The financial support from Innovate UK, Ultra-light Car Bodies (UlCab, reference 101568) and Make it lighter, with less (LightBlank, reference 131818) are gratefully acknowledged. The research leading to these results has received funding from the European Union's Seventh Framework Program (FP7/2007-2013) under grant agreement No. 604240, project title 'An industrial system enabling the use of a patented, lab-proven materials processing technology for Low Cost forming of Lightweight structures for transportation industries (LoCoLite)'. Significant support was also received from the AVIC Centre for Structural Design and Manufacture at Imperial College London, which is funded by Aviation Industry Corporation of China (AVIC).

<ol>
	<li>Miller, W. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+development+in+aluminium+alloys+for+the+automotive+industry.">Recent development in aluminium alloys for the automotive industry.</a> Mater. Sci. Eng. A. 280 (1), 37-49 (2000).</li><li>Bolt, P. J., Lamboo, N. A. P. M., Rozier, P. J. C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Feasibility+of+warm+drawing+of+aluminium+products.">Feasibility of warm drawing of aluminium products.</a> J. Mater. Process. Tech. 115 (1), 118-121 (2001).</li><li>Li, D., Ghosh, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+temperature+and+blank+holding+force+on+biaxial+forming+behavior+of+aluminum+sheet+alloys.">Effects of temperature and blank holding force on biaxial forming behavior of aluminum sheet alloys.</a> J. Mater. Eng. Perform. 13 (3), 348-360 (2004).</li><li>Toros, S., Ozturk, F., Kacar, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Review+of+warm+forming+of+aluminum-magnesium+alloys.">Review of warm forming of aluminum-magnesium alloys.</a> J. Mater. Process. Tech. 207 (1-3), 1-12 (2008).</li><li>Wang, L., Strangwood, M., Balint, D., Lin, J., Dean, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formability+and+failure+mechanisms+of+AA2024+under+hot+forming+conditions.">Formability and failure mechanisms of AA2024 under hot forming conditions.</a> Mater. Sci. Eng. A. 528 (6), 2648-2656 (2011).</li><li>Wang, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> TTP2013 Tools and Technologies for Processing Ultra High Strength Materials. , (2013).</li><li>El Fakir, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Numerical+study+of+the+solution+heat+treatment,+forming,+and+in-die+quenching+(HFQ)+process+on+AA5754.">Numerical study of the solution heat treatment, forming, and in-die quenching (HFQ) process on AA5754.</a> Int. J. Mach. Tool. Manu. 87, 39-48 (2014).</li><li>Raugei, M., El Fakir, O., Wang, L., Lin, J., Morrey, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Life+cycle+assessment+of+the+potential+environmental+benefits+of+a+novel+hot+forming+process+in+automotive+manufacturing.">Life cycle assessment of the potential environmental benefits of a novel hot forming process in automotive manufacturing.</a> J. Clean. Prod. 83, 80-86 (2014).</li><li>Liu, J., Gao, H., Fakir, O. E., Wang, L., Lin, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HFQ+forming+of+AA6082+tailor+welded+blanks.">HFQ forming of AA6082 tailor welded blanks.</a> MATEC Web of Conferences. 21 (05006), (2015).</li><li>Karbasian, H., Tekkaya, A. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+on+hot+stamping.">A review on hot stamping.</a> J. Mater. Process. Tech. 210 (15), 2103-2118 (2010).</li><li>El Fakir, O., Wang, L., Balint, D., Dear, J. P., Lin, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Predicting+Effect+of+Temperature+Strain+Rate+and+Strain+Path+Changes+on+Forming+Limit+of+Lightweight+Sheet+Metal+Alloys.">Predicting Effect of Temperature Strain Rate and Strain Path Changes on Forming Limit of Lightweight Sheet Metal Alloys.</a> Procedia Eng. 81, 736-741 (2014).</li><li>Shi, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> the 3rd International Conference on New Forming Technology. , 100-104 (2012).</li><li>Mohamed, M. S., Foster, A. D., Lin, J., Balint, D. S., Dean, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Investigation+of+deformation+and+failure+features+in+hot+stamping+of+AA6082:+Experimentation+and+modelling.">Investigation of deformation and failure features in hot stamping of AA6082: Experimentation and modelling.</a> Int. J. Mach. Tool. Manu. 53 (1), 27-38 (2012).</li><li>Hosford, W. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comments+on+anisotropic+yield+criteria.">Comments on anisotropic yield criteria.</a> Int. J. Mech. Sci. 27 (7), 423-427 (1985).</li><li>Marciniak, Z., Kuczy&#324;ski, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Limit+strains+in+the+processes+of+stretch-forming+sheet+metal.">Limit strains in the processes of stretch-forming sheet metal.</a> Int. J. Mech. Sci. 9 (9), 609-620 (1967).</li><li>Ma, G., Wang, L., Gao, H., Zhang, J., Reddyhoff, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+friction+coefficient+evolution+of+a+TiN+coated+contact+during+sliding+wear.">The friction coefficient evolution of a TiN coated contact during sliding wear.</a> Appl. Surf. Sci. 345, 109-115 (2015).</li><li>P&#245;dra, P., Andersson, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simulating+sliding+wear+with+finite+element+method.">Simulating sliding wear with finite element method.</a> Tribol. Int. 32 (2), 71-81 (1999).</li><li>Archard, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Contact+and+Rubbing+of+Flat+Surfaces.">Contact and Rubbing of Flat Surfaces.</a> J. Appl. Phys. 24 (8), 981-988 (1953).</li><li>Liu, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+the+interfacial+heat+transfer+coefficient+in+the+hot+stamping+of+AA7075.">Determination of the interfacial heat transfer coefficient in the hot stamping of AA7075.</a> MATEC Web of Conferences. 21 (05003), (2015).</li></ol>

