The technologies, developed over the course of the last decade, have been used to test and characterize structural composite materials, electronics materials, shape memory alloys, and additively manufactured components.
“This suite of technologies has been a game changer in the Navy, enabling accurate material characterization and structural health monitoring for various material systems with an accuracy never before possible with conventional methods,” said Dr. John Michopoulos, head, CMSL, and co-inventor of the technology. “The new strain imaging and measurement technologies are proven to be extremely sensitive, accurate, and computationally efficient when compared to other commonly used methods, granting very high performance capabilities in deformation metrology and structural health monitoring.”
The process enables the non-contact detailed measurement of the strain and displacement states of relevant materials in a manner that is spatially and temporally resolved with high accuracy. This is necessary for mechanical testing, characterizing their constitutive behavior and for monitoring their structural integrity among many other applications.
Since the 1980s, experimental mechanics researchers have used digital imaging methods to measure deformation on an object under mechanical or generalized loading. Digital imaging has become more prominent the last two decades, providing a more cost effective and highly reliable tool for recording and processing images of an experiment using a computational infrastructure that extends from very thin embedded computers up to laptop and desktop sized computers.
CMSL has built upon this body of research focusing on ways to achieve high sensitivity, accuracy, computational efficiency and robustness beyond what traditional techniques provide. CMSL’s work led to three distinct patents: the software implementation of the 2-D Meshless Random Grid (MRG) method; the development of the 3-D MRG method; and the development of the Direct Strain Imaging (DSI) method. Each employs a system comprising of digital cameras, processing hardware, and software algorithms that process captured images and calculate components of the displacement vector and strain tensor either on discrete locations or on full field areas.
To use the MRG and DSI methods, distinct marks are applied randomly to the surface of an object; a camera or a pair of them (if 3-D is required) is then used to capture images before and after force or displacement has been applied. The software then identifies the centroids of the marks and measures the relative distance between any pair of them as they have moved during deformation relative to their initial position. This enables the calculation of the precise displacement vector and strain tensor components.
“The MRG and in a greater degree the DSI methods are more sensitive, more accurate, and faster than other digital imaging techniques such as Digital Image Correlation,” said Dr. Athanasios Iliopoulos, co-inventor, and mechanical engineer, CMSL. “The great advantage of our tools is how easy they make it to measure strain, using simply a marker technique to apply dots along with a camera and a software suite that provides three-dimensional, full field strain measurements in real time.”
After sampling, the MRG and DSI processes use a mesh free approximation computational algorithm to represent the displacement and strain components at every point in the material, thus enabling measuring strain accurately regardless of an object’s irregular shape or imperfections, including holes and notches. In addition, the DSI method applies the mesh-free approximation directly on the strain tensor field components thus avoiding the numerical error amplification due to differentiation of the displacement fields. It also does not require the observance of the continuum hypothesis and is therefore applicable for structures containing discontinuities such as flaws and cracks.
Point Semantics Corporation, CEO and licensee, Christopher Vizas, says he is looking forward to developing MRG and DSI so they may be integrated into products and services for various industrial applications, adding, “While obviously the laboratory and test communities want to get their hands on it, we believe that many industrial customers that employ heavy machinery or build major infrastructure will be interested as well.” Vizas says that increasingly, companies want to replace visual inspection and labor-intensive structural health monitoring with automated, low maintenance solutions. “By measuring strain, and strain over time, users will be able to determine various critical physical quantities associated with operational conditions such as damage, fatigue, creep, etc, that industry wants to know about their equipment and structures.”
Inventors of all licensed patents are John G. Michopoulos and Athanasios Iliopoulos, credited previously, and for the two MRG patents, Emeritus Prof. Nikos P. Andrianopoulos of the National Technical University of Athens.