We acknowledge support from the National Natural Science Foundation of China (NSFC) under grant numbers 11621062, 11772294, U1530402, and 11811530001. This research was also partially supported by the China Postdoctoral Science Foundation (2021M690044). This research used the resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract number DE-AC02-05CH11231 and the Shanghai Synchrotron Radiation Facility. This research was partially supported by COMPRES, the Consortium for Materials Properties Research in Earth Sciences under NSF Cooperative Agreement EAR 1606856.

1. Sample preparation
<ol>
	<li>Obtain 3 nm, 20 nm, 40 nm, 70 nm, 100 nm, 200 nm, and 500 nm nickel powder from commercial sources (see Table of Materials). The morphology characterization is shown in Figure 1.</li>
	<li>Prepare 8 nm nickel particles by heating 3 nm nickel particles using a reaction kettle (see Table of Materials).
	<ol>
		<li>Put ~20 mL of absolute ethanol and ~50 mg of 3 nm nickel powder into the reaction kettle. NOTE: The whole solution should not reach ~70% of the kettle volume.</li>
		<li>Heat the reaction kettle at 80 &#176;C for 24 h.</li>
		<li>Cool the solution to room temperature and drop a little solution to one copper mesh (TEM grid, see Table of Materials).</li>
		<li>Put the dried copper mesh into the Transmission Electron Microscopy (TEM) chamber and observe the sample morphology under 200 kV voltage electron beam. 
		NOTE: The copper mesh was air-dried for ~5 min or used a drying light of 5 min.</li>
		<li>Measure the particle size distribution from the TEM images manually. 
		NOTE: The particle size measurement can also be done using any freely available software such as Image J.</li>
		<li>Take out the solution and vaporize the ethanol at room temperature; then, the rest of the black solid is the pure nickel powder with an average particle size of 8 nm.</li>
	</ol>
	</li>
	<li>Prepare 12 nm nickel powder
	<ol>
		<li>Repeat step 1.2, but change the &#34;absolute ethanol&#34; and &#34;80 &#176;C for 24 h&#34; to &#34;absolute isopropanol&#34; and &#34;150 &#176;C for 12 h&#34; to obtain the pure nickel powder with the average particle of 12 nm.</li>
	</ol>
	</li>
</ol>
2. High-pressure radial DAC XRD measurements
<ol>
	<li>Make X-ray transparent boron-epoxy gasket utilizing a laser drilling machine (see Table of Materials).
	<ol>
		<li>Prepare Kapton (a kind of plastic) supporting gaskets 
		NOTE: Kapton is a polyimide film material (see Table of Materials).
		<ol>
			<li>Cut the inner circle with a laser drilling machine using the mentioned parameters: 35% laser power, three passes, 0.4 mm/s (cutting speed).</li>
			<li>Cut the outer rectangular using the parameters: 80% of laser power, two passes, 1.2 mm/s (cutting speed). The rectangular dimension is 8 x 1.4 mm.</li>
		</ol>
		</li>
		<li>Prepare boron-epoxy gaskets from a larger boron disc with a diameter of ~10 mm. 
		NOTE: The boron disc is made by compressing the mixture of amorphous boron powder and epoxy glue36.
		<ol>
			<li>Polish the raw discs to a thickness of 60-100 &#181;m with sandpaper manually. 
			NOTE: The sandpaper is from ~400 mesh to ~1000 mesh.</li>
			<li>Cut the inner circles with a laser drilling machine using the mentioned parameters: 35% laser power, three passes, 0.4 mm/s (cutting speed).</li>
			<li>Cut the outer circle with a laser drilling machine: 30% of laser power, one pass, 0.4 mm/s (cutting speed). Repeat and stop immediately when it comes off.</li>