The authors have nothing to disclose.

The KBC-FE simulation technique enables advanced simulations to be conducted off site using dedicated modules. It can run functional modules on a cloud environment, that link up nodes from different specializations, to ensure that process simulations are conducted as accurately as possible. The critical aspects in the KBC-FE simulation may involve independency of the FE codes, efficiency of the computation, and accuracy of the functional modules. The realization of each advanced function in a module would rely on the development of a new model and/or a novel experimental technique. For example, the forming limit module is developed based on the new unified forming limit prediction model 11, and the friction tool life prediction module has currently been developed by the implementation of the interactive friction model 20. The KBC-FE simulation technique also offers the function of selective computation, i.e., only the elements fulfilling the selection criteria are selected for further evaluation in the individual modules. For instance, the tool life prediction module automatically selects the elements for which the hard coating tends to breakdown, by ranking the wear rate of all the elements in the 1st forming cycle, thus usually less than 1% of the elements will be selected for further tool life evaluations under multi-cycle loading conditions. In the present research, the tool life prediction after 300 forming cycles can be completed within 5 min.
By conducting the relevant tests and calibrating accordingly, the forming limit model could be applied to forming process simulations to consequently determine the optimal parameters for producing a component from such alloys successfully, and with no incidences of necking. The forming limit prediction model was developed as a cloud module that was independent of the FE software being utilized, and could be applied to any FE software to assess the formability of a material during forming, without complicated subroutines 17. By importing the relevant data into the model, calculations could be carried out to determine whether failure would occur, in regions of the component that the user could specify, saving on computational resources. However, it should be noted that as the stress-strain curves are input into the FE software through a simple look-up table, it may be difficult to fully represent the material properties at various temperatures and strain rates during simulation.&#160;
In the tool life prediction module, the frictional behavior during forming can be predicted by importing the required deformation history data into the verified friction module 20, and then importing the discrete data points calculated by the cloud module for each element back into the FE software. This ensures that the advanced friction module can be used by all FE codes, regardless of their ability to incorporate user-subroutines. Additionally, the module could be run in parallel to further reduce the computation time. The interactive friction/wear model assumed the absence of wear particles during initial sliding, and as a result, it would be reasonable to expect a constant initial value of friction coefficient 0.17 20. Although this model revealed the evolution of friction distribution, the frictional behavior during a forming process is very complicated, and it is difficult to completely integrate the complex frictional behavior from the cloud module into the FE simulation.
As a future technology, the KBC-FE simulation will rely on the development of dedicated and robust internet based FE simulation software packages, which would require a highly profitable, but completely different business model to be established by the software developers. In addition, a dedicated internal network needs to be built within the collaborative parties to ensure data security and the control reliability of the industrial system.

