Making the strain

Servohydraulic testers do more than conventional high-strainrate materials testers. Instron VHS8800 servohydraulic high-strain rate testers log data from up to four transducer channels at sampling rates to 5 MHz. Instron's Fastjaw grip improves upon conventional lost-motion grips for highstrain-rate tensile tests. Special Profiler software, combined with Instron's FastTrack 8800 digital controls, gives constant velocity following load impact. This can reduce velocity drop-off during this critical loading period by a factor of three or more. Structures or components subjected to quickly applied loads see proportionately high rates of strain. But the mechanism by which many materials deform is different at high strain rates than at lower rates. Consequently, quasistatic stress-strain test data may not accurately predict behavior at high strain rates. In fact, the use of such data in the building of dynamically loaded structures can lead to cautious, overweight designs or premature structural failures. Conversely, more optimal designs are possible when they are based on loading and strain rates that better reflect actual operation conditions. High strain rates are generated in the