1,901 research outputs found
High velocity impact resistance of fibre metal laminates
The high velocity impact resistance of fibre metal laminates (FMLs) based on combinations of three
different aluminium alloys (6161-O, 6061-T6, 7075-T6) and a glass fibre reinforced epoxy resin have
been investigated both experimentally and numerically. A series of perforation tests on multilayer
configurations, ranging from a simple 2/1 lay-up to a seven ply 4/3 laminate. High velocity impact was
conducted using a projectile gas-gun launcher, operating in the velocity range between 119 m/s and
252 m/s.[1] The impact response of fibre metal laminates samples was characterised by determining
the energy required to perforate the panels. A stereoscopic Digital Image Correlation (DIC) method
was adopted to measure full-field deformations and strain for FMLs which providing the full field
strain history and 3D measurements up to sample perforation. The perforation resistance of the panels
was predicted using the finite element analysis package Abaqus/Explicit. A vectorized user-defined
material subroutine (VUMAT) was employed to define Hashin’s 3D rate-dependant damage criteria
for the composite layers. The subroutine was implemented into the commercial finite element software
ABAQUS/Explicit to simulate the deformation and failure of FMLs. Agreement between the
predictions of the finite element models and the experimental data was good across the range of
configurations. Ballistic limit of those FMLs was obtained from both the experimental tests and
numerical approaches
Comparative assessment of the effects of climate change on heat- and cold-related mortality in the United Kingdom and Australia.
BACKGROUND: High and low ambient temperatures are associated with increased mortality in temperate and subtropical climates. Temperature-related mortality patterns are expected to change throughout this century because of climate change. OBJECTIVES: We compared mortality associated with heat and cold in UK regions and Australian cities for current and projected climates and populations. METHODS: Time-series regression analyses were carried out on daily mortality in relation to ambient temperatures for UK regions and Australian cities to estimate relative risk functions for heat and cold and variations in risk parameters by age. Excess deaths due to heat and cold were estimated for future climates. RESULTS: In UK regions, cold-related mortality currently accounts for more than one order of magnitude more deaths than heat-related mortality (around 61 and 3 deaths per 100,000 population per year, respectively). In Australian cities, approximately 33 and 2 deaths per 100,000 population are associated every year with cold and heat, respectively. Although cold-related mortality is projected to decrease due to climate change to approximately 42 and 19 deaths per 100,000 population per year in UK regions and Australian cities, heat-related mortality is projected to increase to around 9 and 8 deaths per 100,000 population per year, respectively, by the 2080s, assuming no changes in susceptibility and structure of the population. CONCLUSIONS: Projected changes in climate are likely to lead to an increase in heat-related mortality in the United Kingdom and Australia over this century, but also to a decrease in cold-related deaths. Future temperature-related mortality will be amplified by aging populations. Health protection from hot weather will become increasingly necessary in both countries, while protection from cold weather will be still needed
An efficient numerical integration system for stiff unified constitutive equations for metal forming applications
Unified constitutive equations have been developed in recent years to predict viscoplastic flow and microstructural evolution of metal alloys for metal forming applications. These equations can be implemented into commercial FE code, such as ABAQUS and PAMSTAMP, to predict mechanical and physical properties of materials in a wide range of metal forming processes. These equations are normally stiff and need significant computer CPU time to solve. In this research, a series of numerical analyses are performed to investigate the difficulties within MATLAB of solving these stiff unified constitutive equations. A metric is introduced to allow evaluation of the numerical stiffness to assess the most appropriate numerical integration method. This metric is based on the ratio of maximum to minimum eigenvalue. This metric allows for an appropriate numerical method to be chosen giving more effective modelling of deformation and plasticity processes. Based on the theoretical work described above, a user-friendly system, based on MATLAB, is then developed for numerically integrating these types of stiff constitutive equations. This is particularly useful for metal forming engineers and researchers who need an effective computational tool to determine constitutive properties well based on numerical integration theories
Approximate Lie symmetries and singular perturbation theory
Perturbation theory plays a central role in the approximate solution of
nonlinear differential equations. The resultant series expansions are usually
divergent and require treatment by singular perturbation methods to generate
uniformly valid solutions. However, applying these methods is a subtle art
owing to the lack of globally applicable algorithms. Inspired by the fact that
all exact solutions of differential equations are consequences of (Lie)
symmetries, we reformulate perturbation theory for differential equations in
terms of approximate symmetries, via expansions of the Lie symmetries of the
