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

Development of a Degradation Model for the Collapse Analysis of Composite Aerospace Structures

For stiffened structures in compression the most critical damage mechanism leading to structural collapse is delamination or adhesive disbonding between the skin and stiffener. This paper presents the development of a numerical approach capable of simulating interlaminar crack growth in composite structures as a representation of this damage mecha-nism. A degradation methodology was proposed using shell layers connected at the nodes by user-defined multiple point constraints (MPCs), and then controlling the properties of these MPCs to simulate the initiation and propagation of delamination and disbonding. A fracture mechanics approach based on the Virtual Crack Closure Technique (VCCT) is used to detect growth at the delamination front. Numerical predictions using the degradation methodology were compared to experimental results for double cantilever beam (DCB) specimens to dem-onstrate the effectiveness of the current approach. Future development will focus on address-ing the apparent conservatism of the VCCT approach, and extending the application of the method to other specimen types and stiffened structures representative of composite fuselage designs. This work is part of the European Commission Project COCOMAT (Improved MA-Terial Exploitation at Safe Design of COmposite Airframe Structures by Accurate Simulation of COllapse), an ongoing four-year project that aims to exploit the large strength reserves of composite aerospace structures through more accurate prediction of collapse

Six different football shoes, one playing surface and the weather; Assessing variation in shoe-surface traction over one season of elite football

<div><p>Introduction</p><p>An optimal range of shoe-surface traction (grip) exists to improve performance and minimise injury risk. Little information exists regarding the magnitude of traction forces at shoe-surface interface across a full season of elite football (soccer) using common football shoes.</p><p>Objective</p><p>To assess variation in shoe-surface traction of six different football shoe models throughout a full playing season in Qatar encompassing climatic and grass species variations.</p><p>Methods</p><p>Football shoes were loaded onto a portable shoe-surface traction testing machine at five individual testing time points to collect traction data (rotational and translational) on a soccer playing surface across one season. Surface mechanical properties (surface hardness, soil moisture) and climate data (temperature and humidity) were collected at each testing time point.</p><p>Results</p><p>Peak rotational traction was significantly different across shoe models (F = 218, df = 5, p <0.0001), shoe outsole groups (F = 316.2, df = 2, p < .0001), and grass species (F = 202.8, df = 4, p < 0.0001). No main effect for shoe model was found for translational traction (F = 2.392, p = 0.07).</p><p>Conclusions</p><p>The rotational (but not translational) traction varied substantially across different shoe types, outsole groups, and grass species. Highest rotational traction values were seen with soft ground outsole (screw-in metal studs) shoes tested on warm season grass. This objective data allows more informed footwear choices for football played in warm/hot climates on sand-based elite football playing surfaces. Further research is required to confirm if these findings extend across other football shoe brands.</p></div

Fifth metatarsal stress fracture in elite male football players:An on-field analysis of plantar loading

ObjectiveEvaluate plantar loading during ‘on-field’ common football movements in players after fifth metatarsal (MT-5) stress fracture and compare with matched healthy players.MethodsFourteen elite male soccer players participated in the study conducted on a natural grass playing surface using firm ground football boots. Seven players who had suffered a primary stress fracture (MT-5 group) and seven matched healthy players (controls, CON) performed three common football movements while in-shoe plantar loading data were collected.ResultsLarge between-group differences exist for maximal vertical force normalised to bodyweight (Fmax) at the lateral toes (2-5) of the stance leg during a set-piece kick (MT-5: 0.2±0.06 bodyweight (BW), CON: 0.1±0.05 BW, effect size (ES) 1.4) and the curved run where the MT-5 group showed higher Fmaxwith very large effect size at the lateral forefoot of the injured (closest to curve) limb when running a curve to receive a pass (MT-5 injured−CON=0.01 BW, ES 1.5). Small between-group differences were evident during straight-line running. However, between-limb analysis of MT-5 group showed significant unloading of the lateral forefoot region of the involved foot.ConclusionsElite male football players who have returned to play after MT-5 stress fracture display significantly higher maximum plantar force at the lateral forefoot and lateral toes (2-5) compared with healthy matched control players during two football movements (kick and curved run) with the magnitude of these differences being very large. These findings may have important implications for manipulating regional load during rehabilitation or should a player report lateral forefoot prodromal symptoms.</jats:sec

Current Trends and Future Challenges in the Freight Railroad Industry: Balancing Private Industry Interests and the Public Welfare

