243,889 research outputs found
Progress in strain monitoring of tapestries
No full textThis paper reports interdisciplinary
research between conservators and
engineers designed to enhance the
long-term conservation of tapestries
(tapestry-weave hangings) on longterm
display. The aim is to monitor,
measure and document the strain
experienced by different areas of a
tapestry while it is hanging on display.
Initial research has established that
damage can be identified in the early
stages of its inception, i.e., before it is
visible to the naked eye. The paper also
reports initial results of strain data
visualisation that allows curators and
conservators to examine how strain
develops, thereby facilitating
predictions about the changes in the
form or condition of the tapestry.
Strain data visualisation also allows the
strain process to be recorded, thereby
facilitating the effective documentation
of display methods and conservation
interventions. The paper reports the
use of point measurements (using
silica optical fibre sensors) and full-field
monitoring (using 3-D
photogrammetry with digital image
correlation (DIC))
Development of a D-xylose fermenting and inhibitor tolerant industrial Saccharomyces cerevisiae strain with high performance in lignocellulose hydrolysates using metabolic and evolutionary engineering
No full textBackground: The production of bioethanol from lignocellulose hydrolysates requires a robust, D-xylose-fermenting and inhibitor-tolerant microorganism as catalyst. The purpose of the present work was to develop such a strain from a prime industrial yeast strain, Ethanol Red, used for bioethanol production.
Results: An expression cassette containing 13 genes including Clostridium phytofermentans XylA, encoding D-xylose isomerase (XI), and enzymes of the pentose phosphate pathway was inserted in two copies in the genome of Ethanol Red. Subsequent EMS mutagenesis, genome shuffling and selection in D-xylose-enriched lignocellulose hydrolysate, followed by multiple rounds of evolutionary engineering in complex medium with D-xylose, gradually established efficient D-xylose fermentation. The best-performing strain, GS1.11-26, showed a maximum specific D-xylose consumption rate of 1.1 g/g DW/h in synthetic medium, with complete attenuation of 35 g/L D-xylose in about 17 h. In separate hydrolysis and fermentation of lignocellulose hydrolysates of Arundo donax (giant reed), spruce and a wheat straw/hay mixture, the maximum specific D-xylose consumption rate was 0.36, 0.23 and 1.1 g/g DW inoculum/h, and the final ethanol titer was 4.2, 3.9 and 5.8% (v/v), respectively. In simultaneous saccharification and fermentation of Arundo hydrolysate, GS1.11-26 produced 32% more ethanol than the parent strain Ethanol Red, due to efficient D-xylose utilization. The high D-xylose fermentation capacity was stable after extended growth in glucose. Cell extracts of strain GS1.11-26 displayed 17-fold higher XI activity compared to the parent strain, but overexpression of XI alone was not enough to establish D-xylose fermentation. The high D-xylose consumption rate was due to synergistic interaction between the high XI activity and one or more mutations in the genome. The GS1.11-26 had a partial respiratory defect causing a reduced aerobic growth rate.
Conclusions: An industrial yeast strain for bioethanol production with lignocellulose hydrolysates has been developed in the genetic background of a strain widely used for commercial bioethanol production. The strain uses glucose and D-xylose with high consumption rates and partial cofermentation in various lignocellulose hydrolysates with very high ethanol yield. The GS1.11-26 strain shows highly promising potential for further development of an all-round robust yeast strain for efficient fermentation of various lignocellulose hydrolysates
Exploring Linear Rake Machining In 316L Austenitic Stainless Steel for Microstructure Scale-Refinement, Grain Boundary Engineering, and Surface Modification
No full textThermo-mechanical processing plays an important role in materials property optimization through microstructure modification, required by demanding modern materials applications. Extreme grain size refinement, grain boundary engineering, and surface modification have been explored to establish enhanced performance properties for numerous metals and alloys in order to meet challenges associated with improving degradation resistance and increasing lifetime in harsh environments. Due to the critical role of austenitic stainless steels, such as 316L, as structural components in harsh environments, e.g. in nuclear power plants, improved degradation resistance is desirable. Linear raking, a novel two dimensional plane strain machining process, has shown promise achieving significant grain size refinement through severe plastic deformation (SPD) and imparting large strains in the surface and near surface regions of the substrate in various metals and alloys, imparting enhanced properties. Here, the effects of linear rake machining on the microstructure and related properties of 316L are investigated systematically for the first time. The controlled variation of linear raking processing parameters in combination with detailed micro-characterization using analytical electron microscopy, x-ray diffraction and associated property measurements enables the determination of the influence of changes in strain and strain rate on the developing deformation microstructure and related