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Development of New and Novel Quality Control System for the Inspection of Titanium Components in Safety Critical Applications in the Aerospace Industry

Final Report Summary - QUALITI (Development of new and novel quality control system for the inspection of titanium components in safety critical applications in the aerospace industry)

Executive summary:

The inspection of titanium billets for use in the manufacture of components such as engine turbine blades is of particular interest in the field of aerospace non-destructive evaluation (NDE). This stems from the risk of component failure, induced by material defects in safety-critical components, with the potential for catastrophic consequences. Existing inspection systems can meet the prevailing requirements of production controls in terms of sensitivity to a minimum defect size. However, the increasing demand on the performance of jet engines has created a need to inspect more thoroughly and detect ever smaller defects. In addition, there is a distinct economic advantage in reducing the costs associated with manufacture and inspection. A drive now exists to develop advanced and reliable inspection technologies that support a defined specification for defect inspection, while minimising costs.

Current production billet inspection systems are either 'conventional', using a single ultrasound transducer, or 'multizone inspection' (MZI), using a number of strategically positioned transducers to focus the ultrasonic beam at various depths in the material. The current approach relies on an ultrasonic transducer scanning across the surface of the component. This inspection technique takes place in a water-filled immersion tank, which provides an efficient ultrasonic medium between component and transducer. Conventional inspection systems achieve relatively low sensitivity, particularly on large diameter billets, whereas MZI achieves higher sensitivity but exhibits large variations in response. These variations are attributed to the setup of the individual probes within the system and misalignment of the system with respect to the centre of the billet. The challenge faced in detecting smaller defects is to increase the sensitivity while overcoming the variation due to misalignment.

Previous work has demonstrated that phased-array ultrasonic probes (PAUT) can better, or equal, the sensitivity achieved by MZI systems. The application of PAUT enables the steering and focus of the ultrasonic beam, offering advantages over conventional inspection techniques. The advantages include the inspection of larger areas without moving the probe while minimising the size of the beam spot, which enhances inspection sensitivity.

Therefore, a PAUT probe, generating a number of ultrasonic sound beams that are designed to correct potential misalignments of the probe, can be introduced almost simultaneously at each sampling point on the billet. However, this approach does not automatically overcome the material losses due to the ultrasonic dead zone. This region receives unformed and incoherent acoustic energy, which results in a certain amount of material depth being uninspected. An automated system that overcomes this loss, while maintaining the tighter specification for defect inspection in titanium billets, is a solution that is not currently available in the titanium billet manufacturing industry. The development of an automated system to address the challenges has been carried out by a European part-funded consortium called QUALITI. Comprising several European companies and research institutes, the consortium is developing an integrated solution that brings together two complementary NDT techniques.

Concept design

A two-dimensional (2D) annular-segmented phased array with dual concavity (ASDC) has been manufactured, which detects defects within the volume of the billet, employing beam steering to correct for variations in flaw response caused by misalignments. The ASDC system implements a 255-piezoelectric transducer elements array and has a centre frequency of 5 MHz. The probe has an elliptic shape with a long axis of 98 mm and a short axis of 78 mm, delivering a constant 2.5 mm diameter beam spot at all inspection depths.

To overcome the ultrasonic dead zone, a complementary multicoil eddy current (EC) inspection probe will detect surface and sub-surf.

Project context and objectives:

Strategic objectives

(a) To deliver NDT techniques that will enable a major improvement in the preventive maintenance process by enabling quick and effective detection of defects in safety critical titanium aircraft parts. This in turn will improve the safety of European Union (EU) citizens.
(b) To restore confidence in the use of titanium by developing NDT methods to detect defects that can be missed by older NDT techniques. This will result in safeguarding and increasing the employment prospects in Europe. Furthermore, through automation, the project will reduce the discriminative factor of manually lifting heavy inspection equipment and, hence, expand the employment prospects for females in this traditionally male dominated industry sector.
(c) To enable detection of defects in safety critical titanium components, enabling design optimisation. This will facilitate the development of lightweight aircraft, contributing to the reduction in pollution levels that emanate from fuel combustion in aircraft. A 20 % reduction in mass by using titanium will result in a saving of 115 million litres of fuel during the lifecycle of a large modern civil aircraft. For 4 800 large aircraft, this will result in a saving of 552 billion litres of fuel over the next 20 years. The new inspection routines will enable new fuel-efficient gas turbines to be retrofitted to ageing airframes, providing a further preservation of natural resources.
(d) To develop technology for the small and medium-sized enterprise (SME) NDT companies with significantly higher reliability and rate of detection of defects in titanium components, leading to a major improvement in the safety of civil air transport. Thus, the project will support the European aircraft SME manufacturing industry by improving confidence.

