Elastic Tensile Strain Research Articles

The analysis of the impact of technological processes of hot forging on the dynamics of the crank press

The article deals with a dynamic model of a crank hot stamping press, which allows evaluating the effect of elastic torsional, bending deformations and tensile strains of compression of its elements, taking into account gaps in the kinematic pairs, depending on the technological process implemented on this press. Given that there are always several options to realize a technological process of hot volume forging, designed for a specific part, the proposed method allows you to choose the best option in terms of the working conditions of the press.

Capacitance-based self-sensing of flaws and stress in carbon-carbon composites, with reports of the electric permittivity, piezoelectricity and piezoresistivity

Capacitance-based nondestructive flaw evaluation (NDE), electric permittivity, piezoelectricity (capacitance-based stress/strain self-sensing) and piezoresistivity (resistance-based stress/strain self-sensing) of carbon-carbon composite (C/C, density 1.5 g/cm3, PAN-based carbon fiber) are unprecedentedly reported. The in-plane capacitance measured using coplanar electrodes decreases monotonically with increasing cumulative artificially inflicted damage (1–62 blind/through holes, diameter 1.00 mm), indicating NDE feasibility. The in-plane relative permittivity is 1.1 × 104 (2 kHz); the in-plane DC resistivity is 2.4 × 10−3 Ω .cm. These values are similar to those previously reported for PAN-based carbon fiber. The permittivity increases reversibly by up to 16% with increasing elastic tensile strain (up to 0.0081%). However, the contribution of the stress-dependent permittivity to the piezoelectric effect is negligible. The observed in-plane direct piezoelectric effect is primarily due to the reversible monotonic decrease of the electric field output with the increasing tensile strain. The piezoelectric coupling coefficient d33 is negative, -(8.1 ± 0.2) × 10−9 pC/N, in contrast to the positive value of +(1.7 ± 0.3) × 10−8 pC/N for PAN-based carbon fiber. The in-plane piezoresistivity gage factor is negative, −7804 ± 429, which is much higher in magnitude than −1830 ± 47 previously reported for PAN-based carbon fiber. The differences in d33 and gage factor between C/C and PAN-based carbon fiber are attributed mainly to the carbon matrix in the C/C.

Biaxial tensile drawing of poly(ethylene terephthalate) via environmental crazing as a method for creating a porous structure

Crazing of poly(ethylene terephthalate) thin film has been studied upon its successive biaxial drawing in adsorption-active liquid media in two mutually perpendicular directions. During both primary and secondary drawing, crazes propagate in the direction perpendicular to the drawing axes, thereby leading to the formation of crazes oriented orthogonally relative to each other in the polymer. The secondary drawing occurs at values of elastic modulus, stress, and tensile strain that corresponds to the onset of orientation-induced strengthening decreased due to a lower fraction of undeformed polymer available for crazing. It has been shown that, as compared with the uniaxial drawing, the biaxial deformation of polymers via the crazing mechanism leads to a higher porosity. After the removal of a liquid medium, deformed polymers partly retain their open porosity and remain to be permeable to water vapor, with the vapor permeability being higher for biaxially deformed polymers. Thus, the biaxial crazing is a promising method for the creation of breathful and porous membrane materials, as well as nanocomposites based on them.

(Invited) Strain-Engineered Low-Threshold Group IV Lasers for Photonic-Integrated Circuits

Photonic-integrated circuits (PICs) are a key enabler for the ultimate miniaturization of next-generation optical computers that can fit in the palm of your hand. However, the realization of fully functional PICs is currently limited by the absence of an efficient light source on silicon (Si), thus making a practical Si-compatible light source the Holy Grail. Especially, it has been thus far considered close to impossible to create a practical on-chip laser using Si-compatible group IV semiconductor materials (e.g. germanium (Ge)) owing to their indirect bandgap nature. Strain-engineered Ge material has recently garnered much attention for the dramatic reduction of the lasing threshold of group IV lasers because large tensile strain fundamentally alters the Ge’s bandstructure. Here, we present our recent research works on highly strained group IV materials on a Si chip for the realization of low-threshold on-chip lasers. In the first part, we will introduce our innovative strain engineering platforms that can create direct bandgap Ge nanowires by inducing >5% elastic tensile strain. In the second part, we will present the first experimental observation of low-threshold optically pumped lasing in highly strained Ge nanowires. The strain engineering of direct bandgap germanium-tin will also be described for the ultimate reduction of the lasing threshold.

