Shear Yield Research Articles

Improving the properties of polylactic acid/polypropylene carbonate blends through cardanol-induced compatibility enhancement

Cardanol (CD) is used as a reactive compatibilizer, and blended with polylactic acid (PLA) and polypropylene carbonate (PPC) resin (70/30(w/w)) to obtain a series of PLA/PPC/CD blends. The systematic study was conducted on the thermal properties, optical properties, rheological properties, mechanical properties, and microscopic morphology of the blend, by varying amounts of CD added to the blends. A detailed explanation and comprehensive analysis of the reaction mechanism between CD and PLA/PPC have been made. The study found that CD acts as a “bridge” between the PLA and PPC, forming the structure of a block copolymer (PLA-b-CD-b-PPC), and the copolymer can greatly improve the compatibility of PLA and PPC. When the amount of CD reaches 8 wt%, only one Tg is observed in the blend, simultaneously, PLA/PPC has already transitioned from a partially compatible system to a completely compatible system. At the same time, the addition of CD does not have any negative impact on the thermal stability of the PLA/PPC blend under processing temperature conditions, and the thermal stability of the PLA/PPC/CD blends can even be improved under extreme conditions. In addition, the addition of CD allows the PLA/PPC/CD blends to maintain a high light transmittance while reducing the opacity of the blend (the light transmittance remains above 92 %, and the opacity is reduced from 37 % to about 24 %), demonstrating excellent optical properties. Moreover, the elongation at break and impact strength of the PLA/PPC/CD blend both show a trend of first increasing and then decreasing with the increase of CD amount. When the CD amount varies within the range of 6– 8 wt%, the blends undergoes a brittle-ductile transition, and its toughness is greatly improved while the rigidity can also meet practical needs. When the amount of CD in the system increases to 12 wt%, the toughness of the blend reaches its peak, and its elongation at break and impact strength reach 513.24 % and 9211.5 J/m2 respectively (increased to 2442.84 % and 270.73 % of the PLA/PPC blend). Concurrently, the fracture surface of the blend exhibits large-scale plastic flow in the direction of the applied force, with marked shear yield phenomena, showing obvious characteristics of tough fracture.

Investigation of ultrasound-assisted starch acetylation by single- and dual- frequency ultrasound based on rheology modelling, non-isothermal reaction kinetics, and flow/acoustic simulation

To achieve wheat starch acetylation (AC) with a high degree of substitution (DS), the acetylation process was carried out using various ultrasonication frequencies, including 25 kHz, 40 kHz, and 25 + 40 kHz. In the second step, wheat starch's ultrasound-assisted acetylation (UAA) is simulated using various approaches including the rheology models, non-isothermal reaction kinetics, and flow/acoustic modelling. The computational fluid dynamics (CFD) simulation solves the non-linear acoustic governing equation to determine the flow field and the amount of delivered ultrasound energy. The acetylated starch increased peak and final viscosity, with the highest values observed for the 25 + 40 kHz frequency than other single frequencies (25 kHz and 40 kHz). The viscosity of the starch is specified based on the experimental data using Herschel–Bulkley, power law, and Casson rheology models. According to differential scanning calorimetry (DSC) analysis, the gelatinization parameters and enthalpy of gelatinization (ΔHgel), were found to be lower in acetylated starches at the frequency of 25 + 40 kHz compared to those at frequencies of 25 kHz and 40 kHz, as well as native starches (NS). Moreover, the gelatinization process is examined by implementing the non-isothermal reaction kinetics to obtain the activation energy and reaction order. Based on the results obtained, implementing sonication at 25 kHz reduces the activation energy by 70.3 % compared to native starch. However, the same parameter is obtained to be 69.9 % and 67.1 % for the application of 40 and 25 + 40 kHz transducers, respectively. Additionally, during the sonication treatment, the yield shear stress increases between 24.1 and 31.8 %, based on the applied frequency. Morphology analysis determined by scanning electron microscopy (SEM) revealed that the surfaces and small granules underwent more damage in acetylated starches at frequencies of 25 kHz and 40 kHz. However, in acetylated starches at 25 + 40 kHz, the larger granules were more affected than the smaller ones.

