Advances in Stability of Composite Airframe Structures Regarding Collapse, Robust Design and Dynamic Loading

European aircraft industry demands for reduced development and operating costs, by 20% and 50% in the short and long term, respectively. Structural weight reduction by exploitation of structural reserves in composite aerospace structures contributes to this aim, however, it requires accurate and experimentally validated stability analysis of real structures under realistic loading conditions. This paper presents new achievements from the area of computational and experimental stability research of composite aerospace structures which contribute to that field. The first two topics focus on stringer stiffened panels and the last one on imperfection sensitive unstiffened cylinders. Section 1 presents selected results achieved in the finished EU project COCOMAT, which deals with an accurate and reliable simulation of collapse. The main objective of COCOMAT is a future design scenario which exploits considerable reserves in fibre composite fuselage structures by accurate simulation of collapse. The project results comprise an experimental data base, improved slow and fast computational tools as well as design guidelines. In today’s design process dynamic loading, e.g. due to gusts or landing impact, is assumed to be uncritical, since the dynamic process increases buckling stability. Section 2 shows that rapidly applied loading of stiffened panels can yield critical dynamic behavior in the postbuckling regime. When applying the new design philosophy it has either to be assured that these critical interactions do not occur under the loading velocities to be expected, or they have to be taken into consideration. Section 3 presents a recently developed approach for unstiffened shells which are usually susceptible to imperfections. This robust design approach is based on a single buckle as the worst imperfection mode leading directly to the load carrying capacity of a cylinder. It also promises to improve the knock-down factors which are according the current guidelines very conservative. Future work should facilitate full applicability of the analysis methods in preliminary design. For that purpose speed of the collapse analysis of stiffened panels needs to be increased and for collapse simulation degradation must be taken into account. The application field of the robust design method should be widened towards imperfection sensitive stiffened shells (skin-dominant designs)

Search for High-Mass States with Lepton Plus Missing Transverse Energy Using the ATLAS Detector at Center-of-Mass Energy of 7 TeV

The ATLAS detector has been used to search for high-mass states decaying into a single high momentum lepton and missing transverse energy, such as new heavy charged gauge bosons. The latest search results for a W Prime boson decaying to lepton plus neutrino in 1.04 fb^-1 of proton-proton collisions at a center of mass energy of 7 TeV produced at the Large Hadron Collider are presented.Comment: 8 pages, 10 figures, to be included in APS-DPF 2011 Proceeding

The social costs of climate change: A critical examination

There is a growing body of literature on economic aspects of global warming Whereas the research in greenhouse gas (GHG) abatement costs has provided many studies, the question of greenhouse damage valuation has gained little attention yet Ongoing the first section of this paper provides a brief overview of the main results relating to the costs of reducing CO2 emission. Afterwards the main interest is focused to the benefits of emission abatement, defined as the benefits from avoided damages. A synthesis of both costs and benefits is to find an economical\y efficient war for the optimum amongst emission abatement and not avoided damages otherwise. Guided by the mainly applied Cost-Benefit-Analysis (CBA), there are several examinations to evaluate the social costs of greenhouse gas emissions. Finally same criticism related to the here presented and often applied Cost-Benefit-Approach as well as an outlook will follow. --

Simulating Postbuckling Behaviour and Collapse of Stiffened CFRP Panels

Advanced composite materials are well known for their outstanding potential in weight-related stiffness and strength leading to an ever increasing share in aerospace structural components out of Carbon Fibre Reinforced Plastics (CFRP). In order to fully exploit the load-carrying capacity of such structures an accurate and reliable simulation is indispensable. Local buckling is not necessarily the load bearing limit for stiffened panels or shells; their full potential can be tapped only by utilizing the postbuckling region. That, however, requires fast tools which are capable of simulating the structural behaviour beyond bifurcation points including material degradation up to collapse. The most critical structural degradation mode is skin stringer separation; delamination, especially within the stringer, is a critical material degradation. A reliable prediction of collapse requires knowledge of degradation due to static as well as low cycle loading in the postbuckling region. Earlier projects have shown that it needs considerable experience in simulating the postbuckling behaviour. Though a great deal of knowledge about CFRP structural and material degradation is available its influence on collapse is not yet sufficiently investigated. It is the aim of the project COCOMAT (Improved MATerial exploitation at safe design of COmposite airframe structures by accurate simulation of COllapse) to develop means for and gain experience in fast and accurate simulation of the collapse load of stringer stiffened CFRP curved panels taking degradation and cyclic loading as well as geometric nonlinearity into account. COCOMAT is a Specific Targeted Research Project supported by the EU 6th Framework Programme; it started 2004 and runs for 4 years. Main deliverables are: • test results for buckling and collapse of undamaged and pre-damaged stiffened CFRP panels under static and cyclic loading, • improved material properties and degradation models, computational tools for design and certification of stiffened fibre composite panels which take postbuckling behaviour, degradation and collapse into account, • and finally design guidelines and industrial validation. The work will lead to an extended experimental data base, relevant degradation models and improved simulation tools for certification as well as for design. These results should allow setting up a future design scenario which exploits the existing reserves in primary fibre composite structures. The paper starts out from results provided by the forerunners of COCOMAT, describes the main objectives of the project, gives a general status of the progress reached so far and presents first results

