Shear Effects Research Articles

Effect of shear span-to-depth ratio on flexural and fracture behaviors of reinforced UHPMC beams based on four-point bending test and acoustic emission monitoring

Ultra-high performance manufactured sand concrete (UHPMC), using manufactured sand (MS) as aggregate, belongs to a brand-new ultra-high performance concrete (UHPC). Better understanding the failure behavior of UHPMC beams reinforced with steel reinforcement bars is crucial in structural design. This study investigates the effects of different shear span-to-depth ratios (λ = 1.2, 1.6 and 2.0) on the failure modes, mid-span deflection, concrete and rebar strain, flexural toughness, initial cracking load, ultimate load, energy dissipation capacity, and crack propagation patterns based on four-point bending tests for totally twelve reinforced UHPMC beams. Meanwhile, acoustic emission (AE) monitoring is used to evaluate corresponding fracture characteristics. Results reveal that an increase in shear span-to-depth ratio leads to a significant increase in mid-span strain and better ductility but lower equivalent stiffness. The maximum strain of specimen with λ = 1.2 is 24.8 % lower than that with λ = 2.0, and specimen with λ = 1.6 exhibits 22.3 % greater equivalent stiffness than that with λ = 2.0. Beams with larger shear span-to-depth ratios demonstrate superior ductility and energy absorption capacity, specimen with λ = 2.0 showing a ductility factor 2.85 times higher than that with λ = 1.2. The presence of MS significantly improves initial cracking load by 26.9 %, ultimate load by 4.5 %, and energy dissipation capacity by 37 %. MS also enhances toughness and delays crack propagation in the early stages. This effect can make the fracture transform into more rapid energy release in the later stages, indicating that MS could alter crack propagation patterns, forcing cracks to propagate along paths with greater resistance to crack propagation. These conclusions can offer insights for the safer and economical design and application of UHPMC beams, especially the balance among shear span-to-depth ratio, MS and mechanical performance in the environmentally friendly structures design and failure prevention process.

Self-Lubrication Mechanism of Surface-Textured Polymer-Matrix Composites under the Induction of Frictional Stress.

Polymer-matrix composites have been widely used in the manufacture of seals, bearings, electrical insulators, and self-lubricating films as engineering applications move toward lighter weight, higher strength, and corrosion resistance. However, the high-speed shear effect of the friction pairs in relative motion leads to localized heating of the polymer surface, resulting in deformation or softening of the device. Herein, acer mono maple and canna leaves were used as templates to construct polymer-matrix sulfonated polyether-etherketone/polytetrafluoro-wax (SPEEK/PFW) composites with a surface-textured structure. As the bionic texture reduces the level of direct contact between the friction pairs, the frictional thermosoftening of SPEEK occurs in the localized areas of the bumps and leads to the release of PFW stored in textures, resulting in the formation of a soft polymer sliding layer in the worn area and greatly enhancing the frictional stability. By investigation of the tribological properties of textured SPEEK/PFW composites under different loads and sliding speeds, the mechanisms from surface wear to matrix softening and spontaneous construction of a slipping layer are summarized. The results of scanning electron microscopy and three-dimensional profilometer characterization of the wear scars show the surface state of SPEEK/PFW after friction, revealing the friction-thermotropic deformation of the surface texture. The results of this study not only improve our understanding of the frictional heat-induced surface self-lubrication mechanism of textured polymer composites but also provide a reference for the development of multiphase hybrid polymer-matrix composites with excellent self-lubrication properties.

