Papers by Horacio Espinosa
Experimental Characterization of Composite Structures Subjected to Underwater Impulsive Loadings
Springer eBooks, 2011
... Modelling impact damage in marine composite panels. International Journal of Impact Engineeri... more ... Modelling impact damage in marine composite panels. International Journal of Impact Engineering 2009;36(1):25-39. [3] Tagarielli VL, Deshpande VS, Fleck NA. The dynamic response of composite sandwich beams to transverse impact. ...
ChemInform Abstract: Multiscale Experimental Mechanics of Hierarchical Carbon-Based Materials
ChemInform, Jul 5, 2012
Tailoring the Mechanical Properties of Carbon Nanotube Fibers
Elsevier eBooks, 2014
ABSTRACT Performance and efficiency demands in industrial applications are pushing a need for car... more ABSTRACT Performance and efficiency demands in industrial applications are pushing a need for carbon fibers that can outperform existing technologies. Fibers that incorporate carbon nanotubes (CNTs) to enhance specific mechanical properties are a promising route to addressing this need. Some of the major roadblocks to unlocking the full potential of macroscopic fibers based on CNTs are controlling and optimizing the shear interactions within and between CNTs, geometrical organization of the CNTs, and structural properties of the individual CNTs. Several approaches have been pursued in order to optimize the mechanical behavior of CNT fibers, including irradiation-induced covalent cross-linking, reformable or rehealable bonding, and optimized geometrical and structural fiber designs. These approaches are inspired by nature, which uses hierarchical bonding schemes in optimized orientations to tailor the mechanical properties of its materials to the needs and environment of specific organisms. In this chapter, these approaches for developing high-performance CNT fibers will be reviewed, and an outlook of their potential impact will be discussed.
In-Situ SEM High Strain Rate Testing of Large Diameter Micropillars Followed by TEM and EBSD Postmortem Analysis
Experimental Mechanics, Mar 31, 2021
Background Dislocation dynamic simulations are intended as a tool to understand and predict the m... more Background Dislocation dynamic simulations are intended as a tool to understand and predict the mechanical behavior of metallic materials, but its prediction has never been directly verified by experiments due to differences in specimen strain rate and size. Objective In this work, a comprehensive experimental framework is proposed to attempt direct comparison between experiments and discrete dislocation dynamics (DDD) modelling. Methods By integrating high-throughput sample fabrication and a customized testing apparatus, the sample size and strain rate typically employed in DDD simulations are explored experimentally. Constitutive properties such as stress-strain response are measured, and microstructural information is obtained from transmission electron microscopy (TEM) imaging, electron backscatter diffraction (EBSD), and TEM-based orientation mapping. Results Magnesium and copper were selected, as case studies, to demonstrate the newly developed experimental procedure. Measured stress-strain responses for Mg are consistent with those obtained with a miniaturized Hopkison bar experiments. By exploiting the validated workflow, the effect of strain rate on micropillar heterogeneous deformation and associated dislocation plasticity were revealed. Conclusion The work establishes a methodology for the systematic study of not only metals but also other materials and structures at the microscale and high strain rates.
