Parametric study of the conditions of supershear crack propagation in brittle materials

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in AIP Conference Proceedings 1683, 020209 (2015) and may be found at https://doi.org/10.1063/1.4932899.The paper is devoted to the numerical analysis of the conditions of acceleration of dynamically propagating longitudinal shear cracks from sub-Rayleigh to intersonic/supershear velocities. We showed that an ability of the initial crack to propagate in supershear regime can be predicted with use of the empirically derived dependence of the geometrical criterion of sub-Raleigh-to-intersonic transition on material and crack parameters

Investigation of initiation conditions of relative displacements of the fault-block media units under vibration loading

On the basis of computer modeling by the method of movable cellular automata the theoretical investigation of initiation conditions of relative displacements along the interfaces of complex stressed geological media blocks in the complex intense condition under local vibrating loading has been performed. It is shown, that defining factors at formation of unstable shift on the interblock border of fracture-block geological environments are the relative value of shift stresses and also the frequency of vibrating loading, i. е. time of impulse energy allocation. Low in power, but long-continued loadings on influences on high-voltage borders of section are the most effective in respect to power inputs

FOREWORD

Foreword to the thematic issue entitled: Adhesion and Friction: Simulation, Experiment, Applications

Investigation of regularities of formation and propagation of elastic vortices in surface layers of materials under dynamic contact loading

On the base of computer-aided simulation by movable cellular automaton method regularities of formation of vortices in surface layers of materials under dynamic contact loading were investigated. It was shown that the dynamic contact loading leads to the formation of an elastic vortex in the area of contact interaction and its subsequent propagation in the volume of material. Direction of vortex movement essentially depends on the velocity of contact loading and value of the contact pressure, which are determined features of the interaction of the material surface and the counterbody (e.g. stress state of contact area)

3D modelling of material flow in friction stir welding using movable cellular automaton method

The paper is devoted to the theoretical investigation of the peculiarities of material flow taking place in friction stir welding (FSW). The investigation was based on 3D computer simulation by the movable cellular automaton (MCA) method, which is a representative of the particle methods in mechanics of materials. Usually, material flow in FSW is simulated based on computational fluid mechanics, which assumes that the material is a continuum and does not take into account the material structure. MCA considers a material as an ensemble of bonded particles. Breaking of inter-particle bonds and formation of new bonds enables simulation of crack nucleation and healing, as well as mas mixing and microwelding. The simulation results showed that using pins of simple shape (cylinder, cone, pyramid) without shoulder results in small scattered displacements of the plasticised material in the workpiece thickness direction. Nevertheless, the optimal ratio of the longitudinal velocity to the rotational speed allows transporting of the welded material around the pin several times and producing the joint of good quality. Applying additional ultrasonic vibration to the pin may lead to better mixing of the plasticized material behind the pin

A coupled discrete-element model of fluid-saturated rock and the results of studying of the impact of a fluid on the shear strength of a rock under combined compression and shear

Within a discrete-element model of a porous permeable elastic-plastic rock, filled with a fluid, we have studied the shear strength of a fractured interface zone (a shear band) between blocks of a geological medium subject to compression and shear. Under these conditions, a fluid pore pressure is controlled by interplay of dilation of the elastic-plastic shear band and fluid transport between the blocks and the interface. We have found that the shear strength is a unique function of a combination of parameters, which includes viscosity of a fluid, permeability of the medium, shear rate and a characteristic size of the system. Based on the simulation results we have constructed the generalized binomial dependence of the shear strength of samples on the obtained combination of parameters

Theoretical study of strength of elastic-plastic water-saturated interface under constrained shear

This paper presents a theoretical study of shear strength of an elastic-plastic water-filled interface between elastic permeable blocks under compression. The medium is described within the discrete element method. The relationship between the stress-strain state of the solid skeleton and pore pressure of a liquid is described in the framework of the Biot’s model of poroelasticity. The simulation demonstrates that shear strength of an elastic-plastic interface depends non-linearly on the values of permeability and loading to a great extent. We have proposed an empirical relation that approximates the obtained results of the numerical simulation in assumption of the interplay of dilation of the material and mass transfer of the liquid

Role of vortex-like motion in contact loading of strengthening coating. Movable cellular automaton modeling

Movable cellular automata (MCA) is an efficient numerical method in particle mechanics, which assumes that any material is composed of elementary objects interacting among each other according to many-particle forces. In this paper MCA method is applied to modeling deformation of 3D coating-substrate system under its contact loading by rigid indenter. Main attention of the research is focused on the role of vortex-like structures in the velocity fields in deformation of the strengthening coating and substrate. The mechanical properties of model coating correspond to multifunctional bioactive nanostructured film (TiCCaPON) and the properties of substrate, to nanostructured titanium. Loading is performed by hard conical indenter. The peculiarities of velocity vortex formation and propagation, as well as its interaction with structural elements are studied. One of possible application of the study is non-destructive technique for detecting nanoscale defects in surface layer of a material using frequency analysis of the force resisting to sliding of a small counter-body on the material surface, known as tribospectroscopy. Possibilities of this technique are studied based on 3D modeling by MCA method for the above mentioned coating with nano-pores. It is shown that specific peaks at the friction force spectrum correspond to different geometrical characteristics of the nano-pores