Beitrag zur Frage, ob beim Zugversuch die Bestimmung der oberen oder unteren Streckgrenze vorgeschrieben werden soll/ Contribution to the question whether the determination of the upper or lower yield stress should be specified with the tensile test/ Contribution à la question si, en rapport avec l’essai de traction, il faut prescrire la détermination de la limite élastique supérieure oi inférieure

High fluidity concrete exhibits an excellent self-compacting property. However, the application of typical high-fluidity concrete is limited in the normal strength range (18~35 MPa) due to the large amount of binder. Therefore, it is important to solve these problems by adding a viscosity modifying agent (VMA) with a superplasticizer (PCE), which helps to improve the fluidity of the concrete. In addition, the rheology and stability of the concrete with VMA can be improved by preventing bleeding and segregation issues. Current studies focused on the physical phenomena of concrete such as the fluidity, rheological properties, and compressive strength of normal-strength, high-fluidity concrete (NSHFC) with different types of a polycarboxylate-based superplasticizer (NPCE). The obtained results suggested that the combinations of all-in-one polycarboxylate-based superplasticizers (NPCE) did not cause any cohesion or sedimentation even stored for a long time. The combination of three types of VMA showed the best fluidity (initial slump flow of 595~630 mm) without any segregation and bleeding, and the compressive strength at 28 days was also found to be the highest: 34–37 MPa. From these results, the combination of PCE (2.0%) + HPMC (0.3%) + WG (0.1%) + ST (0.1%) showed an 18% higher plastic viscosity and -4.4% lower yield stress than Plain.

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On the Propagation of Lu¨ders Bands in Steel Strips

Journal of Applied Mechanics ◽

10.1115/1.1328348 ◽

2000 ◽

Vol 67 (4) ◽

pp. 645-654 ◽

Cited By ~ 48

Author(s):

S. Kyriakides ◽

J. E. Miller

Keyword(s):

Yield Stress ◽

Strain Level ◽

Finite Element Models ◽

Localized Deformation ◽

Lower Yield ◽

Lower Yield Stress ◽

Fine Grained ◽

Steel Strips ◽

Initiation And Propagation ◽

Transient Events

The initiation and propagation of Lu¨ders-type localized deformation in thin, fine grained steel strips in tension is studied through combined experimental and analytical efforts. Purely elastic deformation is terminated (upper yield stress) by localized deformation which tends to initiate along preferred directions. The strain level associated with this material instability is limited to two to five percent. When this strain level is achieved locally, the instability propagates via inclined fronts which separate coexisting regions of essentially elastic and plastically deformed materials. Under displacement controlled stretching, one or two fronts propagate in a steady-state manner (lower yield stress). The propagation of one and two fronts are simulated numerically using finite element models in which the material is modeled as a finitely deforming elastoplastic solid with an up-down-up nominal stress-strain response. The simulations capture the major events observed in the experiments such as the initiation process, the propagation of inclined fronts, kinking of the strip and the build up of moments, and the periodic straightening and moment reduction through transient events. This confirms that structural effects play a major role in the evolution of observed events. [S0021-8936(00)01604-4]

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The Yield Phenomena of a Medium Carbon Steel under Dynamic Loading

Proceedings of the Institution of Mechanical Engineers ◽

10.1243/pime_proc_1949_161_017_02 ◽

1949 ◽

Vol 161 (1) ◽

pp. 165-175 ◽

Cited By ~ 8

Author(s):

F. V. Warnock ◽

D. B. C. Taylor

Keyword(s):

Carbon Steel ◽

Yield Stress ◽

Testing Machine ◽

Strain Curve ◽

Medium Carbon Steel ◽

Impact Testing ◽

Lower Yield ◽

Lower Yield Stress ◽

Medium Carbon ◽

True Shape

The paper describes dynamic tensile tests carried out on a medium carbon steel to determine the true shape of the stress-permanent strain curve for rapid straining. The variation of this curve with change in strain rate, and the progressive deformation of the steel are also studied. An impact testing machine was used, straining being carried out as a series of dynamic loadings, and the stress was measured by means of electrical resistance strain gauges attached directly to the specimens. Comparison is effected between dynamic and static stress-strain curves, the existence of a “dynamic upper yield stress” and a “dynamic lower yield stress” being shown, together with a difference in the rate of strain hardening for the two straining conditions. Non-uniform yielding of the metal is shown to be more pronounced for dynamic straining and, like static yielding, to be an integral part of the lower yield stress phenomenon. The manner in which all these factors are affected by normalizing the steel is shown. A special form of deformation of the steel peculiar to rapid straining is indicated. Theoretical and experimental facts are used to deduce a theory for the observed increases in stress, and the use of these dynamic stresses for design purposes is discussed.

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