Search Results (5,432)

Cardiovascular prosthetic devices, stents, prosthetic valves, heart-assist pumps, etc., operate in a wide regime of flows characterized by fluid dynamic flow structures, laminar and turbulent flows, unsteady flow patterns, vortices, and other flow disturbances. These flow disturbances cause shear stress, hemolysis, platelet activation, thrombosis, and other types of blood trauma, leading to neointimal hyperplasia, neoatherosclerosis, pannus overgrowth, etc. Couette-type blood-shearing devices are used to simulate and then clinically measure blood trauma, after which the results can be used to assist in the design of the cardiovascular prosthetic devices. However, previous designs for such blood-shearing devices do not cover the whole range of flow shear, Reynolds numbers, and Taylor numbers characteristic of all types of implanted cardiovascular prosthetic devices, limiting the general applicability of clinical data obtained by tests using different blood-shearing devices. This paper presents the key fluid dynamic parameters that must be met. Based on this, Couette device geometric parameters such as diameter, gap, flow rate, shear stress, and temperature are carefully selected to ensure that the device’s Reynolds numbers, Taylor number, operating temperature, and shear stress in the gap fully represent the flow characteristics across the operating range of all types of cardiovascular prosthetic devices. The outcome is that the numerical data obtained from the presented device can be related to all such prosthetic devices and all flow conditions, making the results obtained with such shearing devices widely applicable across the field. Numerical simulations illustrate that the types of flow patterns generated in the blood-shearing device meet the above criteria. Full article

The collapse failure of rock surrounding caverns involves a progressive collapse process. Based on the nonlinear Hoek–Brown failure criterion and the upper limit theorem, the whole process curve of the progressive collapse of the surrounding rock of a large-span cavern is outlined in this paper. The progressive collapse process of the surrounding rock of the large-span cavern is experimentally studied using an independently developed visualized large-span-cavern geomechanical model test device with variable angles. The results show that, through theoretical calculation and model tests, the surrounding rock at the top of the large-span cavern undergoes three collapses. Under the condition of rock mass and the shape of the cavern, the larger the span of the cavern, the more times the surrounding rock collapses; with the increase in surrounding rock pressure, the first collapse occurs in the middle part of the arch roof. When the overlying load reaches a certain level, the arch foot becomes the weakest part, and the rock undergoes shear failure along the arch foot, gradually extending upwards, accompanied by multiple collapses, forming a progressive collapse process. The theoretical calculation results of this paper are basically consistent with the scope of the model test, and the research results can provide a basis for the construction and support design of the large-span cavern. Full article

Most historical buildings and structures in Oman were built using unreinforced stone masonry. These structures have deteriorated due to the aging of materials, environmental degradation, and lack of maintenance. This research investigates the physical, chemical, and mechanical properties of the local building materials. It also presents the findings of an experimental study on the in-plane shear effectiveness of a modern strengthening technique applied to existing stone masonry walls. The technique consists of the application of a textile-reinforced mortar (TRM) on one or two faces of the walls. Shear loading tests of full-scale masonry samples (1000 mm width, 1000 mm height, and 350 mm depth) were carried out on one unreinforced specimen and six different cases of reinforced specimens. The performances of the unreinforced and reinforced specimens were analyzed and compared. We found that strengthened specimens can resist in-plane shear stresses 1.5–2.1 times greater than those of the unreinforced specimen; moreover, they demonstrate ductility rather than sudden failure, due to the presence of fiberglass and basalt meshes, which restrict the opening of cracks. Full article

To enhance the properties of SBS and crumb rubber-modified asphalts, four different amounts (5%, 10%, 15%, and 20%) of castor oil were added to crumb rubber-modified asphalts to mitigate the adverse effects of high levels of fine crumb rubber particles on the aging resistance of SBS and crumb rubber-modified asphalt. Initially, a conventional test was conducted to assess the preliminary effects of bio-oil on the high-temperature and anti-aging properties of SBS and crumb rubber-modified asphalt. Subsequently, dynamic shear rheometer and bending beam rheometer tests were employed to evaluate the impact of bio-oil on the high- and low-temperature and anti-fatigue properties of SBS and crumb rubber-modified asphalt. Finally, fluorescence microscopy and Fourier transform infrared spectroscopy were used to examine the micro-dispersion state of the modifier and functional groups in bio-oil, SBS and crumb rubber composite-modified asphalts. The experimental results indicated that bio-oil increased the penetration of SBS and crumb rubber-modified asphalt, decreased the softening point and viscosity, and significantly improved its aging resistance. The addition of bio-oil enhanced the anti-fatigue properties of SBS and crumb rubber-modified asphalt. The optimal amount of added bio-oil was identified. Bio-oil also positively influenced the low-temperature properties of SBS and crumb rubber-modified asphalt. Although the addition of bio-oil had some adverse effects on the asphalt’s high-temperature properties, the asphalt mixture modified with bio-oil, SBS, and crumb rubber still exhibited superior high-temperature properties compared to unmodified asphalt. Furthermore, fluorescence microscopy and Fourier transform infrared spectroscopy results demonstrated that bio-oil can be uniformly dispersed in asphalt, forming a more uniform cross-linked structure and thereby enhancing the aging resistance of SBS and crumb rubber-modified asphalt. The modification process involved the physical blending of bio-oil, SBS, and crumb rubber within the asphalt. Comprehensive research confirmed that the addition of bio-oil has a significant and positive role in enhancing the properties of SBS and crumb rubber-modified asphalt with different composite crumb rubber particle size ratios. Full article

