Slip Mode Research Articles

Two end-member earthquake preparations illuminated by foreshock activity on a meter-scale laboratory fault

The preparation process of natural earthquakes is still difficult to quantify and remains a subject of debate even with modern observational techniques. Here, we show that foreshock activity can shed light on understanding the earthquake preparation process based on results of meter-scale rock friction experiments. Experiments were conducted under two different fault surface conditions before each run: less heterogeneous fault without pre-existing gouge and more heterogeneous fault with pre-existing gouge. The results show that fewer foreshocks occurred along the less heterogeneous fault and were driven by preslip; in contrast, more foreshocks with a lower b value occurred along the more heterogeneous fault and showed features of cascade-up. We suggest that the fault surface condition and the stress redistribution caused by the ongoing fault slip mode control the earthquake preparation process, including the behavior of foreshock activity. Our findings imply that foreshock activity can be a key indicator for probing the fault conditions at present and in the future, and therefore useful for assessing earthquake hazard.

Instability mechanism of surrounding rock chain structure in steeply inclined thick seam mining

In view of the difficulty of fully-mechanized mining in steeply inclined coal seam with thickness of 4 to 8 m, the horizontal section short wall fully-mechanized caving mining method is innovatively proposed. In the No. 3-3c steeply inclined coal seam of a Coal Mine, the single roadway integrated with excavation and recovery is arranged as working face, the pillar on sides of roadway is recovered ahead by spiral drilling machine, and the top coal is recovered by the vertical and horizontal self-moving supports. The Z-type ventilation is formed by constructing a ventilation roadway along the side of gob. Through theoretical analysis, numerical calculation and physical similarity simulation, the main mining parameters, including sectional height and ratio of mining height to caving height, were determined, and the characteristics of roof movement evolution, floor failure and sliding and the generalization of surrounding rock bearing structure were revealed. The results show that the effect of coal caving is better when the section height is 10 m and the ratio of mining height to caving height is 2.85. The cross-layer multi-ladder voussoir structure is formed by transformation and migration of the critical layer, and the failure and slip modes of floor are extruding-translation, extruding-underdraught and extruding-upthrust in different areas of horizontal sublevel caving stope. Roof, pillar and floor are interrelated to form the Roof-Pillar-Floor (R-P-F) chain structure. When the height of section with three sublevels is 30 to 45 m, the mutual conversion of strong and weak chains between structural units can be cut effectively in mining process, and the impact disaster caused by the roof falling over great extent and the instability of pillar can be prevented. The new mining method proposed and studied above provides the technological and theoretical basis for the safe and efficient production of such coal seams, and is of great significance to the sustainable development of coal in Xinjiang province and even western China.

A finite deformation framework for mechanism-based constitutive models of the dynamic behavior of brittle materials

A finite deformation mechanism-based thermodynamically consistent constitutive framework is presented for describing the dynamic behaviors of brittle materials under impact loading. The framework is developed based upon a multiplicative decomposition of the deformation gradient in terms of multiple mechanisms, including recoverable elasticity, crack-induced damage, and other inelastic mechanisms such as subgrain and granular plasticity. The finite deformation kinematics that captures the multiple mechanisms is structured within a thermodynamically consistent framework, and the consequent coupling of the various mechanisms is articulated. Specific constitutive equations are formulated for a Mie–Grüneisen equation of state, micromechanics-based dynamic-fracture-induced damage growth, subgrain or lattice plasticity for slip and other deformation modes, and granular plasticity for granular flow and pore collapse post-fragmentation. Using hot-pressed silicon carbide (SiC-N) as the model material, this integrative model is calibrated using available experiments that interrogate specific mechanisms. The effects of loading rate, the influence of confinement, and the path-dependent constitutive behaviors of the material predicted by the model are demonstrated. The model performance at the application scale is then evaluated by simulating previously performed sphere-on-cylinder impact experiments.

