Regions Of High Strain Research Articles

Evaluation of Prediction Accuracy for Anisotropic Yield Functions Using Cruciform Hole Expansion Test

To evaluate the prediction accuracy of the anisotropic yield function, we propose an original cruciform hole expansion test. Displacements on two axes were applied to the cruciform specimens with a hole in the center. The thickness strain in the region near the hole was compared to the simulation results. Because this forming test is free of friction and bending, it is an appropriate method to assess the anisotropic yield function without the influences of friction or the Bauschinger effect, or the need to consider the stress-strain curve in high-strain region. Hill1948, YLD2000-2D, and spline yield function which is an improved version of the Vegter model were selected, and 6000 series aluminum alloy sheets (A6116-T4) were used in this study. The parameter identification method of the spline yield function also proposed in this paper using the pseudo plane strain tensile test and optimization software. As a result, the spline yield function has better predictive accuracy than the conventional anisotropic yield functions Hill1948 and YLD2000-2D.

Impact of local Si segregation on strain localization in ductile cast iron

The distribution of Si content in tensile deformed ductile cast iron has been characterized using electron microscopy and correlated to the strain distribution determined based on 3D tomography data collected before and after tensile deformation and digital volume correlation analysis. The results show that the high plastic strain regions localize in bands consisting of large graphite nodules and deformed matrix with high Si content connecting the graphite nodules in the first-to-solidify regions. The bands are aligned about 45° with respect to the loading direction, which is close to the maximum shear direction.

\xb5PIV measurement of the 3D velocity distribution of Taylor droplets moving in a square horizontal channel

This paper presents a µPIV measurement of the 3D2C velocity distribution of Taylor droplets moving in a square horizontal microchannel at Ca_{mathrm {c}} = 0.005 and Re_{mathrm {c}} = 0.051. We reconstruct the third velocity component and present an accuracy assessment of the reconstruction based on a volume flow balance of the 3D3C velocity field. The velocity field allows the investigation of the 3D flow features such as stagnation regions and the shear rate distribution. The maximum shear rate is located at the entrances and exits of the wall films and at the corner flow (gutter) bypassing the Taylor droplet. The regions of high strain correspond to the cap positions of the Taylor droplets. An experimental data set allows visualization of the streamlines of the velocity distribution on the interface of a Taylor droplet and to directly relate it to the main and secondary vortices of the droplet phase velocity field. The measurement data are provided as a digital resource for the validation of numerical simulation or further assessment.Graphic abstract

Constitutive equation and hot processing map of TA15 titanium alloy

The stress-strain curves of TA15 titanium alloy at 750 ∼ 950 °C and 0.001 ∼ 1 s−1 were obtained by hot compression with Gleeble-1500D. Based on the compression experimental data of TA15 titanium alloy, the Johnson-Cook high temperature thermal deformation constitutive equation was established. By calculating the constitutive equation, the flow stress was compared with the measured stress-strain curve, and the accuracy of the equation was verified. Then, based on the theory of hot processing map of dynamic materials, the hot processing map is drawn when the strain is 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6. The reasonable range of hot processing map of TA15 titanium alloy was determined. When the temperature is between 750 °C–875 °C, the power dissipation factor decreases with increasing strain rate. The maximum power dissipation is distributed between 825 °C–950 °C. This indicates that recrystallization occurred within this range. The safe zone is mainly concentrated in the temperature range of 885 °C–950 °C, the strain rate is less than 0.1 s−1. It can be seen that instability does not occur in the high temperature and low strain region. Therefore, at 885 ≤ T ≤ 950 °C, 0.001 ≤ ≤ 0.1 s−1 or 800 ≤ T ≤ 875 °C, 0.001 ≤ ≤ 0.002 s−1, it is reasonable to perform high temperature deformation on TA15 titanium alloy.

On the Lyapunov spectrum of an ensemble of vortices

In space- and time-dependent dynamical systems, Lyapunov vectors correspond to spatio-temporal patterns of instability. These patterns can be used to parse and predict the interaction and break-down of coherent structures. The computation of Lyapunov vectors, however, is computationally demanding and has hitherto been restricted to systems with a comparatively low attractor dimension. We aim to study the dynamics of vortices in developed turbulence with an attractor dimension of order O(100). To this end, we compute the linear stability spectrum of an unstable periodic orbit embedded in the turbulent attractor and consider it a proxy for the Lyapunov spectrum. Along the periodic orbit at least 25 Lyapunov vectors can give the largest growth rate locally in time and space. We highlight one instance of a mutually induced instability of a vortex pair localized in the high-strain interstitial region.

