This work was supported in part by the Fundamental Research Funds for the Central Universities under Grant 2042022kf1059; the Nature Science Foundation of Hubei Province under Grant 2022CFB757; the China Postdoctoral Science Foundation under Grant 2022TQ0244; the Wuhan University Experiment Technology Project Funding under Grant WHU-2021-SYJS-11; the Provincial Teaching and Research Projects in Hubei Province&#39;s Colleges and Universities in 2021 under Grant 2021038; and the Provincial Laboratory Research Project in Hubei Province&#39;s Colleges and Universities under Grant HBSY2021-01.

In this work, the procedures of the microcantilever beam fracture experiment with cracks are discussed as follows, which is open for free access via&#160;http://civ.whu.rofall.net/virexp/clqd. All the&#160;steps are conducted in the online system based on the virtual simulation approach. Institutional Review Board approval was not required for this study. Consent was obtained from the student volunteers who took part in this study.
1. Accessing the system and entering the interface
<ol>
	<li>Open a web browser, and enter the URL&#160;http://civ.whu.rofall.net/virexp/clqd to access the system. 
	NOTE: The provided URL can be accessed through a mainstream web browser without a username and password.</li>
	<li>Find the virtual simulation interface using the vertical scrollbar. 
	NOTE: The virtual scene is embedded into the web.</li>
	<li>Click on the FullScreen icon at the bottom-right corner to enable a full-screen interface.</li>
	<li>Click on the Start Experiment button to start.</li>
	<li>Click on the Enter button to follow the guidance for beginners, or click on the Skip button to skip this step. 
	&#8203;NOTE: The user can choose to follow (Enter button) or skip (Skip button). The guidance for beginners provides descriptions of the entire system. The interface also highlights the operation instructions step-by-step for performing the intended operations or equipment. Figure 1 shows the equipment used in the experiment, including seven types of equipment in the mechanical and material disciplines. Beginners are recommended to follow this guidance.</li>
</ol>
2. Preparation of the materials
<ol>
	<li>Start the experiment after completing the beginner-level training. Follow the prompts on the interface to &#34;walk&#34; close to the laboratory table that contains the silicon wafers, review the differences between the normal-type and crack-type silicon wafers, and select the crack template. 
	NOTE: Enter the experiment interface, and conduct experiments according to the highlighted pathway guidance. The highlighted guidance is provided throughout the process to offer clear guidance for experimentation.</li>
	<li>Select a material from the provided materials list. 
	NOTE: The provided material list includes gold, silver, PtCuNiP, ZrTiCuNiBe, polyether-ether-ketone (PEEK), and polymethyl methacrylate (PMMA).</li>
	<li>Load the selected material onto the cutter clamp with a click on the highlighted material. Click on the highlighted ON/OFF button (on the right side) to turn on the cutter clamp, click on the Speed button (on the left side), and set the speed of the metallographic cutting machine in a pop-up interface. 
	NOTE: The user can set a proper speed as they wish. Once the speed is set by the user, the cutter clamp will be activated, and the raw bar will be cut into thin slices.</li>
	<li>Stack the mold, metal sheet, and cover sheet together in turn by clicking and dragging the highlighted object as guided in the user interface. 
	&#8203;NOTE: After cutting the material, this assembly step is necessary before nano-mold casting.</li>
</ol>
3. Molding the specimen
<ol>
	<li>Walk virtually to the high-temperature universal creep testing machine following the guidance shown in Figure 2, and virtually place the stacked specimens between the plate clamps of the universal creep testing machine. 
	NOTE: After this step, the virtual computer on the left side of the high-temperature universal creep testing machine will be highlighted.</li>
	<li>Click on the Virtual Computer, and set the test scheme on the control computer of the universal creep testing machine. 
	NOTE: After this step, the auxiliary equipment of the high-temperature universal creep testing machine for heating and vacuum pumping will be highlighted to provide guidance to the user.</li>
	<li>Click on the highlighted Heating and Vacuum Pumping Equipment, and turn on the power supply. Open the virtual mechanical pump and the backing valve in the interface by clicking on the highlighted buttons. 
	NOTE: This step completes the system vacuum control settings in the vacuum control system of the universal creep testing machine.</li>
	<li>Click on the Clear button on the Control Panel of the universal creep testing machine to clear the data. Click on the Run button on the Control Panel of the universal creep testing machine to complete the experiment, which copies the pattern on the mold to the metal sheet using the parallel plate compression molding method. 
	NOTE: After the mold casting is completed, remove the specimen, and close the backing valve and the mechanical pump, etc., of the heating and vacuum pumping equipment by clicking on the buttons in turn as required (in real heating and vacuum pumping equipment, the reverse order may cause the molecular pump to burn out).</li>
