Accurately and efficiently measuring deformation and material strain is essential to understanding material behavior. Even though they are the typical choice, strain gages and extensometers are limited to providing mechanical information at only a single point. Fortunately, a more effective alternative is available to ensure asset integrity: Digital Image Correlation, or DIC.
DIC provides non-contact full-field 3D deformation analysis. The DIC technology used by ADV Integrity is the ARAMIS Adjustable, which is a modular and expandable system. Currently, ADV Integrity’s DIC setup measures volumes of 50 x 38 [mm] (2” x 1.5”) to 350 x 260 [mm] (14 3/4” x 10 1/4”).
According to Emmanuel Valencia, Engineering Assistant at ADV Integrity trained in DIC, this technology is “just as good, if not better, than strain gages. It provides full-field data, which allows us to understand both the global and local behaviors of the parts we analyze. Therefore, during post processing, we can analyze any point of the patterned region without needing to retest. It is very powerful when calibrated correctly, and more efficient.” Because less retesting is required when using DIC, the technology has cost-saving implications as well.
DIC is not a new technology, but it is new to the oil and gas industry. Typically, it was used in vehicle and impact testing and in other laboratory environments.
Valencia said, “Although this technology is not unique to ADV, I believe we are in a unique place because we have DIC trained engineers with sub-scale and full-scale testing experience that can integrate DIC testing to our clients’ needs.”
The testing capabilities of DIC cameras include static and dynamic testing with motion compensation. It is especially useful for testing a bigger area without knowing where a sample may fail—a key advantage compared to extensometers or strain gages. Some examples of the tests that can be performed are tensile tests, shear tests, buckling tests, impact tests, and non-destructive testing (NDT). In addition, the DIC technology can do dynamic photogrammetry for point tracking and digital image correlation for optical strains. DIC technology can also validate numerical simulations with full-field data.
Despite this impressive range of capabilities, Valencia believes the applications of DIC technology can expand even further: “In the future, we will experiment using our DIC technology for pressure tests. The DIC camera can be calibrated for glass distortion in order to record a pressurized vessel through a transparent shield. Because the camera can be calibrated, it can account for any glass distortion from the shield.”
ADV Integrity’s current DIC setup is certified for volumes below 300 mm for displacement testing. This certification is the same used by the ISO 9513 Class 0.5 Extensometer and ASTM E83 Class B1 Extensometer.
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