Heterogeneous matrix deposition in human tissue engineered cartilage changes the local shear modulus and resistance to local construct buckling

Human tissue engineered cartilage is a promising solution for focal cartilage defects, but these constructs do not have the same local mechanical properties as native tissue. Most clinically relevant engineered cartilage constructs seed human chondrocytes onto a collagen scaffold, which buckles at low loads and strains. This buckling creates local regions of high strain that could cause cell death and damage the engineered tissue. Since human tissue engineered cartilage is commonly grown in-vivo prior to implantation, new matrix deposition could improve the local implant mechanics and prevent local tissue buckling. However, the relationship between local biochemical composition and the local mechanics or local buckling probability has never been quantified. Therefore, this study correlated the local biochemical composition of human tissue engineered cartilage constructs using Fourier transform infrared spectroscopy (FTIR) with the local shear modulus and local buckling probability. The local shear modulus and local buckling probability were obtained using a confocal elastography technique. The local shear modulus increased with increases in local aggrecan content in the interior region (inside the scaffold). A minimum amount of aggrecan was required to prevent local construct buckling at physiologic strains. Since the original scaffold was primarily composed of collagen, increases in collagen content due to new matrix deposition was minimal and had little effect on the mechanical properties. Thus, we concluded that aggrecan deposition inside the scaffold pores is the most effective way to improve the mechanical function and prevent local tissue damage in human tissue engineered cartilage constructs.

Comparison of Rheological Characteristics and Mechanical Properties of Fossil-Based and Bio-Based Polycarbonate

Fossil-based PC, bisphenol-A polycarbonate (BPA-PC), is polymerized using bisphenol-A, which is derived from fossil-fuel based chemicals. Bio-based polycarbonate (bio-based PC) is polymerized using isosorbide, which is taken from plants. Accordingly, bio-based PC does not contain toxic polymerization chemicals. The rheological characteristics of fossil-based PC and bio-based PC samples, including viscosity, storage and loss moduli, and melt tension, were studied and compared. The mechanical properties of tensile behavior and impact strength were also measured and discussed. The shear viscosity curves and storage and loss moduli patterns of the bio-based PC were found to be somewhat different from those of fossil-based PC. The bio-based PC had higher tensile strength and elastic modulus than the fossil-based PC. The fossil-based PC exhibited a stress jump in the high strain region of the stress-strain curve, while the bio-based PC exhibited no stress jumps. The bio-based PC had a lower impact strength than the fossil-based PC. The cross-section of the fractured impact specimen of the bio-based PC showed only mirror regions, while that of the fossil-based PC showed both mirror regions and misted regions.

Low cycle fatigue properties of 7050-T7451 aluminum alloy under different strain ratios

The low cycle fatigue properties of 7050-T7451 aluminum alloy was studied. The low cycle fatigue properties of 7050-T7451 aluminum alloy at three strain ratios R = -1, 0.02, and 0.5 were measured by axial strain control method on MTS electro-hydraulic servo testing machine. In this research, the relationship between cyclic stress and strain at strain ratio R = -1 and the average stress relaxation effect of R = -1, 0.05 were given. The equivalent strain model was used to draw the strain-life curve for low cycle fatigue life data. The results show that under different strain ratios of 7050-T7451 aluminum alloy, the same strain amplitude in the high strain region leads to approximate fatigue life, and the effect of the strain ratio is only reflected in the low strain region.

Influence of Aspect Ratio on Rolling Shear Properties of Fast-Grown Small Diameter Eucalyptus Lumber

Eucalyptus is a major fast-grown species in South China, which has the potential for producing structural wood products such as cross-laminated timber (CLT). Aspect ratio (board width vs. board thickness) of eucalyptus lumbers is small due to the small diameter of fast-grown eucalyptus wood. To evaluate its rolling shear modulus and strength for potential CLT applications, three-layer hybrid CLT shear block specimens with different aspect ratios (2,4,6), were tested by planar shear test method. Digital image correlation (DIC) was employed to measure the rolling shear strain distribution and development during the planar shear tests. The mean values of rolling shear modulus and strength of eucalyptus lamination were 260.3% and 88.2% higher than those of SPF(Spruce-pine-fir) lamination with the same aspect ratio of 4, respectively. The rolling shear properties of eucalyptus laminations increased as the aspect ratio increased. Aspect ratio had a significant influence on rolling shear modulus compared to rolling shear strength. The high shear strain regions were primarily found around the gaps between segments of cross layer. The quantity of high shear strain regions increased as the aspect ratio of lamination decreased. Other high shear strain regions also occurred around the pith and along the glue line. The sudden failure of specimen occurred in the high strain region. In conclusion, the rolling shear strength and modulus of fast-grown eucalyptus laminations exceed the respective characteristic values for softwoods in the current standard by roughly factors of 3 and 8, indicating great potential for fast-grown eucalyptus wood cross-layers in CLT.

