Airborne ultrasonics for nondestructive evaluation of leather quality

Our recent research has shown that besides Acoustic Emission (AE), Airborne Ultrasonics (AU) can also be applied for the nondestructive evaluation (NDE) of leather quality. Implementation of these methods in the manufacturing process could save a considerable amount of money, decrease the use of chemicals, reduce production time, increase the value of the leather and increase quality. Our previous paper reported a portable AE system for the evaluation of leather quality. This paper discusses the results of research carried out for nondestructive evaluation by AU. Our experiments showed that this novel technique reveals the presence of areas of different acoustic properties, which are an indication of local variations of the leather material properties. This system offers a great potential for testing entire hides in the manufacturing plant. Our research also showed that data can be gathered from different sections of the hide and along different directions with respect to the backbone. Observation also indicated these AU imaging techniques can reveal the presence of defects in the leather created by healed wounds, insect bites, knife cuts or any other physical discontinuity that could affect the leather quality. Scars, insect bites or major defects can be detected electronically, causing the hide or semi-product to be downgraded before it is subjected to any expensive leather making operations, thus saving money in processing time, chemicals, etc. AU testing showed some degree of correlation with the Nissan Shirley Stiffness data, but it is not as robust as AE with the rolling sensors. Selection of the right AU sensors is critical to achieve enough penetration in order to extract important information related to the properties of leather such as strength and softness. A better correlation between tensile strength and AU data could be achieved when AU tests are performed on a group of leather samples with the same manufacturing process and surface finish.