The use of damage as a design parameter for postbuckling composite aerospace structures

Advanced fibre-reinforced polymer composites have seen a rapid increase in use in aircraft structures in recent years due their high specific strength and stiffness, amongst other properties. The use of postbuckling design, where lightweight structures are designed to operate safely at loads in excess of buckling loads, has been applied to metals for decades to design highly efficient structures. However, to date, the application of postbuckling design in composite structures has been limited, as today’s analysis tools are not capable of representing the damage mechanisms that lead to structural collapse of composites in compression. The currently running four-year European Commission Project COCOMAT [1] is addressing this issue, and aims to exploit the large strength reserves of composite aerospace structures through a more accurate prediction of collapse. A methodology has been developed to analyse the collapse of composite structures that is focused on capturing the critical damage mechanisms. One aspect of the methodology is a global-local analysis technique that uses a strength criterion to predict the initiation of interlaminar damage in intact structures. Another aspect of the approach was developed for representing the growth of a pre-existing interlaminar damage region, and is based on applying multi-point constraints in the skin-stiffener interface that are controlled using fracture mechanics calculations. A separate degradation model was also included to model the in-plane ply damage mechanisms of fibre fracture, matrix cracking and fibre-matrix shear that uses a progressive failure approach. The complete analysis methodology was implemented in MSC.Marc v2005r3 using several user subroutines, and has been validated with a range of experimental tests, including fracture mechanics coupons [2], single-stiffener specimens [3] and multi-stiffener curved panels [4]. The developed methodology was used to design and analyse fuselage-representative composite panels in various pre-damaged configurations. Two panel designs were investigated, D1 and D2, which both consisted of a curved skin adhesively bonded to blade-shaped stiffeners. For the D1 panel, the pre-damage applied was a full-width skin-stiffener debond created using a Teflon insert in the adhesive layer, whilst the D2 panel was investigated with Barely Visible Impact Damage (BVID). For both panels, parametric studies were conducted using the developed methodology in order to recommend a damaged configuration suitable for experimental testing. For the D1 panel, a 100 mm length debond was selected, and the location of the damage was investigated, whilst for the D2 panel both the location and the representation of damage was varied. Based on these parametric studies, two pre-damaged configurations of the D1 panel and one pre-damaged D2 configuration were selected for experimental testing. The selected pre-damaged configurations were manufactured by Aernnova Engineering Solutions and manufactured at the Institute of Composite Structures and Adaptive Systems at the German Aerospace Center (DLR) as part of the COCOMAT project. Following manufacture, panel quality was inspected with ultrasonic and thermographic scanning and panel imperfection data was measured using the three-dimensional (3D) optical measurement system ATOS. During the test, measurements were taken using displacement transducers, strain gauges, the 3D optical measuring system ARAMIS, and optical lock-in thermography. Under compression, the panels developed a range of buckling mode shapes, and the progression of damage was monitored leading to structural collapse. In comparison with the experimental results, the analysis methodology was shown to give accurate predictions of the load-carrying behaviour, damage development and collapse load of both panels. The results demonstrated the capability of the developed tool to capture the critical damage mechanisms leading to collapse in composite structures. The advanced analysis methodology also allowed for damage to be used as a design parameter in postbuckling structures, either in the comparative analysis context of a design procedure, to assess the damage tolerance of a design, or as pre- and post-test simulations of intact and pre-damaged structures. More broadly, the results demonstrated the potential of postbuckling composite structures, and the large strength reserve available in the postbuckling region. The success of the developed analysis methodology and the potential of postbuckling composite structures have application for the next generation of lightweight aerospace structures