	<li>Click on the Virtual Computer again, and check the experimental data on the control computer of the universal creep testing machine.</li>
	<li>Open the cover plate on the metallographic specimen inlaying machine, and place the specimen.
	<ol>
		<li>Click on the highlighted PMMA powder to pour the prepared powder, and click on the highlighted mold to place it on top of the PMMA powder.</li>
		<li>Click on the highlighted hand wheel to adjust the position of the mold, which will cover the cover plate automatically. Click on the ON/OFF button to turn on the inlaying machine. Take out the PMMA inlaid specimen after cooling. 
		NOTE: The molded specimen should be mounted on the inlaying machine in the correct direction, as shown in Figure 3, in which the thermoplastic material PMMA is used in the experiment. Make sure the PMMA powder melts and adheres to the surface of the specimen. The bottom-left corner of Figure 4 illustrates the correct direction after the user confirms the selection shown in Figure 3.</li>
	</ol>
	</li>
	<li>Enter the room for polishing and corrosion following the pathway guidance, as shown in Figure 5. Find the highlighted polishing machine, and click on the gripper of the polishing machine to mount the inlaid specimen to the gripper. Set the speed to grind and polish the specimen to remove the molded material substrate. 
	&#8203;NOTE: Grind the mold on one side of the mold until the pattern on the mold is exposed.</li>
</ol>
4. Specimen characterization
<ol>
	<li>Register in the e-notebook before using a chemical. Open the chemical storage cabinet, and take out the solid KOH and acetone solution. Click on the highlighted beaker to use the acetone solution to clean the specimen. Click on another highlighted beaker and solid KOH for corrosion liquid preparation to prepare a 10% KOH solution. Click on the highlighted KOH solution and the specimen to corrode the specimen into a metallographic specimen. 
	NOTE: In this experiment, to remove the silicon mold, a 6 mol/L KOH solution is usually prepared, the specimen is placed in the preparation solution, and the beaker containing the corrosion solution and the specimen is placed on a hot plate to heat up to accelerate the corrosion rate.</li>
	<li>Clean the specimen after removing the silicon substrate, and run a characterized testing with the prepared specimen under an optical microscope. 
	&#8203;NOTE: Remember to determine the integrity of the specimen after the grinding and corrosion.</li>
</ol>
5. Specimen loading and nanoindenter installation
<ol>
	<li>Load the specimen onto the sample stage of the nanoindenter. Choose the cone indenter to mount it on the driver of the micro- and nanomechanics testing system. Click on the highlighted drive to connect it with the nanoindenter. 
	&#8203;NOTE: The &#34;Pin&#34; must be inserted into the drive shaft when installing the indenter, and since the drive shaft is a slender bar, the latch avoids damaging the drive shaft when screwing the indenter with a threaded end into the drive.</li>
</ol>
6. SEM in situ experiment
<ol>
	<li>Click the Vent button in the SEM control software after installing the indenter of the nanoindenter and loading the specimen as described in 5.1.</li>
	<li>Open the SEM chamber after breaking the vacuum, install the nanoindenter on the SEM sample stage, and connect the wires (Figure 6 shows an example of connecting one of the wires).</li>
	<li>Open the control software of the nanoindenter, and select Loaded Indenter Range &#62; Select Experimental Protocol &#62; Start Controller &#62; Init* (Sample Stage Initialization). 
	NOTE: The position initialization process of the nanoindenter sample stage must be carried out in the state in which the SEM cavity is open to avoid the initialization process of the nanoindenter sample stage hitting the pole of the SEM electron outlet port.</li>
	<li>Close the SEM chamber, and click on the Pump button on the SEM control software.</li>
	<li>Click on the Up or Down button in the SEM control software to adjust the position of the sample stage so that the sample to be measured falls into the SEM field of view. Click on the OK button to fix the position. Click on the highlighted EHT button to turn on the electron gun. Click on the Camera button, and switch to the electron microscopy observation mode. 
	NOTE: The indenter of the nanoindenter should be controlled in observation mode to gradually approach the sample to be measured.</li>
	<li>Click on the Run button on the control software of the nanoindenter. 
	NOTE: During the experiment, it is necessary to observe and record the deformation characteristics and failure process during the loading process of the specimen and to open the original data of the experiment in the data analysis window after the experiment is complete for plotting and exporting the data.</li>
	<li>Click the Stop button on the control software of the nanoindenter to terminate the experiment. 
	NOTE: The virtual simulation experiment ends here. The user is asked to complete the online exam exercise in the virtual interface after the experimentation.</li>
</ol>

