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Title: New Acoustic Methods for Nondestructive Evaluation of Leather Quality

item Liu, Cheng Kung
item Latona, Nicholas - Nick

Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2007
Publication Date: 3/1/2008
Citation: Liu, C., Godinez-Azcuaga, V.F., Latona, N.P., Hanson, M., Finlayson, R.D. 2008. New Acoustic Methods for Nondestructive Evaluation of Leather Quality. Journal of American Leather Chemists Association. 103(3):89-127.

Interpretive Summary: Current testing methods for quality control and quality assurance of leather are time-consuming and often subjective, depending on the operator and the test being performed. Samples must be cut out and destructively tested, which consumes some of the profit since leather is sold by the square foot. Therefore there is a great incentive to develop a nondestructive test that will save time and materials as well as be less subjective than some of the current test methods. Under a cooperative research and development agreement, we recently investigated the feasibility of using the acoustic emission technique to dynamically and nondestructively measure the mechanical properties of leather. The developed tester measures acoustic emission (AE), ultrasonic sound waves emitted by the leather when it is deformed. This investigation showed an excellent correlation between the softness of leather and certain acoustic activities and it also correlated with a standard softness testing method. Data also indicated a close relationship between the maximum strength and the intensity of an AE signal measured from testing. Based on the results of this investigation, we are developing an automated on-line nondestructive AE tester to be applied in the manufacturing site and provide the industry with a nondestructive way to monitor the quality of their products. Therefore poor quality leather will be detected earlier and possibly reprocessed before it is carried all the way through the expensive tanning process. The findings should 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: Currently, there is no on-line test method to monitor the physical properties of semi-products such as wet blue or crust during the leather-making processes. Inferior leather semi-products, such as wet blue, cannot be downgraded earlier or removed before going through many expensive processes (including retanning, fatliquoring, dyeing, drying, staking, milling and finishing). Therefore, developing a nondestructive tester to perform on-line testing of the physical properties of semi-products is very desirable. Recently ARS transferred its knowledge gained over the years to Physical Acoustics Corporation (PAC) and collaborated with the leather industry in order to produce an on-line nondestructive acoustic emission tester. This paper discusses the activities performed by PAC, ARS, and Seton Company during the Small Business Innovative Research (SBIR) Phase I project “Acoustic Emission for the Characterization of Leather.” The main objective of this project was to demonstrate the feasibility of using AE and Airborne UT to assess, characterize, and classify the quality level of various types of leather. The results obtained in this project show that it is feasible to use AE for the evaluation of leather quality during the manufacturing process. A newly designed AE system for the evaluation of leather quality is discussed in this paper. This system, which combines a handheld AE instrument with a rolling sensor probe, offers the potential for testing entire hides in the manufacturing plant. Data could be gathered from different sections of the hide, along different directions with respect to the backbone, and during different stages in the manufacturing process. Finally, we reported a simple method using a mechanical stopwatch as an acoustic wave source. Hits rate were collected when sound traveled though the leather samples. Results show a strong correlation between tensile strength and cumulative hits.