Slip Mode Research Articles

Exploiting an as-extruded fine-grained Mg-Bi-Mn alloy with strength-ductility synergy via dilute Zn addition

Here, a new Mg-1Bi-1Mn-0.3Zn (BMZ110, wt%) wrought alloy designed by the dilute addition of Zn subjected to an appropriate extrusion processing that showed an excellent strength-ductility synergy at room temperature. The main results included four aspects as follows: 1) With dilute Zn addition, the as-cast BMZ110 alloy was refined into an approximately equiaxed-grained structure, since the solid solution of Zn provided a relatively high growth restriction factor. 2) The as-extruded BMZ110 alloy exhibited the finer average grain size and weaker basal texture intensity than the as-extruded BM11 alloy without Zn. The co-segregation of Bi and Zn solutes into grain boundaries was observed to impede grain growth during extrusion and further weaken texture intensity. Moreover, Zn atoms incorporated into Mg3Bi2 phases by replacing Bi atoms increasing the nucleation rate of Mg3Bi2 phases and refining their sizes. 3) Compared with the as-extruded BM11 alloy, the as-extruded BMZ110 alloy demonstrated the higher yield strength (~ 283.4 MPa), ultimate strength (~ 366.2 MPa) and elongation-to-failure (~ 26%). The size refinement of grains and second phases contributed to an extra strength increments. Grain boundary segregation enhanced grain boundary cohesion not only reducing the number density of grain boundary cracks, but also activating more slip modes and grain rotation for increasing the ductility. 4) The as-extruded BMZ110 alloy had the higher grain growth resistance than the as-extruded BM11 alloy during annealing. Solute segregation offered an effective obstacle to restrict grain boundary migration enlarging the activation energy (~ 112.2 kJ/mol) and further delaying the grain growth. Therefore, this work will be helpful for the development of new high performance low-alloyed Mg-Bi based wrought alloys to achieve extensive applications in industries.

Implications of slip transition on the work hardening and texture evolution of nickel‑tungsten‑iron ternary alloy

The present study investigates the microstructure, texture, and work hardening behavior of the hot rolled and homogenized Ni-24W-22Fe alloy. This alloy has a single f.c.c. phase microstructure with some annealing twins. Upon tensile test, the alloy showed unconventional strain hardening behavior which was determined to occur due to transition from single slip to multiple slips. The bulk texture measurement also confirmed the evidence of planar slip during the early stage of deformation. To further ensure the transition in slip modes, i.e., single slip to multiple slips, in-situ electron backscatter diffraction was performed, and evidence of the occurrence of slip transition was shown by grains having rotation path toward <112> direction. Grains of similar orientation were picked and found to rotate in different directions. Some grains rotate toward <112>, while others rotate toward <111> direction. • Work-hardening behavior of concentrated Ni-24W-22Fe alloy was studied. • Kocks-Mecking plot shows the hump formation due to slip transition. • Bulk texture evolution shows the deterioration of [100] fiber and evolution of [111] fiber. • Similar oriented grains takes different rotation paths, some grains rotate toward <112> and others rotate toward <111>.

Microstructure evolution during hot-packed rolling and mechanical properties anisotropy of as-rolled network-structured TiBw/TA15 composites

In this study, the scanning electron microscope (SEM) and electron backscattering diffraction (EBSD) was used to investigate the evolution of the TiB whiskers (TiBw) orientation, microstructure, and texture during hot rolling. The mechanical properties at room-temperature were tested for as-rolled composites in different loading directions. Based on the calculated and measured Schmid Factors (SFs), the effect of texture on the modes of dislocation slip in different directions was researched. A generalized shear-lag model was modified to evaluate the strengthening contribution of TiBw in different directions. The effects of matrix texture, TiBw orientation, and Hall-Petch (H–P) relationship on the anisotropy of mechanical properties of as-rolled composites were comprehensively analyzed. Results show that recrystallization (DRX) mechanisms include continuous DRX (CDRX) and discontinuous DRX (DDRX) during hot rolling. When the rolling reduction was 70%, the matrix alloy displayed the {11 2‾ 0} <101‾ 0> texture (the crystal c-axis point to the TD, i.e. T-Texture) and recrystallization texture. With the increase of rolling reduction, the strength of as-rolled composites increased. The best mechanical properties were obtained in the rolling direction (RD) at 60% rolling reduction, in which the tensile strength and plasticity were increased by 14% and 17.3% respectively compared with as-sintered composites. The prismatic <a> slip and the basal <a> slip were activated in RD and transverse direction (TD) respectively during room-temperature tensile. The strengthening contribution of TiBw decreases from RD to TD. Analysis of the synergistic effect of TiBw load-transfer reinforcement and H–P reinforcement on property anisotropy shows that the combination of the H–P relationship and TiBw orientation weakens the as-rolled composites anisotropy.

