Dynamic Tensile Properties of Dyneema HB-50 Composite at High Strain Rates Using Split Hopkinson Tension Bar

Abstract

Tests to determine properties of materials under static loading conditions are well known for several years but fifty years back, it was not same for the cases where loads were applied at high strain rate. Afterward, in 1950s and 1960s, individuals began studying the high loading rate mechanical properties. This interest was due to the increased military and aerospace applications. Military applications related to protection against high-velocity projectiles, whereas the aerospace industry had an interest in protecting air vehicles from meteorite and bird impact.

Under static loading conditions, material properties were determined by either simple screw type universal testing
machines or more sophisticated servo-hydraulic test systems. The maximum strain rate for these type of machines was up to 0.1 s^-1 [1]. It necessitated development of test systems such as Charpy impact tester or drop weight impact test systems were capable of testing strain rates up to 100 ^s-1. However, complete characterization of dynamic behaviour was not possible from these systems.

Materials undergo high strain rate deformation in many applications. These may be an explosion, attack, accident or tests for the safety of vehicles. Additionally, manufacturing a product by extrusion, rolling and high-speed machining also results in deformation at high strain rate (HSR). Material behaviour under high strain rate is of utmost importance for safety and design. [2]. The most reliable and effective methodology is to test the material characteristics using Split Hopkinson Pressure Bar (SHPB). The tests are conducted at high strain rates up to 10² s^-1 to 10⁴ s^-1 [3-8]. The next criteria is impact behaviour for which dynamic response and energy absorption capacity of Dyneema HB-50 is also tested. In this paper dynamic response and failure behavior of Dyneema HB-50 composite has been evaluated under high strain rate conditions. Experiments were undertaken on Split Hopkinson tension bar at strain rate of 1680s^-1, 2200^s-1 and 2603^s-1.
Failure behaviour of the Dyneema HB-50 composite were obtained at HSR conditions. Results were analysed for stress, stain and strain rate. Microscopy (SEM) was conducted to ascertain and analyze the failure behaviour of the material.