Papers by Keyword: Plasticity

Abstract: This contribution presents a methodology for the structural analysis of the exhaust manifold of an internal combustion engine. In particular, the thermal loading and the related thermal fatigue damage mechanism are addressed. The component investigated is a melted exhaust manifold which includes the turbine involute. The complex geometry of the component derives from the project constrains in terms of engine performance and sound targets. Finite Element simulations are performed to obtain a virtual approval of the component geometry, in advance with respect to the component manufacturing. The Finite Element analysis accurately follow the experimental approval procedure which considers different warming and rapid cooling cycles to mimic typical engine operating conditions. Two particular aspects of the developed numerical methodology are described in details: a) the elasto-plastic behaviour of the material at high temperatures; b) a damage criterion for thermal fatigue. Following the Ferrari expertise derived by previous experimental and numerical analysis of other exhaust manifolds, the increase of the equivalent plastic strain registered for a single thermal cycle (delta PEEQ) is firstly adopted as a damage criterion. The methodology reveals itself to be well correlated with the experimental evidences thus limiting the number of tests necessary for the component approval.

Abstract: Thin-walled pipes made of copper alloys – the brass grades L96, L68, L63, LANKMc; the bronze grade BrOF (the GOST state standard) are of great demand in aircraft, shipbuilding, automotive, defense, diesel and instrument-making industries. Pipe diameter ranges between 4.0 and 20 mm, and wall thickness is in the range from 0.1 to 0.6 mm. The manufacture of these pipes using traditional technological schemes is characterized by high labor input and low stability in providing quality characteristics, such as dimensional accuracy, the presence of surface defects and the level of mechanical properties. This study presents scientific evidence, new technological schemes developed for manufacturing pipes made of copper alloys with the use of the equipment and technology of multiple drawing on a long movable mandrel and results of their adoption at Revda Non-Ferrous Metal Processing Works JSC.

Abstract: The paper focuses on the analysis of the eccentricity effect in the measurement of the hole-drilling residual stress. Relaxed strains were evaluated by computational simulation of the hole-drilling experiment using the finite element method. Errors induced by eccentricity were estimated for elastic and elastic-plastic states in area around the drilled hole due to the stress concentration. The invariance of the stress change with depth was assumed. The correction of eccentricity and plasticity effects in evaluation of residual stresses was realized within the EVAL 7 software (SINT Technology). The analysis shows that in elastic state the eccentricity and angular position of the drilled hole have a significant effect on relative residual stress errors. Correction according to the HDM method is very effective in this case. If the relative error of 5 % is allowed, which is in engineering practice acceptable, eccentricity of ±0.05 mm could be accepted without correction. When the combination of eccentricity and plasticity occurs, the correction of plasticity is more important in method 13-EXT-UN.

Abstract: A theoretical and experimental study was carry out to investigate deformation mechanisms in a textured titanium alloy. In situ neutron diffraction measurements were performed to analyze different {hk.l} family planes ({10.0}, {10.1}, {11.0} and {00.2}) and determine the corresponding internal strain pole figures. This method was applied to a pure titanium (a-Ti) submitted to a uniaxial tensile load up to 2 %. The experimental data was then used to validate the EPSC model in order to predict the distribution of lattice strains determined by neutron diffraction for various diffraction vector directions. This comparison reveals that the model results were in good agreement with the experimental data and the simulations reproduced the lattice strain development observed on the strain pole figures determined by neutron diffraction.

Abstract: Single Point Incremental Forming (SPIF) is a recent technology of forming sheet in several decades. Nowadays, SPIF technology is still continued to be studied, applied and ameliorated in sheet manufacturing in industry. However one of the difficulties of the technology is the forming angle is still small (smaller than 80⁰ according the properties of metal sheets). This paper recommends a measure of increasing the plasticity of the sheet by heating in time of forming by SPIF technology. Naturally, the plasticity of metal sheet increases by the temperature of the material in forming process with its limitation and constraint. The paper represents the effect of heating metal sheet through the empirical process of SPIF technology directed by the design of experiment (DOE). The analyses of the results of experimental process is applied to show the effect of heating to the precision of Titanium sheet. Finally, some private opinions about the heating in SPIF are also mentioned as a very tiny contribution of the research for the new technology.

