•Reactor pressure vessel weld material 73 W.•Flow curves from tensile test data and simplified coarse inverse finite element modelling were determined. Results are better than extrapolation of other ...existing popular models (power law, Voce model)•Tensile flow curves in irradiated and un-irradiated conditions at various temperatures (−100 °C up to room temperature) were obtained.•Application to fracture toughness of irradiated and un-irradiated pre-cracked Charpy V-notch specimens.•The extracted flow curves will be used to model mini compact tension (CT) and 1T-CT geometries in FRACTESUS.
The H2020 FRACTESUS project is aimed to validate miniaturized compact tension specimens usage for fracture toughness characterization of irradiated materials. One of the tasks in the project is devoted to the numerical simulations of the 0.16T and 1T-CT specimens and comparison of their stress/strain fields in. For this purpose accurate material flow curves are necessary to derive comparable mechanical response between the numerical models and experiments. This paper presents a simple technique of flow curve extraction from the tensile test using engineering stress–strain data. The proposed method utilizes a coarse meshed Finite Element Model and a manual flow curve data optimization procedure without additional scripting. The robustness of the method was shown on the example of the 73 W weld material in the unirradiated and irradiated states, tested at various temperatures from −100 °C to 125 °C. The obtained numerical flow curves are in a very good agreement with the experimental results. Moreover, the advantages of the proposed method were shown over either the methods based on extrapolation of the predictions of popular models with parameters fitted to prior necking or the method based on fracture diameter measurements. The final validation of the proposed methodology was demonstrated by numerical simulations of fracture toughness tests on precracked Charpy specimens.
In the last two decades, advances in synthetic, experimental and modeling/simulation methodologies have considerably enhanced our understanding of colloidal suspension rheology and put the field at ...the forefront of soft matter research. Recent accomplishments include the ability to tailor the flow of colloidal materials via controlled changes of particle microstructure and interactions. Whereas hard sphere suspensions have been the most widely studied colloidal system, there is no richer type of particles than soft colloids in this respect. Yet, despite the remarkable progress in the field, many outstanding challenges remain in our quest to link particle microstructure to macroscopic properties and eventually design appropriate soft composites. Addressing them will provide the route towards novel responsive systems with hierarchical structures and multiple functionalities. Here we discuss the key structural and rheological parameters which determine the tunable rheology of dense soft deformable colloids. We restrict our discussion to non-crystallizing suspensions of spherical particles without electrostatic or enthalpic interactions.
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•Classification of soft colloids using particle elasticity and interaction potential•Softness impacts significantly vitrification, crystallization and jamming.•Rheology is an exquisite tool to probe thermodynamic and kinetic transitions.•Mixtures of soft colloids exhibit rich state diagrams with new glassy and gel states.•Design strategies for colloidal materials with desired flow properties
Die kontinuierliche Beschreibung des Werkstoffverhaltens in großen Bereichen der Dehngeschwindigkeit (10
–10
s
) bei gleichzeitig hohen Temperaturen erfordert die Kombination verschiedener ...Formulierungen für die unterschiedlichen physikalischen Vorgänge während der Verformung. Im Bereich hoher Temperaturen bei gleichzeitig niedrigen Dehnraten sind Kriechprozesse maßgeblich, für den Bereich erhöhter Dehnraten (< 10
s
) bei niedrigeren Temperaturen findet plastisches Fließen statt. Im dynamischen Bereich (>10
s
) kann linear viskoses Werkstoffverhalten angenommen werden. Der Übergang zwischen diesen Prozessen wird mit Hilfe einer kontinuierlichen Funktion beschrieben. Anhand von Fließkurven an AA7075, Ck45N und TiA16V4, die bei Dehnraten von 10
–10
s
und Temperaturen von Raumtemperatur bis zu 900 °C ermittelt wurden, wird eine neue Beschreibung verifiziert, die diese drei Verformungsmechanismen in einer kombinierten Formulierung berücksichtigt.
Metal sheets are forward extruded at large plastic strains up to 1.6. The sheet specimens are placed between two half-cylindrical billets and cold-extruded collectively. While extruding the sheets, ...their central zone is plastically deformed nearly homogeneously under a deviatoric stress state equivalent to simple tension. Tensile test specimens are extracted from the extruded sheets at various extrusion strains delivering flow stresses at discrete large plastic strains of the flow curve. Sheet thicknesses as thin as 0.2 mm could be tested successfully. Steel and aluminum alloys with different strengths were investigated. Results were compared with in-plane torsion test measurements.
This review reflects different aspects of wide current studies of the phenomena related to the shear-induced structure transformation in various complex liquids. Experimental data, being the basis of ...this discussion, were obtained for polymeric liquids (melts, blends, solutions) and different dispersions (colloidal solutions, suspensions, emulsions). The general initial input of shearing is the creation of inhomogeneities which can continue to remain as separate domains, become the nuclei of new phases, or become diffuse, leading to phase separation. The following effects are discussed: diffusion-induced phase separation, phase transitions occurring mainly due to the deformation-driven orientation of polymer chains and worm-like micelles that results in the formation of a liquid-crystal state, as well as self-assembly effects. It can be stressed that the appearance of regular structures takes place in systems that can coexist in different concentrations or phase states at the same stress or shear rate. This is linked with the existence of two-value points on flow curves (part of a flow curve with negative slope) or transient regimes of deformation that lead to instability of the flow. The described experimental facts are briefly discussed on the basis of the application of different constitutive molecular or phenomenological rheological models.