Experimental and Numerical Study on the Shear Performance of the Stone Panel–Panel Joint in Stone Cladding

The evaluation of the shear performance of stone panel–panel joints (SPPJs) in stone cladding has important engineering significance, as it plays a crucial role in stone cladding failure. The purpose of this paper is to analyze and predict the influence of the dimension and the Young’s modulus of sealant on the shear performance of SPPJs. Based on monotonic and cyclic loading tests, the effects of Young’s modulus and the dimension of sealant on the failure characteristics, stress–strain characteristics, stiffness degradation, and energy dissipation capacity of an SPPJs were investigated. According to finite element analysis, the strain distribution of an SPPJ under monotonic loading was analyzed for different sealant widths and number of sealant layers. The results indicate that the failure modes of SPPJs change with the variation of sealant amount. As the Young’s modulus of the sealant increases, the shear failure strength and shear yield strain of SPPJs increase. The increase in sealant thickness reduces the shear failure strength and stiffness of SPPJs. Based on the same shear strain, the increase in the sealant thickness enhances the cumulative energy consumption of SPPJs. The strain concentration zone of the specimens with two sealant layers in unilateral SPPJs becomes larger with the increase in sealant width.

Orientation-dependent dynamic shearing properties and underlying failure mechanisms of laser powder bed fusion of CoCrFeNi high-entropy alloy

In order to study the influence of building orientation on the dynamic shearing properties and failure mechanism of laser powder bed fusion (LPBF) of CoCrFeNi high-entropy alloy (HEA) under impacting load, a series of high speed impact tests were systematically conducted on a split Hopkinson pressure bar (SHPB) device at different strain rates. For this purpose, flat hat-shaped samples with a preset shear region were designed. The samples HS0 and HS90 respectively possessed a shear direction parallel and perpendicular to the building orientation. The respective columnar grain orientations of HS0 and HS90 influence the synergistic interaction between dislocation slip and deformation twinning, which is reflected in the differences in mechanical properties. It was observed that HS0 had higher shear yield strength whereas HS90 exhibited better plasticity. Moreover, the two samples show different adiabatic shear sensitivities as adiabatic shear bands (ASBs) were observed when the shear strain reached ∼9.5 and 11.2, respectively. Typical dynamic responses such as adiabatic temperature rise and grain refinement took place in the shear regions. Further, the formation of ultrafine equiaxed grains may be explained using the classical rotational dynamic recrystallization (RDRX) mechanism, which can furnish a sound theoretical basis to understand the deformation behaviors and mechanisms of LPBF CoCrFeNi HEA under impact loads.

A model for predicting the stability of ceramic suspensions

The prediction of the stability of ceramic suspensions with multiple particles is limited depend on classical DLVO theory or Stokes equation. The mechanical effect of particles settling in suspension was studied, and a simplified mechanical equilibrium model of particles was proposed, shown as follows: u=Δρgd218η−τyd36η. The sedimentation of particles is mainly influenced by the density difference between particles and fluid Δρ, particle size d, suspension viscosity η, as well as shear yield stress τy. For a given suspension, Δρ, d and η are constants, and τy can be directly measured through rheological methods. When calculated settling velocity of particles approaches infinitely small values, the suspensions can be considered stable. The expression derived in this work had been verified by the experimental data. In addition, correlation between the results from improved settlement height method and the calculated settling velocity was established.To further investigate the impact of additives on suspensions stability, the Kelvin-Voigt rheological model was employed to characterize viscoelastic properties during oscillation, and a coefficient K (K=τy−G'γcτy) was proposed to quantitatively determine the contribution of the “dashpot” component in influencing the yield stress τy. The regulation strategy for additives in suspensions was established based on experiments: a K value exceeding 0.274 indicates excessive additives concentration and necessitates reduction, whereas a K value below 0.274 suggests an insufficient additives concentration and requires additional dosage. In summary, the above model is helpful to predict the stability of ceramic suspensions.