Technical objectives

This project is designed to develop techniques specifically aimed at the inspection of titanium components destined for use in the civil aerospace sectors, and to establish inspection codes which currently do not exist. An automated phased array ultrasonic NDT method, supported with EC technology, will be developed so it is suitable for integration with the manufacturing process. The main component concepts are described below:

(a) Phased array ultrasonics inspection: Specifically, the consortium is aiming to develop the world's first three-dimensional ultrasonic testing (UT) beam steering system, which is capable of producing a high level of sensitivity whilst interfacing with billet geometry. This will involve the development of a new probe that can produce a focussed ultrasonic beam able to propagate into a billet geometry, with at least one plane of curvature in the beam axis, and then dynamically and electronically rotate the focal point in a circular motion. One method to be investigated in QUALITI is to use a 2D ASDC probe. This is difficult to achieve in practice as the individual elements need to have the same surface area in order to have matched impedance, and the design pattern needs to be optimised to prevent the production of energy side lobes.

(b) EC inspection: UT applications are known to generate a 'dead zone' at an interface where they are totally insensitive to the presence of defective material. Consequently, alternative inspection methods are always employed to detect defects in this region (< 5 mm from the surface). Therefore EC probes will be developed which will compensate for the 'dead zone'. The new and novel probes will address design concepts such as variable frequency, multi-elements and matrix arrangement. Conventional probes, using single frequency sinusoidal excitation and measure flaw responses as impedance or voltage changes on an impedance plane display, lack the information necessary to completely characterise a defect, particularly at deeper material depths. Also, using systematic activation of excitation coils will allow detection of defects in any orientation.

Automated NDT sensor deployment by mechanical mechanisms: The UT and EC (ET) probes will be mounted together in order to be scanned over the titanium billets during the billet manufacture process. This will be achieved with the development of an encircling collar from which three axis-manipulating arms, housing the full suite of UT and ET probe sensors will extend. It is imperative that the system maximises component area coverage at a known sensitivity, with maximum repeatability and positional accuracy, in both absolute and relative terms.

(c) Man machine interface: A unique and simple operator interface in combination with a varied collection of analysis tools will be designed. Advanced data processing and state of the art computer technology will transform the signals received by the NDT sensors from discontinuity indications into an optically enhanced colour graphic package, which will encompass automated sentencing of defects. Note: The PANI trials carried out to assess the effectiveness of manual inspections have shown that operators detect only 50 % of defects during manual inspections.

In summary the objectives are:

(a) to develop a novel phased array system capable of inspecting a 1-inch titanium billet, at various depths, with high sensitivity;
(b) to develop a novel EC array system capable of inspecting the near surface area of the titanium billet;
(c) to integrate the two NDT systems in a fully functional system to be used during the manufacturing process;
(d) to improve the reliability compared to existing NDT inspection systems.

Project results:

WP1: System specification

Work package (WP) objectives
Specification statements for each of the NDT methods with regard to technique development, sensor development, deployment parameters and test piece / reference standards required to validate the inspection systems.

Overall progress
This WP was successfully completed on time by all partners. Deliverable D1 'Signed Consortium Agreement' document; D2 'Project website' and D3 'Report detailing the system specification were submitted to the EC on schedule'.

Task 1.1: Produce specification document

Collectively, the partners provided specifications of the final inspection system, which included the type of defects to be detected, NDT techniques and sensors, deployment parameters, test pieces required for NDT process, validation and integration schedule, laboratory and field trials requirements and constraints. The phased array system is intended to meet the requirements specified in Table 1. The EC system will aim to detect surface and sub-surface defects (0.2 mm notches) in any direction.

End-user TIMET organised a visit to their facility in Birmingham, United Kingdom (UK) to allow the partners to see the inspection challenges of billet components. Partners TWI and ZUT were able to visit TIMET in order to get a better understanding of the inspection requirements.

It was agreed between the partners that the project would develop PAUT and EC probe that will take into account possible mechanical misalignment of the probe relative to the surface of the component, and apply electronic steering to compensate for the misalignment and its effects on the quality of the beam at the focal points.

WP2: Provision of samples

WP objectives
A number and type of test pieces required, together with the method of representing the defect types specified in task 1.1 will be derived. Input to this task is expected from all partners in conjunction with the end users.

Overall progress
This WP was completed by all partners. D4 'Provision of samples', a report detailing the samples and the flaws to be used for the validation was submitted to the EC on schedule.

Task 2.1: Provision of samples

The type of test pieces and the methods of representing the defect types specified in task 1.1 were defined. Although TIMET provided the samples, they were unable to provide samples containing real defects. The samples provided by TIMET had to be sectioned by TWI to facilitate practical use in the experiments. In addition, in order to validate the developed systems it was necessary to have calibration blocks containing known location, type and size of flaws. None of the partners had the specialised resources to manufacture the flaws according to the size and position accuracy requirements. Therefore, it was necessary to involve a third party specialist manufacturer to produce the flaws.
One phased-array billet sample and four sets of EC samples have been produced from the samples provided by TIMET.
The annex 1 did not take into account that, for the calibration blocks, the artificial defects had to be precisely manufactured and this was not in the capability of any partner. As such, a third party specialist company was used to manufacture the flaws. However, this introduced a delay because the manufacture took longer to complete the work than expected. Although the report D4: Provision of samples was delivered according to the project schedule, milestone M2: Provision of samples was not completed until month 12.

