Uniaxial Deformation Research Articles

Development and validation of a device for in vitro uniaxial cell substrate deformation with real-time strain control

Substrate deformation affects the behaviour of many cell types, including bone, skeletal muscle and endothelial cells. Nowadays, in vitro tests are widely employed to study the mechanotransduction induced by substrate deformation. The aim of in vitro systems is to properly reproduce the mechanical stimuli sensed by the tissue in the cellular microenvironment. Accurate strain measurement and control is therefore necessary to ensure the cell senses the proper strain for the entire treatment. Different types of in vitro systems are commercially available or can be custom-designed; however, none of these devices performs a real-time measurement of the induced strains. In this study, we proposed a uniaxial strain device for in vitro cell stimulation with an innovative real-time strain control. The system was designed to induce sinusoidal waveform stimulation in a huge range of amplitude and frequency, to three silicone chambers stretched by a linear actuator. The real-time strain measurement and control algorithm is based on an optical tracking method implemented in LabVIEW 2015, and it is able to adapt the input amplitude to the linear motor, if necessary, hanging the stimulation signal for about 120 ms. Validation of the strain values measured during the real-time tracking algorithm was carried out through a comparison with the digital image correlation (DIC) technique. We investigated the influence of number of reference points and image size on the algorithm accuracy. Experimental results showed that the tracking algorithm allowed for a real-time measurement of membrane longitudinal strains with a relative error of 0.3%, on average, in comparison to the strains measured with DIC in post-processing analysis. We showed a high homogeneity of the strain pattern on the entire chamber base for different stimulation conditions. Finally, as proof of concept, we employed the uniaxial strain device to induce substrate deformation in a human osteosarcoma cell line (SaOS-2). The experimental results showed a consistent change in cell shape in response to the mechanical strain.

Deformation nanomechanics and dislocation quantification at the atomic scale in nanocrystalline magnesium

Abstract Classical molecular dynamics (MD) simulation method is employed to study the uniaxial tensile deformation of nanocrystalline magnesium (Mg) of varying grain size levels. The mean grain size of the sample is varied from 6.4 nm to 45 nm, with each sample containing about 43 million atoms in the modeling system. The deformation nanomechanics reveals two distinct deformation mechanisms. For larger grain-sized samples, dislocation dominated deformation is observed while, in smaller grain-sized samples, grain boundary-based mechanisms such as grain boundary sliding, grain boundary rotation are observed. The transition of normal and inverse Hall–Petch relation occurs at around 10 nm. Dislocation density quantification shows that the dislocation density in the sample drastically reduces with decreasing grain size. Elastic modulus of nanocrystalline Mg with mean grain size above 20 nm remains comparable to that of the coarse-grained polycrystalline bulk, followed by a rapid reduction below that grain size. The present work reveals the nanomechanics of nanocrystalline Mg, facilitating the design and development of Mg-based nanostructured alloys with superior mechanical properties.

Deformation Behavior Causing Excessive Thinning of Outer Diameter of Micro Metal Tubes in Hollow Sinking

The deformation behavior of microtubes during hollow sinking was investigated to clarify the mechanism of the excessive thinning of their outer diameters. Stainless-steel, copper, and aluminum alloy tubes were drawn without an inner tool to evaluate the effect of Lankford values on outer diameter reduction. Drawing stress and stress-strain curves were obtained to evaluate the yielding behavior during hollow sinking. The observed yielding behavior indicated that the final outer diameter of the drawn tube was always smaller than the die diameter due to the uniaxial tensile deformation starting from the die approach end even though the drawing stress was in the elastic range. The results of a loading-unloading tensile test demonstrated that the strain remained even after unloading. Therefore, the outer diameter is considered to become smaller than the die diameter during hollow sinking due to microscopic yielding at any Lankford value. Furthermore, the outer diameter becomes smaller than the die diameter as the Lankford value increases, as theorized. As the drawing stress decreases or the apparent elastic modulus of the stress-strain curve increases, the outer diameter seems to approach the die diameter during unloading, which is caused by the elastic recovery outside the microscopic yielding region.