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	<li>Chong, K., Chuang, T. J., Anderson, P. M., Wu, M. K., Hsieh, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nano+mechanics/materials+research.">Nano mechanics/materials research.</a> Nanomechanics of Materials and Structures. , 13-22 (2006).</li><li>Ratner, B. M., Ratner, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Nanotechnology: A Gentle Introduction to the Next Big Idea. , (2003).</li><li>Li, Y., Wang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Precipitation+behavior+in+boundaries+and+its+influence+on+impact+toughness+in+22Cr25Ni3W3CuCoNbN+steel+during+short-term+ageing.">Precipitation behavior in boundaries and its influence on impact toughness in 22Cr25Ni3W3CuCoNbN steel during short-term ageing.</a> Materials Science and Engineering A. 809, 140924 (2021).</li><li>Li, Y., Wang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strengthening+mechanisms+and+creep+rupture+behavior+of+advanced+austenitic+heat+resistant+steel+SA-213+S31035+for+A-USC+power+plants.">Strengthening mechanisms and creep rupture behavior of advanced austenitic heat resistant steel SA-213 S31035 for A-USC power plants.</a> Materials Science and Engineering A. 775, 138991 (2020).</li><li>Wang, X., Li, Y., Chen, D., Sun, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Precipitate+evolution+during+the+aging+of+Super304H+steel+and+its+influence+on+impact+toughness.">Precipitate evolution during the aging of Super304H steel and its influence on impact toughness.</a> Materials Science and Engineering A. 754, 238-245 (2019).</li><li>Juri, A. 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The authors have nothing to disclose.

One of the advantages of virtual simulation experiments is that they allow users to conduct the experiments without concerns regarding damaging the physical system or causing any harm to themselves11. Thus, users can conduct any operations, including either correct or wrong operations. However, the system gives the user a warning message that is integrated into the interactive experiment to guide them to conduct the experiments correctly when a wrong operation is conducted. In this way, users can ...