Effects of Basal-texture Inclination on Bending Formability in Mg-Al-Zn-Ca Alloys

Flame-resistant magnesium alloy containing Ca is attracting attention in the transportation field because it is safe and lightweight. In this study, the effects of texture on bending formability were investigated for samples having different forms of texture that were cut from an extruded Mg-Al-Zn-Ca alloy plate at different angles ranging from 0° to 90° from the extrusion direction. Tensile and compressive deformation behaviors were also examined to discuss the shift of a neutral layer in bending. For bending, it was shown to be preferable that the basal texture not be inclined in low-strain region because of tension/compression asymmetry. However, in high-strain region, the influence of the shift of the neutral layer was weakened. In the experiment, the sample with a cutting angle of 45° exhibited the best bending formability. Furthermore, the result of a verification test using a sheet fabricated by a lateral extrusion, named friction-assisted extrusion (FAE), in which the basal texture was controlled to be inclined, showed that FAE improves the bending formability. This was confirmed by microstructural observation of the cross section near the tension surface at the same bending radius. The number of deformation twins that cause voids and cracks was reduced by controlling the basal texture to be inclined.

Secondary osteon structural heterogeneity between the cranial and caudal cortices of the proximal humerus in white-tailed deer.

Cortical bone remodeling is an ongoing process triggered by microdamage, where osteoclasts resorb existing bone and osteoblasts deposit new bone in the form of secondary osteons (Haversian systems). Previous studies revealed regional variance in Haversian systems structure and possibly material, between opposite cortices of the same bone. As bone mechanical properties depend on tissue structure and material, it is predicted that bone mechanical properties will vary in accordance with structural and material regional heterogeneity. To test this hypothesis, we analysed the structure, mineral content and compressive stiffness of secondary bone from the cranial and caudal cortices of the white-tailed deer proximal humerus. We found significantly larger Haversian systems and canals in the cranial cortex but no significant difference in mineral content between the two cortices. Accordingly, we found no difference in compressive stiffness between the two cortices and thus our working hypothesis was rejected. As the deer humerus is curved and thus likely subjected to bending during habitual locomotion, we expect that similar to other curved long bones, the cranial cortex of the deer humerus is likely subjected primarily to tensile strains and the caudal cortex is subject primarily to compressive strains. Consequently, our results suggest that strain magnitude (larger in compression) and sign (compression versus tension) affect the osteoclasts and osteoblasts differently in the basic multicellular unit. Our results further suggest that osteoclasts are inhibited in regions of high compressive strains (creating smaller Haversian systems) while the osteoid deposition and mineralization by osteoblasts is not affected by strain magnitude and sign.

Strain field distribution of asphalt mortar using digital image processing

The difference between the modulus of asphalt mixture components leads to the complex deformation phenomenon that the strain primarily accumulates in asphalt mortar. Conventional deformation testing methods cannot easily capture the local deformation, limiting the usage of isotropic deformation measurement of asphalt mixture. This study aimed (1) to propose a method to extract stain field of asphalt mortar by digital image correlation (DIC) and digital image process method, as well as (2) to delve into the strain field in the asphalt mortar position at various temperatures and loading rates. In the present study, DIC was first applied to calculate the full strain field of asphalt mixture; subsequently, the aggregate, asphalt mortar as well as void were obtained using digital image process method. Based on digital image processing method, the strain at asphalt mortar position was achieved. According to the results of the strain field distribution of asphalt mortar in indirect tensile test, probability density of low strain region decreased, while that of medium and high strain region increased in the loading process. The results illustrated that asphalt mixture with low filling factor (the area ratio of mortar to the whole mixture) had higher strain in a smaller area. In the meantime, at low temperature, the mean strain of high strain zone was lower, and the area of that became smaller.

