A deflectometer is a device used to measure how much a given object or material displaces when it is subjected to a load. Such devices are used in materials testing, forensic evaluation of failed materials for legal purposes, and routine evaluation of materials during construction and development to make sure they are safe. They come in a variety of sizes and styles for different applications, ranging from devices intended for use in the lab to deflectometers used in the field.
Deflection is a measurement of how a material responds to a load. A high rate of deflection indicates the material is significantly displaced. It may bend, warp, or otherwise shift in response to the pressure. Lower rates indicate more stiffness. Different levels of stiffness are required for varying applications. If a material is too stiff, it can be brittle and may break when it is overloaded. Overly flexible materials can deform so much that their structural integrity is compromised.
Roads and tarmacs at airports are commonly studied with a deflectometer to see how much they will deform during regular use. Impact simulating the weight of tires with different loads, from a lightweight car to a jumbo jet, is used to measure deflection in different settings. If the material is too stiff or not stiff enough, it may need to be reinforced or replaced for safety.
Deflectometer testing can be used in a routine assessment of a material to make sure it is functioning as intended and to check for signs of weakness. It can also be used if there is a specific concern about a material, such as reports from personnel who work around it that it appears to be cracking or bending under pressure. In forensic evaluations, materials that failed will be subjected to a range of tests to learn more about why they failed and to determine if they were appropriate for the setting. If a deflectometer reveals, for example, that beams were too stiff, the manufacturer can be held liable for failing to install appropriate structural supports.
Sensitivity levels vary with a deflectometer. Some are extremely sensitive and can detect minute fluctuations. Others have more limited capabilities. In all cases, calibration before use is important to make sure the device is working properly, as otherwise it may return false results. This could potentially be dangerous if the device is being used to measure materials for quality assessments.
By Mary McMahon
Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a About Mechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.