NONDESTRUCTIVE EVALUATION OF LEATHER BASED ON ACOUSTIC EMISSION

Authors: Liu, Cheng Kung; Latona, Nicholas - Nick

Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2003
Publication Date: 6/1/2004
Citation: Liu, C., Latona, N.P. 2004. Nondestructive evaluation of leather based on acoustic emission. Journal of American Leather Chemists Association. 99(6):251-257.

Interpretive Summary: Currently, the physical testing of leather is a destructive process, wherein cutouts are taken off the tannery floor for testing. This wastes a lot of leather, which otherwise could be sold for profit. In addition, currently, no in-line test method is available to monitor the physical properties of semi-products during the leather-making processes or finished products. With the right monitoring tool, inferior leather semi-products, such as wet blue, could be downgraded earlier or removed before going through many expensive leather-making processes. Therefore, we have begun the development of an in-line nondestructive tester for improving quality control. The tester measures acoustic emission (AE), ultrasonic sound emitted when leather is deformed. This investigation showed that the tear strength and softness of leather can be nondestructively measured by applying a rotational AE sensor over a leather sample. This research has demonstrated a nondestructive means to measure the quality of leather without breaking the leather. Based on the results of this investigation, we are collaborating with industry to design an automated in-line nondestructive AE tester to be applied in the manufacturing site. Production of an in-line AE instrument will provide the industry with a nondestructive way to monitor the quality of their product at each intermediate leather-making stage. Our objective is to strengthen the competitiveness of the U.S. hides and leather industries by encouraging cost-effective production while imparting better quality to the finished product.

Technical Abstract: The physical testing of leather is currently a destructive process, wherein cutouts are taken off the tannery floor for mechanical testing. These destructive tests are not only time-consuming, but also wasteful of leather. Therefore, there is great incentive to develop a nondestructive test that will drastically improve leather quality control. We recently examined the feasibility of using the acoustic emission (AE) technique to nondestructively measure the mechanical properties of leather, particularly tear strength and softness; both properties are critical for leather, especially for upholstery and automobile applications. In this investigation, a rotational acoustic sensor was contacted with the leather samples to collect their AE quantities and properties. Observations showed an excellent correlation between the tear strength of leather and the corresponding acoustic counts, read from an acoustic emission analyzer. Data also indicated a close relationship between the softness of leather and the corresponding ratio of acoustic hits to energy. The observed phenomena implied that the tear strength and softness of leather can be nondestructively determined by measuring the acoustic quantities with a rotational sensor crossing over the leather to be tested. The results of this research have become the framework in designing an in-line nondestructive evaluation method for leather quality.