Shear Type Research Articles

Investigation of the role of von Willebrand factor in shear-induced platelet activation and functional alteration under high non-physiological shear stress.

von Willebrand factor (vWF) plays a crucial role in physiological hemostasis through platelet and subendothelial collagen adhesion. However, its role in shear-induced platelet activation and functional alteration under non-physiological conditions common to blood-contacting medical devices (BCMDs) is not well investigated. Fresh healthy human blood was treated with an anti-vWF antibody to block vWF-GPIbα interaction. Untreated blood was used as a control. They were exposed to three levels of non-physiological shear stress (NPSS) (75, 125, and 175 Pa) through a shearing device with an exposure time of 0.5 s to mimic typical shear conditions in BCMDs. Flow cytometric assays were used to measure the expression levels of PAC-1 and P-Selectin and platelet aggregates for platelet activation and the expression levels of GPIbα, GPIIb/IIIa, and GPVI for receptor shedding. Collagen/ristocetin-induced platelet aggregation capacity was characterized by aggregometry. The levels of platelet activation and aggregates increased with increasing NPSS in the untreated blood. More receptors were lost with increasing NPSS, resulting in a decreased capacity of collagen/ristocetin-induced platelet aggregation. In contrast, the increase in platelet activation and aggregates after exposure to NPSS, even at the highest level of NPSS, was significantly lower in treated blood. Nevertheless, there was no notable difference in receptor shedding, especially for GPIIb/IIIa and GPVI, between the two blood groups at the same level of NPSS. The block of vWF exacerbated the decreased capacity of collagen/ristocetin-induced platelet aggregation. High NPSS activates platelets mainly by enhancing the vWF-GPIbα interaction. Platelet activation and receptor shedding induced by high NPSS likely occur through different pathways.

X-ray computed tomography study of compressive failure in a notched unidirectional glass fiber-reinforced composites

An experimental study on the axial compressive failure of a notched unidirectional (UD) glass fiber-reinforced composites has been performed to better understand the failure mechanisms in three dimensions (3D). A sequence of failure initiation and propagation has been monitored based on X-ray computed tomography (CT) images of the sample during failure. The CT images have shown that fiber kinking failure is the main failure mechanism, and there are two different types of kink bands, classified as type 1 and type 2 by final geometric form. The type 1 kink band, which has an X shape, extends outward from the notch along the width direction before finally creating a shear type 2 kink band at a distance from the notch. The novelty of this work involves observing the nucleation and propagation of fiber kink bands in three-dimensional space, as well as defining and quantifying kink band variables.

Compression-shear fracture of nickel-based superalloy during rotary tube piercing

Large-diameter nickel-based superalloy seamless tubes are the key component of pipeline transmission system in nuclear power, thermal power and petroleum industries. The rotary tube piercing (RTP) process is suitable to prepare large-diameter seamless tubes. However, the high temperature dynamic compression-shear fracture, also known as separation layer defect (SLD), is inevitable in the RTP process of nickel-based superalloy. In the study, the SLD was systematically studied by the combination of simulation and experiment. Firstly, the isothermal compression-shear experiments were designed to study the fracture behaviors. The results reveal that the plasticity of Inconel 718 alloy decrease with the increase of temperature and strain rate within the range of temperature 1080-1160℃ and strain rate 5–40/s, and the shear angle has significant effects on the fracture behavior. Secondly, based on the isothermal compression-shear experiment results, the SLD was explored by RTP experiments. The results reveal that the compression-shear deformation extent has significant effects on the SLD, and the folding defect is generated before the SLD is observed. The fracture morphology further confirms that the SLD belongs to typical shear fracture, which is generated under specific strain and stress state. Finally, the formation mechanism of SLD is revealed by combining finite element simulation and experiment. It is found that the formation of SLD includes crack initiation and crack propagation. Crack initiation is related with the maximum shear strain and maximum shear stress, and the crack propagation is controlled by radial deformation gradient.

