scholarly journals Characterization of the Formability of High-Purity Polycrystalline Niobium Sheets for SRF Applications

2021 ◽  
pp. 1-19
Author(s):  
Jean-Francois Croteau ◽  
Guillaume Robin ◽  
Elisa Cantergiani ◽  
Said Atieh ◽  
Nicolas Jacques ◽  
...  
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
High Purity ◽  
High Speed ◽  
Theoretical Calculations ◽  
Rate Sensitivity ◽  
Forming Limit Diagram ◽  
Forming Limit ◽  
Zone Model ◽  
Nominal Strain Rate

Abstract The forming limit diagram of high-purity niobium sheets used for the manufacturing of superconducting radiofrequency (SRF) cavities is presented. The Marciniak (in-plane) test was used with niobium blanks with a thickness of 1 mm and blank carriers of annealed oxygen-free electronic copper. A high formability was measured, with an approximate true major strain at necking for plane-strain of 0.441. The high formability of high-purity niobium is likely caused by its high strain rate sensitivity of 0.112. Plastic strain anisotropies (r-values) of 1.66, 1.00, and 2.30 were measured in the 0°, 45°, and 90° directions. However, stress–strain curves at a nominal strain rate of ~10−3 s−1 showed similar mechanical properties in the three directions. Theoretical calculations of the forming limit curves (FLCs) were conducted using an analytical two-zone model. The obtained results indicate that the anisotropy and strain rate sensitivity of niobium affect its formability. The model was used to investigate the influence of strain rate on strains at necking. The obtained results suggest that the use of high-speed sheet forming should further increase the formability of niobium.

Cohesive Zone Model for Crack Propagation in a Viscoplastic Polycrystal Material at Elevated Temperature

2006 ◽  
Vol 306-308 ◽  
pp. 187-192
Author(s):  
Yan Qing Wu ◽  
Hui Ji Shi
Keyword(s):  
Grain Boundary ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Matrix Material ◽  
Rate Sensitivity ◽  
Zone Model ◽  
Dissipation Energy ◽  
Plastic Dissipation

This study looks at the crack propagation characteristics based on the cohesive zone model (CZM), which is implemented as a user defined element within FE system ABAQUS. A planar crystal model is applied to the polycrystalline material at elevated temperature in which grain boundary regions are included. From the point of energy, interactions between the cohesive fracture process zones and matrix material are studied. It’s shown that the material parameter such as strain rate sensitivity of grain interior and grain boundary strongly influences the plastic and cohesive energy dissipation mechanisms. The higher the strain rate sensitivity is, the larger amount of the external work will be transformed into plastic dissipation energy than into cohesive energy which could delay the rupturing of cohesive zone. By comparisons, when strain rate sensitivity decreases, plastic dissipation energy is reduced and the cohesive dissipation energy increases. In this case, the cohesive zones fracture more quickly. In addition to the matrix material parameter, influence of cohesive strength and critical displacement in CZM on stress triaxiality at grain interior and grain boundary regions are also investigated. It’s shown that enhancing cohesive zones ductility could improve matrix materials resistance to void damage.

scholarly journals Experimental determination and numerical prediction of the dynamic forming limits of a press hardened steel

2021 ◽  
Author(s):  
Nathalie Weiß-Borkowski ◽  
Junhe Lian ◽  
Anne Suse Schulz-Beenken ◽  
Thomas Tröster
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Rate Sensitivity ◽  
Numerical Prediction ◽  
Forming Limit ◽  
Failure Behavior ◽  
Rate Dependency ◽  
Strength Failure ◽  
Force Criterion ◽  
Automotive Steel

Material characteristics such as yield strength, failure strain, strain hardening and strain rate sensitivity parameter are affected by loading speed. Therefore, the strain rate dependency of materials for plasticity and failure behavior is taken into account in crash simulations. Moreover, a possibility for consideration of instability at multi-axial dynamic loadings in crash simulations is the use of dynamic forming limit curves (FLC). In this study, the dynamic FLC of the press hardened automotive steel Usibor 1500 (AlSi coated 22MnB5) is investigated. The experimental results are obtained from a unique high-speed Nakajima setup. Two models are used for the numerical prediction. One is the numerical algorithm CRACH as part of the modular material and failure model MF GenYld+CrachFEM 4.2. Furthermore, the extended modified maximum force criterion considering the strain rate effect is also used to predict the dynamic FLC. The comparison of the experimental and numerical results are presented and discussed.