In situ X-ray computed tomography (CT) investigation of crack damage evolution for cemented paste backfill with marble waste block admixture under uniaxial deformation

Cemented waste rock backfill (CWRB), which is a mixture of tailings, waste rock, cement, and water, is subjected to the combination actions in underground mining operations. While the strength requirement of CWRB has been widely studied, the mesoscopic damage evolution mechanisms of waste block proportion (WBP) on its geomechanical characteristics are still not well understood. In the present paper, the crack damage evolution of CWRB samples were characterized using real-time X-ray CT under uniaxial compression. The effects of waste block on the stress strain responses, stress dilatancy behaviors, meso-structure changes, and the cracking behaviors were investigated. The results show that strength of CWBR is influenced by waste block proportion, and strength increases are due to geomechanical effects related to propagation of tortuous failure surfaces. Besides, for sample with high WBP, interlocking among the waste blocks also improves the overall stiffness and strength of CWRB compared with tailing paste sample. Volumetric dilatancy caused by the damage and cracking behavior has a close link with the meso-structural changes, which are controlled by the interactions between the waste rock and cemented tailing paste. The crack damage behavior is quite inhomogeneous and strongly influenced by the waste block size, shape, and distribution. Our study demonstrates that it is feasible to reveal the physical mesoscopic mechanism of crack damage evolution for CWRB by using X-ray CT, and the meso-damage cracking behaviors should be deeply studied to ensure stability of pillar during mining activities.

Capillary thinning of elastic and viscoelastic threads: From elastocapillarity to phase separation

The formation and destabilisation of viscoelastic filaments are of importance in many industrial and biological processes. Filament instabilities have been observed for viscoelastic fluids but recently also for soft elastic solids. In this work, we address the central question how to connect the dynamical behavior of viscoelastic liquids to that of soft elastic solids. We take advantage of a biopolymer material whose viscoelastic properties can be tuned over a very large range by its pH, and study the destabilization and ensuing instabilities in uniaxial extensional deformation. In agreement with very recent theory, we find that the interface shapes dictated by the instabilities converge to an identical similarity solution for low-viscosity viscoelastic fluids and highly elastic gels. We thereby bridge the gap between very fluid and strongly elastic materials. In addition, we provide direct evidence that at late times an additional filament instability occurs due to a dynamical phase separation.

Prediction of Tensile Strength and Deformation of Diffusion Bonding Joint for Inconel 718 Using Deep Neural Network

Due to the acceptable high-temperature deformation resistance of Inconel 718, its welding parameters such as bonding temperature and pressure are inevitably higher than those of general metals. As a result of the existing punitive processing environment, it is essential to control the deformation of parts while ensuring the bonding performance. In this research, diffusion bonding experiments based on the Taguchi method (TM) are conducted, and the uniaxial tensile strength and deformation ratio of the experimental joints are measured. According to experimental data, a deep neural network (DNN) was trained to characterize the nonlinear relationship between the diffusion bonding process parameters and the diffusion bonding strength and deformation ratio, where the overall correlation coefficient came out to be 0.99913. The double-factors analysis of bonding temperature–bonding pressure based on the prediction results of the DNN shows that the temperature increment of the diffusion bonding of Inconel 718 significantly increases the deformation ratio of the diffusion bonding joints. Therefore, during the multi-objective optimization of the bonding performance and deformation of components, priority should be given to optimizing the bonding pressure and duration only.

Double Yielding in Deformation of Semicrystalline Polymers

AbstractDifferent semicrystalline polymers including poly(l‐lactic acid), poly(ethylene terephthalate), syndiotactic polystyrene, and polyamide 12 are studied in terms of their mechanical response to uniaxial compression deformation. Apparent decoupling of yielding of amorphous and crystalline phases is identified as separate peaks in the stress–strain curve in the vicinity of the glass transition temperature. The same feature is also observed for the uniaxial extension of predrawn semicrystalline poly(ethylene terephthalate). It is indicated that in absence of a strong amorphous phase a semicrystalline polymer is unable to yield and undergo plastic deformation and it fails in a brittle manner in the uniaxial compression. Treating a semicrystalline polymer as a composite of amorphous and crystalline phases, putting emphasis on the crucial role of amorphous phase in acting as connectors between crystalline domains and indicating that the yielding of amorphous phase is a prerequisite for yielding of crystalline phase, work toward a better understanding of the mechanical properties of semicrystalline polymers at the molecular level is done.

