Mechanical Testing With Optical fiber Sensors

Applications > Mechanical Testing

Mechanical Testing

In many industries, mechanical designers, materials engineers and structural engineers use finite element analysis (FEA) models to help them improve the performance/weight and performance/cost ratios of their products. Validation of these FEA models by mechanically testing both material coupons and sample components is a fundamental requirement, and numerous materials test houses are established to provide this valuable service.

Concrete rebar with embedded Bragg gratings under test

Cyclic mechanical testing (often combined with variations in other service parameters) provides a useful accelerated life model and can help predict fatigue and failure modes. Typically, such mechanical testing would involve applying tension and compression to a unit under test, perhaps with the unit instrumented with electrical strain gauges to monitor stresses induced at key locations. Due to their miniature dimensions (recorded in optical fiber of less than 150 micron diameter, the sensor itself can be less than 1mm long) a Bragg grating sensor array allows the test engineers to instrument even the smallest unit under test at a density that was not previously practical.

Instrumented cable stay tension testing

Also, with many, many sensors on a few fibers attached to a single multiplexing instrument, highly instrumenting a test specimen is now relatively simple and inexpensive with optical fiber sensors.

Furthermore optical fiber sensors are compatible with internal embedment in all manner of structural materials including glass or carbon reinforced plastics, concretes and even certain metals. This unique capability provides for the monitoring of internal changes that were previously impossible to detect.

Space telescope component instrumented prior to cryogenic load tests.

Another benefit of optical fiber sensors worthy of note is their exceptional survivability under the most extreme of conditions. Unlike electrical equivalents, optical sensors are immune to electromagnetic radiation and most chemicals. Their totally passive operation makes them intrinsically safe, and their relative intolerance to extremes of temperature allows them to provide accurate data from high temperatures down to cryogenic levels.

These numerous benefits that FBG sensors offer over conventional measurement techniques opens up a new avenue of possibilities for designers and researchers to benefit from instrumentation in locations and in applications where it had to date been impossible.