Empirical Equations for a Study on Strain Rate Sensitivity of Polypropylene Syntactic Foam

2010 ◽  
Vol 143-144 ◽  
pp. 303-307
Author(s):  
En Yang Wang ◽  
Masaki Omiya
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Viscoelastic Properties ◽  
Elastic Moduli ◽  
Syntactic Foam ◽  
Rate Sensitivity ◽  
Empirical Equations ◽  
Syntactic Foams ◽  
Nominal Strain Rate ◽  
Nominal Strain

The strain rate sensitivity of polypropylene syntactic foams with polymer microballoons in the relative density from 0.5 to 0.8 is studied at the nominal strain rate ranged from 10-1 to 102 s -1. Two equations of matrix materials are introduced to represent the viscoelastic properties, and another two equations are proposed with respect to the parameters of matrix materials to estimate the elastic moduli and yield stresses of polymeric syntactic foams.

scholarly journals Formability of the 5754-Aluminum Alloy Deformed by a Modified Repetitive Corrugation and Straightening Process

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 633 ◽  
Author(s):  
Marco Ezequiel ◽  
Sergio Elizalde ◽  
José-María Cabrera ◽  
Josep Picas ◽  
Ignacio A. Figueroa ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Microstructural Analysis ◽  
Rate Sensitivity ◽  
Tensile Tests ◽  
Orientation Distribution ◽  
Sensitivity Coefficient ◽  
Mechanical Tests ◽  
Forming Limit

Sheets of 5754-aluminum alloy processed by a modified repetitive corrugation and straightening (RCS) process were tested in order to measure their formability. For this purpose, forming limit curves were derived. They showed that the material forming capacity decreased after being processed by RCS. However, they kept good formability in the initial stages of the RCS process. The formability study was complemented with microstructural analysis (derivation of texture) and mechanical tests to obtain the strain-rate sensitivity. The texture analysis was done by employing X-ray diffraction, obtaining pole figures, and the orientation distribution function. It was noticed that the initial texture was conserved after successive RCS passes, but the intensity dropped. RCS process did not induce β-fiber, contrary to common deformation process. The strain-rate sensitivity coefficient was measured through tensile tests at different temperatures and strain rates; the coefficient of the samples processed after one and two passes were still relatively high, indicating the capacity to delay necking, in agreement with the good formability observed in the initial passes of the RCS process.

scholarly journals Study on the Formability and Texture evolution of AA6061 Alloy Processed by Repetitive Corrugation and Straightening.

2021 ◽  
Vol 19 (5) ◽  
pp. 548-561
Author(s):  
Sergio Elizalde ◽  
Marco Ezequiel ◽  
José María Cabrera ◽  
Ignacio Alejandro Figueroa ◽  
María Teresa Baile ◽  
...  
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Texture Component ◽  
Texture Evolution ◽  
Cube Texture ◽  
Rate Sensitivity ◽  
Distribution Functions ◽  
Forming Limit ◽  
Uniaxial Tensile ◽  
Ultrafine Grained