Giant Mechano-Optoelectronic Effect in an Atomically Thin Semiconductor

Transition metal dichalcogenides (TMDs) are particularly sensitive to mechanical strain because they are capable of experiencing high atomic displacements without nucleating defects to release excess energy. Being promising for photonic applications, it has been shown that as certain phases of layered TMDs MX2 (M = Mo or W; X = S, Se, or Te) are scaled to a thickness of one monolayer, the photoluminescence response is dramatically enhanced due to the emergence of a direct electronic band gap compared with their multilayer or bulk counterparts, which typically exhibit indirect band gaps. Recently, mechanical strain has also been predicted to enable direct excitonic recombination in these materials, in which large changes in the photoluminescence response will occur during an indirect-to-direct band gap transition brought on by elastic tensile strain. Here, we demonstrate an enhancement of 2 orders of magnitude in the photoluminescence emission intensity in uniaxially strained single crystalline WSe2 bilayers. Through a theoretical model that includes experimentally relevant system conditions, we determine this amplification to arise from a significant increase in direct excitonic recombination. Adding confidence to the high levels of elastic strain achieved in this report, we observe strain-independent, mode-dependent Grüneisen parameters over the entire range of tensile strain (1-3.59%), which were obtained as 1.149 ± 0.027, 0.307 ± 0.061, and 0.357 ± 0.103 for the E2g, A1g, and A21g optical phonon modes, respectively. These results can inform the predictive strain-engineered design of other atomically thin indirect semiconductors, in which a decrease in out-of-plane bonding strength may lead to an increase in the strength of strain-coupled optoelectronic effects.

Strain distribution along geogrid-reinforced asphalt overlays under traffic loading

While there is significant field evidence of the benefits of geosynthetic-reinforced asphalt overlays, their use has focused on minimizing the development of reflective cracks. Yet, geogrids in asphalt overlays are also expected to develop reinforcement mechanisms that contribute to the pavement structural capacity. Specifically, the use of geosynthetics in asphalt overlays may also improve the mechanical behavior of paved roads by controlling permanent displacements and reducing strains in the pavement layers. While relevant advances have been made towards identifying the mechanisms in geosynthetic stabilization of base courses, such mechanisms may differ from those that develop in geosynthetic-reinforced asphalt overlays. This paper investigates the development and distribution of tensile strains along geogrids used to reinforce asphaltic layers. Experimental data was collected from large-scale paved road models subjected to the repeated loading imparted by wheel traffic. Specifically, the study examines both the elastic and permanent components of displacements induced in geogrids by using mechanical extensometers attached to the geogrids. The testing program includes a number of geosynthetic-reinforced paved road models, as well as a control (unreinforced) section that was also instrumented for comparison purposes. Asphalt strain gauges were used to measure strains within the asphalt concrete layer, providing an additional source of information that proved to be highly consistent with the results obtained from the extensometers. The experimental results showed a progressive mobilization of permanent geogrid strains that reached a final profile beyond which additional traffic loading did not result in additional straining. In comparison, higher strains developed in the unreinforced model, which showed a continuously increasing trend. Elastic tensile strains in the asphalt mixture and rutting under the wheel load were comparatively smaller when using geogrids. Overall, the results generated in this study indicate that the presence of geogrids in asphalt overlays results in a lateral restraining mechanism that influences on the mechanical behavior of flexible pavements.

(Invited) Tuning Physicochemical Properties of MoS2 By Mechanical Strain

Monolayers of 2D materials have ultrahigh mechanical strength, which enables application of very large elastic strains (e.g., ~11% for MoS2 and 25% for graphene). The ability of sustaining such large elastic strain offers unprecedented opportunities to engineer the physicochemical properties by applying mechanical strain. In this talk, I will present two examples on the effect of strain on the properties of MoS2 layer. The first example shows that elastic tensile strain reduces the bandgap of MoS2. When a gradient strain field is applied to MoS2 monolayer, the created bandgap gradient acts as an efficient funnel of photogenerated excitons that leads to enhanced photoluminescence. The second example shows that when elastic strain is applied to the sulfur vacancy on the basal planes of monolayer 2H-MoS2, the strain modifies the local electronic structure and catalytic activity. The proper combination of S-vacancy and strain allows us to achieve higher intrinsic activity for hydrogen evolution reaction than the edge site of MoS2.

Organic strain sensor comprised of heptazole-based thin film transistor and Schottky diode

A strain sensor presenting a voltage signal has been studied, as comprised of an organic thin-film transistor (OTFT) and an organic Schottky diode which are connected in series to sensitively measure elastic tensile strain (up to ∼0.64%, bending radius of ∼4 mm). We chose organic heptazole TFT as a sensor component and large area heptazole Schottky diode as a strain-insensitive load incorporated into this strain sensor gauge circuit, because our heptazole TFTs have shown anisotropic response to the elastic tensile strain. Our organic strain sensor exhibits a decent amount of gauge factor (GF > 1.51) performance in both static and dynamic ways.

