Structural Integrity: emerging imaging technologies make a difference in detecting deformations and displacements

Technological advances in the area of ​​sensors, information technologies and image capture have been catapulting innovation in the area of ​​structural health monitoring (SHM), allowing the exploration of emerging technologies and development of new solutions for the management of the infrastructure life cycle.

Structures such as buildings, bridges, tunnels, railways, among many others, require periodic assessments of their structural health. To understand the behavior of a structure there are several techniques, but imaging methods that have stood out as the most innovative.

The term "health" encompasses the safety of the structure, durability, degree of deformation, and several other factors, in a set of essential information to validate new designs and structures, or to determine the maintenance, rehabilitation, or even replacement of aged structures.

The acquisition of parameters to support these decisions can take many forms, but there is one method in particular that has been gaining wide acceptance as one of the most promising technologies: Digital Image Correlation (DIC, Digital Image Correlation).

It is an image method for measuring, without contact, displacement fields and deformations in 2D and 3D on the component surface, based on the correlation of images acquired in different application states, namely before and after deformation.

It allows the simultaneous detection of longitudinal and transverse deformations with any load, such as traction, compression, flexion, torsion or a combination of different loads. In addition, it also allows the use of virtual strain gauges to carry out point-to-point measurements, ideal for applications in which the expected deformations are very high, as well as the measurement of very fast transient phenomena, as with high speed loading.

The advantages of this technology relate to the fact that it is a non-contact, full-field method that can measure deformations in and out of plane, with high resolution, while being relatively insensitive to environmental conditions.

The rapid development of information technologies and equipment for the storage and transmission of images, as well as the progressive decrease in the cost of this equipment, contributed to accelerate the development of this technology.

These factors make imaging methods even more attractive, as they enable the implementation of wireless image sensor networks, expanding the range of sensing capabilities in large areas and supporting the transmission of the resulting data securely to decision centers.

With a view to an even wider use, this technology continues to be the target of new developments, namely to overcome some inherent challenges, such as the need for calibration or the use of multiple scales.

This is also a challenge assumed by INEGI, which has been using and developing Digital Image Correlation technology in components whose dimensions vary between a few millimeters and several meters, in static and dynamic applications.

Among recent projects, the application of this technology in the study of the behavior of civil structures stands out. This work was carried out in collaboration with the Earthquake and Structural Engineering Laboratory of the Faculty of Engineering of the University of Porto, and demonstrated the clear superiority of this technique in relation to the traditional method using extensometry for monitoring large structures, in the context in question.

The easy application on large objects was also evidenced during the LighTRAIN project, which concerned the design and development of an innovative aluminum platform for passenger carriages. In comparison with conventional extensometry, the results obtained with Digital Image Correlation demonstrated a good correlation and provided important information for the design of the structure.

More recently, INEGI collaborated with Madeira Airport in monitoring deformations of the runway support beams, using once again Digital Image Correlation to monitor the deformations that occur during landing or other operations on the runway.