Apparent Slip Research Articles

Structural inheritance, morphotectonics and Holocene activity of the Cucalón-Pancrudo extensional fault (Iberian Chain, Spain)

A large active extensional fault is characterized, which will contribute to improve seismic hazard assessment in an intraplate region of the Mediterranean domain whose seismic potential until today has been underestimated. The Cucalón-Pancrudo fault (CPF) is a NNW-SSE striking extensional fault that represents the negative (extensional) inversion of a previous, Late Variscan and Paleogene, transpressional fault. It is part of the Río Grío-Pancrudo fault zone, the largest active structure in the intraplate central-eastern Iberian Chain. This study focuses on characterizing the CPF structure, morphotectonics and paleoseismology. The fault offsets a well-known regional planation surface (lower level of the Fundamental Erosion Surface, FES3, 3.5 Ma), providing a basis for calculating the maximum fault throw (c. 280–300 m, including the contribution of a minor synthetic fault and a gentle accommodation monocline), and hence estimating the net slip (c. 305–325 m) and the long-term slip rate (0.09 mm/a). A trench dug in a Holocene fluvial terrace reveals an ensemble of listric, domino-style ruptures synthetic to the main fault. They were activated during at least two paleoseismic events (X, Z), 14.9 ± 1.4 ka and 6.9 ± 0.4 ka in age. An intermediate event (Y), dated to 11.0 ± 1.0 ka, as an uncertainty because the attribution of their ruptures to event Z cannot be ruled out. The total net slip accumulated during these events (1.15–1.25 m) provides an apparent short-term slip rate of 0.07–0.09 mm/a, very similar to the long-term slip rate. Nevertheless, it is very likely that the faults exposed in the surveyed trench do not represent a complete paleoseismic record. Therefore, the actual slip rate during Late Pleistocene-Holocene times could be significantly higher, approaching that reported for most of the recent extensional faults in the central Iberian Chain. The inclusion of CPF in the map of Active Faults of Iberia (QAFI database) will result in improving seismic hazard assessment in Spain.

Hydrogen embrittlement of the nickel alloy UNS N07718 for two different heat-treating schedules

The role of the nickel alloy 718 microstructure has been widely discussed and it is well established the δ phase detrimental effect on the material’s ductility and toughness when exposed to hydrogen. However, other microstructural features that might influence the embrittlement process are more elusive, which requires more in-depth studies. Having selected heat-treating schedules to mitigate δ phase precipitation, this work aims to assess the hydrogen embrittlement of two alloy 718 variants with nominal yield strengths of 120 and 150 ksi. Fundamentally, the idea is to understand the extent of the hydrogen damage caused by an increase in mechanical strength beyond the limit of 140 ksi specified in the API 6ACRA. Slow strain rate (SSR) and fracture toughness (FT) testing were applied to evaluate the mechanical behavior under cathodic polarization. The microstructure of both variants is comprised of recrystallized austenite grains and a very low content of grain boundary δ phase. Nanosized disk-shaped γ″ particles are also present for both variants, although the 150 ksi material shows a higher volume fraction and a finer distribution of this phase. Despite having the same overall fracture features, nanostructure differences between the variants and the consequent impact on hydrogen apparent solubility and slip planarity produced lower values of plastic elongation and initiation fracture toughness for the stronger material.

Bulk fluidity and apparent wall slip of deflocculated kaolin suspensions

The influence of different electrolytes on the apparent wall slip (AWS) of aqueous kaolin suspensions is studied experimentally. The fluidity and AWS characteristics of purely aqueous and deflocculated kaolin suspensions are measured by gap-dependent rotational viscometry using unconventional cone–cone geometry. The applied sensors are made of different materials: stainless steel (smooth and sandblasted), titanium, and duralumin (with an anodized surface). Both the quality of the sensor surface and the presence of electrolytes strongly influence the observed AWS behavior. In the case of a purely aqueous 40% kaolin suspension, positive AWS (depleted layer formation) is measured on the stainless steel and titanium sensors, while negative AWS (stagnant layer formation) is observed on the anodized duralumin sensor. In the case of fully deflocculated suspensions, Newtonian flow behavior is observed with almost no measurable AWS effects. In the case of partially deflocculated suspensions, the type of deflocculant becomes important. While the presence of Na2CO3 or NaOH does not qualitatively change the AWS trends and only slightly increases them, the presence of SHMP (sodium hexametaphosphate) leads to positive AWS on anodized duralumin. However, the addition of NaCMC (sodium salt of carboxymethylcellulose) induces negative AWS on all the surfaces studied.