Economic limitations often hinder the extensive use of fiber-reinforced concrete in full-scale structures. Addressing this, the present study explored localized reinforcement at critical interfaces, deploying a novel synchronized casting mold that deviates from segmented casting interface studies. The research prioritized the flexural, compressive, and shear characteristics at the interface between fiber-reinforced concrete and ordinary concrete with continuous casting. The results demonstrated that polyethylene (PE) fibers significantly enhance anti-cracking capabilities, surpassing steel fibers in all mechanical tests. PE fibers’ high modulus of elasticity and tensile strength considerably augmented the interface’s bending resistance, facilitating better load transfer and capitalizing on the fibers’ tensile properties. Additionally, their low density and greater dispersion negated the sinking behavior typical of steel fibers, thereby strengthening the compressive capacity of the interface. Although a 0.75% PE fiber volume is ideal for ductility, volumes as low as 0.25% or 0.5% are economically viable if dispersion is optimal. Conversely, steel fibers, prone to sinking and clustering, offer inferior shear resistance at the interface than PE fibers, marking a significant finding for structural applications. Full article

A large-scale triaxial shear test was performed on a waste slag dam created from the accumulation of waste slag during the construction of a pumped-storage power station. By integrating previous experience, the particle breakage index was refined to study the relationship between particle breakage and the deformation strength characteristics of the soil-rock mixture under different dry densities and stress states. The results show that as the confining pressure increases, various dry densities enhance particle breakage, leading to a transition from initial dilatancy to shear shrinkage in the soil-rock mixture. This change results in a decrease in the nonlinear internal friction angle and a decrease in the shear strength. This research explores the shear failure mechanism caused by the breakage of soil-rock mixtures. Examination of the particle grade before and after shearing shows that the extent of particle breakage expands with higher confining pressure, especially within the 20~60 mm grain size range. The fractal dimension is calculated concurrently, showing a strong correlation with the breakage index. The concepts of the phase transition stress ratio and failure dilatancy ratio were applied to describe the deformation characteristics. Experimental results demonstrate that the influence of the phase transition stress ratio on the dilatancy becomes more significant with increased dry density, yet this effect diminishes with higher confining pressure. As the breakage index increases, the failure dilatancy rate decreases following a power function, resulting in a gradual reduction in the dilatancy phenomenon. Considering the substantial influence of clay particles on the cohesion of the soil-rock mixture and the negligible effect of breakage on fine particles, it is proposed that the cohesion remains unchanged for determining the friction parameter. With increasing breakage index, the internal friction angle decreases nonlinearly, weakening the shear strength. This analysis shows that the refined particle breakage index effectively captures the particle breakage characteristics of soil-rock mixtures, providing valuable insights into the deformation and strength characteristics of engineering structures affected by particle breakage. Full article

I-shaped concrete girders are widely used in precast bridge and roof construction, making them a common structural component in existing infrastructure. Despite well-established strengthening techniques using various innovative materials, such as externally bonded carbon fibre reinforced polymer (CFRP) reinforcement, the shear strengthening of an I-shaped concrete girder is not straightforward. Several research studies have shown that externally bonded CFRP reinforcement might exhibit early debonding at the concave corners of the I-shape, resulting in a marginal increase in shear capacity. This research study aims to assess the performance of two different CFRP shear strengthening strategies for I-shaped concrete cross-sections. In the first strategy, CFRP was bonded along the I-shape of the cross-section with the provision of additional anchorage. In the second strategy, the I-shape was transformed into a rectangular shape by using in-fill blocks over which the CFRP was bonded in a U-configuration. In addition to the strengthening strategies, the investigated parameters included two different materials for the in-fill blocks (conventional and aerated concrete) and two different anchoring schemes (bolted steel plate anchor and CFRP spike anchor). To avoid testing on large-scale girders, a new test methodology has been implemented on concrete I-sections. The test results demonstrate the feasibility of comparing different shear strengthening configurations dedicated to I-sections. Among other findings, the results showed that the local transformation of the I-shape to an equivalent rectangular shape could be a viable solution, resulting in shear strength enhancement of 12% to 53% without and with the anchorages, respectively. Full article

