Development of high-speed photoelasticity for visualization of shear stress field in pressure-sensitive gel

Solutions of the interfacial shear and normal stresses in plate flexural-strengthened beams based on different complementary strain energy assumptions

The paper discusses informative possibilities and prospects of application of digital nature-like methodology for computational visualization of natural processes of natural system formation based on the proposed order parameter—intensity of integral geophysical field created by host structure-forming outer space. Since the designated order parameter defines the structure and properties of natural systems and processes, the gradient of the parameter defining the structure of the natural object is a measure of its order parameter and, therefore, can serve as a predictor of forecasting the change in its properties and structure. The declared approach is tested using an example of forecasting the process of flood formation and processes of visualization of tectonic stress fields. The authors have developed a method of point prediction of the onset time and flood level based on a three-level neural network model and a method of vector space-time visualization of a hierarchy of tectonic stress fields on the territory of an unlimited area. The research shows that computational operations with the parameter of the regional temperature gradient along with intelligent forecasting methods illustrate the prospects of point medium-, long-term forecasting of hydrometeorological processes provided with long rows of instrumental observation data. Computational visualization of general, background and local fields of tectonic stresses in the territories of unlimited area serves as a source of parametric data for geoinformation-mathematical modeling of tectonic stress field restructuring in processes of tectonosphere self-organization, calculation of position of geodynamic instability loci—epicenters of possible earthquakes, visualization of tectonic currents in the Earth’s crust. Monitoring geophysical data at geodynamic instability loci opens up prospects for point prediction of earthquakes. Calculation of order parameters of natural objects and processes opens up prospects of their computational modeling, derivation of numerical laws of their conjugate development and a scale series of interaction, as well as prediction of the state of geo objects and geo processes at a given geo space point in conditions of increasing global natural variability.

An experimental study is conducted on the qualitative visualization of the flow field in separation and reattachment flows induced by an incident shock interaction by several techniques including shear-sensitive liquid crystal coating (SSLCC), oil flow, schlieren, and numerical simulation. The incident shock wave is generated by a wedge in a Mach 2.7 duct flow, where the strength of the interaction is varied from weak to moderate by changing the angle of attack α of the wedge from 8° and 10° to 12°. The stagnation pressure upstream was set to approximately 607.9 kPa. The SSLCC technique was used to visualize the surface flow characteristics and analyze the surface shear stress fields induced by the initial incident shock wave over the bottom wall and sidewall experimentally which resolution is 3500 × 200 pixels, and the numerical simulation was also performed as the supplement for a clearer understanding to the flow field. As a result, surface shear stress over the bottom wall was visualized qualitatively by SSLCC images, and flow features such as separation/reattachment and the variations of position/size of separation bubble with wedge angle were successfully distinguished. Furthermore, analysis of shear stress trend over the bottom wall by a hue value curve indicated that the relative magnitude of shear stress increased significantly downstream of the separation bubble compared with that upstream. The variation trend of shear stress was consistent with the numerical simulation results, and the error of separation position was less than 2 mm. Finally, the three-dimensional schematic of incident shock-induced interaction has been achieved by qualitative summary by multiple techniques, including SSLCC, oil flow, schlieren, and numerical simulation.

Assessment of predominant microstructural features controlling 3D short crack growth behavior via a surrogate approach in Ti-6Al-4V

