On compression and damage evolution in two thermoplastics.

N K Bourne,E N Brown,D S Eastwood,S A Mcdonald,C Rau,P J Withers,S Parry,S C Garcea

doi:10.1098/rspa.2016.0495

Abstract

The well-known Taylor cylinder impact test, which follows the impact of a flat-ended cylindrical rod onto a rigid stationary anvil, is conducted over a range of impact speeds for two polymers, polytetrafluoroethylene (PTFE) and polyetheretherketone (PEEK). In previous work, experiments and a model were developed to capture the deformation behaviour of the cylinder after impact. These works showed a region in which spatial and temporal variation of both longitudinal and radial deformation provided evidence of changes in phase within the material. In this further series of experiments, this region is imaged in a range of impacted targets at the Diamond synchrotron. Further techniques were fielded to resolve compressed regions within the recovered polymer cylinders that showed a fracture zone in the impact region. The combination of macroscopic high-speed photography and three-dimensional X-ray imaging has identified the development of failure with these polymers and shown that there is no abrupt transition in behaviours but rather a continuous range of responses to competing operating mechanisms. The behaviours noted in PEEK in these polymers show critical gaps in understanding of polymer high strain-rate response.

Highlights

The adaptability of polymeric materials in function and processing has allowed manufacturers to realize new diverse applications
The Taylor cylinder impact test is a useful integrated experiment in which a range of strain rates and flow fields upon deformation can be realized under relatively low velocity conditions [2,3,4]
The complex behaviour probed in previous work on different classes of polymer suggested the two thermoplastics chosen for this study, with well-defined physical properties over a large stress and temperature range

Summary

Introduction

The adaptability of polymeric materials in function and processing has allowed manufacturers to realize new diverse applications. Polymers have been employed as a binder phase in composites with other material classes introduced as fibres or as embedded, second-phase particles Their strength and flexibility has allowed them to be cast, and drawn in a manner that optimizes material microstructure which benefits from the inherent strength in the polymer chain. Within one diameter back from the impact face, the stress attenuates so that the rest of the cylinder experiences quasi-elastic wave propagation followed by specimen deceleration Despite this range of stresses and operating mechanisms, the behaviour (of at least the deformation of metals) was initially predicted with reasonable accuracy using an elementary mathematical model applicable to elastoplastic metals [2,6]. Material models typically only used to compare the transient sample profile/geometry and do not include failure mechanisms

Methods

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Discussion

Conclusion