Mechanics is one of the basic disciplines in engineering, as shown by the emphasis placed on the foundation of mathematical mechanics and theoretical knowledge and the attention given to the cultivation of students&#39; practical abilities. With the rapid advancement of modern science and technology, nanoscience and technology have had a huge impact on human life and the economy. Rita Colwell, the former director of the US National Science Foundation (NSF), declared in 2002 that nanoscale technology would have an impact equal to the Industrial Revolution1 and noted that nanotechnology is truly a portal to a new world2. The mechanical properties of materials at the nanoscale are one of the most fundamental and necessary factors for the development of high-tech applications, such as nano-devices3,4,5. The mechanical behavior of materials at the nanoscale and the structural evolution under stress have become important issues in current nanomechanical research.
In recent years, the development and improvement of nanoindentation technology, electron microscopy technology, scanning probe microscopy, etc., have made &#34;in situ mechanics&#34; experiments an advanced testing technique important in nanomechanics research6,7. Obviously, from the perspective of teaching and scientific research, it is necessary to introduce frontier experimental techniques into the traditional teaching content regarding mechanical experiments.
However, experiments of microscopic mechanics are significantly different from macroscopic basic mechanics experiments. On the one hand, although the relevant instruments and equipment have been popularized in almost all colleges and universities, their number is limited because of the high price and maintenance cost. In the short term, it is impossible to purchase enough equipment for offline teaching. Even if there are financial resources, the management and maintenance costs of offline experiments are too high, since this type of equipment has high-precision characteristics.
On the other hand, in situ mechanics experiments such as scanning electron microscopy (SEM) are very comprehensive, with high operational requirements and an extremely long experimental period8,9. Offline experiments require students to be highly focused for a long time, and misoperation can damage the instrument. Even with very skilled individuals, a successful experiment requires a few days to complete, from preparing qualified specimens to loading the specimens for in situ mechanics experiments. Therefore, the efficiency of offline experimental teaching is extremely low.
To address the above issues, virtual simulation can be utilized. The development of virtual simulation experiment teaching can address the cost and quantity bottleneck of in situ mechanics experimental equipment and, thus, allow students to easily use various advanced pieces of equipment without damaging high-tech instruments. Simulation experiment teaching also enables students to access the virtual simulation experiment platform via the internet anytime and anywhere. Even for some low-cost instruments, students can use virtual instruments in advance for training and practice, which may improve teaching efficiency.
Considering the accessibility and availability of web-based systems10, in this work, we present a web-based virtual simulation experimentation system that can provide a set of experiments related to fundamental operations in mechanics and materials, with a focus on the in situ mechanics experiment.

<table><tbody><tr><td>Virtual interface</td><td>None</td><td>None</td><td>http://civ.whu.rofall.net/virexp/clqd</td></tr></tbody></table>

a virtual simulation experiment of mechanics: material deformation and failure based on scanning electron microscopy

This work presents a set of comprehensive virtual experiments to detect material deformation and failure. The most commonly used pieces of equipment in mechanics and material disciplines, such as a metallographic cutting machine and a high-temperature universal creep testing machine, are integrated into a web-based system to provide different experimental services to users in an immersive and interactive learning environment. The protocol in this work is divided into five subsections, namely, the preparation of the materials, molding the specimen, specimen characterization, specimen loading, nanoindenter installation, and SEM in situ experiments, and this protocol aims to provide an opportunity for users regarding the recognition of different equipment and the corresponding operations, as well as the enhancement of laboratory awareness, etc., using a virtual simulation approach. To provide clear guidance for the experiment, the system highlights the equipment/specimen to be used in the next step and marks the pathway that leads to the equipment with a conspicuous arrow. To mimic the hands-on experiment as closely as possible, we designed and developed a three-dimensional laboratory room, equipment, operations, and experimental procedures. Moreover, the virtual system also considers interactive exercises and registration before using chemicals during the experiment. Incorrect operations are also allowed, resulting in a warning message informing the user. The system can provide interactive and visualized experiments to users at different levels.

The system provides clear guidance for the user&#39;s operations. First, beginner-level training is integrated when a user enters the system. Second, the equipment and the laboratory room to be used for the next-step operation are highlighted.
The system can be used for several different educational purposes for different levels of students. For example, Figure 1 includes seven of the most commonly used types of equipment in the mechanical and mat...

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A Virtual Simulation Experiment of Mechanics: Material Deformation and Failure Based on Scanning Electron Microscopy

This work presents a three-dimensional virtual simulation experiment for material deformation and failure that provides visualized experimental processes. Through a set of experiments, users can become familiar with the equipment and learn the operations in an immersive and interactive learning environment.