Vascular adaptation model from force balance: Physarum polycephalum as a case study

Understanding vascular adaptation, namely what drives veins to shrink or grow, is key for the self-organization of flow networks and their optimization. From the top–down principle of minimizing flow dissipation at a fixed metabolic cost within flow networks, flow shear rate resulting from the flows pervading veins is hypothesized to drive vein adaptation. Yet, there is no proposed mechanism of how flow forces impact vein dynamics. From the physical principle of force balance, shear rate acts parallel to vein walls, and hence, naively shear rate could only stretch veins and not dilate or shrink them. We, here, resolve this paradox by theoretically investigating force balance on a vein wall in the context of the vascular network of the model organism Physarum polycephalum. We propose, based on previous mechanical studies of cross-linked gels, that shear induces a nonlinear, orthogonal response of the actomyosin gel making up vein walls, that can indeed drive vein dilatation. Furthermore, our force balance approach allows us to identify that shear feedback occurs with a typical timescale and with a typical target shear rate that are not universal properties of the material but instead depend smoothly on the vein’s location within the network. In particular, the target shear rate is related to the vein’s hydrostatic pressure, which highlights the role of pressure in vascular adaptation in this context. Finally, since our derivation is based on force balance and fluid mechanics, we believe our approach can be extended, giving attention to specific differences, to describe vascular adaptation in other organisms.

An EBSD analysis of a commercial immiscible Cu43%Cr alloy after high-pressure torsion processing and annealing

ABSTRACT The influence of high-pressure torsion (HPT) and annealing on microstructure, texture and thermal stability of an immiscible composite Cu43%Cr alloy was studied using electron backscatter diffraction, X-ray diffraction and microhardness measurements. As-received alloy samples were subjected to HPT and subsequent annealing treatment in the range of 210–850°C for 1 h in order to develop ultrafine-grained (UFG) microstructures and highlight their thermal stability. The Cu and Cr grains were refined to ∼0.45 and ∼0.39 µm, respectively and exhibited equiaxed morphology. The crystallographic texture was of shear type in both Cu and Cr with the domination of C and F orientations, respectively. The UFG microstructure and texture were retained in the Cu43%Cr alloy up to 850°C. The global results show that the immiscible composite Cu43%Cr alloy exhibits a high thermal stability up to 850°C. The evolution of the microstructure, texture and thermal stability of the UFG Cu43%Cr alloy was compared to published data and available models.

Phase field study on fracture behavior of crushable polymer foam

Polymer foam is a widely used material across various industries for its lightweight and exceptional energy absorption capability. Nevertheless, its porous structure and compaction properties present challenges in simulating crack initiation and propagation. The phase field method has attracted much attention for its advantages in predicting cracks. In this paper, we combine the phase field method with the “crushable foam” model and introduce the modified Drucker-Prager failure criterion to establish the phase field model of polymer foam materials. Material parameters are calibrated using experimental data from uniaxial compression, uniaxial tensile and shear punching experiments. The typical tensile, shear and compression instability fracture processes of polyurethane are then simulated using the proposed model, and the numerical results agree well with the experimental results. This indicates that the coupled phase-field crushable foam model not only exhibits the compaction properties of polymer foam materials but also accurately predicts its crack propagation under complex loading. Studying the fracture behavior of polymer foams under complex loads can enhance their engineering applications.

Effects of Tremella fuciformis Mushroom Polysaccharides on Structure, Pasting, and Thermal Properties of Chinese Chestnuts (Castanea henryi) Starch Granules under Different Freeze-Thaw Cycles.

The purpose of this study was to investigate the effect of Tremella fuciformis polysaccharides on the physicochemical properties of freeze-thawed cone chestnut starch. Various aspects, including water content, crystallinity, particle size, gelatinization, retrogradation, thermal properties, rheological properties, and texture, were examined. The results revealed that moderate freezing and thawing processes increased the retrogradation of starch; particle size, viscosity, shear type, hinning degree, and hardness decreased. After adding Tremella fuciformis polysaccharide, the particle size, relative crystallinity, and gelatinization temperature decreased, which showed solid characteristics. Consequently, the inclusion of Tremella fuciformis polysaccharide effectively countered dehydration caused by freezing and thawing, reduced viscosity, and prevented the retrogradation of frozen-thawed chestnut starch. Moreover, Tremella fuciformis polysaccharide played a significant role in enhancing the stability of the frozen-thawed chestnut starch. These findings highlight the potential benefits of incorporating Tremella fuciformis polysaccharides in starch-based products subjected to freeze-thaw cycles.

