AN AUTOMATED ASSESSEMENT TOOL OF NLF CRITERIA FOR AIRFRAME JOINTS

An ever increasing awareness of the ecological impact of air travel and associated regulatory measures demands for a cut in aircraft fuel consumption to reduce CO2 emissions and operating costs. Among improvements in engine technology or use of alternative fuels, the sustainment of laminar flow on surface areas of transport aircraft is seen as an important contribution to the solution of this challenge. The reduced friction drag of a natural laminar flow (NLF) wing can lead to a reduction in fuel consumption and thus reduction of CO2 emissions of up to 8 % on aircraft level [1]. Laminar flow's sensitivity to surface disturbances however requires specific shapes and high surface quality: Structural features like steps, gaps and surface waviness can cause early laminar/turbulent transition [2]. This calls for novel structural design concepts for laminar flow applications and tools to enable their practical implementation in aircraft operation. Through the course of several national and EU-funded projects, a multi-material leading edge concept using CFRP with an integrally bonded steel foil erosion shielding is being developed by DLR [3] with a distinct focus on operability. The leading edge and an associated interchange-enabling attachment concept are realized in a 2.3 m ground based demonstrator representing an outer wing section. A test stand is designed to recreate "wing on ground" and "cruise flight" surface deformations to enable interchange trials of the leading edge [4]. To enable an assessment against NLF criteria of the achieved step at the joint between leading edge and wing cover, an automated step measurement tool is developed and verified against manual assessments. Such a tool is a necessary step not only to validate suitability to support NLF on aircraft wings of the leading edge design and attachment concept. It also serves as a key contribution to a possible closed loop system supporting the assembly of airframe structures with intended laminar flow characteristics by providing direct feedback of the surface quality and informing on necessary adjustments to be made by the technicians. The paper will focus on the development of the assessment tool, framed by the results it delivered on the NLF leading edge installation trials

On measuring laminate strains of a bent tapered Double-Double panel – Comparing strain data from an FE calculation, a high-resolution 3D camera system (ARAMIS) and a fiber-optical sensor system (FOSS)

The article reports on a preliminary experimental study, which was executed to validate the laminate tapering approach for Double-Double (DD) laminates A cantilever scenario is examined, in which a defined vertical tip displacement is applied to a panel, whose shape is evaluated. Therefore, FE model predictions are compared with the real shape of correspondingly manufactured panels. The second ambition of the study was to validate the strain output of a novel fiber-optical sensor system (FOSS). For this purpose, fiber-optical sensors were embedded during manufacturing in the tapered DD panel. Three fiber sensors were positioned at different locations within the tapered laminate stack. They provide continuous strain information along their entire length, with a resolution of approximately 0.6 mm. The 500 mm long panel has been subjected by a 50 mm tip displacement, while strain is evaluated along the bent. The panel’s top-surface strain is additionally measured using a novel 24M GOM ARAMIS system. A comparison of the determined strain distributions from FE analysis (ABAQUS), FOSS and the optical measurement represents the core of the present article. Additional tests were executed to assess the strain data quality for different sensor-application approaches. Integrated and attached sensors are compared

Concept development of a visual assistance system for manual scarf repairs of composite structures made of fibre reinforced plastics

Manual repairs of composite structures are state-of-the-art across various industries. Regarding scarf repairs of carbon fibre reinforced plastics in particular, the underlying manual grinding process is time-consuming and therefore cost-intensive. Furthermore the grinding quality is inconstant and the achievable accuracy is limited. Due to multiple technological challenges in the automation of scarf repairs a largely manual execution can be expected to remain in the future. A concept of a visual assistance system is presented, which can contribute to increase the process robustness and decrease the impact of individual capabilities. This system scans the actual shape of the repair area and compares it to a reference geometry. An integrated projector displays the result on the processed surface by using a multi-colour scheme. Thereby the technician obtains a feedback about the current state of the grinding process. A first experimental test of the system demonstrates the principle feasibility of the assistance concept. Based on these results the potential for improvements of the process performance is shown and further development needs are derived

Digital Image Correlation Strain Measurement of Thick Adherend Shear Test Specimen Joined with an Epoxy Film Adhesive

Abstract Structural bonding and bonded repairs of composite materials become more and more important. Understanding the strain within the bondline leads to suitable bonding design. For new design approaches the strain distribution within the bondline has to be analyzed. Thus, often finite element analysis (FE) are used. However, a huge challenge is the availability of reliable material properties for the adhesives and their validation. Previous work has shown that it is possible to measure the small displacements resulting within thin epoxy film adhesives using high resolution digital image correlation (DIC). In this work a 2D DIC setup with a high resolution consumer camera is used to visualize the strain distribution within the bondline over the length of the joint as well as over the adhesive thickness. Therefore, single lap joints with thick aluminum adherends according to ASTM D 5656 are manufactured and tested. Local 2D DIC strain measurements are performed and analyzed. Two different camera setups are used and compared. The evaluation provides reliable material data and enables a look insight the bondline. The results of the full field strain data measured with DIC are compared with numerical simulations. Thus, material models as well as chosen parameters for the adhesive are validated. Compared to extensometers, giving only point-wise information for fixed measuring points, the DIC allows a virtual point-wise inspection along the complete bondline. Furthermore, it allows measuring close to the bondline to reduce the influence of adherend deformation

On-ground Testing of a Laminar Flow Wing Leading Edge

Natural laminar flow on surface areas of transport aircraft is seen as an important contribution to reduction of air travel`s CO2 emissions. Through the course of several national and EU-funded projects, a multi-material leading edge concept was developed and built by the German Aerospace Center, DLR. To validate the design and to demonstrate operational applicability of the leading edge and its specialized NLF compatible attachment concept, a test stand was designed. Capable of deforming a 2.3m Ground Based Demonstrator outer wing section to different surface deformation states, this test stand enables the analysis of the leading edge joint with the upper wing cover and the achieved aerodynamic step height under cruise deformations. It also enables the demonstration of the replacement of a damaged leading edge on a flexible wing on ground

Energy Efficiency of Sequence Alignment Tools - Software and Hardware Perspectives

Kierzynka M, Kosmann L, vor dem Berge M, et al. Energy Efficiency of Sequence Alignment Tools - Software and Hardware Perspectives. Future Generation Computer Systems. 2016;67:455-465

FPGA-accelerated Heterogeneous Hyperscale Server Architecture for Next-Generation Compute Clusters

Griessl R, Peykanu M, Hagemeyer J, et al. FPGA-accelerated Heterogeneous Hyperscale Server Architecture for Next-Generation Compute Clusters. Presented at the First International Workshop on Heterogeneous High-performance Reconfigurable Computing (H2RC‘15), held in conjunction with Supercomputing 2015, Austin Texas, USA

EVALUATION OF A VISUAL ASSISTANCE SYSTEM TO SUPPORT MANUAL SCARF REPAIRS FOR A DIGITALIZED AIRCRAFT MAINTENANCE

Currently, technicians for scarf repairs in aviation maintenance use their experience to assess the quality of the final scarf geometry. In this paper a visual assistance system is examined in pilot tests to evaluate whether visual feedback provides appropriate support for the technician and improves the scarf quality