This work presents a set of comprehensive virtual experiments to detect material deformation and failure. The most commonly used pieces of equipment in ...

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2.0K Views.  Wuhan University. This work presents a three-dimensional virtual simulation experiment for material deformation and failure that provides visualized experimental processes. Through a set of experiments, users can become familiar with the equipment and learn the operations in an immersive and interactive learning environment.

Video: A Virtual Simulation Experiment of Mechanics: Material Deformation and Failure Based on Scanning Electron Microscopy

In Situ Time-dependent Dielectric Breakdown in the Transmission Electron Microscope: A Possibility to Understand the Failure Mechanism in Microelectronic Devices

The time-dependent dielectric breakdown (TDDB) in on-chip interconnect stacks is one of the most critical failure mechanisms for microelectronic devices. The aggressive scaling of feature sizes, both on devices and interconnects, leads to serious challenges to ensure the required product reliability. Standard reliability tests and post-mortem failure analysis provide only limited information about the physics of failure mechanisms and degradation kinetics. Therefore it is necessary to develop new experimental approaches and procedures to study the TDDB failure mechanisms and degradation kinetics in particular. In this paper, an in situ experimental methodology in the transmission electron microscope (TEM) is demonstrated to investigate the TDDB degradation and failure mechanisms in Cu/ULK interconnect stacks. High quality imaging and chemical analysis are used to study the kinetic process. The in situ electrical test is integrated into the TEM to provide an elevated electrical field to the dielectrics. Electron tomography is utilized to characterize the directed Cu diffusion in the insulating dielectrics. This experimental procedure opens a possibility to study the failure mechanism in interconnect stacks of microelectronic products, and it could also be extended to other structures in active devices.

In Situ Time-dependent Dielectric Breakdown in the Transmission Electron Microscope: A Possibility to Understand the Failure Mechanism in Microelectronic Devices

The time-dependent dielectric breakdown (TDDB) in on-chip interconnect stacks is one of the most critical failure mechanisms for microelectronic devices. This paper demonstrates the procedure of an in situ TDDB experiment in the transmission electron microscope, which opens a possibility to study the failure mechanism in microelectronic products.

The time-dependent dielectric breakdown (TDDB) in on-chip interconnect stacks is one of the most critical failure mechanisms for microelectronic devices. ...

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

The optical, electrical, and structural properties of dislocations and of grain boundaries in semiconductor materials can be determined by experiments performed in a scanning electron microscope. Electron microscopy has been used to investigate cathodoluminescence, electron beam induced current, and diffraction of backscattered electrons.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...

A Coupled Experiment-finite Element Modeling Methodology for Assessing High Strain Rate Mechanical Response of Soft Biomaterials

This study offers a combined experimental and finite element (FE) simulation approach for examining the mechanical behavior of soft biomaterials (e.g. brain, liver, tendon, fat, etc.) when exposed to high strain rates. This study utilized a Split-Hopkinson Pressure Bar (SHPB) to generate strain rates of 100-1,500 sec-1. The SHPB employed a striker bar consisting of a viscoelastic material (polycarbonate). A sample of the biomaterial was obtained shortly postmortem and prepared for SHPB testing. The specimen was interposed between the incident and transmitted bars, and the pneumatic components of the SHPB were activated to drive the striker bar toward the incident bar. The resulting impact generated a compressive stress wave (i.e. incident wave) that traveled through the incident bar. When the compressive stress wave reached the end of the incident bar, a portion continued forward through the sample and transmitted bar (i.e. transmitted wave) while another portion reversed through the incident bar as a tensile wave (i.e. reflected wave). These waves were measured using strain gages mounted on the incident and transmitted bars. The true stress-strain behavior of the sample was determined from equations based on wave propagation and dynamic force equilibrium. The experimental stress-strain response was three dimensional in nature because the specimen bulged. As such, the hydrostatic stress (first invariant) was used to generate the stress-strain response. In order to extract the uniaxial (one-dimensional) mechanical response of the tissue, an iterative coupled optimization was performed using experimental results and Finite Element Analysis (FEA), which contained an Internal State Variable (ISV) material model used for the tissue. The ISV material model used in the FE simulations of the experimental setup was iteratively calibrated (i.e. optimized) to the experimental data such that the experiment and FEA strain gage values and first invariant of stresses were in good agreement.