Microscopic substructures of stainless steel 304 undergoing a uniaxial ratcheting deformation

Under asymmetrical stress-controlled cyclic loading accompanied by ratcheting, the evolution of microscopic substructures of stainless steel 304 (SS304), a face-centered cubic metal, was detected using transmission electron microscopy (TEM). This observation demonstrates that dislocation slip is the main mechanism of uniaxial ratcheting in the non-steady stage (stage I). Dislocation proliferate rapidly duo to the high stress level of the cyclic tests, and dislocation density increases continuously with the the number of cycles. The ratcheting rate decreases continuously due to the interaction of moveable dislocations, and the planar dislocation substructures (dislocation pileups and tangles) are the dominant patterns in this stage. In the later stage I, distinct lath $$\alpha $$ -martensite was observed in the material due to the nucleation of martensite and the phase transformation zones increase gradually with the growth of axial ratcheting strain in the stage II of uniaxial ratcheting. The multiply and cross-slip were activated gradually in increasing numbers of grains, and the prevailing dislocation configurations evolve into more complicated and stable ones (dislocation walls and cells). In addition the dislocation configurations after various prescribed tensile strain of the monotonic tension and creep deformation with three different holding times were also observed by TEM. Comparing the evolution of microscopic substructures in various loading modes, the physical mechanism of uniaxial ratcheting of SS304 can be revealed as combination of the evolution of dislocation configurations and martensite transformation in the stage II of uniaxial ratcheting.

Tissue Rheology as a Possible Complementary Procedure to Advance Histological Diagnosis of Colon Cancer.

In recent years, rheological measurements of cells and tissues at physiological and pathological stages have become an essential method to determine how forces and changes in mechanical properties contribute to disease development and progression, but there is no standardization of this procedure so far. In this study, we evaluate the potential of nanoscale atomic force microscopy (AFM) and macroscopic shear rheometry to assess the mechanical properties of healthy and cancerous human colon tissues. The direct comparison of tissue mechanical behavior under uniaxial and shear deformation shows that cancerous tissues not only are stiffer compared to healthy tissue but also respond differently when shear and compressive stresses are applied. These results suggest that rheological parameters can be useful measures of colon cancer mechanopathology. Additionally, we extend the list of biological materials exhibiting compressional stiffening and shear weakening effects to human colon tumors. These mechanical responses might be promising mechanomarkers and become part of the new procedures in colon cancer diagnosis. Enrichment of histopathological grading with rheological assessment of tissue mechanical properties will potentially allow more accurate colon cancer diagnosis and improve prognosis.

Influence of Uniaxial Deformation along the [110] Direction on the Relaxation of Arsenic Shallow Donor States in Germanium

The relaxation rates of arsenic donor states in germanium upon interaction with acoustic phonons are analyzed depending on uniaxial crystal compression deformation along [110] direction at low temperatures (<10 K). It is shown that the formation of the inverse population of donor levels, which depends on the crystal-deformation magnitude, occurs under optical excitation, which gives us grounds to assume the possibility of the effect of stimulated radiation in the THz frequency range at intracenter transitions of shallow arsenic donors under their optical excitation. It is shown that uniaxial deformation can lead to switching of the laser transition and, consequently, to a variation in the stimulated-radiation frequency.

Molecular Dynamics Simulation and Theoretical Model of Elasticity in Slide-Ring Gels.

In this study, molecular dynamics (MD) simulations were carried out on the uniaxial deformation of slide-ring (SR) networks with slidable cross-links to understand the relationship between the sliding of the cross-linking points and the Young's moduli of SR gels, which are lower than those of covalently cross-linked gels with the same cross-linking densities. The slidability of the cross-links in SR gels was characterized by the rate of change of the segment number between the cross-links, Nslide, estimated by the MD simulation. We have successfully constructed a molecular model for the elasticity of SR gels and proposed a simple equation for the Young's moduli of SR gels as a function of Nslide. The theoretical model was compared with the MD simulation results and experimental data.

Confirmation of rapid-heating β recrystallization in wire-arc additively manufactured Ti-6Al-4V

The coarse columnar β grains in Ti-6Al-4V WAAM can be refined by relatively low strain inter-pass deformation. Simulation, with rapid heating, has shown this may partly occur by a novel recrystallization mechanism that involves twinning during β regrowth through the α-β transus, as a result of the prior deformation promoting faults in the α-β interface, which produces a unique micro-texture in each parent β grain. Here, this potential mechanism has been investigated further, using a different deformation mode – uniaxial tensile deformation rather than plane strain compression – to enable the texture contribution from conventional recrystallization to be more unambiguously discriminated. The tensile-deformed samples are shown to produce the same unusual unique micro-texture seen previously, at low strains, despite the different deformation mode, but this disappeared at higher strains, which provides more evidence in support of this new rapid heating β recrystallization mechanism.

