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Modelling and numerical investigation of the residual stress state in a green metal powder body
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0003-0910-7990
2005 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 155, no 3, p. 196-208Article in journal (Refereed) Published
Abstract [en]

Die pressing of metal powder results in a green body. After release from the die, the green body must have enough strength to be handled, to endure transport to a sintering furnace and heating to the sintering temperature. Drilling, turning and milling, which are common operations in the green state, require a green body of high strength, with no defects and excellent mechanical properties. A plane strain finite element model is used to analyse pressing of metal powder into a rectangular bar. The powder behavior is described by a "cap" model, which is implemented as a user material subroutine in the non-linear finite element program LS-DYNA. To improve modelling of strength in the green state a new non-linear density dependent failure envelope has been used. The model is adjusted to the properties of a water atomised metal powder from Hoganas AB. To resolve the severe stress gradient at the side surface of the green body, the smallest element size was chosen to be 65 μm. The aim of this work is to numerically capture and understand the development of the residual axial stress in particular at the side surface. The influence of kinematics, friction, compacting pressure and die taper are studied. Results from the numerical study show that the thickness of the compressive stress region close to the side surface of the green body varies between 50 μm and 600 μm along the surface. Compacting pressure, "upper punch hold down" and die taper geometry all have a significant influence on the residual stress state while die wall friction has only a small influence. The numerical results are in agreement with results from X-ray and neutron diffraction measurements.

Place, publisher, year, edition, pages
2005. Vol. 155, no 3, p. 196-208
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-6928DOI: 10.1016/j.powtec.2005.05.056ISI: 000231626600006Scopus ID: 2-s2.0-23744467718Local ID: 5424da80-ac89-11db-aeba-000ea68e967bOAI: oai:DiVA.org:ltu-6928DiVA, id: diva2:979814
Note

Validerad; 2005; 20061103 (ysko)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved

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Jonsén, PärHäggblad, Hans-åke

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