Development of material models to predict the crashworthiness of tubes

Metallic tubes have been extensively studied for their crashworthiness as they closely resemble automotive crash rails. Recently, the demand to produce light weight yet safer vehicles has led to the need to understand the behaviour of novel materials such as composites, metallic foams and sandwich structures durign a crash. This paper presents a method to predict the crashworthiness of structural components using material modes. The material factors that most affect the crushing response are determined and quantified by developing and validating the crushing of a square tube model in Abaqus. The inputs from the model are used to construct a simple, physically realistic constitutive model and new test methods for predicting the material behaviour at high strain rates using low test speeds. These material models enable a designer to predict the crash behaviour of a structure without the need to perform extensive physical tests, thus reducing the time and cost of development.

Conductivity, NMR and crystallographic study of N,N,N,N-tetramethylammonium dicyanamide plastic crystal phases : an archetypal ambient temperature plastic electrolyte material

N,N,N,N-Tetramethylammonium dicyanamide (Me₄NDCA) has been examined via differential scanning calorimetry (DSC), thermogravimetric analysis, conductivity, single crystal X-ray diffraction and ¹H nuclear magnetic resonance (NMR) analyses, and was found to be highly conductive in the solid state (σ =10−3 S cm⁻² at 420 K) and to also exhibit unusual plastic crystal behaviour. To investigate the correlation between such behaviour and the occurrence of molecular rotations in the crystal, ¹H NMR second moment measurements are compared with calculated values predicted from the crystal structure. While DSC analysis indicates a number of solid–solid transitions at ambient temperatures, subsequent ¹H NMR analysis of the Me₄N⁺ cation shows that a variety of rotational motions become active at low (<240 K) temperatures, and that such transitions in rotational states occur over a range of temperatures rather than in a sharp transition. Conductivity analysis reveals that between 320 K and 420 K the conductivity increases by more than six orders of magnitude in the solid state, in line with the transition of the Me₄N⁺ cation to a diffusive state, and that other phase transitions observed in this temperature range have no marked effect on the conductivity. Conduction in this solid state is therefore envisaged to involve a vacancy-diffusion model, involving Me₄N⁺ cation vacancies.

The effect of skin passing on the material behavior of metal strip in pure bending and tension

The metal strip used in roll forming has often been preprocessed by (tension or roller) leveling or by skin-pass rolling, and as a consequence, may contain residual stresses. These stresses are not well observed by the tensile test, but could have a significant effect on the bending and springback behavior. With the advent of improved process design techniques for roll forming, including advanced finite element techniques, the need for precise material property data has become important. The major deformation mode of roll forming is that of bending combined with unloading and reverse bending, and hence property data derived from bend tests could be more relevant than that from tensile testing.

This work presents a numerical study on the effect of skin passing on the material behavior of stainless steel strip in pure bending and tension. A two dimensional (2-D) numerical model was developed using Abaqus Explicit to analyze the affect of skin passing on the residual stress profile across a section for various working conditions. The deformed meshes and their final stress fields were then imported as pre-defined fields into Abaqus Standard, and the post-skin passing material behavior in pure bending was determined. The results show that a residual stress profile is introduced into the steel strip during skin passing, and that its shape and stress level depend on the overall thickness reduction as well as the number of rolling passes used in the skin passing process. The material behavior in bending and the amount of springback changed significantly depending on the skin pass condition.

A heuristic model selection scheme for representing hot flow data using the hot torsion test results

The problem of "model selection" for expressing a wide range of constitutive behaviour adequately using hot torsion test data was considered here using a heuristic approach. A model library including several nested parametric linear and non-linear models was considered and applied to a set of hot torsion test data for API-X 70 micro-alloyed steel with a range of strain rates and temperatures. A cost function comprising the modelled hot strength data and that of the measured data were utilized in a heuristic model selection scheme to identify the optimum models. It was shown that a non-linear rational model including ten parameters is an optimum model that can accurately express the multiple regimes of hardening and softening for the entire range of the experiment. The parameters for the optimum model were estimated and used for determining variations of hot strength of the samples with deformation.

