Fracture in Taylor Rod Impact Test Specimens

High velocity contact-impact problems are of great interest in industries related to aerospace, mechanical and civil engineering. Ductile fracture often occurs in such applications. Taylor rod impact tests are used as experimental and numerical tests for determining the mechanical behaviour of materials subjected to high strain rates. At sufficiently high velocities, a significant plastic deformation leading to fracture is observed. In this paper, ductile fracture in Taylor rod made of AISI1045 steel is simulated using a continuum damage mechanics model. Simulations are performed for the velocity of 250 and 300 m/s. It is observed that, at lower velocities, tensile cracks are observed at the outer edge of the impact surface. On the other hand, at higher velocities, the fracture is observed at the central axis (confined fracture) as well as at the outer edge leading to fragmentation. Both the results are consistent with the experimental results available in the literature.

On the Transition From Creeping to Inertial Flow in Arrays of Cylinders

Many important natural processes involving flow through porous media are characterized by large filtration velocity. Therefore, it is important to know when the transition from viscous to the inertial flow regime actually occurs in order to obtain accurate models for these processes. In this paper, a detailed computational study of laminar and inertial, incompressible, Newtonian fluid flow across an array of cylinders is presented. Due to the non-linear contribution of inertia to the transport of momentum at the pore scale, we observe a typical departure from Darcy’s law at sufficiently high Reynolds number (Re). Our numerical results show that the weak inertia correction to Darcy’s law is not a square or a cubic term in velocity, as it is in the Forchheimer equation. Best fitted functions for the macroscopic properties of porous media in terms of microstructure and porosity are derived and comparisons are made to the Ergun and Forchheimer relations to examine their relevance in the given porosity and Re range. The results from this study can be used for verification and validation of more advanced models for particle fluid interaction and for the coupling of the discrete element method (DEM) with finite element method (FEM).

Numerical Simulations as a Reliable Alternative for Landmine Explosion Studies: The AUTODYN Approach

In order to validate the numerical procedure, the explosion of a mine was recreated within the non-linear dynamics software, AUTODYN. Two models were created and analysed for the purposes of this study — buried and flush HE charge in sand. The explosion parameters — time of arrival, maximum overpressure and specific impulse were recorded at two stand-off distances above the ground surface. These parameters are then compared with LS-DYNA models and published experimental data. The results, presented in table format, are in reasonable agreement.

Simulation of Thrombus Formation Process Using Lattice Boltzmann Method With Consideration of Adhesion Force to Wall

Recently artificial organs, especially rotary blood pumps, have been developed in the worldwide, but in this development, thrombus occurs in the pumps. In general, the main physical factors of thrombus formation are considered to be shear rate, wall properties for blood’s adhesion. But, there are no proper CFD codes for predicting thrombus formations using physical parameters in shear flows. In this paper, new model for predicting thrombus formation by considering aggregation and adhesion force to the wall by lattice Boltzmann method is proposed, and the trend of thrombus’s adhesion to the wall can be simulated more adequately than that of previous one.

Damage in Adhesive Joints During Low Cycle Fatigue

The objective of this research is to study the damage behavior of bulk adhesive and single lap joint (SLJ) specimens during low cycle fatigue (LCF). Fatigue tests under constant stress amplitude were done and strain response was measured through cycles to failure using the bulk adhesive and SLJ data. A non linear damage model was used to fit experimental results. Identification of the damage parameters for bulk adhesive was obtained from the damage against accumulated plastic strain plot. It is shown that the plastic strain can be obtained from the constant stress test if the instantaneous elastic modulus, i.e. modulus affected by damage, is evaluated for each cycle. On the other hand, damage in SLJ was seen mainly in the adhesive for itself — no substrate failure — this fact is used to propose that fatigue response in the joint is due to continuum damage accumulation in the adhesive as the number of cycles increases. Damage behavior under compressive loads was not taken into account but good correlation of numerical and experimental data was obtained. It was found that damage evolution behaves in a non linear manner as the plastic deformation grows for each cycle: on fatigue onset an accelerated damage grow is observed, then a proportional evolution, and finally a rapid failure occurs; this characteristics were seen in both the SLJ and bulk adhesive specimen. So far, this research takes the damage model found in a standard adhesive specimen and assumes it is accurate enough to represent the damage behavior of the SLJ configuration.