Understanding the role of local texture variation on slip activity in a two-phase titanium alloy

During plastic deformation of engineering alloys with a hcp crystal structure, slip systems with different critical resolved shear stresses can be activated. In the case of two-phase titanium alloys such as Ti-6Al-4V, it is well established that various a→ and c→+a→ type slip systems can be activated in the α-phase, which dominates this alloy. However, their relative likelihood is less well established particularly when comparing prismatic a→ and basal a→ slip which are known to have similar critical resolved shear stress values. By combining EBSD-based grain orientation mapping and high-resolution digital image correlation, grain specific shear strain mapping and Burgers vector direction analysis was carried out after small levels of plasticity in two differently microtextured Ti-6Al-4V samples. This enabled the different types of strain heterogeneity and strain patterns to be linked to the underlying microstructure and microtexture. The detailed analysis shows that the dominance of a particular a→ type slip mode greatly varies with the local texture and that shear strain patterns extend across many grains when soft macrozones (clusters of similarly orientated grains) are present. The work highlights that the relative displacement ratio analysis significantly improves slip trace analysis in hcp crystals by reducing the cases of ambiguous solutions and that grain neighbourhood can have a greater impact on slip system activation than Schmid factor.

Anisotropic nitriding behavior upon formation of expanded hcp in Co-Cr alloys

The transformation from hexagonal close packed (hcp) to face-centered cubic (fcc) crystal structure upon gaseous nitriding of Co-Cr alloy with initial hcp crystal structure was investigated. During early stages of low-temperature nitriding at 400°C, new reflections on the low-angle side of the hcp-substrate reflections in X-ray diffraction patterns can be attributed to the formation of hcp phase with an expanded lattice on the surface. Prolonged nitriding treatment and nitriding at higher temperatures result in transformation of this expanded hcp into an expanded fcc. An anisotropic progress of mentioned transformation on differently-oriented hcp crystallites is observed. The transformation is slower in hcp orientations with the highest Schmid factor of the basal slip mode with respect to the nitriding direction. This is discussed in a view of developed macrostress in early stages of nitriding and its influence on plastic anisotropic deformation of hcp variants.

Deformation mechanisms of CoCrFeMnNi high-entropy alloy under low-cycle-fatigue loading

Plastic deformation during low-cycle fatigue (LCF) in equiatomic face-centered cubic (FCC) CoCrFeMnNi high-entropy alloys (HEAs) is accumulated by dislocation substructure formation, which leads to crack initiation. Whilst these substructures have been reported before, little has been done to clarify their formation mechanisms and the effects of strain amplitude, cycle number and grain orientation. In this study, cyclic deformation behavior and microstructural evolution of CoCrFeMnNi were examined for two different grain sizes at room temperature. Microstructural investigations by transmission electron microscopy showed that, while the dislocation structures at low strain amplitude (0.3%) mainly consisted of planar slip bands, at higher strain amplitudes (0.5% and 0.7%), wavy-substructures including veins, walls, labyrinth and cells prevailed. Slip mode also changes from initially planar-slip to wavy-slip with cycle numbers. Dislocations in veins, walls, labyrinth and cells are found to have different Burgers vectors, suggesting that apart from wavy-slip, multiple-slip also contributes to their formation. Moreover, distinct dislocation substructure in grains is dictated more by the constraints from neighboring grains rather than by their orientation. Additionally, the formation of various dislocation structures in a single grain is also linked to the constraint effects from the neighboring grains.

High-temperature anisotropic behaviors and microstructure evolution mechanisms of a near-α Ti-alloy sheet

The high-temperature anisotropy and microstructure evolution mechanisms of the rolled TA32 titanium alloy sheet were studied. The hot deformation behaviors of the TA32 sheet along the rolling direction (RD), diagonal direction (DD), and transverse direction (TD) were studied by the uniaxial tensile tests in the temperature range of 700–900 °C and the strain rate range of 0.0001–0.1 s-1. The anisotropic coefficients were calculated by interrupted tensile tests. The microstructure and texture characteristics were observed by electron backscatter diffraction (EBSD) characterization. The effects of dislocation slip, texture evolution, dynamic recrystallization (DRX), and grain morphology on high-temperature anisotropy were comprehensively studied. Results show that the TD sample exhibited the largest peak strength and the DD sample displayed the highest elongation. The r-values decreased with increasing temperature and decreasing strain rate, and increased with increasing strain. The dominant dislocation slip modes of RD, DD, and TD samples were prismatic slip, the coupling of basal and prismatic slips, and pyramidal slips, respectively. The DRX mechanism of TA32 titanium alloy during hot deformation was the combined effects of DDRX (discontinuous dynamic recrystallization) and CDRX (continuous dynamic recrystallization), and DDRX could weaken the anisotropy. The grain growth and refinement caused by thermal effect and DRX led to the decrease and increase of r-value, respectively. In addition, the room-temperature tensile strength of the TD deformed sample showed the largest drop compared with the initial sheet, which can be attributed to the accumulation of damage and the increase of basal texture in the TD sample during the hot working.

