According to NASA, the validity of a hammer test is not determined by its waveform. Instead, the accuracy of the measurements and the test's objectives are crucial. The test's force and response should be measured precisely, taking into account factors such as bandwidth and signal-to-noise ratio.
The shape of the force applied during the test can affect the results, but it does not necessarily invalidate them. NASA recommends evaluating the test's adequacy based on its purpose and the quality of the measurements. This includes verifying that the response measurements have sufficient bandwidth and signal-to-noise ratio.
The test's excitation should cover the required frequency, amplitude, and nonlinear-response ranges. A test should only be rejected or repeated if there is a identified measurement or excitation deficiency. NASA's research suggests that the appearance of a half-sine waveform is not a reliable indicator of a test's validity or adequacy.
NASA's findings are based on research by Joel W. Sills and others, as outlined in a recent publication. The research highlights the importance of accurate measurements and test objectives in determining the validity of a hammer test.