Rheo-PIV study of slip effects on oscillatory shear measurements of a yield-stress fluid

The influence of apparent slip on oscillatory shear measurements of a viscoplastic microgel [0.6 wt. % of poly(acrylic acid)] is analyzed by Couette and parallel-plate rheometry and particle image velocimetry (Rheo-PIV). We first provide direct evidence of a critical shear stress for the onset of slip of the microgel under oscillatory (σos) and nonoscillatory measurements (σs). Afterward, we describe the effect of slip on oscillatory measurements via waveforms, Bowditch–Lissajous curves, Fourier transform (FT) rheology, PIV, and as a sequence of physical processes (SPP). The effect of slip is mainly observed at low oscillating frequencies. For amplitudes of the oscillating stresses σ0 ≤ σos, the microgel exhibits linear viscoelastic behavior with in-phase strain response. For σos < σ0 ≤ yield stress (σy), slip introduces a phase shift in the strain response with a forward-tilted waveform and “mango” shape Bowditch–Lissajous curves. Meanwhile, FT rheology shows negligible even harmonics. The strain measured by the rheometer does not match the true strain determined by PIV in the presence of slip, resulting in waveforms that depend on how the displacement distribution is interpreted. This result indicates a break in the symmetry of the flow, that is, the microgel response no longer follows the imposed oscillation, which makes any attempt to correct oscillatory data for slip complex. This behavior arises from recoil of the slipping microgel after reaching its maximum displacement in a cycle. Finally, we provide an overall picture of the kinematics of the process of yielding in the presence of slip as an SPP.

Microscopic mechanism of plastic heterogeneous deformation of columnar-grained polycrystalline ice

Studying ice deformation starting from crystal scale can provide insight into the microscopic mechanisms of ice deformation. In this paper, a crystal plasticity constitutive model of ice considering the dislocation slip mechanism and grain-size dependence was implemented within the finite element framework, and a modeling approach starting from ice single crystals based on the crystal plasticity finite element method (CPFEM) was proposed to study the elastic-viscoplastic deformation of polycrystalline ice samples. Finite element models of ice single crystals and columnar-grained polycrystalline ice characterizing the microstructure were established successively, and the proposed method was validated by comparing the uniaxial compression prediction results of ice single crystals and columnar-grained polycrystalline ice with the existing experimental data. Finally, the microscopic mechanism of plastic heterogeneous deformation of columnar-grained polycrystalline ice under constant strain rate compression conditions was analyzed. The results indicate that the modeling approach from ice single crystals to polycrystalline ice samples based on CPFEM can reasonably describe the mechanical properties of ice deformation. The deformation of columnar-grained polycrystalline ice globally exhibits apparent slip bands around 30° - 60° relative to the loading direction and locally presents intragranular localization bands parallel or perpendicular to the C-axis. This plastic heterogeneous deformation phenomenon is related to the elastic-viscoplastic anisotropy of ice single crystals and the interaction of neighboring grains at grain boundaries (GBs).

Power-law fluid annular flows between concentric rotating spheres subject to hydrodynamic slip

ABSTRACT We report analytical solutions to the problem of non-Newtonian power-law fluid flows in the annular space between a pair of concentric spherical surfaces rotating at distinct angular velocities with the inner and outer wall boundaries subject to general asymmetric hydrodynamic slip conditions. Analytical solutions are possible because of assuming constant valued apparent hydrodynamic slip lengths in the linearized kinematic slip conditions, and our solutions can be validated against the limiting results of Newtonian fluids, no-slip conditions or a single rotating sphere reported in previous literature. Comprehensive systematic parametric studies show that (additional to the power-law fluid flow behavior index) the degree of hydrodynamic slip at the inner surface is the dominant factor that determines the limiting values of the viscous torque exerted on the inner sphere as the outer-to-inner radius ratio assumes significantly large values. Nonetheless, the flow behavior index and outer slip length prove to be the crucial key parameters responsible for a variety of torque responses, which can be categorized by a compact analytical expression, as the outer-to-inner radius ratio is increased in the small to moderate regime. We propose a criteria which identifies the proper slip length and outer-to-inner radius ratio combinations for a given power-law flow behavior index such that the hydrodynamic slip wall effects of the outer surface can be minimized or eliminated. A simple method is also presented to characterize and quantify the apparent hydrodynamic slip effects by use of the concentric rotating spheres viscometer.

