A comprehensive investigation of plowing and grain-workpiece micro interactions on 3D ground surface topography
Abstracts:The accumulation of plowing effect in the grinding process which is ignored in previous researches has an essential influence on the surface topography of the workpiece. In this study, a new grinding surface topography modeling method considering the plowing effect is proposed. The modeling method of the grinding wheel based on the replicated method is given to obtain the real and accurate wheel surface topography. According to the cutting path of abrasive particles extracted from the wheel topography, the instantaneous undeformed chip thickness is calculated to determine the contact stages of rubbing, plowing and cutting. The influence of material accumulation caused by the plowing effect on the microstructure is discussed, and the mechanism of complex changes in the surface topography resulting from the interference between the grains is analyzed to generate the grinding surface topography. Based on the proposed model, the effects of plowing effect and grain-workpiece micro interactions on 3D ground surface topography have been studied. And topography parameters (Sa, Sp, Sv, Sku ) are utilized to evaluate the difference between the simulated result and experimental result. It has been found that the experimental result is in good agreement with the surface topography model and plowing effect could not be ignored. The modeling method of grinding surface topography considering the influence of the plowing stacking effect in this study may serve as a novel and more practical way to predict the grinding surface topography.
Analyzing thermo-hydrodynamics of nanofluid flowing through a wavy U-turn channel
Abstracts:In this paper, the thermo-hydrodynamics of Al2O3-water nanofluid in a wavy U-turn channel with hot walls is numerically investigated by means of lattice Boltzmann modeling. At first, the numerical technique is validated by simulating fluid flow in a (non-)wavy straight channel. Then, the effects of various active parameters, e.g. pressure gradient in the channel, nanoparticles volume fraction, and number of sinusoidal waves along the channel, on the flow field and heat transfer is studied. Furthermore, the thermal–hydraulic performance factor is determined to investigate whether heat transfer enhancement outweighs the greater frictional losses caused by both complex wavy wall geometry and nanoparticles. The results show that the heat transfer rises by increasing pressure gradient in the channel while drops by increasing number of waves. Also, the effect of nanoparticles volume fraction on dimensionless Nusselt number becomes more pronounced at higher pressure gradients. The results indicate that the thermal–hydraulic performance factor grows by increasing nanoparticles volume fraction or decreasing the number of waves.
Mechanical behavior of composite structures subjected to constant slamming impact velocity: An experimental and numerical investigation
Abstracts:The interaction between deformable structures and free water surfaces can modify the fluid flow and change the estimated hydrodynamic loads in relation to rigid bodies, due to the appearance of hydroelastic effects. The flexibility and damage failure modes in composite materials introduce additional complexity for predicting hydrodynamic loads when interactive with water. This is considered to be a key challenge when using these materials in marine applications. Therefore, particular attention should be paid to this fact in the design phase and over their period of use. The aim of this work is to study the structural behavior and the effect of the flexibility of composite panels on hydrodynamic loads and the dynamic deformation response experimentally and numerically. To study these effects, composite panels with two different rigidities were subjected to various impact velocities and investigated. It should be noted that all the panels tested at a10° deadrise angle. A high velocity shock machine was used to maintain constant velocity during water entry at impact velocities of 4 m/s, 6 m/s, 8 m/s and 10 m/s. The general analysis of experimental results indicated that compared to the higher stiffness panels, the more flexible panel has a higher peak force as velocity increases. This has been attributed to the change in local velocity and local deadrise angle along the water-panel interface. The numerical model was implemented based on the Coupled Eulerian–Lagrangian Model (CEL) built-in Abaqus/Explicit finite element software. The numerical results showed a good agreement compared with experimental data for both the hydrodynamic force and the deformation response. These quantitative structural-loading data can provide a clear guide for maritime ship design.
An adaptive multi-grid peridynamic method for dynamic fracture analysis
Abstracts:The standard way of implementing Peridynamics is a meshfree approach which uses a uniform discretization. This is inefficient when a very dense grid spacing for a localized area is required. In this paper, a radically new strategy to couple grids with different spacing is put forward. It is free of ghost forces in static cases and spurious waves in dynamic problems can be controlled and made negligible thanks to proper discretization. There is no loss of volume due to non-uniform discretization at the interface between different grids. An efficient algorithm is developed to apply the refinement adaptively. It permits to increase the resolution of the analysis only in the critical zones. The performance is investigated by solving dynamic problems, including cases of crack propagation in brittle materials. We compare the solutions of the proposed method with those of a standard peridynamic model, which employs uniform discretization, and show that the same accuracy is obtained at a much smaller computational cost.
