Strains In Different Directions Research Articles

Numerical and experimental investigation on cold drawing process of high spiral angle tube

A novel method of cold drawing process of high spiral angle tube made of 304 stainless steel is proposed. Forming principles of high spiral angle tube are calculated. New drawing dies are designed and manufactured. Numerical simulation and corresponding experiments are carried out. Forming quality and defects of cold drawing are discussed. Various factors affecting metal flow during cold drawing process are studied in detail. Finite element model of cold drawing process is established. The variation of drawing load is presented. The distributions of equivalent stress and equivalent strain in different directions during cold drawing process are analyzed. Displacements of points in axial direction and circumference direction during cold drawing process are compared respectively. The evolutions of microstructure during cold drawing process are studied.

Comparison of Flexoelectric and Piezoelectric Distributed Sensing Signal of Toroidal Shell

In this study, the flexoelectric and piezoelectric distributed sensing signal of the toroidal shell is discussed. By considering the curvature radii and Lamé parameters of the toroidal shell, dynamic strains are derived based on the double-curvature shell. Flexoelectric and piezoelectric distributed sensing models of the toroidal shell are established. Based on the direct flexoelectric effect and direct piezoelectric effect, the flexoelectric/piezoelectric distributed sensing signal is evaluated respectively. The local neural sensing signal is discussed while the flexoelectric and piezoelectric sensor patches approach to infinitesimal. The neural sensing signal is made of different signal components, and the components effects are discussed to elaborate the difference between the flexoelectric and piezoelectric sensing signal. The results indicate that the membrane-induced signal components and bending-induced signal components both affect the piezoelectric sensing signal, while only the bending-induced signal components affect the flexoelectric sensing signal. To elaborate the significance of the components in different directions, signal induced by different strains in different directions are discussed. The signal induced by the meridional bending strain dominates for the flexoelectric sensing while signal induced by the meridional membrane strain is dominant for piezoelectric sensing.

Structural, electronic and mechanical properties of Mo2GeC under strain engineering

A new type of nitride and carbide with excellent properties of metals and ceramics, known as MAX phase materials, is a new guide for structural modification in various engineering applications and novel technologies. The Mo 2 GeC MAX phase is regarded as a promising material for applications such as new coatings, high pressure resistant materials, and fission and fusion program reactors. In this work, the structural, electronic, and mechanical properties of Mo 2 GeC under strain engineering are predicted by first-principles calculations. When Mo 2 GeC is tensioned or compressed by various strain conditions, effective mass decreases and increases in electrical conductivity are observed. Under uniform biaxial strain, the degeneracy at the top of the valence band is significantly increased. Mo 2 GeC possesses small Young’s modulus, shear modulus, and large bulk modulus, indicating that it can be desired for large strain engineering applications. However, the layered structure of Mo 2 GeC leads to low shear strength and hardness, which makes it less resistant to shear deformation. We also investigate the structural deformation and mechanical properties of Mo 2 GeC in different directions of uniaxial tensile strain up to the fracture limit. For tension along the a -direction, the strain ε value is 45% when Mo 2 GeC reaches the ideal tensile strength. The different bond strengths of Mo 2 GeC explain its anisotropy and show more significant differences under different strain conditions. Our results provide a strategy for tuning the various properties of Mo 2 GeC. Mo 2 GeC is subjected to uniaxial strain in different directions

Multidirectional strain-induced thermoelectric figure of merit enhancement of zigzag bilayer phosphorene nanoribbons

We have theoretically investigated strain-induced thermoelectric power generation properties of zigzag bilayer phosphorene nanoribbon. Since energy bandgap size and edge state dispersion play a significant role in the thermoelectric properties of such a structure, we have investigated the effect of strain in different directions on these two quantities. We have shown that by applying both tensile and compressive strains in different directions, it is possible to properly tune the energy bandgap size and adjust the edge state dispersion. We have also selected strain combinations in different directions that simultaneously increase the size of the energy bandgap and decrease the dispersion of the edge state. It has shown that with such combinations of strains, the maximal figure of merit has been improved by about two times compared to the pristine case.