Laboratory Study on the Effect of Fluid Pressurization Rate on Fracture Instability

Fluid injection-induced earthquakes have been a scientific and social issue of wide concern, and fluid pressurization rate may be an important inducement. Therefore, a series of stepwise and conventional injection-induced shear tests were carried out under different fluid pressurization rates and effective normal stresses. The results show that the magnitude of fluid pressure is the main factor controlling the initiation of fracture slipping. The contribution of fluid pressure heterogeneity and permeability evolution on the initiation of fracture slipping is different with the increase of fluid pressurization rate. When the fluid pressurization rate is small, permeability evolution plays a dominant role. On the contrary, the fluid pressure heterogeneity plays a dominant role. The increase of fluid pressurization rate may lead to the transition from creep slip mode to slow stick-slip mode. Under the laboratory scale, the fluid pressure heterogeneity causes the coulomb failure stress to increase by about one times than the predicted value at the initiation of fracture slipping, and the coulomb stress increment threshold of 1.65 MPa is disadvantageous to the fracture stability.

Afterslip and Spontaneous Aseismic Slip on the Anza Segment of the San Jacinto Fault Zone, Southern California

AbstractUnderstanding the interplay of seismic and aseismic slip is key in seismic hazard evaluation. It is particularly important to know if the same or nearby fault segments can host different slip modes and understand the transition between modes of slip. We investigate this in the trifurcation area of the Anza segment of the San Jacinto fault where deep creep driving seismicity below the geodetic locking depth has been proposed. We focus on periods following local moderate‐sized earthquakes by combining the occurrence of highly correlated families of earthquakes (i.e., closely spaced or partially overlapping events) that we describe here as near‐repeating earthquakes, seismicity, and borehole strainmeter data. We find that all Mw > 4.5 earthquakes between 2010 and 2020 triggered afterslip with coplanar families of near‐repeating earthquakes and off‐fault microseismicity. These observations include newly detected afterslip following the June 10, 2016 Mw 5.2 and April 4, 2020 Mw 4.9 local earthquakes. Afterslip geometries defined by the near‐repeating earthquake families are consistent with strain change observations. We conclude that families of near‐repeating earthquakes, similar to low‐frequency earthquakes within tremor, can be useful indicators of aseismic slip transients and can reveal faulting complexities during aseismic slip. Further, we identify the first evidence of spontaneous aseismic slip in the Anza region from near‐repeating earthquake families on two minor faults in 2015. Taken together, our observations support a model where deep microseismicity is located in a transitional region at the bottom of the seismogenic zone with spatially heterogeneous frictional properties that produce frequent aseismic slip transients near Anza.

Manipulating deformation mechanisms with Y alloying of Mg

The effect of Y concentration on the slip and twinning mechanisms in binary Mg–Y alloys are investigated using transmission electron microscopy, electron backscattered diffraction, and visco-plastic self-consistent polycrystal constitutive modeling. Four concentrations of Y are studied in hot-rolled and recrystallized sheet material. The materials were deformed in tension and compression in the rolling direction and compression in the normal direction in order to invoke distinct proportions of slip and twin mechanisms with each test. Within the single crystal hardening model used in polycrystal modeling, a slip-twin interaction law is introduced to account for dislocation density reductions due to dislocation absorption during twin boundary migration. We show that increasing Y concentration reduces the intensities of both the initial and deformation textures. During deformation, the plastic anisotropy in yield stress, the tension-compression asymmetry, and amount of 101‾2⟨1‾011⟩ twinning is shown to decrease with increasing Y. For each alloy, the model identifies a single set of material parameters that successfully reproduced all measured stress-strain curves and achieved agreement with measured deformation textures and twin area fractions. Transcending texture effects, the model interpretation of the flow responses suggests that increased concentrations of Y increase the critical resolved shear stress for basal slip but have negligible effects on the other slip modes. The reduced plastic anisotropy with increases in Y is explained by a concomitant decrease in the prismatic-to-pyramidal slip critical resolved shear stress ratio. The model suggests that their nearly equivalent critical resolved shear stress values lead to the enhanced non-basal activity of Mg–Y alloys, which was confirmed by transmission electron microscopy. The calculations suggest that beyond any texture differences, this reduction in twinning can be attributed to a slightly increased resistance for 101‾2⟨1‾011⟩ twin propagation, particularly in the binary with the highest Y content.