Found footage: recycling historic material a-historically

The digital has speeded up multi-platform image delivery, to impose sampling and collagic strategies into the way we process information. This is a trauma inducing situation. During an earlier period of technological change reading the moving landscape similarly overwhelmed the early train traveller. Wolfgang Schivelbusch noted that ‘The inability to acquire a mode of perception adequate to technological travel crossed all political, ideological and aesthetic lines.’ (1983) New perceptual strategies had to be developed that contextualized the blur and the streak produced by looking out the train window without overwhelming the viewer. Utilizing Chris Brewin’s (2001) model of two parallel memory systems, this paper argues that, as another round of unprecedented technological change impacts on our senses, another ‘re-alignment’ of the senses is required. Chris Brewin’s (2001) model of two parallel memory systems, of Verbally Accessible Memory (VAM) and Situational Accessible Memory (SAM), suggests that the current information explosion requires a greater emphasis on the SAM system for processing information and critical thinking. Processed through the amygdala, SAM is implicit, situationally triggered, information intensive and conveys no sense of time. Found footage films, like those of Martin Arnold and Peter Tscherkassky that cut up, layer, repeat and recycle historic imagery perform the sampling and collagic strategies that characterize this SAM memory system to demonstrate a more visually based mode of critical thinking.

Material world: learning and teaching chemistry

 In the Australian National Curriculum, the science understanding of overarching ideas of matter and energy covers science topics in the conceptual area of chemistry, such as the properties, forms and uses of different materials, the states of matter (solid, liquid and gas), and energy, such as forces, movement and electricity. This chapter focusses on explaining the abstract science ideas related to matter and energy through the use of appropriate vocabulary, examining ways of organising knowledge and linking scientific models and theories to observations and experiences. The particle model of matter is used to explain common observations, demonstrating the value of scientific inquiry and the role of models and representations in scientific thinking. A directed inquiry teaching approach in which there is a focus on the use of representations is recommended for these abstract topics. Representations are a vital component of communicating the abstract ideas of matter and energy. The use of the pedagogical approach in which students construct and evaluate representations of scientific ideas is used in the negotiation and development of their understandings.

Development of an inverse routine to predict residual stresses in the material based on a bending test

Bending and reverse bending are the dominant material deformations in roll forming, and hence property data derived from bend tests could be more relevant than tensile test data for numerical simulation of a roll forming process. Recent investigations have shown that residual stresses change the material behavior close to the yield in a bending test. So, residual stresses introduced during prior steel processing operations may affect the roll forming process, and therefore they need to be included in roll forming simulations to achieve improved model accuracy. Measuring the residual stress profile experimentally is time consuming and has limited accuracy while analytical models that are available require detailed information about the pre-processing conditions that is generally not available for roll forming materials. The main goal of this study is to develop an inverse routine that determines a residual stress profile through the material thickness based on experimental pure bend test data. A numerical model of the skin passing (temper rolling) process is performed to introduce a residual stress profile in DP780 steel sheet. The skin passed strips are used in a pure bending simulation to record moment-curvature data and this data is then applied in an inverse analysis to predict the residual stress profile in the material. Comparison of the residual stress profile predicted by the inverse routine with that calculated by finite element analysis (FEA) indicates an inverse approach combined with pure bend test may present an alternative to predict residual stresses in sheet metals.

Using the solid-shell element to model the roll forming of large radii profiles

Roll forming is an incremental bending process for forming metal sheet, strip or coiled stock. Although Finite Element Analysis (FEA) is a standard tool for metal forming simulation, it is only now being increasingly used for the analysis of the roll forming process. This is because of the excessive computational time due to the long strip length and the multiple numbers of stands that have to be modelled. Typically a single solid element is used through the thickness of the sheet for roll forming simulations. Recent investigations have shown that residual stresses introduced during steel processing may affect the roll forming process and therefore need to be included in roll forming simulations. These residual stresses vary in intensity through the thickness and this cannot be accounted for by using only one solid element through the material thickness, in this work a solid-shell element with an arbitrary number of integration points has been used to simulate the roll forming process. The system modelled is that of roll forming a V-channel with dual phase DP780 sheet steel. In addition, the influence of other modelling parameters, such as friction, on CPU time is further investigated. The numerical results are compared to experimental data and a good correlation has been observed. Additionally the numerical results show that the CPU time is reduced in the model without friction and that considering friction does not have a significant effect on springback prediction in the numerical analysis of the roll forming process.