properties. Varying the linear raking process parameters, and consequently the strain and strain rate, affects the volume fractions of deformation induced α’-martensite and the degree of grain refinement, to the nanoscale, through SPD in the chips produced. Additionally, linear raking is identified as a way to produce surface modified structures in the specimen substrate surface of 316L, with observations of various degrees of deformation and strain up to a depth of 150m. This research clearly demonstrates that materials property modification can be achieved effectively by linear raking processing, and that resulting surface modified structures provide significant stored energy for recovery and recrystallization. This study provides a fundamental understanding of linear raking as a thermo-mechanical processing technique, which may in the future be capable of creating grain boundary engineered surface modified components for use in harsh environments like those in commercial nuclear power plants
A continuous/discontinuous Galerkin formulation for a strain gradient-dependent damage model
No full textThe numerical solution of strain gradient-dependent continuum problems has been hindered by continuity demands on the basis functions. The presence of terms in constitutive models that involve gradients of the strain field means that the continuity of standard finite element shape functions is insufficient. Despite a resurgence of research interest in strain gradient continuum models to represent micro-mechanical effects, a sound, effective and simple framework for the numerical solution of strain gradient-dependent problems is lacking. Here, a formulation is presented which allows the use of finite element shape functions for the solution of a prototype strain gradient-dependent damage model. The formulation is examined in two dimensions for the simulation of crack propagation. Particular attention is paid to the application of non-standard boundary conditions
Intermediate strain rate testing methodologies and full-field optical strain measurement techniques for composite materials characterisation
No full textTwo optical full-field strain measurement techniques, Digital Image Correlation and the Grid Method, are applied to characterise the strain-rate dependent constitutive behaviour of composite materials. Optical strain measurement techniques based on full-field images are well established for material characterisation in the quasi-static strain rate region, however in this work they are developed to study the material behaviour at intermediate strain rates, which is relatively unexplored. For this purpose a testing methodology that combines high speed imaging and the use of a high speed test machine is devised. The overall goal is to extract composite materials constitutive parameters to be used in the modelling of strain rate dependent behaviour. Particularly the strain rate dependence of the stiffness of glass and carbon fibre reinforced epoxy materials is investigated. A characterisation procedure based on off-axis specimens with oblique end-tabs is developed and applied to the study of the shear behaviour of a carbon/epoxy composite material.The research in the PhD programme constitutes an essential first step for more profitable applications of full-field measurement techniques to high speed testing. Full-field data acquired with the experimental methodology devised here can be used to investigate non linear material behaviours. Furthermore this experimental methodology, applied to specimens that generate non uniform strain fields, can produce strain maps useful for the application of the Virtual Fields Method. This will lead to a reduction of the experiments needed to characterise materials
Discontinuous modelling of strain localisation and failure
No full textThe computational simulation of failure in solids poses many challenges. A proper understanding of how structures respond under loading, both before and past the peak load, is important for safe and economical constructions. This requires numerical models for failure which are both faithful to the physical reality and mathematically well founded. A serious computational issue is that of objectivity with respect to the spatial discretisation of a problem. This requires that upon refinement of the spatial discretisation of a problem, a unique, physically meaningful result is approached. One approach to ensure objectivity with respect to spatial discretisation when simulating failure in solids is to allow displacement discontinuities in the solution. In this work, different techniques, of varying complexity, are developed to simulate displacement discontinuities which are independent of the spatial discretisation using finite elements. The different techniques are then critically evaluated. The first model examined involves adding only the effect of a displacement discontinuity to a finite element as an incompatible strain mode. This allows a traction–separation relationship to be applied at an interface and can be implemented simply in a standard finite element code. It is however shown that this type of model can be cast in an equivalent continuum format, a form which is known to be sensitive to the spatial discretisation. The second approach developed involves the addition of the Heaviside function to the underlying finite element interpolation basis. This method is based on the partition of unity concept, and allows the Heaviside function to be added locally to a finite element mesh to simulate a propagating displacement discontinuity. The approach is formulated for geometrically linear, geometrically nonlinear, quasi-static and dynamic problems. It is shown to be completely independent of the spatial discretisation. The partition of unity-based model is used also to simulate failure using a regularised strain softening model. When a critical level of inelastic deformation is reached, a displacement discontinuity is inserted. This model is better suited to modelling the entire failure process than a continuum or discontinuous model alone. Through numerical examples, it is shown that the inclusion of a displacement discontinuity during the failure process can lead to a different failure mode than for a continuum-only model
