Guided Waves for Damage Monitoring in Plates for Notch and Corrosion Defects

Abstract

Non destructive testing techniques are the preferred techniques in this new era of development and progress. Also healthy monitoring of different mechanical and civil structures during its service is very important for the safety of human beings. Health monitoring of these structures using ultrasonic technique is an emerging field. It uses high frequency sound waves into the material to detect and locate defects, discontinuities in the material. This report presents the use of pulse echo technique of ultrasonic to detect, locate and quantify magnitude of defects such as notch, corrosion and correlate tensile stress with ultrasonic voltage by doing destructive tensile test. In this whole study testing of mild steel plates was done in by pulse echo mode. The exact location of the defect and its change in magnitude as the percentage of defect increases was determined using this technique. Negative spike pulse is used as an input signal for sending and receiving signals through pulser/receiver system. The transducers were held in direct contact with the plate through a coupling medium (ultrasonic gel). The wave signatures obtained are analysed using digitizer card. The parametric study for notch defect was carried out by increasing the depth of notch and taking signatures at each stage. In case of corrosion study testing of plate was done after corroding plate by impressed current corrosion and signatures were taken at different stages of corrosion. For correlation of ultrasonic with tensile stress, both ultrasonic testing and destructive tensile testing was done for different specimens having different percentage of defect and a generalized trend was obtained. Final results obtained were reported in the form of voltage-time curves. For different damage types, most ideal modes and frequencies were selected for testing.