Dynamic Tensile Testing of Kevlar 49 Fabrics

Measurement of deformation history during a high-speed mechanical test plays an important role in establishing the dynamic behavior of materials. Traditional strain measuring techniques such as extensometers and strain gauges have limitations such as frequency response and range of strain. Kevlar 49 fabrics were tested in tension within a strain-rate range of 25 to 170 s-1 using a high-speed servohydraulic testing system. Results show that the dynamic material properties in terms of Young’s modulus, tensile strength, maximum strain, and toughness increase with increasing strain rate. The woven nature of Kevlar 49 fabric results in large displacements and shape changes during tests. Noncontacting strain measuring technique is therefore highly preferred. A technique was developed using image analysis to obtain the deformation of Kevlar 49 fabrics at the tested strain rates. Using image analysis results, the stress-strain curves of Kevlar 49 fabrics at different strain rates were constructed and compared with those based on stroke measurement. Good agreement was obtained between these two methods.