Finite Element (FE) simulations have become a powerful tool for optimizing process parameters in the metal forming industry. The reliability of FE simulation results is dependent on the accuracy of the material definition, input in the form of flow stress data or constitutive equations, and the assignment of the boundary conditions, such as the friction coefficient and the heat transfer coefficient. In the past few years, advanced FE simulations have been developed via the implementation of user-defined subroutines, which have significantly broadened the capability of FE software.
The use of such advanced FE simulations in the design of forming processes for structural components has been investigated by both the aviation and automotive industries, with the intention of producing lightweight structures that reduces operating costs and CO2 emissions. Particular focus has been placed on the replacement of steel components with lower density materials, such as aluminum alloys and magnesium alloys. However, these alloys, especially the stronger variants, offer limited formability at room temperature and thus complex-shaped components cannot be manufactured using the conventional cold stamping process. Therefore, advanced high temperature forming technologies, such as warm aluminum forming 1-4, hot stamping of aluminum alloys 5-9 and hot stamping of high strength steels 10, have been developed over the past decades to enable complex-shaped components to be formed. In general, high temperature forming processes involve significant temperature variations, strain rate and loading path changes 11, which would, for instance, cause inevitable viscoplastic and loading history dependent responses from the work piece materials. These are intrinsic features of high temperature forming processes and may be difficult to represent using conventional FE simulation techniques. Another desirable feature would be the ability to predict the tool life over multiple forming cycles in such processes, since they require low friction characteristics achieved through coatings that degrade with each forming operation. To represent all these features via the implementation of user-defined subroutines would be computationally very expensive. Moreover, the development and implementation of multiple subroutines would require excessive multi-disciplinary knowledge from an engineer conducting the simulations.
In the present work, a novel Knowledge Based Cloud FE (KBC-FE) simulation technique is proposed, based on the application of modules on a cloud computing environment, that enables an efficient and effective method of modeling advanced forming features in conjunction with conventional FE simulations. In this technique, data from the FE software is processed at each cloud module, and then imported back into the FE software in the relevant consistent format, for further processing and analysis. The development of these modules and their implementation in the KBC-FE is detailed.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>AA6082-T6</td>
			<td>AMAG</td>
			<td></td>
			<td>Material</td>
		</tr>
		<tr>
			<td>AA5754-H111</td>
			<td>AMAG</td>
			<td></td>
			<td>Material</td>
		</tr>
		<tr>
			<td>&#160;1000 kN high-speed press</td>
			<td>ESH</td>
			<td></td>
			<td>Forming press</td>
		</tr>
		<tr>
			<td>ARGUS</td>
			<td>GOM</td>
			<td></td>
			<td>Optical forming analysis</td>
		</tr>
		<tr>
			<td>PAM-STAMP 2015</td>
			<td>ESI</td>
			<td></td>
			<td>FE simulation software</td>
		</tr>
		<tr>
			<td>Matlab&#160;</td>
			<td>MathWorks</td>
			<td></td>
			<td>Numerical calculation software</td>
		</tr>
		<tr>
			<td>Gleeble 3800</td>
			<td>DSI</td>
			<td></td>
			<td>Uniaxial tensile test</td>
		</tr>
		<tr>
			<td>High Temperature Tribometer (THT)</td>
			<td>Anton Paar</td>
			<td></td>
			<td>Friction property test</td>
		</tr>
		<tr>
			<td>NewViewTM 7100</td>
			<td>ZYGO</td>
			<td></td>
			<td>Surface profilometer</td>
		</tr>
		<tr>
			<td>&#160;Magnetron sputtering equipment</td>
			<td></td>
			<td></td>
			<td>Coating deposition</td>
		</tr>
		<tr>
			<td>Microhardness tester</td>
			<td>Wolpert Wilson Instruments</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Nano-hardness indenter&#160;</td>
			<td>MTS</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