The physical visualisation of a three-dimension (3D) stress field is a promising method for quantitatively analysing and revealing the stress distribution and evolution of a porous solid, and it significantly contributes to the understanding of the governing effects of stress fields on the mechanical behaviours of complex porous solids. However, experimental limitations regarding the manufacture of complex porous models and the extraction of the stress distributions in matrices inhibit the accurate visualisation of the 3D stress fields of porous structures. This paper presents a method of experimentally visualising and elucidating the 3D structures and stress fields of porous solids using photopolymer materials, 3D printing, the frozen-stress method, and photoelastic tests. Transparent thick discs containing various randomly distributed pores were produced using photopolymer materials and 3D printing technology. Experimental measures, including the frozen-stress method, photoelastic testing, and the phase-shifting method, were applied to quantitatively characterise the 3D stress fields distributed throughout the porous discs under radial-direction compressive loads. The temperature for ‘freezing’ stresses in the photopolymer materials was experimentally determined. The effects of pore distribution and population on the stress-field characteristics were investigated. The experimental results were used to validate the numerical analysis of the stress-field characteristics of the porous models. The visualisation test results agreed well with those of the numerical simulations. The proposed method can be used to visually quantify the characteristics and evolution of the 3D stress fields of porous solids.

Natural resource reservoirs usually consist of heterogeneous aggregated geomaterials containing a large number of randomly distributed particles with irregular geometry. As a result, the accurate characterization of the stress field, which essentially governs the mechanical behaviour of such geomaterials, through analytical and experimental methods, is considerably difficult. Physical visualization of the stress field is a promising method to quantitatively characterize and reveal the evolution and distribution of stress in aggregated geomaterials subjected to excavation loads. This paper presents a novel integration of X-ray computed tomography (CT) imaging, three-dimensional (3D) printing, and photoelastic testing for the transparentization and visualization of the aggregated structure and stress field of heterogeneous geomaterials. In this study, a glutenite rock sample was analysed by CT to acquire the 3D aggregate structure, following which 3D printing was adopted to produce transparent models with the same aggregate structure as that of the glutenite sample. Uniaxial compression tests incorporated with photoelastic techniques were performed on the transparent models to acquire and visualize the stress distribution of the aggregated models at various loading stages. The effect of randomly distributed aggregates on the stress field characteristics of the models, occurrence of plastic zones, and fracture initiation was analysed. The stress field characteristics of the aggregated models were analysed using the finite element method (FEM). The failure process was simulated using the distinct element method (DEM). Both FEM and DEM results were compared with the experimental observations. The results showed that the proposed method can very well visualize the stress field of aggregated solids during uniaxial loading. The results of the visualization tests were in good agreement with those of the numerical simulations.

Decision letter: Mechanical basis and topological routes to cell elimination

Editor's evaluation: Mechanical basis and topological routes to cell elimination

We present particle tracking velocimetry measurements and flow visualization of pulsatile flow fields in a stented cerebrovascular lateral aneurysm model with a wide ostium anchored on a curved parent vessel. Among the stent parameters, the blocking ratioC α ranging from 0% to 75% was selected to study its effect on the changes of intra-aneurysmal hemodynamics for the reference of minimally invasive endovascular aneurysm treatment. The Womersley number was 3.9 and the mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 850, and 300, respectively. The results are characterized in terms of velocity vector field, coded streak images, region averaged velocity, vorticity, and wall shear stress. A critical range ofC α related to the inflow location as well as the shape and number of intra-aneurysmal vortices is identified. The intra-aneurysmal flow activity, vortex strength, and wall shear stress are found to decrease with increasingC α. Among theC α examined,C α=75% is the most favorable in attenuating the risk of aneurysmal rupture and promoting intra-aneurysmal thrombus.

Vulnerable plaque has been associated with local macrophage accumulation and local high matrix metalloproteinase-2 (MMP-2) and MMP-9 activity. Since shear stress is a known local modulator of plaque location, we have determined whether local shear stress was associated with local plaque composition and with local MMP activity. In 17 NZW rabbits plaque was generated by denudation of the infrarenal aorta over a region of 5 cm and feeding them a high cholesterol diet for 2 months. After 2 months, a motorised IVUS pullback of the infrarenal aorta was performed with a 40 MHz IVUS catheter (CVIS, Boston Scientific, USA). IVUS derived vessel wall-lumen contours were reconstructed in 3D with in-house developed software. These reconstructions served as an input for a computational fluid dynamics technique, from which the 3-D shear stress field was calculated. Plaque regions were divided in 5 regions (n=8) to identify the location of highest macrophage accumulation or selected on basis of shear stress to identify whether high shear stress selects macrophage accumulation (n=8). In a second series, shear stress values were used to select regions -containing both latent and active MMP-2 and MMP-9. Segments were sectioned with a microtome and stained for smooth muscle cells (SMC), macrophages (MPhi) and collagen (COL). MPhi, displayed the highest density upstream of the plaque (6.9+/-2.4%, p<0.05), while SMC accumulated downstream (74.8+/-1.9%) of the plaque. High shear stress was associated with MPhi accumulation and MMP-9 activity (p<0.05). Upstream location of macrophages in plaques is associated with high shear stress and MMP-9 accumulation. These findings are discussed in relation to rheological theories reported previously in atherosclerosis.

