Showing papers on "Slip (materials science) published in 2022"

Tensile deformation behavior of ferrite-bainite dual-phase pipeline steel

Abstract: In-situ tensile test accompanied by electron backscatter diffraction (EBSD) analyses were performed on polygonal ferrite (PF) and bainite dual-phase steel, selected regions of interest were analyzed following plastic deformation of the steel. Deformation-induced crystal orientation evolution, localized strain concentration, slip transfer, and geometrically necessary dislocation (GND) density were tracked. Results revealed that heterogeneity deformation facilitated formation subregions with crystal orientation deviation in grain and fragmented the grain by the new low angle grain boundaries (LAGBs) or medium angle grain boundaries (MAGBs). The PF grains with ND// preferred crystal orientation exhibited high orientation stability, and almost all load axes of the selected PF grains moved to the [101] pole, resulting in enhancing {111} orientation component at high strain levels. With the lattice rotation during deformation, the high angle grain boundaries (HAGBs) can change to MAGBs, which was beneficial to maintain coordination deformation among grains. Localized strain concentration can be decreased by the slip transfer across the PF grain boundaries or bainite/PF phase boundaries, which reduced the risk of micro-void formation. Additionally, the variation of α12 GND tensor average value (Ave. α12) revealed that the ferrite was continuous plastic deformation, while the bainite occurred stage hardening. The required strain for the coordination deformation was controlled by strain hardening behavior.

Influence of cooling rate on ω phase precipitation and deformation mechanism of a novel metastable β titanium alloy

Abstract: This work investigated the effect of cooling rate (water quenching and air cooling) on the precipitation of ω phase after solution treatment in β-phase region, and its effect on the mechanical properties in a novel metastable β titanium alloy (Ti–5Mo–3Cr–Fe–3Zr). The initial microstructures, phase composition and deformation-induced microstructures have been investigated using SEM, EBSD, XRD, and TEM. The phase composition of water-quenched alloy and air-cooled alloy are β, α", and ω phase. The size and volume fraction of ω phase of air-cooled alloy are larger than that of water-quenched alloy, resulting in an increase in tensile strength and a decrease in ductility. Deformation mechanisms of Ti–5Mo–3Cr–Fe–3Zr alloy with different cooling rate change from stress-induced ω phase transformation and dislocation slip to only dislocation slip. The stress-induced ω lamellas parallel to [1-11]β direction along the [0001]ω1 direction, which is formed by {112}β β slip. Dislocations can cut through the encountered ω phase to form ω-free deformation bands, which accounts for the ductility.

Apparent slip in colloidal suspensions

Abstract: In this study, we have carried out experiments to characterize the wall slip of colloidal suspensions of kaolinites. To demonstrate slip, the rheological measurements were carried out with parallel-plate geometry with smooth and rough plates. The asperities of the rough surface penetrated the slip layer and created a nearly no-slip region, whereas the smooth plate showed significantly higher slip, a conclusion drawn by comparing the macroscopic flow curves in both cases. Two slip regimes were identified, namely, (i) an elastic slip regime below the yield stress of the suspension where the material slips like a solid and (ii) a slip regime above the yield stress where the material yields and flows. The slip velocity was quantified using a simple phenomenological slip model that seems to capture slip in both flow regimes. The transition from the first slip regime to the other has been resolved numerically as the material starts yielding first at the edge of the parallel-plate geometry with the yield point propagating inwards as the rotational speed is increased. The numerical method also establishes uniquely the yield stress value, which was found to agree with data obtained from parallel-plate, cone-and-plate, and concentric cylinder geometries.

