Slip Direction Research Articles

Analysis of Influence of Ultrasonic Shot Peening on Surface Plastic Behavior of Superalloy

This work focuses on the effects of ultrasonic shot peening (USP) on grain refinement and orientation behavior in the surface region of GH4151 superalloy. The microstructure evolution of the alloy under USP durations were studied. The effects of USP-induced grain refinement, orientation, and dislocation motion behavior were analyzed. The results indicated that during the USP process, the plastic deformation of the surface layer of superalloys is accompanied by changes in grain size and orientation. The random impact of the spheres on the surface area promotes grain refinement and grain rotation, enhancing the randomness of grain orientations and reducing the texture strength and the proportion of “soft” orientation distribution. Over a long period of treatment, a large number of spheres cause the slip planes and slip directions of each grain to rotate due to the additional shear stress from the impact, resulting in relatively consistent plastic deformation on the surface and the enhanced randomness of grain orientations, thus reducing the high texture strength introduced by previous machining processes. The understanding of dislocation pile-up behavior and the relationship between externally applied shear stress, pile-up characteristics, and grain refinement is essential for optimizing the USP process and achieving the desired material properties.

Comparisons of data-driven models for detecting slip occurrence and direction based on simulations of tactile sensing

Slip detection based on tactile sensing plays a crucial role for a robot to achieving stable grasps by promptly adjusting its grasping state. Detecting the occurrence of slippage has been a focus of previous research, but identifying the direction of slippage can provide richer reference information for correcting grasp issues. Due to the variations of experiment setup, the performances of these data-driven models have not been sufficiently compared. In this study, we compared the performance of three traditional machine learning algorithms—Random Forest (RF), Support Vector Machine (SVM), and k-Nearest Neighbors (KNN)—with four deep learning models—Gated Recurrent Unit (GRU), Convolutional Gated Recurrent Unit (CNN-GRU), Convolutional Long Short-Term Memory (ConvLSTM), and 3D Convolution(Conv3D)—in detecting slippage states and directions. We conducted experiments using a simulated dataset collected in Gazebo. Additionally, we compared the noise resistance capability of each model and their generalization performance when facing new objects. The results show that when facing known grasped objects, all models can effectively detect slippage occurrences and their directions. However, as noise increases, Conv3D exhibits the strongest robustness. When generalized to unknown grasped objects, the deep learning models outperforms the three traditional learning algorithms, with CNN-GRU showing the best performance.

Adding friction to Third Medium Contact: A crystal plasticity inspired approach

This paper presents the first method to enable friction in the Third Medium Contact (TMC) method. TMC embeds a solid in a highly compliant medium, which becomes infinitely stiff under ultimate compression, thus allowing forces to be transferred between the solids when the medium between the solids is compressed. This approach is increasingly adopted for integrating internal contact in structural design processes, owing to its continuous, fully implicit characteristics, simplicity, and its stability when applying regularisation to the third medium regions. The lack of friction has previously restricted the use of the TMC method in simulating real-world contact conditions. Here, we address this issue by (1) integrating an anisotropic term into a Neo-Hookean material model to provide shear resistance, and (2) employing a framework inspired by crystal plasticity that includes a yield criterion specifically designed to replicate the effects of Coulomb friction.The effectiveness of the method is demonstrated through two examples: (1) a smooth sliding contact problem and (2) a non-smooth C-shaped structure. Results demonstrate a close agreement with reference solutions obtained by a conventional Lagrange multiplier approach. While the method, for now, requires user-defined slip directions, it represents a significant advancement by enabling the integration of friction into TMC, thereby broadening its applicability to problems involving realistic frictional contact. Future research should focus on restoring the fully implicit nature of TMC in the presence of friction, and on developing automated slip direction definitions to enhance usability and expand the method’s versatility.