The enhanced mechanical properties obtained by refining the grain size down to the ultrafine-grained (UFG) regime have attracted considerable attention in recent years. The severe plastic deformation (SPD) techniques allow obtaining ultrafine-grained materials. Different SPD techniques permit processing sheet shape materials such as repetitive corrugation and straightening (RCS) and accumulative roll bonding (ARB). In this study, the formability of an AA 6061-T6 processed by RCS was evaluated. The forming limit diagrams (FLD) were obtained by Nakazima tests of samples in initial condition (T6 state) and after one and two RCS cycles. The FLD curves showed that the forming capacity decreased from the first RCS cycle. Likewise, uniaxial tensile tests at different temperatures and strain rates were conducted to analyze the effect of the RCS process on the strain rate sensitivity. They showed a relatively high strain rate sensitivity coefficient in the samples after one and two RCS cycles, which indicates an improvement of i) the capacity of the material to delay the onset of the necking and ii) the formability at increasing temperatures. Finally, texture analysis was carried out employing X-ray diffraction, calculating the orientation distribution functions (ODFs). The initial texture showed a predominant cube texture component, whereas, for further RCS cycles, a weakening of the cube texture and an increment of the S texture component were observed.

scholarly journals Compressive Behaviour of Additively Manufactured Periodical Re-Entrant Tetrakaidecahedral Lattices at Low and High Strain-Rates

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1196
Author(s):  
Michaela Neuhäuserová ◽  
Tomáš Fíla ◽  
Petr Koudelka ◽  
Jan Falta ◽  
Václav Rada ◽  
...  
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
High Speed ◽  
Mechanical Response ◽  
Split Hopkinson Pressure Bar ◽  
Deformation Behaviour ◽  
Rate Sensitivity ◽  
Image Correlation ◽  
Strain Rates ◽  
Static Compression

Compressive deformation behaviour of additively manufactured lattice structures based on re-entrant tetrakaidecahedral unit-cell geometry were experimentally investigated under quasi-static and dynamic loading conditions. Specimens of four different structures formed by three-dimensional periodical assembly of selected unit-cells were produced by a laser powder bed fusion technique from a powdered austenitic stainless steel SS316L. Quasi-static compression as well as dynamic tests using split Hopkinson pressure bar (SHPB) apparatus at two strain-rates were conducted to evaluate the expected strain-rate sensitivity of the fundamental mechanical response of the structures. To evaluate the experiments, particularly the displacement fields of the deforming lattices, optical observation of the specimens using a high-resolution camera (quasi-static loading) and two synchronised high-speed cameras (SHPB experiments) was employed. An in-house digital image correlation algorithm was used in order to evaluate the anticipated auxetic nature of the investigated lattices. It was found that neither of the investigated structures exhibited auxetic behaviour although strain-rate sensitivity of the stress–strain characteristics was clearly identified for the majority of structures.

scholarly journals Advanced Crystal Plasticity Modeling of Multi-Phase Steels: Work-Hardening, Strain Rate Sensitivity and Formability

2021 ◽  
Vol 11 (13) ◽  
pp. 6122
Author(s):  
Jesús Galán-López ◽  
Behnam Shakerifard ◽  
Jhon Ochoa-Avendaño ◽  
Leo A. I. Kestens
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Crystal Plasticity ◽  
High Strength Steels ◽  
Grain Morphology ◽  
Rate Sensitivity ◽  
High Strength ◽  
Constitutive Law ◽  
Forming Limit ◽  
Biaxial Tests

This work presents an advanced crystal plasticity model for the simulation of the mechanical behavior of multiphase advanced high-strength steels. The model is based on the Visco-Plastic Self-Consistent (VPSC) model and uses information about the material’s crystallographic texture and grain morphology together with a grain constitutive law. The law used here, based on the work of Pantleon, considers how dislocations are created and annihilated, as well as how they interact with obstacles such as grain boundaries and inclusions (carbides). Additionally, strain rate sensitivity is implemented using a phenomenological expression derived from literature data that does not require any fitting parameter. The model is applied to the study of two bainitic steels obtained by applying different heat treatments. After fitting the required parameters using tensile experiments in different directions at quasi-static and high strain rates, formability properties are determined using the model for the performance of virtual experiments: uniaxial tests are used to determine r-values and stress levels and biaxial tests are used for the calculation of yield surfaces and forming limit curves.

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