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

Guiding adults impartially : a Scottish study

In Scotland, the development of guidance for adults has been significant in the last few years. A 1992 Inspectorate report concluded that: 'Considerable progress has been made in developing effective arrangements for student guidance' (SOED, 1992: 36). However, the same document also called for improved pre-entry guidance and better course induction, the development of policy statements on guidance, and the commitment of resources to improving facilities, staff training and advocating. Since 1993, the Scottish Office-backed Adult Guidance Initiative-Scotland (AEGIS) has been responsible for raising awareness about good practice in guidance, and has produced policy documents and staff development materials on quality assurance and networking and held a number of national conferences. Researchers at the Scottish Council for Research in Education published four major studies in 1993-4, describing the experiences of adult returners, patterns of progression in post-school education and adult guidance practice. In 1996, the Scottish Office published strategy proposals for adult guidance, to include a telephone helpline (SOEID, 1996). TI1is was followed by an action plan on lifelong learning and guidance, including support for local guidance networks and increased marketing of learning opportunities (SOEID, 1997a and 1997b). Further research reports on the provision of guidance as part of access to higher education in Scotland were also published in 1996 (Blencowe et al, 1996; Blair and Tett, 1996). This article is based on research carried out to investigate the extent to which the principle of impartiality is perceived to be relevant and applicable by guidance practitioners in their work with adults. Guidance professionals have drawn attention to the importance of impartiality as a basic principle governing their practice. Also, the imperative of giving adults information and advice which is impartial and not influenced, for example, by recruitment targets for courses, is stressed in statements of good practice and practitioners' charters. The person-centred counselling approach underpinning these statements and charters tends to be strongly 'non-directive'. Guidance services have developed considerably in the last few years, but there is increasing competition between course providers and this has raised concerns about jeopardising impartiality

Design specifications for hardware assisted rollback computation

Journal ArticleAn overview of rollback computation is given, followed by a series of possible design strategies to implement rollback computations in hardware. Design issues and trade-offs are examined for each of the strategies as an iteration to the chosen strategy. The implementation of the chosen strategy is discussed along with an outline of remaining work

Leadership for innovation – why manufacturing has a future in Australia

In this paper, business leaders discuss the leadership styles they have used to ensure their companies are manufacturing success stories, and then these experiences are analysed to outline the leadership needs for innovation in Australia. Introduction With dire predictions about the future of manufacturing in Australia, we should remember that manufacturing has been an important contributor to national development. There was a thriving manufacturing industry up to 1945, sufficient to supply most domestic needs. Post-war, new industries flourished and a golden era of manufacturing followed. By the late 1950s manufacturing accounted for 29% of Australia’s GDP. By the 1960s, growth and productivity was faltering and manufacturing had begun to stagnate. Today, manufacturing accounts for less than 10% of Australia’s GDP, the lowest level since early colonial times. This is due, in large part, to global economic changes and the economic processes of comparative advantage. However, the innovative spirit that drove previous successes remains and a new generation of leaders and enterprises has emerged. Two of these innovative leaders presented case studies of their firms at a Swinburne Leadership Dialogue in June 2014. Richard Simpson of Furnace Engineering and Robert Wilson of the Wilson Transformer Company discussed the leadership styles and approaches they have used to ensure their companies are – and remain – national manufacturing success stories. Scott Thompson-Whiteside of Swinburne University of Technology then analyses their experiences to outline the leadership needs for innovation in Australia

Real and Virtual Nucleon Compton Scattering in the Perturbative Limit

We present the results of calculations analyzing nucleon Compton scattering to lowest order using perturbative QCD (pQCD) methods. Two scenarios are considered: (1) the incoming photon is real; and (2) the incoming photon is virtual. The case of a real photon has been previously analyzed at least 5 times using pQCD, but no two results are in agreement. Here it is shown that our result agrees with that of Brooks and Dixon published in 2000. The case of a virtual photon has been previously analyzed only once using pQCD. However, doubt has been cast on the validity of that result. The results presented here for virtual photon are believed to be more reliable. Some consideration is given of how to compare these results with experiment. Following the lead of Brooks and Dixon, for the proton, this involves normalizing the cross section using the Dirac proton form factor, which we also calculate. Finally, there is a comparison of our results with recent experiments.Comment: 36 pages, 11 figure

Development of a Finite Element Analysis Methodology for the Propagation of Delaminations in Composite Structures