A deep insight of re-entrant martensitic transformation mechanism in Co2Cr(Ga,Si) shape memory alloys

Co2Cr(Ga,Si) shape memory alloys have a wide application temperature range due to the unique re-entrant martensite phase transformation (RMT) behavior. Nevertheless, the microscopic mechanism of RMT remains elusive and unsystematic. The heart of this investigation lies the comprehensive exploration of phase stability, phase transformation path, and martensite slip direction during RMT from martensite (D022-PM) to austenite (L21-FM). In this work, we systematically investigate the re-entrant martensitic transformation of Co2Cr(Ga,Si) SMAs using first-principles methods for the first time. Firstly, the density of states (DOS) calculation indicates that the stability of L21-FM is higher than D022-PM. The charge density calculation further indicates that the bonding strength between Co atoms and Cr (Si) atoms in the L21-FM phase is the highest. In addition, Fermi surface calculation further reveals that phase instability is due to the Fermi surface nesting caused by electron-phonon coupling. Moreover, the minimum energy path was calculated by the G-SSNEB method for the first time, which indicates the RMT can occur. Finally, the calculation of the elastic constants indicates that RMT is caused by the crystal plane slip of the D022-PM phase along the <110> direction. Our calculations provide the electronic-level and thermodynamic mechanism for RMT of Co2Cr(Ga,Si) alloy and shed some light on the revelation of the phase transformation mechanism.

Spatial correlation assessment of multiple earthquake intensity measures using physics-based simulated ground motions

Predictive models for spatial correlation play an effective role in the assessment of seismic risk associated with distributed infrastructure and building portfolios. However, existing models often rely on simplified approaches, assuming isotropy and stationarity. This paper verifies these assumptions by presenting a comprehensive study using a database of 3D physics-based simulated broadband ground motions for Istanbul, generated by the SPEED software. The results reveal significant event-to-event variability and nonstationary and anisotropic characteristics of spatial correlation influenced by source, path, and site effects. The development of nonstationary correlation models requires exploring influential metrics beyond spatial proximity and gaining a deep understanding of their impact, which is the focus of this study. Analysis of the spatial correlations of peak ground displacement, peak ground velocity, peak ground acceleration, and response spectral accelerations at different periods, employing both stationary and nonstationary correlation modelling methods and considering the finite fault model, indicates that the slip distribution pattern, direction and distance of station pairs relative to earthquake rupture, soil softness, and homogeneity of soil properties significantly influence the spatial correlations of near-field earthquake ground motions. Implementation of the introduced parameters in predictive spatial correlation models enhances the precision of regional seismic hazard assessments.

Formation of orientation-dependent surface morphologies on tungsten after low energy helium plasma exposure: multiscale characterization and new insights

In ITER, the helium (He) impurity produced by the deuterium-tritium reaction will bombard the tungsten (W) divertor armor at the strike points. Consequently, strong interaction occurs therein that both impact the performance of the plasmas and the lifetime of the divertor. Despite an ever-increasing understanding of this interaction, some experimental phenomena remain mysterious, especially the formation of orientation-dependent surface morphologies. Here, we combine multiscale experimental characterization and theoretical models to shed new light on this problem. After low-energy He plasma exposure in a linear plasma generator, the polycrystalline W surface developed various morphologies. Through electron backscatter diffraction analysis, we found that the {111} grains developed cube-corner structures, the {110} grains developed ripple structures, whereas the {100} grains remained smooth. Then, electron-transparent lamellae were extracted from such grains to observe the subsurface He bubbles by transmission electron microscopy. The volume density, size distribution, and depth range of the He bubbles weakly depend on the crystallographic orientation, suggesting that the migration of W atoms causes the morphology variety. Accordingly, we proposed a two-stage formation mechanism. First, W atoms generated by over-pressurized He bubbles glide on the slip plane and in the slip direction to reach the surface, forming characteristic patterns that are enclosed by the slip traces. Second, morphological instability drives the evolution of the surface patterns, in which the initial surface structure and surface self-diffusion kinetics mediate. The proposed mechanism has been incorporated into a topographical instability model to enable asemi-quantitative analysis. The obtained new insights are valuable to the impurity control of the core plasmas and the lifetime analysis of the divertor for ITER.