Multiple slip effects on nanofluid dissipative flow in a converging/ diverging channel: a numerical study

Abstract: A mathematical model is developed for viscous slip flow and heat transfer in water/Ethylene glycol-based nanofluids containing metallic oxide nanoparticles, through a converging/diverging channel geometry. Our approach is based on the single-phase Tiwari– Das nanofluid model considering nanoparticles and base fluid masses as a substitute volume concentration of nanoparticles. The governing (dimensional partial differential) equations are transformed to a set of dimensionless ordinary differential equations with the help of similarity transformation, before being solved numerically using Maple17. Extensive validation of the velocity gradient and temperature solutions is achieved with the second order implicit finite difference Keller Box method (KBM). Further validation is included for the special case of noslip nanofluid flow in the absence of viscous heating. The effects of the emerging parameters namely velocity slip, thermal jump, channel apex angle, Eckert number, Prandtl number, Reynolds number and nano-particle volume fraction on velocity, temperature, skin friction and heat transfer rate are investigated in detail. Two different nanofluids are studied, namely water-Titanium oxide- and Ethylene glycol-Titanium oxide. Both convergent and divergent channels are addressed, and significantly different thermofluid characteristics are computed due to slip and viscous heating effects. The novelty of the current work is that it extends previous studies to include multiple slip effects and viscous heating (Eckert number effects) which are shown to exert a significant influence on heat and momentum transfer characteristics. The study is relevant to certain pharmaco-dynamics devices (drug delivery), next generation 3-D nanotechnological printers and also nano-cooling systems in energy engineering where laminar flows in diverging/converging channels arise.

Mechanistic fatigue in Ni-based superalloy single crystals: A study of crack paths and growth rates

Abstract: The mechanistic basis of microstructurally short crack paths and growth rates is investigated in Ni-based superalloy single crystals using Crystal Plasticity (CP) and eXtended Finite Element (XFEM) analyses of experimental edge-cracked samples over a range of crystal orientations. Crack paths are determined to be those along crystallographic slip systems within which the slip is highest. Crack growth rates are determined by the crack tip critical stored energy density. Experimental observations of tortuous crack paths and their dependence on crystal orientation are reasonably well captured by the mechanistic model. Key features of alternating and straight crack paths are reproduced. The experimentally measured crack growth rates as a function of crystal orientation are also captured by the mechanistic model and controlled by the crack tip critical stored energy density which was found to be 385 Jm−2 in the Ni-based superalloy single crystals analysed. A new methodology for determination of critical stored energy density and mechanistic quantification of short crack growth rates is presented.

The influence of salt-frost cycles on the bond behavior distribution between rebar and recycled coarse aggregate concrete

Abstract: In this paper, the influence of salt-frost cycles on the bond behavior distribution between rebar and recycled coarse aggregate concrete (RAC) was studied by pull-out test. The results show that the ultimate bond strength and the normalized bond strength decrease with the increase of salt-frost cycles, while the rebar slip increases; the difference in the rebar strain and the difference in concrete strain at different anchorage positions increase with the increase of pull-out load; the shape of rebar strain distribution curve along the anchorage length changes from concave to convex with the increase of salt-frost cycles; the difference in the relative slip at different anchorage positions increases with the increase of pull-out load; the relative slip distribution curve gradually transitions from dense to loose with the increase of salt-frost cycles; the slope of the bond-slip curve at different anchorage positions decrease with the increase of salt-frost cycles.

Velocity-driven frictional sliding: Coarsening and steady-state pulses

Abstract: Frictional sliding is an intrinsically complex phenomenon, emerging from the interplay between driving forces, elasto-frictional instabilities, interfacial nonlinearity and dissipation, material inertia and bulk geometry. We show that homogeneous rate-and-state dependent frictional systems, driven at a prescribed boundary velocity — as opposed to a prescribed stress — in a range where the frictional interface is rate-weakening, generically host self-healing slip pulses, a sliding mode not yet fully understood. Such velocity-driven frictional systems are then shown to exhibit coarsening dynamics saturated at the system length in the sliding direction, independently of the system’s height, leading to steadily propagating pulses. The latter may be viewed as a propagating phase-separated state, where slip and stick characterize the two phases. While the coarsening process is limited by the system’s length — leading in the presence of periodic boundary conditions to a pulse train with periodicity identical to the system’s length —, the single pulse width, characteristic slip velocity and propagation speed exhibit rich properties, which are comprehensively understood using theory and extensive numerics. Finally, we show that for sufficiently small system heights, the pulse is accompanied by periodic elasto-frictional instabilities.