An Experimental Comparison of Standard Test Methods for the Determination of Tensile, Compressive and Flexural Properties of "Kevlar"

ABSTRACT: This paper is one of a series describing work aimed at comparing and eval-uating various standard methods for the mechanical testing of laminated composites. The work is based on test methods specified by the American Society of Testing and Materials (ASTM), the British Standards Institution (BSI) and the Composites Research Advisory Group (CRAG). Previous papers [1,2] describe the use of these methods for testing carbon fibre and glass fibre reinforced plastics composites respectively. The current paper describes the extension of the earlier work to cover "Kevlar " fibre reinforced plastics (KFRP). Tests were made in tension, compression and flexure modes; the standard tests used here evaluated the strength and stiffness of the laminates studied. It was found that although the recommendations of the standards by the three institutes are broadly similar a number of substantial differences arose in the results. 1. SPECIMEN PREPARATION HE &dquo;KEVLAR&dquo; FIBRE used was in the form of bi-directional woven fabric fromT DuPont (K-285) (Crowfoot satin style) impregnated with resin from Cyanamid (Cycom-919). Each ply thickness was 0.25 mm and the laminates were 8 plies (2 mm) thick. The material was laid up and cured in an autoclave to the manufacturer’s recommendations. Two lay-ups were used: 0/90 ° and 45 /- 45 °. In the present case specimens were cut using a high speed diamond impreg-nated circular saw with water cooling. Saws made specifically for &dquo;Kevlar&dquo; were used: these have a toothed rim with spaces between the teeth that allow clearance of debris. The specimens were finished by using fine emery paper when wet. Some compressive testpieces required a waisted centre section (e.g. the ASTM *To whom all correspondence should be addresse