Periodic stick–slip mode of ice surface premelting during friction

The rheological nonlinear model of ice surface softening during friction is developed. Analytical and numerical schemes describing stick–slip frictional oscillations for three boundary relations between the shear strain, stress, and temperature relaxation times are built. The phase portraits and time dependencies of friction force are calculated. The random force (additive uncorrelated noise) effect on found damped oscillation mode is revealed. It is shown that white noise influence leads to an undamped oscillation mode corresponding to a periodic intermittent (stick–slip) regime of friction that is basically responsible for destruction of rubbing surfaces. The most pronounced such oscillatory behavior occurs if relaxation time of the temperature is much longer that its value for shear strain and stress.

Experimental and numerical evaluations of composite concrete-to-concrete interfacial shear strength under horizontal and normal stresses.

Effects of different surface textures on the interface shear strength, interface slip, and failure modes of the concrete-to-concrete bond are examined through finite element numerical model and experimental methods in the presence of the horizontal load with ‘push-off’ technique under different normal stresses. Three different surface textures are considered; smooth, indented, and transversely roughened to finish the top surfaces of the concrete bases. In the three-dimensional modeling via the ABAQUS solver, the Cohesive Zone Model (CZM) is used to simulate the interface shear failure. It is observed that the interface shear strength increases with the applied normal stress. The transversely roughened surface achieves the highest interface shear strength compared with those finished with the indented and smooth approaches. The smooth and indented surfaces are controlled by the adhesive failure mode while the transversely roughened surface is dominated by the cohesive failure mode. Also, it is observed that the CZM approach can accurately model the interface shear failure with 3–29% differences between the modeled and the experimental test findings.

A Mobile Mathieu Oscillator Model for Vibrational Locomotion of a Bristlebot

Abstract Terrestrial locomotion that is produced by creating and exploiting frictional anisotropy is common amongst animals such as snakes, gastropods, and limbless lizards. In this paper we present a model of a bristlebot that locomotes by generating frictional anisotropy due to the oscillatory motion of an internal mass and show that this is equivalent to a stick–slip Mathieu oscillator. Such vibrational robots have been available as toys and theoretical curiosities and have seen some applications such as the well-known kilobot and in pipe line inspection, but much remains unknown about this type of terrestrial locomotion. In this paper, motivated by a toy model of a bristlebot made from a toothbrush, we derive a theoretical model for its dynamics and show that its dynamics can be classified into four modes of motion: purely stick (no locomotion), slip, stick–slip, and hopping. In the stick mode, the dynamics of the system are those of a nonlinear Mathieu oscillator and large amplitude resonance oscillations lead to the slip mode of motion. The mode of motion depends on the amplitude and frequency of the periodic forcing. We compute a phase diagram that captures this behavior, which is reminiscent of the tongues of instability seen in a Mathieu oscillator. The broader result that emerges in this paper is that mobile limbless continuum or soft robots can exploit high-frequency parametric oscillations to generate fast and efficient terrestrial motion.

Deformation Mechanisms of CoCrFeMnNi High-Entropy Alloy Under Low-Cycle-Fatigue Loading

Plastic deformation during low-cycle fatigue (LCF) in equiatomic face-centered cubic (FCC) CoCrFeMnNi high-entropy alloy (HEA) is accumulated by dislocation substructure formation, which leads to crack initiation. Whilst these substructures have been reported before, little has been done to clarify their formation mechanisms and the effects of strain amplitude, cycle number and grain orientation. In this study, cyclic deformation behavior and microstructural evolution of CoCrFeMnNi were examined for two different grain sizes at room temperature. Microstructural investigations by transmission electron microscopy showed that, while the dislocation structures at low strain amplitude (0.3%) mainly consisted of planar slip bands, at higher strain amplitudes (0.5% and 0.7%), wavy-substructures including veins, wall, labyrinth and cells prevailed. Slip mode also changes from initially planar-slip to wavy-slip with increasing cycle numbers, which defines the cyclic stress response. Dislocations in veins, walls, labyrinth and cells are found to have different Burgers vectors, suggesting that apart from wavy-slip, multiple-slip also contributes to their formation. Moreover, distinct dislocation substructure in grains is dictated more by the constraints from neighboring grains rather than by their orientation. Additionally, the formation of various dislocation structures in a single grain is also linked to the constraint effects from the neighboring grains.