Analysing the collapse of skin-stiffened structures requires capturing the critical phenomenon of skin-stiffener separation, which can be considered analogous to interlaminar cracking. This paper presents the development of a numerical approach for simulating the propagation of interlaminar cracks in composite structures. A degradation methodology was applied in MSC.Marc that involved modelling the structure with shell layers connected by user-defined multiple point constraints (MPCs). User subroutines were written that apply the Virtual Crack Closure Technique (VCCT) to determine the onset of crack growth, and modify the properties of the user-defined MPCs to simulate crack propagation. Methodologies for the release of failing MPCs are presented and are discussed with reference to the VCCT assumption of self-similar crack growth. Numerical results applying the release methodologies are then compared with experimental results for a double cantilever beam specimen. Based on this comparison, recommendations for the future development of the degradation model are made, especially with reference to developing an approach for the collapse analysis of fuselage-representative structures

Methane Production by a Packed-Bed Anaerobic Digester Fed Dairy Barn Flush Water

Packed-bed digesters are an alternative to covered lagoon digesters for methane production and anaerobic treatment of dilute wastewaters such as dairy barn flush water. The physical media of packed-beds retain biofilms, often allowing increased treatment rates. Previous studies have evaluated several types of media for digestion of dilute wastewaters, but cost and media fouling have setback commercial development. A major operational cost has been effluent recirculation pumping. In the present effort, a novel approach to anaerobic digestion of flush dairy water was developed at pilot-scale: broken walnut shells were used as a low-cost packed-bed medium and effluent recirculation was replaced by reciprocation mixing to decrease pumping costs and the risk of media clogging. Three packed-bed digesters containing walnut shells as media were constructed at the on-campus dairy and studied for about six months. Over that time, several organic loading rates (OLRs), measured as both chemical oxygen demand (COD) and volatile solids (VS) were applied to the new packed-bed digesters to allow modeling of methane production. The influence of temperature on methane production was also investigated. Additionally, the study measured solids accumulation in the walnut shell packed-bed as well as the effectiveness and durability of walnut shells as packing media. Finally, a simple economic analysis was developed from the methane model to predict the financial feasibility of packed-bed digesters at flush water dairies under similar OLR conditions. Three methane production models were developed from organic loading: saturation-type (following the form of the Monod equation), power and linear. The models were evaluated in terms of regression analysis and the linearity of experimental to predicted methane production. The best model was then chosen to develop the economic predictions. Economic predictions for packed-bed digesters were calculated as internal rate of return (IRR) using the methane models along with additional input variables. Comparisons of IRRs were made using electric retail rates of $0.10 to$0.20 per kilowatt-hour and capital cost subsidies from zero to 50%. Sludge accumulation in the packed-bed was measured via change in porosity, and walnut shell durability was measured as the change in mass of representative walnut shells over the course of the study. The linear-type model of methane production from volatile solids OLR best represented this data set. Digester temperature was not found to influence methane production in this study, likely due to the small daily average ambient temperature range experienced (14°C to 24°C) and the greater influence of organic loading. Porosity of the walnut shell packed-bed decreased from 0.70 at startup to 0.34±0.06 at the end of the six-month study, indicating considerable media fouling. Sludge accumulated in each digester from zero at startup to 281±46 liters at termination. Walnut shells in the packed-bed lost on average 31.4±6.3% mass during the study period which may be attributed to degradation of more readily bio-degradable cellulose and hemi-cellulose within the walnut shells. Given the predicted methane production and media life, at present, the economic outlook for packed-bed digesters at commercial dairies is quite dependent on utility electrical rates, available subsidies and future improvements to packed-bed digester technology. The predicted IRRs ranged from below 0% (at 0% capital subsidy and $0.10/kWh) up to 25$0.20/kWh) at large dairies (3000 milking cows). Increases in organic loading were not shown to necessarily increase IRR, particularly at OLRs above 10 g/Lliquid-d (as COD or VS). Ultimately, to better assess the value of packed-bed digesters for flush dairies, additional study is needed on topics such as sludge accumulation prevention, long-term walnut shell degradation, dairy barn flush water mixing, and more detailed economic analysis

Laser interferometric holography investigation of free convection about a vertical plate of non-uniform temperature

An experimental investigation was conducted using a holographic interferometer to detect the temperature variation in a free convection boundary layer about a vertical heated plate. The heated plate was non-isothermal and investigations were conducted for four temperature distributions; the maximum plate temperature ranged from 200F to 493F. Photographs were taken of the fringe patterns and boundary layer thickness measurements, as well as temperature measurements, were made. A theoretical model was constructed by applying the integral method to the energy and momentum equations. The experimental values agree quite well with this model. The advantages of the holographic interferometer over other systems are discussed --Abstract, page ii