Applied Physics Letters, Jan 3, 2005
We report on the performance of a microelectromechanical system (MEMS) designed for the in situ e... more We report on the performance of a microelectromechanical system (MEMS) designed for the in situ electron and x-ray microscopy tensile testing of nanostructures, e.g., carbon nanotubes and nanowires. The device consists of an actuator and a load sensor with a gap in between, across which nanostructures can be placed, nanowelded, and mechanically tested. The load sensor is based on differential capacitance measurements, from which its displacement history is recorded. By determining the sensor stiffness, the load history during the testing is obtained. We calibrated the device and examined its resolution in the context of various applications of interest. The device is the first true MEMS in which the load is electronically measured. It is designed to be placed in scanning and transmission electron microscopes and on x-ray synchrotron stages (18 refs.) Inspec No.: 8247135 2 Low-force contact heating and softening using micromechanical switches in diffusive-ballistic electrontransport transition
Micro- And nano-technologies for bioloigcal studies of adherent cells - Delivery and analysis
Dynamic Inelasticity of Polymer-Matrix Composites with Continuous Fibers
Facile fabrication of 2D material multilayers and vdW heterostructures with multimodal microscopy and AFM characterization
Materials Today, 2022
Reliable transfer processes that enable manipulation of two-dimensional (2D) materials, e.g., tra... more Reliable transfer processes that enable manipulation of two-dimensional (2D) materials, e.g., transition metal dichalcogenides (TMDCs) and MXenes, from one substrate to another has been a necessity for successful device fabrication. With both mechanical exfoliation and chemical vapor deposition (CVD) widely used, a versatile, clean, deterministic, and yet simple transfer technique is highly needed. To address such need, we developed a transfer method that takes advantage of wettability contrast between interfaces without the use of sacrificial layers or chemical processes. More importantly, a setup was developed to carry out this transfer method with high sample selectivity and fine control of the position and orientation of transferred TMDC crystals, a feature required for fabrication of the devices based on vertical 2D heterostructures. Using both exfoliated and CVD grown materials and subsequent atomic force microscopy (AFM), photoluminescence (PL), confocal Raman and tip enhanced Raman spectroscopy (TERS) characterization, we ascertained the quality of interfaces resulting from the transfer process while preserving excellent 2D material integrity. PL and TERS maps revealed nanometer-scale heterogeneities in the interfaces of fabricated heterostructures, which should enable further perfection of the transfer technique. TERS/TEPL information were employed to identify areas suitable for nanodevice fabrication, making the reported transfer and characterization methods ideal for making high quality assembly of 2D heterostructure more accessible, which should facilitate exploration of vertical 2D heterostructures for applications in electronics, batteries, solar cells, and twistronics.
Experimental observations and numerical modeling of inelasticity in dynamically loaded ceramics
Recent Advances and Applications of Machine Learning in Experimental Solid Mechanics: A Review
Applied Mechanics Reviews, Jul 17, 2023
For many decades, experimental solid mechanics has played a crucial role in characterizing and un... more For many decades, experimental solid mechanics has played a crucial role in characterizing and understanding the mechanical properties of natural and novel artificial materials. Recent advances in machine learning (ML) provide new opportunities for the field, including experimental design, data analysis, uncertainty quantification, and inverse problems. As the number of papers published in recent years in this emerging field is growing exponentially, it is timely to conduct a comprehensive and up-to-date review of recent ML applications in experimental solid mechanics. Here, we first provide an overview of common ML algorithms and terminologies that are pertinent to this review, with emphasis placed on physics-informed and physics-based ML methods. Then, we provide thorough coverage of recent ML applications in traditional and emerging areas of experimental mechanics, including fracture mechanics, biomechanics, nano- and micromechanics, architected materials, and two-dimensional materials. Finally, we highlight some current challenges of applying ML to multimodality and multifidelity experimental datasets, quantifying the uncertainty of ML predictions, and proposing several future research directions. This review aims to provide valuable insights into the use of ML methods and a variety of examples for researchers in solid mechanics to integrate into their experiments.
Nano and Microscale Origami Engineering: Present and Future
With the advent of a variety of novel nanometer-scale diagnostic techniques such as DNA micro-and... more With the advent of a variety of novel nanometer-scale diagnostic techniques such as DNA micro-and nanoarrays, increasing focus has been placed on developing methods to quickly and accurately create these nanometer scale patterns. One promising technique for depositing DNA, proteins, and other liquid molecular "inks" with submicron resolution is the nanofountain probe (NFP) . The NFP is a specially designed atomic force microscope cantilever that works like a microfluidic pen, transporting inks from a remote reservoir to the substrate. During patterning, a liquid ink meniscus forms between the probe's tip and the substrate. The shape of the meniscus, and thus the working resolution of the NFP, is dependent upon the properties of both the substrate and the ink. Ink transport can be aided by the forces created by an electrophoretic voltage . AN SYS finite element Dip Pen Nanolithography analysis softwa re was used to model the forces created on the in k meniscus due to an applied voltage, and these forces were evaluated in their ability to modulate patterning resolution. A working qualitative model was created and used to evaluate the system for variou s meniscus geometries.