A Large-Deformation Theory for Thermally-Actuated Shape-Memory Polymers and its Application

The most common shape-memory polymers are those in which the shape-recovery is thermally-induced. A body made from such a material may be subjected to large deformations at an elevated temperature above its glass transition temperature &Vthgr;g. Cooling the deformed body to a temperature below &Vthgr;g under active kinematical constraints fixes the deformed shape of the body. The original shape of the body may be recovered if the material is heated back to a temperature above &Vthgr;g without the kinematical constraints. This phenomenon is known as the shape-memory effect. If the shape recovery is partially constrained, the material exerts a recovery force and the phenomenon is known as constrained-recovery.

Interaction Between Multiple Solid Objects and Bubbles

In the present study, bubble-particle interactions in suspensions are investigated by a coupled immersed-boundary and volume-of-fluid method (IB-VOF method), which is proposed by the present authors. The validity of the numerical method is examined through simulations of a rising bubble in a liquid and a falling particle in a liquid. Dilute particle-laden flows and a gas-liquid-solid flow involving solid particles and bubbles of comparable sizes to one another (Db/Dp = 1) are simulated. Drag coefficients of particles in particle-laden flows are estimated and flow fields involving multiple particles and a bubble are demonstrated.

Domain Reduction Method for Periodic Nanostructure Modeling: Gold Nanorods, Carbon Nanotubes and Graphene Applications

A domain-reduction approach for the simulation of one- and two-dimensional nanocrystalline structures is demonstrated. In this approach, the domain of interest is partitioned into coarse and fine scale regions and the coupling between the two is implemented through a multiscale interfacial boundary condition. The atomistic simulation is used in the fine scale region, while the discrete Fourier transform is applied to the coarse scale region to yield a compact Green’s function formulation that represents the effects of the coarse scale domain upon the fine/coarse scale interface. This approach facilitates the simulations for the fine scale, without the requirement to simulate the entire coarse scale domain. Robustness of the proposed domain-reduction method is demonstrated via comparison and verification of the results with benchmark data from fully atomistic simulations. Demonstrated applications include deformation of crystalline Au (111) nanorods, CNT bending and buckling, and graphene nanoindentation.

Performance Comparison of Frame Structures: Discrete Michell or Wolff?

The presented work highlights parallels between natural and human designs for optimization purposes. Wolff’s law predicts that bone trabeculae orientation alterations within a dynamic environment occur in such a way as to use bone material in a structurally efficient manner; this occurs because trabeculae orientations align themselves along principal stress trajectories. Michell has also demonstrated how to optimize structures under a given a set of mechanical loads. Some researchers have recently defined a special case for optimal tensegrity structures that produces the discrete Michell truss. In this paper we have carried out a performance comparison between two different frame structures modeled based on the Wolff’s hypothesis and optimal tensegrity formulation.

Effect of Interfacial Trellis Contact Forces in a Wire Rope

Tension resisting elements like wire ropes are critical elements in countless engineering applications ranging from material handling, construction site applications, tethers in underwater platforms, apart from stay cables in cable stayed bridges. The main advantage of the wire rope lies in its capacity to support large axial loads with high flexibility in bending and torsional modes. These properties are useful for their own storage, transportation and also in engineering applications where frequent bending is encountered in pulleys/sheaves/drums. The source of such a peculiar mechanical property of the rope can be attributed to the local relative movements between adjacent wires of the rope. A wire rope is a cable assembly consisting of a central core strand surrounded by a number of strands wound helically in a single or multi layers. The wires making up the strand are of helix patterns and when such strand combine to form a rope it takes up invariably another helix pattern, involving many times, a double helix arrangement. Depending on the nature of the contact of the helical wires at their interfaces the rope behaviour can be examined. Point or line contact forces, may arise, resulting in localised stresses. When these strands are assembled to form a wire rope, the complexity of the interfacial contact arrangement generally lead to simplified assumptions for predicting the rope response. An attempt is made in this paper to model a wire rope strand and deduce its equations of equilibrium, considering the interfacial contact forces and studying the associated slip of the wires. A mathematical model is developed to estimate the axial and torsional response of the rope. The effect of the interfacial forces is studied and compared with earlier researchers, where such considerations are not or partially made.