Tensile Behavior of Polyetheretherketone over a Wide Range of Strain Rates

Zakaria El-Qoubaa,Ramzi Othman

doi:10.1155/2015/275937

Abstract

Polyetheretherketone (PEEK) is used in several engineering applications where it has to bear impact loads. Nevertheless, the tensile behavior has only been studied in the quasi-static range of loading rates. To address the lack of data in the impact strain rate range, the tensile mechanical behavior of PEEK is investigated at room temperature over a large range of strain rates (from 0.001 to 1000/s). The macroscopic volume change is studied under uniaxial tension using digital image correlation (DIC) method, showing a significant dilatation that reaches 16% at a logarithmic axial strain of 40%. The true stress-strain behavior is therefore established based on the measured volume change. Elsewhere, the yield stress shows a significant sensitivity to strain rate. Besides, a new constitutive equation is proposed to take into account the increase in strain rate sensitivity at high strain rates. It assumes an apparent activation volume which decreases as the strain rate increases. The new constitutive equation gives similar results when compared to the Ree-Eyring equation. However, only three material constants are to be identified and are physically interpreted.

Highlights

Thanks to its high chemical and physical properties, polyetheretherketone (PEEK) is nowadays regarded as one of the most efficient thermoplastics
The macroscopic volume change is studied under uniaxial tension using digital image correlation (DIC) method, showing a significant dilatation that reaches 16% at a logarithmic axial strain of 40%
The tensile mechanical behavior of PEEK was characterized over a large domain of strain rates using a conventional tensile machine and a customer-designed tensile crossbow machine

Summary

Introduction

Thanks to its high chemical and physical properties, polyetheretherketone (PEEK) is nowadays regarded as one of the most efficient thermoplastics. PEEK is widely used as a matrix in composites within several industrial applications, in automotive and aeronautic industries. PEEK can be used as a medical implant due to its biocompatibility [1, 2]. PEEK’s behavior depends on strain rate and temperature as well. Researchers, when testing polymers, have constantly assumed the incompressibility hypothesis regarding the evolution of the cross-sectional area, in order to characterize the true stress-strain. This assumption is more suitable for metals than polymers. It is of major importance to check the volume change of PEEK

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