Three-dimensional failure behavior and cracking mechanism of rectangular solid sandstone containing a single fissure under triaxial compression

In actual rock engineering, fissures play an important role in determining the mechanical parameters of rock mass, whereas it is very difficult to construct fissures in cylindrical specimens. Therefore, the pre-fissured rectangular rock specimens were constructed innovatively. Moreover, a series of triaxial compression experimental results on the failure mechanical behavior of rectangular solid sandstone specimens containing a single fissure were reported. The lateral strain in different directions was monitored and the experimental results show that elastic modulus and axial strain increase non-linearly with confining pressure, and the average Poisson’ s ratio parallel to fissure (μ2) is larger than that vertical to fissure (μ3). The cohesion, Hoek-Brown parameters of peak strength show similar trends with that of crack damage threshold to the fissure angle (α), and the parameters of the peak strength are larger than those of crack damage threshold. However, the internal friction angles of the peak strength and crack damage threshold are almost equal. Based on the geometries and properties of cracks, ten typical crack types are identified. Cracks vertical to pre-existing fissures occur in specimens under uniaxial compression, whereas cracks parallel to pre-existing fissures occur under triaxial compression. Finally, X-ray micro-computed tomography (CT) observations are conducted to analyze the internal damage mechanism of sandstone specimens with respect to various fissure angles. Reconstructed 3-D CT images indicate obvious effects of confining pressure and fissure angle on the crack system of sandstone specimens. This research elucidates the fundamental nature of rock failure under triaxial compression.

Anisotropy in creep-aging behavior of Al–Li alloy under different stress levels: experimental and constitutive modeling

The anisotropy in creep aging behavior and microstructural evolution of AA2195-T34 A l–Li alloy plates under different stress levels at 180 °C were systematically investigated by constant-stress creep aging, mechanical property testing and microstructure characterization. The results indicated that the creep strain initially increases and then decreases with the angle relative to the rolling direction by cause of the divergences in the dislocation density and the number of movable sliding systems. The creep strain in 45° direction is 1.15 times and 1.41 times larger than that in 0° and 90° directions at a stress of 160 MPa, respectively. The creep strain in-plane anisotropy (IPA) value first increases rapidly, followed by a slight decrease with time, and declines with stress at the primary creep stage. The strength first increases and then tends to fluctuate around a constant value with the aging time because of the evolution of T1 precipitates. As shown by the gradual reduction in the difference among the volume fractions of the brass texture of the alloy in the three directions, the strength IPA rapidly declined at the primary creep stage. The IPA values of the yield strength during the steady creep stage are 4.8%, at a stress of 160 MPa. Since the Schmidt factor of the material in the 45° direction is the largest, the yield strength in this direction is the lowest. A constitutive model considering the anisotropy of creep deformation and aging strengthening was established, of which the predicted results showed excellent consistency with the experimental values. The relative errors between the predicted and experimental values of the yield strength/steady creep strain in different directions do not exceed 1.7% and 4.3%, respectively.

Deformation mechanisms of additively manufactured Hastelloy-X: A neutron diffraction experiment and crystal plasticity finite element modeling

The development of strong textures can affect mechanical anisotropy in the specimens produced by the laser powder bed fusion (LPBF) additive manufacturing (AM) technique. In this study, in-situ neutron diffraction experiments were conducted on nickel superalloy specimens to understand how mechanical ansitropy and the evolution of internal strains are affected by changing the LPBF-AM parameters. In addition, Electron Backscatter Diffraction (EBSD) measurements were performed to characterize the initial microstructure of the specimens. The measured EBSD maps were imported into a crystal plasticity finite element (CPFE) model to further study how different AM parameters, specifically laser power and scanning speed, affect the development of internal strains. At higher specific energy (SE) inputs, columnar grains are observed, and samples developed a 〈110〉 texture along the building direction and a 〈100〉 texture along the scanning direction, while at lower SEs random texture is observed. The development of texture affects elastic and plastic anisotropy, as well as the development of internal strains in different directions, particularly for the {200} lattice strains measured in the laser scanning direction. It is shown that (111) 〈110〉 slip system is the most active one for the range of applied strains.