Effect of crystallographic orientation on the deformation and mechanical behavior of CoCrFeNi in Berkovich nanoindentation

The hardness and plastic deformation behavior of single-phase concentrated solid solution alloy CoCrFeNi were studied for selected crystallographic orientations (⟨001⟩, ⟨011⟩ and ⟨111⟩) using Berkovich nanoindentation. The integration of transmission electron microscopy (TEM) and molecular dynamics (MD) simulations was carried out to elucidate comprehensively the distinction in the deformation mechanisms, the evolution of dislocation structures, and the pile-up of differently oriented CoCrFeNi alloys subjected to indentation by a Berkovich indenter. In MDs, a Berkovich indenter, meticulously crafted to replicate its real geometry, was effectively employed in investigating the nanoindentation. The ⟨001⟩-oriented CoCrFeNi exhibited the highest hardness and the lowest magnitude of pop-in events, followed by the ⟨011⟩ and then the ⟨111⟩ orientations. The pile-up behavior was strongly dependent on the crystallographic orientation and occurred by three sequential processes. The deformation twinning was activated only in the ⟨001⟩ orientation and inclined toward the center direction of the indent due to the force inclining toward the radial direction of the indent. The clear manifestation of the evolution of dislocations in the three orientations during indentation was elucidated. More SFTs or Stair-rods were observed in the ⟨001⟩ orientation, attributable to the intensified reaction of Shockley partials stemming from its higher density of Shockley partials, followed by the ⟨011⟩ and then the ⟨111⟩ orientations. The anisotropic nanoindentation-hardness was correlated with the microstructures. The highest hardness and lowest magnitude of pop-in events of the ⟨001⟩ orientation could be ascribed to its intense dislocation interactions, high-density SFTs and the formation of twins. In the ⟨111⟩ orientation, the three-fold symmetry emission of prismatic dislocation loops along the three slip directions not parallel to the surface leaded to a weak interaction between dislocations, and then resulted in the lowest hardness. This research may be helpful to enhance our comprehension of the intricate mechanical behaviors exhibited by different oriented FCC high entropy alloys under Berkovich indentation.

Source parameters and aftershock pattern of the October 7, 2021, M5.9 Harnai earthquake, Pakistan

On October 7, 2021, a magnitude 5.9 earthquake struck the Harnai (Baluchistan) region of Pakistan, causing several fatalities and injuries within the epicentral area. First-order tectonic deformation in this region is caused by the convergence of the Indian Plate with respect to the Eurasian Plate. The Katwaz Block hinders the motion of the Indian Plate, resulting in the formation of strike-slip faults. In this study, the P-wave first-motion polarity technique was used to determine the mainshock faulting style. Cyclic scanning of the polarity solutions was applied to determine the most suitable focal mechanism solution among the available solutions generated by the FOCMEC (focal mechanism) software. The nodal planes correspond to different faulting styles (i.e., thrust and strike-slip faulting). A nodal plane oriented in the NW-SE direction corresponded to a strike-slip mechanism, which was considered to be the fault plane. Tectonically, this earthquake was associated with the Harnai-Karahi strike-slip fault zone owing to the fault strike and direction of slip. The apparent stress drop, fault length, and moment magnitude of the Harnai earthquake were 35.4 bar, 6.1 km, and 5.9, respectively. A lower b-value for the Gutenberg-Richter law was observed prior to the earthquake. Higher α- than b-values (α >b) indicate that this earthquake was governed by large events as opposed to small-magnitude events. The Harnai sequence had a decay exponent close to unity, lasted for 145 days, and produced few aftershocks. The study will help the future hazard mitigation in the region.