Abstract: In several last decades, Single Point Incremental Forming named as SPIF, a branch of Incremental Sheet Forming (ISF), is an advanced flexible manufacturing process to produce complex 3D sheet products especially for unique models such as personal cranium, cheek-bone,…applied in surgery. Presently, the SPIF technology has been continuously studied, applied and perfected for metal sheet manufacturing, especially Titanium and its alloys in some industrial sectors like aerospace, chemical engineering, and medical surgery. However, the formability of Titanium alloys is limited at room temperature that causes so many failures and tears of sheet workpiece when forming. This paper recommends a measure of increasing the plasticity of the formed metal sheet by heating. This paper studies on the effect of the control of temperature to increase the plasticity of the sheet workpiece. The accuracy of dimensions of the products under the effect of springback phenomenon in forming process at normal and high temperature of workpiece is also studied to show the effect of hot SPIF. The design of experiment (DOE) is also mentioned in this paper to select a set of suitable input parameters for the empirical process.

Abstract: Studies of the properties steels and alloys in the liquid and solidity conditions bear witness that the technical peculiarities of the receipt liquid metal in particular overheating have influence on the its properties and structure. The time-temperature treatment of the liquid metal influence on the structure of the liquid metal. The structure of the liquid metal influence on the character hardening and properties of the solidity samples in the one's turn. It should be noted the fact that place the just regularity take place: than extent of the melt equilibrium before crystallization is higher the solid metal distinguish oneself the better figures of the quality.

Abstract: Surface cracks have long been recognized as a major cause for potential failures of metal pipes. In fracture analysis, the widely used method is based on linear elastic fracture mechanics. However, for ductile metal pipes, it has been known that the existence of plasticity results in easing of stress concentration at the crack front. This will ultimately increase the total fracture toughness. Therefore, when using linear elastic fracture mechanics to predict fracture failure of ductile metal pipes, the plastic portion of fracture toughness should be excluded. Otherwise, the value of fracture toughness will be overestimated, resulting in an under-estimated probability of failure. This paper intends to derive a model of elastic fracture toughness for steel pipes with a circumferential crack. The derived elastic fracture toughness is a function of crack geometry and material properties of the cracked pipe. The significance of the derived model is that the well-established linear elastic fracture mechanics can be used for ductile materials in predicting the fracture failure.

Abstract: A succinct description of advanced constitutive models for applications to forming process simulations is provided. These models are continuum-based because they are more efficient in terms of computation time than microstructure–based models. However, they are so–called advanced because they are considered in many scientific studies but rather scarcely used in industrial applications. In addition, the relationship between these continuum constitutive models and multi-scale approaches based on crystal plasticity, dislocation dynamics and mechanics of multi-phase materials, such as advanced high strength steels, is substantiated.

Abstract: Metal forming of magnesium alloys often performed at elevated temperature, because magnesium alloys exhibit peculiar stress-strain relation and inferior ductility compared to conventional metals at room temperature. In the present study, deformation behavior and formability of cast and extruded AZ31 magnesium alloys under uniaxial and biaxial compressions at room temperature and at elevated temperatures were investigated. The results revealed that the compressive stress-strain relation of AZ31 magnesium alloy changed not only with the initial texture but also with the deformation temperature. The temperature dependency of flow stress of the cast alloy was smaller than that of the extruded alloy probably because of less influence of pre-deformation. In addition, the influence of compressive deformation pattern upon flow stress of the extruded alloy remained even at elevated temperature to 523 K. The temperature dependency of compressive fracture was also discussed and it was found that the equi-biaxial condition improved the compressive formability at elevated temperatures.