Effect of deformation temperature on the slip activity in pure Mg and AZX211

The microstructural evolution and slip activity in a pure Mg and AZX211 alloy during room and cryogenic temperatures (CT: −50 °C, −100 °C and −150 °C) deformation has been systematically investigated. The influence of alloying and deformation temperature on the texture, twinability and subsequently on the deformation mechanisms has been examined. Moreover, a detailed post-mortem analysis was conducted using EBSD to reveal the enabled deformation modes in 5%-strained samples at each temperature condition. The results showed that AZX211 exhibited exceptional strength/ductility synergy with 102 MPa YS, 16.4% ductility as compared to 110 MPa YS, 10.9% ductility in pure Mg at RT. Moreover, AZX211 demonstrated superior ductility as compared to pure Mg at various cryogenic temperatures. The improved performance of AZX211 was attributed to grain refinement (24.5 and 10.1 μm for pure Mg and AZX211, respectively), texture softening (20.1 mrd and 4.9 mrd for pure Mg and AZX211, respectively) and Ca-containing second phase particles dispersed in the matrix. In addition, at 5% RT and CT deformation, both the samples displayed limited twinability. To analyze the slip modes activated at a specific condition, the in-grain misorientation axes (IGMA) analysis based on the EBSD data of tensile deformed samples was carried out. Higher activities of basal <a> and prismatic <a> slip was found in AZX211, while the low deformation temperature promoted the activation of pyramidal <c+a> dislocation slip in pure Mg.

Frictional constitutive behavior of chlorite at low shearing rates and hydrothermal conditions

Chlorite is a common, but understudied phyllosilicate mineral along continental and subduction zone faults. To understand the potential role of chlorite in different modes of fault slip, we measure the constitutive frictional properties of chlorite at low rates of deformation and shallow hydrothermal conditions by shearing powdered samples of water-saturated chlorite in the triaxial saw-cut configuration. Experiments were conducted at 25 to 130 °C, 130 MPa confining pressure, pore pressures from 10 MPa to 120 MPa, slip rates from 0.001 to 10 μm/s, and shear displacements up to 7.5 mm. The frictional strength of chlorite increases with increasing temperature from 25 to 130 °C (μ = 0.4 to 0.46), accompanied by an increased abundance of Riedel shears. Chlorite also transitions from rate-strengthening behavior at fast slip rates (0.1 to 10 μm/s) to rate-weakening or rate-neutral behavior at lower slip rates (0.001 to 0.01 μm/s), consistent with one hypothesis for the cause of slow slip. This transition in frictional behavior reflects different microphysical processes controlling the direct and evolution effects of friction. At low deformation rates, the magnitude and temperature sensitivity of the direct effect (a) are consistent with subcritical fracture. In contrast, the evolution effect (b) is insensitive to temperature and increases systematically with decreasing strain rate. We propose the increase in b and resulting rate-weakening behavior of chlorite with decreasing slip rate is controlled by time-dependent properties of adsorbed water to mineral surfaces.

Heterogeneous deformation and damage mechanisms in multi-phase TA15 Ti-alloy: Insights from experiments informed damage-crystal plasticity modelling

Understanding the mesoscale heterogeneous deformation and its induced material damage is significant to enhance the mechanical properties of polycrystalline aggregates. In this work, a damage-coupled crystal plasticity finite element (DC-CPFE) model based on high-fidelity microstructure was developed to investigate the heterogeneous deformation and damage behavior of TA15 Ti-alloy with tri-modal microstructure composed of globular alpha (αp), lamellar alpha (αl) and transformed beta (βt). A three-step procedure combining the nanoindentation test, stress relaxation test, and uniaxial tensile test was proposed to determine the material parameters in the crystal plasticity constitutive and damage models of the three constituent phases. Based on the developed DC-CPFE model, the heterogeneous slip modes and traces of tri-modal microstructure were predicted and analyzed. The heterogeneous deformation of tri-modal microstructure was found to be mainly caused by the heterogeneous deformation in α phases, which was featured by the deformation bands and local shear bands. Deformation bands occurred in both of the deformation-preferential and -lagged αp grains and the hard-to-deform αl grains. Local shear bands only produced in αl grains, which were related to both of the soft geometry orientation and the activation of prismatic slip systems. Meanwhile, the formation of deformation bands and local shear bands could be promoted by the local lattice rotation. The above heterogeneous deformation led to four types of damage, which were caused by the slip band intersection, the slip transfer impedance, the local shear band, and the property and orientation mismatches among the adjacent grains, respectively.