Uncovering the phonon spectra and lattice dynamics of plastically deformable InSe van der Waals crystals

Stacking two-dimensional (2D) van der Waals (vdW) materials in a layered bulk structure provides an appealing platform for the emergence of exotic physical properties. As a vdW crystal with exceptional plasticity, InSe offers the opportunity to explore various effects arising from the coupling of its peculiar mechanical behaviors and other physical properties. Here, we employ neutron scattering techniques to investigate the correlations of plastic interlayer slip, lattice anharmonicity, and thermal transport in InSe crystals. Not only are the interlayer slip direction and magnitude well captured by shifts in the Bragg reflections, but we also observe a deviation from the expected Debye behaviour in the heat capacity and lattice thermal conductivity. Combining the experimental data with first-principles calculations, we tentatively attribute the observed evidence of strong phonon-phonon interactions to a combination of a large acoustic-optical frequency resonance and a nesting effect. These findings correlate the macroscopic plastic slip and the microscopic lattice dynamics, providing insights into the mechano-thermo coupling and modulation in 2D vdW materials.

Accurate determination of active slip systems using a novel lattice rotation analysis: Quasi-in-situ EBSD/ECCI study on the homogeneous/heterogeneous deformation of polycrystalline zirconium

The accurate determination of slip systems is crucial for understanding deformation mechanisms of metals in particular, how slip/twining transfer or blocking occurs. This paper proposes a novel crystallographic lattice rotation analysis, which combines quasi-in-situ Electron Back Scatter Diffraction (EBSD) and Electron channeling contrast imaging (ECCI) techniques to precisely predict the active slip system with specific slip directions in polycrystalline Zr. Large data sets for hundreds of grains were quantitatively analyzed by this method to statistically gain deep insight on the deformation mechanism of Zr. Our results show that prismatic 〈a〉 slip is the primary slip system in most grains, and pyramidal 〈a〉 slip plays a secondary role in coordinating the local stress state of plastic deformation. The predicted slip direction is the same as the direction in which dislocation density increases. This method can serve as a complementary tool to the intragranular misorientation axis (IGMA) method, bridging the gap between macro-mechanical response and microstructural deformation mechanisms.

Operative slip systems and their critical resolved shear stresses in η-Fe2Al5 investigated by micropillar compression at room temperature

The plastic deformation behavior of single crystals of orthorhombic η-Fe2Al5 has been investigated by micropillar compression at room temperature as a function of crystal orientation and specimen size. Plastic flow is observed even at room temperature by the operation of six slip systems; (001)<010>, (001)<110>, (001)<130>, {22‾3}<110>, {311}<1‾03> and {301}<1‾03>. The CRSS values for the six identified slip systems are very high all in the range of 1.1∼1.5 GPa and do not vary much with specimen size. In the middle of the stereographic projection, the (001)<010>, (001)<110>, (001)<130> and {22‾3}[110] slip systems operate according to the relative Schmid factors with the similar CRSS values in the range of 1.08∼1.23 GPa. In orientations close to [001], the {311}<1‾03> slip system as well as the {301}<1‾03> slip system operate with a much higher CRSS values around 1.5 GPa, producing wavy slip traces due to the occurrence of frequent cross-slip among these slip planes. In orientations close to the [100]-[110]-[010] symmetry line, on the other hand, premature failure occurs without the operation of any slip systems, although, the Schmidt factor-wise, the {311}<1‾03> and {301}<1‾03> slip systems could operate. The selection of slip systems, their CRSS values and the possible dislocation dissociation modes are discussed based on the overlapped atomic volume that occurs during shear along the slip direction on the slip plane, taking into account the partial occupancies of Al atoms in the linear atomic chain along the orthorhombic c-axis direction.