Deregulation has put the freight railroad industry on a more secure financial footing. In general, the transformation of the rail industry since the Staggers Rail Act of 1980 has been viewed by stakeholders at many levels as verwhelmingly positive. Perhaps most important to note is that deregulation has allowed the rail industry to fully realize the benefits of operating as a private business — cutting costs, boosting productivity, eliminating unprofitable lines, and gaining a higher degree of business autonomy. One consequence of this reduction in physical capacity is that often only one railroad company's lines run on a particular route, resulting in monopolistic pricing practices

Trematodes of the Great Barrier Reef, Australia: emerging patterns of diversity and richness in coral reef fishes

The Great Barrier Reef holds the richest array of marine life found anywhere in Australia, including a diverse and fascinating parasite fauna. Members of one group, the trematodes, occur as sexually mature adult worms in almost all Great Barrier Reef bony fish species. Although the first reports of these parasites were made 100 years ago, the fauna has been studied systematically for only the last 25 years. When the fauna was last reviewed in 1994 there were 94 species known from the Great Barrier Reef and it was predicted that there might be 2,270 in total. There are now 326 species reported for the region, suggesting that we are in a much improved position to make an accurate prediction of true trematode richness. Here we review the current state of knowledge of the fauna and the ways in which our understanding of this fascinating group is changing. Our best estimate of the true richness is now a range, 1,100–1,800 species. However there remains considerable scope for even these figures to be incorrect given that fewer than one-third of the fish species of the region have been examined for trematodes. Our goal is a comprehensive characterisation of this fauna, and we outline what work needs to be done to achieve this and discuss whether this goal is practically achievable or philosophically justifiable

Unraveling the mysteries of dog evolution

The increased battery of molecular markers, derived from comparative genomics, is aiding our understanding of the genetics of domestication. The recent BMC Biology article pertaining to the evolution of small size in dogs is an example of how such methods can be used to study the origin and diversification of the domestic dog. We are still challenged, however, to appreciate the genetic mechanisms responsible for the phenotypic diversity seen in 'our best friend'

Targeted Expression of Cre Recombinase Provokes Placental-Specific DNA Recombination in Transgenic Mice

Background: Inadequate placental development is associated with a high incidence of early embryonic lethality and serious pregnancy disorders in both humans and mice. However, the lack of well-defined trophoblast-specific gene regulatory elements has hampered investigations regarding the role of specific genes in placental development and fetal growth. Principal Findings: By random assembly of placental enhancers from two previously characterized genes, trophoblast specific protein a (Tpbpa) and adenosine deaminase (Ada), we identified a chimeric Tpbpa/Ada enhancer that when combined with the basal Ada promoter provided the highest luciferase activity in cultured human trophoblast cells, in comparison with non-trophoblast cell lines. We used this chimeric enhancer arrangement to drive the expression of a Cre recombinase transgene in the placentas of transgenic mice. Cre transgene expression occurred throughout the placenta but not in maternal organs examined or in the fetus. Significance: In conclusion, we have provided both in vitro and in vivo evidence for a novel genetic system to achieve placental transgene expression by the use of a chimeric Tpbpa/Ada enhancer driven transgene. The availability of thi

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

Polyamine-dependent regulation of spermidine-spermine N-1-acetyltransferase mRNA translation

Spermidine-spermine N-1-acetyltransferase (SSAT) is induced in response to an elevation in intracellular polyamine pools. The increased enzyme activity is the result of an increase in gene transcription, mRNA translation, and protein stability. Induction of SSAT by polyamine analogues can lead to intracellular polyamine depletion and apoptosis. The mechanism by which polyamines alter the translational efficiency of SSAT mRNA is not well understood. In this study, we investigated the regulation of SSAT translation by the polyamine analogue N-1,N-11-diethylnorspermine ( DENSPM). DENSPM induced expression of both FLAG-tagged SSAT and SSAT fused to Renilla luciferase in a time- and concentration-dependent manner. This effect was not inhibited by actinomycin D indicating that changes in gene transcription did not explain the enhanced expression in the presence of DENSPM. Furthermore, because FLAG-SSAT did not contain the 5'- or 3'-untranslated regions of SSAT, translational regulation involved the coding sequence only. By contrast, cycloheximide completely inhibited induction by DENSPM, indicating a requirement for new protein synthesis. Deletion constructs identified two regions of the SSAT protein-coding RNA sequence that conferred polyamine responsiveness. Using these regions as probes in RNA electrophoretic mobility shift assays, we observed specific binding of a cytoplasmic protein. In addition, we found that the interaction between the RNA probes and the binding protein could be inhibited by DENSPM in a concentration-dependent manner. These results suggest that polyamines regulate SSAT mRNA translational efficiency by inhibiting a repressor protein from binding to regions of the coding sequence of the SSAT transcript