WP3: Development of an UT-phased-array inspection and calibration surface

WP objectives
The objectives of this WP are to develop a new and novel phased array UT inspection. Hardware and software will be developed to achieve the required sensitivities and resolution specified in task 1.1 in WP1.

Overall progress
This WP caused significant delays within the project. The first design of the PA probe was modelled and validated, however the probe did not beam steer. Further, modelling work was undertaken to enable the probe to allow beam steering as well as beam focusing, however significant work was required in updating the simulation package to include this function for complex probe designs. Manufacturing such a complex probe was also found to be a challenge, as was machining such a high accuracy calibration surface. However, with all these delays and challenges, all tasks were able to be completed.

Task 3.1: Modelling of the UT-phased-array inspection requirements
This work program reviewed algorithms, investigated 2D and 3D array simulations, and explored associated wave propagation issues. The result will be a set of probe element designs required to produce all the necessary sound beams at the various focussing depths and steering angles. Three different probe designs have been investigated: Flat 2D matrix type, curved 2D matrix type and an annular array (1st iteration).

Modelling software has been used to design PA probes for the inspection of titanium billet without the use of costly experimental trials. The requirement of the design is that the PA probe be placed in water at 76.2 mm (3 inches) from the front surface of the titanium billet. The transducer focuses the beam at different depths. Also, the beam width is uniform and equal to 2.54 mm, and the frequency of the probe is 5 MHz. These requirements were used as inputs in Probe Designer software in order to build a 3D shape of the optimum probe. A tolerance of 60 degrees was enforced as the maximum phase variation over the surface of each element.

The first PA probe designed using Probe Designer required only 18 elements. It is clear from Figure 6 that the probe is large and has a complex shape. Although the curvature changes continuously along any profile of the probe, the radius of curvature in the index direction is about 380 mm, and in the axial direction is approximately 180 mm. It is clear that the design gives an array with a small number of elements, i.e. 18. However, the surface area of the elements varies with a factor of 20. Although such a surface area variation poses no problem acoustically, it can result in dramatic electrical impedance variations, which can degrade the performance of the probe if impedance matching components are not used.

The limitation for the first PA probe design is that it cannot beam steer, hence a new PA ultrasonic probe was designed. This new probe will take into account possible mechanical misalignment of the probe relative to the surface of the component. A specialised 2D annular-segmented PA probe with dual concavity was designed and developed for the inspection of titanium billets. There are a number of advantages associated with the ASDC probe:

(a) excellent steering and focussing capability in 3D;
(b) spherical focusing;
(c) focusing depth and angle is electronically selected;
(d) smaller focal spot and therefore better defect sensitivity can be achieved;
(e) more volume coverage from one probe position;
(f) electronic compensation for probe misalignment.

The ASDC probe is expected to have the following characteristics and capabilities:

(a) 2D sectorial annular probes;
(b) element number greater than 128;
(c) frequency range 5 to 10 MHz;
(d) probe design will provide uniform focal spot independent of inspection depth;
(e) ultrasonic beam steering;
(f) longitudinal waves.

The final ASDC probe design uses a customised contour represented by a fifth order set of cosine basis functions. The probe has an elliptic shape with an index axis of 98 mm and an axial axis of 78 mm. The probe was designed to deliver a 2.5 mm diameter beam spot at all inspection depths from just beyond the dead zone (5 mm) to half an inch past the centre of the 10-inch billet (139 mm from the surface). The optimisation of the surface shape was targeted at reducing the phase variation across any one PA element.

The first ASDC probe determined by Probe Designer uses only 132 elements. However, the segmentation scheme means that many of the elements had a much greater surface area than others; the largest element being 10 times larger than the smallest. An element's surface area affects its electrical impedance, and hence its sensitivity. Therefore, the segmentation scheme was re-designed to minimise the variation between the element sizes. The probe was re-segmented into 255 elements of approximately equal size, and the probe design was complete, the largest element being only 1.6 times larger than the smallest.

Task 3.2: Validation of proposed probe design

Simulation and modelling methods were used to validate the probe design. Beam profiling was carried out at all proposed focussing depths and steering angles to ensure that beam shape and focal spot is maintained, and that side and grating lobes are avoided. As part of this WP, a new probe specification file format was devised, that accurately describes the position of all elements in three axes. Validation results can be seen in D5.

In the case of beam spot size as a function of beam steering, the probe remained normal to the billet, so the beam steering resulted in a lateral shift of the focal spot. It can be seen that the beam spot is approximately 2.5 mm in both the axial direction and the circumferential direction at low beam steering angles, but eventually diverges. As the beam steering passes 29 mm of displacement, which corresponds to 3 degrees, the beam spot size expands rapidly.

