Crystallinity Increases in Semi Crystalline Polymers During High Rate Testing

Abstract

During low rate deformation in tension semi-crystalline polymers can undergo a strain induced c r y s m o n during deformation which leads to increases in flow stress. This work extends studies of crystallinity in the polymers PM, PEEK and PET to compression at high strain rates at a variety of temperatures. All three polymers show large increases in crystallinity when tested at high rates with PEK and PEEK showing increases only at rates of 10' 1s. It is speculated that the rapid increases in flow stress reported in polymers at high strain rates may be due to the rapidity of strain induced crystallisation at these strain rates.Rksumk: Pendant une deformation B basse vitesse en traction, les polymkres semi-cristallins peuvent subu une cristallisation induite par deformation qui conduit B une augmentation de la contrainte d'ecoulement. Ce travail concerne 1'Ctude de la cristallinit6 des polymkres PEK, PEEK et PET provoquee par la deformation en compression I vitesses de dkformation klevdes et I differentes temp8ratures. Les trois polymeres montrent une forte augmentation de cristallinitk lorsqu'ils sont testes B grande vitesse; le PEK et le PEEK ne montrant qu'une augmentation qulB partir d'une vitesse de 10' 1s. On suppose que I'augmentation rapide de la contminte d'6coulement revel6e par les polymkres vitesse &levee pourrait dtre due B la rapidit6 de la cristallisation induite B ces vitesses de deformation correspondantes.

The high strain rate compressive behaviour of polycarbonate and polyvinylidene difluoride

“…For example, Dioh et al attributed it to specimen size effects in the Hopkinson bar, and present results that show the effect is reduced for smaller specimen thicknesses [16,17]. Hamdan and Swallowe [13], Al-Maliky et al [12] and Swallowe and Fernandez [18,19] suggested that the behaviour was due to an increase in crystallinity occurring during deformation. However, Swallowe and Lee [20] showed that for PET this increase develops too late in the deformation to contribute to the yield and flow stress.…”

Thermomechanically stable dielectric composites based on poly(ether ketone) and BaTiO3 with improved electromagnetic shielding properties in X‐band

“…. where Δ H f is heat of fusion of samples, and Δ for 100% crystalline PEK (130 J/g) taken from literature, and w is weight fraction of BT. It can be clearly seen from Figure (b) that incorporation of BT decreases the crystallization temperature ( T c ).…”

Effects of blown film process on initial properties of HPDE geomembranes of different thicknesses

“…According to Swallowe et al (1997), the crystallinity of semi-crystalline polymer is affected by compression. Therefore, encapsulating the test specimens by covering the specimens in the pan with an aluminium lid then crimping the specimens, could affect the stress history of the test specimens and, consequently, the DSC scan.…”