Study on the influencing factors and evolution of loess bank collapse with physical modelling

BackgroundReservoir bank collapse in loess areas may lead to the siltation of reservoir and bank retreat. Therefore, the study of reservoir bank collapse has practical significance. Almost of the bank collapse width prediction method were based on the classical graphical method which do not consider the process of bank collapse. But practice shows that this method can overestimate the width of bank collapse. Meanwhile, there are few studies specifically focused on the collapse of loess bank slopes.MethodsTo improve the prediction method of loss bank collapse width, the influence of water depth, dry density and bank slope angle on loess bank collapse was studied by physical modelling. The bank collapse width and the morphology of the bank slope were recorded during the experiment.ResultsThe bank collapse width increases with the increase of water depth, increases with the increase of slope angle, and decreases with the increase of dry density. The modeling process shows that the loess bank collapse occurs firstly underwater, the erosion niche will be formed underwater, and then the above water slope is damaged. This process is repeated until the underwater accumulation slope reaches the stable state, and then bank collapse stops. After the bank collapse, the above water slope is polyline, while the underwater slope is curved. When the slope angle is less than 27°, the bank collapse will not occur, and when the slope angle is between 27° and 40°, the bank collapse type is abrasion type. When the slope angle is greater than 40°, the bank collapse type is dumping type or shear type. Based on this, the improved balanced alluvial accumulation approach was proposed, which considers the mechanical equilibrium of above water bank slope and the morphology of underwater slope. The new method can reflect the stage characteristics of loess bank collapse, which is more reasonable than the empirical graphical method.ConclusionsThe experimental results indicate that when predicting the width of loess bank collapse, it is necessary to combine the bank collapse width and process of bank collapse. The relevant conclusions have a certain role in exploring the mechanism of loess bank collapse and bank collapse prediction methods.

Experimental study and mechanism analysis of out-of-plane seismic performance of reinforced concrete shear walls

Compared with the in-plane seismic performance, the out-of-plane seismic performance of reinforced concrete shear walls is weak and usually neglected, which leads to an inadequate study of the out-of-plane damage mechanism of shear walls and a lack of clear protective measures. In order to compare the similarities and differences in seismic performance of reinforced concrete shear walls when subjected to in-plane and out-of-plane loads in different directions and to clarify the key influencing factors, low cyclic loading tests were carried out on typical shear wall specimens in both in-plane and out-of-plane directions. The moment-curvature simulations of shear wall sections in both in-plane and out-of-plane directions are analyzed. The effects of parameters such as axial pressure ratio, wall thickness, height to width ratio and concrete grade on in-plane and out-of-plane seismic performance were analyzed at the member level in combination with finite element variable parameter analysis; at the structural system level, the time history analysis of 2 frame shear wall structures for single seismic action and main-aftershock sequence is established, and the structural damage is evaluated through the maximum story drift and rotation. The results reveal that the out-of-plane seismic performance of shear walls is significantly weaker than their in-plane seismic performance, with a difference of 1/20∼1/15 times in bearing capacity, where wall thickness and aspect ratio are the main parameters affecting in-plane and out-of-plane seismic performance; when the shear walls in the structure are subjected to seismic action in the out-of-plane direction, their out-of-plane direction will undergo large deformation and damage will occur easily, especially in the Single directional wall with less structure. The out-of-plane nonlinear analysis of the cross-section can be performed more accurately and quickly by using the new principal structure model proposed in this manuscript and some traditional principal structures. In the seismic design of shear walls, both in-plane and out-of-plane seismic performance should be ensured, and the wall thickness and height to width ratio of shear walls should be reasonably controlled.