Task 3.3: Manufacture of complex phased array probe

The proposed probe design is innovative and includes several challenges that needed to be overcome during probe manufacture:

(a) The first challenge is related to the large dimensions of the probe. Standard PA probes are linear, with the acoustical head relatively small (about 50 × 10 mm) while the proposed design exhibits 98 × 74 mm on its main axis. Each transducer requires the manufacture of a large piezocomposite plate (which is the core material of the probe).
(b) The large number of elements (255) is also challenging: in NDT applications, the number of elements is mostly limited to 128.
(c) The positioning of the elements and the correct addressing is also critical for the tests. Numbering of the elements was agreed between TWI and Vermon to avoid any misunderstanding.
(d) Variation in transducer element areas is also an issue for the performance of the probe. This will lead to different electrical impedance for the elements along the probe as no individual impedance matching was performed for the first prototype. To limit the effect of this parameter, it was decided to have uniformity of element area at ring level as discussed in D5.
(e) The last (but not least) challenge associated with the probe manufacture is the complex shape geometry. High precision manufacturing tools have been prepared to match the shape requirements.

During manufacture of the first prototype probe there was an issue with the probe shape, which delayed the manufacture of the final probe. This was later resolved by modifying the tools and changing the curing time for the chemical parts. However, this did cause a 1.5-month delay.

Task 3.4: Specification of the calibration surface

The design of the calibration surface shape was undertaken using MatLab. The process followed includes the following steps:

(a) identify the near field of the probe, which sets the minimum water gap between the probe and calibration surface;
(b) using the simulated probe model, identify small areas (sub-elements) and the unit vector normal to the surface at that point;
(c) project equidistance rays from each sub-element and create a surface at the end of the rays;
(d) identify normal vectors of the surface at the endpoints of the original rays;
(e) project rays back along the new surface normals to identify how much error there is in the position of the reflected rays.

A calibration surface was designed for the 255-element ASDC probe, more details can be found in D6.

Task 3.5: Manufacture of calibration surface

Using the designed calibration surface from task 3.4 Vermon manufactured a stainless steel sample with the designed contour. Due to requiring precision tools to manufacture the calibration surface, a one-month delay was encountered. The calibration was used to assess the performance of manufactured ASDC phased array probe.

Task 3.6: Development UT phased-array system

Due to the designed ASDC probe having 255 elements, the Zetec DYNARAY system was required to drive the probe. The DYNARAY system uses commercial software UltraVision in which measurements and post-processing can be conducted. However, the software was not able to calculate the focal laws for such a complex probe design. Therefore, focal laws were calculated within ultrasonic modeller and converted into the UltraVision format.

Results
The calibration surface was required to assess the performance of the designed phased array probe. The surface was designed using MATLAB software to calculate the surface contour. Possible errors in the surface were calculated. Once the calibration surface was designed, it was manufactured and used to test the performance of the designed 2D annular-segmented phased array probe with dual concavity.

A very complex 2D annular-segmented PA with dual concavity was designed and manufactured in the frame of the QUALITI project. Several challenges were overcome in the production of this probe. During the initial design, the modelling software used to design the PA ultrasonic probe had considerable delays in delivery. Due to the complexity of the probe, the software required many modules to be reprogrammed. Many other delays were also incurred during designing and manufacture of the ASDC probe. A 5-month extension was granted due to these delays. The validation simulation results show that the new ASDC probe design meets the specification of achieving a 2.5 mm circular beam spot size, at all required inspection depths. However, the side lobe energies produced during 3-degree probe tilt does develop large side lobes that can create false indications. However, the 2-degree probe tilt does not incur the same problem. Therefore, it was concluded that a 2-degree probe tilt, which is 8.5 degrees in titanium, would be used in inspecting the material under test.

Manufacturing the ASDC probe also was a challenge, with the main issues being related to the big dimensions of the probe, and the need for very accurate tools to manufacture this type of probe.

WP5: Development of an EC array inspection

WP objectives
WP5 has the following objectives:
(i) Utilisation of the NDT modelling software (CIVA, Comsol) for the development of sensors and EC testing techniques;
(ii) develop a new EC technique for the sub-surface inspection of titanium components in a production line environment; and
(iii) development of EC array system to perform to the sensitivity required in task 1.1 and task 2.1.

Overall progress
This WP has been completed. D7 'Complete EC system' a report detailing design and development of the EC system was submitted to the EC on schedule.

Task 5.1: Modelling of EC array inspection

Modelling has been used as an effective way of designing the appropriate transducer and set up inspection parameters for a specific application. Development was based on a two-step approach. One tool will be devoted to the calculation of EC fields induced by transducers into components. Another simulates the interaction of the EC field with defects in titanium components as defined in task 1.1 and task 2.1.
Three different configurations (UNIBIG, MATDIFF, UNIBIG2DIFF) of EC transducers have been considered and evaluated using numerical analysis. UNIBIG type configuration was concluded as the best configuration.