		</ol>
		</li>
		<li>Assemble the gaskets
		<ol>
			<li>Place a Kapton supporting gasket (prepared in step 2.1.1) on a glass slide.</li>
			<li>Place a drilled boron gasket on the inner hole of the Kapton gasket. Ensure that the larger end of the boron gasket is at the top.</li>
			<li>Put another clean glass slide on the top. Hold it firmly and press it till the gasket is firmly inserted in the hole of Kapton gasket.</li>
			<li>Store the fabricated gasket assemblies between two clean glass slides and wrap them with glue tape for future use. 
			NOTE: The gasket diameter, &#216; = diamond culet size + 150 &#181;m. For better reproducibility, the same setups can be used (possibly with small adjustments if something is found wrong) for the laser drilling and cutting during the gasket preparation. For good size matching, the diameter of gaskets entered for laser cutting is &#216; + 23 &#181;m while the diameter of the inner hole of the Kapton supporting gaskets (entered for laser cutting) is &#216; - 23 &#181;m.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Radial DAC experiment loading
	<ol>
		<li>Mount the gasket assembly
		<ol>
			<li>On the viewing computer monitor (connected to the optical microscope), mark a dot to locate the center of the diamond (the piston diamond of the DAC).</li>
			<li>Mount the boron-epoxy gasket (prepared in step 2.1) and the mark at the center of the gasket hole.</li>
			<li>Use a glass slide to press down the gasket assembly such that the gasket firmly sets on the diamond of the piston. 
			NOTE: A DAC has two identical pieces of diamonds. Generally, the upper one is called cylinder diamond, and the lower one is called piston diamond.</li>
		</ol>
		</li>
		<li>Cleaning and compacting the gasket setup
		<ol>
			<li>Load samples with a chunk size smaller than the gasket hole such that there is no overflow of materials on the gasket surface. 
			NOTE: The samples here mean the candidate materials that we studied in our experiments. In this study, the samples are different-sized Ni powders and Pt chips.</li>
			<li>Close the cell after the loading of a new piece of sample to achieve compactness.</li>
		</ol>
		</li>
		<li>Loading of soft materials (such as gold)
		<ol>
			<li>Load only one piece of the soft sample (make the soft material as a small fraction of the loaded materials).</li>
			<li>Use hard amorphous materials to fill up the gasket hole for good compactness.</li>
		</ol>
		</li>
		<li>Loading of low atomic number materials (such as spinel, pyrope, serpentine)
		<ol>
			<li>Mix the sample with 10% Pt or Au. Fill up the gasket hole with the mixture but without overflow.</li>
			<li>If necessary, put hard amorphous materials on the top for good compactness.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>X-ray diffraction study
	<ol>
		<li>Mount the X-ray transparent boron-Kapton gasket (prepared in step 2.1) with a thickness of 100 &#181;m and a chamber hole of 60 &#181;m on the top of 300 &#181;m culet of DAC with the support of the clays.</li>
		<li>Place a small piece of Pt chip on top of the Ni sample as a pressure calibrant. 
		NOTE: No pressure medium was used to maximize the differential stress between the axial and radial.</li>
		<li>Use a monochromatic synchrotron X-ray (see Table of Materials) with an energy of 25 or 30 keV to conduct the x-ray diffraction experiments.</li>
		<li>Focus the X-ray beam to ~30 x 30 &#181;m2 surface area on the sample.</li>