knowledge based cloud fe simulation of sheet metal forming processes

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the efficiency and lowering the development time of such processes, whilst reducing costs involved in trial-and-error prototyping. Recent focus on the substitution of steel components with aluminum alloy alternatives in the automotive and aerospace sectors has increased the need to simulate the forming behavior of such alloys for ever more complex component geometries. However these alloys, and in particular their high strength variants, exhibit limited formability at room temperature, and high temperature manufacturing technologies have been developed to form them. Consequently, advanced constitutive models are required to reflect the associated temperature and strain rate effects. Simulating such behavior is computationally very expensive using conventional FE simulation techniques.
This paper presents a novel Knowledge Based Cloud FE (KBC-FE) simulation technique that combines advanced material and friction models with conventional FE simulations in an efficient manner thus enhancing the capability of commercial simulation software packages. The application of these methods is demonstrated through two example case studies, namely: the prediction of a material's forming limit under hot stamping conditions, and the tool life prediction under multi-cycle loading conditions.

KBC-FE Simulation for Necking Prediction
In a hot stamping process, the use of a shape-optimized blank will not only save material cost but also help to reduce the presence of defects, such as necking, cracking, and wrinkling. The initial blank shape affects the material flow significantly during forming, and hence a sensible design of the blank shape is critical to the success of the hot stamping process and quality of the final products. To reduce the efforts of trial-and-error experiments to determine the optimal blank geometry, KBC-FE simulation was proven to be a highly efficient and effective method for minimizing the areas with necking. Using this technique, each simulation takes approximately 2 hours, while the parallel cloud module computation for necking prediction is completed within 4 hours.
Figure 4 shows the evolution of the blank shape used in the hot stamping, an example of automotive door inner component. The initial blank shape, adopted from a conventional cold stamping process, was first used in the KBC-FE simulation. Experimental results in Figure 4(a) show that large failure (cracking or necking) areas are visible after the hot stamping. After one iteration of the blank shape optimization, it can be seen in Figure 4(b) that an almost fully successful panel is formed with much less necking, compared to using the initial blank shape. It can be seen that there is still an indication of necking at the pockets in the top right and left corners of the panel. After further optimization in Figure 4(c), the optimized blank shape was finally obtained with no visible necking on the panel. The optimized blank shape determined by the KBC-FE simulation was verified experimentally through hot stamping trials conducted on a fully automated production line offered by a production system manufacturer.
KBC-FE Simulation for Tool Life Prediction
Conventional FE simulations of metal forming processes are performed for a single cycle. However, in a production environment, multiple forming cycles are performed on a given tool, where it is found that an increase in the number of forming cycles results in an increased variation between the formed components. This variation during multi-cycle tool loading is the result of changing surface topography. For example, the multi-cycle loading of forming tools with functional coatings will lead to a coating thickness reduction due to wear. Moreover, the breakdown of the coating will also be influenced by forming parameters, such as the load/pressure, forming speeds, etc. The KBC-FE technique enables the simulation of sheet metal forming processes under multi-cycle loading conditions, which is essential for the in-service life prediction of forming tools with advanced functional coatings.
To investigate the effects of blank holding force on the tool life, blank holding force values of 5, 20, and 50 kN were examined for a constant forming speed of 250 mm/s. Figure 5 shows the remaining tool coating thickness distribution with different blank holding forces after 300 forming cycles. It clearly indicates that the remaining coating thickness decreases with an increase in the blank holding force.
