Fracture of materials at the microscopic level involves a characteristic length related to microstructure. However, a clear structure-property relationship is still absent in metallic glasses. Therefore, a physics-based expression is derived for the characteristic length (relevant to brittle fracture) in metallic glasses (MGs) in order to link the microscopic material features controlling the fracture process to the macroscopic material parameters. The derived characteristic length is associated to micro/nano structural fracture patterns, critical crack tip opening displacement as well as fracture toughness. Characteristic lengths of various metallic glasses are determined using the proposed expression and compared to the experimental results. Theoretical results are in very good agreement with the experimental results of various metallic glasses. Furthermore, the contribution of characteristic length as well as macroscopic material parameters such as Poisson’s ratio, yield strength, and Young’s modulus on fracture toughness (and fracture energy) is investigated and compared to the experimental results.

The butterfly plastic zone theory based on Mohr Coulomb criterion has been widely used in coal mine production. In order to verify the universality of the theory, it is necessary to compare the distribution of plastic zone under different strength criteria. Based on the elastic-plastic mechanics, the principal stress distribution function around the circular tunnel is deduced in the paper, and the boundary and radius of the plastic zone under different strength criteria are calculated. The results show that the change laws of the plastic zone around the circular tunnel under different strength criteria has the following commonness: firstly, with the increase of the lateral pressure coefficient, the shape of the plastic zone presents the change laws of “circle ellipse butterfly”; Secondly, with the increase of the lateral pressure coefficient, the radius of the plastic zone is exponential distribution, while the characteristic value is different when the radius of the plastic zone is infinite. At same time, it shows that the butterfly plastic zone has a low sensitivity dependence on the strength criterion, no matter which strength criterion is adopted, and the butterfly plastic zone will inevitably appear in the surrounding rock mass of circular tunnel in the high deviator stress environment; The plastic zone with butterfly shape is highly sensitive to the stress change, and the small stress change may promote the expansion of the plastic zone. This result is significant for us to understand and prevent rock engineering disasters and accidents.

This paper reported the designed approaches of cycloidal mechanisms, studied its dynamic forces and failure characteristics using finite element methods (FEM). A simplified cycloidal mechanism (CM) is constructed to fulfill dynamic analysis and reliability evaluation. The studied results show that the loads of the mechanism are shared mainly by a half of the outer rollers and the inner pins. The possible failures of the mechanism will occur at the inner pins caused by the bending stress, and at the cycloid disc induced by the contacting stress. The failure of the inner pins will dominate the damage of the mechanism. A method of evaluating stress variation is proposed for fulfilling reliability design. The stress variations are derived according to the data in dynamic analysis by regression analysis. The methods of design modification are reported for improve the reliabilities. The allowable loads of the CM can be decided accordingly based on the analyzed information.

In this investigation, the magnetohydrodynamic pulsatile flow of Casson nanofluid through a vertical channel embedded in porous medium with thermal radiation and heat generation/absorption has been analyzed using Buongiorno model. The influence of viscous and Joules dissipations are taken into account. The governing coupled partial differential equations are reduced to ordinary differential equations using perturbation scheme and then solved numerically by using Runge-Kutta fourth order technique along with shooting method. The impact of various emerging parameters on velocity, temperature, nanoparticles concentration, Nusselt number and Sherwood number distributions are analyzed in detail. Analysis indicates that the temperature distribution increases for a given increase in Brownian motion parameter and thermophoresis parameter, while it decreases with an increase in Hartmann number. Further, the nanoparticles concentration distribution decreases with an increase in the chemical reaction parameter and the Lewis number, while it increases for a given increase in the Brownian motion parameter.