Temperature-dependent yield stress and wall slip behaviour of thermoresponsive Pluronic F127 hydrogels.

This study explores the temperature-dependent dynamic yield stress of a triblock thermoresponsive polymer, Pluronic F127, with chemical structure (PEO)100(PPO)65(PEO)100, during the sol-gel transition. The yield stress can be defined as static, dynamic, or elastic, depending on the experimental protocol. We examine the dynamic yield stress estimation for this study, which usually entails utilizing non-Newtonian models like the Herschel-Bulkley (HB) or Bingham models to extrapolate the flow curve (shear rate against shear stress). Initially, we determine the yield stress using the HB model. However, apparent wall slip makes it difficult to calculate yield stress using conventional methods, which could lead to underestimates. To validate the existence of apparent wall slip in our trials, we carry out meticulous experiments in a range of rheometric geometries. To determine the true yield stress corrected for slip, we first use the traditional Mooney method, which requires labor-intensive steps and large sample sizes over various gaps in the parallel plate (PP) design. To overcome these drawbacks, we use a different strategy. We modify the Windhab model equation by adding slip boundary conditions to the HB equation, which allowed us to calculate the slip yield stress in addition to the true yield stress. In contrast to other typical thermoresponsive polymers like poly(N-isopropyl acrylamide) (PNIPAM), our findings demonstrate that PF127's yield stress obeys the Boltzmann equation and increases with temperature.

Visualizing flow dynamics and restart of Carbopol gel solutions in tube and parallel-plates geometries with wall slip.

The present study examines the impact of slip in Carbopol solutions during the restart flow in pipelines utilizing in situ visualization techniques. Rheological tests were conducted using smooth and hatched parallel plate geometries to obtain the rheological characteristics of the solutions. The behavior of the solutions in the creep tests is compared with those in the experimental unit. Three flow regimes were identified through rheological and experimental setup tests: non-flow, slip, and yielded. The slip regime allowed the establishment of a slip static yield stress value, indicating significant deformation states, and a restart pressure decrease of about 61% when compared to the static yield stress. The flow dynamics under the wall slip effect is captured by velocity profiles, velocity contour maps and velocity gradient. Transient correlations of the scaling law type were determined, with wall slip in proportion to the velocity gradient and wall shear stress. Additionally, the concentration of viscoplastic material in the solution increased the scaling law index. This research seeks to provide valuable findings by quantifying the effects of apparent wall slip through in situ measurements. Such insights are crucial for designing and managing pipeline transport systems that handle yield stress fluids, applicable across various industries including cosmetics, food processing, and the production of waxy oils.

Non-Stick Length of Polymer-Polymer Interfaces under Small-Amplitude Oscillatory Shear Measurement.

Interfaces in soft materials often exhibit deviation from non-slip/stick response and play a determining role in the rheological response of the overall system. We discuss detection techniques for the excess interface rheology using small-amplitude oscillatory shear (SAOS) measurements. A stacked bilayer of different polymers is sheared parallel to the interface and the dynamic shear response is measured. Deviation of the bilayer shear modulus from the superposition of the shear moduli of the component layers is analysed. Furthermore, we introduce a frequency-dependent non-stick length based on the bilayer SAOS response to characterize the excess interface rheology. We observe an approximate stick response in the interface in bilayers composed of the chemically same monomer as well as an apparent slip in the interface between immiscible polymers. The results suggest that the proposed non-stick length in SAOS is capable of detecting the apparent interfacial slip. The non-stick length in SAOS is readily applicable to other complex interfaces of different soft materials and offers a convenient tool to characterize the excess interface rheology.