Figure 6 shows the pressure and remaining coating thickness distribution with blank holding forces of 5, 20, and 50 kN, respectively, along the curvilinear distance of the die after 300 forming cycles. Since the region A-B represents the die entrance region during the U-shape bending process, the pressure and the relative wear distance in this region were much higher than other regions of the die. Consequently, the wear of the coating mainly occurred in this area. There are two peak values of coating thickness reduction at 20 kN and 50 kN that correspond to the two peaks under the pressure. Meanwhile, the remaining coating thickness decreases with the increase of blank holding force. The lowest remaining coating thicknesses with blank holding forces of 5, 20, and 50 kN, were 0.905, 0.570, and 0.403 microns, respectively, where the initial coating thickness was 2.1 microns.
<img alt="Figure 1" src="/files/ftp_upload/53957/53957fig1.jpg" /> 
Figure 1: Comparison between experimental and predicted forming limit strains at different temperatures. The forming limit strains increase as temperature rises, at a constant speed of 250 mm/s, or equivalently, a strain rate of 6.26 s-1. <a href="https://www.jove.com/files/ftp_upload/53957/53957fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/53957/53957fig2.jpg" /> 
Figure 2: Schematic chart for knowledge based cloud FE simulation of a sheet metal forming process. Commercial FE simulation software, is used to run the simulation and export the results required for the individual modules. The modules, e.g., formability, heat transfer, post-forming strength (microstructure), tool life prediction, tool design, etc., work simultaneously and independently in the cloud, hence enabling the integration of cutting edge knowledge from multiple sources into FE simulations. <a href="https://www.jove.com/files/ftp_upload/53957/53957fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/53957/53957fig3.jpg" /> 
Figure 3: Geometry of the work piece and tools for the U-shape bending simulation. The tools, i.e., punch, blank holder and die, are modeled using rigid elements. Shell elements are used for the work piece (blank) elements. <a href="https://www.jove.com/files/ftp_upload/53957/53957fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/53957/53957fig4.jpg" /> 
Figure 4: Evolution of blank shape for hot stamping of a door inner panel (displayed in FE simulation). Left: The figures in green frames represent blank shapes at each optimization stage, and the ones in red frames correspond to the blank shape before its optimization. Right: Necking prediction results at each optimization stage. (a) Initial results with large failure (cracking/necking shown in red color), (b) Reduced failure with some necking after first stage of optimization, (c) Final optimized blank shape with no visible necking. <a href="https://www.jove.com/files/ftp_upload/53957/53957fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/53957/53957fig5.jpg" /> 
Figure 5: The remaining coating thickness distribution (displayed in FE simulation) with blank holding forces of: (a) 5 kN, (b) 20 kN, and (c) 50 kN, after 300 forming cycles at a constant stamping speed of 250 mm/s. <a href="https://www.jove.com/files/ftp_upload/53957/53957fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/53957/53957fig6.jpg" /> 
Figure 6: Prediction of contact pressure and remaining coating thickness with blank holding forces of: (a) 5 kN, (b) 20 kN, and (c) 50 kN, along the curvilinear distance of the die at a constant stamping speed of 250 mm/s. <a href="https://www.jove.com/files/ftp_upload/53957/53957fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Knowledge Based Cloud FE Simulation of Sheet Metal Forming Processes at JoVE.com

Knowledge Based Cloud FE Simulation of Sheet Metal Forming Processes

The following paper presents a novel FE simulation technique (KBC-FE), which reduces computational cost by performing simulations on a cloud computing environment, through the application of individual modules. Moreover, it establishes a seamless collaborative network between world leading scientists, enabling the integration of cutting edge knowledge modules into FE simulations.

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the ...

knowledge-based-cloud-fe-simulation-of-sheet-metal-forming-processes

Research

Education

JoVE Core

JoVE Journal

Civil Engineering

Engineering

Unit 1

Introduction to Concrete

SCIENTISTS IN ACTION

12.0K Views.  Imperial College London. The following paper presents a novel FE simulation technique (KBC-FE), which reduces computational cost by performing simulations on a cloud computing environment, through the application of individual modules. Moreover, it establishes a seamless collaborative network between world leading scientists, enabling the integration of cutting edge knowledge modules into FE simulations.

