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Rubbers are ubiquitous in engineering applications where they are often subjected to loading leading to high strain rate deformation. The strong rate and temperature dependence of rubbers and their composites motivates research into understanding their mechanical response under a wide range of conditions. However, experimental characterisation of the rate-temperature dependence of soft rubbers is challenging. In this methods paper, an improved methodology is proposed for conducting Dynamic Mechanical Analysis (DMA) experiments on rubbers. The higher quality data produced can be used in time-temperature superposition (TTS) applications to derive a more accurate definition of the rubber’s rate-temperature dependence. Overall, the improvements obtained can be summarised as follows: • Reducing clamping artefacts due to volume expansion • Ensuring high quality temperature stability • Improving the contact area between the specimen and the clamps

Polycarbonate is widely used in engineering applications in which its mechanical properties need to be well understood over a wide range of strain rates and temperatures. These properties can be dependent on the molecular structure. In this research, the thermomechanical properties of three homo-polycarbonates with different melt flow rates, and a modified co-polycarbonate, were extensively characterized to produce a large dataset of mechanical properties based on consistent thermal histories. Dynamic Mechanical Analysis was performed to obtain modulus data from which time-temperature superposition master curves were constructed. Quasi-static tensile tests were conducted at two loading speeds, using a digital image correlation system to calculate strain fields. Compression properties were measured at strain rates from 0.001 to 3000 s−1 at 20 °C, and from −60 to 120 °C at a constant true strain rate of 0.01 s−1. The mechanical response of the polycarbonates is highly rate- and temperature-dependent, and the yield stresses at a wide range of rates and temperatures show time-temperature equivalence: the yield stress increases with an increase in strain rate or a decrease in temperature. Curves of yield stresses versus logarithm strain rate present an increasing gradient with increasing rate, which results from the secondary transition. Comparisons are drawn between time-temperature superposition parameters obtained from modulus data and from yield stress data, and between stress-strain curves obtained at different strain rates and at different temperatures. In the large strain region, apparent thermal softening can be observed during the medium rate tests, consistent with the transition from adiabatic to isothermal loading, whilst softening is less than expected at the higher rates.

Polymers are widely used in applications where they may be subjected to impact loading leading to high strain rate deformation. Plastic work on deformation generates heat in the material. At high strain rates, there is insufficient time for this heat to diffuse out of the material, leading to adiabatic conditions. This leads to post-yield thermal softening in the mechanical response, which modifies the material response and must be considered in Engineering design. In this paper, a novel technique is presented in which this adiabatic self-heating can be simulated experimentally at low strain rates using programmed temperature profiles. We show that, in some cases, these simulations can very accurately capture the mechanical response at higher rates, but in others, the replication is less accurate. This may give further insights into the thermodynamics of high strain rate polymer mechanics. This technique therefore enables a number of avenues of research: the work to heat conversion can be investigated systematically; diagnostic tools that are limited to low strain rates can be applied; and we can better understand material behaviour and thereby improve predictive models.