A New Cyclic Impact Test Instrument and Methodology for Hand-Struck Tools

The use of hand-struck tools is still a necessary job function for technicians in several industries throughout the world. Despite the importance of these tools, evolving concerns regarding the detrimental effects of their long-term use continue to grow. Repetitive motion injuries, nerve damage of the hands and arms, and hearing loss are some of the problems that continue to afflict users of these types of tools. Although hammer-tool systems are relatively simple mechanical systems that have required very little improvement historically, the growing concerns associated with their use necessitate a thorough evaluation of current tool designs. In addition, the introduction of new and modified tools with improved performance characteristics will be essential to maintaining their long term, effective use in the workplace. Currently, no standard test methods exist to assess the performance characteristics of hand-struck tools. This makes evaluations and comparisons very difficult since performance characteristics are significantly influenced by the user of the tool. As a result, for the purposes of assessing the performance of current hammer-tool systems as well as evaluating alternate designs, a new testing device for hand-struck tools was developed. The device is designed to simulate the approximate cyclic kinematic motion of a user repeatedly hitting a tool with a conventional hammer. A computer controller automates the striking and return stroke actions, and the resulting impact velocity and force exerted by the hammer are adjustable and approximate the performance of a human. For the purpose of development, the testing device was designed to accept steel hand-struck chisels. As configured, a chisel is placed in the device and used to shear a standard, replaceable work piece. The key output of this test is the number of impacts needed to fail the standard piece. Other features integrated into the device include a load cell under the work piece to capture the force exerted during a hammer impact, measurement of the hammer velocity at impact, noise measurements, and an automatic counter to record the number of hammer impacts required to fail the work piece. Preliminary tests with standard, conventional chisels indicate the device is capable of failing a standard 6.5 mm steel drill rod work piece in the same number of hammer blows as an experienced chisel user. Subsequent work will focus on characterizing and improving the properties of hammer-chisel systems relevant to the detrimental effects associated with their long term use.