surface of the samples and in the mechanical behavior before fracture which would allow the prediction of the failure.…”

“…Energy absorption up to fracture of ABS sample 2, prestressed in creep tests as a function of the preloading stress (preloading in % of yield stress ' y of material) (from[6]). …”

Study of structure property correlations in polymers by techniques of electron microscopy

“…An unexpected effect of embrittlement has been reported in some ABS grades [17]. If in creep tests these ABS materials are loaded below the actual damage limit and are afterwards tested in a usual tensile mode, atypically they will brittle break at a low strain level.…”