The response of polyether ether ketone to one-dimensional shock loading

Abstract

The behaviour of the polymer polyether ether ketone (PEEK) has been investigated under conditions of one-dimensional shock loading. This has involved measurement of the Hugoniot in terms of stress, shock velocity and particle velocity, and measurements of the lateral stress, which have been used to determine the shear strength, and its variation with shock stress. Analysis of the relationship between shock velocity and particle velocity shows a simple linear response, in common with many other materials. Shear strength has also been shown to increase with shock stress, with a break in slope at ca 1.0 GPa. Below this stress, the material appears to behave in a simple elastic manner, which suggests a Hugoniot elastic limit of 1 GPa. Shear strength has also been observed to increase significantly behind the shock front both above and below 1 GPa. This behaviour has been observed in other polymeric materials, where it was suggested that these materials were responding by a viscoplastic mechanism.

The effect of orientation on the shock response of a carbon fibre–epoxy composite

“…Such behaviour has been seen in a number of other materials, including metals such as titanium aluminides [26] and polymers such as polyether ether ketone [27], epoxy [28] and polycarbonate [29]. Further, independent measurements of the shear strength in these materials [26,27,29,30] confirmed that the shear strength did indeed increase with shock stress. Therefore, it would appear that in the through thickness orientation, the response to shock loading is controlled in large part by the epoxy binder phase.…”

Shear strength measurements in a shock loaded commercial silastomer

“…In metals, c 0 has been equated with the measured bulk sound speed (c B ), thus this discrepancy needs explanation. However, this behaviour has been observed in a number of other polymers, both by ourselves (see for example PEEK [17] and epoxy resins [16]) and in the compendium of polymer shock data published by Carter and Marsh [32]. In semicrystalline polmers [24], it was suggested that this be due to a deviation below the accepted linear response at very low particle velocities by a transition from elastic to inelastic behaviour in the stronger crystalline phase.…”

“…In all four materials, a significant increase in shear strength was also observed behind the shock front [17,18], again ascribed to a degree of tacticity between adjacent polymer chains. However, in the case of fluorinated polymers such as polytetrafluoroethylene (PTFE), PCTFE and polyvinylidene difluoride (PVDF), the situation is rather different [23,24].…”

“…Assuming that x is constant behind the shock front, then this implies, from equation 3, that the shear strength is increasing until releases enter the gauge location. Such a response has been seen in a number of materials, including face-centred cubic metals, where it was explained in terms of dislocation multiplication [11], and more pertinently polymers such as PMMA [33], PEEK [17], polycarbonate [34], epoxy [16] and polyethylene, polypropylene and polystyrene [18]. Clearly dislocation based mechanisms cannot be operating, especially as these materials represent a range of semi-crystalline (PE, will again lead to a high degree of steric interference.…”

“…However, from equation 2, it can be seen that shear strength can also be measured using suitably orientated manganin stress gauges. This methodology has been used by ourselves and others on a variety of materials including metals and alloys [10][11][12], ceramics and silicate glasses [13][14][15] and polymers [16][17][18]. It can be seen that this is an invasive procedure, in that a manganin stress gauge must be introduced into a sectioned target assembly, and as such, it has been suggested that in doing so, the lateral stress recorded by the gauge is more a function of the layer of adhesive it sits in due to target assembly [19].…”