		<li>Collect the X-ray diffraction patterns at pressure intervals of 1-2 GPa by a two-dimension image plate (see Table of Materials) with a resolution of 100 &#181;m/pixel. The setup used is shown in Figure 2 and Figure 3.</li>
	</ol>
	</li>
	<li>The experimental data analysis
	<ol>
		<li>Process each X-ray diffraction image into a file containing 72 spectra over 5&#176; azimuthal steps using Fit2d37,38,39,40,41,42. 
		NOTE: A two-dimensional diffraction image contains 360&#176; information. To analyze the stress and texture information, it is needed to separate into 72 files with 5&#176; azimuthal information contained in each one. Fit2d is the software used to analyze X-ray diffraction data37,38,39,40,41,42.</li>
		<li>Refine the diffraction pattern with the Rietveld method in the MAUD37 software. The lattice strain of each lattice plane was obtained by fitting the pattern37,40.</li>
		<li>Calculate the differential stress and yield strength according to the lattice strain theory38 and von Mises yield criterion38,39 following step 2.5.</li>
	</ol>
	</li>
	<li>The lattice strain theory for the experimental data analysis
	<ol>
		<li>Determine the differential stress (the difference between these maximum (&#963;22 = &#963;33) and minimum stress (&#963;11) components) that provides a lower-bound estimate of a material&#39;s yield strength38, &#963;y, based on the von Mises yield criterion following equation (1)38: 
		(1)&#160;t= &#963;11-&#963;33&#60;2&#964;= &#963;y.</li>
		<li>Obtain the direction-dependent deviatoric strain Qhkl by measuring the d-spacings from different diffraction directions by following equation (2)38: 
		(2) <img alt="Equation 1" src="/files/ftp_upload/61819/61819eq01.jpg" /> 
		where d0&#176; and d90&#176; are the d-spacings measured from &#936; = 0&#176; and &#936; = 90&#176; (the angle between the diffraction vector and load axis), respectively.</li>
		<li>Then, derive the value of t using equation (3)38: 
		<img alt="Equation 2" src="/files/ftp_upload/61819/61819eq02.jpg" /> 
		where GR(hkl) and Gv are the shear modulus of the aggregates under the Reuss (iso-stress) condition and Voigt (iso-strain) condition, respectively; &#945; is the factor to determine the relative weight of Reuss and Voigt conditions40. 
		NOTE: Considering the current experiments&#39; complicated stress/strain conditions, &#945; = 0.5 is used in this study.</li>
		<li>For a cubic system, calculate GR(hkl) and Gv as follows using equations 4-638,40,41: 
		(4) <img alt="Equation 3" src="/files/ftp_upload/61819/61819eq03.jpg" /> 
		(5) <img alt="Equation 4" src="/files/ftp_upload/61819/61819eq04.jpg" /> 
		(6) <img alt="Equation 5" src="/files/ftp_upload/61819/61819eq05.jpg" /> 
		where Sij are the single crystal elastic compliances and can be obtained from the elastic stiffness constants Cij of materials.</li>
	</ol>
	</li>
</ol>
3. TEM measurements
<ol>
	<li>Prepare thin pressurized Ni foils for TEM using a focused ion beam (FIB) system (see Table of Materials). To reduce possible artifacts during ion milling of the specimen, deposit a protective Pt layer using the Pt gun equipped in the SEM with a thickness of ~1 &#181;m on the candidate region.</li>
	<li>Perform TEM measurements on a 300 kV aberration-corrected transmission electron microscope equipped with high angle annular dark-field (HAADF) and bright-field (BF) detectors.</li>
	<li>Take high-resolution TEM images.</li>
</ol>