Clustering of earthquakes along the Pidima-Anthia normal fault: New data from palaeoseismology and tectonic geomorphology and their significance on the earthquake's regularity and recurrence across southern Greece

The Pidima-Anthia Fault provides an opportunity to unravel the long palaeoseismic records of the Eastern Messinia Fault Zone (EMFZ) that defines the western border of the Taygetos Mtn range in Peloponnese (southern Greece). This fault zone is segmented and includes a complex system of primarily normal fault segments dipping westwards with a strike of NNW-SSE to N–S, with a traceable length from 6 to 10 km. We applied geomorphological and palaeoseismological analysis across the Pidima-Anthia Fault. The palaeoseismological trench performed across the Pidima-Anthia Fault provide evidence for five M > 6.4 earthquakes hosted on this fault and indicate an apparent slip rate of 0.23 mm/a. Geomorphologically, based on modelling the triangular facets, we estimated the slip rate as 0.28–0.44 mm/a. These data highlight that the slip rate of the fault is remarkably stable for the approximately 17 ka period, and that this duration is enough for a morphogenic active fault to create seismic landscapes. The earthquake history of the Pidima-Anthia Fault allows its comparison with six other known faults that dominate the earthquake history of southern Greece. The pattern of earthquake history in southern Greece shows clustering features (“Wallace-type” behaviour) during Late Quaternary. In particular, the Pidima-Anthia Fault's seismic history resembles with time predictable earthquakes and clustering during the Holocene. Overall, clustering appears prevalent in earthquake behaviour in southern Greece. However, the Pidima-Anthia Fault during the current period (i.e., post 1 ka A.D.)does not display cluster time-predictable behaviour and a strong earthquake can happen at any time.

Incorporating the complex rheological behavior of blood in microvascular network simulations: Two-phase modeling and a model reduction approach

Vessel flow resistance in microvascular network simulations is often computed using the single-phase approximation, where the no-slip boundary condition is imposed on the microvessel wall, and the "in vitro viscosity law" or "the relative hematocrit" relationships proposed by Pries et al. (1992) are utilized. However, these models have limitations due to their reliance on experimental data, which inherently contain measurement errors, thereby affecting their consistency and accuracy. To moderate these limitations, biphasic flow models can be employed, allowing for adaptable rheological descriptions of blood. Nevertheless, this approach presents challenges in terms of automation and computational cost. In order to address these challenges, we propose a monophasic steady-state model that consistently incorporates a wall-slip condition in place of the cell-free layer contribution. Model reduction is achieved by establishing an explicit relationship for the apparent slip length, which is calibrated through the regression of biphasic model results. Subsequently, simulations are conducted on microvessel network structures. The predictions of wall shear stress by the monophasic model exhibit deviations of less than 2 % from the expected values, within the range of vessel radii (10–75 μm) and discharge hematocrits (0.2–0.7). Furthermore, the computational time required is reduced by almost an order of magnitude compared to the biphasic model, rendering it suitable for multiscale biochemical simulations. The developed model closely approximates the flow resistance predictions of the biphasic model, while its modular nature allows for easy implementation of future modifications. Both models successfully reproduce experimental data by Lipowsky et al. (1978). Finally, we derive semi-analytical expressions for the apparent slip length and discuss why it is more appropriate to impose only the "relative hematocrit" relationship as a global constraint for calculating the hemodynamics in microvessels, rather than relying on the "in vitro viscosity law", which provides unreliable predictions at low values of the discharge hematocrit.

Hydrophobic and oleophobic nanopillars reduce viscous drag in slit nanofluidic channels

Nanofluidics exploiting 100 nm nanochannels has developed, and ultrasmall analytical applications in single-molecule level are expected. However, with downscaling the channel size, the required external pressure for driving liquids becomes exceedingly high due to increased fluid resistance and causes a problem to miniaturize a fluidic system. In the present study, we developed a drag reduction method of slit nanochannels with micrometers-width and nanometers-depth for both aqueous and organic reagents by integrating hydrophobic and oleophobic nanostructured surface. A fabrication process based on electron beam lithography and dry etching was established to realize inverted-trapezoidal shaped hydrophobically modified nanopillars with 300 nm width and 210 nm height on a fused-silica substrate. We optimized the geometry of nanopillars, and those with an upper base angle of 78° and an interval of 400 nm induced hydrophobic property for water with a contact angle of 139° and also oleophobic property for hexadecane with that of 108° by the Cassie–Baxter state with the pinning effect. By integrating the nanopillars, drag reduction of slit nanochannels for both water and hexadecane by slipping with the gas–liquid interface at the nanopillar interval was achieved with apparent slip lengths of 269 nm (water) and 108 nm (hexadecane). The drag reduction rate increased with decreasing the channel depth, and for a nanochannel with 208 nm depth, rates of 87% (water) and 80% (hexadecane) were achieved. We demonstrated miniaturization and energy saving of nanofluidic system based on the developed method. This work will greatly contribute to advancement of nanofluidics and engineering for dust proof materials.