Characterization of lithographically printed resistive strain gauges
No full textThis paper reports progress in sensor fabrication by the conductive lithographic film (CLF) printing process. Work describing strain-sensitive structures manufactured using a modified printing process and conductive inks is addressed. The performance of a "single-ink" strain-sensitive structure when printed on six alternative substrates (GlossArt, PolyArt, Teslin, Mylar C, Melinex, and Kapton) is analyzed. Though not intending to compete with conventional gauges in high-tolerance measurement, the structures exhibit properties that indicate suitability for novel applications
Strain-engineering of twist-angle in graphene/hBN superlattice devices
No full textThis is the author accepted manuscript. The final version is available on open access from American Chemical Society via the DOI in this recordThe observation of novel physical phenomena such as Hofstadter’s butterfly, topological currents, and unconventional superconductivity in graphene has been enabled by the replacement of SiO2 with hexagonal boron nitride (hBN) as a substrate and by the ability to form superlattices in graphene/hBN heterostructures. These devices are commonly made by etching the graphene into a Hall-bar shape with metal contacts. The deposition of metal electrodes, the design, and specific configuration of contacts can have profound effects on the electronic properties of the devices possibly even affecting the alignment of graphene/hBN superlattices. In this work, we probe the strain configuration of graphene on hBN in contact with two types of metal contacts, two-dimensional (2D) top-contacts and one-dimensional edge-contacts. We show that top-contacts induce strain in the graphene layer along two opposing leads, leading to a complex strain pattern across the device channel. Edge-contacts, on the contrary, do not show such strain pattern. A finite-elements modeling simulation is used to confirm that the observed strain pattern is generated by the mechanical action of the metal contacts clamped to the graphene. Thermal annealing is shown to reduce the overall doping while increasing the overall strain, indicating an increased interaction between graphene and hBN. Surprisingly, we find that the two contact configurations lead to different twist-angles in graphene/hBN superlattices, which converge to the same value after thermal annealing. This observation confirms the self-locking mechanism of graphene/hBN superlattices also in the presence of strain gradients. Our experiments may have profound implications in the development of future electronic devices based on heterostructures and provide a new mechanism to induce complex strain patterns in 2D materials.Engineering and Physical Sciences Research Council (EPSRC)Royal SocietyNewton FundLeverhulme TrustHigher Committee for Education Development in Iraq (HCED)Royal Academy of Engineerin
Acquiring Uniaxial Stress-Strain Curve by Fast Finite Element Analysis for Characterization of Whole-Cell Elastic Property
No full textAn understanding of whole-cell elastic property can provide insight into cellular response to mechanical loading. Hertz model is often used to extract the Young’s modulus from the atomic force microscopy (AFM) force indentation depth curve (F-D curve) for characterization of cell’s elastic property. However, Hertz model is only relatively accurate when the sample can be regarded as infinite half space and its material is linear elastic, which is contradictory with the fact that cell is usually very thin and cell’s elastic properties are considered to be highly nonlinear, especially when the deformation is very large. Finite element analysis can be used to handle the nonlinear elastic property and large deformation by using the hyperelastic model to model the cell material. However, previous studies have not demonstrated a convenient way to search for the model parameters that can fit the experimental data. In this paper, we put forward a method based on finite element analysis. Our new method adopts a general uniaxial stress-strain curve (associated with a hyperelastic model) to represent cell’s material and uses a recursive method to search for this uniaxial stress-strain curve by minimizing the difference between the experimental and simulated F-D curve. This new recursive approach not only offers a high match accuracy between the experimental and simulated F-D curve(error rate less than 5% is ready to be obtainable), but also minimizes the number of recursions in searching for the stress-strain curve(less than 10 recursions are enough for the good enough match in normal situation)
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