Size effect during dynamic shear tests with hat-shaped specimens

The failure mechanism and size effect during the quasi-static and dynamic shear tests of hat-shaped specimens were investigated in this study. Three types of specimens with different shear ring thicknesses (800, 400, and 50 μm) were designed. Quasi-static tests were carried out using an electronic universal testing machine, while dynamic impact tests were carried out using split Hopkinson pressure bar (SHPB) tests. The adiabatic temperature rises with different strain rates, and the shear ring thickness was calculated. We found that the adiabatic temperature rises of the specimens with shear ring thicknesses of 800 and 400 μm were much larger than those of the specimens with shear ring thicknesses of 50 μm. The failure surfaces after the SHPB test were investigated via scanning electron microscopy, and the failure surfaces after the SHPB test could be divided into three zones: tensile, shear, and impact zones. The effect of the shear ring thickness and impact speed on the failure surface morphology was discussed. The typical shear stress–strain curves could be divided into three sections: elastic, plastic rise, and plastic plateau sections. Subsequently, a modified Johnson–Cook constitutive model was employed to fit the shear stress–strain results, and the fitted curves showed good agreement with the tested curves.

Experimental and numerical investigations on shear behavior of high-strength bolted connections after impact

For structures subjected to extreme loading, such as impact, the plastic deformation of structural connections is vital to life safety. Despite its importance, a loss of deformation capacity in connections via fracture of bolts has been repeatedly noted experimentally and in situ. To further investigate the residual strength of high-strength bolted connections after impact damage, this paper presents investigations on shear performance of high-strength bolted connections. This is the first study to report strength and deformation performance for structural bolts after impact damage. A total of 144 specimens were tested for the study, with varying impact height, steel plate thickness, bolt shank diameter, and high-strength bolt grade as the main variables. Experimental results involving failure modes, strain development, and effect of parameters are presented in detail. The observed failure mode is typical bolt shear failure, characterized by extrusion deformation around the bolt hole. The increasement of the thickness of steel plate, the diameter of bolt shank, and grade of bolt would improve the ultimate strength. The shear stiffness is positively correlated with impact height, thickness of steel plate and grade of bolt, but the ductility is decreased with the increment of thickness of steel plate. In addition, the results obtained from the finite element simulation are in agreement with the experimental findings. The simulation analysis shows that the specimens after impact damage are different from those of conventional specimens. Parameters formulae are then proposed with sufficient accuracy for the ultimate strength of high-strength bolted connections with impact damage.

Numerical study of precast segment columns with shear keys under vehicle collision

It is commonly understood that precast technology has been rapid development and application due to its short construction period and environmental friendly, etc. Among all precast structure, precast segment column has been widely concerned in the substructure of bridges. The precast segment columns will not only suffer from the earthquake loads but also be subjected to the collision of vehicle and barges. The concrete segments of precast segment column subjected to vehicle collision are prone to slip and even punching failure. In order to enhance the shear resistance between concrete segments, the precast segment column with shear key is designed, and the dynamic performance and shear mechanism under vehicle collision are analysed in this work. The results indicate that the shear key improves the shear capacity between segments and effectively reduces the relative displacement between segments, and makes the deformation mode of precast segment column change from shear type to bending type under vehicle collision. The maximum impact force of precast segment column with shear key is larger than that without shear key. Besides, the shear mechanism of precast segment column is revealed, and the calculation formula of local shear resistance is proposed.

Quasistatic deformation of yield stress materials: Homogeneous or localized?

We analyze a mesoscopic model of a shear stress material with a three-dimensional slab geometry, under an external quasistatic deformation of a simple shear type. Relaxation is introduced in the model as a mechanism by which an unperturbed system achieves progressively mechanically more stable configurations. Although in all cases deformation occurs via localized plastic events (avalanches), we find qualitatively different behavior depending on the degree of relaxation in the model. For no or low relaxation, yielding is homogeneous in the sample, and even the largest avalanches become negligible in size compared with the system size (measured as the thickness of the slab L_{z}) when this is increased. On the contrary, for high relaxation, the deformation localizes in an almost two-dimensional region where all avalanches occur. Scaling analysis of the numerical results indicates that in this case, the linear size of the largest avalanches is comparable with L_{z}, even when this becomes very large. We correlate the two scenarios with a qualitative difference in the flow curve of the system in the two cases, which is monotonous in the first case and velocity weakening in the second case.