Vibration based damage identification of a scale-model steel frame structure subjected to bolt connection failures

Large-span steel frame structures prove to be an ideal choice for their speed of construction, relatively low cost, strength, durability and structural design flexibility. For this type of structure, the beam-column connections are critical for its structural integrity and overall stability. This is because a steel frame generally fails first at its connectors, due to the change in stress redistribution with adjacent members and material related failures, caused by various factors such as fire, seismic activity or material deterioration. Since particular attention is required at a steel frame’s connection points, this study explores the applicability of a comprehensive structural health monitoring (SHM) method to identify early damage and prolong the lifespan of connection points of steel frames. An impact hammer test was performed on a scale-model steel frame structure, recording its dynamic response to the hammer strike via an accelerometer. The testing procedure included an intact scenario and two damage scenarios by unfastening four bolt connections in an accumulating order. Based entirely on time-domain experimental data for its calibration, an Auto Regressive Average Exogenous (ARMAX) model is used to create a simple and accurate model for vibration simulation. The calibrated ARMAX model is then used to identify various bolt-connection related damage scenarios via R² value. The findings in this study suggest that the proposed time-domain approach is capable of identifying structural damage in a parsimonious manner and can be used as a quick or initial solution.

Numerical modeling of dual phase microstructure behavior under deformation conditions on the basis of digital material representation

Development of a digital material representation (DMR) model of dual phase steel is presented within the paper. Subsequent stages involving generation of a reliable representation of microstructure morphology, assignment of material properties to component phases and incorporation of the model into the commercial finite element software are described within the paper. Different approaches used to recreate dual phase morphology in a digital manner are critically assessed. However, particular attention is placed on innovative identification of phase properties at the micro scale by using micro-pillar compression tests. The developed DMR model is finally applied to model influence of micro scale features on failure initiation and propagation under loading conditions.

Identifying affinity classes of inorganic materials binding sequences via a graph-based model

Rapid advances in bionanotechnology have recently generated growing interest in identifying peptides that bind to inorganic materials and classifying them based on their inorganic material affinities. However, there are some distinct characteristics of inorganic materials binding sequence data that limit the performance of many widely-used classification methods when applied to this problem. In this paper, we propose a novel framework to predict the affinity classes of peptide sequences with respect to an associated inorganic material. We first generate a large set of simulated peptide sequences based on an amino acid transition matrix tailored for the specific inorganic material. Then the probability of test sequences belonging to a specific affinity class is calculated by minimizing an objective function. In addition, the objective function is minimized through iterative propagation of probability estimates among sequences and sequence clusters. Results of computational experiments on two real inorganic material binding sequence data sets show that the proposed framework is highly effective for identifying the affinity classes of inorganic material binding sequences. Moreover, the experiments on the structural classification of proteins (SCOP) data set shows that the proposed framework is general and can be applied to traditional protein sequences.