Excellent dynamic properties and corresponding deformation mechanisms in a microband-induced plasticity steel with dual-heterogeneous structure

A dual-heterogeneous structure with dual phases and heterogeneous grains was designed in a high Mn microband-induced-plasticity (MBIP) steel. The heterogeneous structured sample exhibits similar dynamic shear yield strength, while exhibiting enhanced dynamic uniform shear strain and dynamic shear toughness by 36 % and 47 %, respectively, as compared to the homogeneous structured sample. The strain hardening mechanisms contributing to the excellent dynamic shear properties in the heterogeneous structured sample have been revealed. Firstly, the superior hetero-deformation-induced hardening capability of the heterogeneous structured sample arises from a higher density of geometrically necessary dislocations induced in each phase. Secondly, a pronounced strain rate effect is observed in body-centered cubic (BCC) grains and face-centered cubic (FCC) ultra-fine grains, leading to an elevated level of strain rate sensitivity. Finally, the MBIP effect is also observed in FCC coarse grains under dynamic loading. Moreover, the MBIP effect in FCC ultra-fine grains is more likely to occur at high strain rates due to the emergence of single-wall domain boundaries, which is not observed during quasi-static tensile testing. The present results provide new routes for designing impact-tolerant structures in advanced metals and alloys.

Rheological behavior of cellulose nanofibril suspensions with varied levels of fines and solid content

The rheological behavior of mechanically disk refined cellulose nanofibril (CNF) aqueous suspensions with 50, 60, 70, 80, 90, 100 % fines contents at 1 and 3 wt% solid concentrations was studied by conducting various dynamic and steady-state rheological experiments, including oscillatory shear, flow sweep, startup, flow loop, and three-step oscillation experiments. All the samples exhibited a gel-like behavior in oscillatory shear tests and samples, with 50 % fines showed the highest levels of dynamic moduli for both solid contents. Suspensions with higher concentrations of CNFs showed higher values for viscosity, complex viscosity, and dynamic moduli. A critical shear rate of 10 s−1 independent of the solid contents of the suspensions was found for varying fines levels, where viscosity measurements above this critical shear rate converged and viscosity measurements below it diverged. All samples exhibited yield in shear flow and yield stresses exhibited a decreasing trend followed by a plateau as fines levels increased. The level of yield stress for 3 wt% suspensions was higher than that of 1 wt% suspensions. The lowest structure recovery was observed for samples containing 50 % fines content. Moreover, a rheopectic-thixotropic transition was observed for samples with high fines content (90 and 100 %) at low solid content (1 wt%).

Comparative studies of LC3- and fly ash-based blended binders in fibre-reinforced printed concrete (FRPC): Rheological and quasi-static mechanical characteristics

Supplementary cementitious materials (SCMs) became in recent decades popular and promising materials as partial replacements for cement in construction engineering. These neutralise the effects of high cement content required for the extrusion process of 3D concrete printing and enhance its sustainable benefits. The crucial advantages are the reduction of CO2 emission and energy consumption of cement-based materials, high performance, and cost-effectiveness. This study compares the rheology and hardened mechanical properties of fibre-reinforced printed concrete (FRPC) containing limestone calcined clay cement (LC3-FRPC) and fly ash (FA-FRPC). Microstructural evolution, including the porosity, CT image, and pore volume distribution in mould-cast and extrusion-based 3D printed fibre-reinforced concrete was analysed by X-ray computed tomography to examine its influence on mechanical performance. Scanning electron microscopy, augmented by Energy dispersive X-ray spectroscopy was also used to analyse the macropores structure of the mixtures. SCMs mixtures considered exhibit more than 160 min printing open time, thereby displaying satisfactory material rheological performance and suitable for 3D printability. However, LC3-FRPC enhanced the workability, open time, and buildability by 1.7 %, 15.4 %, and 19 %, respectively, in comparison to FA-FRPC. The yield shear stresses and shear modulus of the mixtures, particularly LC3-FRPC increased linearly with resting time intervals and are within the minimum recommended limits for sound shape retention and buildability of materials. The results confirm higher strengths for mould-cast and intralayer concrete specimens, particularly D3 in compression and D1 in tension and flexure for FA-FRPC compared to its 3D-printed interlayer counterpart. The strengths obtained in LC3-FRPC follow the trends observed in the literature, with mould-cast > D1 > D3 by 18.4 % and 41.7 %, and mould-cast > D1 > D3 by 6.5 % and 57.4 % for tension and flexure, respectively. These could be ascribed to the low total porosity and critical pore diameter at the interface of the specimens. Although there is a slight reduction in the compressive, tensile, and flexural strengths of LC3-FRPC (due to the high-water demanded) compared to FA-FRPC, the significant levels of C-A-S-H gel polymerisation and ettringite formation in LC3-FRPC is beneficial for improving the flexural strength of the fibre-matrices. The polypropylene fibres in the macropores, as seen by SEM imaging enhance the mechanical characteristics of the mould-cast and printed specimens of both mixtures. Then, the interfacial bond strength is enhanced in LC3-FRPC compared to FA-FRPC by 8.1 % and 9.8 % for tension and flexure, respectively, thereby implying lower level of anisotropy in tension (7.2 %) and flexure (9.2 %). Conclusively, the observed mechanisms of FA- and LC3-based blend binders incorporated in FRPC strengths development, and their influence based on the macropores structure at the interfacial regions of mould-cast and printed concrete are presented.

