The thermomechanical properties of aromatic polymers

High performance aromatic polymers such as PEEK and PEK are widely used in composite and related applications. However, their high rate thermomechanical properties are not well understood. This thesis describes a series of investigations into their mechanical behaviour over a large range of strain rates (10-3 -103 s-1 ) and temperatures (20-200° C) which were carried out in order to more fully understand their properties and to assess the applicability of standard polymer property models to their behaviour. The experiments involved the design and construction of two novel sets of high rate test apparatus. These were a cross-bow based system which enabled high strains to be obtained at strain rates of 103 s-1 and a drop-weight system based around a high speed camera which enabled direct measurements of radial strain and observation of sample behaviour to take place. The cross-bow apparatus incorporated a laser-photodiode system to enable direct strain measurements to be made and thus had an advantage over conventional Hopkinson bars of direct, rather than derived, strain measurements with a sufficiently energetic projectile to produce large deformations. These systems were used in addition to standard hydraulic ram and dropweight equipment. A heater unit to enable tests to be carried out over the desired temperature range was also designed and constructed and used with all the above systems. A comprehensive set of Differential Scanning Calorimetry and X-ray tests were carried out on samples before and after mechanical testing in order to provide structural data to aid the interpretation of the mechanical test results