Nonlocal vibrations and potential instability of monolayers from double-walled carbon nanotubes subjected to temperature gradients
Abstracts:Using nonlocal elasticity theory of Eringen, free transverse thermo-elastic vibrations of vertically aligned double-walled carbon nanotubes (DWCNTs) with a membrane configuration is going to be explored methodically. Accounting for nonlocal heat conduction along the side walls of DWCNTs with allowance of heat dissipation from the outer surfaces, the nonlocal temperature fields within the constitutive tubes are assessed for a steady-state regime. The van der Waals interactional forces between atoms of each pair of DWCNTs as well as the innermost and outermost tubes are displayed by laterally continuous springs whose constants are appropriately evaluated. By establishing suitable discrete and continuous models on the basis of the Rayleigh and higher-order beam theories, nonlocal in-plane and out-of-plane vibrations of thermally affected nanosystems of monolayers of DWCNTs are examined and discussed. The critical values of the temperature change are stated explicitly and the role of influential factors on this crucial factor as well as the free vibration behavior are investigated in some detail. Through conducting a fairly comprehensive numerical study, the influences of the slenderness ratio, temperature change in the low and high temperatures, number of nanotubes, small-scale parameter, intertube distance, and stiffness of the surrounding environment on the nonlocal-fundamental frequency are explained. The obtained results from this work could provide crucial guidelines for the design of membranes or even jungles of vertically aligned DWCNTs as thermal interface nanostructures.
A theoretical model of the shrinking metal tubes
Abstracts:In this paper, a theoretical model of the shrinking metal tube is proposed. According to the relation between the actual die radius and the critical die radius decided by the tube and the conical die angle, the deformation is classified into three modes. Then, the published experimental data are used to validate the theoretical model. Within a large range of geometry parameters, numerical simulations are performed to confirm the applicable range of the current model. It is found that the compressional force, the final reduced radius and the equivalent plastic strain predicted are close to the simulation results for the conical angle smaller than 40° and radius-thickness ratio larger than 10. From the simulation results, several factors such as friction, dynamic effect, unsteady deformation stages, conical angle are analyzed. By comparing the tube shrinking and expansion, the energy absorption ability of shrinking tube is higher than expansion with the same deformation ratio. In the end, an optimization to maximize the specific energy absorption (SEA) is given for the shrinking tube.
Three-dimensional characterization and modeling of diamond electroplated grinding wheels
Abstracts:This paper presents a study on the three-dimensional characterization and modeling of morphology of diamond abrasive grains and electroplated diamond grinding wheels. A diamond abrasive grain was modeled by a cubo-octahedron that was determined by the intersection between an octahedron and a cube. The study revealed that the side length of octahedron and its side-length ratio followed a normal distribution and a generalized extreme value distribution, respectively. High-precision characterizations of grain density and protrusion height were realized by measuring wheel replicas with laser scanning confocal microscopy (LSCM). It was found that the grain protrusion height followed a normal distribution with an average of ∼40% of the grain size. Considering the randomly-distributed shape, size, position and protrusion height of abrasive grains, a geometric model of electroplated diamond wheels was established. The results show that the predicted morphology of grinding wheels agreed well with the experimentally measured. The model enables an accurate kinematic simulation for designing precision grinding processes.
Calculation analysis of yaw bearings with a hardened raceway
Abstracts:The yaw bearing is a key support structure of wind turbines and is often exposed to substantial complex loads that cause damage and fatigue failure. Raceway surfaces accommodate high contact stress and require a hardening treatment. The hardened depth has a great influence on both the carrying capacity and fatigue life. We establish a whole finite element model of a yaw bearing and use non-linear springs instead of a ball to obtain the maximum contact load. The results of a strain gauge experiment and an empirical formula are compared to verify the spring model results. A local finite element model of a ball and raceway with different hardened depths is established to analyse the stress distribution and fatigue life. The raceway is divided into a hardened layer, transition layer, and core layer. An indentation experiment verifies the raceway model with different layers. The stress results are compared with Hertz contact theory, and the fatigue life results are compared with yaw bearing fatigue life theory. The influence of different hardened depths on the stress and lifetime of yaw bearings is analysed.
Ultimate swelling described by limiting chain extensibility of swollen elastomers
Abstracts:In this study, we study ultimate swelling characterized by limiting chain extensibility of swollen elastomers. Limiting chain extensibility is introduced into the Flory–Rehner theory using the Arruda–Boyce eight chain model and the Gent phenomenological model. The difference between these models is unified by defining a single scalar function. The inequality derived from this function allows for analysis to provide an ultimate value of swelling ratio. This ultimate value is not exceeded at equilibrium swelling regardless of the set of material constants. Under uniaxial loading at equilibrium swelling, deswelling can occur even in tension. Further, the very large swelling behavior of pH sensitive hydrogels is found to originate from the resistance generated by approaching the ultimate value of swelling ratio.
The plane mixed problem for an elastic semi-strip under different load types at its short edge
Abstracts:The mixed problem for the fixed semi-strip is investigated in this article for the three cases of the applied mechanical load. The solution of the boundary problem is reduced to the solution of the singular integral equation (SIE) with regard to the unknown displacements derivative. Three cases of SIE are investigated: when the mechanical load is applied on the center of the semi-strips edge, when the mechanical load is distributed near the left lateral side and when the mechanical load is distributed on the whole semi-strip’s edge. In the first case SIE is solved by the using of the orthogonal polynomials method. In the second and third cases the corresponding transcendental equations to SIE are constructed, and the SIE are solved with the help of the generalized method. The stress state of the semi-strip is investigated for the three cases.