Superior Stable, Highly Efficient, and Anisotropic Electrothermal Composite Heater in Various Directions with Fast Response Based on Aligned Carbon Nanotube Sheets

Flexible electrothermal heaters have a great potential for applications of warm‐keeping and thermotherapy. However, those common electrothermal heaters are so sensitive to strain that they are hard to resistant to deformation while still keeping the stable and outstanding electrothermal performance. Here, a flexible and elastic composite heater with a stable electrothermal property under varied strain with large deformation is developed by mimicking the wrinkle feature of human skin in a carbon nanotube (CNT)/polydimethylsiloxane (PDMS) bilayered structure. The created wrinkle feature of CNT film from the resilience of PDMS makes the electrothermal heater a stable electrothermal performance within 30–40% strain in different directions. The aligned preference of CNTs in the CNT film gives the electrothermal heater an ability that shows different electrothermal performance depending on different angles between the direction of CNT alignment and the long axis of the sample. This composite electrothermal heater also presents a highly efficient electrothermal performance that can reach 200 °C within 30s upon 2 V.

Spatial-light-modulator-based dual shearing direction shearography.

We propose a dual shearing shearography system based on a spatial light modulator (SLM). Compared to spatial phase shift shearography, the advantages of this system include its simple structure, relatively high light efficiency, and good phase map quality. Digital shearography is a fast, practical, non-contact, whole-field, and anti-turbulent optical approach to non-destructive testing (NDT) and strain measurement. Because the shearing direction determines the strain direction being measured, tests using multiple shearing directions are sometimes required to obtain strain in different directions and detect all defects. Various setups, based on the spatial phase shift method, have been proposed to solve the issue. While some of these setups perform well, they may also introduce new problems, such as poor phase map quality and low light efficiency. We present a sequential dual shearing shearographic system with good phase map quality and high light efficiency. Due to the SLM's high-speed response, capable of reaching hundreds of hertz, SLM-based dual shearing direction shearography allows for fast temporal phase shifting and shearing direction switching while providing very good phase map quality. Unlike the spatial phase shift method, which has low light efficiency due to its need for a small aperture to enable a relatively large speckle size to cover multiple pixels, the proposed method is based on a fast temporal phase shift and does not have this limitation. In addition, SLM can provide a programmable and adjustable shearing method in any direction and distance, which is beneficial for strain measurements and NDT requiring strain measurements in different directions using a small and precise shearing distance. We describe in detail the theory derivation and non-destructive testing application results for the SLM-based dual shearing direction shearography system.

Isotherms and kinetics of deformation of coal during carbon dioxide sequestration and their relationship to sorption

An in-depth understanding of the carbon dioxide (CO2) sorption behavior on coal is critical for CO2 sequestration in coal seams and enhanced coalbed methane recovery. However, CO2 induces the deformation of coal through physical and/or chemical reactions during the CO2 injection process, which has a significant effect on the gas flow and stability of the coal seams. This study investigates the isotherms and kinetics of CO2 sorption and hence deformation of a bituminous coal sample during isotherm tests at three different temperatures. The isotherms and kinetics curves of sorption and deformation can be described by the Langmuir and the pseudo-second-order (PSO) models, respectively. The experiment results and PSO model parameters indicate that a pore-filling effect at low pressure results in an overestimated amount of excess sorption, leading to a mismatched phenomenon between the sorption and swelling, that is the maximum amount of sorption fails to induce corresponding maximum swelling. The CO2-induced deformation is anisotropic and heterogeneous during the whole sorption process, which can be attributed to the bedding structure of coal and heterogeneous maceral distribution in coal. Because of the difference in the sorption characteristic between different macerals, the clay + inertinite-rich regions first rapidly swell and then suffer from compression through the later swelling of the vitrinite + liptinite -rich regions in coal, showing an “overshoot” behavior. The dissolution of CO2 induces a structural rearrangement of coal, leading to strains in different directions maintain changes without further CO2 intake. This phenomenon is observed in the first few sorption steps until the structure of coal reaches a stable state. The kinetic relationships between sorption and deformation in individual pressure steps are nearly linear or are linear up to a certain point but slopes of these curves are different, resulting in a simple quadratic polynomial relationship between sorption and deformation isothermals during the whole sorption process.

