Papers by Keyword: Plastic Strain

Abstract: The susceptibility of advanced high-strength steels (AHSS) to hydrogen embrittlement (HE) limits the broad utilization of these materials for body-in-white (BIW) components. The considerable decrease of both ductility and toughness due to local hydrogen accumulation inside of formed components may cause unpredictable time-delayed failure. In particular deep-drawn and punched AHSS components are prone to hydrogen absorption. This work investigates the influence of plastic deformation on hydrogen absorption of dual phase (DP) steels. For that purpose, tensile samples were machined out of three commercial 1.2 mm-thick DP sheets with ultimate tensile strengths of 626 MPa, 826 MPa and 1096 MPa. Samples were uniaxially pre-strained to 2 %, 5 %, 10 %, 15 % and 20 %. After pre-straining the samples were electrochemically charged with hydrogen, and the actual hydrogen contents were determined using a thermal desorption analyser (TDA). Before and after charging, the hardness of the samples was measured and the uniaxial quasi-static tensile properties were determined. In order to quantify the influence of plastic deformation on HE, slow strain rate tests (SSRT) were performed. The results of the tests were correlated with the fraction of martensite determined for each of the three steels.

Abstract: In this paper the issues of modeling the process of forming sheet materials using method of incremental forming for the manufacture of thin-walled non-axisymmetric parts. The proposed method of forming implemented by deformation of sheet material by providing the required trajectory of movement of the working tool in order to obtain the surface of a product of a given shape. Simulation and analysis of all experiment results are carried out.

Abstract: This paper examines the forming of sheet materials by incremental forming. Proposed and researched methods of deformation and the tool path based on which choice is the most appropriate circuits and paths for receiving the hemispherical parts. Abaqus software package is used to develop a method to model incremental forming. All simulation results are analyzed and considered during making conclusion about this forming process.

Abstract: — tailoring material properties to specific application requirements is one of the major challenges in materials engineering. Grain size is a key factor affecting physical and mechanical properties of polycrystals materials. Grain size reduction in the metals and alloys can be achieved using Equal channel angular pressing (ECAP) method. In this work, Nanostructure thin walled copper tube specimens with 1 mm wall thickness and 23mm diameter have been produced successfully with ECAP method using flexible polyurethane rubber pad to prevent the tube walls from collapsing. Furthermore, this paper details the development of a numerical simulation to analyse the fabrication of thin walled tube through ECAP process. A copper tube was pushed through a channel with a series of 90° bends. During each successive bend, the magnitude of plastic strains accumulate in the copper tube. A three dimensional numerical simulation was used to model the process and determine the extent of plastic deformation that takes place during each bend process. The numerical simulation was developed using the finite element (FE) code, ABAQUS V6.13, and analysed using the explicit solver.

Abstract: In this paper an experimental investigation of mechanical behavior of a thermoplastic polymer (polyamide PA 66) processed by constrained groove pressing (CGP) using several passes is presented. To this end, corrugating and straightening tools are designed and manufactured. The effects of the number of passes and the hold time on the mechanical behavior of the polyamide have been highlighted. The obtained results show that the material properties and the microstructure are significantly altered under CGP process. It has been found that the microhardness and the tensile properties have been progressed accordingly to the number of cycles, especially when the samples are processed using a hold time of five minutes. Hence, it can be concluded that this latter plays a very important role on the reorientation and stabilization of the microstructure when the processed material is a polymer.

Abstract: The object of this study is to highlight one the most encountered problems in the sheet metal forming. Cases of rupture on the mild steel sheet were recorded in a deep drawing workshop, during the forming operation of the wheelbarrows. The phenomenon appearance, led us to carry out a study of the material behavior during the metal forming. A characterization of the material is proposed and 3D simulations of the forming operation were performed on the finite element code Abaqus/CAE Explicit. The objective is to highlight the influence of the different deep drawing parameters on the sheet behavior during the deformation, especially the holding force, the die radius, the coefficient of friction between the contact surfaces and the punch velocity.The results are summarized in a representation of the strain curves in the three directions of the drawn part at the end of deep drawing operation, localization of the sheet areas which present a risk of tearing and the proposals to avoid this phenomenon depending on the variation of the operating parameters.

Abstract: Hammers are the key machine element of high-speed hammer mills which lead to the coal pulverisation process. Progressive material loss from the hammer occurs due to the mechanical interactions between the coal particles and the hammer surface. Coal pulveriser industries implement extensive efforts to combat against premature material loss from the hammer surface due to coal particle impact which may result in premature failure. This work investigates the erosion wear mechanism through computational simulation. A numerical model is developed using Abaqus^® to simulate the solid coal particle impacting onto the hammer (target).The Abaqus/Explicit^® dynamic simulation solver is used for this analysis. The interactions between the solid coal particles and the target are modelled using the Abaqus/Explicit^® element deletion method. The Johnson and Cook plasticity model is employed to analyse the flow stress behaviour of ductile materials during impact. The developed stress and plastic strain are analysed through simulation on the impact surface. This model is applied to different ductile alloys to determine the best erosion wear resistance hammer material for extending the operating life of hammers in the coal pulverisation process.

Abstract: The paper presents the dynamic behavior of gain for higher quality steel (armor) for the numerical simulation of fast processes, implemented in programs CAE, determined on the basis of results obtained from tensile tests of round samples conducted on the MTS testing machine type and rotary hammer, in terms of strain rate from 0,0001 to 500 s^-1 in tabular and equation JC. Posted simulation results armor penetration high quality steel bullet caliber 12,7 mm compared with experimental results.

Abstract: This work consists of determining the plastic strain value undergone by a material during a forming process using the instrumented indentation technique (IIT). A deep drawing steel DC01 is characterized using tensile, shear and indentation tests. The plastic strain value undergone by this steel during uniaxial tensile tests is determined by indentation. The results show that, the identification from IIT doesn’t lead to an accurate value of the plastic strain if the assumption that the hardening law follows Hollomon law is used. By using a F.E. method, it is shown that using a Voce hardening law improves significantly the identification of the hardening law of a pre-deformed material. Using this type of hardening law coupled to a methodology based on the IIT leads to an accurate determination of the hardening law of a pre-deformed material. Consequently, this will allow determining the plastic strain value and the springback elastic strain value of a material after a mechanical forming operation.

Abstract: Copper alloys are characterized by high plasticity and good resistance to corrosion. They are applied in electrical industry, telecommunication, in transport and machine building, particularly in the production of elements for deep drawing. The scope of investigation enclosed production of testing single crystals, determination of their crystallographic orientation, deformation of selected single crystals by compression in a temperature range from 20 °C to 400 °C, applying strain rate from 10^-5 s^-1 to 10^-1 s^-1 as well as microstructure observations. Typical plastic strain effects were observed in the microstructures of studied single crystals in the form of parallel and intersecting lines and slip bands with locally intensified density in different areas of cross section of examined specimen and the deflection bands with slightly marked slip lines in the primary system.