Computation of embodied energy and carbon dioxide emissions of geopolymer concrete in high-rise buildings: a case study in Chennai city

The total primary embodied energy (EE) and carbon dioxide (CO2) emissions (ECO2e) of geopolymer concrete (GPC) in high-rise (60 m height) residential buildings located at Chennai city, India, were carefully examined in this study. The buildings were analysed and designed with the same aspect ratio and loading with two structural systems; Reinforced concrete (RC) framed and Shear wall type. The computation was performed for floor area, building volume, and concrete quantity. The results show that for the same grade of concrete, compared with conventional concrete (CC), GPC's EE is reduced by 46%, ECO2e is reduced by 42%, and the cost is reduced by 7%. The primary energy consumption (EET) and CO2 emissions (ECO2eT) towards material transportation in GPC shear wall and framed structures are 8% lower and associated cost is 22% cheaper than CC buildings. Compared to CC, the total primary EE and ECO2e of GPC RC shear wall and framed buildings are 46 and 55% lower, respectively. From the study, it has been observed that GPC is more environmentally beneficial than that of using CC in high-rise structures.

Performance of UHPC shear keys in box girder bridges-field and finite element study

The typical shear key in some box girder bridges historically featured longitudinal cracks on the key-girder interface as a result of temperature gradients. Ultra high-performance concrete (UHPC) is currently used as a shear key filling material in some box girder bridges as an alternative to a non-shrink grout. However, field data on long term performance of UHPC shear keys is lacking in available literature and therefore a long term study is essential to understand its performance under temperature gradients. This study investigated the long term performance of UHPC shear keys by collecting data from a bridge for a period of 2 years. The field results indicate that UHPC shear keys experienced satisfactory performance with no indication of crack due to temperatures fluctuating between 40 °C to −30 °C. During the winter months, the tensile stress reached about 95 % of the cracking threshold of UHPC while the stresses in the girders exceeded the concrete tensile strength which indicates cracking. The results from the finite element model confirm the field behavior and indicate that damage and subsequent debonding initiates at the top of the shear key and progresses further down the shear key under additional increments of cold temperature. After debonding, the dowel experiences substantial increase in stress due to thermally caused degradation and therefore the presence of dowels is essential for preventing separation between the shear key and the girder.

Experimental study on replaceable shear link on reinforced concrete shear wall

Experimental study has been conducted on specimens of a half-scale coupled reinforced concrete shear wall with steel coupling beam and an inserted shear link, to investigate the seismic performance of the core-wall and the replaceability of the shear link as a mechanical damper to dissipate the seismic energy. The link was designed following requirements for typical shear link, while the coupling beams as well as the shear wall were designed based on the link capacity. The result showed that under the prescribed cyclic loading (AISC 341-2016), the sub-assembly performed as expected, as shown by a good hysteretic curve with the plastic strain of shear link exceeded 0.08 radian. The damage was limited on the shear link, while the steel coupling beam and steel bar in the reinforced concrete wall remained elastic. Moreover, the experimental study showed no permanent distortion on the steel coupling beam after series of shear-link replacement. This confirmed the replaceability of the shear links as an excellent seismic device in the core-wall system.

Texture evolution of refill friction stir spot welding in alclad 2A12-T42 aluminum alloy

Electron backscatter diffraction (EBSD) was used to investigate the microstructure and texture evolution of 2A12-T42 aluminum alloy during refill friction stir spot welding (refill FSSW). The stir zone (SZ) and the thermo-mechanically affected zone (TMAZ) occurred dynamic recrystallization (DRX), with typical shear texture components. The texture is dominated by B component in the SZ, and dominated by A∗ and B components in the TMAZ. As the occurrence of the DRX, the storage energy of the grains gradually decreases, and there is a tendency to form lower energy grain orientations and texture weakening. The welding parameters determine the composition of the texture in different regions by influencing the degree of recrystallization. In the test group with the highest degree of crystallization, the SZ and TMAZ are dominated almost entirely by the B component. The TMAZ has more grains with soft orientation due to the difference in shear pattern and degree of recrystallization, which makes the texture reduce the mechanical properties of the joints. However, this reduction is not significant, with <10% variation for different test groups and regions. Compared to other strengthening mechanisms, the effect of texture strengthening is limited.