Video: Knowledge Based Cloud FE Simulation of Sheet Metal Forming Processes

Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

Metamaterials (MM), artificial materials engineered to have properties that may not be found in nature, have been widely explored since the first theoretical1 and experimental demonstration2 of their unique properties. MMs can provide a highly controllable electromagnetic response, and to date have been demonstrated in every technologically relevant spectral range including the optical3, near IR4, mid IR5 , THz6 , mm-wave7 , microwave8 and radio9 bands. Applications include perfect lenses10, sensors11, telecommunications12, invisibility cloaks13 and filters14,15. We have recently developed single band16, dual band17 and broadband18 THz metamaterial absorber devices capable of greater than 80% absorption at the resonance peak. The concept of a MM absorber is especially important at THz frequencies where it is difficult to find strong frequency selective THz absorbers19. In our MM absorber the THz radiation is absorbed in a thickness of ~ &lambda;/20, overcoming the thickness limitation of traditional quarter wavelength absorbers. MM absorbers naturally lend themselves to THz detection applications, such as thermal sensors, and if integrated with suitable THz sources (e.g. QCLs), could lead to compact, highly sensitive, low cost, real time THz imaging systems.

This protocol outlines the simulation, fabrication and characterization of THz metamaterial absorbers. Such absorbers, when coupled with an appropriate sensor, have applications in THz imaging and spectroscopy.

Metamaterials (MM),  artificial materials engineered to have properties that may not be found in  nature, have been widely explored since the first ...

Simulation of the Planetary Interior Differentiation Processes in the Laboratory

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process.

The high-pressure and high-temperature experiments described here mimic planet interior differentiation processes. The processes are visualized and better understood by high-resolution 3D imaging and quantitative chemical analysis.

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to ...

Picoinjection of Microfluidic Drops Without Metal Electrodes

Existing methods for picoinjecting reagents into microfluidic drops require metal electrodes integrated into the microfluidic chip. The integration of these electrodes adds cumbersome and error-prone steps to the device fabrication process. We have developed a technique that obviates the needs for metal electrodes during picoinjection. Instead, it uses the injection fluid itself as an electrode, since most biological reagents contain dissolved electrolytes and are conductive. By eliminating the electrodes, we reduce device fabrication time and complexity, and make the devices more robust. In addition, with our approach, the injection volume depends on the voltage applied to the picoinjection solution; this allows us to rapidly adjust the volume injected by modulating the applied voltage. We demonstrate that our technique is compatible with reagents incorporating common biological compounds, including buffers, enzymes, and nucleic acids.

We have developed a technique for picoinjecting microfluidic drops that does not require metal electrodes. As such, devices incorporating our technique are simpler to fabricate and to use.

Existing methods for picoinjecting reagents into microfluidic drops require metal electrodes integrated into the microfluidic chip. The integration of ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

Visualizing Hyporheic Flow Through Bedforms Using Dye Experiments and Simulation

Advective exchange between the pore space of sediments and the overlying water column, called hyporheic exchange in fluvial environments, drives solute transport in rivers and many important biogeochemical processes. To improve understanding of these processes through visual demonstration, we created a hyporheic flow simulation in the multi-agent computer modeling platform NetLogo. The simulation shows virtual tracer flowing through a streambed covered with two-dimensional bedforms. Sediment, flow, and bedform characteristics are used as input variables for the model. We illustrate how these simulations match experimental observations from laboratory flume experiments based on measured input parameters. Dye is injected into the flume sediments to visualize the porewater flow. For comparison virtual tracer particles are placed at the same locations in the simulation. This coupled simulation and lab experiment has been used successfully in undergraduate and graduate laboratories to directly visualize river-porewater interactions and show how physically-based flow simulations can reproduce environmental phenomena. Students took photographs of the bed through the transparent flume walls and compared them to shapes of the dye at the same times in the simulation. This resulted in very similar trends, which allowed the students to better understand both the flow patterns and the mathematical model. The simulations also allow the user to quickly visualize the impact of each input parameter by running multiple simulations. This process can also be used in research applications to illustrate basic processes, relate interfacial fluxes and porewater transport, and support quantitative process-based modeling.