MEMS Based Material Testing Systems: In-situ electron microscopy testing of nano objects
Nanoelectromechanical Systems (NEMS) - Experiments and Modeling
An Experimental Investigation of Deformation and Fracture of Nacre�Mother of Pearl
Experimental Mechanics, Mar 2, 2007
Special Issue: In Honor of Rodney James Clifton on the Ocassion of His 70th Birthday Anniversary
Size Effects and Passivation Effects on the Plasticity of Freestanding Submicron Gold Films
The Membrane Deflection Experiment was used to examine size effects on freestanding thin film gol... more The Membrane Deflection Experiment was used to examine size effects on freestanding thin film gold membranes. It is the first micro-scale testing scheme where the loading procedure is straightforward and accomplished in a highly sensitive manner while preserving the independent measurement of stress and strain. Stress-strain curves were obtained on films 0.3, 0.5 and 1.0 μm thick including membrane widths of 2.5, 5.0, 10.0 and 20.0 μm for each thickness. Both membrane thickness and width were shown to cause size effects on the mechanical properties. By far, thickness played a major role in deformation behavior exhibiting a major transition in the material inelastic response occuring when thickness was changed from 1.0 to 0.5 μm. In this transition, the yield stress more than doubled when film thickness was decreased, with the 0.5 μm thick specimen exhibiting a more brittle-like failure and the 1.0 μm thick specimen exhibiting a strain softening behavior. Results of the effect of surface passivation, with 30 nm SiO2 layers, showed a decrease in yield stress with passivation opposite to that reported in other studies. INTRODUCTION Most knowledge of material properties exists at the bulkscale regime where known constitutive laws material describe behavior. When specimen size becomes small, in the micron regime, these laws fail to describe material response. Thin films, which are commonly employed in microelectronic components and MEMS devices, often display mechanical behavior that cannot be described by traditional means. Their mechanical properties are often essential to the device function and therefore accurate identification is key in determining the device reliability. The affect of specimen size on material mechanical behavior has been experimentally studied by several researchers. Results on nanoindentation [1-5], torsion of microscale rods [6], and bending of thin films [7] have all shown that as specimen size decreased to the micron regime the strength of the film increased. However, in these studies each method subjects the specimens to large strain gradients. Modified plasticity theories have incorporated these strain gradients into a continuum description of microscale deformation behavior [6,8-11]. In this work the Membrane Deflection Experiment (MDE) is used to test the mechanical response of sub-micron gold films [12-15]. The MDE test has certain advantages for the microscale mechanical testing of thin films. The simplicity of sample microfabrication and ease of handling lend confidence in repeatability. The loading procedure is straightforward and accomplished in a highly sensitive manner while preserving the independent measurement of stress and strain. The measurements are also performed under macroscopic homogeneous axial deformation, i.e., in the absence of deformation gradients, in contrast to nanoindentation, torsion, and bending of thin films where deformation gradients naturally occur. We will also evaluate the effect of 30 nm thick SiO2 passivation layers on plasticity and fracture of thin gold film. EXPERIMENTAL PROCEDURE Specially designed thin film Au specimens were microfabricated on (100) Si wafers. Specimen shape was defined on the topside by photolithography and lift off with selective etching of bottom side windows with the purpose of creating suspend membranes, see Espinosa et al. [13] for further details. Passivation layers were grown on both sides of the gold membrane through plasma assisted CVD. The geometry of the suspended thin-film membranes can be described best as a double dog-bone tensile specimen. Fig. 1(a) shows an optical image of the Au membranes. Membrane width was varied in each die, to examine size effects, while preserving the ratio of gauge-length/width. Dimensions of four differently sized membranes can be described by their widths, W, of 2.5, 5, 10 and 20 um. Fig. 1. (a) An optical image showing the topside of the Au membranes and (b) a side view of the MDE test. Parameters are defined in the text. PV Wafer
Anisotropic Evaporation of GaN Nanowires Analyzed Using Atom Probe Tomography
Guest Editorial: Modeling and Experiments in Cell and Biomolecular Mechanics
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Papers by Horacio Espinosa