The new wilderness: A practice-led model for arts based enquiry

The New Wilderness is a practice-led, multidisciplinary arts project first piloted by artists, writers, teachers and academics from Geelong, Deakin University and Courthouse ARTS Centre in 2013. In a series of workshops run by artists, and working to specific themes, the project provided a platform for participants to explore and respond creatively to change in the community; it culminated in a large-scale installation at Courthouse ARTS Centre’s main gallery. Our paper positions the project as a able to cut across convention, empowering young artists to respond to ‘big questions’ of relevance to the changing material, spatial and social relations within their communities. In questioning and seeking to transform communities into sustainable media, economic, environmental and social ecologies, this emergent model begins with a localised focus, which is designed to travel across time and place, and pedagogical frameworks. The paper positions Geelong as a community under radical transformation in its economic foundations and demographics. As artists and academics living and working in the region we see it as an experimental ground for investigations into a series of provocations that mirror the shape of the paper we intend to give. The provocations, as outlined in the workshops, might also be envisaged as new relations to:Object – From consumable to unusable to play. In revisiting the first iteration of The New wilderness in 2013 we discuss the ‘superfictional’ (Hill, 2000) enquiry that participants were asked to engage with. Its premise described Geelong as an abandoned, post-apocalyptic site. Participants were asked to imagine themselves as a group of future explorers and excavate objects from the city’s old tip. In unearthing their choices and re-presenting the objects in the gallery the participant was prompted to analyse site, situation, object and process as phenomena for ‘being’ or ‘telling stories’, providing insights into wider realms of cultural experience (Ellis, Adams and Bochner, 2010). Parallel to this ‘autoethnographic’ reflection our paper uses the philosopher Giorgio Agamben’s analysis of consumer and material culture. He traces the subject’s relation to objects from use-value, to exchange-value and in the era of extreme capitalism, to pure exhibition-value. He searches for ways that the objects produced in our material culture can be ‘profaned’ (Agamben, 2007). Space – From the material to the spatial to the situation. We are interested in how objects and the practices they elicit can be ‘profaned’ by their situation (Agamben, 2007; Wark, 2103). To profane, according to Agamben, is to open up the possibility that the object loses its exhibition-value to ‘a special form of negligence’ (Agamben). He uses the example of the child’s ability to insinuate any object into a new logic of play (Agamben). Like the objects excavated for The New Wilderness they could be from a variety of spheres – business, household, industry, health etc… The child, like the artist, reconstitutes, reorders and assembles new relations between things. In reflecting on the first New Wilderness project the paper correlates the creative response of the participant (student, child, artist) with the occupier. The Occupy Movement, which took up residence in many of the world’s cities’ financial districts in 2011, used a number of strategies commensurate with both Agamben’s notion of profanation and McKenzie Wark’s reading of the Situationist International’s use of détournement - as a strategy that releases objects and subjects back into the field of play (Wark, 2013). The field was taken by the occupy movement to be the space in which they occupied – capitalism, its logic and its practices, were, for a short time, redundant in the occupied field. The New Wilderness conceptualises the city as a localised field, from which its discarded objects can be ‘profaned’ or, repurposed, to reflect on shared histories, responsibilities, pedagogies and future action. Subject: self/other– As much as we propose New Wilderness to be a pedagogical initiative we see it as personal, critical and political. In the themed workshops, designed to elicit personal responses to the object and the site, which culminated in a multi-disciplinary installation, performance and/or text based work, participants were encouraged to think critically, and importantly, collectively. Through the four workshops run in the first iteration of the project participants were asked to re-consider their material value-systems, much as the occupy movement was trying to do, and like the occupiers, participants were empowered to be agents of change. Our paper reflects on the practical outcomes and the conceptual, political and pedagogical strategies embedded in The New Wilderness project. The paper affords us the additional opportunity to imagine a life for it in other geographical, socio-economic and educational situations. Merinda Kelly and Cameron Bishop, 2013Bio: Merinda Kelly is a sculptor and installation artist, educator and PhD student at Deakin University. Her research interests include Visual Culture, Practice Led Research, the Ontology of Art, and Autoethnography. Her most recent work includes the Pop Archaeology' and the Globo-Touro Projects.Bio: Dr Cameron Bishop is an artist and academic working in Visual Arts at Deakin University. He exhibits regularly and has written a number of journal articles and book chapters. His research has focused on the philosophical and postcolonial dimensions of space and subjectivity and more recently has evolved into an active interest in strategic interventions into space and practice.

A microstructure based analytical model for tensile twinning in a rod textured Mg alloy

Abstract A model for tensile twinning during the compression of rod textured magnesium is developed based on the idea that these twins nucleate at grain boundaries and that when the twin number density per grain is low these twins readily give rise to the formation of other 'interaction' twins in adjacent grains. Experimental observations of twin aspect ratios measured at a single grain size and twin number densities measured over four grain sizes were used to determine model material parameters. Using these, the model provides reasonable predictions for the observed magnitudes and trends for the following observations:Effect of grain size and stress on twin volume fraction, fractional twin length and the fraction of twin contact.Effect of grain size on the yield stress.Effect of grain size on the general shape of the stress-strain curve at low strains. A parametric study shows the model to be quite robust but that it is particularly sensitive to the value of the exponent assumed for the twin nucleation rate law. It is seen that preventing the formation of interaction twins provides an important avenue for hardening and that the flow stress is also particularly sensitive to the relaxation of the twin back stresses. The model shows the importance of taking microstructure into account when modelling twinning.