High-cycle and low-cycle fatigue characteristics of multilayered dissimilar titanium alloys

Multilayered structures of dissimilar titanium alloys can achieve excellent fracture ductility and strength, while their fatigue characteristics especially dislocation networks and twin formation are rarely reported. Heterogeneous microstructures are observed in the multilayered TC4/TB8 alloys, including fine acicular α grains, continuous α layer at prior β grain boundaries (αGB) and β matrix on the TB8 layer, together with equiaxed α grains on the TC4 layer. High-cycle fatigue (HCF) and low-cycle fatigue (LCF) tests show that the initial fatigue damage appears at the αGB/β matrix interfaces on the TB8 layer instead of the boned TC4/TB8 interfaces. Since the stress concentration induced by dislocation pile-up is prone to micro-void formation and crack propagation at the αGB/β interfaces. For LCF, the αGB/β interfaces can not only act as impenetrable barriers and sources of lattice dislocations, but also allow the dislocations cross boundaries during cyclic tension and compression because of the high boundary energy. The formation characteristic of deformation twins that is beneficial for the plastic deformation of α grains in TC4 layer during cyclic strain is investigated. Furthermore, the hexagonal dislocation networks are also found within the equiaxed α grains of TC4 layer after LCF, and the role between interface barrier and slip direction in the formation mechanism is analyzed.

Quantitative evaluation of orientation effects in wear and friction characteristics of pure nickel using experiments and atomistic simulations

Nanoscale tribological behavior of Ni for its applications such as MEMS is an important area of study. The present study investigated the nanoscale friction and wear behavior of Ni on different crystallographic orientations using experiments and molecular dynamics simulations. Results showed an anisotropic friction response, with (100) [001] case showing high COF followed by (111) [1¯10] and (110) [1¯10] cases. Analysis showed that such a trend in COF is observed due to variation in activation of the number of slip systems in each case as determined by the Schmid factor calculations. Dislocation analysis showed that (100) [001] case developed the highest number of glissile dislocations which is attributed to high COF value. The wear volume followed an opposite trend of COF order, and the spatial distribution of displaced material is found to be different in each case, indicating an anisotropic ploughing mechanism. Such behavior is observed due to variations in the availability of the number of slip directions, their orientation on the scratch plane, and dislocation evolution during nanoscratch. Overall, this study provides insights into the complex deformation mechanism and wear behavior associated with scratch tests and has implications for the development of wear-resistant materials.

Impact of injection pressure and polyaxial stress on hydraulic fracture propagation and permeability evolution in graywacke: Insights from discrete element models of a laboratory test

Understanding the hydromechanical behavior and permeability stress sensitivity of hydraulic fractures is fundamental for geotechnical applications associated with fluid injection. This paper presents a three-dimensional (3D) benchmark model of a laboratory experiment on graywacke to examine the dynamic hydraulic fracturing process under a polyaxial stress state. In the numerical model, injection pressures after breakdown (postbreakdown) are varied to study the impact on fracture growth. The fluid pressure front and crack front are identified in the numerical model to analyze the dynamic relationship between fluid diffusion and fracture propagation. Following the hydraulic fracturing test, the polyaxial stresses are rotated to investigate the influence of the stress field rotation on the fracture slip behavior and permeability. The results show that fracture propagation guides fluid diffusion under a high postbreakdown injection pressure. The crack front runs ahead of the fluid pressure front. Under a low postbreakdown injection pressure, the fluid pressure front gradually reaches the crack front, and fluid diffusion is the main driving factor of fracture propagation. Under polyaxial stress conditions, fluid injection not only opens tensile fractures but also induces hydroshearing. When the polyaxial stress is rotated, the fracture slip direction of a fully extended fracture is consistent with the shear stress direction. The fracture slip direction of a partly extended fracture is influenced by the increase in shear stress. Normal stress affects the permeability evolution by changing the average mechanical aperture. Shear stress can induce shearing and sliding on the fracture plane, thereby increasing permeability.