Kinetic Study of Hydrogen Evolution Reaction over Strained MoS2 with Sulfur Vacancies Using Scanning Electrochemical Microscopy.

Molybdenum disulfide (MoS2), with its active edge sites, is a proposed alternative to platinum for catalyzing the hydrogen evolution reaction (HER). Recently, the inert basal plane of MoS2 was successfully activated and optimized with excellent intrinsic HER activity by creating and further straining sulfur (S) vacancies. Nevertheless, little is known about the HER kinetics of those S vacancies and the additional effects from elastic tensile strain. Herein, scanning electrochemical microscopy was used to determine the HER kinetic data for both unstrained S vacancies (formal potential Ev0 = −0.53 VAg/AgCl, electron-transfer coefficient αv = 0.4, electron-transfer rate constant kv0 = 2.3 × 10(–4) cm/s) and strained S vacancies (Esv0= −0.53 VAg/AgCl, αsv = 0.4, ksv0 = 1.0 × 10(–3) cm/s) on the basal plane of MoS2 monolayers, and the strained S vacancy has an electron-transfer rate 4 times higher than that of the unstrained S vacancy. This study provides a general platform for measuring the kinetics of two-dimensional material-based catalysts.

Implantation damage in heavy gas implanted 4H-SiC

Single crystals of SiC were implanted with heavy inert gases (Xe, Ar) at elevated temperatures (300–800°C) and for a large range of fluence (1×1012–1×1015ions cm−2). Thermodesorption measurements suggest that gas is trapped by implantation-induced vacancy-type defects impeding any gas diffusion. The damage accumulation versus dose was studied through the tensile elastic strain determined by using X-ray diffraction. Results show that at low dose the strain is predictable via a thermally activated direct impact model. The low thermal activation energy at saturation suggests a dynamic recovery process dominated by the migration of interstitial-type defects as its relaxation during post thermal annealing. As compared with light-gas implantation the heavy-gas to defect ratio is low enhancing the formation of strongly perturbed zones rather than the formation of bubble precursors.

Strain engineering of graphene: a review.

Graphene has intrigued the science community by many unique properties not found in conventional materials. In particular, it is the strongest two-dimensional material ever measured, being able to sustain reversible tensile elastic strain larger than 20%, which yields an interesting possibility to tune the properties of graphene by strain and thus opens a new field called "straintronics". In this article, the current progress in the strain engineering of graphene is reviewed. We first summarize the strain effects on the electronic structure and Raman spectra of graphene. We then highlight the electron-phonon coupling greatly enhanced by the biaxial strain and the strong pseudomagnetic field induced by the non-uniform strain with specific distribution. Finally, the potential application of strain-engineering in the self-assembly of foreign atoms on the graphene surface is also discussed. Given the short history of graphene straintronics research, the current progress has been notable, and many further advances in this field are expected.

First principles study of silicene symmetrically and asymmetrically functionalized with halogen atoms

Using first principles calculations, we predicted that a direct-band-gap between 0.98 and 2.13 eV can be obtained in silicene by symmetrically and asymmetrically (Janus) functionalisation with halogen atoms and applying elastic tensile strain.

Structure and properties of amorphous finemet alloy microwires produced by the Ulitovskii-Taylor method

Amorphous Fe73.5Si13.5B9Nb3Cu1 alloy microwires 19–50 μm in diameter are fabricated by the Ulitovskii-Taylor method. The mechanism of crystallization of the amorphous microwires is shown to be analogous to the mechanism of crystallization of an amorphous ribbon made of the same alloy. Microwires up to 30 μm in diameter are found to exhibit ductility upon bending. The near-surface magnetic properties of the microwires are shown to depend on the microwire diameter. The magnetic properties of the amorphous microwires are highly sensitive to elastic tensile and torsional strains in an ac magnetic field.

Strain- and defect-mediated thermal conductivity in silicon nanowires.

