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  • Periodic Reporting for period 1 - CompInnova (An Advanced Methodology for the Inspection and Quantification of Damage on Aerospace Composites and Metals using an Innovative Approach)

CompInnova Report Summary

Project ID: 665238
Funded under: H2020-EU.1.2.1.

Periodic Reporting for period 1 - CompInnova (An Advanced Methodology for the Inspection and Quantification of Damage on Aerospace Composites and Metals using an Innovative Approach)

Reporting period: 2015-09-01 to 2016-08-31

Summary of the context and overall objectives of the project

Aerospace industries are obliged, by the European Aviation Safety Agency (EASA) and Federal Administration Aviation (FAA), to inspect all aircraft components for possible defects/flaws, before and during their service life. In most of the cases a reliable and efficient Non Destructive Testing (NDT) techniques are applied. Aircraft maintenance costs usually represent approx. 20% of the overall operating costs, while often inefficient and ineffective inspection procedures reduce the ability to plan and schedule labour productivity by 50% or more. The undetected flaws due to inefficient inspection or improper repair may lead to its catastrophic failure and eventually to life and aircraft loss. Consequently, there is a huge industrial and scientific interest for reducing the time and cost for aircraft infrastructure maintenance, providing in parallel as much as possible efficient and reliable damage inspection and proper repair.

For the identified need of improving the existing aircraft maintenance policies, the main motivation of the CompInnova project is to develop a revolutionary automated multipurpose and multifunctional aircraft inspection Vortex robot. The robot will carry for the first time in worldwide terms the ultrasonic Phased Array (PA) and Infrared Thermography (IRT) equipment for inspecting metallic and composite aircraft structures respectively, as well as a novel surface material removal and repair system for the inspected damaged aircraft components. The main aim of this achievement is to drastically improve the quality of maintenance procedures and thus significantly reduce its time and cost. The CompInnova aims include also improving in quality and productivity of the maintenance procedures, and providing a relative decrease in direct and indirect costs by strongly reducing direct costs and weight.

The ultimate objective of the CompInnova project is to deliver a novel automated prompt for NDT approach capable for the first time to detect, evaluate and repair damages on either metallic or composite aircraft components. Within, the project will develop a novel and adequate PA technique for complex surfaces (e.g. wing) inspection, provide two novel approaches for assessing damage in composite and metalic materials, develop innovative image recognition methodology capable of fusing the PA and IRT imaging subsystems and providing a reliable and automatic detection of different types of defects in metal and composites and depth assessment of the recognized defects, for the first time, address the problem of bonding composite patch repair of ageing aluminum, as well as composite aero-structures, and develop a high precision spatial positioning system, capable of tracking the position of a PA ultrasonic and IRT sensors relative to the component under inspection.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the first year, the consortium has established the specifications and requirements of the projects and performed a detailed literature reviews on the mechanical behaviour of metallic and composite materials for aircraft structural parts, as well as Non-Destructive Testing approached on the aircraft structures. The mechanical and physical properties of such materials were recorded along with their merits and possible limitations. The review included description of typical defects created in the materials during service time and analysis of their origin or causes of initiation. The literature review also explored the applications of the Phase Array (PA) in aircraft maintenance and challenges in automation of Ultrasonic Testing (UT) and Phase Array. The NDT methods available and capable of aiding the damage tolerance stage for any integrated inspection procedure were outlined while the characteristics and capabilities of methods in relation with different materials used for the construction of aircraft components were identified.

We have developed an entirely novel IR thermography approach based on the combination of pulsed phase (PPT) and lockin (LT) IR thermography techniques, after identifying that none of the existing techniques can individually perform on-line damage assessment using the Vortex robot. The new IR approach enables fast (about 60 sec) inspection and detection of size, type and depth of defects both qualitatively and quantitatively. In addition, a portable Phased Array hardware suitable for in-service inspection has been designed and purchased. The PA transducer performance is being investigated through laboratory trials with different damages in calibration samples. A PA methodology was proposed for in-service inspection of aircrafts; first the PA transducer was designed based on empirical rules, manufacturing and economic considerations. Then the designed PA transducer is modelled using FE simulation. This is followed by PA calibration studies on metallic specimens and mock specimens. The FE model facilitates the implementation of ultrasonic wave propagation and interaction with defects and select the optimum transducer frequency and number of elements in the PA transducer.