Manufacturing carbon fabric composite structural batteries using spray with high-pressure and high-temperature and vacuum-bag assisted infusion techniques

This paper introduces a strategy for manufacturing composite structural batteries, integrating the dual roles of energy storage and load-bearing functionality. In the manufacturing process, both cathodes and anodes were produced by coating electrode materials on woven carbon fabrics via high-pressure and high-temperature spray method. A modified vacuum-bag assisted technique was employed to infuse electrolytes and assemble entire battery cells. Scanning electron microscopy was utilized to observe that the active electrode particles were effectively dispersed throughout the woven carbon fabrics. Electrochemical characterization demonstrated that the fabricated batteries could achieve a high energy density of 34.12 Wh/kg with benign rate performance and high Coulombic efficiency. Meanwhile, uniaxial tensile tests illustrated that the structural batteries had an ultimate tensile strength of 118.70 MPa and Young's modulus of 13.07 GPa along the yarn direction. Bias-extension experiments indicated that the shear modulus and yield strength were 2.87 GPa and 20.82 MPa, respectively. These results suggest that the multifunctional efficiency of the manufactured structural batteries was over 1, validating the effectiveness of the proposed manufacturing approach for composite structural batteries.

Mechanical Anisotropy of Injection-Molded PP/PS Polymer Blends and Correlation with Morphology.

The molecular orientation formed by melt-forming processes depends strongly on the flow direction. Quantifying this anisotropy, which is more pronounced in polymer blends, is important for assessing the mechanical properties of thermoplastic molded products. For injection-molded polymer blends, this study used short-beam shear testing to evaluate the mechanical anisotropy as a stress concentration factor, and clarified the correlation between the evaluation results and the phase structure. Furthermore, because only shear yielding occurs with short-beam shear testing, the yielding conditions related to uniaxial tensile loading were identified by comparing the results with those of three-point bending tests. For continuous-phase PP, the phase structure formed a sea-island structure. The yield condition under uniaxial tensile loading was interface debonding. For continuous-phase PS, the phase structure was dispersed and elongated in the flow direction. The addition of styrene-ethylene-butadiene-styrene (SEBS) altered this structure. The yielding condition under uniaxial tensile loading was shear yielding. The aspect ratio of the dispersed phase was found to correlate with the stress concentration factor. When the PP forming the sea-island structure was of continuous phase, the log-complex law was sufficient to explain the shear yield initiation stress without consideration of the interfacial interaction stress.

Modulating particle-particle interaction in phyllosilicate serpentine aqueous suspensions using sodium citrate

The depletion of high-grade nickel sulfide ores has led to an increased interest in low-grade ultramafic ores, which are widely available but challenging to process due to their high content of phyllosilicate serpentine. The anisotropic surface charge and shape of serpentine particles lead to attractive interactions, which increase the viscosity of ore slurry and associated operational and equipment costs. To overcome this challenge, we investigate the application of an environmentally benign reagent, sodium citrate, to modify the particle-particle interactions in serpentine aqueous suspensions. Our results show that at alkaline pH (10), sodium citrate selectively adsorbs on the brucite plane of serpentine, making the entire particle overall negatively charged, which weakens the interparticle attraction and reduces the suspension's shear viscosity, yield stress, and storage modulus. We confirmed these results using colloidal probe atomic force microscopy (AFM) technique, which showed a significant weakening of attraction between silica and brucite surfaces upon the addition of citrate. This work enhances the understanding of surface interaction mechanisms of phyllosilicate serpentine particles in aqueous media with the addition of sodium citrate and provides useful implications for the application of green reagents in mineral operations involving phyllosilicate gangues. Our findings suggest that sodium citrate has great potential as an effective and sustainable reagent in the processing of abundantly available low grade ultramafic nickel ores.