Effect of mechanical strain on the energy of graphene-graphane interface: Theoretical study

The effect of uniaxial mechanical deformation in the zigzag and armchair directions on the stability and structure of the graphene-graphane interface is studied. The specific energy of this interface is determined depending on the strain. The temperature dependence of the maximum length of the stable boundary is estimated. The energy barriers of the hydrogen diffusion from graphane to graphene as a function of deformation are found. Possibilities of stabilization of the interface by mechanical deformation are investigated. The suitable deformation results in twice increasing of the acceptable interface length.

Bioinspired, Mechanically Robust Chemiresistor for Inline Volatile Organic Compounds Sensing

AbstractThere are advantages to polymer/nanoparticle composite‐based volatile organic compounds (VOCs) sensors, such as high chemical and physical stability, operability under extreme conditions, flexible use in manufacturing, and low cost. Nevertheless, their lower limit of detection due to thickness‐dependent diffusion has constrained their application. Inspired by the metaxylem in vascular plants and its vertical conduits and horizontal pits that enable efficient transpiration, a polymer/nanoparticle composite‐based sensor is fabricated with a controllable, spontaneously formed, hollow core for inline VOCs transportation, and porous microstructure for radial direction diffusion. The hollow core is surrounded by an inner porous layer (thermoplastic polyurethane (TPU)), a middle sensing layer (TPU/graphene nanoplatelets/multiwalled carbon nanotubes), and an outer mechanically durable layer (TPU). This multilayered structure shows a 600% higher response rate compared to a single‐layered composite fiber sensor, with a low limit of detection (e.g., ≈15 ppm for xylene) and high selectivity based on the Flory–Huggins interaction parameter. This flexible and stretchable sensor also demonstrates a dual parameter sensing capability from VOC concentrations and uniaxial strain deformation. Via a one‐step fiber spinning procedure, this self‐induced hollow fiber offers a unique method of microstructural design, which enables the detection of low‐concentration VOCs by polymer/nanoparticle‐based sensors.

Helium implantation effects on the tensile response of nano-twinned copper

Metallic materials used in fission and fusion reactors will internally accumulate numerous lattice defects and bubbles because of high radiation. An in-depth understanding on the influence of bubbles is significant to the safety and life assessment of relevant engineering equipment. Here, molecular dynamics simulations are performed to investigate the effects of twin boundary (TB) spacing, inner-bubble pressure, temperature and bubble number density on uniaxial tensile deformation behaviors of helium bubbles implanted nano-twinned copper (nt-Cu). Simulation results reveal that the TB can significantly enhance the strength of nt-Cu because of the Hall–Petch effect. The increase of inner-bubble pressure reduces the critical stress of dislocation emission, which in turn reduces the yield stress. High temperature softens the models and increases the inner-bubble pressure. The weaken effect of pressure component is remarkable in the yield strength, while that has little impact on the elastic modulus and the average flow stress. In addition, the larger bubble number density is accompanied by the lower elastic modulus, yield stress and average flow stress. The present findings provide valuable suggestions for upgrading the design and fabrication of high radiation-resistant metallic materials.

Experimental Investigation on the Influence of Water Content on the Mechanical Properties of Coal under Conventional Triaxial Compression

The presence of water is one of the most important factors in coal mining, and it has a dual influence on the mechanical behavior of rock. To study the influence of water content on the mechanical properties of coal under complicated stress conditions, dry coal specimens and wet coal specimens with water contents of 1.8% and 3.6% were conducted by uniaxial and conventional triaxial compression tests. The relations between the uniaxial compressive strength, deformation, and water content were observed. The reductions in the strength and elastic modulus under different confining pressures were obtained. The mechanical properties of coal specimens with different water contents under triaxial compression were studied. The influences of water content on the microstructure, clay minerals, internal friction angle, and cohesive force of coal were discussed. The results show that the strengths and elastic moduli of wet specimens are clearly lower than those of dry specimens under different confining pressures. The water content has a significant influence on the postfailure mechanical behavior of coal. The loss rates of strength and elastic modulus decrease with increasing confining pressure. The water content has almost no effect on the internal friction angle, while the cohesive force of the saturated specimens is 36.5% lower than that of the dry specimens. The results can provide a reference for inhibiting the occurrence of disasters during coal mining and exploiting coal efficiently.

