The American Society of Non-destructive Testing (ASNT) defines non-destructive testing as “the determination of the physical condition of an object without affecting that object’s ability to fulfill its intended function. Non-destructive testing techniques typically use a probing energy form to determine material properties or to indicate the presence of material discontinuities (surface, internal or concealed).”
Non-destructive testing is an integral part of structural and material testing as it allows for the detection of physical properties, including internal anomalies, which cannot be observed with the human eye. The techniques of non-destructive testing are mainly used to measure non-uniformity in a material. This is extremely important as a deformity may affect the material’s ability to withstand loading.
Destructive tests are often done on a separate material sample and can test for impact resistance, flexibility, yield, UTS, and structure toughness. While traditional techniques may damage the building material, NDT’s allow assessors and engineers to complete assessments for internal flaws or metallurgical conditions; examining the suitability of the material for the application it will be used in, while limiting the reduction of future usability.
The methods and therefore the sensors that can be used for non-destructive testing are numerous. These sensor systems include the use of eddy current, ultrasonic, induction, corrosion-detection, and EMAT.
The most popular non-destructive material tests are acoustic emission testing, interferometry, leak testing, magnetic particle testing, thermal/infrared testing, radiographic testing, tomography, guided wave testing, neutron radiographic testing, and vibration analysis. The sensors used in these tests collect data about the material in a way that can be read and understand by the users. The testers may then begin to remedy any failures in the material before they affect the serviceability of the material.
While these tests are mainly used in the construction industry, it should be noted that many areas of engineering use them too; including automotive manufacture and aviation, in which the sensors can discover defects in landing gear and other airplane components. In most cases, the detection system can reveal cracks and physical imperfections early, before a structure or product can fail.
Ultrasonic and eddy current testing use a silicon pressure sensor and accelerometer. One of the most common and necessary tests in structural engineering is a precision thickness in metal to metal bonding, such as welding. The three probes used to do this are pitch-catch probes, mechanical impedance analysis probes, and resonance probes. The joints in structures are one of the most likely areas to fail, and therefore it is essential to be able to test them after application.
In certain situations, more specialized non-destructive tests are needed. These are not usually required in the building and construction industry. However, the specialized non-destructive tests include magnetic particle inspection, which uses fluorescent coated iron oxide particles suspended in a liquid. This is then sprayed onto the material and magnetized. When the test sample is subjected to ultraviolet light, the magnetic field is shown.
No matter where non-destructive testing is used, the sensors allow an assessor to ensure the quality of materials and the safety of the products in which they are used.