Effect of Bi content and temperature on the shear mechanical properties of Fe-Bi nanocomposites: a molecular dynamics study

In this study, the effects of Bi content and temperature on the mechanical properties of Fe–Bi nanocomposites were investigated using molecular dynamics simulation. The research reveals that the nanocomposite’s shear strength reaches a peak of 3.785 GPa at a Bi content of 0.15%, attributed to the impediment of dislocation movement by twin boundaries during shearing, resulting in a dynamic ‘Hall–Petch’ effect and exceptional shear performance of the material. The abundant twinning induced around Bi phase inclusions introduces orientational disparities within the crystal, leading to grain misalignments, with dislocations in the grains slipping near the twin boundaries. In the nanocomposites, <100> dislocations merely act as initial sites for reactions, reducing their impact on the material’s strength and fracture behavior. The maximum stress decreases with increasing temperature while the magnitude of atomic transformations increases. The proportion of atoms at grain boundaries is higher at higher temperatures, and the arrangement of atoms at grain boundaries is more complex. At a temperature of 100 K, the dislocation density is highest with the smallest variation, forming a reinforced region within the material. The above results have significant implications for the design of environmentally friendly Bi-containing free-cutting steels.

Cushioning property and structure optimization of double-arrow sandwich composite based on modified genetic algorithm

Owing to the ability of negative Poisson’s ratio (NPR) structures in enhancing the stiffening effectof shear stiffening gels (SSG), combining the two in cushioning applications has attracted much attention. This paper presents the design of NPR flexible cushioning sandwich composites featuring a double-arrow structure (DAS). The DAS is optimized using a modified genetic algorithm, and the cohesive property is leveraged to reinforce the stiffening effect of SSG, thereby improving the material’s cushioning efficiency. The synergistic effect of the DAS and SSG and the law of SSG arrangement on the energy absorption efficiency of cushioning were revealed using the finite element method and experiment. It can be found that the size effect of the DAS significantly contributed to the enhancement of the energy-absorption efficiency of the SSG stiffening. In double-arrow sandwich composite (DASC), the larger reversed-triangle deformation and the increased number of reversed-triangle configurations, amplified the shear stiffening of the SSG, improving the impact load dissipation and energy absorption efficiency of sandwich composite. The energy absorption efficiency of the DASC was improved owing to the synergistic effect of the DAS cohesive effect and the SSG stiffening properties, with the energy absorption ratio and mass specific energy absorption increased by 83.02% and 136% compared to neat polyurethane. The DASC optimized in this study has good flexibility and energy absorption capacity and is promising for application in the field of flexible protection.

Effects of shear and bending strains on domain structures in freestanding ferroelectric thin films from phase-field simulations

Freestanding ferroelectric thin films, free from substrate constraints, present a platform for advanced strain engineering owing to their exceptional mechanical flexibility. The strain state in freestanding ferroelectric thin films can be modulated through various mechanical deformations, enabling precise control over the physical properties and performance of the ferroelectric films. Here, we utilized phase-field simulations to explore the polarization evolution and switching behavior of freestanding BaTiO3 ferroelectric thin films under bending and shear strains. Our findings reveal that shear strain transforms flux-closure domains into a monoclinic phase, increasing the coercive field, maximum polarization, and remanent polarization, thereby broadening the ferroelectric polarization–electric field hysteresis loop. The underlying mechanism involves the competition between elastic and electrostatic energies, which becomes more pronounced with increasing shear strain. Additionally, this contrasts with the modulation of domain structures by bending strain, which causes a rightward shift in the ferroelectric polarization–electric field hysteresis loop due to the flexoelectric fields generated by bending deformation. These findings provide profound insights into the strain effects in ferroelectrics, highlighting the complex interplay between mechanical deformation and electrical response. The ability to manipulate domain structures and polarization behaviors through controlled mechanical strains paves the way for designing high-performance, flexible ferroelectric devices.