DFT study of intrinsic mechanical properties of Mn2AlB2

Mechanically strong materials are vital components of a high temperature tribosystem. We used density functional theory to investigate the intrinsic elastic and plastic properties of Mn2AlB2- a novel MAB phase tribomaterial. The most vulnerable slip system and direction of Mn2AlB2 are (100)[100] and [001], respectively. The ideal shear strength of Mn2AlB2 is 18.75 GPa and its ideal tensile strength is 20.56 GPa. The deformation mechanisms of Mn2AlB2 are closely related to its magnetic and bonding properties. The shear deformation mechanism involves the breaking of old bonds (i.e. Al-B), formation of new bonds (i.e. Mn-Al, Al-Al (along the a-axis)) and anisotropy of the existing bonds (i.e. Mn-B(short) and B-B). The lattice instability of Mn2AlB2 at the critical strains is triggered by abrupt changes in its magnetic behavior and subtle changes in its bonding properties. The predicted mode I, II and III fracture toughness of Mn2AlB2 are 1.88 MPa.m1/2, 1.58 MPa.m1/2 and 1.40 MPa.m1/2, respectively. This study elucidates the intrinsic mechanical behavior of Mn2AlB2 in terms of lattice stability and plasticity under different loading conditions for extreme environment applications.

Energy evolution and strain localization in fractured sandstone under freeze-thaw cycling and uniaxial loading-unloading

In cold regions, combined cyclic freeze-thaw (F-T) and loading-unloading can cause rock slope instability and sliding. The macro-failure of rock masses originates from the expansion of strain localization areas driven by energy. Therefore, a deep understanding of the energy evolution and strain distribution can reveal the instability process. Along these lines, in this work, intact and intermittently jointed sandstones were subjected to a cyclic F-T environment and subsequently carried out uniaxial graded loading-unloading to obtain their mechanical parameters and X-ray computed tomography images. By investigating the energy density, it was found that the input, elastic, dissipated, and damage energies all increased with loading according to a quadratic polynomial function, with the energies obeying a linear allocation law. Meanwhile, F-T changed the energy storage capacity and energy dissipation coefficient of the rock by causing meso-damage. To measure the meso-scale strain localization characteristics, the advanced digital volume correlation technique was also used to obtain three-dimensional strain fields. In terms of local strain, the failure behavior of intact specimens under the application of low and high numbers of F-T cycles was controlled by potential fracture bands and frost-heave cracks, respectively, while fractured specimens were mainly dependent on the macro-fracture arrangement. However, both frost heaving and thawing transformed sandstone from brittle to ductile. In terms of statistical strain, the equivalent strain (εeq) showed a log-normal distribution and continued to deviate to the right due to loading-unloading. Meanwhile, the normal strain (εxx, εyy, εzz) exhibited a normal distribution, where fractured sandstone mainly developed along with the slip direction. Finally, the intrinsic correlations among the energy parameters, meso-damage, and macro-failure were discussed. From our analysis, three stages of energy allocation and transformation were revealed, namely the uniform allocation of damage energy, banded accumulation of damage energy, and fracture caused by the elastic energy release.

Extensive phase transformation in an equiatomic CrCoNi medium entropy alloy under extreme uniaxial tension

The dynamic tension behavior of an equiatomic CrCoNi medium entropy alloy (MEA) has been studied at both room temperature (RT, 298 K) and liquid nitrogen temperature (LNT, 77 K). Microstructural observations show that extensive phase transformations were activated in this alloy under dynamic tension at LNT instead of the activation of the deformation twins under high strain rate only or quasi-static loading at LNT. The appearance of massive nanoscale phase transformation bands along multiple slip directions even created a network structure of HCP lamellae in the FCC grains. This leads to defect accumulation at the intersection regions and results in the formation of new HCP variants, inverse phase transformations to FCC structure and even amorphous domains. Such transformation induced plasticity (TRIP) effects including the mutual interactions of crossover phase transformation bands on the plasticity and tension fracture of the MEA under extreme loading conditions were further discussed. These findings provide a deeper understanding of the deformation mechanisms in the equiatomic MEA under extreme loads.