Design and development of a filament wound composite overwrapped pressure vessel

A detailed design optimization of a composite over wrapped pressure vessel (COPV) is performed through finite element analysis (FEA) and testing. The design optimization of a type IV polymer-lined composite overwrapped pressure vessel is performed by means of the finite element method using ABAQUS software. A plug-in named WCM in ABAQUS is used that automates the entire process of constructing a COPV FEA model. This work investigates the influence of winding angle, number of layers, and sequence of layers on the burst strength of COPV. Maximum stress, maximum strain, Tsai Hill, Tsai Wu and Hashin progressive failure criteria are used to find the burst strength of the COPV. Comparing all the results obtained using above the failure criteria, it is found that the maximum strain criterion is more conservative, and the Hashin criterion is the least conservative. Digital Image Correlation (DIC) was utilized during burst testing to quantify the failure strain in different directions. The numerical results were compared with the experimental burst testing results and a reasonably good comparison was found.

Novel Graphene Planar Architecture with Ultrahigh Stretchability and Sensitivity.

Graphene has attracted increasing attention for strain sensing due to its unique electrical and mechanical properties by tailoring and assembling functional macrostructures with a well-defined configuration. Here a novel graphene-based planar network (GPN) with highly stretchable strain sensing is developed by direct ink writing. The integrated and regulated structure of GPN indicates an excellent response sensitivity and cyclic stability to various strain modes compared with the traditional graphene-based woven fabric (GWF) structure. An equivalent resistance network is introduced to analyze the resistance change mechanism and fracture failure mode of the network structures, in which the difference can be mainly attributed to the interfacial resistance at the crosspoints of the crossed ribbons. The tunable and interconnected GPN shows a significant difference in the response sensitivity under stretching strain in different directions, and the relative resistance change is up to 20 and 3 in horizontal and vertical directions after 1000 cycles for a 20% stretching strain, respectively, which can be explained by the transformation of the stretching mode from macro-structural stretching to micromaterial stretching. The controllable fabrication of GPN can be utilized not only for the detection of full-range human activities but monitoring external stress distribution in real-time by integration.

Study of Rock Blasting Failure Pattern with One Free Boundary

The study of rock blasting failure pattern is of engineering importance. In order to investigate rock blasting failure pattern with one free boundary, high‐speed photography technology is introduced into the two‐dimensional granite model. Through high‐speed camera images, a crack that originated from spalling is observed and then propagates inward. By using the high‐speed digital image correlation method, the full‐strain fields on the surface of the specimens are calculated. The preliminary results show that von Mises strain localization appears on the specimen surface near the free boundary. The axial strains near that crack present three kinds of characteristics. There are the joint action areas of the strain localization by analyzing strains in different directions, and the strain localizations are related to the crack propagation. Ultimately, after analysis of the experimental results, the preliminary diagrammatic drawing of rock blasting failure pattern under stress wave action with one free boundary is drawn.

Mechanical response and plastic deformation of coherent twin boundary with perfect and defective structures

