MSU Technologies

High Strain Rate Tensile Testing Apparatus

Executive Summary

Characterizing the material response of thermoplastic polymers at intermediate strain rates (1s^-1 to ≤ 200s^-1), commonly encountered in automotive collisions and crashes, is critical for predicting their failure strength and post-impact behavior. However, investigative experimental techniques required to generate tensile stress-strain data at these loading rates are not well established. Researchers at Michigan State University have recently developed a new apparatus for testing materials at intermediate strain rates. The apparatus can deliver reliable tensile stress-strain data, particularly for soft thermoplastic polymers that undergo large deformations before yield and failure.

Description of the Technology

The technology is based on a double-acting drop weight impact apparatus with load cells, whereby vertical impact force is bifurcated into equal horizontal forces on both ends. A laser detection system with a high-speed camera, data acquisition system, and digital image correlation is used to obtain strain information. The system has been tested on various plastic and composite materials and validated with Aluminum Alloy 6061-T6 data reported in the literature corresponding to two unique strain rates.

Benefits

Allows quasi-homogenous stress and strain fields (dynamic equilibrium) along the sample gage length
Flexibility of changing the impact force simply by changing the height of impact or adding weights to the carriage
Eliminates the possibility of mode-I failure of the test sample; failure is purely tensile
Provides a smooth load response without further data filtration
Minimal preload on the sample
Intertial correction can be applied
Samples of different sizes and geometries can be tested