The study of the mechanical properties of polycrystalline alloy materials under dynamic impact, namely, the prediction of mechanical behavior after yield stress and the establishment of a constitutive model, has attracted much attention in the field of engineering. The stress-strain curves of 5083 aluminum alloy were obtained under strain rates varying from 0.0002 s-1 to 7130 s-1 through uniaxial compression experiments. The equipment used included a CRIMS RPL100 tester, Instron tester, and split Hopkinson test system. In addition, based on dislocation dynamics and the strengthening mechanism of metals, the plastic flow of the 5083 aluminum alloy was systematically analyzed under a wide range of strain rates. It was found that the abnormal yield behavior of the 5083 aluminum alloy under a wide range of strain rates increased, and the experimental phenomenon of hardening rate decreased with an increase in strain rate. This study also revealed that the abnormal yield behavior is caused by the different dislocation mechanisms of two-phase alloy elements under different strain rates. Based on the thermal activation theory and the experimental data, a constitutive model was developed. A comparison showed good agreement between the experimental and model curves. This indicates that this model has good plastic flow stress prediction ability for such types of materials.

This paper presents a numerical model for accurately representing the behaviors of lead-rubber bearings during earthquakes. This model, which is implemented in OpenSees as a user-defined element, accounts for the mechanical characteristics of bearings as follows: firstly, the bi-lateral interaction effect of hysteretic behaviors, as well as the variation in horizontal stiffness due to vertical load, is considered; secondly, the reduced vertical stiffness under large lateral displacement is incorporated by the piecewise linear formulation, and the linear reduction method is employed to determine the stability limit of bearings in the deformed configuration; furthermore, the cavitation and permanent damage effects in bearings are mathematically included. To validate the numerical model, simulation analyses are performed for a series of static and dynamic loading tests, and the numerical results show reasonable agreement with experimental ones, which indicates that the proposed model provides an effective tool for the failure mode analyses of bearings and the dynamic analyses of seismic isolated structures.

In the dynamic analysis of discretized elastic bodies with contacts/impacts, the common formulations to model contact force include the penalty method and the Lagrangian method, which are different in the constraint imposition strategies. Traditionally, the Lagrangian method is thought to be less efficient due to additional multipliers and numerical complexity, however, the viewpoint is challenged in this paper. The goal of this paper is to investigate how numerical efficiency and accuracy using the two different methods are influenced by some non-physical chosen parameters such as stiffness coefficient, time step size and spatial discretization. An experimental sphere-rod impact problem and a multi-point impact problem are solved to evaluate certain numerical intricacies of the two implementations. The results show that in dealing with normal impact problems, the choice of penalty factor and time step size using the penalty method is not an omissible act to obtain accuracy and stability, while there are no such manually-defined parameters using the Lagrangian method. Moreover, there seems to be a clear advantage of the Lagrangian method in which much less mesh elements are needed to achieve the same accuracy compared to those of the penalty method.

A novel micromechanical approach is proposed to calculate the effective thermal conductivities of fiber reinforced composite materials. The key advantage of the present formulation is its ability to yield closed form solutions for the effective thermal conductivity of composites in both longitudinal and transverse directions for three dimensional heat transfer problems. The obtained results are in good agreement with the experimental data reported in the literature. When compared with analytical and finite element solutions, the results are seen to be in better agreement with the hexagonal packed array compared to the square packed array which thus represents a more realistic model of the fiber distribution in the matrix medium.

The paper analyzes the issues relating to the applicability of innovative material systems for flexible composite armors. The authors made several samplings of aramid fibers (Kevlar 49) by replacing the epoxy resin base, which is often described in the literature, with the thermoplastic matrix - polyethylene (HDPE) and polypropylene (PP). The samples were fired with .38 Special Full Metal Jacketed (FMJ) ammunition produced by the S&B Company, and then the process of firing was modeled in the ABAQUS program. The advantages and disadvantages of the new material system including the possibility of its use in the construction of hybrid composite armors have been presented on the basis of the results of numerical analyses and ballistic tests.

A numerical study was undertaken to investigate the mechanical properties of metal-ceramic multilayer micro-pillars under compression. The model system contains alternating layers of aluminum (Al) and silicon carbide (SiC) above a thick silicon (Si) substrate. The finite element analyses show that the pillar deformed in a non-uniform manner under compression, especially when a tapered side wall was included in the model. The heterogeneous feature of the structure plays a significant role in influencing the apparent stress-strain response. The elastic property of the pillar compares favorably with the true composite modulus, but a large discrepancy was found in the plastic response. The difference in deformation behavior between homogeneous pillars and multilayer pillars, along with other geometric effects, were examined in detail.

In this paper, the comparisons of thermomechanical fatigue behavior of C/SiC and SiC/SiC fiber-reinforced ceramic-matrix composites (CMCs) subjected to different phase angles of θ = 0, π/3, π/2 and π have been investigated. The relationships between the fatigue damage mechanisms, phase angle, fatigue hysteresis dissipated energy, fatigue hysteresis modulus and fatigue peak strain, fiber/matrix interface debonding and sliding have been established. The differences between C/SiC and SiC/SiC composites under thermomechanical fatigue loading with different phase angles have been analyzed. The damage accumulation of 2.5D C/SiC and 2D SiC/SiC composites under thermomechanical fatigue loading have been predicted. With increasing of the phase angle, the fatigue hysteresis dissipated energy, fatigue peak strain and interface debonded length decrease for the SiC/SiC composite; however, for the C/SiC composite, the fatigue hysteresis dissipated energy, fatigue peak strain and the interface debonded length increase at the same cycle number.