Numerical and analytical investigations on punching shear performance of UHTCC-enhanced RC slab-column joints

The excellent tensile strain-hardening behavior of ultra-high toughness cementitious composite (UHTCC) makes it applicable for enhancing the punching shear performance of reinforced concrete (RC) slab-column joints. However, construction of an entire slab-column structure employing UHTCC would inevitably lead to uneconomical designs. To balance the economic benefits with the punching performance, utilizing UHTCC in the core region of a slab-column joint is a promising approach. In this study, the impact of UHTCC application range (UAR) on the punching shear performance of UHTCC-enhanced RC slab-column joints (USCJs) was investigated, and an approach for determining the optimal UAR was also presented. Two USCJ specimens with different UAR were tested, and experimental results were compared with the counterpart numerical results to validate the finite element (FE) models. Twenty FE USCJ models with different UAR were established. Then the impact of UAR on development of critical cracks, ultimate resistance, and ductile behavior was examined. Analytical approaches based on the critical shear crack theory as well as on the combination of critical shear crack theory and yield line theory were adopted to predict the ultimate and flexural resistances, respectively. The failure mode was determined by comparing these two resistances and considering the ductile coefficient, based on which the effect of UAR on the failure mode was determined. The results show that the location of critical shear cracks and the appearance of flexural cracks vary with UAR. By increasing UAR, the ultimate resistance increases, but the ductile coefficient first increases and then slightly decreases. Provided that the UAR is increased to some extent, the growth rate of the ultimate resistance evidently slows down and the ductile coefficient peaks, indicating the optimal UAR considering both the economic efficiency and the punching performance. The presented approach shows promise for determining the optimal UAR in practical engineering designs.

Grain size dependent mechanical properties of CoCrFeMnNi high-entropy alloy investigated by shear punch testing

The effect of grain size on the mechanical properties of an equiatomic CoCrFeNiMn high-entropy alloy (HEA) was investigated by shear punch testing (SPT) as a miniature test method and Vickers hardness measurements. A Hall–Petch relationship was developed for the dependency of shear yield stress (SYS) on the average grain size (D). The correlation of the SYS and ultimate shear strength (USS) to the tensile yield stress (TYS) and ultimate tensile strength (UTS) values were also studied. A wide range of grain sizes was obtained by the thermomechanical processing of cold rolling and annealing at hot temperatures, where the primary recrystallization and grain growth phenomena were used for grain refinement and grain coarsening, respectively. Based on the obtained results and literature data, the Hall–Petch relationships of SYS = 88.9 + 301.1/√D and TYS = 167 + 520/√D were proposed, respectively. Moreover, the correlation of tensile test properties with those predicted by the shear punch test was also investigated. Accordingly, the relationships of TYS = 1.76 × SYS and UTS = 1.33 × USS were obtained, where the former is in excellent agreement with the von Mises yield criterion based on the plasticity theory, and the latter is influenced by the work-hardening behavior of the material and dynamic phenomena during plastic deformation.

Intelligent decision-making support system for the commissioning of a small hydroelectric power plant in the Republic of Tyva

This paper investigates the cutting forces arising when using a single abrasive grain. Analytical studies were carried out using a model of a single abrasive grain in the form of a rod with a radiused apex acting on the workpiece material. The slip-line method (method of characteristics) was used to calculate the deformation intensity of a plastically edged workpiece material under the action of a single grain. Mathematical models were developed for the following factors: plastic deformation of the material, edging of the stagnated zone and its friction against the grain surface when moved upwards in the form of chippings, grain friction against the plastically deformed material, and the action of the dynamic component of plastic deformation. The significance of the dynamic component in the overall balance of forces related to plastic deformation was established by determining the ratio of dynamic stress on the break line and shear yield point. This dependence calculated for D16T and 30HGSA materials showed the feasibility of accounting for the dynamic component system based on a small hydropower station located in the Todzhinsky district of the Republic of Tyva. For an adequate assessment of the operational reliability of hydropower units, a logical and probabilistic method based on the kinetic theory of fault tree was used. The method allows the failures of the used equipment, as well as unplanned shutdowns of units due to a shortage of water resources in the Great Yenisey (low water, overdrying, and frozen frost), to be taken into account. The development of a generation system based on a small hydroelectric power plant for the settlements in the Todzhinsky district of the Republic of Tyva offers a load of up to 2,500 kW, which helps to reduce the cost of purchasing, delivering, and storing diesel fuel, while diesel generators can be used as backup power sources. 3 scenarios of structuring a small hydroelectric power plant were considered that involved various numbers and total capacity of hydrogenating units: 5x500 kW, 4x630 kW, and 3x800 kW. Therefore, by using the multi-criteria optimization method, the optimal structure of the generating system based on a small hydroelectric power plant having three hydroelectric units (each characterized by a capacity of 800 kW) was selected from the three proposed options, taking into account the reliability and uncertainty of the initial information.

