Specimen strain and displacement measurements are important material testing activities. Specimen strain measurements are used especially in high-temperature tensile tests. They are essential when strain-controlled fatigue tests according to ASTM E606 are performed. Crack opening displacement (COD) tests detect crack growth with CT specimens.
It is important that the specimen strain or COD measuring sensor is attached to the specimen. Any distance from the specimen testing section will expose the measurement to the error caused by the loading device/specimen holder/specimen compliance.
Typically specimen strain or COD is measured using extensometers or "clips". Extensometers are very accurate transducers but they do not usually survive the operation environment. Extensometers can be used with high-temperature furnaces but in high pressure, the presence of liquids and aggressive chemical environment remains a challenge.
LVDT sensors, short for Linear Variable Differential Transformers, are highly accurate and versatile transducers used for linear displacement or strain measurements. These sensors convert mechanical displacements into proportional electrical signals, allowing precise measurement and monitoring of corrosion-induced material degradation. Cormet utilizes LVDT sensors in stress corrosion cracking (SCC) applications where the transducer is immersed in a corrosive environment and potentially too high temperature and pressure.
Cormet can provide LVDT transducers for ambient and high-temperature applications. Ambient environment LVDT sensors are used in SCC tests where the operation pressure is ambient, but the maximum operation temperature is about 80°C. Stainless steel sensors are used in high-temperature high-pressure applications. Cormet also has LVDT sensors manufactured of Hastelloy (Alloy C-276) for aggressive environments containing, for example, H2S and high chloride concentration.
To learn more about Cormet Oy's corrosion testing services and application of LVDT sensors, please visit the website or contact our knowledgeable team of experts.