In engineering, it is quite often to have applications of the heat transfer of conduction having domain heat generation present inside. The paper aims to present boundary element formulations for analyzing the three-dimensional heat-conduction in dissimilarly bonded anisotropic media involving quadratic volume heat sources. In this paper, the additional volume integral present in the boundary integral equation is analytically transformed to the boundary surface for the volume heat sources modeled by quadratic functions. The technique of domain-mapping is employed to treat the three-dimensional anisotropic heat conduction in multiply adjoined media with proper interfacial conditions provided. For showing our successful implementation, a few example cases are analyzed with verification of independent analyses by the finite element method.

This study presents a new exact-analytical solution for convective heat transfer of thermally fully-developed laminar nanofluid flows in a circular tube for the first time. In this problem, the pipe wall is exposed to a constant temperature. The solution is based on the Whittaker function and perturbation technique. In the nanofluid model, it is assumed that nanoparticles and base-fluid behave as a single-phase with average properties. In this study, the effects of Reynolds number, volume fraction of the particles, Peclet number, and particle diameter are investigated on the average heat transfer coefficient, surface mass transfer, and Nusselt number.

Convective heat transfer in a parallel plate microchannel gas flow is investigated analytically and numerically, considering the effects of viscous dissipation, pressure work, shear work, axial conduction and rarefaction. Analysis is performed with constant wall temperature and constant wall heat flux boundary conditions for both gas cooling and heating. The results presented demonstrate the significance of the combined effect of pressure work and viscous dissipation, shear work, rarefaction degree and axial conduction on microchannel convective heat transfer, in both the thermally developing and fully developed flow regions. Viscous dissipation and pressure work in a pressure-driven microchannel gas flow are of comparable magnitudes and may not be neglected from the energy equation. The shear work at the wall, which is effectively the combined effect of viscous dissipation and pressure work, needs to be included in the Nusselt number for better predictions of heat transfer.

In the present paper, we analyzed the effects of magnetic field on the three dimensional flow of a nanofluid having the suspension of ferrous nano-particles within the framework of a non-uniformly thicked sheet in a slip flow regime. The sheet of variable thickness is assumed to be stretched in horizontal and transverse directions. The effects of thermophoretic forces and Brownian motion have also been incorporated into the governing equations. The RK-Fehlberg-integration scheme with shooting technique is employed to resolve the altered governing non-linear differential equations. Velocity, temperature and concentration profiles are presented and discussed for two cases namely uniform thickness stretching sheet UTSS (n = 1) and variable thickness stretching sheet VTSS (n ≠ 1), and skin friction coefficient, reduced Nusselt number and Sherwood number are computed and analyzed through tables. The results reveal that heat and mass transfer processes over slendering sheet matches with those over a flat sheet in the presence of slip flow regime.

An underwater shock loading experimental device is used to simulate underwater explosion shock waves. The aim of this study is to investigate the influence of flyer momentum on the response of an aluminium plate to this underwater shock loading experimental device. The simulation accuracy can be verified by comparing theoretical data with the simulation and experimental results. Through simulations, an aluminium plate’s deformation and pressure specific impulse can be determined when flyers impact the piston at different velocities but at the same momentum. The aluminium plate's deformation and pressure specific impulse are constant when the flyers had constant momentum because both are directly proportional to the flyer momentum. The results have an important practical value for understanding and using this type of experimental device.

This study investigates the effect of bracket bonding-debonding on the tribological properties of human tooth enamel, when two different adhesives are applied. The nano-scratch experiment was performed on the enamel at untreated and under the bracket regions to obtain wear resistance, scratch hardness and friction coefficient. The results indicated that the tribological properties of the enamel vary significantly after bracket bonding-debonding. However, no significant difference exists between the effects of bracket bonding by the nano-composite and the composite adhesives on the tribological properties. Therefore, considering the mechanical and physical properties of the nano-composite adhesive, its bond strength for orthodontic bracket bonding and the influences on the enamel after removing the bracket, the use of nano-composite adhesive is suitable for orthodontic treatments.

This paper analyzes the speed of lateral movement of the Cross-stream Active Mooring (CSAM) system in an ocean current and its control methods in order to study the system's capability of tracking short term meandering of ocean currents for maximizing power generation capacity. The CSAM concept for marine current power features a hydro sail system that can deploy generator turbines transversely across streams in a marine current. The hydro sail system can further adjust the horizontal position of the turbines, by changing the angle of attack of the hydro sail, to actively track fast streams in the marine current to increase power generation capacity. A two-step motion model with analytical formulas was developed and analysis based on mechanics indicated that the simplified model is adequate to estimate the system speed. Using an example system, it was estimated that the proposed active mooring system is capable of matching typical lateral speed of short term meandering and tracking fast streams in an ocean current without any external propulsion other than controlling the angle of attack of the hydro sails. Methods of controlling the system speed of moving from one location to another were also developed.