Intensive characterization of fatigue properties of materials is a key feature for industries with high-end safety rules and regulation, like for aerospace or nuclear industries.
Moreover, relevant information and prediction which could be extracted from data analysis of huge database needs numerous characterization, reliable and reproducible testing conditions, and detailed description of specimen and/or component tested (mechanical properties, manufacturing route, residual stresses, microstructure and treatment ,…).
If manual testing is today the most common way of mechanical testing of materials, massive characterization linked to quality control or new material development required the use of automatic system, which give access to high specimen throughput, high repeatability and reproducibility of testing conditions, which is a key for relevant and valuable data.
If most of high cycle fatigue test are performed today without any extensometers, some important material properties require the use of local displacement and/or strain measurement like the low cycle fatigue test, the fatigue crack propagation rate, the fracture toughness.
For such characterization, the use of contacting extensometer, sometime imposed by existing standard (because the only reliable technology existing at that time), prevent/complexify the use of automatic characterization, may induce damage when attached to specimen, or may prevent / generate complex solution to characterize thin specimen.
Non-contact extensometer is use for mechanical characterization of material since years. If most of the technology need markings of specimen with stickers or sprayed pattern, some solutions use physical interaction of monochromatic light with the surface of material to generate natural pattern without any marking. However, the use of extensometer dedicated to static test could not be used for fatigue testing, because of sampling frequency and/or data transfer and treatment.
After a brief description of the real time technology mandatory for dynamic non-contact extensometers, this paper gives numerous example of the comparison between contacting/non-contacting extensometers in fatigue of materials, opening new doors for material characterization.