Microstructure and texture evolution of Ti–6Al–4V alloy T-joint fabricated by dual laser beam bilateral synchronous welding

The microstructure and microtexture evolution of Ti–6Al–4V T-joints produced by dual laser beam bilateral synchronous welding (DLBSW) were investigated using the optical microscopy (OM) and electron back-scattered diffraction (EBSD) and correlated with the mechanical properties of the joint. We demonstrate important differences in temperature field, grain morphology, misorientation angles and texture intensity between the base material (BM), the skin-side heat-affected zone (SK-HAZ), the stringer-side heat-affected zone (ST-HAZ) and the weld seam (WS). Through in-depth crystallographic analysis, we demonstrate that the kernel average misorientation curve of the WS is steeper and the peak misorientation angle is larger, revealing that the WS has a lower geometrically necessary dislocations density and a smaller residual strain. Due to the different orientation of each a-phase colony at the interface of the two phases, it is not conducive to the deformation mode of dislocation slip, so a large number of twins are generated in the WS. Furthermore, the WS has a strong crystal preferential orientation and the maximum polar density of the pole figure is 17.05, which is significantly higher than the polar density of the base material. It is found that the gradient of microstructure variation in the narrow HAZ is higher than that in the WS, which leads to more heterogeneous properties in the HAZ compared to the weld. This research result is consistent with the phenomenon that all the fractures of the resultant T-joints occurred in the HAZ.

Temperature effects on deformation substructures and mechanisms of a Ni-based single crystal superalloy

Mechanical behaviors of a Ni-based single crystal superalloy have been investigated by tensile testing at various temperatures. Deformation substructures and mechanisms have been systemically revealed from micrometer to atomic scales by using advanced scanning electron and scanning transmission electron microscopes. Results show that deformation mode of the alloy strongly depends on the temperature due to competitive responses of the γ and γ′ phases under mechanical loading and their original stress statuses. At temperatures from ambient to 750 °C, plasticity is governed by dislocation shearing in both phases, where slip modes of γ are <110>{111} and those of γ′ are <112>{111}, <110>{111} and <110>{001}. At moderate temperatures (850 °C ≤ T ≤ 900 °C), plasticity mainly involves microscopically uniform deformation of both phases. The matrix deforms first so that channels parallel to tensile direction are narrowed due to the Poisson's effect, after that deformation of γ′ follows. The active slip modes are <110>{111} for γ, <112>{111}, <110>{111}, <110>{001}, and <001>{001} for γ′. At temperature higher than 1000 °C, plastic strain is also derived from deformation of both phases, but deformation of the matrix plays critical roles, due to relatively weak strength of this phase. The operative slip modes are <110>{111} for γ, but mainly <110>{001} and <001>{001} for γ′. Our results clearly provide a comprehensive and multiscale (from micrometer to atomic) understanding on the deformation mechanism of Ni-based superalloys, which can be critically beneficial and offer mechanistic guidelines to design new/next generation superalloys.

Controls of fault geometry and thermal stress on fault slip modes: Implications for permeability enhancement and injection-induced seismicity

Fluid pressurization within the fault zone generates increasing pore pressure and stress change which is liable to create shear and/or brittle fractures within the reservoir volumes and subsequently generating earthquakes of varying magnitudes. Here, we explored time-dependent fault weakening processes in the fault zone which are dependent on several factors, including the rate of cold-water injection, modes of injection (hydromechanical (HM) and thermo-hydro-mechanical (THM) interactions), and changing fault spatial configurations using data from Niger Delta Basin. The variation in the stability of different fault models in withstanding stresses induced by HM and THM fluid interactions is evident. Fault permeability enhancement and the behaviour of slip event under isothermal and non-isothermal conditions revealed that stress and pore pressure perturbations have a first order control on the rate of fault dilation and compression. It is observed that the progressive cooling of the reservoir induced thermal stress which induced the timing of slip by unloading the fault to earlier seismic rupture in the non-isothermal case, and accelerates the magnitude of the fault reactivation and the accompanied induced seismicity. Owing to increased tendency of shear failure during injection, fracture opening through shear dilation is more enhanced in THM simulation as the fracture permeability is significantly higher than in HM. This effect becomes increasingly more dominant with intermediate fault angle and joint orientation. Certain fault/joint configurations which were resistant to shear failure under isothermal injection had their frictional resistance broken by thermal stress. The results also indicate that there is higher pore pressure build-up in THM than in HM as the injection rate increases and reservoir temperature drops during cold injections.. This study has demonstrated the importance of fully characterizing the fracture geometries and configurations of normal faulting regime in addition to fluid injection conditions when developing fractured reservoirs to mitigate seismic risks and hazards that could result from early fault reactivation.