Method for processing experimental data when investigating residual stresses by drilling probe holes and digital image correlation

This paper investigates the cutting forces arising when using a single abrasive grain. Analytical studies were carried out using a model of a single abrasive grain in the form of a rod with a radiused apex acting on the workpiece material. The slip-line method (method of characteristics) was used to calculate the deformation intensity of a plastically edged workpiece material under the action of a single grain. Mathematical models were developed for the following factors: plastic deformation of the material, edging of the stagnated zone and its friction against the grain surface when moved upwards in the form of chippings, grain friction against the plastically deformed material, and the action of the dynamic component of plastic deformation. The significance of the dynamic component in the overall balance of forces related to plastic deformation was established by determining the ratio of dynamic stress on the break line and shear yield point. This dependence calculated for D16T and 30HGSA materials showed the feasibility of accounting for the dynamic component subsequently processed by free orthogonal cutting and rolling contact deformation using a special machine with numerical control. Further, using the same machine, drilling of probing holes was performed with video recording of the surface image prior to and following drilling. By varying the speckle images, the displacements of material particles on the sample surface were determined by the digital image correlation method, following which the radial deformations were determined by differentiating the obtained displacement values. Statistical analysis of a sample of radial deformations equidistant from the centre of the hole while varying the rotation angle by Fourier transformation with the calculation of the distribution period showed that the distribution is periodic. It is established that the periodograms constructed using experimental data have local maxima at a period value close to 180 degrees. This determines that the main calculated components of the residual stresses and the angle of their rotation be constant when selected to calculate the values of radial deformations at arbitrary points around the hole. The paper presents an approach that allows residual stresses to be determined by drilling probing holes and assessing the displacement of material particles on the sample surface due to the redistribution of residual stresses. For the analytical description of experimental data, it is proposed that an approximating periodic function be used, and the physical meaning of its coefficients is determined.

Experimental investigation on a novel curved steel damper for the beam-column joints of steel structures

Researchers have developed many passive damping devices to dissipate seismic energy using steel’s yielding property. Some proposed thick curved steel plates, while others proposed complex-shaped steel dampers. For instance, some have developed Shear Yielding Panel Devices (SYPD) and Triangular-plate Added Damping and Stiffness (TADAS) dampers for moment-resisting frames. However, these devices require additional steel bracings to be fitted into the structure. The present work reports an experimental study on a new energy dissipation device. The proposed damper is made of a steel plate cut into a curved shape (diaphragm), welded to flanges, and stiffened to create sub-panels. The damper can be fitted to the beam-column joints of steel structures using a bolted connection and does not need bracings; hence, it can be easily replaced after a seismic event. Eight devices were fabricated and tested under quasi-static cyclic loading protocol as per ATC 24. The results showed that all specimens exhibited hysteresis behavior, dissipated between 10 and 20 kJ of input energy, and provided a damping ratio of up to 40 %, depending on the damper’s geometry. Thus making it an effective seismic-resistant design system for new constructions and an alternative retrofitting tool for existing structures.

Shear capacity of PVC-CFRP confined concrete column-RC beam interior joint strengthened with core steel tube

This paper presents an experimental investigation on polyvinyl chloride (PVC)-carbon fiber reinforced polymer (CFRP) confined concrete (PCCC) column-RC beam interior joint strengthened with core steel tube (CST). Thirteen interior joints are designed and tested under low cyclic loading considering the impacts of six variables, such as diameter-thickness ratio of CST, stirrup ratio of joint, axial compression ratio, CFRP strips spacing, reinforcement ratio of beam and reinforcement ratio of column. Distinct shear deformation in joint region finally dominates the failure of specimens. The load-displacement hysteretic curves are relatively full and eventually show inverse S shape, indicating the specimens have considerable seismic behavior and energy dissipation capacity. The yield and peak shear capacities increase as diameter-thickness ratio, stirrup ratio of joint, reinforcement ratio of column or reinforcement ratio of beam increases. Comparatively, the axial compression ratio and CFRP strips spacing exert less influence on shear capacity. Considering the impact of diameter-thickness ratio, stirrup ratio of joint and reinforcement ratio of column, a formula for estimating shear capacity of PCCC column-RC beam interior joints strengthened with CST is proposed and its accuracy is verified by test data.