Task 5.2: Development of the EC probe

Development of the EC inspection has focussed on developing optimum techniques that can be used for the rapid inspection of large titanium components. This inspection covers the volume of material lying at a depth close to the surface. Experiments were carried out to determine the optimum frequency range to be used with the multi-coil EC probes. From these parameters, the adoption of transient, pulsed and multi-frequency systems were assessed.

Task 5.3: Development of EC system

Two EC systems were designed and developed: the lock-in ECT system and the impulse ECT system. ZUT built its own lock-in amplifier module. The lock-in module was designed; the printed circuit boards (PCBs) were prepared and mounted with the required elements. The lock-in was preliminary tested and correct operation was confirmed.

Task 5.4: EC system validation test plan

The five-column transducer and E-type transducer were compared with a commercial EC system, and the results can be seen in D9. It was concluded that the EC transducers for the lock-in ECT system out preformed the commercial system. The designed EC transducers were able to detect defects down to 7 mm below the surface whereas the commercial system was able to detect defects down to 4 mm below the surface.

Task 5.5: EC circular sample manufacture and test

A titanium billet with artificial holes of different depths was manufactured. The billet was made from a TIMET 6-4 titanium alloy (Ti-6Al-4V; ASTM Grade 5). The holes were drilled from the side of the billet, diameter 2 mm with a depth of 50 mm. The holes were drilled at d = 2, 3, 4, 5 and 6mm below the surface. Using this sample, it was possible to carry out measurements with scanning only in the circumferential direction. In order to carry out laboratory trials a simple motorised rotating scanner was also constructed. More details can be seen in D9.

WP6: Physical integration of the inspection systems

WP Objectives
The objectives of this WP are to develop the physical integration of the two sensors and probe holder, fully integrated software and NDT hardware for field deployment and a family of integrated NDT fully validated in the production environment.

Overall progress
This WP has been completed. D8 'Completed integration inspection system' a report detailing the integration of both PAUT and EC probes.

Task 6.1: Preparation of integration of the two inspection systems

A bar follower was designed in order to physically integrate the PAUT and EC probe. The follower is built from high-grade stainless steel, weighs approximately 35 kg and is attached to the existing immersion system. The probe holder rides on a low friction roller device, which is totally flexible when engaged onto the bar under test. This flexibility allows the probes to follow the bar's deformities and maintain a constant water interface distance between the ultrasonic transducer and the rotating billet.

The bar follower was directly linked to a pair of encoders, which ensure exemplary accuracy on positional data to maximise the flexibility and accuracy of the finished system. An incremental line encoder will be used to measure the axial axis. However, to measure the circumferential axis requires a rotary encoder. An encoder arm was designed and built to measure the circumferential axis. This bar follower was also designed so that it can be used in the TIMET tanks for field trials.

Software integration was not possible due to the Zetec DYNARAY 256/256PR system using commercial software (Zetec's UltraVision 3) for data acquisition. With the requirements from WP1, a phased array probe of 255 elements was required. It was originally intended that the probe would have no more than 128 elements due to TWI (Wales) having the PeakNDT Micropulse system. The PeakNDT system is fully programmable in the MATLAB environment. With such a high element probe, the Zetec's DYNARAY 256/256PR was chosen to drive this type of probe. However, the downside to this is that the Zetec DYNARAY 256/256PR system uses commercial software (Zetec's UltraVision 3) for data acquisition. The Zetec's UltraVision 3 software controls the ultrasonic (UT) signal acquisition, displays real-time imaging of these signals, and provides online as well as offline data analysis. Using the DYNARAY meant that both systems used separate post processing software, making data fusion not possible.

The EC systems were driven by software developed using the LabVIEW programming environment. The program enables the set-up of all parameters (excitation current and frequency, sampling rate, etc.). It allows also for visualisation of the signal in the time domain and on a complex plane. Post processing for the data is carried out using custom scripts using MATLAB software.

Task 6.2: Physical integration of the two inspection systems
The PAUT and EC probes were physical integrated on to the bar follower and results can be seen in D9.

Results
Physical integration of the QUALITI system was carried out with a bar follower manufactured for mounting the two probes. Encoders were used to ensure accurate measurement of the position of the probes. Both ultrasonic and EC systems ran on two independent computers, with independent post processing techniques.

WP7: Laboratory and field trials

WP objectives
The objective of this WP is to carry out extensive laboratory and workplace environment trials for the inspection of aerospace safety critical titanium components. The operation of the NDT sensors and systems (PAUT and EC) and the automated sensor deployment system will be fully debugged and validated.

Overall progress
This WP has been completed. D9 'Tested and validated final system', a report detailing the results from laboratory and field trial experimentations.

Task 7.1: Laboratory trials

Comprehensive laboratory tests were carried out on the two NDT technologies developed in earlier WPs. The initial testing involved 'shake down' experiments designed to 'debug' the systems in both the hardware and software domains so that they work efficiently. Further experimentation proved the validity of the developed techniques by running a series of trials on the application of the systems to the deliverable samples (WP1 and WP2).