Tunable Electromechanical Properties of a Barium Strontium Titanate Ferroelectric Film Under a Uniaxial Stress

The possibility of the development of MEMS devices based on the tunable ferroelectric film Ba 0.8Sr 0.2O3 properties under uniaxial deformation was studied theoretically. The thermodynamic model of the phase transitions for the film under uniaxial stress was constructed. The behavior of the material constants for the film in various phase states was investigated. The propagation properties of the surface acoustic wave (SAW) under the uniaxial stress were studied for the film located on the single-crystal silicon substrate. It was shown that the SAW resonance frequency changes within 3 MHz for the frequency of 274 MHz, and 9 MHz for the frequency of 512 MHz.

2-D Strain Sensors Implemented on Asymmetrically Bi-Axially Pre-Strained PDMS for Selectively Switching Stretchable Light-Emitting Device Arrays

Crack phenomenon is one of the most well-known mechanisms to turn a conductive thin film into a strain sensor. However, there is a limitation that most of the crack-based strain sensors using elastomeric materials with high Poisson's ratio only allow uni-axial deformation because unintended cracks are easily formed into arbitrary directions even under low strain. Therefore, if directional crack formation can be engineered and thus a strain sensor only responds to a specific axial-direction strain, it can be used as an excellent trigger sensing deformation direction and will act an interesting role in various stretchable electronics fields. In this work, we introduce an anisotropic crack formation mechanism and implement micro-crack based strain sensors with silver thin films that are inkjet-printed on an asymmetrically pre-strained roughened poly(dimethylsiloxane) (PDMS) substrate. Anisotropic crack formation combined with the asymmetric buckling structure remarkably differentiates sensors' sensitivity to axial directions of the applied strain. We demonstrate a resolution-sustainable and 2-dimensionally stretchable LED array with feedback functionality between sensing strain directions and turning on corresponding axial LEDs by using two orthogonally arranged strain sensors. This work will provide an insight emphasizing a new role of strain sensors in stretchable electronics applications.

Mechanically modulated spin-orbit couplings in oligopeptides

Recently experiments have shown very significant spin activity in biological molecules such as DNA, proteins, oligopeptides and aminoacids. Such molecules have in common their chiral structure, time reversal symmetry and the absence of magnetic exchange interactions. The spin activity is then assumed to be due to either the pure Spin-orbit (SO) interaction or SO coupled to the presence of strong local sources of electric fields. Here we derive an analytical tight-binding Hamiltonian model for Oligopeptides that contemplates both intrinsic SO and Rashba interaction induced by hydrogen bond. We use a lowest order perturbation theory band folding scheme and derive the reciprocal space intrinsic and Rashba type Hamiltonian terms to evaluate the spin activity of the oligopeptide and its dependence of molecule uniaxial deformations. SO strengths in the tens of meV are found and explicit spin active deformation potentials. We find a rich interplay between responses to deformations both to enhance and diminish SO strength that allow for experimental testing of the orbital model. Qualitative consistency with recent experiments shows the role of hydrogen bonding in spin activity.

Effect of specimen orientation to the rolling direction on uniaxial tensile forming and failure limits

Alteration of forming and failure limits due to planar anisotropy of the sheet metal significantly affects the safe forming operation region and finally successfully manufacturing of a sheet metal formed component. This article presents the effect of planar anisotropy on uniaxial tensile properties, forming and failure limits of cold-rolled ferritic and dual-phase steels. In-situ three dimensional digital image correlation technique is used to measure the evolution of local strain components during uniaxial tensile test. For both the steels, necking limit is highest for the specimen at an orientation of 90° to rolling direction, while failure limit is highest for those specimen whose orientation is 45° to rolling direction for ferritic steel, and both 0° and 90° to rolling direction for dual-phase steel. Uniaxial tensile deformation path for ferritic steel holds lower slope than dual-phase steel as depicted in major versus minor strain plot.