The understanding of erythrocyte deformation under conditions of high shear stress and short exposure time is central to the study of hemorheology and hemolysis within prosthetic blood contacting devices. A combined computational and experimental microscopic study was conducted to investigate the erythrocyte deformation and its relation to transient stress fields. A microfluidic channel system with small channels fabricated using polydimethylsiloxane on the order of 100 μm was designed to generate transient stress fields through which the erythrocytes were forced to flow. The shear stress fields were analyzed by three-dimensional computational fluid dynamics. Microscopic images of deforming erythrocytes were experimentally recorded to obtain the changes in cell morphology over a wide range of fluid dynamic stresses. The erythrocyte elongation index (EI) increased from 0 to 0.54 with increasing shear stress up to 123 Pa. In this shear stress range, erythrocytes behaved like fluid droplets, and deformed and flowed following the surrounding fluid. Cells exposed to shear stress beyond 123 Pa (up to 5170 Pa) did not exhibit additional elongation beyond EI=0.54. Two-stage deformation of erythrocytes in response to shear stress was observed: an initial linear elongation with increasing shear stress and a plateau beyond a critical shear stress.

Quantitative measurements were made in silica glass of highly graded stress fields, as they developed: (i) in the K-dominated zone ahead of the tip of a median-type indentation micro-crack; and, (ii) at a silicon-silica interface of a metal-oxide semiconductor (MOS) device. Stress fields could be visualized on a microscopic scale using a field-emission scanning electron microscope (FE-SEM) equipped with a spectrally resolved cathodoluminescence (CL) device, according to piezo-spectroscopic (PS) assessments. The peculiarity of this newly proposed PS assessment resides in the fact that the performed CL/PS analysis exploited a peculiar luminescence emitted by optically active oxygen point defects in silica glass.

This paper deals with the use of classical experimental technique of photoelasticity as well as modern one – digital image correlation by stress analysis. Both mentioned methods were used to compare the corresponding stress fields obtained on a sample with stress concentrators loaded by bending. The paper contains the basic principle of photoelasticity, methodology of static analysis with polariscope and briefly describes the measurement with low-speed digital image correlation system. Taking into account that the used correlation system does not allow to evaluated stress fields, calculation and visualization of stress fields were realized in program Q-STRESS v.1.0 developed at the authors department.

Shear stress provided by a hydrocyclone was employed to remove the oil from oil‐contaminated catalysts. Understanding the deoiling mechanism and quantitative analysis of the interaction between shear stress fields and deoiling are necessary to improve deoiling efficiency. A numerical simulation was conducted for the velocity field and shear stress field of a hydrocyclone. The shear stress field in the wall layer, where oil‐contaminated catalysts are usually located, was robust. Increasing inlet flow rates resulted in a higher shear rate distribution along the wall layer. Numerical results were compared with experimental data. In the deoiling process, higher shear stress rates promoted faster transport of oil from catalysts into the fluid, thereby increasing the deoiling efficiency. Deoiling by the shear stress of a hydrocyclone is an efficient method for cleaning oil‐contaminated catalysts within a short time.

Detailed visualization of pulsatile flow fields produced by modelled arterial stenoses