A multi-frequency spectrogram method was utilised in order to identify the real optimal frequency. The frequency range utilised during measurements was between 700 Hz and 32 kHz. The measured spectrograms correlated well with the simulation results. This confirmed that the proposed transducer could be used for detection of minor flaws in titanium billets located up to 5 mm below the surface. The differences between experimental and modelling were not significant and it confirms usability of the numerical models in practical applications. It is observed that all defects can be detected with good signal to noise ratios. The optimal testing frequency is from 4 kHz (in the case of a defect 6 mm below the plate surface) up to 8 kHz in the case of a defect 1 mm below the sample surface. The measurements prove that the proposed system and transducers are very sensitive, and defects can be detected even below 7 mm of the material surface.

The custom phased array probe was designed to use the full array of 255 elements to focus at the greatest required depth into the material. At lesser depths, fewer elements are required to form a focused wave front that produces an optimal response from any defects. Due to the issue in procuring a DYNARAY system, the Zetec Tomoscan III system was used so that further delays would not occur. The Zetec Tomoscan III was used to inspect the near surface defects, due to the system being able to fire a maximum of 32 elements simultaneously; and the deeper defect would be detected using the Zetec DYNARAY system. The use of the Tomoscan III system meant that laboratory trials could be started without the need to wait for a replacement DYNARAY system.

Trials with the Tomoscan III concluded that 0.8 mm flat bottom holes (FBHs) up to a depth of 28mm can be clearly identified. 3-degree beam steering measurements were concluded, and FBH indications can be clearly distinguished from background noise and grain artefacts. The use of beam steering has the advantage of picking up detects in opposing directions and compensates for any probe misalignment.

Once a DYNARAY system was procured, the designed calibration surface was used to test each individual element. It was discovered, that there were 48 dead elements on the phased array probe. The working elements had a percentage variation of 5.3 in response from the calibration surface. With time restrictions, there was not enough time to build another prototype probe, therefore measurements were carried out with the dead elements taken into account. The deepest FBH could still be detected with the phased array probe, which was another reason to go ahead with laboratory trials.

With the knowledge that there were 48 dead elements in the phased array probe, it was possible that the beam spot size would be affected by this considerable element reduction. Therefore, the beam spot size was measured at all hole depths in the axial and index directions. All 13 FBHs can be clearly identified using the phased array system, with received signals exhibiting a favourable signal-to-noise ratio (SNR). The beam spot sizes have, however, in many cases exceeded the design specification of 2.5 mm. The lower depth FBH (5 - 69 mm) beam spot sizes have not significantly increased with the loss of the elements, though the beam spot size for the deeper holes (69 - 140 mm) has greatly increased. This increase in beam spot size would decrease the SNR of the FBH, but despite this, the worst observed SNR is found to be 3.63 which is within the guidelines of the AMS 2628 standard where a SNR of greater than 2.5 is required.

Using the DYNARAY system, each FBH was tested individually using a helical scan. Each FBH was scanned using 0-degree focal laws and beam steering focal laws of 2 degrees. From the results, it was concluded that the FBHs could be clearly identified. For the beam steering measurements, the angle that gave the largest reflection signal was used to measure the FBH response. Both beam steering and non-steering measurements detect the FBHs at all depths within the required SNR. All results can be seen in D9.

Task 7.2: Field trials

Successful field trials were carried out at TIMET. Results from the trials can be observed in D9. The end users concluded that QUALITI was suitable for detecting the required defects within the titanium billet. This is a major improvement in the manufacturing process by enabling effective detection of defects in safety critical titanium aircraft parts. This in turn will improve the safety of EU citizens.

The end users acknowledged that the ASDC phased array and EC probes need to be more robust if they were to be implemented in the manufacturing environment. The EC probes were manufactured from ferrite material, which was brittle and susceptible to cracking, and the ASDC probe developed 48 dead elements.

Results

Two independent inspection systems were developed within the QUALITI project. Two different EC systems were created, and the lock-in ECT system detected the required defects efficiently. Two probes were developed for this system, of which both probes out preformed the commercial system.

All FBHs were detected using beam steering even with a 1-degree misalignment in the phased array probe confirming that, if the probe was misaligned, this designed ASDC phased array probe can still detect the FBHs efficiently.

There were difficulties in procuring a DYNARAY system. This did delay the project, however; conducting measurements with the Tomoscan III did mean that some trials could be conducted while waiting.

Potential Impact:

The SME partners consider that the QUALITI system will deliver a step change in technology through its product development. This will provide sufficient competitive advantage to enable annual growth rates of at least 20 % in SME sales turnover over the four years following project completion. The results of the project will improve the competitiveness of the SMEs by diversifying their product portfolios, and improving the efficiency of their processes so that titanium can be inspected, as well as traditional aerospace materials, and those used in other industrial sectors. This will enable the SMEs to increase their share of the inspection segment since QUALITI systems will have an important competitive advantage over products which are currently based on manual NDT of conventional materials. The project will provide products of increased reliability and quality and increased functionality.

