Beitrag zur Ermittlung von Fließkurven im Verdrehversuch

Hecker, F. W.

doi:10.1002/srin.197102670

Cited by 5 publications

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“…However, since in most in length during the bending process. Another important fibre is the one where the circumferential cases the change of the initial flow stress will be less than 10 per cent [39,40] and the affected region will stress equals zero (radius r s ). In contrast to the unelongated fibre, the neutral fibre or surface remain relatively small, the omission of an explicit consideration of this effect is normally not likely to (radius r n ) in a further infinitesimally small strain does not undergo a change of length.…”

Section: Basics Of the Process Modelmentioning

confidence: 99%

Semi-analytical process modelling and simulation of air bending

Heller

Kleiner

2006

The Journal of Strain Analysis for Engineering Design

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Mathematical models for a fast semi-analytical simulation of the air bending process of thin as well as of thick sheets have been developed, implemented, and successfully been tested. In contrast to a large number of available approaches in this field that -for reasons of assuming the neutral fibre to coincide with the central fibre and the sheet thickness to remain constant -are limited to thin sheets, in the present work special attention has been paid to the mathematical description of the shift of individual fibres and the changes of thickness. The adequate modelling of these two effects is essential to ensure that the resulting simulation procedure is applicable in the same way to the bending of thin and, in particular, of thick sheets.The realistic mathematical modelling of the forming process, the accuracy of the results, and the very short computation times permit the simulation system to be used in productionrelated applications, such as CAPP systems, virtual prototyping environments, and machine control systems, in which commercial finite element analysis software can be utilized either not at all or only in a limited way. the focus of this paper, the solutions resulting from JSA113

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Section: Basics Of the Process Modelmentioning

confidence: 99%

Semi-analytical process modelling and simulation of air bending

Heller

Kleiner

2006

The Journal of Strain Analysis for Engineering Design

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“…However, the effect of the change in length of the specimen can normally be neglected. 20 Adiabatic heating of the specimen at high strain rates 21 and anisotropy22 are not only present in the torsion test but also in real metal forming processes. As the last step of test evaluation, a yield criterion has to be assumed for calculating the flow curve (Jf(¢' cP) from the curve riYp, Yp) obtained from equations (26), (27), (29), and (33).…”

Section: ·5mentioning

confidence: 99%

“…¢ time derivative of ¢ a radius of solid or tubular specimen at inner radius of tubular specimen B constant defined by equation (30) C constant in equation (8) Dij deformation rate tensor f mean value of fey, y) defined by equation (20) fey, y) 'correction function' for shape of flow curve f2(yp, Yp) second approximation of fey, y), for r = rp F force h height of upsetting test specimen jk(a, at) parameter defined by equation (19) 10 length of cylindrical section of specimen m strain rate sensitivity index M torque Mo calculated torque assuming zero approximation for flow curve n strain hardening exponent p abbreviation (p = n +m) P normalized torque r distance from axis of specimen distance) r p critical radius R notch radius x relative variation of dimension z axial coordinate (distance from median plan of specimen) f3 constant defined by equation ( (1) O"rt constant in equation (2) TO zero approximation for shear stress T 2 second approximation for shear stress…”

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confidence: 99%

Torsion testing – plastic deformation to high strains and strain rates

Pöhlandt¹,

Tekkaya²

1985

Materials Science and Technology

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A new method of calculating stress-strain curves from torsion measurements is .described. Contrary to the usual calculation of stress and strain at the surface of the specimen -where the material properties are distorted by microcracks, notch effects, etc. -stress and strain are determined at a 'critical radius' inside the specimen. For this purpose an initial approximation for the flow curve of the type (Jf""" ¢o¢m is improved by calculating a 'correction function' from the test results. This calculation is based on a Taylor series expansion which converges more strongly if tubular specimens are used instead of solid ones. Tubular specimens are therefore used if the flow curve appears to deviate strongly from the exponential law. The new method of test evaluation makes use of the fact that contrary to tensile and upsetting tests, in torsion tests the measured curve gives an almost undistorted linear projection of the flow curve. In fact the test evaluation consists only of 'calibrating' the measured torque and angle of twist in terms of yield stress or equivalent strain, respectively. MST/94 . cP. equivalent strain ¢ time derivative of ¢ a radius of solid or tubular specimen at inner radius of tubular specimen B constant defined by equation (30) C constant in equation (8) Dij deformation rate tensor f mean value of fey, y) defined by equation (20) fey, y) 'correction function' for shape of flow curve f2(yp, Yp) second approximation of fey, y), for r = rp F force h height of upsetting test specimen jk(a, at) parameter defined by equation (19) 10 length of cylindrical section of specimen m strain rate sensitivity index M torque Mo calculated torque assuming zero approximation for flow curve n strain hardening exponent p abbreviation (p = n +m) P normalized torque r distance from axis of specimen distance) r p critical radius R notch radius x relative variation of dimension z axial coordinate (distance from median plan of specimen) f3 constant defined by equation (10) y shear strain (finite Lagrangian strain tensor component) y shear strain rate Ya shear strain at radial distance r = a (surface) Ya time derivative of Ya Yat shear strain at inner radius r = at of tubular specimen Yat time derivative of Yat Yp shear strain at critical radius rp Y P time derivative of Yp Yr shear strain at radial distance r Yr time derivative of Yr e angle of twist e time derivative of e (J f yield stress O"t constant in equation (1) O"rt constant in equation (2) TO zero approximation for shear stress T 2 second approximation for shear stress

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“…Fur realistische Werte von pa weicht die vorgelegte ,,optimale" Losung von den Losungen nach [12, 141 nur wenig ab (dies gilt fiir alle praktisch moglichen Werte von p bzw. pot weil Schubspannung und Schiebung gemal3(17), (3) und(19) nur schwach von p b m . po abhangen).Daher kann fiir praktische Anwendungen die Frage nach dem zweckmaBigen Losungsverfahren aufgrund der Einfachheit entschieden werden: am einfachsten ist es, die Schiebung nach Jufenov und Cejko gemaB G1.…”

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Prüfung des plastischen Verhaltens metallischer Werkstoffe in Torsionsversuchen

Pöhlandt

Tekkaya

Lach

1983

Materialwissenschaft Werkst

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Testing the Plastic Behaviour of Metallic Materials by TorsionTests.The torsion test on cylindrical bars (bulk material) and the plane torsion test on thin sheet which has been developed recently are described and discussed with respect to their communities and their differences. In the torsion test on cylindrical bars the experimental data are conventionally used for calculating shear stress and shear strain for the specimen surface. However, the material properties are strongly distorted at the surface; therefore it is recommended to calculate shear stress and shear strain for a ,,critical radius" for which shear stress is only weakly dependent on the properties of the estimated shape of flow curve. It is shown that for this critical radius, stress and strain are almost independent of the notch effect caused by the shape of specimen. For the plane torsion test on thin sheet a "critical radius" is defined by the condition that shear strain is only weakly dependent on the properties of the estimated shape of flow curve. The calculation of stress and strain for the "critical radius" seems to result in a loss of information. However, the flow curve obtained this way is more reliable than that one obtained by the conventional method.

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Beitrag zur Ermittlung von Fließkurven im Verdrehversuch

Cited by 5 publications

References 0 publications

Semi-analytical process modelling and simulation of air bending

Semi-analytical process modelling and simulation of air bending

Torsion testing – plastic deformation to high strains and strain rates

Prüfung des plastischen Verhaltens metallischer Werkstoffe in Torsionsversuchen

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