Multistage serrated flow behavior of a medium-manganese high-carbon steel

The deformation mechanisms and the flow stress behavior of a medium-manganese high-carbon steel during cold deformation at a strain rate of 10−5 s−1 were explored using a universal testing machine, an X-ray diffractometer, a field emission scanning electron microscope and a high-resolution transmission electron microscope. The results show that continuous step-up serrated flow behavior appears after the yielding point, and the true stress–strain curve is roughly divided into five stages based on distinctive densities and amplitudes of serration. The strengthening mechanisms of the experimental steel involve Cottrell atmosphere, twinning-induced plasticity (TWIP) effect and transformation-induced plasticity (TRIP) effect. TWIP effect is the dominant deformation mechanism, and deformation twins formed by TWIP effect comprise primary, secondary and nanotwins. Furthermore, TRIP effect arises in the local high-strain region. Carbon element plays a key role in the transformation of the deformation mechanism. A small amount of carbide precipitates around twin boundaries lead to the formation of local carbon-poor regions, and Md temperature and stacking fault energy of medium-manganese high-carbon steel are propitious to the occurrence of TRIP effect. In addition, the contributions of various deformation mechanisms to plasticity are calculated, and that of TWIP effect is the greatest.

Disturbance Rejection for an Unmanned Rotary Aircraft System Using Strain Sensing

This paper presents a bioinspired approach for fast reaction to external disturbances as applied to small unmanned aerial systems platforms. A disturbance rejection method for a quadrotor vehicle is proposed by means of force-adaptive feedback using strain measurements. These strain measurements provide a reactive mechanism to counteract atmospheric disturbances acting on the vehicle. The reactive response from force-sensitive strain measurements is initiated before the disturbance propagates to lower-order pose and velocity states, while simultaneously reducing the latency in the feedback. These measurements are provided by means of strain gauges attached to the quadrotor arms. The location and feedback gain of the strain gauges were determined based on expected forces and moments as well as regions of high strain. The airframe section that hosted the strain sensors was manufactured and designed for a balance between structural stability and force sensitivity. The response of the quadrotor system was characterized using an induced disturbance to simulate a vertical gust. This heave perturbation was mitigated using a strain feedback controller. Improvements in gust response were demonstrated by measuring the effects of the disturbance on vehicle states.

Modeling of Crystallographic Texture in Plastic Flow Machining

Plastic flow machining (PFM) is proposed as a new severe plastic deformation (SPD) technique capable of producing ultrafine‐grained sheet metal from bulk sample. Herein, a model is proposed for the three strain paths that the material follows during the PFM extrusion process. The proposed strain paths are justified by modeling the texture evolution in good agreement with the experiments in the three deformation zones. Two polycrystal models are used to simulate texture evolution: the viscoplastic self‐consistent (VPSC) polycrystal approach and the Taylor‐type lattice curvature‐based grain fragmentation (GR) model. The simulations reproduce faithfully all three textures observed experimentally within the sheet. The experimental texture in the zone carrying the smallest strain is obtained with the VPSC approach, whereas in the higher strain region, the GR model reproduced the texture. The two main results of this modeling are as follows: 1) an example is presented for the successful identification of the deformation mode in a new SPD process with the help of the crystallographic texture. 2) At large strains, the VPSC model fails; it is the Taylor deformation‐based GR approach which is able to reproduce the experimental texture evolution.

Crystallographic preferred orientations of plagioclase via grain boundary sliding in a lower-crustal anorthositic ultramylonite

To clarify the rheological properties and deformational mechanisms that operate within lower-crustal shear zones, we analyzed deformation microstructures and fabrics in plagioclase grains from high-strain regions of intrafolial drag folds of an anorthositic ultramylonite from Langoya, Vesteralen, northern Norway. These grains have developed weak crystallographic preferred orientations (CPOs). Other than deformation twinning, they do not show any indications of intracrystalline plasticity or dynamic recrystallization. In some domains of the drag fold, plagioclase CPOs are more distinct, but the majority of inferred slip systems are not consistent with the main slip systems in plagioclase. These suggest that neither dislocation creep nor dislocation-accommodated grain boundary sliding (GBS) produced the plagioclase CPOs but rather grain rotation via GBS along specific grain boundaries parallel or subparallel to crystallographic planes of (010), (100) or (110), which led to an alignment of the easy-slip grain boundaries in the flow direction that produced the observed CPO patterns. The anisotropy of dissolution and growth rates may have been responsible for the development of the specific grain boundaries.