The authors have nothing to disclose.

Computational simulations have been widely employed to study the grain size effect on the strength of nanometals5,6,16,17,27,42. Perfect dislocations, partial dislocations, and GB deformation have been proposed to play decisive roles in the deformation mechanisms of the nanomaterials. In a molecular dynamics simulation, Yamak...

The resistance to plastic deformation determines the materials&#39; strength. The strength of the metals usually increases with the decreasing grain sizes. This size strengthening phenomenon can be well illustrated by the traditional Hall-Petch relationship theory from the millimeter down to submicron regime1,2, which is based on the dislocation-mediated deformation mechanism of bulk-sized metals, i.e., dislocations pile up at grain boundaries (GBs) and hinder their motions, leading to the mechanical strengthening in metals3,4.
In contrast, mechanical softening, often referred to as the inverse Hall-Petch relationship, has been reported for fine nanometals in the last two decades5,6,7,8,9,10. Therefore, the strength of the nanometals is still puzzling as continuous hardening was detected for grain sizes down to ~10 nm11,12, while the cases of size softening below 10 nm regime were also reported7,8,9,10. The main difficulty or challenge for this debated topic is to make statistically reproducible measurements on the mechanical properties of ultrafine nanometals and establish a reliable correlation between the strength and grain size of the nanometals. Another part of the difficulty comes from the ambiguity in the plastic deformation mechanisms of the nanometals. Various defects or processes at nanoscale have been reported, including dislocations13,14, deformation twinning15,16,17, stacking faults15,18, GB migration19, GB sliding5,6,20,21, grain rotation22,23,24, atomic bond parameters25,26,27,28, etc. However, which one dominates the plastic deformation and thus determines the strength of nanometals is still unclear.
For these above issues, traditional approaches of mechanical strength examining, such as tensile test29, Vickers hardness test30,31, nano-indentation test32, micropillar compression33,34,35, etc. are less effective because the high quality of large pieces of nanostructured materials is so difficult to fabricate and conventional indenter is much larger than single nanoparticle of materials (for the single-particle mechanics). In this study, we introduce radial DAC XRD techniques36,37,38 to material science to in situ track the yield stress and deformation texturing of nano nickel of various grain sizes, which are used in the geoscience field in previous studies. It has been found that the mechanical strengthening can be extended down to 3 nm, much smaller than the previously reported most substantial sizes of nanometals, which enlarges the regime of conventional Hall-Petch relationship, implying the significance of rDAC XRD techniques to material science.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>20 nm Ni</td>
			<td>Nanomaterialstore</td>
			<td>SN1601</td>
			<td>Flammable</td>
		</tr>
		<tr>
			<td>3 nm Ni</td>
			<td>nanoComposix</td>
			<td></td>
			<td>Flammable</td>
		</tr>
		<tr>
			<td>40, 70, 100, 200, 500 nm Ni</td>
			<td>US nano</td>
			<td>US1120</td>
			<td>Flammable</td>
		</tr>
		<tr>
			<td>Absolute ethanol</td>
			<td></td>
			<td></td>
			<td>as the solution to make 8 nm Ni</td>
		</tr>
		<tr>
			<td>Absolute isopropanol</td>
			<td></td>
			<td></td>
			<td>as the solution to make 12 nm Ni</td>
		</tr>
		<tr>
			<td>Amorphous boron powder</td>
			<td>alfa asear</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Copper mesh</td>
			<td>Beijing Zhongjingkeyi Technology Co., Ltd.</td>
			<td></td>
			<td>TEM grid</td>
		</tr>
		<tr>
			<td>Epoxy glue</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td></td>
			<td></td>
			<td>clean experimental setup</td>
		</tr>
		<tr>
			<td>Focused ion beam</td>
			<td>FEI</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Glass slide</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Glue tape</td>
			<td>Scotch</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Kapton</td>
			<td>DuPont</td>
			<td></td>
			<td>Polyimide film material</td>
		</tr>
		<tr>
			<td>Laser drilling machine</td>
			<td></td>
			<td></td>
			<td>located in high pressure lab of ALS</td>
		</tr>
		<tr>
			<td>Monochromatic synchrotron X-ray</td>
			<td>Beamline 12.2.2, Advanced Light Source (ALS), Lawrence Berkeley National Laboratory</td>
			<td></td>
			<td>X-ray energy: 25-30 keV</td>
		</tr>
		<tr>
			<td>Optical microscope</td>
			<td>Leica</td>
			<td></td>
			<td>to mount the gasket and load samples</td>
		</tr>
		<tr>
			<td>Pt powder</td>
			<td>thermofisher</td>
			<td>38374</td>
			<td></td>
		</tr>
		<tr>
			<td>Reaction kettle</td>
			<td>Xian Yichuang Co.,Ltd.</td>
			<td></td>
			<td>50 mL</td>
		</tr>
		<tr>
			<td>Sand paper</td>
			<td></td>
			<td></td>
			<td>from 400 mesh to 1000 mesh</td>
		</tr>
		<tr>
			<td>Transmission Electron Microscopy</td>
			<td>FEI</td>
			<td></td>
			<td>Titan G2 60-300</td>
		</tr>
		<tr>
			<td>Two-dimension image plate</td>
			<td>ALS, BL 12.2.2</td>
			<td></td>
			<td>mar 345</td>
		</tr>
	</tbody>
</table>