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•The starting reason for shear-induced transitions is initial inhomogeneities.•Shear can initiate different effects related to the existence of separate.•The most significant phenomena are phase transitions and their segregation.•Shear-induced transitions can lead to structure and mechanical self-oscillations.•Shear-induced transitions are usually linked to double-values on flow curves.
Understanding and linking mechanical properties obtained by spherical indentation experiments to uniaxial data is extremely challenging. Since the first attempts in the early 20th century numerous ...advances gradually allowed to expand the output of indentation tests. Still, the extraction of flow curves from spherical nanoindentation has not yet been fully established, as tip shape problems and size effects impede a straight-forward implementation. Within this study, we show new calibration procedures originating from fundamental geometrical considerations to account for tip shape imperfections. This sets the base for strain-rate controlled tests, which in turn enables us to measure rate-dependent material properties either with constant strain-rate or by strain-rate jump tests. Finally, experimental evaluation of the constraint factor in consideration of the mechanical properties and induced strain enables the extraction of flow curves. Testing materials with refined microstructures ensures the absence of possible size-effects. This study contributes to a significant improvement of current experimental protocols and allows to move flow curve measurements from single spherical imprints one step closer to its implementation as a standard characterization technique for modern materials.
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•Novel calibration procedure for spherical tips based on fundamental geometrical considerations•Implementation of strain-rate controlled tests enhances utility of spherical nanoindentation test•Successful determination of strain-rate sensitivity by multiple constant strain-rate tests and strain-rate jump tests•Experimental determination of the constraint factor and introduction of a method to continuously obtain C* during testing•Extracted nanoindentation flow curve are in excellent agreement with comparative micropillar tests on the identical samples
•The conditions for the occurrence of magnetic fluid wall slip was studied.•The effect of wall slip on the magnetic fluid flow curve and yield stress was investigated.•A method for inhibiting the ...wall slip of the magnetic fluid was studied.
Magnetic fluid is a new type of smart material, and its rheological properties have always been a hot research topic, and how to measure quickly and accurately is also a research difficulty, among which wall slip is one of the important influencing factors. In this work, we studied the effect of wall slip on the flow curve and yield stress of the magnetic fluid. To this end, we used multiple rheometer rotors with different surface roughness. The flow curves of two magnetic fluids with different viscosities were drawn, and the Herschel-Bulkley model was used to fit them to determine the yield stress. In addition, a forced shear oscillation test was carried out on the magnetic fluid. We found when using a rotor with a smooth measuring surface to measure the flow curve of the magnetic fluid, the shear stress of magnetic fluid is underestimated at low shear rates. At the same time, the fitted values of yield stress of various roughness measurement surfaces were similar and greater than those of smooth measurement surfaces. From an engineering point of view, the fitting values of non-smooth measurement surfaces were more reliable. Affected by the wall slip, the storage modulus curve of the magnetic fluid often dropped suddenly during the frequency sweeping oscillation process. By changing the surface roughness of the measuring rotor, the wall slip during the oscillation sweep process was effectively restrained. The research results will have certain guiding significance for the study of the state of the solid–liquid interface junction in applications such as magnetic fluids sealing and lubrication.
The article presents the results of testing the flow curves of cast magnesium alloy MgAl9Zn1. Experimental tests were carried out on a deformation dilatometer in a compression test of cylindrical ...specimens heated to 380 °C, 400 oC, 420 °C at strain rates of 0,1 s-1, 1 s-1, 10 s-1. The experimental curves were described by functions used in programs for simulating metal forming processes based on the finite element method. The Generalized Reduced Gradient optimization method (GRDM) implemented in Microsoft Excel was used to determine the function coefficients. Based on the results obtained, the best functions characterizing the flow curves were selected for use in describing the material models used in numerical simulations of cast magnesium alloy MgAl9Zn1.
•Determination of flow curves for three different steels (DP600, DP1000, CP1000) up to strains of 1.159 with grooved torsion test.•Determination of fracture strains up to 1.159 for an AHSS with ...ultimate strength > 1150 MPa.•Analysis of preparation strategy of specimen on flow curves and fracture strain.•Milling with fine surface roughness recommended for determination of fracture strain.•Electrical discharge machining recommended for determination of flow curves.
In-plane torsion tests offer advantages such as a proportional loading path and a homogeneous stress and strain distribution when characterizing the material behavior in the state of in-plane shear. The use of a grooved specimen is mandatory for the characterization of the damage behavior. The manufacturing of the groove by turning, milling, and electrical discharge machining for a DP600, DP1000, and CP1000 showed a strong influence on the experimentally measurable strain values at failure. Fine machining by milling displayed good results for all tested materials. The notch-effect in turned grooves led to an early fracture initiation. A straightforward parameter identification scheme for the Hosford–Coulomb fracture criterion as proposed by 16 was used to show the sensitivity of fracture curves on the experimental database.
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