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?

A technique to compensate for temperature history effects in the simulation of non-isothermal forging processes

The design of a closed-die forging process requires the esti­ mation of maximum forging load and the necessary forging energy To determine the forging energy, the forging load at various stroke positions must be estimated In the past, empirical methods have been used with varying degrees of success The present study attempts to predict the forging load and stresses through relatively basic analytical methods Using the example of an axisymmetric forging, consisting of a flange and a shaft, the slab or Sachs method has been applied to develop a computer-simulation technique The forging process is analyzed in small steps of deformation The stress distribu­ tion, the load, and the magnitude of filling of the die and the flange have been estimated at each deformation step The theoret­ ical predictions have been compared with experimental results in forging the part from both lead and aluminum to various stroke positions with a hydraulic press The computer program simulating the axisymmetric forging pro­ cess, applied to an example in the present study, can be extended to other shapes and be used for various billet sizes, part dimen­ sions, temperature, ram speeds, and frictionconditions

Computer simulation to predict load, stress, and metal flow in an

An iterative FE simulation approach enhanced with numerical optimization schemes has been implemented for determination of optimum loading paths for tube hydroforming (THF) processes. A general optimization code, PAM‐OPT, has been applied to optimize several THF processes simulated by PAM‐STAMP. This paper discusses formulations of optimization of loading paths for various THF processes including a Y‐shape and a complex structural part. In the process optimization, the loading paths were represented by piecewise‐linear curve functions of which the control points were the design variables. Several objective functions and constraints were formulated to express the critical desirable part qualities.

Optimization of Loading Paths for Tube Hydroforming

Design of dies for radial forging of rods and tubes

The design of a closed-die forging process requires the estimation of maximum forging load and the necessary forging energy. To determine the forging energy, the forging load at various stroke positions must be estimated.

Taylan Altan

Papers

A technique to compensate for temperature history effects in the simulation of non-isothermal forging processes

Computer simulation to predict load, stress, and metal flow in an

Optimization of Loading Paths for Tube Hydroforming

Design of dies for radial forging of rods and tubes

Computer Simulation to Predict Load, Stress, and Metal Flow in an Axisymmetric Closed-Die Forging