This manuscript describes how to create regular bedforms in a flume, visualize flow through the bedforms, and use computer simulations to simulate the hyporheic flow. The computer simulations compare well with the experimental observations. This coupled simulation and experiment is well-suited for both research and educational purposes.

Advective exchange between the pore space of sediments and the overlying water column, called hyporheic exchange in fluvial environments, drives solute ...

Experimental Methods for Investigation of Shape Memory Based Elastocaloric Cooling Processes and Model Validation

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor compression based cooling process. Nickel-Titanium (Ni-Ti) based alloy systems, especially, show large elastocaloric effects. Furthermore, exhibit large latent heats which is a necessary material property for the development of an efficient solid-state based cooling process. A scientific test rig has been designed to investigate these processes and the elastocaloric effects in SMAs. The realized test rig enables independent control of an SMA&#39;s mechanical loading and unloading cycles, as well as conductive heat transfer between SMA cooling elements and a heat source/sink. The test rig is equipped with a comprehensive monitoring system capable of synchronized measurements of mechanical and thermal parameters. In addition to determining the process-dependent mechanical work, the system also enables measurement of thermal caloric aspects of the elastocaloric cooling effect through use of a high-performance infrared camera. This combination is of particular interest, because it allows illustrations of localization and rate effects &#8212; both important for efficient heat transfer from the medium to be cooled.
The work presented describes an experimental method to identify elastocaloric material properties in different materials and sample geometries. Furthermore, the test rig is used to investigate different cooling process variations. The introduced analysis methods enable a differentiated consideration of material, process and related boundary condition influences on the process efficiency. The comparison of the experimental data with the simulation results (of a thermomechanically coupled finite element model) allows for better understanding of the underlying physics of the elastocaloric effect. In addition, the experimental results, as well as the findings based on the simulation results, are used to improve the material properties.

Experimental methods for investigation of solid state cooling processes and characterization of elastocaloric material properties of Shape Memory Alloys (SMA) are presented. A custom-built test rig has been designed for controlling and comprehensive monitoring of elastocaloric cooling processes. Furthermore, it provides a validation platform for thermomechanically coupled modeling approaches.

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor ...

Simulation of Human-induced Vibrations Based on the Characterized In-field Pedestrian Behavior

For slender and lightweight structures, vibration serviceability is a matter of growing concern, often constituting the critical design requirement. With designs governed by the dynamic performance under human-induced loads, a strong demand exists for the verification and refinement of currently available load models. The present contribution uses a 3D inertial motion tracking technique for the characterization of the in-field pedestrian behavior. The technique is first tested in laboratory experiments with simultaneous registration of the corresponding ground reaction forces. The experiments include walking persons as well as rhythmical human activities such as jumping and bobbing. It is shown that the registered motion allows for the identification of the time variant pacing rate of the activity. Together with the weight of the person and the application of generalized force models available in literature, the identified time-variant pacing rate allows to characterize the human-induced loads. In addition, time synchronization among the wireless motion trackers allows identifying the synchronization rate among the participants. Subsequently, the technique is used on a real footbridge where both the motion of the persons and the induced structural vibrations are registered. It is shown how the characterized in-field pedestrian behavior can be applied to simulate the induced structural response. It is demonstrated that the in situ identified pacing rate and synchronization rate constitute an essential input for the simulation and verification of the human-induced loads. The main potential applications of the proposed methodology are the estimation of human-structure interaction phenomena and the development of suitable models for the correlation among pedestrians in real traffic conditions.

A protocol is presented for the characterization of the in-field pedestrian behavior and the simulation of the resulting structural response. Field-tests demonstrate that the in situ identified pacing rate and synchronization rate among the participants constitute an essential input for the simulation and verification of the human-induced loads.

For slender and lightweight structures, vibration serviceability is a matter of growing concern, often constituting the critical design requirement. With ...

