DOTNAC project

    Applus+, in collaboration with several companies and institutions, is involved in this European project aimed at developing and optimizing nondestructive testing techniques for composite materials using Terahertz (THz) techniques

    This project is called DOTNAC.

    What is DOTNAC?

    Currently, very little research is carried out using THz radiation for NDT in the Air Space Industry, and very little is known about how the typical defects of composite materials, such as delamination, pores and inclusions, can be detected by THz waves.

    Due to the rapid increase in the use of composites, especially in critical parts, at any industry, whether civil or military, that manufactures and/or maintains these types of structures, can benefit from this system, both in terms of cost savings and regarding the integrity of the parts.

    Composite materials containing aramid fibers, glass fibers, carbon fibers, polyurethane foam, etc., that are used in specific structures, such as honeycomb and multi-layered structures, are known for their high strength/weight ratio. And it has also been discovered that they are useful as structural components in applications for demanding work conditions, such as aircraft. The problem arises because, despite these advantages, they have vulnerabilities that are most exposed during the manufacture and maintenance phases. For example, during manufacture, problems may arise during the stage in which the layers are formed, when Foreign Object Damage (FOD) may be caused by metal, plastic and reinforcement materials and/or other traces related to the manufacture can become embedded within the layers of the uncured composite material.

    These and other defects decrease the integrity of the bond between layers and the total resistance of the composite components, resulting in high rejection rates. To meet the high standards required for the construction and repair of composite materials, new nondestructive testing techniques are required to improve the effectiveness of the inspection. To meet this need, a new noninvasive and contactless inspection system is being created to assess the integrity of these materials.

    Over recent years, there has been great interest in the potential for detection using terahertz (THz) to detect images of hidden weapons, explosives, and chemical and biological agents. There are two important factors contributing to this interest: (1) THz radiation is readily transmitted through most non-metallic and non-polarized mediums, thereby allowing THz systems to make materials "transparent", (2) THz radiation is non-ionizing and poses no health risks for the system's operator. Taking advantage of these unique radiation properties, THz imaging can be used for Non Destructive Testing (NDT). FOD and other defects, such as delaminations, voids and thermal damage can be identified in a variety of pre-cured and in-service composite structures.

    Project Goals

    The main goal of the DOTNAC project is to create a fast, high resolution, non-invasive and contactless inspection system to evaluate aircraft composite parts, either during production or during maintenance. The NDT tool being developed will be easily integrated into industrial facilities and will fill the performance gaps that are still present in existing NDT techniques. Therefore, it will be an extremely useful tool in NDT in terms of sensor fusion. This new method will not directly replace existing NDT techniques, but will provide supplementary results that in certain cases may be more accurate for some defects.

    Achieving this involves the following specific goals:

    • Create an integrated (hardware-software) THz imaging system using pulsed signals/optical fiber.
    • Create an integrated (hardware-software) THz imaging system by using signals from continuous waves/electrical cables.
    • Prove, in an industrial setting, the effectiveness of a NDT tool based on THz.
    • Evaluate the performance of the 2 NDT THz tools created to evaluate parts.

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