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?

Process Simulation to Improve Quality and Increase Productivity in Rolling, Ring Rolling and Forging

Edge fracture is a common problem when forming advanced high strength steels (AHSS). A particular case of edge fracture occurs during a collar forming/hole extrusion process, which is widely used in the sheet metal forming industry. This study attempts to relate the edge stretchability in collar forming to the strain hardening along the pierced edge; thus, Finite Element (FE) simulations can be used to reduce the number of experiments required to improve cutting settings for a given material and thickness. Using a complex-phase steel, CP-W 800 with thickness of 4.0 mm, a single-stage piercing operation is compared with a two-stage piercing operation, so called shaving, in terms of strains along the pierced edge, calculated by FE simulation. Results indicated that strains were reduced along the pierced edge by shaving. These results are correlated with experimental observations made at the Technical University of Munich (TUM) where better hole expansion ratios (HERs) were obtained using shaving as opposed to single-stage piercing. Moreover, in this study, the combination of cutting parameters that would generate the least edge strain hardening is evaluated based on simulation results. This approach could reduce the need for hardness measurements along the pierced edge as well as the number of experiments required to improve the shaving process.

Estimation of Cutting Parameters in Two-Stage Piercing to Reduce Edge Strain Hardening

Plastic Deformation of Copper and Steel in Hot Extrusion Through Conical Dies

: See also AD-711 544.(*forging, mechanics), dies, forge presses, stresses, deformation, stainless steel, titanium alloys, hydraulic presses, instrumentation*closed die forgingThe report represents the results of work completed under this manufacturing improvement program. The program covered the following specific areas; (a) flow stresses of metals, (b) instrumentation of forging presses, (c) evaluation and comparison of screw presses and mechanical presses for forging, (d) uniform compression tests and ring tests for determining the flow stress of metals, and (e) methods for predicting and measuring forging load under production conditions. It is expected that the information developed in this program will contribute to the improvement in the design and execution of forging operations.

Mechanics of Closed-Die Forging (Phase II)

The major purpose of the present study is to evaluate the performance of various galvanized (GI) or galvannealed (GA) mild steels and AHSS in stamping applications. Finite Element Analysis (FEA) of selected stamping operations was conducted to estimate the critical pressure boundary conditions that exist in practice. Using this information, laboratory tribotests, e.g. Twist Compression (TCT), Deep Drawing (DDT) and Strip Drawing (SDT) Tests, were developed to evaluate the performance of selected lubricants and die materials/coatings in forming galvanized steels of interest. The sheet materials investigated included mild steels and AHSS (e.g. DP600 GI/GA, DP780 GI/GA, TRIP780 GA and DP980 GI/GA). Experimental results showed that galvanized material resulted in more galling, while galvannealed material showed more powdering and flaking. The surface roughness and chemical composition of galvanized sheet materials affected the severity of galling under the same testing conditions, i.e. lubricants and die materials/coatings. The results of this study helped to determine the critical interface pressure that initiates lubricant failure and galling in stamping selected galvanized sheet materials. Thus, to prevent or postpone the critical interface conditions, the results of this study can be used to select the optimum combination of galvanized sheet, die material, die coating and lubricant for forming structural automotive components.

Taylan Altan

Papers

Process Simulation to Improve Quality and Increase Productivity in Rolling, Ring Rolling and Forging

Estimation of Cutting Parameters in Two-Stage Piercing to Reduce Edge Strain Hardening

Plastic Deformation of Copper and Steel in Hot Extrusion Through Conical Dies

Mechanics of Closed-Die Forging (Phase II)

Investigation of Galling In Forming Galvanized Steel Sheet