Analysis of periodic pulsating blood flow of fractional Maxwell power-law fluid in carotid artery with elastic vessel wall

Hemodynamic analysis reveals a highly significant effect on the prevention, diagnosis, and treatment of human vascular diseases. This article goes deeply into the periodic pulsatile blood flow in the carotid artery with an elastic vessel wall. In view of blood rheological experimental data, the constitutive equation of fractional Maxwell power-law fluid with yield stress, which can describe the four characteristics of yield stress, viscoelasticity, shear thinning, and thixotropy is established. Meanwhile, drawing support from the data of pulsatile flow, the finite Fourier series of pressure gradient with a period of 1 s has been proposed. Leading into Hooke’s law can build the fluid-structure coupling boundary condition of blood flow and elastic vessel wall. The numerical solutions are got hold of finite difference method integrated with the newly developed L1-algorithm, and their convergence and stability of which are verified. The axial velocities of blood under different constitutive relationships are compared. The results throw light that other constitutive relationships underestimate the velocity of blood. Furthermore, the flow rate and wall shear stress on different fluid are calculated. It can be concluded that compared with Bingham fluid, the maximum and minimum flow rate/wall shear stress of fractional Maxwell power-law fluid with yield stress increases by 19% and 32%, respectively. The flow rate lags behind the pressure gradient and has time delay effect, on the contrary, the velocity of blood vessel wall is keeping pace with the pressure gradient. The effects of relevant physical parameters on velocity are discussed. In addition, the spatiotemporal distribution of blood flow in cerebral artery and femoral artery are analyzed.

Influence of novel additives and antiwear agents on the properties of PAO-based magnetorheological fluids

Aiming to prepare high-property magnetorheological fluids (MRFs), experiment materials, optimized preparation processes, experimental methods, experimental procedures and test methods were elaborated for high-performance MRFs. Two carrier fluids, novel additives and three antiwear agents were selected to prepare MRFs. The characteristics of the MRFs samples including the settlement stability, zero-field viscosity, shear yield stress and wear resistance were tested and analyzed. The measurement of shear yield stress was obtained using a self-designed MRFs characteristics testing test-bed. The microstructure of unworn and worn magnetic-particles were observed using scanning electron microscope. Experimental results showed that HFGEL-310 and SD-104 mixed in a certain proportion can enhance settlement stability of MRFs, three antiwear agents can slow down the wear of MRFs to a certain extent and MRFs-31 with AlN had the best anti-wear performance. MRFs based on PAO10 with HFGEL-310 2.7%, SD-104 2.9% and AlN 5% was high-performance MRFs with good overall properties.

Pressure Model Study on Synchronous Grouting in Shield Tunnels Considering the Temporal Variation in Grout Viscosity

The grout pressure in the shield tunnel tail void during synchronous grouting is the key to controlling ground settlement and restraining the segment. However, the circumferential, longitudinal, and radial distribution of grout pressure considering the temporal variation in grout viscosity has not been well explored yet. In this study, a theoretical model of grout pressure distribution and dissipation considering the temporal variation in Bingham grout viscosity was established. The simulation results of the pressure model were verified by field-measured data. The results showed that the radial and longitudinal distributions of grout pressure considering the temporal variation in grout viscosity were closer to the field-measured data. The impacts of the main parameters on the pressure distribution and dissipation were analyzed. Compared with the effect of the shield tail void thickness, tunnel radius and yield shear stress have greater effects on grout pressure during the circumferential filling phase. During the longitudinal and radial diffusion phases, the increase in soil porosity and permeability coefficient was conducive to grout diffusion. The increase in the grout viscosity reduces the pressure loss during the grout flow process. The results of this research can provide a theoretical basis for the grout design process in shield tunnels.