Coherent twin boundary (CTB) is an important structural defect, which is generally considered to have a perfect structure in the previous theoretical and computational studies. However, the CTBs observed in the recent experimental research in the submicrometer range were found to have inherent imperfections. In this work, we investigated the difference between perfect and defective CTB structures in mechanical responses and deformation mechanisms using molecular dynamics simulations. Two typical defective CTB structures with either incoherent twin boundary (ITB) step or self-interstitial atoms (SIA) cluster were considered. The simulation samples were deformed under uniaxial strain in different directions and were deformed under shear strain. Compare to the CTB with perfect structure, the stability of the defective CTB decreased significantly, and the simulated samples softened due to the existence of the ITB step and SIA cluster. When the critical stress was reached, the first dislocations were nucleated in the crystal lattice of the bicrystal sample with a perfect CTB structure. However, the CTB with structural defects played a role as the dislocation source to release dislocations, thus reducing the yield stress. Under uniaxial tension and compression, the yield stress of CTB with the SIA cluster was lower than that of CTB with ITB step in all simulated conditions. Dislocation analysis indicated that the difference was ascribed to the dissociation of an existed Frank dislocation loop on the twin plane rather than the nucleation of new dislocations from the CTB/ITB junction. Under shear deformation, the shear strain separated the structural defects from the CTB plane and transformed the defective CTB structure into a single perfect CTB. The simulation results provide a better understanding of the mechanical properties and deformation mechanisms of CTB-strengthened materials.

Strain-tunable electronic and optical properties of novel anisotropic green phosphorene: a first-principles study

The effect of in-layer strain on the optical and electrical properties of monolayer green phosphorene, a new anisotropic two-dimensional (2D) material, has been systematically studied. The studied strain includes in-layer uniaxial strain and biaxial strain. Green phosphorene can be viewed as a combination of black and blue phosphorene segments in regular order. We adopt the HSE06 method to correct the calculated results. The results reveal that, firstly, strain-free monolayer green phosphorene is a stable direct band gap 2D semiconductor with the anisotropic optical property. The transmittance of infrared and visible light along the zigzag direction is better than that along the armchair direction. However, the transmittance of the UV-light along the armchair direction is better than that along the zigzag direction. Secondly, the optical properties, such as the absorption coefficient and reflectivity, along armchair and zigzag direction respond very differently to the various applied strains. As for the electronic properties, the band gap exhibits different changing trends by applying either in-layer biaxial strain or uniaxial strain in different directions. Besides, the near-band-edge electronic orbitals exhibit different bond nature in different directions. These results suggest that green phosphorene shows strong anisotropy in electronic and optical properties. By calculating and comparing the energies of near-band-edge states after applying different strains on green phosphorene, the reason for the anisotropy of the new 2D material is analyzed. This study implies that the electronic and optical properties of green phosphorene, a stable direct band gap anisotropic semiconductor, could be efficiently tuned by in-layer biaxial or uniaxial strain. Therefore, green phosphorene can be used in linear polarizers and other anisotropic photoelectric devices.

Monitoring of Multidirectional and Cure-Induced Strain in CFRP Laminates Using FBG Sensors

During the curing cycle, the residual stress has influence on cure-induced deformation for carbon fiber reinforced plastics (CFRP) laminates, which is highly susceptible to the ply design. Therefore, the change laws of strain and the effect of residual stress in CFRP laminates after curing, which is of great significance to ply design, were cleared by using the combining pattern of thermocouple and fibre Bragg grating (FBG) sensors. For the FBG sensors embedded with different directions in lay-up CFRP laminates, the temperature and strain in different directions of composite laminates were obtained in real-time. Monitoring results show that compared with strain in 45° direction, the carbon fibers (CF) act stronger to inhibit strain in 0° direction and weaker to inhibit strain in 90° direction of resin. After curing, the residual strain in 0° direction is tensile strain, and the residual strain in 45° direction and 90° direction are compressive strain. Meanwhile the value of residual strain in 90° direction is greater than that in 45° direction.

Strain and ferroelectric soft-mode induced superconductivity in strontium titanate

We investigate the effects of strain on superconductivity with particular reference to SrTiO$_3$. Assuming that a ferroelectric mode that softens under tensile strain is responsible for the coupling, an increase in the critical temperature and range of carrier densities for superconductivity is predicted, while the peak of the superconducting dome shifts towards lower carrier densities. Using a Ginzburg-Landau approach in 2D, we find a linear dependence of the critical temperature on strain: if the couplings between the order parameter and strains in different directions differ while their sum is fixed, different behaviours under uniaxial and biaxial (uniform) strain can be understood.