Improvements in Drilling Fluid Rheology Predictions Using Rotational Viscometer

Summary The success of an oilwell drilling operation is directly associated with the correct formulation of drilling fluids and their rheological measurements. The goal of this study is to investigate the usage of a Fann 35A viscometer and the methodology for rheological characterization of drilling fluids by comparison with the use of a rotational rheometer. Flow curves and gel strength tests were performed considering classic measurement artifacts such as apparent wall slip, secondary flows, steady-state (SS) regime, and inertial effects, among others. In addition, a study of the relationship between pressure drop and flow rate in a tube and in an annular space was carried out to investigate the influence of the viscosity function and of the rheological properties on the design of pipelines and the correct sizing of pumps. Use of American Petroleum Institute (API) equations and curve fitting were explored as potential choices for viscosity functions. The results indicate that the use of API equation predictions can compromise the effectiveness of the drilling process, while the choice of an adequate viscosity function is essential for the correct sizing of pumps. The gel strength was evaluated in the viscometer and presented divergent results from those obtained in the rheometer. Furthermore, a grooved geometry was developed for the viscometer to avoid the effects of apparent slip at low shear rates. Some recommendations are made based on the results obtained, which lead to better accuracy in the rheological results of drilling fluids and, consequently, better performance of some functions assigned to it. The proposed improvements and methodologies proved to be promising, although in some cases the cost-benefit remained unchanged.

Micromechanical testing for quantitative characterization of apparent slip system: Extinction of persistence of slip in carbon bearing Fe-3% Si

The effect of carbon on the persistence of the slip in Fe–3 mass% Si was investigated. We applied micro-sized cantilever bending tests to obtain ψ–χ relationships that enable quantitative analysis of the persistence of the slip. It was demonstrated that the result from decarburized specimens using this method is consistent with those obtained in previous studies from bulk-sized tensile test specimens. This novel method eliminates the difficulty of preparing bulk-sized single-crystal specimens for investigating the persistence of the slip. The persistence of the slip weakened in aged specimens containing 0.016 mass% C and disappeared in quenched specimens with the same carbon content, where wavy slip bands were observed. The reason for these changes in the macroscopically apparent slip plane is explained by the assumption that the frequency of nucleating kink-pair in the competitive {110} planes is a function of the resolved shear stress.

Ubiquitin modulates 26S proteasome conformational dynamics and promotes substrate degradation.

The 26S proteasome recognizes thousands of appropriate protein substrates in eukaryotic cells through attached ubiquitin chains and uses its adenosine triphosphatase (ATPase) motor for mechanical unfolding and translocation into a proteolytic chamber. Here, we used single-molecule Förster resonance energy transfer measurements to monitor the conformational dynamics of the proteasome, observe individual substrates during their progression toward degradation, and elucidate how these processes are regulated by ubiquitin chains. Rapid transitions between engagement- and processing-competent proteasome conformations control substrate access to the ATPase motor. Ubiquitin chain binding functions as an allosteric regulator to slow these transitions, stabilize the engagement-competent state, and aid substrate capture to accelerate degradation initiation. Upon substrate engagement, the proteasome remains in processing-competent states for translocation and unfolding, except for apparent motor slips when encountering stably folded domains. Our studies revealed how ubiquitin chains allosterically regulate degradation initiation, which ensures substrate selectivity in a crowded cellular environment.

Dynamic behavior of a magnetorheological fluid radial-flow-based energy absorber considering apparent slip boundary condition

Accurate theoretical models play a key role in the development of magnetorheological energy absorbers (MREAs). Traditionally, the apparent slip caused by non-uniformity interface (i.e., the separation of carrier fluid and magnetic particles at the wall) of the working medium is often ignored for simplifying theoretical models. However, the apparent slip influence the cross-sectional flow and decreased the theoretical accuracy of the damping force for MREA applied in the impact absorption area. In this study, a dynamic model with apparent slip boundary condition for radial-flow-based MREA was proposed. The effect of apparent slip layer thickness on the dynamic behavior of an MREA was qualitatively and quantitatively compared in terms of the following three aspects: (1) with the Power-Law constitutive model, theoretical models of the dynamic characteristics of the magnetorheological fluid (MRF) squeeze and MREA are presented based on the apparent slip boundary condition with the MRF behavior of the Navier–Stokes equation; (2) the accuracy of the theoretical model to predict MREA peak force and boundary velocity with different slip-layer thicknesses; and (3) global agreement of the dynamic force and range curves between the modeling and experimental results. The results show that the absolute values of the relative errors in the two models with a 2- and 0-µm thick slip layer were less than 3.73 and 7.41%, respectively, and that a 2-µm thickness can help predict the actual dynamic characteristic more efficiently under accidental collision loading conditions.