This work examines the μ(I) relation that describes the effective friction coefficient μ of a dense granular flow as a function of flow inertial number I, at the center of a rotating drum from its flow onset to steady state using DEM. We want to see how the internal friction coefficient of an accelerating flow may be predicted so that the associated tangential stress can be estimated with the proper knowledge of the normal stress. Under the three investigated drum speeds (3, 4.5 and 6 rpm), the bulk normal stress, σn(y), is found to be a consistent linear depth profile throughout the flow development with a slope degraded from the hydrostatic value, Ph(y), due to lateral wall friction. With the discovery of a non-constant depth-decaying effective wall friction coefficient, we derive analytically a wall-degradation factor K(h) to give σn(y)= K(h)Ph(y). The depth profile of tangential stress, however, varies in time from a concave shape upon acceleration, τa(y), to a more linear trend at the steady state, τss(y). Hence, the μa-Ia profile (with μa=τ/σn) upon flow acceleration offsets from the steady μss(Iss) relation. A pseudo-steady acceleration modification number, ΔI, is proposed to shift the inertial number in the acceleration phase to I* = Ia+ΔI so that the μa-I* data converge to μss(Iss). This finding shall allow us to predict a transient tangential stress by τa(y) = μss(I*)K(y)Ph(y) using the well-accepted knowledge of steady flow rheology, hydrostatic pressure, and the currently developed wall-degradation factor.

The neuro-endoscopy is a surgical technique that allows the neurosurgeon to maintain a visual contact while operating inside the brain of a patient. A special instrument called the neuro-endoscope is inserted in the brain until the neurosurgeon reaches his/her target. Its manipulation requires a high level of training for neurosurgeons. To enforce both quality and safety of neuro-endoscopy, we propose a robotic manipulator based on a Spherical Decoupled Mechanism. This mechanical architecture has been modified from a 5-Bar Spherical Linkages and adapted to this medical application. It is able to generate a Remote Center of Motion of 2 Degrees of Freedom. It merges the advantages of parallel mechanisms with the kinematic and control simplicity of decoupled mechanisms, while having a very simple architecture. Motion capture experiments using a brain simulation model have been performed with a team of neurosurgeons to obtain the kinematic data of the neuro-endoscope during brain exploration. Based on the identified workspace, the mechanism has been optimized using kinematic performance and architectural compactness as criteria. An optimum mechanism has been selected, showing better kinematic performances than the original 5-bar spherical linkage mechanism.

The basic constitutive equations of theory of mixtures obtained for a mixture of two linear elastic solids can be used as an alternative way to describe the mechanical behavior of binary composite materials. Determining the load ratios carried by each constituent solid of a binary composite is one of challenges of this theory. In this study, the results of directly calculating the ratios of external load carried by each constituent solid for the case of perfectly bonded interface between binary mixture constituents are discussed. Thus, the effects of loading type and volume fraction of the constituent solids to the load ratios carried by each constituent solid are investigated by using three different loading cases and three different volume fractions. Finally, displacement, stress and diffusive force results of two constituent solids using the calculated load ratios are given.

In this research, the thermal transport behavior of the branched carbon nanotube (CNT) with T-junction was investigated using non-equilibrium molecular dynamics simulation. Both symmetric and asymmetric temperature-controlled simulations were imposed to evaluate how the heat flowed inside the branched CNT with three branches of equal length and same chirality. The branch length and strain effects on the heat flow were examined. In addition, the simulated heat flow was compared with the prediction made by conventional thermal circuit calculation based on diffusive phonon transport. The heat was observed to flow straight rather than sideway inside the branched CNT with T-junction under the asymmetric temperature setup; this finding contradicts the conventional thermal circuit calculation. There are two possible explanations for this phenomenon. One is ballistic phonon transport and the other is phonons have different interactions or scattering with the defective atomic configurations at the T-junction. Moreover, the tensile strain could tune the heat flow, a finding that might be useful in thermal management applications.

When dealing with ice structure interaction modeling, such as designs for offshore structures/icebreakers or predicting ice cover’s bearing capacity for transportation, it is essential to determine the most important failure modes of ice. Structural properties, ice material properties, ice-structure interaction processes, and ice sheet geometries have significant effect on failure modes. In this paper two most frequently observed failure modes are studied; splitting failure mode for in-plane failure of finite ice sheet and out-of-plane failure of semi-infinite ice sheet. Peridynamic theory was used to determine the load necessary for inplane failure of a finite ice sheet. Moreover, the relationship between radial crack initiation load and measured out-of-plane failure load for a semi-infinite ice sheet is established. To achieve this, two peridynamic models are developed. First model is a 2 dimensional bond based peridynamic model of a plate with initial crack used for the in-plane case. Second model is based on a Mindlin plate resting on a Winkler elastic foundation formulation for out-of-plane case. Numerical results obtained using peridynamics are compared against experimental results and a good agreement between the two approaches is obtained confirming capability of peridynamics for predicting in-plane and out-of-plane failure of ice sheets.