Mechanical behavior of rock-like specimen containing hole-joint combined flaw under uniaxial loading: findings from DIC and AE monitoring

Holes and joints are widespread and coexisting flaws in natural rock. The spatial distribution of combined flaw significantly affects the instability process of fractured rock. To study the influence of ligament length and joint angle on failure characteristics, uniaxial compression experiments are carried out on specimens containing hole-joint combined flaw assisted by acoustic emission (AE) and digital image correlation (DIC) technologies. As the ligament length increases, the mechanical parameter curves decrease first and then rise, showing a U-shape or V-shape. DIC results show that the hole performs a strong inhibition on the crack propagation from the inner joint tips, which will be weakened with the increase of ligament length. The driving displacement field of wing cracks and the type of cracks outside the joint are affected by joint angle variation. The cracks in rock bridge area are generally tensile-shear or shear type. According to AE analysis, the proportion of tensile signals decreased from the pre-peak failure stage to the post-peak stage, and the tensile signal is lower than 50% in the late loading stage, indicating that the shear crack dominates the final failure of specimens.

A numerical approach for simulation of stress-controlled cyclic shear loading in a soil column considering partial drainage

Liquefaction strength curves (LSCs) are commonly generated based on undrained stress-controlled cyclic testing to define the liquefaction potential of sands. However, these LSCs do not consider the effect of partial drainage on liquefaction potential. This is mainly because there are very limited experimental techniques to run stress-controlled tests for partially drained sands. This manuscript proposes a procedure to numerically simulate a saturated sand column with a free drainage boundary at the top (or top and bottom), accelerated horizontally at the bottom with constant acceleration cycles of duration designed to generate constant cyclic shear stress histories in the column. This is done for columns subjected to low and high overburden pressures. The paper starts with numerical simulations of a typical undrained cyclic direct simple shear, CDSS tests by applying a stepped velocity wave to a single soil element, an already established approach. This approach only works for a single element in undrained condition which is fixed at the base. Then, the proposed procedure is implemented by applying stepped acceleration time histories at the base of soil columns having one or two drainage boundaries. In these stepped acceleration runs, the durations of the acceleration cycles are controlled to achieve a partially drained stress-controlled CDSS kind-of-loading at specific elevations within the soil columns. The technique is used to show the effect of partial drainage on sand liquefaction behavior at both low and high overburden pressures. The results show that the effect of drainage is much more significant at higher overburden. The existence of both top and bottom drainage boundaries resulted in less liquefaction vulnerability, as compared to having only one drainage boundary at the top of the sand column. The results show that liquefiable sand layers in the field may be less prone to liquefaction under high overburden pressure than predicted by the current state-of-practice, which relies mainly on undrained small-scale cyclic tests.

Deterioration mechanism of physical and mechanical properties of phosphate rock under seismic disturbance and saturation

Introduction: To explore the influence of seismic disturbance and saturation on the mechanical properties of phosphate rock, the paper divided phosphorus rock into natural group, water-saturated Group and “earthquake and water-saturated” group.Methods: Fatigue loading and conventional triaxial compression tests were carried out to study the physical characteristics, degeneration characteristics, strength characteristics and failure characteristics of the samples.Results: The conclusions are as follows: The average wave velocity of samples of water-saturated group and “earthquake and saturation” group is 29.7% and 52.9% lower than that in natural group, respectively, and the average peak strength under various confining pressure conditions is 32.2% and 48.3% lower than that in natural group, respectively, indicating that both seismic stress loading and saturation have deterioration effects on the samples.Discussion: Compared with natural group and watersaturated group, after simulated seismic stress loading, the stress-strain curve of “earthquake and water-saturated” group shakes obviously after the peak, and the steps appear frequently, showing obvious plastic characteristics. Due to the different deterioration degree of the samples, the samples of the natural group were in the overall state of compression during the triaxial test, while the samples of the water-saturated group were compressed before failure and expanded after failure. The sample of earthquake and water-saturated group is in the whole state of expansion. The failure characteristics of natural samples and water-saturated samples are shear or shear failure. The shear plane starts from the edge of sample end face and presents typical diagonal shear failure. The failure characteristics of “earthquake and water-saturated” group samples are heavy shear and through failure. There are several fracture zones extending inward from the end of the sample, resulting in obvious transverse expansion.