To evaluate the possibility of using phosphorus slag powder instead of mineral powder as a filler in asphalt mastic, this study investigates the micro-characteristics of phosphorus slag powder and its viscoelastic mechanical properties in asphalt mastic. A systematic approach combining macro and micro test methods was used to analyze the physical and surface characteristics, void structure, and surface energy of phosphorus slag powder. The viscoelastic mechanical properties of phosphorus slag powder were evaluated using appropriate indexes. Meanwhile, the correlations between and limitations of various evaluation indexes and the high-temperature rheological properties were identified. The results demonstrate that phosphorus slag powder exhibits low density, small overall particle size, difficulty in forming agglomerates, developed pores, large specific surface area, and high surface energy, which is suitable for replacing mineral powder as a filler in asphalt mastic. The main factors affecting the viscoelastic properties of asphalt mastic are the particle size and dosage of phosphorus slag powder. Generally speaking, phosphorus slag powder asphalt mastic with particle sizes ≤ 18 μm exhibits the best performance. In practical engineering applications, the appropriate dosage (7%, 10%, 13%) can be selected based on different regions and specific design and construction requirements. Additionally, zero-shear viscosity (ZSV), non-recoverable creep compliance (J_nr), and creep recovery percentage (R) exhibit a strong correlation with the high-temperature rheological properties of asphalt mastic. At the same time, the rutting factor (G*/sin δ) presents certain limitations. Full article

In structures manufactured using 3D concrete printing, cracks can easily propagate along the interface between printed layers. Therefore, it was necessary to determine the interlayer bond strength. In this study, direct shear and tensile tests were performed to determine the interlayer bond stability of the 3DCP members. To confirm the appropriateness of the mix proportion used to fabricate the specimens, the open time available for printing was identified via a mixing test, and the extrudability and buildability were verified via a printing test. In addition, direct shear and tensile tests were performed using the specimen manufacturing method (i.e., mold casting and 3D printing) and printing time gap (PTG) between the laminated layers as key test variables. The interlayer bond strengths of the specimens, according to the variables obtained from the test results, were compared and analyzed based on the interfacial shear strength standards presented in the current structural codes. In the direct shear test, failure occurred at the interlayers of all the specimens, and the interlayer bond strength tended to decrease with increasing PTG. In addition, the interlayer bond strength of the direct shear specimens exceeded the interfacial shear strength suggested by current structural codes. In contrast, in the direct tensile test, interlayer surface failure occurred only in some specimens, and there was no distinct change in the interlayer bond strength owing to PTG. Full article

A dynamic impact test was performed on as-rolled AZ31 alloys with gradient microstructure under various strains. The microstructural evolution and mechanical properties were systematically investigated. As the strain rate gradually increased, an increasing number of twins were formed, facilitating dynamic recrystallization (DRX), and the mechanical properties were also gradually improved. The microstructure became heterogeneous at higher strain rates, but the peak stress decreased. The impact process resulted in a significantly higher performance due to microstructural refinement, work hardening by dislocations, and precipitates. In addition, both the adiabatic shear band and the adjacent crack experienced a temperature rise that exceeded the recrystallization temperature of the alloys. This observation also explains the presence of ultrafine recrystallized grains within the adiabatic shear band and the appearance of molten metal around the crack. Full article

This study aims to investigate the effect of plastic fine content on the undrained monotonic behavior of sandy soils (mixtures of host sand and various plastic fine content from 0 to 25%), and in particular, their static liquefaction resistance (undrained shear strength). Illite Arvel is considered as a plastic fine to add to the host sand, the Fontainebleau sand. Binary mixture samples are reconstituted by using the moist tamping technique. A series of undrained triaxial tests were carried out to study the influence of different parameters, such as the fine content, the initial density index, the confining pressure, and the over-consolidation ratio (OCR) on the behavior of sandy soil mixture. Based on the results acquired from these tests, the liquefaction susceptibility of the sandy soil is discussed by using Chinese criteria. Full article