Dislocation slip mechanism and prediction method during the ultra-precision grinding process of monocrystalline silicon

Prediction of dislocation depth during ultra-precision grinding of monocrystalline silicon is a major challenge. To provide atomistic perspective, a single grain scratching molecular dynamics (MD) model of monocrystalline silicon is established to analyze the initiation and slip mechanism of dislocation. The simulation results show that the initiation of dislocations depends on the normal scratching force, and the dislocation length decreases with the decrease of scratching force and the increase of scratching velocity. Besides, the active slip system was identified by calculating Schmid factor, and the slip stress τ(111)[110],p (i.e. Peierls stress) of 2 GPa for ±1/2[110] dislocation on (1 1‾ 1) plane was obtained. Furthermore, a prediction model for dislocation depth was established based on the analysis of shear stress τ(111)[110]. Finally, a set of nano-scratch experiments were carried out, and the depth and slip direction of dislocation that close to the predicted were obtained by TEM method. This study provides a new method for predicting and controlling dislocation damage of monocrystalline silicon during ultra-precision grinding.

Macroscopic low-friction via twinning assisted lattice reconstruction in magnesium

One-fourth of the global energy losses are spent to overcome friction, making it particularly important to reduce and minimize friction between contacting materials. Hexagonal close-packed (HCP) metals are an important class of structural materials. It has not been possible to reduce their friction, primarily because of friction-induced dislocation slip and twinning. Here, we find particularly low friction when sliding perpendicular to the a-axis on the basal plane in HCP Mg single crystals. This is in contrast to the common belief that friction is small along the preferred dislocation slip direction (a-axis). This macroscopic low-friction stems from twinning assisted lattice reconstruction sharing a common rotation axis, confirmed by atomistic simulations and strain energy analysis. While sliding along the a-axis and other directions, 〈c + a〉 dislocation activity accounts for high frictional resistance. By unambiguously decoupling the contributions of dislocation slip and twinning, this discovery reveals potential opportunities in mitigating the energy dissipation at tribological interfaces of HCP metals, e.g. through crystallographic texture design.

Influence of orientation of the intermediate principal stress on fracture reactivation in granite

Fracture (fault) reactivation can lead to dynamic geological hazards including earthquakes, rock collapses, landslides, and rock bursts. True triaxial compression tests were conducted to analyze the fracture reactivation process under two different orientations of σ2, i.e. σ2 parallel to the fracture plane (Scheme 2) and σ2 cutting through the fracture plane (Scheme 3), under varying σ3 from 10 MPa to 40 MPa. The peak or fracture reactivation strength, deformation, failure mode, and post-peak mechanical behavior of intact (Scheme 1) and pre-fractured (Schemes 2 and 3) specimens were also compared. Results show that for intact specimens, the stress remains nearly constant in the residual sliding stage with no stick-slip, and the newly formed fracture surface only propagates along the σ2 direction when σ3 ranges from 10 MPa to 30 MPa, while it extends along both σ2 and σ3 directions when σ3 increases to 40 MPa; for the pre-fractured specimens, the fractures are usually reactivated under all the σ3 levels in Scheme 2, but fracture reactivation only occurs when σ3 is greater than 25 MPa in Scheme 3, below which new faulting traversing the original macro fracture occurs. In all the test schemes, both ε2 and ε3 experience an accumulative process of elongation, after which an abrupt change occurs at the point of the final failure; the degree of this change is dependent on the orientation of the new faulting or the slip direction of the original fracture, and it is generally more than 10 times larger in the slip direction of the original fracture than in the non-slip direction. Besides, the differential stress (peak stress) required for reactivation and the post-peak stress drop increase with increasing σ3. Post-peak stress drop and residual strength in Scheme 3 are generally greater than those in Scheme 2 at the same σ3 value. Our study clearly shows that intermediate principal stress orientation not only affects the fracture reactivation strength but also influences the slip deformation and failure modes. These new findings facilitate the mitigation of dynamic geological hazards associated with fracture and fault slip.