Soils usually exhibit state-dependent frictional behaviour that undergoes plastic volumetric deformation. To correctly capture such response under the framework of classical plasticity, a non-associated flow rule using additional plastic potential is inevitably needed. Recently, a novel fractional plasticity (FP) without using plastic potential has been developed, and successfully applied in modelling the state-dependent nonassociated behaviour of soils. However, the energy dissipation characteristics of FP has not been probed in depth. This note examines the plastic dissipation behaviour of FP, when modelling the constitutive behaviour of soils. It is found that the plastic dissipation of FP increases continuously with the shear strain. However, the rate of plastic dissipation depends on the initial material state in relation to the critical state line.

This study presents the heat transfer analysis of 90° elbow microchannel flow with sharp and curved turn designs. Experimental technique of temperature-sensitive paint was adapted in the experiment for measuring both fluid and surface temperature. The detailed information of fluid and surface temperature data were successfully acquired with a microscope system at Reynolds number varying from 50.5 to 101.1. Micro heaters were fabricated and positioned underneath the microchannel to provide the constant heat flux boundary condition. The utilization of micro heaters can prevent the axial heat conduction. The Nusselt number contours were obtained in this study with sharp and curved corners, which can provide detailed information of localized region with high and low heat transfer. The experimental approach performed in this study could be applied in the future for micro heat exchanger or heat sink design with complex microchannel systems.

Design of a new gear pump requires many considerations to get good pump efficiency. In order to achieve optimal results, all parameters must be optimized from the design stage. In this study, ANSYS CFX was used to make parametric analysis in order to optimize a new design of gear pump. Two parameters which are inlet diameter and rotation speed are considered. The response surface method gives an optimum design point for inlet diameter of 15mm and rotation speed of 3500 rev/min. Twin vortices are created in the inlet and the outlet of pump, which strangle the flow. In order to reduce their negative effects on the flow, fillets are created at the inlet and the outlet of the pump.

To evaluate the dynamic properties of a coupled structure based on the dynamic properties of its substructures, this paper investigates the dynamic substructuring issue from the perspective of response prediction. The main idea is that the connecting forces at the interface of substructures can be expressed by the unknown coupled structural responses, and the responses can be solved rather easily. Not only rigidly coupled structures but also resiliently coupled structures are investigated. In order to further comprehend and visualize the nature of coupling problems, the Neumann series expansion for a matrix describing the relation between the coupled and uncoupled substructures is also introduced in this paper. Compared with existing response prediction methods, the proposed method does not have to measure any forces, which makes it easier to apply than the others. Clearly, the frequency response function matrix of coupled structures can be derived directly based on the response prediction method. Compared with existing frequency response function synthesis methods, it is more straightforward and comprehensible. Through demonstration of two examples, it is concluded that the proposed method can deal with structural coupling problems very well.

For a vibration system, the best designed spring is compliant to a desired vibration mode while it is robust to other undesired modes. There are several types of spring design for displacing the proofmass along the x and y axes, however, very few designs of spring compliant to the z axis are introduced. Therefore, we propose a z axis microactuator in which the suspending spring is designed so that it is only compliant to vibration along the z axis. The suspending spring consists of straight beam stages mechanically coupled with each other via frames which are symmetrically designed around a center plate. The operation characteristics of the microactuator is investigated by theoretical expresses and numerical simulation. The frequency split between the z axis mode and undesired modes can obtain more than 45%. The operation frequency can be modified in a wide range, from 68 kHz to 400 kHz, by changing the dimensional parameters of spring beams. The spring beams can be lengthened to increase displacement in the z axis while the mode cross-talk is still suppressed. Compared to the previously reported researches, the current microactuator shows robustness to undesired vibration modes, which is potential for integration in low mode cross-talk multi-axis micro-stages and low-noise mechanical sensors.