Strengthening the competitiveness of the SME participants

The SME partners are in the business of non-destructive testing (NDT) for the aerospace industry, and have achieved reasonable sales growth of 8 - 12 % over the past three years. Evaluation of the aerospace industry revealed trends towards the increasing use of titanium; the SMEs have identified the NDT of aerospace titanium components as a major growth area and have decided to strengthen their core competencies in this area.

At least seven major market studies by management consultancy companies and academics concluded that NDT sensors and systems, as used for the inspection of safety critical aircraft titanium components, are expected to experience growth rates exceeding 20 % per annum for the next five years. The rationale for this growth and the growth in the field of automated NDT is:

(a) use of safety critical titanium components in the manufacture of aircraft is to drastically increase;
(b) the same studies concluded that the current level of NDT performance is inadequate for detection of the type of defects found in titanium, the report goes on to recommend development of PAUT and EC techniques and equipment;
(c) air travel is to triple in the next 20 years resulting in an increased volume of aircraft production requiring the type of NDT techniques to be developed in this project;
(d) the fact that manual NDT has been shown to miss major defects as recent PANI trials sponsored by the UK Health and Safety Executive has proven. The report stated that manual inspections often detect only 50 % of the defects as they are repetitive, monotonous and allow operator subjectivity;
(e) new European legislation for the protection of EU workers and HSE fears over repetitive strain syndrome will drastically reduce manual inspections and increase automated NDT sales.

Savings generated as a result of this project: The four titanium specific applications highlighted as exploitable deliverables (designed and developed as a result of this project) are expected to reduce the spending on individual inspection by airlines, aircraft and titanium manufacturers. The savings will be generated by virtue of the faster NDT techniques developed in the project, reducing inspection times. The increased probability of defect detection (POD) facilitated by the new techniques will eliminate destructive batch testing of components, thus generating huge savings. The individual stand-alone NDT systems will also be used in aircraft, aeroengine and other service sectors. Here, the industry will realise further benefits from the QUALITI system, which will be derived by the fact that the aircraft will spend less time in maintenance and more time flying; thus generating more revenue for the European airline or power by the hour supplier.

Impacts on Community societal objectives

The transport policy of the EU aims to deliver a fully integrated and efficient pan-European transport network that meets the demands for a cleaner environment, safety and reliability. The EU has identified research and technological development (RTD) as an instrument for achieving its transport policy. It has been stated that major programmes should focus on making travel safer, easier and less polluting. This project will encourage use of lightweight titanium resulting in considerable fuel savings. In the Sixth Framework Programme (FP6)'s key action relating to aeronautics the EU has identified enhanced NDT and analysis for improving operational capability and safety of aircraft as an important area. The field of aircraft safety is such an important issue to the Commission that a directive was approved on 15 September 1998 that requires Member States to carry out inspection of third countries' aircraft that show signs of poor maintenance condition. Airframe failure due to fatigue cracking in the fuselage and engines is a major cause of accidents involving hull loss and fatalities. This project will develop technology with significantly higher reliability and rate of detection of defects, leading to a major improvement in the safety of civil air transport. The project will, therefore, contribute to the implementation of EU transport policy. Additionally, this project will contribute to EU social and economic policy through the involvement of Eastern European airlines through the associated RTD performers in the project.

Quality of life, health and safety: A major cause of air accidents is structural failure of the fuselage, undercarriage, wing or engine. This usually leads to hull-loss and fatalities. Data indicates that the average number of accidents and fatalities has steadily increased over the past 20 years averaging over 1 600 fatalities per year between 1997 and 2001. These fatalities and aircraft losses have resulted in a sharp increase in insurance pay-outs over the past 20 years, currently over EUR 1 600 million per annum. Statistically, such steady and predictable behaviour in terms of accidents and fatalities is indicative of process rather than chance variability. In other words, the process needs to be improved to reduce the alarming upward trend. This improvement is critically dependent on progress in preventive maintenance. In this respect, technology is a limiting factor and, until this is improved, significant enhancements in airworthiness cannot be achieved. This project will deliver NDT techniques that will enable a major improvement in the preventive maintenance process by enabling quick and effective detection of defects in safety critical titanium aircraft parts. This in turn will improve the safety of EU citizens and halt the upward trend.

Employment: The European aerospace industry directly employs some 429 000 people whilst the second tier suppliers employ a further 500 000 people. European industry has taken bold steps to use an increasing amount of titanium in their aircraft structures. Consequently, their aircraft have, on average, considerably more titanium than United State (US) suppliers such as Boeing, making their aircraft significantly lighter than US aircraft of similar seat capacity. This gives SME European manufacturers a considerable advantage over those in the US. This advantage is threatened by a loss of confidence in the use of titanium following recent air disasters caused by undetected defects in such components. This is causing the SMEs considerable problems which, unless solved, will create a drop in confidence in NDT markets. This project will restore confidence in the use of titanium by developing NDT methods to detect defects that can be missed by older NDT techniques. This will result in safeguarding and increasing the employment prospects in Europe. Furthermore, through automation, the project will reduce the discriminative factor of manual lifting heavy inspection equipment and hence expand the employment prospects for females in this traditionally male dominated industry sector.

