Life Extension and Management of Ageing Fleets I
Chair: Jerzy Komorowski
CONCEPT OF THE A320 NEW FATIGUE TEST|
Nils Roessler, Carsten Peters, Olaf Tusch, Gerhard Hilfer, Clemens Herrmann
Abstract: Within the scope of the Extended Service Goal (ESG) for the A320 family fleet fatigue tests (NEF) have been decided by Airbus in order to support analysis/justification for an extension of the limit of validity (LoV) of the maintenance program to ensure continuation of safe aircraft operation. A320/A321 major fatigue tests are developed by Airbus as supporting test basis for the analytical development of fatigue and damage tolerance justification of all A320 family aircraft up to 60000 operational flight cycles (120000 SF) as prime objective and up to 90000 operational flight cycles (180000 SF) as target objective for an extended LoV. The test aims will be achieved by ‘Multiple Sections’ testing, which divides the aircraft into three major test specimens: NEF1 representing the forward fuselage, NEF 2 representing the centre fuselage and wings and NEF3 representing the rear fuselage. For all three tests up to 180.000 SF have to be performed to simulate the fatigue and damage tolerance behaviour of the airframe. As with all previous aircrafts, Airbus has chosen to cooperate with IABG, which is thus responsible test institute for the NEF2 & NEF3 test.
The concepts of the new fatigue tests have been developed based on the experience and cognitions of all former aircraft tests for Airbus and in particular the A320 EF tests about 20 years ago, when EF2 was accomplished by IABG and EF3 by Airbus Hamburg. Nevertheless, since the new tests have been taken into Airbus` program at very short notice, the realisation of the test set-up required unique and very time efficient solutions in all needs. Due to this tight scheduling the implementation of NEF2 & NEF3 is incomparable to all previous aircraft tests for Airbus and one of its kinds, although many components – or at least the ideas - of the test set-up have been adopted from former tests. The application of established technologies and structures does not only save time, but also reduces the potential risk of faults caused by the use of non-field-tested technologies and structures.
Some innovations of the A380 EF test, which were necessary to test an aircraft of this size in a full scale fatigue test, have been adapted to the A320 multiple section tests:
No filling of the fuselage with foamed polystyrene blocks, which had to be removed for every inspection in former tests, has been implemented thus allowing primarily for a lot more time efficient inspections during the test. Instead of that more pneumatic power is needed to compensate the missing volume reduction.
The wing pad bonding technology (fixation of pad bonding via low pressure device) of the A380 has been improved again: It is no more limited to rectangular pad group layouts, but allows for arbitrary pad group layouts, e.g. the centre of gravity of each pad group row can be placed on the datum line of the ribs.
Unlike all other tests - including NEF2 and A380 – NEF3 is not equipped with the commonly used Logidyn system, but with an FCS control system. Different to A380 EF the data acquisition system (DAS) concept of NEF2 & NEF3 is based on a centralised measuring amplifier system. Furthermore, just one DAS is used for NEF2 & NEF3, which is very cost-saving. For switching between NEF2 und NEF2 data acquisition channels a special patch panel arrangement is used.
The proposed paper will present the test concept for the A320 NEF2 & NEF3. It will highlight the improvements of the load introductions systems and show the application of new technologies. Presented topics are the following:
• Description of the A320 NEF 2/3 Full Scale Fatigue Test: test program and time scale
• Overview of the mechanical test-set-up and loading jack arrangement
• New possibilities of IABG load pad arrangements
• Advancements of the control and measuring systems
The paper will give an overview of a state of the art full-scale fatigue test and the load introduction concepts used by IABG to improve testing of large aircraft structures.
THE USE OF COMPOSITE MATERIAL STRIPS TO EXTEND THE DAMAGE-TOLERANCE LIFE OF INTEGRALLY STIFFENED ALUMINUM PANELS|
Abraham Brot, Yuval Peleg-Wolfin, Iddo Kressel, Ziv Yosef
Abstract: Israel Aerospace Industries (IAI) has studied the damage-tolerance behavior of integrally stiffened metallic structures as part of an international project called DaToN (Innovative Fatigue and Damage Tolerance Methods for the Application of New Structural Concepts), which was partially funded by the European Commission. IAI has performed both analytical and experimental studies of integrally stiffened metallic structures, in the framework of this project. This paper describes testing performed, under the DaToN framework, where composite material strips were used to enhance the crack growth resistance of the panels. The paper also describes the analytical calculations supporting the experimental results.
In order to improve the performance of a two-stringer integral panel, two 35mm wide strips of AS4/3502 carbon-epoxy were bonded to the panels. Each strip consisted of three layers of carbon-epoxy material. The purpose of the strips is to reduce the stress-intensity of a crack that grows under it, thereby increasing the crack growth life of the panel. On an identical panel, two 35mm wide strips of Textron 5521 F/4 boron-epoxy were bonded. Each strip consisted of two layers of boron-epoxy material. Both hybrid panels were tested at room temperature.
The results show that both hybrid panels had a significantly slower crack growth rate than the unreinforced panel. The crack growth life of the three-layer carbon-epoxy gave somewhat better results than the two-layer boron-epoxy strips.
An additional test was performed with a carbon-epoxy reinforced panel at an ambient temperature of -50C. The results show that the crack grew significantly slower at -50°C than at room temperature, showing that the reduced crack growth rate of aluminum at -50°C was more decisive than the presence of tensile residual stresses.
A NASTRAN finite-element model (FEM) was built to study the effect of the reinforcing strips. The stress-intensity results, obtained from the FEM, were input into NASGRO ver. 5 (crack growth software) in order to compute the expected crack growth characteristics.
This experimental and analytical study demonstrated the large potential that exists by use of CFRP or BFRP patches to increase the crack growth life of integrally stiffened aluminum panels. Further testing and analysis is needed to confirm quantitatively these results.
STRUCTURAL INTEGRITY OF A WING UPPER SKIN WITH EXFOLIATION CORROSION|
Andreas Uebersax, Cyril Huber, Guillaume Renaud, Min Liao
Abstract: This paper presents the modeling and testing aspects of a collaborative research program on the effects of exfoliation corrosion on a wing structural integrity. Finite Element (FE) and fatigue strength analyses were carried out to quantify the impact of exfoliation corrosion at fastener holes on a wing upper skin on a fighter aircraft. The analytical models were validated by test results. Based on the results, corrosion maintenance recommendations are provided.