The current study prescribes a coupled experiment-finite element simulation methodology to obtain the uniaxial dynamic mechanical response of soft biomaterials (brain, liver, tendon, fat, etc.). The multiaxial experimental results that arose because of specimen bulging obtained from Split-Hopkinson Pressure Bar testing were rendered to a uniaxial true stress-strain behavior when simulated through iterative optimization of the finite element analysis of the biomaterial.

This study offers a combined experimental and finite element (FE) simulation approach for examining the mechanical behavior of soft biomaterials (e.g. ...

Bioengineering

Full-field Strain Measurements for Microstructurally Small Fatigue Crack Propagation Using Digital Image Correlation Method

A novel measurement approach is used to reveal the cumulative deformation field at a sub-grain level and to study the influence of microstructure on the growth of microstructurally small fatigue cracks. The proposed strain field analysis methodology is based on the use of a unique pattering technique with a characteristic speckle size of approximately 10 &#181;m. The developed methodology is applied to study the small fatigue crack behavior in body centered cubic (bcc) Fe-Cr ferritic stainless steel with a relatively large grain size allowing a high spatial measurement accuracy at the sub-grain level. This methodology allows the measurement of small fatigue crack growth retardation events and associated intermittent shear strain localization zones ahead of the crack tip. In addition, this can be correlated with the grain orientation and size. Thus, the developed methodology can provide a deeper fundamental understanding of the small fatigue crack growth behavior, required for the development of robust theoretical models for the small fatigue crack&#160;propagation in polycrystalline materials.

Microstructurally small fatigue crack growth behavior is investigated using a novel methodological approach combining crack growth rate measurement and strain-field analysis to reveal the cumulative deformation field at sub-grain level.

A novel measurement approach is used to reveal the cumulative deformation field at a sub-grain level and to study the influence of microstructure on the ...

Visualization of Failure and the Associated Grain-Scale Mechanical Behavior of Granular Soils under Shear using Synchrotron X-Ray Micro-Tomography

The rapid development of X-ray imaging techniques with image processing and analysis skills has enabled the acquisition of CT images of granular soils with high-spatial resolutions. Based on such CT images, grain-scale mechanical behavior such as particle kinematics (i.e., particle translations and particle rotations), strain localization and inter-particle contact evolution of granular soils can be quantitatively investigated. However, this is inaccessible using conventional experimental methods. This study demonstrates the exploration of the grain-scale mechanical behavior of a granular soil sample under triaxial compression using synchrotron X-ray micro-tomography (&#956;CT). With this method, a specially fabricated miniature loading apparatus is used to apply confining and axial stresses to the sample during the triaxial test. The apparatus is fitted into a synchrotron X-ray tomography setup so that high-spatial resolution CT images of the sample can be collected at different loading stages of the test without any disturbance to the sample. With the capability of extracting information at the macro scale (e.g., sample boundary stresses and strains from the triaxial apparatus setup) and the grain scale (e.g., grain movements and contact interactions from the CT images), this procedure provides an effective methodology to investigate the multi-scale mechanics of granular soils.

The protocol describes procedures to acquire high-spatial resolution computed tomography (CT) images of a granular soil during triaxial compression, and to apply image processing techniques to these CT images to explore the grain-scale mechanical behavior of the soil under loading.

The rapid development of X-ray imaging techniques with image processing and analysis skills has enabled the acquisition of CT images of granular soils ...

