Machining of metal matrix composites: effect of ceramic particles on residual stress, surface roughness and chip formation

Machining forces, chip formation, surface integrity and shear and friction angles are important factors to understand the machinability of metal matrix composites (MMCs). However, because of the complexity of the reinforcement mechanisms of the ceramic particles, a fair assessment of the machinability of MMCs is still a difficult issue. This paper investigates experimentally the effects of reinforcement particles on the machining of MMCs. The major findings are: (1) the surface residual stresses on the machined MMC are compressive; (2) the surface roughness is controlled by feed; (3) particle pull-out influences the roughness when feed is low; (4) particles facilitate chip breaking and affect the generation of residual stresses; and (5) the shear and friction angles depend significantly on feed but are almost independent of speed. These results reveal the roles of the reinforcement particles on the machinability of MMCs and provide a useful guide for a better control of their machining processes

Deformation mechanisms of MMCs under indentation

This paper investigates the deformation mechanisms of MMCs subjected to micro-indentation by a spherical indenter using a three-dimensional finite element modeling. It was found that deformation behavior, hardness and work hardening of MMCs were highly dependant on the location of indentation relative to particles, volume percentage of the particle, and the size ratio of indenter to particle. The hardness of an MMC varied in a complex manner depending on the restriction on the matrix flow by reinforced particles and work hardening of the matrix material. Hardness increased with the increase of volume percentage of reinforced particles and decrease of the size ratio of indenter to particle. Matrix flow due to indentation was highly non-uniform which generated an inhomogeneous strain filed in an MMC. These pose a question that the conventional definition of micro-hardness is not very appropriate for characterizing MMCs

Prediction of cutting forces in machining of Metal Matrix Composites

This paper presents a mechanics model for predicting the forces of cutting aluminium-based SiC/Al2O3 particle reinforced MMCs. The force generation mechanism was considered to be due to three factors: (a) the chip formation force, (b) the ploughing force, and (c) the particle fracture force. The chip formation force was obtained by using Merchant’s analysis but those due to matrix ploughing deformation and particle fracture were formulated, respectively, with the aid of the slip line field theory of plasticity and the Griffith theory of fracture. A comparison of the model predictions with the authors’ experimental results and those published in the literature showed that the theoretical model developed has captured the major material removal/deformation mechanisms in MMCs and describes very well the experimental measurements

An FEM investigation into the behaviour of metal matrix composites: tool–particle interaction during orthogonal cutting

An analytical or experimental method is often unable to explore the behavior of a metal matrix composite (MMC) during machining due to the complex deformation and interactions among particles, tool and matrix. This paper investigates the matrix deformation and tool–particle interactions during machining using the finite element method. Based on the geometrical orientations, the interaction between tool and particle reinforcements was categorized into three scenarios: particles along, above and below the cutting path. The development of stress and strain fields in the MMC was analyzed and physical phenomena such as tool wear, particle debonding, displacements and inhomogeneous deformation of matrix material were explored. It was found that tool–particle interaction and stress/strain distributions in the particles/matrix are responsible for particle debonding, surface damage and tool wear during machining of MMC

A concurrent multiscale method based on the meshfree method and molecular dynamics analysis

This paper presents a concurrent simulation technique for analysing the deformation of systems that need the integration of material properties from nanoscopic to macroscopic dimensional scales. In the continuum sub-domain, a weak-form meshfree based method using the radial basis function interpolation was employed, but in the atomic sub-domain, molecular dynamics analysis was used. The transition from the atomic to continuum domains was realized by transition particles which are independent of either the nodes in the continuum sub-domain or the atoms in the atomic sub-domain. A simple penalty method was used to ensure the compatibility of displacements and their gradients in the transition. A virtual cell algorithm was developed using a local quasi-continuum approach to obtain the equivalent continuum strain energy density based on the atomic potentials and Cauchy-Born rule. Numerical examples showed that the present method is very accurate and stable, and has a promising potential to a wide class of multiscale systems

Single-point scratching of 6061 A1 alloy reinforced by different ceramic particles

Aluminium alloys reinforced by ceramic particles have been widely used in aerospace and automotive industries for their high stiffness and wear resistance. However, the machining of such materials is difficult and would usually cause excessive tool wear. The effect of ceramic particles on the cutting mechanisms is also unclear. The purpose of this study is to investigate the cutting mechanisms and the relationship between specific energy of scratching and depth of cut (size effect). The single-point scratch test was carried out on 6061 Al and its composites reinforced by Al2O3 and SiC ceramic particles using a pyramid indenter. The results indicated that the scratch process was composed of rubbing, ploughing, plastic cutting and reinforcement fracture. A simple model was proposed to interpret the apparent size effect. The effect of reinforcement on the specific energy was correlated to the ratio of volume fraction to particle radius. The paper found that for machining MMCs, a larger depth of cut should be used to maintain a lower machining energy, especially for those with a larger ratio of volume fraction to particle radius

Engineering Education and Management - vol.2

This is the proceedings of the selected papers presented at 2011 International Conference on Engineering Education and Management (ICEEM2011) held in Guangzhou, China, during November 18-20, 2011. ICEEM2011 is one of the most important conferences in the field of Engineering Education and Management and is co-organized by Guangzhou University, The University of New South Wales, Zhejiang University and Xi’an Jiaotong University. The conference aims to provide a high-level international forum for scientists, engineers, and students to present their new advances and research results in the field of Engineering Education and Management. This volume comprises 122 papers selected from over 400 papers originally submitted by universities and industrial concerns all over the world. The papers specifically cover the topics of Management Science and Engineering, Engineering Education and Training, Project/Engineering Management, and Other related topics. All of the papers were peer-reviewed by selected experts. The papers have been selected for this volume because of their quality and their relevancy to the topic. This volume will provide readers with a broad overview of the latest advances in the field of Engineering Education and Management. It will also constitute a valuable reference work for researchers in the fields of Engineering Education and Management

Numerical Characterization of Machining-Induced Surface Damage in Composites

The surface integrity of a machined component influences its performance. For a fibre- reinforced polymer (FRP) composite, fragments during machining can get into a surface with micro-cracks, causing difficulties to the experimental assessment of surface integrity. This paper proposes a numerical characterization approach with the aid of the finite element (FE) method. It was found that this approach is convenient to show the fibre/matrix fracture and fibre-matrix debonding. The analysis revealed that fibre orientation significantly influences the surface topography and subsurface damage of a cut surface, and that vibration-assisted cutting can reduce the effect of fibre orientation