determining the mechanical strength of ultra-fine-grained metals

The mechanical strengthening of metals is the long-standing challenge and popular topic of materials science in industries and academia. The size dependence of the strength of the nanometals has been attracting a lot of interest. However, characterizing the strength of materials at the lower nanometer scale has been a big challenge because the traditional techniques become no longer effective and reliable, such as nano-indentation, micropillar compression, tensile, etc. The current protocol employs radial diamond-anvil cell (rDAC) X-ray diffraction (XRD) techniques to track differential stress changes and determine the strength of ultrafine metals. It is found that ultrafine nickel particles have more significant yield strength than coarser particles, and the size strengthening of nickel continues down to 3 nm. This vital finding immensely depends on effective and reliable characterizing techniques. The rDAC XRD method is expected to play a significant role in studying and exploring nanomaterial mechanics.

Under hydrostatic compression, unrolled X-ray diffraction lines should be straight, not curved. However, under non-hydrostatic pressure, the curvature (ellipticity of the XRD rings, which translates into the non-linearity of the lines plotted along the azimuth angle) significantly increases ultrafine-grained-nickel at similar pressures (Figure 4). At a similar pressure, the differential strain of the 3 nm sized nickel is the highest. The mechanical strength results (stress-strain curves) are...

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Determining the Mechanical Strength of Ultra-Fine-Grained Metals

The protocol presented here describes the high-pressure radial diamond-anvil-cell experiments and analyzing the related data, which are essential for obtaining the mechanical strength of the nanomaterials with a significant breakthrough to the traditional approach.

The mechanical strengthening of metals is the long-standing challenge and popular topic of materials science in industries and academia. The size ...

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2.0K Views.  Harbin Institute of Technology. The protocol presented here describes the high-pressure radial diamond-anvil-cell experiments and analyzing the related data, which are essential for obtaining the mechanical strength of the nanomaterials with a significant breakthrough to the traditional approach.

Video: Determining the Mechanical Strength of Ultra-Fine-Grained Metals

Determining 3D Flow Fields via Multi-camera Light Field Imaging

In the field of fluid mechanics, the resolution of computational schemes has outpaced experimental methods and widened the gap between predicted and observed phenomena in fluid flows. Thus, a need exists for an accessible method capable of resolving three-dimensional (3D) data sets for a range of problems. We present a novel technique for performing quantitative 3D imaging of many types of flow fields. The 3D technique enables investigation of complicated velocity fields and bubbly flows. Measurements of these types present a variety of challenges to the instrument. For instance, optically dense bubbly multiphase flows cannot be readily imaged by traditional, non-invasive flow measurement techniques due to the bubbles occluding optical access to the interior regions of the volume of interest. By using Light Field Imaging we are able to reparameterize images captured by an array of cameras to reconstruct a 3D volumetric map for every time instance, despite partial occlusions in the volume. The technique makes use of an algorithm known as synthetic aperture (SA) refocusing, whereby a 3D focal stack is generated by combining images from several cameras post-capture 1. Light Field Imaging allows for the capture of angular as well as spatial information about the light rays, and hence enables 3D scene reconstruction. Quantitative information can then be extracted from the 3D reconstructions using a variety of processing algorithms. In particular, we have developed measurement methods based on Light Field Imaging for performing 3D particle image velocimetry (PIV), extracting bubbles in a 3D field and tracking the boundary of a flickering flame. We present the fundamentals of the Light Field Imaging methodology in the context of our setup for performing 3DPIV of the airflow passing over a set of synthetic vocal folds, and show representative results from application of the technique to a bubble-entraining plunging jet.