Sample Preparation and Experimental Design for In Situ Multi-Beam Transmission Electron Microscopy Irradiation Experiments

There is a need to understand materials exposed to overlapping extreme environments such as high temperature, radiation, or mechanical stress. When these stressors are combined there may be synergistic effects that enable unique microstructural evolution mechanisms to activate. Understanding of these mechanisms is necessary for the input and refinement of predictive models and critical for engineering of next generation materials. The basic physics and underlying mechanisms require advanced tools to be investigated. The in situ ion irradiation transmission electron microscope (I&#179;TEM) is designed to explore these principles.
To quantitatively probe the complex dynamic interactions in materials, careful preparation of samples and consideration of experimental design is required. Particular handling or preparation of samples can easily introduce damage or features that obfuscate the measurements. There is no one correct way to prepare a sample; however, many mistakes can be made. The most common errors and things to consider are highlighted within. The I&#179;TEM has many adjustable variables and a large potential experimental space, therefore it is best to design experiments with a specific scientific question or questions in mind.
Experiments have been performed on large number of sample geometries, material classes, and with many irradiation conditions. The following are a subset of examples that demonstrate unique in situ capabilities utilizing the I3TEM. Au nanoparticles prepared by drop casting have been used to investigate the effects of single ion strikes. Au thin films have been used in studies on the effects of multibeam irradiation on microstructure evolution. Zr films have been exposed to irradiation and mechanical tension to examine creep. Ag nanopillars were subjected to simultaneous high temperature, mechanical compression, and ion irradiation to study irradiation induced creep as well. These results impact fields including: structural materials, nuclear energy, energy storage, catalysis, and microelectronics in space environments.

Sample preparation techniques are outlined with specific considerations for in situ ion irradiation TEM experiments. Ion species, energy, and fluence are discussed with methods for how to select and compute them. Finally, procedures for conducting an experiment are described and accompanied by the representative results.

There is a need to understand materials exposed to overlapping extreme environments such as high temperature, radiation, or mechanical stress. When these ...

Imaging of the Microstructural Failure Mechanism in the Human Hip

Imaging the bone microstructure under progressively increasing loads allows for observing the microstructural failure behavior of bone. Here, we describe a protocol for obtaining a sequence of three-dimensional microstructural images of the entire proximal femur under progressively increasing deformation, causing clinically relevant fractures of the femoral neck. The protocol is demonstrated using four femora from female donors aged 66-80 years at the lower end of bone mineral density in the population (T-score range = &#8722;2.09 to &#8722;4.75). A radio-transparent compressive stage was designed for loading the specimens replicating a one-leg stance, while recording the applied load during&#160;micro-computed tomography (micro-CT) imaging. The field of view was 146 mm wide and 132 mm high, and the isotropic pixel size was 0.03 mm. The force increment was based on finite-element predictions of the fracture load. The compressive stage was used to apply the displacement to the specimen and enact the prescribed force increments. Sub-capital fractures due to opening and shear of the femoral neck occurred after four to five load increments. The micro-CT&#160;images and the reaction force measurements were processed to study the bone strain and energy absorption capacity. Instability of the cortex appeared at the early loading steps. The subchondral bone in the femoral head displayed large deformations reaching 16% before&#160;fracture, and a progressive increase in the support capacity up to&#160;fracture. The deformation energy linearly increased with the displacement up to&#160;fracture, while the stiffness decreased to near-zero values immediately before&#160;fracture. Three-fourths of the fracture energy was taken by the specimen during the final 25% force increment. In conclusion, the protocol developed revealed a remarkable energy absorption capacity, or damage tolerance, and a synergic interaction between the cortical and trabecular bone at an advanced donor age.

The protocol enables the measurement of the deformation of the bone microstructure in the entire proximal human femur and its toughness by combining large-volume micro-CT scanning, a custom-made compressive stage, and advanced image processing tools.

Imaging the bone microstructure under progressively increasing loads allows for observing the microstructural failure behavior of bone. Here, we describe ...

