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

Passive in Nature: How May Swenson Approaches the Natural World

The poet May Swenson speaks frequently of the relationship of humans and the environment, as her speakers attempt connection with the natural world. Various studies in ecocriticism have argued whether humankind is \u27part of or apart from the natural world,\u27 and how the former association of which can lead to an unhealthy over-revering of nature (Orr). The latter viewpoint, \u27apart from,\u27 has become more prevalent now that our planet has entered the Anthropocene, described as \u27our contemporary geologic era, marked by humanity\u27s fateful emergence as a climatological force\u27 intent on obtaining the world\u27s resources (Marrs 201). Swenson places humankind\u27s reverence for nature at a level attaining the spiritual in her poems \u27Sunday in the Country\u27 and \u27Summer in New Hampshire,\u27 and pronounces humankind\u27s desire to capture and cultivate the natural world as they see fit in \u27The Red Bird Tapestry\u27 and \u27Another Spring Uncovered.\u27 Swenson\u27s approach to the natural elements within the poems, however, actually strive for a harmonious and equal relationship. Her speakers observe and interact with nature by taking a passive role, sometimes offering up or sacrificing their own ways of being in an attempt at connection focused on humility. As the separation of human and natural worlds becomes ever more apparent through over-reverence, and as the current ecological climate moves further into the Anthropocene, examining Swenson\u27s passive take on cohabitation provides a new approach of equality in connecting to the natural world we are each a part of

Portrait of Rich County

Portrait of Rich County presents the small town of Randolph, Utah in poems describing its wildlife, recreational activities, and the perspectives of citizens in the contemporary rocky mountain west. Special attention to the imagination of the poems’ speaker toward the more dreamlike qualities of Rich County establishes itself throughout, in order to convey a feeling of hope within harsh terrain. This collection examines the theme of salvaging items not often considered, such as rusted junk, ancient houses, or roadside garbage, both in the actions of the speaker and through the act of naming these items upon the page. An over-arching theme, the ever present threat of death in isolation, contrasts the danger, remoteness and shocking weather of Rich County with its moments of beauty, sublimity and respite. In effect, a wider portrait is painted of the whole

Norse Women Cast Adrift: A Christian Literary Trope in the Sagas of Iceland

During the late Middle Ages, three literary sources present a Christian textual trope known as “the woman cast adrift.” This trope features a woman of saintly or other prominence, who is “cast” upon the sea in a boat often lacking a rudder, oars or a sail. By divine will, against the sea and its storms, the woman reaches her intended destination. While these prominent sources were written in western Europe from the fourteenth to fifteenth centuries, similar tales of “women castadrift” are present in the Norse sagas of Iceland and Greenland, written earlier during the thirteenth and early fourteenth centuries. Gudrid Thorbjarnardottir of the Vinland sagas especially shows this Christian trope occurring a century earlier within European texts. This presentation seeks to contextualize Gudrid as an earlier figure within the trope of “the woman cast adrift,” based upon the trope\u27s usual motifs. Presentation Time: Wednesday, 12-1 p.m. Zoom link: https://usu-edu.zoom.us/j/83570709111?pwd=dGpYQzZvT3dqdHdGNjMzaVZ3QnFLUT0

Self-Discovery, Self-Sufficiency: Assuming the Role of a Listener While Tutoring

My discovery of the method of student self-discovery in tutor sessions established itself early on in my path of wearing the ‘two different hats’ of tutor and lecturer. By forming a spiel that represents my own personality within established Writing Center philosophy, I attempt to allow the student to control the session and discover improvements of their paper on their own. I do so by taking the role of a listener, which may lend itself as well to my teaching endeavors

An estimator to reduce mail survey nonresponse bias in estimates of recreational catch: a case study using data from the Panulirus cygnus fishery of Western Australia

Accurate recreational catch estimates are important in fisheries management. The mail survey is an easy and low cost method for collecting data for making these estimates. Unfortunately, this survey method results in estimates that can be seriously affected by nonresponse bias. This research develops estimators that reduce this bias and demonstrates their effectiveness using the recreational western rock lobster fishery as a case study

N: A Sea Monster of a Research Project

Ever since time and the world began, dwarves have always fought cranes. Ever since ships set out on the northern sea, great sea monsters have risen to prey upon them. Such are the basics of life in medieval and Renaissance Scandinavia, Iceland, Scotland and Greenland, as detailed by Olaus Magnus\u27 Description of the Northern Peoples (1555), its sea monster-heavy map, the Carta Marina (1539), and Abraham Ortelius\u27 later map of Iceland, Islandia (1590). I first learned of Olaus and Ortelius in the summer of 2013, and while drawing my own version of their sea monster maps a thought hit me: write a book series, with teenage characters similar to those in How to Train Your Dragon, but set it amongst the lands described by Olaus, in a frozen world badgered by the sea monsters of OrteIius. I flipped the paper over and wrote the title: N, a symbol for all that a northern world of legend embodies. The aim of this project was to plan an epic fantasy adventure novel based upon the teachings and maps of Olaus and Ortelius, as well as the real history, culture, mythology and cryptozoology of Scandinavia, Iceland, Scotland and Greenland, and discover how to adapt these sources into my fictional text. The research I have done concerning these 95 separate concepts as I call them, five of which I have written within scenes, has beautifully bolstered by idea of how such items are adapted, and mapping out the chapter plots and arcs of my four characters has provided endless growth in both my idea of them and of myself. Drawing five of the sea monsters and including the sample chapter allowed me to truly judge the overall scope. This project not only taught me about novel writing, but how I can make N the best novel it can be

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

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

Electrocardiogram-gated Kilohertz Visualisation (EKV) Ultrasound Allows Assessment of Neonatal Cardiac Structural and Functional Maturation and Longitudinal Evaluation of Regeneration After Injury

The small size and high heart rate of the neonatal mouse heart makes structural and functional characterisation particularly challenging. Here, we describe application of electrocardiogram-gated kilohertz visualisation (EKV) ultrasound imaging with high spatio-temporal resolution to non-invasively characterise the post-natal mouse heart during normal growth and regeneration after injury. The 2-D images of the left ventricle (LV) acquired across the cardiac cycle from post-natal day 1 (P1) to P42 revealed significant changes in LV mass from P8 that coincided with a switch from hyperplastic to hypertrophic growth and correlated with ex vivo LV weight. Remodelling of the LV was indicated between P8 and P21 when LV mass and cardiomyocyte size increased with no accompanying change in LV wall thickness. Whereas Doppler imaging showed the expected switch from LV filling driven by atrial contraction to filling by LV relaxation during post-natal week 1, systolic function was retained at the same level from P1 to P42. EKV ultrasound imaging also revealed loss of systolic function after induction of myocardial infarction at P1 and regain of function associated with regeneration of the myocardium by P21. EKV ultrasound imaging thus offers a rapid and convenient method for routine non-invasive characterisation of the neonatal mouse heart