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An Advanced Methodology for the Inspection and Quantification of Damage on Aerospace Composites and Metals using an Innovative Approach

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

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