Surface Defects in NiTi Files After Single and Multiple Uses in Endodontic Retreatment

Scanning Electron Microscopic Evaluation of Surface Defects of Remover Retreatment File After Single and Multiple Uses

This study aimed to evaluate surface defects of Remover rotary Nickel-Titanium (NiTi) files after single and multiple uses in conventional endodontic retreatment procedures using scanning electron microscopy (SEM). Eighty acrylic blocks, simulating root canals with a 1.5 mm internal diameter, a 5 mm radius of curvature, and a 55&#176; curvature, were utilized. After chemomechanical preparation and obturation, 24 new Remover files (N30, 7%, L23) were randomly assigned to three groups: single use, triple use, and six uses. The files were operated at 600 rpm with a torque of 2.5 Ncm, cleaned, and sterilized after each use.
SEM analysis at magnifications of 100x, 250x, and 500x revealed surface defects, including tip deformation, microcracks, fracture, unwinding, surface pitting, and blade disruption. Deformation was observed in 75% of the files after a single use and in 100% of the files after three and six uses. Microcracks were absent after single use but appeared in 25% and 87.5% of files after three and six uses, respectively, showing a statistically significant increase (p &#60; 0.001). Surface pitting also significantly increased among groups (p = 0.004).
No fractures were observed in any group. The most common defects were tip deformation (91.7%) and surface pitting (70.8%). The findings suggest that repeated use of NiTi files significantly increases surface defects, elevating the risk of fatigue fractures. Thus, the results recommend limiting the reuse of Remover files to a maximum of 3x. Further research is needed to correlate defect types with anatomical factors and to assess file effectiveness in retreatment scenarios.

Here, we present a protocol for evaluating the surface characteristics of endodontic retreatment files after repeated use in retreatment procedures, utilizing scanning electron microscopy to identify and analyze potential surface defects.

This study aimed to evaluate surface defects of Remover rotary Nickel-Titanium (NiTi) files after single and multiple uses in conventional endodontic ...

Medicine

Stress-Strain Characteristics of Aluminum

Source:&#160;Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA
Aluminum is one of the most abundant materials in our lives, as it is omnipresent in everything from soda cans to airplane components. Its widespread use is relatively recent (1900AD), primarily because aluminum does not occur in its free state, but rather in combination with oxygen and other elements, often in the form of Al2O3. Aluminum was originally obtained from bauxite mineral deposits in tropical countries, and its refinement requires very high-energy consumption. The high cost of producing quality aluminum is another reason why it is a very widely recycled material.
Aluminum, especially when alloyed with one or more of several common elements, has been increasingly used in architectural, transportation, chemical, and electrical applications. Today, aluminum is surpassed only by steel in its use as a structural material. Aluminum is available, like most other metals, as flat-rolled products, extrusions, forgings, and castings. Aluminum offers superior strength-to-weight ratio, corrosion resistance, ease of fabrication, non-magnetic properties, high thermal and electrical conductivity, as well as ease of alloying.

Uniaxial Tensile Strength and Stress-Strain Test of Aluminum

Source:&#160;Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA
Aluminum is one of the most abundant materials ...

A Virtual Simulation Experiment of Mechanics: Material Deformation and Failure Based on Scanning Electron Microscopy

Summary

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Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

A Coupled Experiment-finite Element Modeling Methodology for Assessing High Strain Rate Mechanical Response of Soft Biomaterials

Full-field Strain Measurements for Microstructurally Small Fatigue Crack Propagation Using Digital Image Correlation Method

Visualization of Failure and the Associated Grain-Scale Mechanical Behavior of Granular Soils under Shear using Synchrotron X-Ray Micro-Tomography

Sample Preparation and Experimental Design for In Situ Multi-Beam Transmission Electron Microscopy Irradiation Experiments

Imaging of the Microstructural Failure Mechanism in the Human Hip

Scanning Electron Microscopic Evaluation of Surface Defects of Remover Retreatment File After Single and Multiple Uses

Stress-Strain Characteristics of Aluminum