Shear-imposed falling film on a vertical moving plate with disrupted time-reversal

We propose a mathematical model to study the stability and dynamics of a shear-imposed thin film flow on a vertical moving plate, incorporating the influence of odd viscosity. This odd viscosity effect is vital in conventional fluids when there is a disruption in time-reversal symmetry. Our motivation to study the dynamics with odd viscosity arises from recent studies (Kirkinis & Andreev, vol. 878, 2019, pp. 169–189; Chattopadhyay & Ji, vol. 455, 2023, pp. 133883) where the odd viscosity effectively reduces flow instabilities under different scenarios. Utilizing a long wave perturbation method, we derive a nonlinear evolution equation at the liquid–air interface, which is influenced by the motion of the vertical plate, imposed shear, odd viscosity, and inertia. We first perform a linear stability analysis of the model to get firsthand information on various flow parameters. Three distinct conditions for the vertical plate, quiescent, upward-moving, and downward-moving, are considered, accounting the imposed shear and odd viscosity. Additionally, employing the method of multiple scales, we conduct a weakly nonlinear stability analysis for the traveling wave solution of the evolution equation and explore its bifurcation analysis. The bifurcation analysis reveals the existence of subcritical unstable and supercritical stable zones for crucial flow parameters: odd viscosity, imposed shear, and motion of the vertical plate. Both linear and weakly nonlinear stability analyses demonstrate that the destabilizing effect induced by the upward motion of the vertical plate can be alleviated by applying uphill shear, while the destabilizing effect of downhill shear can be mitigated when the vertical plate is in a downward motion. Moreover, we define an eigenvalue problem that mirrors the Orr–Sommerfeld (OS) model for analyzing normal modes and identifying the critical Reynolds number. We investigate the dynamics of surface waves through numerical solutions of the OS eigenvalue problem using the Chebyshev spectral collocation method. We observe the consistent enhancement of stabilization in the presence of odd viscosity. In the low to moderate Reynolds number range, vertical plate motion and odd viscosity show similar behavior in OS analysis, while imposed shear exhibits distinct changes. The Benney-type model does not agree with the OS problem when the Reynolds number is moderate with or without the three key parameters: vertical plate motion, imposed shear, and odd viscosity. However, when the Reynolds number is low with or without the three key parameters: vertical plate motion, imposed shear, and odd viscosity, the Benney-type model agrees with the OS. Further, numerical simulations of the evolution equation corroborate the results obtained from linear stability, weakly nonlinear stability, and OS analyses. Finally, the Hopf bifurcation analysis of the fixed point reveals that the wave speed is influenced by both the motion of the plate and the imposed shear while it remains independent of odd viscosity.

Aerodynamic performance and flow field characteristics of wind turbines under shear incoming flow conditions

Abstract With the large size of the units, wind farms are evaluated in order to improve the accuracy of the incoming flow measurement and to improve the unit control strategy. In this paper, the turbulent wind field generated by autoregressive linear filtering using a large eddy simulation turbulence model is used to study the wind speed-induced zone under shear incoming flow conditions. At the same time, the wake and aerodynamic performances of the wind turbine under different incoming flow conditions are investigated, and conclusions are obtained. 1) The larger the shear index is, the larger the amplitude is at the first frequency component of the power and the thrust, and the larger the fatigue load is for the wind turbine. 2) For the wind turbine wake flow in the case of smaller wind turbine size, the wake velocity profiles at different shear indices cross and overlap in the transition and far wake regions. At position 0.5 D, the turbulence profiles with different shear indices basically overlap; the larger the shear index is, the more intense the wake flow exchange is and the greater the turbulence intensity in the wake region will be. 3) For the wind speed-induced region, at position −0.1 D, the incoming flow velocity distribution is subject to the combined effect of induction and shear, and the induction effect of the wind turbine wheel is a little larger. The larger the shear index, the greater the turbulence intensity.

