Elastic Wave
Non-destructive testing relies on transient elastic waves generated by the rapid release of localized energy within a substrate under mechanical or thermal stress. Microscopic deformations such as micro-cracking in paperboard or fiber breakage in composite structures create these waves, which are known as acoustic emission. The resulting stress waves propagate through the medium to the boundary of the material.
Detection Mechanism
Sensor arrays mounted on the surface of the specimen capture the arriving displacement oscillations and translate them into electrical signals. These instruments often employ ceramic elements that convert mechanical strain into voltage. The resulting high-frequency signals require filtration to remove background noise from surrounding machinery.
Very low amplitude signals must be boosted immediately by a preamplifier to prevent loss of information during transmission to the main processor. This amplification stage must occur as close to the transducer as possible to minimize electrical interference from neighboring power lines or motors.
Industrial Application
Manufacturing lines use this method to detect structural failures during high-speed folding or stamping operations. In the paper converting industry, acoustic emission monitoring identifies microscopic fiber damage before a complete web break occurs. Operators adjust the tension profiles based on the detected wave frequency and amplitude.
Web breaks decrease when tension is controlled dynamically.
