Traditional aircraft structures use Aluminium stiffened panels for fuselage, wing and tail plane skins. In recent years stiffened skin panels are manufactured from composite materials instead of Aluminium. The use of composite materials has the potential to reduce aircraft weight, and therefore fuel consumption, and also to reduce maintenance and operational costs. Stiffened panels can be made by attaching stiffeners to a thin panel or by producing integrally stiffened panels, reducing costly assembly operations as well as composite machining operations which are costly and polluting. In this way, a composite stiffened panel has been developed as part of the JTI "Eco Design" technology demonstrator A2 with many ecological, technical and economic benefits.
This proposal has two objectives. The first one is to perform a large-scale test to validate the structural performance of the developed eco panel. The second one is to develop and validate an advanced measurement procedure based on distributed strain measurement systems. One of the main issues of the large-scale tests is the strain measurement. Classic methods can only measure the strain in local positions. To obtain a quasi – continuous strain distribution a very dense grid of strain gauges or rosettes is necessary. Strain measurement with a large number of strain gauges and rosettes is a time consuming and expensive task that could be minimized with the use of distributed strain measurement systems.
To fulfil the first objective two eco panels will be tensile and compression tested in a MTS 2.5MN system. Text fixtures will be designed and produced according the interface areas previously defined together with the Topic Manager.
For the second objective, two distributed strain measurement systems will be used: Photogrametry (ARAMIS) and Fibre Optic Sensors (FBG). The developed measurement procedure will be validated with the readings of the classic strain measurement sensors: Strain gauges and rosettes.
Traditional aircraft structures use Aluminium stiffened panels for fuselage, wing and tail plane skins. In recent years, as composite materials become more prevalent in modern aircraft structures, stiffened skin panels are made of composite materials instead of Aluminium due to its light weight and therefore its fuel consumption reduction.
Composites materials traditionally require expensive and polluting manufacturing techniques that shadow the possible advantages of these theoretically greener kinds of materials. Due to these composite materials’ limitations, new methodologies are intended to solve the named problems.
In the present project, comparison between different Liquid Resin Infusion manufacturing processes (one-shot stringer and panel infusion vs. bonded stringer over infusion panel) has been done in the common playground of structural testing. Two geometrically similar wing skin panel coupons were manufactured and tested for quantifying their performance. Moreover, a third panel with different geometry but same manufacturing technique was tested as well.
Transducers and instrumentation in Structural Testing is a wide field in which several measurement techniques can be applied for every magnitude to measure. These options have different advantages and disadvantages, which leads to an unknown most convenient or feasible option to employ.
Thus, further comparison for conventional (Contact measures, Extensometry, etc.) and new measurement techniques (Digital Image Correlation, Optical Fibre, etc.) is needed in order to classify and organize the most appropriate and efficient option for the every project.
The ACID project explored and analysed these topics on the frame of the project. Tasks done on this project has a double value:
First, perform an evaluation of the manufacturing techniques that are the trend in the present aeronautical materials. Failure Load and mode are the key points for comparing. This knowledge will settle these novel manufacturing techniques and its results and will lead to further material and processes development.
Second, to realize a benchmarking for the measurement devices that has applicability in the Aeronautical Structural Testing. Cross comparison will prove the most convenient system for the study case and will give an assessment for the deviations of the readings. Advantages and disadvantages for the measurements are highlighted.