Flow structures in large-scale bank erosion zone of Lower Yangtze River

The bank erosion process in the densely populated Lower Yangtze River can pose a great threat to riparian residents and industries. It is characterized by rapid development within a few hours, a large-scale soil collapse of 106 m3, and an arc shape. During its development, flow field inside the bank erosion area continuously evolves and interacts with the bank soil. However, the mechanisms behind the bank erosion process are still unclear. Therefore, laboratory experiments were conducted to investigate flow structures and turbulences inside bank erosion areas. A pulsed particle image velocimeter was employed to obtain high-quality velocity data inside the bank erosion zone. Results show that the bank erosion zone can be divided into a backflow zone, a mixing zone, and a mainstream zone, according to variations in flow structure; in the mixing zone, water flow is highly turbulent, and the mixing width gradually increases downstream because of the shear effects between the mainstream and backflow; the backflow zone can be subdivided into a central zone and a peripheral zone, based on the pattern of velocity changes along the radial axis from the backflow center to its periphery. A formula for calculating the flow velocity within the backflow zone was proposed, and we found that the velocity gradient in the peripheral zone was approximately four times higher than that in the central zone. This indicated that shear stress exerted by the flow near the backflow boundary was significantly intensified.

The combined effects of quantum and strong coupling on the nonlinear collective excitation in quantum dusty plasmas

The quantum hydrodynamic model for electrons and ions and the generalized hydrodynamic model for the strongly coupled dust particles are proposed in the strongly coupled quantum dusty plasma, where the combined quantum effects of quantum diffraction, quantum statistic pressure, as well as electron exchange and correlation effects are all considered in the quantum hydrodynamic model. The shear and bulk viscosity effects are included in the viscoelastic relaxation, which leads to the decay of the dust-ion-acoustic waves. The approximate time-dependent solitary solution is obtained by the momentum conservation law in the presence of viscosity.

A slip-line field model for independently characterizing shearing and ploughing effects in metal cutting processes

This study proposes a new slip-line field model to separately characterize the shearing-included cutting process and the pure-plough cutting process. The shear plane and dead metal zone in relation to the shearing effect are modelled by straight slip-lines, while the deformation area in relation to the ploughing effect is treated to have straight boundaries. The boundaries of the dead metal zone and ploughing area are determined by considering tool-workpiece frictional behaviours. The stresses acting on the boundaries of the ploughing area, dead metal zone and shear plane are separately modelled considering the thermal–mechanical coupling effect. Based on the minimum energy principle, the shear angle is originally modelled by following the dynamic requirement of chip flow to balance the forces acting on dead metal zone, shear plane and rake face. By iteratively solving the coupling effect among the temperature, stress and shear angle, the total cutting forces are acquired by integration operation through straight slip-lines. Experiment results and finite element simulations validate the proposed slip-line field model in predicting the shear angle and cutting forces for both micro and regular milling processes.

The effect of shear on nucleation and movement of basal plane dislocations in 4H-SiC

The effect of shear on nucleation and movement of basal plane dislocations in 4H-SiC

Solution temperature influence on CRSS of the secondary γ′ phase in nickel-based superalloy FGH4096

Nickel-based superalloy components are capable of being manufactured by direct hot isostatic pressing (HIP) process with near-net shape and nearly 100 % raw materials utilization. However, they cannot be applied directly, due to the poor mechanical properties of HIPed components. Fortunately, heat treatment can improve the properties via regulating the microstructure. Therefore, the effects of varied solution temperatures on the tensile properties of FGH4096 nickel-based superalloy disk at room and high temperatures were studied. The results revealed that the disk after sub-solution treatment (1130 °C) has higher tensile properties (room temperature yield strength: 1194 MPa, elongation: 15.5 %; high temperature yield strength: 1075 MPa, elongation: 10.5 %). The antiphase boundary (APB) shear stress, Orowan bypass stress, stacking faults (SF) shear stress, and micro-twins (MT) shear stress affected by the size and distribution of the secondary γ′ phase were calculated. The results show that the main strengthening mechanism at room temperature is APB shear, and the APB shear stress of solution treatment at 1190 °C is the highest. The high temperature strengthening mechanism is due to SF shear and MT strengthening effects. The difference in SF shear stress between various solution temperatures is minimal. 1190 °C has a higher MT strengthening effect than 1090 °C. This is consistent with the actual result that the tensile properties at 1190 °C are superior to those at 1090 °C. The conclusion is that the combination of high strength reflected by several critical resolved shear stresses and considerable plasticity reflected by the MT strengthening effect can lead to a comprehensive improvement in alloy tensile properties.

