Computational modelling of impact damage in brittle materials

Electrical discharge machining (EDM) is a well-established machining option for manufacturing geometrically complex or hard material parts that are extremely difficult-to-machine by conventional machining processes. The non-contact machining technique has been continuously evolving from a mere tool and die making process to a micro-scale application machining alternative attracting a significant amount of research interests. In recent years, EDM researchers have explored a number of ways to improve the sparking efficiency including some unique experimental concepts that depart from the EDM traditional sparking phenomenon. Despite a range of different approaches, this new research shares the same objectives of achieving more efficient metal removal coupled with a reduction in tool wear and improved surface quality. This paper reviews the research work carried out from the inception to the development of die-sinking EDM within the past decade. It reports on the EDM research relating to improving performance measures, optimising the process variables, monitoring and control the sparking process, simplifying the electrode design and manufacture. A range of EDM applications are highlighted together with the development of hybrid machining processes. The final part of the paper discusses these developments and outlines the trends for future EDM research.

http://zclient.persiangig.com/ScienceDirect/M02.pdf

State of the art electrical discharge machining (EDM)

Introduction Metal forming process Analysis and technology in metal forming Plasticity and viscoplasticity Methods of analysis The finite element method (1) The finite element method (2) Plane-strain problems Axisymmetric isothermal forging Steady state processes of extrusion and drawing Sheet metal forming Thermo-viscoplastic analysis Compaction and forging of porous metals Three dimensional problems Preform design in metal forming Solid formulation, comparison of two formulations, and concluding remarks Index.

/pdf/metal-forming-and-the-finite-element-method-5ev6lca5h5.pdf

Metal Forming and the Finite-Element Method

http://digitalknowledge.cput.ac.za/bitstream/11189/4942/3/Makinde_Oluwole_D_Aziz_A_Eng_2011.pdf

Boundary layer flow of a nanofluid past a stretching sheet with a convective boundary condition

An account is given of the development of the idea of a yield stress for solids, soft solids and structured liquids from the beginning of this century to the present time. Originally, it was accepted that the yield stress of a solid was essentially the point at which, when the applied stress was increased, the deforming solid first began to show liquid-like behaviour, i.e. continual deformation. In the same way, the yield stress of a structured liquid was originally seen as the point at which, when decreasing the applied stress, solid-like behaviour was first noticed, i.e. no continual deformation. However as time went on, and experimental capabilities increased, it became clear, first for solids and lately for soft solids and structured liquids, that although there is usually a small range of stress over which the mechanical properties change dramatically (an apparent yield stress), these materials nevertheless show slow but continual steady deformation when stressed for a long time below this level, having shown an initial linear elastic response to the applied stress. At the lowest stresses, this creep behaviour for solids, soft solids and structured liquids can be described by a Newtonian-plateau viscosity. As the stress is increased the flow behaviour usually changes into a power-law dependence of steady-state shear rate on shear stress. For structured liquids and soft solids, this behaviour generally gives way to Newtonian behaviour at the highest stresses. For structured liquids this transition from very high (creep) viscosity (>106 Pa.s) to mobile liquid (

The yield stress—a review or ‘παντα ρει’—everything flows?

Third International Conference on Cold and Warm Forging Technology 1996 and Second International Conference on Sheet Forming Technology 1996

The trend in metal forming is to produce parts with increased precision and geometric complexity. Thus, research and development is being conducted worldwide to develop presses and tooling for near-net and net shape forming of difficult-to-form components. As a result, presses with increased precision and multi-action tooling are being used routinely by advanced companies around the world. This paper will discuss the interactions between press characteristics and part production in precision forming and review some of the new press and tooling designs recently developed by various domestic and foreign manufacturers.

Characteristics of forming presses and recent developments for precision and net shape forming

Ball-nose end milling operations are extensively used for 3-axis machining of sculptured surfaces. The process variables, such as chip thickness distribution and cutting speed distribution, can be simulated by means of discrete representation of the workpiece surface and the cutting tool. In the current approach, the workpiece surface is represented with a Z-map. The cutting edge of the tool is represented by a set of nodes. The purpose of this work was to develop a methodology for selecting the geometric resolution parameters required by the workpiece and the cutting tool. The selection criteria include: a) a prescribed amount of error in the prediction of the chip thickness and cutting speed and b) minimization of computation time. The current methodology is demonstrated for a finish milling operation with a ball-nose end mill.

/pdf/simulation-of-ball-nose-end-milling-operations-selection-of-3ld0uh62qp.pdf

Simulation of Ball-nose End Milling Operations - Selection of Geometric Resolution Parameters

Nonlinear elastic behavior and degradation of the E-modulus with increasing plastic strain in advanced high strength steels makes springback prediction more challenging. The conventional method for determining the E-modulus degradation with plastic strain is the loading-unloading-loading tensile test. This paper proposes a new methodology to determine E-modulus variation using a wipe bending operation. During wipe bending, the sheet material experiences simultaneous tension and compression loading through the sheet thickness, so the test conditions closely emulates actual metal forming conditions. Wipe bending tests for 1.2 mm MP980 steel sheet samples were conducted using different bending angles and springback was measured for each sample. A finite element model of the bending process was also developed. A constant apparent E-modulus was determined for each bending angle by comparing the springback predicted by the finite element model with the springback measured during the wipe bending test. Average effective strain was also calculated for each bending angle using FE simulations. A curve relating the E-modulus variation to effective strain was developed by correlating the apparent E-modulus and the average effective strain at each bending angle. Inputting this curve into the FE simulation revealed that springback prediction improved significantly compared to the case of using a constant E-modulus.

https://iopscience.iop.org/article/10.1088/1757-899X/418/1/012102/pdf

Determination of variable E-modulus through wipe bending test: application to springback prediction

An expansion device 2402 for radially expanding and plastically deforming a tubular member 1702, the expansion device comprising: a first tapered outer surface 2404 comprising one or more of the following: a curvature defined by a polynomial equation; and a first angle of attack ranging from about 6 degrees to about 20 degrees. The expansion device may have a second tapered outer surface having a second angle of attack ranging from about 4 degrees to about 15 degrees. The first tapered surface may comprise one or more facets in cross section, the number of facets ranging from about 12 to about 16.

Taylan Altan

Papers

Third International Conference on Cold and Warm Forging Technology 1996 and Second International Conference on Sheet Forming Technology 1996

Characteristics of forming presses and recent developments for precision and net shape forming

Simulation of Ball-nose End Milling Operations - Selection of Geometric Resolution Parameters

Determination of variable E-modulus through wipe bending test: application to springback prediction

Expansion cone for expanding a tubular member