In order to reveal the mechanism of sleeved stud connectors, 15 push-out specimens were designed, and static loading tests were conducted to evaluate the mechanical performance. The shear performance differences between the novel sleeved studs and conventional welded studs were compared. Referring to the experimental results, an Abaqus nonlinear finite element model was established to study the shear mechanism of sleeved stud connectors. Parametric analysis was conducted to investigate the effects of stud height, sleeve filling material, and sleeve diameter on the mechanical performance of the connectors. The experimental and finite element analysis results indicated that the ultimate shear bearing capacity and shear stiffness of the sleeved stud connectors were higher than those of ordinary welded studs, and the maximum slip was relatively small. Compared to conventional welded studs, the ultimate bearing capacity of sleeved studs increased by 4% to 8%, and the shear stiffness increased by 25% to 35%. Since the shear behavior of sleeved studs mainly occurred at the base of the studs, the influence of stud height on shear performance was relatively small. However, sleeve and stud diameter have a great influence on bearing capacity and stiffness. As the Ultra-High Performance Concrete (UHPC) near the base of the stud effectively enhanced the shear carrying capacity of the sleeved stud connectors, the shear carrying capacity and shear stiffness increased with the increase in the sleeve diameter. Full article

This study investigated the impact of temperature, time, and homogenisation on the transient liquid phase bonding of Inconel 617 to stainless steel 310, employing AWS BNI2 foil as an interlayer. Nine test series were conducted at temperatures of 1050 °C and 1100 °C, with bonding durations ranging from 10 to 60 min. The homogenisation process was carried out on specimens that underwent full isothermal solidification at a temperature of 1170 °C for 180 min. The microscopic analysis indicated that extending the time and raising the bonding temperature resulted in the extension of the isothermal solidified zone, accompanied by a reduction in the quantity of eutectic phases. Complete isothermal solidification was seen exclusively in samples bonded at temperatures of 1050 °C for 60 min and 1100 °C for a duration of 50 min. The size of the diffusion-affected zone expanded as the bonding temperature and duration rose, but the presence of brittle intermetallic phases diminished. The microstructure of the homogenised sample indicated that the diffusion-affected zone had been almost completely eliminated. Hardness variations indicated heightened hardness in the diffusion-affected zone (DAZ) and athermal solidified zone (ASZ). Shear strength is maximised in homogenised specimens with minimised ASZ. Full article

The relationship between acoustic parameters and the microstructure of a Cu30Zn brass plate subjected to plastic deformation was evaluated. The plate, previously annealed at 550 °C for 30 min, was cold rolled to reductions ranging from 10% to 70%. Linear ultrasonic measurements were performed on each of the nine specimens, corresponding to the nine different reductions, using the pulse-echo method to record the times of flight of longitudinal waves along the thickness axis. Subsequently, acoustic measurements were conducted to determine the nonlinear parameter $\beta$ through second harmonic generation. Microstructural analysis, carried out by X-ray diffraction, Vickers hardness testing, and optical microscopy, revealed an increase in deformation twins, reaching a maximum at 40% thickness reduction. At higher deformations, the microstructure showed the generation and proliferation of shear bands, coinciding with a decrease in the twinning structure and an increase in dislocation density. The longitudinal wave velocity exhibited a 0.9% decrease at 20% deformation, attributed to dislocations and initial twin formation, followed by a continuous increase up to 2% beyond this point, resulting from the combined effects of twinning and shear banding. The nonlinear parameter $\beta$ displayed a notable maximum, approximately one order of magnitude greater than its original value, at 40% deformation. This peak correlates with a roughly tenfold increase in twinning fault probability at the same deformation level. Full article

Generally, rejuvenators are used to supply missing components of aged asphalt, reverse the aging process, and are widely used in asphalt maintenance and recycling. However, compared with traditional rejuvenators, bio-oil rejuvenators are environmentally friendly, economical and efficient. This study looks into the effect of the three different bio-oils, namely sunflower oil, soybean oil, and palm oil, on the physical properties, rheological properties and chemical components of aged asphalt at different dosages. The asphalt physical properties and Dynamic Shear Rheological (DSR) test results show that with the increase in bio-oil, the physical properties and rheological properties of rejuvenated asphalt are close to those of virgin asphalt, but the high-temperature rutting resistance needs to be further improved. The results of Fourier Transform Infrared Spectroscopy (FTIR) show that the carbonyl and sulfoxide indices of rejuvenated asphalt are much lower than those of aged asphalt. Moreover, the rejuvenation efficiency of aged asphalt mixed with sunflower oil is better than that with soybean oil and palm oil at the same dosage. Full article