Design and Analysis of Composite Panels

European aircraft industry demands for reduced development and operating costs, by 20% and 50% in the short and long term, respectively. Contributions to this aim are provided by the completed project POSICOSS (5thFP) and the running follow-up project COCOMAT (6thFP), both supported by the European Commission. As an important contribution to cost reduction a decrease in structural weight can be reached by exploiting considerable reserves in primary fibre composite fuselage structures through an accurate and reliable simulation of postbuckling up to collapse. The POSICOSS team developed fast procedures for postbuckling analysis of stiffened fibre composite panels, created comprehensive experimental data bases and derived design guidelines. COCOMAT builds up on the POSICOSS results and considers in addition the simulation of collapse by taking degradation into account. The results comprise an extended experimental data base, degradation models, improved certification and design tools as well as design guidelines. The projects POSICOSS and COCOMAT develop improved tools which are validated by experimental results obtained during the projects. Because the new tools must consider a wide range of different aspects a lot of different structures had to be tested. These structures were designed under different design objectives. For the design process the consortium applied already available simulation tools and brought in their own design experience. This paper deals with the design process within both projects and the analysis procedure applied within this task. It focuses on the experience of DLR on the design and analysis of stringer stiffened CFRP panels gained in the frame of these projects

TRTViewer: the ATLAS TRT detector monitoring and diagnostics tool

The transition radiation tracker (TRT) is the outermost of the three sub-systems of the ATLAS inner detector at the Large Hadron Collider (LHC) at CERN. It is designed to combine the drift tube tracker with the transition radiation detector, providing an important contribution to the charged particles precise momentum measurement and particle (mainly electron) identification. The TRT consists of a barrel section at small pseudorapidity (eta) and two separate end-cap partitions at large eta. The detector performance and its operational conditions were permanently monitored during all commissioning and data-taking stages using various software tools, one of which - TRTViewer - is described in the present paper. The TRTViewer is the dedicated program for monitoring the TRT raw data quality and detector performance at different hardware levels: individual straws, readout chips and electronic boards. The data analysis results can be presented on the event-by-event basis or in the form of color maps representing the operation parameters (efficiencies, timing, occupancy, etc.) according to the real geometrical position of the detector hardware elements. The paper describes the TRTViewer software package as the event displaying tool, raw data processor and histogram and operation parameters presenter, which works with the different sources of input information: raw data files, online monitoring histograms, offline analysis histograms and TRT DAQ Configuration database. The package proved to be one of the main instruments for the fast and effective TRT diagnostics during debugging and operation periods.Comment: 7 pages, 2 figures. Proc. of the 4th Workshop on Advanced Transition Radiation Detectors for Accelerator and Space Applications, Bari, Italy, Sept. 14-16, 2011. Submitted to Nucl. Instr. Meth.

Global behaviour of a composite stiffened panel in buckling. Part 1: Numerical modelling

The present study analyses an aircraft composite fuselage structure manufactured by the Liquid Resin Infusion (LRI) process and subjected to a compressive load. LRI is based on the moulding of high performance composite parts by infusing liquid resin on dry fibres instead of prepreg fabrics or Resin Transfer Moulding (RTM). Actual industrial projects face composite integrated structure issues as a number of structures (stiffeners, …) are more and more integrated onto the skins of aircraft fuselage. A representative panel of a composite fuselage to be tested in buckling is studied numerically. This paper studies which of the real behaviours of the integrated structures are to be observed during this test. Numerical models are studied at a global scale of the composite stiffened panel. Linear and non linear analyses are conducted. The Tsai–Wu criterion with a progressive failure analysis is implemented, to describe the global behaviour of the panel up to collapse. Also, three stiffener connection methods are compared at the intersection between two types of integrated structures. Load shortening curves permit to estimate the expected load and displacements

Probabilistic Approach for better Buckling Knock-down Factors of CFRP Cylindrical Shells - Tests and Analyses

The industry in the fields of civil and mechanical engineering, and in particular of aerospace demands for significantly reduced development and operating costs. Reduction of structural weight at safe design is one avenue to achieve this objective. The running ESA (European Space Agency) study Probabilistic Aspects of Buckling Knock Down Factors – Tests and Analyses contributes to this goal by striving for an improved buckling knock-down factor (the ratio of buckling loads of imperfect and perfect structures) for unstiffened CFRP (carbon fiber reinforce plastics) cylindrical shells, and by validation of the linear and non-linear buckling simulations based on test results. DLR is acting as study contractor. The paper presents an overview about the DLR buckling tests, the measurement setup and the buckling simulations which are done so far, and gives an outlook to the results which are expected until the end of the running project