solutions. This is a change in perspective from the usual method for obtaining
series expansions of the solutions themselves. We show that these approximate
symmetries are straightforward to calculate and are never singular; their
integration is therefore a powerful way of constructing uniformly convergent
solutions. This geometric viewpoint naturally implies that several key singular
perturbation methods such as the general perturbative RG-inspired approach of
Chen, Goldenfeld and Oono (CGO RG), the method of multiple scales (MMS), and
the Poincare-Lindstedt method (PLM), exploit a fundamental class of approximate
symmetries that we term ``hidden scale symmetries''. In turn, this clarifies
when and why these methods succeed and just as importantly, when they fail. Our
algorithmic method directly identifies and integrates these hidden scale
symmetries, making it often simpler to implement, and permitting solution of
problems where other methods are impractical. Finally, we show how other kinds
of approximate symmetry can be exploited to solve systems that do not possess
integrable hidden scale symmetries.Comment: 23 pages, 7 figure
OC009—An Assessment Of The Accuracy Of Horizon Scanning Predictions Of Medicine Use In The Scottish National Health Service
Solution heat treatment, forming and in-die quenching of a commercial sheet magnesium alloy into a complex-shaped component: experimentation and FE analysis
Interest in lightweight materials, particularly magnesium alloys, has increased significantly with rising efficiency requirements in the automotive sector. Magnesium is the lightest available structural metal, with a density approximately 35% lower than that of aluminium. The potential is great for magnesium to become a primary material used in future low carbon vehicle structures; however, there are significant obstacles, namely low ductility and formability, particularly at room temperature. The aim of this work is to present the feasibility of using the solution Heat treatment, Forming, and in-die Quenching (HFQ) process to produce complex shapes from a sheet magnesium alloy, and to use the results to verify a simulation of the process developed using commercial FE software. Uniaxial tensile tests were initially conducted to establish the optimum parameters for forming the part. Stamping trials were then carried out using these parameters, and a simulation set up modelling the forming operation. It was shown that the HFQ process could be used to form a successful component from this alloy, and that a good match was achieved between the results of the forming experiments and the simulation.The authors gratefully acknowledge the support from the EPSRC (Grant Ref: EP/I038616/1) for TARF-LCV: Towards Affordable, Closed-Loop Recyclable Future Low Carbon Vehicle Structures
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Universality of filamentous aggregation phenomena.
We use perturbative renormalization group theory to study the kinetics of protein aggregation phenomena in a unified manner across multiple timescales. Using this approach, we find that, irrespective of the specific molecular details or experimental conditions, filamentous assembly systems display universal behavior in time. Moreover, we show that the universality classes for protein aggregation correspond to simple autocatalytic processes and that the diversity of behavior in these systems is determined solely by the reaction order for secondary nucleation with respect to the protein concentration, which labels all possible universality classes. We validate these predictions on experimental data for the aggregation of several different proteins at several different initial concentrations, which by appropriate coordinate transformations we are able to collapse onto universal kinetic growth curves. These results establish the power of the perturbative renormalization group in distilling the ultimately simple temporal behavior of complex protein aggregation systems, creating the possibility to study the kinetics of general self-assembly phenomena in a unified fashion
A Comparative Study on the Failure Criteria for Predicting the Damage Initiation in Fiber-Reinforced Composites
Evaluation of environmental design strategies for university buildings
This paper examines the performance of environmental strategies in seven recently constructed or refurbished university buildings in the UK. These buildings contain a range of administrative spaces, classrooms, libraries and studios, reflecting their often complex, multi-use, heterogeneous nature. The key features of each environmental strategy are described (including passive, mixed-mode or active systems), in the context of the occupants and spaces they serve and the level of interaction that they afford. Energy performance and occupant thermal comfort (assessed by user surveys) are analysed and compared with studies of other non-domestic buildings, which have typically focused on more predictable single administrative uses (e.g. government offices), and unusually effective operation scenarios (e.g. continuous monitoring by expert building managers). The paper concludes by examining two of the case studies that reflect an increasingly common model of ‘flexible’ environmental design in more detail, identifying key features of the strategies for each building that have had a significant impact on their performance. The design assumptions leading to these features will be explored, and key lessons identified, contributing towards the development of a more robust evidential basis for choosing appropriate environmental strategies for university and other non-domestic buildings in the UK
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