Chinmaya R. Dandekar

Multiphase Finite Element Modeling of Machining Unidirectional Composites: Prediction of Debonding and Fiber Damage

A multiphase finite element model using the commercial finite element package ABAQUS/EXPLICIT is developed for simulating the orthogonal machining of unidirectional fiber reinforced composite materials. The composite materials considered for this study are a glass fiber reinforced epoxy and a tube formed carbon fiber reinforced epoxy. The effects of varying the fiber orientation angle and tool rake angle on the cutting force and damage during machining are considered for the glass fiber reinforced epoxy. In the case of carbon fiber reinforced epoxy, only the effect of fiber orientation on the measured cutting force and damage during machining is considered. Two major damage phenomena are predicted: debonding at the fiber-matrix interface and fiber pullout. In the multiphase approach, the fiber and matrix are modeled as continuum elements with isotropic properties separated by an interfacial layer, while the tool is modeled as a rigid body. The cohesive zone modeling approach is used for the interfacial layer to simulate the extent of debonding below the work surface. Bulk deformation and shear failure are considered in the matrix for both the models and the glass fiber. A brittle failure criterion is used for the carbon fiber specimen and is coded in FORTRAN as a user defined material (VUMAT). The brittle failure of the carbon fibers is modeled using the Marigo model for brittle failure. For validation purposes, simulation results of the multiphase approach are compared with experimental measurements of the cutting force and damage. The model is successful in predicting cutting forces and damage at the front and rear faces with respect to the fiber orientation. A successful prediction of fiber pullout is also demonstrated in this paper.

Laser-Assisted Machining of a Fiber Reinforced Metal Matrix Composite

Metal matrix composites, due to their excellent properties of high specific strength, fracture resistance, and corrosion resistance, are highly sought after over their nonferrous alloys, but these materials also present difficulty in machining. Excessive tool wear and high tooling costs of diamond tools make the cost associated with machining of these composites very high. This paper is concerned with the machining of high volume fraction long-fiber metal matrix composites (MMCs), which has seldom been studied. The composite material considered for this study is an Al―2% Cu aluminum matrix composite reinforced with 62% by volume fraction alumina fibers (Al―2% Cu/Al 2 O 3 ). Laser-assisted machining (LAM) is utilized to improve the tool life and the material removal rate while minimizing the subsurface damage. The effectiveness of the laser-assisted machining process is studied by measuring the cutting forces, specific cutting energy, surface roughness, subsurface damage, and tool wear under various material removal temperatures. A multiphase finite element model is developed in ABAgUS/STANDARD to assist in the selection of cutting parameters such as tool rake angle, cutting speed, and material removal temperature. The multiphase model is also successful in predicting the damage depth on machining. The optimum material removal temperature is established as 300°C at a cutting speed of 30 m/min. LAM provides a 65% reduction in the surface roughness, specific cutting energy, tool wear rate, and minimum subsurface damage over conventional machining using the same cutting conditions.

Mechanics and Modeling of Chip Formation in Machining of MMC

Metal matrix composites (MMCs) offer high strength-to-weight ratio, high stiffness and good damage resistance over a wide range of operating conditions, making them an attractive option in replacing conventional materials for many engineering applications. Typically the metal matrix materials of MMCs are aluminum alloys, titanium alloys, copper alloys and magnesium alloys, while the reinforcement materials are silicon carbide, aluminum oxide, boron carbide, graphite etc. in the form of fibers, whiskers and particles. This chapter covers the mechanics of chip formation during machining of MMCs and various modeling techniques. Especially, modeling techniques dealing with cutting force, chip morphology, temperature and subsurface damage are covered.

Multi-Phase Finite Element Modeling of Machining Unidirectional Fiber Reinforced Composites

A multi-phase and a continuum based finite element model using the commercial finite element package ABAQUS is developed for simulating the orthogonal machining of composite materials. The materials considered for this study are a glass fiber reinforced epoxy composite and a ceramic matrix composite. The effect of varying the fiber orientation and tool rake angle on the cutting force, temperature distribution and damage during machining are considered. In the multi-phase approach the fiber and matrix are modeled as continuum elements with isotropic properties separated by an interfacial layer while the tool is modeled as a rigid body. The cohesive zone modeling approach is used for the interfacial layer. Bulk deformation and shear failure is considered in the fiber and matrix while the traction separation in the cohesive zone is used to ascertain the extent of delamination below the work surface. For validation purposes simulation results of the multi-phase approach are compared with experimental measurements. Parametric studies are conducted utilizing the equivalent homogenous (EHM) material model. The EHM simplifies the composite material into an anisotropic but locally homogenous material. External heating effect on the workpiece is considered in the EHM model to include preliminary results on Laser Assisted Machining. The model is successful in predicting cutting forces, temperature distribution entry and exit damage with respect to the fiber orientation.Copyright