Experimental Investigation on Permeability and Mechanical Deformation of Coal Containing Gas under Load

Coalbed effective permeability is widely used as a primary index to evaluate gas‐drainage effect in CBM exploitation field. However, it seems to be difficult to obtain by the reason of dynamic change in close relationship with crustal stress, methane pressure, porosity, and adsorption. Due to their dissimilar adsorption properties and tectonic deformation degrees, different types of coal containing gas have various stress‐strain and gas seepage curves. The paper presents the experimental investigations of the dynamic relationship between coal permeability and deformation under load. In this work, stress‐strain and permeability investigations were performed using anthracite lump with a vitrinite reflectance of about 3.24% at various pressures and temperatures. The permeability (including the initial, minimum, and maximum) decreased with increasing temperature. At a constant confining pressure, the strains in different directions almost all increased with increasing axial stress and decreased with increasing pore methane pressure during the prefracture stage. At a constant pore pressure, the compression strength of the coal specimens increased approximately linearly during the prefracture stage and sharply decreased during the postfracture stage, while the permeability decreased rapidly and then increased slowly during the prefracture and remained stable during the postfracture stage. The permeability of the coal specimens mainly depended on the inner fissures. The permeability was greater during the postfracture than that during the prefracture stage. At the same temperature, the gas seepage curve of each coal specimen could be divided into three sections: decreasing, increasing, and constant sections. The necessary time for the permeability to reach a steady state increased as the confining and pore pressures increased. At high confining pressures (i.e., 6 MPa and 8 MPa), no significant differences between the methane seepage velocities of the specimens were evident, and their seepage curves were similar to prefracture. However, clear differences were observable at the postfracture stage. The seepage abilities of the coal specimens were more sensitive to stress than temperature in the same condition.

FEM-simulation of machining induced surface plastic deformation and microstructural texture evolution of Ti-6Al-4V alloy

When high speed machining polycrystalline metal, severe plastic deformation usually undergoes in the machined surface layer, accompanied by the microstructural variation of the crystallographic orientation. In the present paper, the machined surface plastic deformation and microstructural texture evolution during high speed machining of titanium alloy Ti-6Al-4V were investigated using finite element method (FEM) simulation. Firstly, a two dimensional FEM model was established, and was validated in terms of cutting forces and chip shape characteristics with experimental results of orthogonal machining. The plastic deformation on the machined surface was analyzed on the basis of finite element simulation. Results revealed that the plastic shear strain was much larger than the other strains in different directions. In addition, the variation of plastic shear strain and strain rate versus cutting time was obtained. When the feed rate was constant, the strain decreased and the maximum strain rate increased as cutting speed increased. Finally, the machined surface texture was simulated and analyzed using the Viscoplastic Self-consistent (VPSC) program based on the variation of plastic shear strain and strain rate, combined with polycrystalline plasticity theory. The machined surface texture evolution during machining was expressed by pole figures and orientation distribution function (ODF) diagrams. And the cylinder texture was identified from the pole figures. Four typical shear textures, including Y, C1, C2, and B fiber textures, were obtained from the ODF diagrams. Meanwhile, the orientation density of texture decreased with the increasing of cutting speed.

Self-correction method of out-of-plane motions in two-dimensional digital image correlation

Strain monitoring is very important in the manufacturing, assembling, installation and servicing processes in both mechanical and civil engineering fields. Two-dimensional digital image correlation is a simple, efficient strain monitoring method, but one major bottleneck is the unacceptable error due to the unavoidable out-of-plane motions of the object in practice. We propose a “self-correction” method: employing the originally extracted strain values in different directions to correct the errors due to out-of-plane motions. It is applicable to many engineering applications with known relationship of strains in different directions. A uniaxial tension test was conducted to demonstrate the effectiveness and practicality of this self-correction method. Compared with other correction methods, this method is not only simpler but also more efficient in correcting errors due to the lens distortion caused by self-heating. Both the experiment and theoretical analyses demonstrate that this self-correction method maintains the high accuracy of the digital image correlation method.