CRREL (Cold Regions Research and Engineering Laboratory) Hopkinson Bar Apparatus

摘要

Most materials at low temperatures change their modulus and tend to become brittle. When using these materials in structural components that are likely to be subjected to impact it is important to understand their behavior at low temperatures under dynamic loading. The CRREL split Hopkinson Test Bar was designed and set up to conduct compressive strain rate tests (up to 1000 strains/s, i.e., in./in. per s) at low temperatures (down to -100 C). The results provide dynamic stress strain relationships of materials at low temperatures by considering the transmission of the stress wave through a test specimen sandwiched between two elastic bars. The specimen is contained in a liquid nitrogen operated cooling environment. During the test an elastic striker impacts the bar; as a result a stress wave passes down the bar. At the specimen a part of the wave is reflected and the rest is transmitted to the second bar. Strain gauges mounted on the bars record the wave shapes, which are analyzed to obtain the dynamic stress-strain relationships. The test bars are 1-1/2 in. in diameter and each is 8 ft long. The apparatus is suitable for testing light metals, plastics, composites, rocks, ice, and frozen soil. The data acquisition and analysis system are completely automatic, using software developed at CRREL, so the system provides for a rapid and low-cost method for high strain rate behavior studies of materials.