Experimental and numerical research for the failure behavior of the dieless clinching joints

In this work, the failure behavior of dieless clinching joints for AA5052-H32 aluminum alloy under cross tension and tensile shear loading conditions was investigated by experimental and simulation methods. Firstly, The VUMAT subroutine for the N–H shear-modified GTN model (Proposed by Nahshon and Hutchinson, a modified GTN model considering hole shear effects) was written. Subsequently, the conventional and shear parameters calibration was accomplished. A finite element model (FEM) for the failure process of dieless clinching joints based on the N–H shear-modified GTN microscopic damage model, elimination of large deformation mesh distortion and consideration of the material hardening history was established. In addition, the deformation, damage and destruction processes of the joint under two loading conditions were analyzed. And macro/microfracture analysis of the failed joints was performed to further reveal the failure behavior. The results show that the established FEM of the failure process agrees well with the experimental results and failure modes are consistent. The model accuracy in predicting the tensile and shear loads is 91.9% and 92.7%, respectively. This provides a reference for the process design and joint arrangement of the dieless clinching joints in practical applications.

Liquid–liquid flow characteristics and mass transfer enhancement in a Taylor–Couette microreactor

AbstractThe liquid–liquid immiscible flow and mass transfer were investigated in a novel Taylor–Couette microreactor (TCMR). Due to the rotation shear and microscale effects, each phase flowed in the form of helical strips/bands, instead of dispersion droplets as in conventional equipment. Based on the movement and inclination of the bands, the helical vortex (HV), mixed helical vortex (MHV) and stationary helical vortex (SHV) were distinguished. The characteristics of the regimes were strongly influenced by rotation speed and flow rate, but the specific surface area only slightly varied. The flow regimes also influenced the two phase mass transfer. It was shown that the mass transfer coefficient kLa monotonically increased with the rotation speed in the HV regime, while it slightly decreased when the flow shifted into the MHV/SHV regime. According to the parametric studies, empirical correlations were developed for the flow regime transition and mass transfer prediction.

Effect of rubber particles on mechanical properties of calcareous sand under large displacement shear

To reveal the influence of rubber particles on the mechanical properties of calcareous sand under the large-displacement shear effects of earthquakes and waves, indoor ring shear tests were conducted on rubber particle-calcium sand mixtures. The effects of rubber particle size and content on the mechanical properties of calcareous sand were studied via indoor ring shear test. Then, based on PFC3D, a numerical model of a ring shear test that can restore the shape of calcareous sand particles is established, and a mesomechanical analysis of mixed sand is carried out. The results showed that the effect of the rubber particle content on the crushing characteristics and strength of calcareous sand was significant and that the effect of the particle size was small. The rubber content causes a gradual decrease in the peak strength and particle crushing rate and increases the deformation stability of the mixed sand. The softening coefficient and relative crushing rate were significantly reduced to 0.01–0.06 and 0.28–1.2%, respectively, at 40% rubber content. The numerical simulations and experimental results were in good agreement. An increase in the rubber content significantly influences chain development, which explains the macroscopic mechanical properties of mixed sand at the fine level.

Shear Strengthening of Stone Masonry Walls Using Textile-Reinforced Sarooj Mortar

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.

