Abstract
An adaptable flexural test fixture is proposed to characterise the mechanical properties of miniature beam specimens (≤10 mg) at ambient conditions or in the presence of fluids at elevated temperatures. The fixture is validated using representative amorphous and semi-crystalline polymers. The response of miniature specimens is compared against that of medium-sized specimens (≤1 g) on the same fixture and on conventional test equipment. Good agreement is found between the specimen sizes for all materials, but the comparisons highlight small differences attributed to factors such as specimen dimensional accuracy, crystallinity and span-to-thickness ratios. Flexural tests in water at 37 °C using both specimen sizes were performed to investigate the evolution of mechanical behaviour of hydrolytically degraded polylactides. Here, specimen size influences the diffusion timescale of acidic by-products which can reduce or enhance autocatalysis.
Highlights
Mechanical testing of miniature specimens to determine bulk prop erties has been pursued over the last 40 years to support material development in industries such as nuclear, power generation and aero space, with an emphasis on metallic materials
Test methods typically used to evaluate metals, for example small punch tests, have been applied to polymeric materials but the discs specimens lead to complex stress states that are challenging to relate to conventional tensile tests
In this study we propose a test fixture to determine mechanical properties that provides (1) a simple path to the constitutive response (i. e. stress-strain data) without the need for complex transformations or model fitting, and (2) the versatility of testing in terms of specimen di mensions and environmental conditions, for example, the submerging the specimen in fluids across a range of temperatures
Summary
Mechanical testing of miniature specimens to determine bulk prop erties has been pursued over the last 40 years to support material development in industries such as nuclear, power generation and aero space, with an emphasis on metallic materials. Test methods typically used to evaluate metals, for example small punch tests, have been applied to polymeric materials but the discs specimens lead to complex stress states that are challenging to relate to conventional tensile tests. Constraints of tensile and flexural microtesters and of mechanical analysers (e.g. dynamic and thermomechanical) include the requirements for specific specimen shapes, significant specimen gripping challenges, limited force and displacement range, and the need for specialised equipment accessories to test in different environmental conditions [2,3]. The main disadvantages of the punch approach come from the complex contact mechanics involving compression, tension and shear, and the complexity in transforming load-displacement data into stress-strain data to yield the bulk mechanical properties. The transformation can be carried out by an empirical approach, an analytical solution, or via an assumed constitutive model, there is limited applicability of the approach to all experimental datasets, and limited availability of corroborating data from standard tests for bulk properties to compare against
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