The unique thermal transport of insulating nanostructures is attributed to the convergence of material length scales with the mean free paths of quantized lattice vibrations known as phonons, enabling promising next-generation thermal transistors, thermal barriers, and thermoelectrics. Apart from size, strain and defects are also known to drastically affect heat transport when introduced in an otherwise undisturbed crystalline lattice. Here we report the first experimental measurements of the effect of both spatially uniform strain and point defects on thermal conductivity of an individual suspended nanowire using in situ Raman piezothermography. Our results show that whereas phononic transport in undoped Si nanowires with diameters in the range of 170-180 nm is largely unaffected by uniform elastic tensile strain, another means of disturbing a pristine lattice, namely, point defects introduced via ion bombardment, can reduce the thermal conductivity by over 70%. In addition to discerning surface- and core-governed pathways for controlling thermal transport in phonon-dominated insulators and semiconductors, we expect our novel approach to have broad applicability to a wide class of functional one- and two-dimensional nanomaterials.

Strain build-up in SiC implanted at different temperatures

Single crystals of 4H-SiC were implanted with helium ions at temperatures of 400 and 700°C in a large range of fluences. The damage accumulation versus fluence was studied through the tensile elastic strain determined by using X-ray diffraction measurements. Results were analyzed via the multi-step damage accumulation model. At low dose (step 1) the strain can be described assuming a thermally activated process with low activation energy. Damage cross-sections, independent of implantation temperature, for interstitial-type defects were determined. With increasing dose, the contribution of other defects arises leading to an accelerated strain build-up namely the second step of the disordering process. However, in this regime, the strain cannot be fully described due to others operative mechanisms such as the formation of tiny bubbles under severe conditions of implantation. The formation of bubbles accelerates the development of the elastic strain. The values of damage cross-sections show that only small clusters contribute to the tensile elastic strain.

Experiment on the Mechanics Properties of Hot-Pepper in the Process of Hot-Air Drying

In order to reduce the damage rate of hot-pepper in the process of drying and transportation, and to improve the quality of dried hot-pepper. In this paper, the mechanical properties of hot-pepper were studied in the process of hot-air drying. The experimental results showed that the hot-pepper’s compressive ability dropped with the decrease of moisture content after the moisture content reached the safe moisture content. With the moisture content decreasing, the variation tendency of the elastic modulus and tensile strain of hot-pepper were first increased and then decreased and finally tended to be stable when it reached 12％. Effect of hot-pepper’s shape on tensile strain is greater than on the maximum load and displacement in the process of drying.

Temperature dependence of the short-range order of Cu65Zr35 metallic glass

The thermal behaviour of the short-range order of Cu65Zr35 metallic glass has been investigated by means of in situ high energy synchrotron X-ray diffraction. The temperature dependence of the X-ray structure factor and the atomic pair correlation function was analysed within the glassy state. In addition to the effect of volume expansion and thermal atomic oscillations changes occur in the short-range order. Local atomic rearrangements take place as a consequence of the structural heterogeneity in the glass. The structural transformations depend linearly on temperature. The changes of the short-range order of the glass by thermal expansion are found to be different from those under elastic tensile strain.

Top-down fabricated silicon nanowires under tensile elastic strain up to 4.5%

Strained Si nanowires are among the most promising transistor structures for implementation in very large-scale integration due to of their superior electrostatic control and enhanced transport properties. Realizing even higher strain levels within such nanowires are thus one of the current challenges in microelectronics. Here we achieve 4.5% of elastic strain (7.6 GPa uniaxial tensile stress) in 30 nm wide Si nanowires, which considerably exceeds the limit that can be obtained using SiGe-based virtual substrates. Our approach is based on strain accumulation mechanisms in suspended dumbbell-shaped bridges patterned on strained Si-on-insulator, and is compatible with complementary metal oxide semiconductor fabrication. Potentially, this method can be applied to any tensile prestrained layer, provided the layer can be released from the substrate, enabling the fabrication of a variety of strained semiconductors with unique properties for applications in nanoelectronics, photonics and photovoltaics. This method also opens up opportunities for research on strained materials.

Strain dependent resistance in chemical vapor deposition grown graphene

The strain dependence of conductance of monolayer graphene has been studied experimentally here. The results illustrate the notable transitions: the slight increase, the dramatic decrease, and the sudden dropping of the conductance by gradually increasing the uniaxial strain. The graphene conductance behaves reversibly by tuning of the elastic tensile strain up to 4.5%, while it fails to recover after the plastic deformation at 5%. The change in conductance due to strain is surprisingly high, which indicates the potential applications in electromechanical devices.

Measurement of the hysteresis characteristics of pipe steels under elastic and plastic tensile strain

The changes in the shape and characteristics of the major and asymmetric hysteresis loops of low-carbon pipe steels under the action of elastic and plastic tensile strains were studied. The hysteresis loop segments that experienced the most considerable transformations under the tension of a material were determined. The possibilities of the inspection of tensile strains by the coercive return magnetization and the magnetic field corresponding to a fixed magnetization on the descending branch of a hysteresis loop were shown.