Influence of strain rate on the stress-strain curve in the range of Lüders strain

Abstract

The influence of strain rate on the stress-strain curve of materials showing yield point phenomenon are determined in the range of small strains and high strain rates by means of the indirect impact tension test. With increasing deformation velocity, the LOders strain is found to increase considerably. The stress reduction after reaching the upper yield point, is not abrupt and takes place gradually with increasing strain. These phenomena are investigated on Armco iron, on the tempered steel 42 CrV 6, on pure tantalum and tungsten alloys. A simple mechanical model is introduced which shows that the LOders front velocity increases with strain rate approaching asymptotically the value of the plastic wave velocity as an upper limit. With this restriction, the local strain within the LOders band must increase by increasing the rate of elongation of the tensile specimen. The LOders strain could be estimated quantitatively as a function of strain rate. The model describes also the stress-strain function after reaching the upper yield point considering the limited stiffness of the test arrangement. EinfluB der Dehngeschwindlgkeit auf die Spannungs-Dehnungs-Kurve im Bereich der Ludersdehnung. Der EinfluB der Dehngeschwindigkeit auf die Spannungs-Dehnungs-Kurven von Werkstoffen mit ausqepraqter Streckgrenze wird im Bereich kleiner Dehnungen und hoher Dehngeschwindigkeiten im indirekten Schlagzugversuch ermittelt. Mit steigender Verformungsgeschwindigkeit nlrnrnt die LOdersdehnung deutlich zu, Der Spannungsabfall nach Erreichen der oberen Streckgerenze erfolgt bei hohen Dehngeschwindigkeiten nicht abrupt, sondern graduell und erstreckt sich Ober einen groBeren Dehnungsbereich. Diese Erscheinungen werden an Armco-Elsen, am vergOteten Stahl 42 CrV 6. an Reintantal und an Wolframlegierungen untersucht. Anhand eines einfachen, mechanischen Modells wird gezeigt, daB mit steigender Dehngeschwindigkeit die Geschwindigkeit der LOdersfront zunimmt und dem Wert der plastischen Wellengeschwindigkeit als oberem Grenzwert asymptotisch zustrebt. Durch diese Elnschrankunq muB die lokale Dehnung innerhalb des LOdersbandes mit steigender, globaler Verlangerung der Zugprobe zunehmen. DarOber hinaus beschreibt das Modell die Spannungs-Dehnungs-Kurven nach Erreichen der oberen Streckgrenze unter BerOcksichtigung der Nachgiebigkeit der PrOfanordnung.0 ' -------------------1 STRAIN Figure 1. Schematic representation of the stress-strain curve showing a yield point phenomenon the slip plane, the dislocation breaks away from the solute atom atmosphere. An alternative model [7] explains the stress drop at the upper yield point by dislocation multiplication in connection with dependence of the dislocation velocity on the stress.Under quasi-static loading, the localised yielding was studied early by determining the distribution of the reduction of area along tensile specimens [8]. In later investigations, the local strain was determined continuously at different points along the specimen as a function of time using strain gages [9; 10] or inductive ...

Suppression of Inhomogeneous Plastic Deformation in Medium-Carbon Tempered Martensite Steel

“…The B4 band grows from points 4 ⃝~7 ⃝, and then degenerates from points 8 ⃝~10 ⃝. At point 12 ⃝, the B5 band forms along another direction at the initial positions of the B3 and B4 bands. At point 13 ⃝, a new band (B6 band) forms at the left side of the B5 band.…”

“…Lüders deformation in a material is dependent on its microstructural factors and working environments. The former involves the microstructure type, microstructural morphology and grain size [5][6][7][8], and the latter includes applied stress [9,10], strain rate [11][12][13], specimen size [13,14], and temperature [15].…”

Influence of specimen geometry and strain rate on elongation in tensile testing of packaging steel

“…Likewise, there is also strain rate dependency in the expansion of slip bands. Magd et al [7] explored a proportional relationship between slip band velocity and strain rate since the stress reduction after reaching the upper yield point occurs not abruptly at high strai-rates, but gradually and extends over a wider range of strain. In 2003 Sun et al [8] proposed a model, which expresses Lüders strain as a function of gauge-length strain rate.…”

Plastic Instability in Medium-Carbon Tempered Martensite Steel

“…The type of plastic instability can be identified from the typical characteristic on the tensile curve: a yield plateau for the Lüders deformation [ 4 , 5 ] or a jerky flow (a series of serrations) for the PLC effect [ 7 , 8 , 9 , 10 , 11 ]. Lüders deformation is dependent on the applied stress [ 12 , 13 ], grain size [ 14 , 15 ], strain rate [ 16 , 17 , 18 ], specimen size [ 18 , 19 ], and temperature [ 20 ]. The PLC effect is strongly influenced by the temperature [ 21 ] and strain rate [ 22 ].…”