Variations in the distribution of local strain energy within different realizations of a representative volume element

Numerical simulations are used to study the variations in microscopic fields between different random realizations of representative volume elements (RVE) with the same macroscopic properties. We focus on the strain energy of the matrix in unidirectional fiber composites with Neo-Hookean components, considering linear and non-linear applied loading. The simulations show significant variations in the strain energy between different realizations of the RVEs, particularly for the regions of high strain and stress concentrations that often govern damage and failure initiation. Results show a strong dependence on the volume fraction, minimum fiber distance and RVE size, as well as poor correlation between the local and the global response, which is characterized using the homogenized stiffness. In the case of non-linear loading, the rearrangement of the microstructure results in even lower correlation with the macroscopic response, as well as very strong variations according to the loading direction. We also show very poor correlation between the response in the linear and non-linear regimes for the same RVE.

Internal tidal currents and solitons in the southern Bay of Bengal

Tidal currents and higher-frequency internal solitons are observed from current and hydrographic fields that were recently measured at six deep-water moorings in the southern Bay of Bengal by the Naval Research Laboratory. Current, temperature and salinity were measured in the upper 500 m of the water column between December 2013 and August 2015. Harmonically-fitted (coherent) tidal currents, in the upper 500 m, showed maximum amplitudes for the M2 constituent, with velocities of the order of 3 cm s−1; M2 tidal ellipses were generally oriented towards the north-northeast. Incoherent internal tides accounted for at least 60% of the total semidiurnal tide energy. Solitons were generated at multiple source regions along the Andaman Islands and contribute significantly to the high frequency energy (greater than 1 cph). Solitons were present throughout the measurement period but their activity was reduced during the 2014–2015 winter monsoon. Soliton and internal-tide amplitudes show a fortnightly modulation, consistent with the spring-neap cycle of the semidiurnal tide. The interaction of tides and the associated high-frequency waves (20–40 min periods) with mesoscale eddies produced regions of enhanced shear and strain in the thermocline. High-strain regions were found within cyclonic eddies and high-shear regions were found within anticyclonic eddies. Shear-strain-based dissipation models indicate that mixing rates can be enhanced by a factor of 3–5 by tidal and higher frequencies during interactions with eddies. This study further suggests that tidal harmonics and internal tides have an important impact on the near-surface currents away from coastal boundaries, in the interior of the Bay of Bengal, while the effects of the depth-averaged tides are more important deeper in the water column.

A dynamic spectrally enriched subgrid-scale model for preferential concentration in particle-laden turbulence

A new subgrid-scale (SGS) model for turbulent velocity fluctuations is proposed for large-eddy simulations (LES) of dispersed multi-phase flows. The modeled velocity contains scales smaller than the LES grid resolution, thereby enabling the prediction of small-scale phenomena such as the preferential concentration of particles in high-strain regions. The construction of the spectrally enriched velocity field in physical space is made dynamically, and is based on (1) modeling the smallest resolved eddies of sizes comparable to the LES grid size via approximate deconvolution, and (2) reconstructing the SGS fluctuations via non-linear generation of small-scale turbulence. The model does not contain tunable parameters, can be deployed in non-uniform grids, and is applicable to inhomogeneous flows subject to arbitrary boundary conditions. The performance of the model is assessed in LES of isotropic turbulence laden with inertial particles, where improved agreement with direct numerical simulation results is obtained for the statistics of preferential concentration.

Decoupled epineurial and axonal deformation in mouse median and ulnar nerves.

Peripheral nerves accommodate mechanical loads during joint movement. Hypothesized protective features include increased nerve compliance near joints and axonal undulation. How axons perceive nerve deformation is poorly understood. We tested whether nerves increase local axonal undulation in regions of high epineurial strain to protect nerve fibers from strain-induced damage. Regional epineurial strain was measured near the elbow in median and ulnar nerves of mice expressing axonal fluorescence before and after decompression. Regional axonal tortuosity was quantified under confocal microscopy. Nerves showed higher epineurial strain just distal to the medial epicondyle; these differences were eliminated after decompression. Axonal tortuosity also varied regionally; however, unlike in the epineurium, it was greater in proximal regions. In this study we have proposed a neuromechanical model whereby axons can unravel along their entire length due to looser mechanical coupling to the peri/epineurium. Our findings have major implications for understanding nerve biomechanics and dysfunction. Muscle Nerve 59:619-619, 2019.