A technique for performing quantitative three-dimensional (3D) imaging for a range of fluid flows is presented. Using concepts from the area of Light Field Imaging, we reconstruct 3D volumes from arrays of images. Our 3D results span a broad range including velocity fields and multi-phase bubble size distributions.

In the field of fluid mechanics, the resolution of computational schemes has outpaced experimental methods and widened the gap between predicted and ...

Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for detailed observation, scenarios that make it challenging to observe with conventional imaging systems. One of these is the drop impact of liquids, which usually happens within one tenth of millisecond. To tackle this challenge, a fast imaging technique is introduced that combines a high-speed camera (capable of up to one million frames per second) with a macro lens with long working distance to bring the spatial resolution of the image down to 10 &#181;m/pixel. The imaging technique enables precise measurement of relevant fluid dynamic quantities, such as the flow field, the spreading distance and the splashing speed, from analysis of the recorded video. To demonstrate the capabilities of this visualization system, the impact dynamics when droplets of non-Newtonian fluids impinge on a flat hard surface are characterized. Two situations are considered: for oxidized liquid metal droplets we focus on the spreading behavior, and for densely packed suspensions we determine the onset of splashing. More generally, the combination of high temporal and spatial imaging resolution introduced here offers advantages for studying fast dynamics across a wide range of microscale phenomena.

Drop impact of non-Newtonian fluids is a complex process since different physical parameters influence the dynamics over a very short time (less than one tenth of a millisecond). A fast imaging technique is introduced in order to characterize the impact behaviors of different non-Newtonian fluids.

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for ...

Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many cases validated experimentally, for light weight or impact energy absorbing structures, as high surface area heat exchangers or electrodes, as implants to the body, and many more. Although great progress has been made in understanding their structure-properties relationships, the large number of different processing techniques, each producing material with different characteristics and structure, means that understanding of the individual effects of all aspects of structure is not complete. The replication process, where molten metal is infiltrated between grains of a removable preform material, allows a markedly high degree of control and has been used to good effect to elucidate some of these relationships. Nevertheless, the process has many steps that are dependent on individual &#8220;know-how&#8221;, and this paper aims to provide a detailed description of all stages of one embodiment of this processing method, using materials and equipment that would be relatively easy to set up in a research environment. The goal of this protocol and its variants is to produce metal foams in an effective and simple way, giving the possibility to tailor the outcome of the samples by modifying certain steps within the process. By following this, open cell aluminum foams with pore sizes of 1&#8211;2.36 mm diameter and 61% to 77% porosity can be obtained.

Replication is one of the processing techniques used for the production of porous metal sponges. In this paper one implementation of the method for the production of open celled porous aluminum is shown in detail.

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many ...

Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at a frequency above the acoustic range (20 kHz). As a solid-state technology, ultrasonic lubrication can be used where conventional lubricants are unfeasible or undesirable. Further, ultrasonic lubrication allows for electrical modulation of the effective friction coefficient between two sliding surfaces. This property enables adaptive systems that modify their frictional state and associated dynamic response as the operating conditions change. Surface wear can also be reduced through ultrasonic lubrication. We developed a protocol to investigate the dependence of friction force reduction and wear reduction on the linear sliding velocity between ultrasonically lubricated surfaces. A pin-on-disc tribometer was built which differs from commercial units in that a piezoelectric stack is used to vibrate the pin at 22 kHz normal to the rotating disc surface. Friction and wear metrics including effective friction force, volume loss, and surface roughness are measured without and with ultrasonic vibrations at a constant pressure of 1 to 4 MPa and three different sliding velocities: 20.3, 40.6, and 87 mm/sec. An optical profilometer is utilized to characterize the wear surfaces. The effective friction force is reduced by 62% at 20.3 mm/sec. Consistently with existing theories for ultrasonic lubrication, the percent reduction in friction force diminishes with increasing speed, down to 29% friction force reduction at 87 mm/sec. Wear reduction remains essentially constant (49%) at the three speeds considered.