Level of skill: This project will lead to an improvement in the level of skills for European citizens, as it will implement new NDT technology with automated application. This greater level of sophistication represents a step change over current technology that is based on manual NDT methods. The project will develop and sustain EU expertise in new NDT technology, particularly in versatile automated application.

Environment and natural resources: QUALITI will significantly contribute to increasing the operational life of aircraft thereby supporting the EU projected strong growth in air transportation. It is estimated that the technology developed herein will increase the operational life of aircraft by 10 years, as well as reducing operational cost and the number of accidents. The global increase in air transportation, as estimated by the Commission, will require 24 000 new airliners in the next 20 years. In the region of 20 % of this demand will be from EU airlines, this translates to the production of 4,800 new aircraft requiring approximately 540 million tons of aluminium alloys. Obviously, extending the life of current aircraft will save considerable resources and contribute to preserving the environment.

Reduced fuel consumption: The older generation of aircraft manufactured from traditional materials are a major contributor to air pollution as a result of heavy fuel consumption. Considerable effort is currently being expended in the EU on the development of aircraft that utilise advanced lightweight materials. Current NDT methods are not capable of detecting all the defects in titanium and are, therefore, limiting its use. The NDT technology developed herein will enable detection of defects in safety critical titanium components, enabling design optimisation. This will facilitate the development of lightweight aircraft, hence contributing to the reduction in pollution levels that emanate from fuel combustion in aircraft. According to one study, a 20% reduction in mass by using titanium can result in a saving of 115 million litres of fuel during the lifecycle of a large modern civil aircraft. For 4 800 large aircraft, this will result in a saving of 552 billion litres of fuel over the next 20 years. The new inspection routines will enable the benefit of new fuel-efficient gas turbines that can also be retrofitted to ageing airframes, providing a further preservation of natural resources.

Source of Value for the QUALITI consortium

The SME to LE supply chain, the RTD expertise and the relevant industry knowledge necessary for successful completion of QUALITI is spread across Europe. The members of the consortium already supply many industries and therefore have existing contacts in other sectors that will accelerate the horizontal exploitation of the project results. QUALITI systems will be of benefit to the nuclear, power generation, chemical, surface transport, medical, structural engineering, boiler and pressure vessel sectors, indeed any industry that requires complicated structures (of many engineering materials) to be tested by automated NDT systems. The consortium is supported by a large company, TIMET (France), which supplies goods and services and is represented in the majority of European countries and worldwide. TIMET constitutes the end-user panel of this project and is also a partner providing 'in-kind' contributions as well as bringing a vast array of background knowledge to the project.

As part of the QUALITI project, TWI LTD hosted a website on behalf of the consortium with the domain name http://www.qualiti.eu. The purpose of the website is twofold:

(1) A public area for the dissemination of information about the QUALITI project. A project page provides an introduction to the project. In addition, a contact page on the website provides for specific enquiries to be automatically forwarded to all relevant project partners.

(2) A project page provides an overview of the project. As the project advances, it is expected that more information relating to the project activities, including project work descriptions and publications, will be added to the website. An agreement has been made by the consortium that prior to any new information appearing on the website, it is first distributed via Vermon SA, to all the partners in order for their approval.

Due to the project delays, the majority of the significant results were not reported until the end of the project. The QUALITI website has undergone an update and redesign. The redesign is to make the website more appealing to the general public as well as to the NDT community. With this redesign, a blog page has been included to start discussions with site visitors. It is intended that visitors leave questions and comments for the QUALITI consortium to address. Results and conclusions from the project have been included in the update.

Finally it should be noted that the URL used for the project website have been purchased up to September 2011, with the option to extend beyond this date should the SME partners so decide. Therefore, the website will be usable for dissemination purposes up to six months after the completion of the project. This will enable the consortium to publicise the results obtained and research carried out during the work programme.

QUALITI consortium acknowledgement

QUALITI is collaboration between the following organisations: TWI NDT Validation Centre, Wales (Dr Harshad Virji Patel, harshad.patel@twi.co.uk); West Pomeranian University of Technology, Poland (Prof Tomasz Chady, tchady@zut.edu.pl); TIMET, UK; Vermon SA, France; Tecnitest Ingenieros SL, Spain; and I.SO. Test Engineering SRL, Italy. The project is co-ordinated and managed by TWI LTD and is partly funded by the European Commission's 'Research for the benefit of specific groups' project with Grant Agreement No 222476.

List of websites: http://www.qualiti.eu

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