Application of non-contact ultrasonic method in air to study fiber-cement corrugated boards

The fiber-cement and cellulose boards are materials commonly used in architectural engineering for exterior and interior applications such as building facades or as wall and roof covering materials. The aim of the study was to present the ultrasonic non-contact method of testing fiber-cement boards with Lamb waves and to discuss the results and limitations of the method in context of quality control of the material. The experiments were performed for the corrugated boards using a laboratory non-contact ultrasonic scanner. Lamb waves were generated in the tested materials by a transmitter excited by a chirp signal with a linearly modulated frequency. Waves transmitted through the tested material are acquired by the receiver and registered by the PC based acquisition system. The tests were done on reference plate board and the corrugated boards. As the main descriptor to assess the quality of tested boards the maximum amplitude of transmitted Lamb waves was selected. The significant role of boundary effects and frequency of waves was noticed. The obtained results have confirmed the usefulness of the applied ultrasonic method for testing macroscopic inhomogeneity of corrugated fiber-cement boards.