Case 74: How to determine impact forces when troubleshooting

摘要

When troubleshooting failures, it is not unusual for the metallurgical report to indicate that the failure was the result of an impact type of force. The investigator who receives this information must then determine the source of the force and its magnitude. Only then can the investigator calculate the stresses or deflections that caused the failure and what corrective actions should be taken. Determining the magnitude of these type forces is not a simple task. However, for preliminary troubleshooting purposes, approximations are useful. When Brinell-type imprints are made in metals, by the impact, these can sometimes be used to estimate the force.1 Most of the time, the only data available is the velocity, V (in./sec) of the impacting object, its mass, m (lb-sec~2/in.), and the time interval of impact, At (sec). An example of this situation would be a bat hitting a pitched baseball and the resulting force on the bat and ball. The impact contact time would be available from high-speed videos as would the relative velocities of the ball before and after impact.