Flow and slip process of Santotrac 50‐based lubricant under high shear by molecular dynamic simulation

AbstractWe investigate flow and slip behaviour of Santotrac 50 molecules under high shear in Couette cell by means of Molecular Dynamic simulation to understand reduced friction force. Molecular chain stretches and oriented to shear direction, and move. Slip starts on metal surface at 2 × 108 s−1, and increases with shear rate. Slip length keeps scale at nanometre. Molecular conformation and occurrence of slip both indicate a reduced shear stress. Furthermore, when changing wettability, slip length increases in power law and thus decreases shear stress greatly. Occurrence of low‐density region near surface can explain slip. And thus, we extended apparent slip model, which divided lubricant into liquid layers with different viscosities, to elucidate the relationship between molecule distribution inner layer and slip on surface influenced by shear velocity and wettability. Above all, our research sheds light on flow and slip behaviour of complex fluid and can be applied in improving lubrication property.

Characterization of the shallow subsurface structure across the Carrascoy Fault System (SE Iberian Peninsula) using P-wave tomography and Multichannel Analysis of Surface Waves

The seismicity in the SE Iberian Peninsula is distributed parallel to the coast in a well-developed strike-slip fracture system known as the Eastern Betic Shear Zone (EBSZ). This work focuses on the characterization of the shallow subsurface structure of the Algezares-Casas Nuevas Fault, within the Carrascoy Fault System of the EBSZ. The Carrascoy Fault borders the Guadalentín Depression to the south, which is a densely populated area with extensive agricultural activity. Therefore, this faults system represents a seismic hazard with significant social and economic implications. We have constructed two velocity-depth models based on P-wave tomography and Multichannel Analysis of Surface Waves (MASW) acquired from seismic reflection data. The resulting velocity models have allowed us to interpret the first ~250m depth and have revealed: i) the thickness of the critical zone; ii) the geometry of the Algezares-Casas Nuevas Fault; iii) the depth of the Messinian/Tortonian contact and iv) the presence of blind thrusts and damage zones under the Guadalentín Depression. Our results have also helped us to estimate an apparent vertical slip rate of 0.66±0.06m/ky for the Algezares-Casas Nuevas Fault since 209.1±6.2ka. Our results provide a methodological and backflow protocol to study the shallow subsurface of active faults, complementing previous geological models based on paleoseismological trenches, and can be used to improve the seismic hazard assessment of tectonically active regions around the world.

Interseismic Masking of Fault Slip Deficit Rates by Earthquake Cycle Processes and Local Block Rotations

Abstract Interseismic geodetic observations at active boundaries contain information about tectonic motions and earthquake cycle processes. The combined effects of these two processes may serve to mask tectonic signals near active faults. Motivated by the observation of coseismic rotational motion during the 2016 Mw 7.8 Kaikōura New Zealand earthquake we develop idealized models for the masking of tectonic motions near blocks with local rotation poles. We show that differential interseismic velocities may reach local, rather than far field, maxima contributing to suppression of apparent slip deficit rates. This effect is most pronounced for small (<100 km) tectonic blocks with deep (>10 km) effective locking depths.

Temperature-dependent nanoindentation and activation volume in high-purity body-centered cubic chromium

The thermally activated dislocation plasticity of body-centered cubic (BCC) metals is controlled by the nucleation of dislocation kink pairs at low temperatures. We probed this deformation mechanism with high-temperature nanoindentation in chromium using very fine temperature increments. The established kink pair nucleation models are modified for the high-temperature nanoindentation method and applied to characterize the deformation behavior of high-purity BCC chromium from room temperature to 698 K. The measured hardness, strain rate sensitivity, and apparent activation volume are compared with a modified kink-pair nucleation model based on Seeger’s work. A change in the apparent slip plane from {110} to {112} with increasing temperature is inferred from self-consistent predictions and experimental measurements of the hardness-dependent activation volume from temperature-dependent hardness measurements using the line tension model for kink-pair nucleation.