Development and Validation of an NDT Based on Total Sound Signal Energy

Abstract
This study proposes a new nondestructive testing (NDT) method for assessing the compressive strength of various materials. The method is based on the total sound signal energy, which is determined using the sound signal generated from impacting an object. A device was devised to generate an impact sound with a test object using a rotating, freefalling impact ball and subsequent repetitive impacts from the rebound action. First, to validate the method, soil cement, cement paste, pine wood, shale, and granite specimens were tested to examine the correlation between the direct compressive strength and the total sound signal energy. Next, the method was applied to a number of concrete test specimens with various sizes and strengths. The test results of the concrete specimens showed a direct relationship between the direct compressive strength and the total sound signal energy, which was dependent on the size of the specimen. Correlation equations between the total sound signal energy and the direct compressive strength were determined for different specimen sizes through regression analysis. The equations were then used to estimate the concrete compressive strength and validate the method. Statistical analysis indicated that the estimated compressive strength determined by the total sound signal energy quite reliably agreed with the directly measured compressive strength, regardless of the specimen size. It is expected that the new NDT method will play a meaningful role in nondestructively estimating the compressive strength of various materials in the future, including concrete.