We present a protocol for using a piezoelectrically-assisted tribometer and optical profilometer to investigate the dependence of ultrasonic wear and friction reduction on linear velocity, contact pressure, and surface properties.

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at ...

Indirect Fabrication of Lattice Metals with Thin Sections Using Centrifugal Casting

One of the typical methods to manufacture 3D lattice metals is the direct-metal additive manufacturing (AM) process such as Selective Laser Melting (SLM) and Electron Beam Melting (EBM). In spite of its potential processing capability, the direct AM method has several disadvantages such as high cost, poor surface finish of final products, limitation in material selection, high thermal stress, and anisotropic properties of parts. We propose a cost-effective method to manufacture 3D lattice metals. The objective of this study is to provide a detailed protocol on fabrication of 3D lattice metals having a complex shape and a thin wall thickness; e.g., octet truss made of Al and Cu alloys having a unit cell length of 5 mm and a cell wall thickness of 0.5 mm. An overall experimental procedure is divided into eight sections: (a) 3D printing of sacrificial patterns (b) melt-out of support materials (c) removal of residue of support materials (d) pattern assembly (e) investment (f) burn-out of sacrificial patterns (g) centrifugal casting (h) post-processing for final products. The suggested indirect AM technique provides the potential to manufacture ultra-lightweight lattice metals; e.g., lattice structures with Al alloys. It appears that the process parameters should be properly controlled depending on materials and lattice geometry, observing the final products of octet truss metals by the indirect AM technique.

An indirect additive manufacturing method combining a 3D printing of polymers with a centrifugal casting is outlined for manufacturing 3D octet truss metals (Al and Cu alloys) having a unit cell length of 5 mm with a wall thickness of 0.5 mm.

One of the typical methods to manufacture 3D lattice metals is the direct-metal additive manufacturing (AM) process such as Selective Laser Melting (SLM) ...

Data Acquisition Protocol for Determining Embedded Sensitivity Functions

The effectiveness of many structural health monitoring techniques depends on the placement of sensors and the location of input forces. Algorithms for determining optimal sensor and forcing locations typically require data, either simulated or measured, from the damaged structure. Embedded sensitivity functions provide an approach for determining the best available sensor location to detect damage with only data from the healthy structure. In this video and manuscript, the data acquisition procedure and best practices for determining the embedded sensitivity functions of a structure is presented. The frequency response functions used in the calculation of the embedded sensitivity functions are acquired using modal impact testing. Data is acquired and representative results are shown for a residential scale wind turbine blade. Strategies for evaluating the quality of the data being acquired are provided during the demonstration of the data acquisition process.

The data acquisition procedure for determining embedded sensitivity functions is described. Data is acquired and representative results are shown for a residential scale wind turbine blade.

The effectiveness of many structural health monitoring techniques depends on the placement of sensors and the location of input forces. Algorithms for ...

A Robotic Platform to Study the Foreflipper of the California Sea Lion

The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most of their thrust with their large foreflippers. This protocol describes a robotic platform designed to study the hydrodynamic performance of the swimming California sea lion (Zalophus californianus). The robot is a model of the animal&#39;s foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the &#39;clap&#39;). The kinematics of the sea lion&#39;s propulsive stroke are extracted from video data of unmarked, non-research sea lions at the Smithsonian Zoological Park (SNZ). Those data form the basis of the actuation motion of the robotic flipper presented here. The geometry of the robotic flipper is based a on high-resolution laser scan of a foreflipper of an adult female sea lion, scaled to about 60% of the full-scale flipper. The articulated model has three joints, mimicking the elbow, wrist and knuckle joint of the sea lion foreflipper. The robotic platform matches dynamics properties&#8212;Reynolds number and tip speed&#8212;of the animal when accelerating from rest. The robotic flipper can be used to determine the performance (forces and torques) and resulting flowfields.