Study of Siphon Breaker Experiment and Simulation for a Research Reactor

Under the design conditions of a research reactor, the siphon phenomenon induced by pipe rupture can cause continuous outward flow of water. To prevent this outflow, a control device is required. A siphon breaker is a type of safety device that can be utilized to control the loss of coolant water effectively.
To analyze the characteristics of siphon breaking, a real-scale experiment was conducted. From the results of the experiment, it was found that there are several design factors that affect the siphon breaking phenomenon. Therefore, there is a need to develop a theoretical model capable of predicting and analyzing the siphon breaking phenomenon under various design conditions. Using the experimental data, it was possible to formulate a theoretical model that accurately predicts the progress and the result of the siphon breaking phenomenon. The established theoretical model is based on fluid mechanics and incorporates the Chisholm model to analyze two-phase flow. From Bernoulli&#39;s equation, the velocity, quantity, undershooting height, water level, pressure, friction coefficient, and factors related to the two-phase flow could be obtained or calculated. Moreover, to utilize the model established in this study, a siphon breaker analysis and design program was developed. The simulation program operates on the theoretical model basis and returns the result as a graph. The user can confirm the possibility of the siphon breaking by checking the shape of the graph. Furthermore, saving the entire simulation result is possible and it can be used as a resource for analyzing the real siphon breaking system.
In conclusion, the user can confirm the status of the siphon breaking and design the siphon breaker system using the program developed in this study.

The siphon breaking phenomenon was investigated experimentally and a theoretical model was proposed. A simulation program based on the theoretical model was developed and the results of the simulation program were compared with experimental results. It was concluded that the results of the simulation program matched the experimental results well.

Under the design conditions of a research reactor, the siphon phenomenon induced by pipe rupture can cause continuous outward flow of water. To prevent ...

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Although electrostatic mechanisms have been proposed in the past to describe the existence of this critical thickness, the importance of chemical defects has been recently accentuated. Here, we describe the growth of metal/LAO/STO heterostructures in an ultra-high vacuum (UHV) cluster system combining pulsed laser deposition (to grow the LAO), magnetron sputtering (to grow the metal) and X-ray photoelectron spectroscopy (XPS). We study step by step the formation and evolution of the q2DES and the chemical interactions that occur between the metal and the LAO/STO. Additionally, magnetotransport experiments elucidate on the transport and electronic properties of the q2DES. This systematic work not only demonstrates a way to study the electrostatic and chemical interplay between the q2DES and its environment, but also unlocks the possibility to couple multifunctional capping layers with the rich physics observed in two-dimensional electron systems, allowing the fabrication of new types of devices.

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

We fabricate metal/LaAlO3/SrTiO3 heterostructures using a combination of pulsed laser deposition and in situ magnetron sputtering. Through magnetotransport and in situ X-ray photoelectron spectroscopy experiments, we investigate the interplay between electrostatic and chemical phenomena of the quasi two-dimensional electron gas formed in this system.

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide ...

Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in industry. The wettability of the produced surface was analyzed by bouncing drop experiments and the topography was analyzed by confocal microscopy. In addition, we show various methodologies to measure its durability and anti-icing properties. Superhydrophobic surfaces hold a special texture that must be preserved to keep their water-repellency. To fabricate durable surfaces, we followed two strategies to incorporate a resistant texture. The first strategy is a direct incorporation of roughness to the metal substrate by acid etching. After this surface texturization, the surface energy was decreased by silanization or fluoropolymer deposition. The second strategy is the growth of a ceria layer (after surface texturization) that should enhance the surface hardness and corrosion resistance. The surface energy was decreased with a stearic acid film.
The durability of the superhydrophobic surfaces was examined by a particle impact test, mechanical wear by lateral abrasion, and UV-ozone resistance. The anti-icing properties were explored by studying the ability to repeal subcooled water, freezing delay, and ice adhesion.

We illustrate several methodologies to produce superhydrophobic metal surfaces and to explore their durability and anti-icing properties.

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in ...