Moreover, algorithms to process the acquired data based on Signal processing techniques using higher order techniques for non-stationary ultrasound signals by employing the Spectral Co-variance technology are developed. Traditionally, the covariance is estimated in time domain, here however, the covariance is proposed to be estimated in the frequency domain. The advantage of estimating the proposed covariance in the frequency domain instead of the time domain is that localization of the frequency components of interest (e.g. resonance harmonics, etc.) could be performed. Additionally, during phased array FE modelling, Python scripts have been generated for successive model generation, execution and data extraction along with specific programs for transmit and receive beam forming and focal laws. Simulation study revealed that larger number of elements in the transducer increases the area of inspection. Simulation study has concluded that both 5 MHz and 7.5 MHz transducer with focusing during inspection show detection and sizing of side drilled hole (SDH) with an acceptable 0.1mm error. From the simulation results and practical considerations such as the size of the PA transducer and attenuation being larger at higher frequencies, we have chosen 5 MHz 64 element transducer for general inspection of composite and metallic aircraft structures.

Another focus of the project was oriented in the development of an online storage database able to collect and store a vast amount of PA and IRT data in real time. Additionally, defect detection and sizing characterization algorithms able to feed the Damage Tolerance modelling analysis with the required data from both inspection systems have been developed. MySQL database management system was selected as the most suitable open source software. Golden Sample and Threshold Value are the preferable effective image processing techniques for both inspection systems capable to provide an automatic detection of different types of defects (in metal and composite materials), sizing assessment and characterization. The integration of all the developed algorithms into one Graphical User Interface environment has been occurred. The combination of both PA and IRT imaging subsystems, providing a reliable and automatic process, will be examined and developed during the lab trials.

The consortium spent an amount of time of the development of a prototype for automatic laser-based material cutting/grinding of composites targeted as a pre-cursor for testing and demonstration of the repair module(s) to be incorporated on the Vortex Robot. A suitable laser was identified after a thorough review in of available lasers, and the state of art in of repairs with using lasers. The laser selected is a lightweight green laser, which can be used on both metals for surface pre-treatment and composites for material removal. As the weight is a challenging restriction of the material removal module, because it results in the weight reduction of the Vortex robot, emphasis was given to the replacement of the galvo-scanner for the laser beam delivery with the stepper motors in a way that the laser is moving over the predefined area and the laser beam acts exactly where material has to be removed. In order to start with first material removal trials on composites, a prototype was built at the premises of UoP comprising of a XY movement stage, the laser head as well as in house developed software for the communication of the stage with the laser head. That gave the ability of successful initial trials on composite material plates by programming the material removal area with pre-specified laser parameters and resulting in the automation of the material removal procedure.

In terms of Vortex robot development, the main tasks first included the conceptualization of the Vortex Robot Platform (VRP), whose main purpose will be the successful attachment and motion onto the target surfaces, via the novel combination of different actuation methods, while possessing the design characteristics for the incorporation of the NDT inspection and repair equipment. Specifically, a review of the state of the art in wall-climbing robotics was initially performed, which gave a solid understanding of the adhesion strategies and locomotion mechanisms used in existing wall-climbing robotic approaches. Moreover, a conceptual outline of the design specifications was presented, regarding mass and dimension restrictions, as well as modular properties and safety measures, which were deemed crucial to the implementation and the successful operation of this innovative and challenging method for NDT inspection and repair.

For the definition of the VRP’s specifications, soft constraints were identified in order to highlight restrictions related to weight, dimension and manipulation specifications. That particular knowledge led to the identification of components related to the main requirements: a) vortex generation, b) locomotion mechanism, and c) robotic manipulation, as most suitable for their incorporation in the VRP. In addition and in order to test and analyze the selected adhesion mechanism, further research has been performed regarding the simulation and experimental evaluation of the vortex actuator. Specifically, a simplified approach was proposed for modeling of the vortex actuator’s chamber pressure, which was evaluated via closed-loop simulations by utilizing a proportional-derivative (PD) control. In parallel, a small-scale vortex actuator setup was constructed, consisting of a commercially available Electric-Ducted-Fan (EDF), whose purpose was to measure the generated negative pressure when the EDF system is operated at its maximum limits.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Since this is the first reporting period, the CompInnova project has not yet progressed beyond the state of the art.

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