A robotic platform is described that will be used to study the hydrodynamic performance&#8212;forces and flowfields&#8212;of the swimming California sea lion. The robot is a model of the animal&#39;s foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the &#39;clap&#39;).

The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most ...

Characterization of Ultra-fine Grained and Nanocrystalline Materials Using Transmission Kikuchi Diffraction

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and nanocrystalline materials. The traditional techniques associated with scanning electron microscopy (SEM), such as electron backscatter diffraction (EBSD), do not possess the required spatial resolution due to the large interaction volume between the electrons from the beam and the atoms of the material. Transmission electron microscopy (TEM) has the required spatial resolution. However, due to a lack of automation in the analysis system, the rate of data acquisition is slow which limits the area of the specimen that can be characterized. This paper presents a new characterization technique, Transmission Kikuchi Diffraction (TKD), which enables the analysis of the microstructure of UFG and nanocrystalline materials using an SEM equipped with a standard EBSD system. The spatial resolution of this technique can reach 2 nm. This technique can be applied to a large range of materials that would be difficult to analyze using traditional EBSD. After presenting the experimental set up and describing the different steps necessary to realize a TKD analysis, examples of its use on metal alloys and minerals are shown to illustrate the resolution of the technique and its flexibility in term of material to be characterized.

This paper provides a detailed method to characterize the microstructure of ultra-fine grained and nanocrystalline materials using a scanning electron microscope equipped with a standard electron backscatter diffraction system. Metal alloys and minerals presenting refined microstructures are analyzed using this technique, showing the diversity of its possible applications.

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and ...

A Novel Biaxial Testing Apparatus for the Determination of Forming Limit under Hot Stamping Conditions

The hot stamping and cold die quenching process is increasingly used to form complex shaped structural components of sheet metals. Conventional experimental approaches, such as out-of-plane and in-plane tests, are not applicable to the determination of forming limits when heating and rapid cooling processes are introduced prior to forming for tests conducted under hot stamping conditions. A novel in-plane biaxial testing system was designed and used for the determination of forming limits of sheet metals at various strain paths, temperatures, and strain rates after heating and cooling processes in a resistance heating uniaxial testing machine. The core part of the biaxial testing system is a biaxial apparatus, which transfers a uniaxial force provided by the uniaxial testing machine to a biaxial force. One type of cruciform specimen was designed and verified for the formability test of aluminum alloy 6082 using the proposed biaxial testing system. The digital image correlation (DIC) system with a high-speed camera was used for taking strain measurements of a specimen during a deformation. The aim of proposing this biaxial testing system is to enable the forming limits of an alloy to be determined at various temperatures and strain rates under hot stamping conditions.

This protocol proposes a novel biaxial testing system used on a resistance heating uniaxial tensile test machine in order to determine the forming limit diagram (FLD) of sheet metals under hot stamping conditions.

The hot stamping and cold die quenching process is increasingly used to form complex shaped structural components of sheet metals. Conventional ...

Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory

Given their potential for significant property improvements relative to their large grained counterparts, much work has been devoted to the continued development of nanocrystalline metals. Despite these efforts, the transition of these materials from the lab bench to actual applications has been blocked by the inability to produce large scale parts that retain the desired nanocrystalline microstructures. Following the development of a method proven to stabilize the nanosized grain structure to temperatures approaching that of the melting point for the given metal, the US Army Research Laboratory (ARL) has progressed to the next stage in the development of these materials - namely the production of large scale parts suitable for testing and evaluation in a range of relevant test environments. This report provides a broad overview of the ongoing efforts in the processing, characterization, and consolidation of these materials at ARL. In particular, focus is placed on the methodology used for producing the nanocrystalline metal powders, in both small and large-scale amounts, that are at the center of ongoing research efforts.

This paper provides a brief overview of the ongoing efforts at the Army Research Laboratory on the processing of bulk nanocrystalline metals with an emphasis on the methodologies used for the production of the novel metal powders.

Given their potential for significant property improvements relative to their large grained counterparts, much work has been devoted to the continued ...