Investigation of cold tube structure on flow characteristics and energy separation in vortex tube based on numerical and thermodynamic analyses

A combined approach of computational fluid dynamics modelling, experimental validation and thermodynamic analysis is used to investigate the effect of cold end tube geometry (namely, straight tube, divergent tube, convergent tube, and convergent-divergent tube) on flow characteristics and energy separation, which to improve the energy efficiency and sustainability of the vortex tube in industrial applications. The analyses indicate that the highest axial velocity (212 m/s) and swirl velocity (193 m/s) at different axial locations in the cold tube are demonstrated in the divergent and convergent-divergent structures, respectively. The divergent tube shows better energy separation at lower cold mass fraction, while the convergent-divergent tube is dominant at higher cold mass fraction. The highest coefficient of performance is found at μc = 0.6, with maximum cooling and heating energy transfer efficiencies of 0.112 and 0.103, respectively. By innovatively incorporating the work-heat transfer theory into structural investigation of cold tubes, it is found that tangential viscous shear effect is the dominant factor in energy separation process. It is noteworthy that the highest net energy transfer of 973 W is achieved by convergent-divergent tube at a cold mass fraction of 0.7.

Towards accurate prediction of the dynamic behavior and failure mechanisms of three-dimensional braided composites: A multiscale analysis scheme

In this paper, a dynamic multiscale model is proposed for three-dimensional four-directional (3D4D) braided composites, considering the effects of strain rate and shear enhanced failure mechanism. The strain rate-dependent constitutive models are established for both resin and yarns. The accuracy of the yarn model is validated by comparing the simulated stress-strain curves with the experimental results obtained from the Split Hopkinson Pressure Bar (SHPB) tests with various strain rates. The shear enhancement coefficient of the yarn is determined from the failure envelopes with a discussion of crack propagation angles. The results show that, based on the calculated microscale properties, the mesoscale model accurately predicts both the longitudinal and transverse compressive strain-stress behavior of 3D4D braided composites at different strain rates. A comparative analysis reveals that the shear-enhanced failure model achieves a better prediction compared with other counterparts, such as Hashin-Rotem and Tsai-Wu Models. The proposed dynamic multiscale scheme for 3D braided composites is an efficient and accurate tool to characterize their multiscale features and strain rate-dependent behavior.

Behavior of magnetic systems of different dimensions in a magnetic field

Purpose. To investigate the influence of the magnetic field on the formation of structures in magnetic media of various dispersities. Methods. Experiments to study the dynamics of magnetic inclusions were carried out on a self-made installation in flat transparent cells by microscopy. The magnetic field was created by an electromagnet FL-1 connected to a power source. Magnetite particles of various sizes, as well as metal balls with a diameter of 0.5 mm, were studied as a magnetic medium. Video recording was performed using a MICMED WiFi 2000X 5.0 microscope. Results. The dynamics of magnetic inclusions in a viscous liquid medium under the influence of a magnetic field, as well as under conditions of mechanical shear effects, have been studied. The influence of the magnetic field strength on the growth rate of chain structures, as well as on the angle of deflection under shear action, has been studied. A theoretical interpretation of the observed phenomena is proposed. Conclusion. During the experiment, it was found that under the influence of a magnetic field, magnetic inclusions form chain structures. Their size, growth rate and dynamics depend on the physical parameters of the system and the external magnetic field. An intensive increase in the formation of chains of magnetic inclusions was detected at low and medium values of the magnetic field strength. An experimental dependence of the angle of deviation of chain structures from the equilibrium position on the magnetic field strength is obtained, which correlates with known theoretical data, on the basis of which a computational model is proposed. The results of the study can be used to visualize numerical calculations of the dynamics of dispersed systems under external influences.

Study on scour stripping of oil-wax gels in pipes

In this study, soft gel stripping experiments were conducted under different temperatures and flow velocity conditions by a flow loop. The flow area of pipes increased with an increase in flow velocity. However, partial or complete removal of soft gels occurred when flow velocity increased to a critical point. The hydrodynamic force from oil flow, adhesive contact force and yield stress of soft gels were calculated and compared. The hydrodynamic force increased with an increase in flow velocity. Under the dissolution and shear effect, the flow area showed a step-wise increase when hydrodynamic force did not meet the requirements of adhesion failure and structural failure. The soft gels were stripped completely when the force met the requirements. The lower strength of soft gels resulted in lower requirements of adhesion failure and structural failure. Thus, accumulation problems of soft gels can be solved by changing flow parameters.