The results are then compared to an undamaged reference sample to show defects. Holographic testing uses a laser to detect changes in the surface of the material which has been subjected to stress such as heat, pressure or vibration. Laser testing falls into three categories including holographic testing, laser profilometry and laser shearography. The waves are reflected or refracted when they encounter a buried object or material boundary with different electromagnetic properties. ![]() This geophysical NDT method sends radar pulses through the surface of a material or subsurface structure, such as rock, ice, water or soil. There are three types of electromagnetic testing, including eddy current testing, alternating current field measurement (ACFM) and remote field testing (RFT).Įddy current testing uses an alternating current coil to induce an electromagnetic field into the test piece, alternating current field measurement and remote field testing both use a probe to introduce a magnetic field, with RFT generally used to test pipes. This testing method uses an electric current or magnetic field which is passed through a conductive part. Leaks and active corrosion are detectable AE sources too. Frequently a method for use during proof tests of a pressure vessel, AE testing is also a continuous Structural Health Monitoring (SHM) method, for example on bridges. ![]() It is even possible to detect AE from plasticisation in highly stressed areas before a crack forms. Sensors dispersed over the surface the structure detect the AE. This is a passive NDT technique, which relies on detecting the short bursts of ultrasound emitted by active cracks under a load. ![]()
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