Effect of crystallographic orientation on mechanical properties of single-crystal CoCrFeMnNi high-entropy alloy

Using molecular dynamics (MD) simulation, the influence of crystallographic orientation on the mechanical properties and microstructure evolution of the single-crystal CoCrFeMnNi high-entropy alloy as a face-centered cubic (FCC) metal is explored and quantified by nanoindentation. At the elastic stage of P-h curve, the results of MD-simulation are almost consistent with that of Hertz contact theory fitting, which ensures the accuracy of our results. The plastic deformation is studied by correlating the P-h curve with the instantaneous defect structure, and dominated by nucleation of Shockley partial dislocations or the movements of stacking faults. Furthermore, we discuss the effects of crystallographic orientations [ 001 ] , [ 110 ] , and [ 111 ] on the mechanical response of materials and the microstructure evolution. The slip mode and the stress-concentrated region are controlled by the crystallographic orientations, and an obvious pop-in behaviors are viewed in [ 111 ] -oriented sample, without appearing in other samples. The microstructure evolution exhibits distinct anisotropy causing the discrepancy of dislocation density and hardness. By analyzing the evolution of dislocation density and hardness, the linear relationship between the square root of dislocations density and hardness is revealed, and in good agreement with the classic Taylor hardening expression where the pre-factor is strongly dependent on the crystallographic orientation. In the study, the atomistic results are consistent with those predicted by the classic continuum mechanical theory, which contributes to the application of classic mechanical theory in molecular dynamics simulation.

Impact of short range ordering on the anomalous four-stage strain hardening behavior of low solid-solution hardening Ni–Cr alloys

The effect of short range ordering (SRO) on the strain hardening behavior of low solid-solution hardening Ni–Cr alloys with high stacking fault energies (SFEs) was systematically investigated under uniaxial compression to a high true strain ε t of 0.9 at room temperature. An unexpected four-stage (including Stages A, B, C and D) changing law in strain hardening rate was revealed, which is completely different from the case of conventional high-SFE alloys whose strain hardening rate just monotonously declines as the strain increases. Observations on the deformation microstructures strongly demonstrate that the recovery of strain hardening rate in Ni–Cr alloys (Cr ≥ 20 at.%) at Stages B (0.11 < ε t < 0.21) and D ( ε t ≥ 0.65) should be ascribed to the transformation in dislocation slip mode from wavy slip to planar slip, and the occurrence of the extensive deformation twins (DTs) together with the secondary DTs, respectively. Besides, in the later period of Stage C (0.21 < ε t < 0.65), microbands (MBs) and DTs have been locally formed in the Ni–Cr alloys with high SRO degree, which delays the decrease of strain hardening rate to a certain extent. Based on these experimental observations, the impacts of SRO on the formation of planar slip bands, MBs and DTs are analyzed, and the effect of SRO on the four-stage strain hardening behavior is also discussed systematically based on the different deformation mechanisms. In brief, an enhancement of SRO in low solid-solution hardening Ni–Cr alloys with high SFEs has been convincingly confirmed to be capable of improving the strain hardening capacity.

Grain-size effect on the deformation of Mg–3Al–3Sn alloy: Experiments and elastic-viscoplastic self-consistent modeling

Grain refinement can significantly change the tensile behavior of Mg alloys. The underlying mechanisms are unclear yet. Here we report that grain refinement of a Mg–3Al–3Sn (wt.%, AT33) alloy increases the yield strength (σ0.2) following the Hall-Petch law, while decreases the strain hardening exponent (h). Tensile stress-strain curves and lattice strain evolution of four rolled AT33 samples with different grains sizes (10–97 μm) can be simulated by an elastic-viscoplastic self-consistent (EVPSC) model that takes grain size into account. The key to the model's success is that it allows both the initial critical resolved shear stress (CRSS) and the dislocation nucleation coefficient of different slip modes to be functions of the grain size. The coarse-grained samples have higher dislocation nucleation coefficient due to concurrently formed deformation twins. The model predicts that prismatic slip is the dominant deformation mode in this AT33 alloy; pyramidal <a> and <c+a> slips are more active in coarse-grained samples than in fine-grained samples.