Effect of initial state on formability of AA1060 alloy under quasi-static and electromagnetic forming

It has been reported that the forming limit of materials can be improved during electromagnetic forming (EMF). However, the detailed mechanism of this phenomenon remains unclear. The effect of initial state on the EMF process of AA1060 is systematically investigated. AA1060-O and AA1060-H24 alloys are subjected to quasi-static (Q-S) stamping and EMF, respectively. Compared to the Q-S stamping, the forming limit and hardness of AA1060-H24 sheet are increased by 68.3% and 9.4% under EMF. However, the forming limit of AA1060-O sheet is not improved. It is found that both groups of aluminum alloys exhibit high dislocation density after Q-S stamping and the dislocation movement occurs via the plane slip mode. Moreover, dislocation cells and wavy slips are observed in AA1060-H24 sample after EMF. In the case of AA1060-O sample, the intragranular dislocation density is low without wavy slip. Therefore, the wavy slip mode may be the reason for improved forming limit under the influence of EMF. In addition, the textural strength of EMF sample is different from the Q-S deformation sample and EMF sample exhibits a higher Taylor factor value. The changes in grain size, dislocation density and texture strength alter the overall strength. The current study provides the theoretical basis for the mechanism of improved forming limit under the action of EMF.

The High-Frequency Signature of Slow and Fast Laboratory Earthquakes.

Tectonic faults fail through a spectrum of slip modes, ranging from slow aseismic creep to rapid slip during earthquakes. Understanding the seismic radiation emitted during these slip modes is key for advancing earthquake science and earthquake hazard assessment. In this work, we use laboratory friction experiments instrumented with ultrasonic sensors to document the seismic radiation properties of slow and fast laboratory earthquakes. Stick‐slip experiments were conducted at a constant loading rate of 8 μm/s and the normal stress was systematically increased from 7 to 15 MPa. We produced a full spectrum of slip modes by modulating the loading stiffness in tandem with the fault zone normal stress. Acoustic emission data were recorded continuously at 5 MHz. We demonstrate that the full continuum of slip modes radiate measurable high‐frequency energy between 100 and 500 kHz, including the slowest events that have peak fault slip rates <100 μm/s. The peak amplitude of the high‐frequency time‐domain signals scales systematically with fault slip velocity. Stable sliding experiments further support the connection between fault slip rate and high‐frequency radiation. Experiments demonstrate that the origin of the high‐frequency energy is fundamentally linked to changes in fault slip rate, shear strain, and breaking of contact junctions within the fault gouge. Our results suggest that having measurements close to the fault zone may be key for documenting seismic radiation properties and fully understanding the connection between different slip modes.

Texture evolution and slip mode of a Ti-5.5Mo-7.2Al-4.5Zr-2.6Sn-2.1Cr dual-phase alloy during cold rolling based on multiscale crystal plasticity finite element model

The complex micromechanical response among grains remains a persistent challenge to understand the deformation mechanism of titanium alloys during cold rolling. Therefore, in this work, a multiscale crystal plasticity finite element method of dual-phase alloy was proposed and secondarily developed based on LS-DYNA software. Afterward, the texture evolution and slip mode of a Ti-5.5Mo-7.2Al-4.5Zr-2.6Sn-2.1Cr alloy, based on the realistic 3D microstructure, during cold rolling (20% thickness reduction) were systematically investigated. The relative activity of the <112¯0>{0001} slip system in the α phase gradually increased, and then served as the main slip mode at lower Schmid factor (<0.2). In contrast, the contribution of the <112¯3>{101¯1} slip system to the overall plastic deformation was relatively limited. For the β phase, the relative activity of the <111>{110} slip system showed an upward tendency, indicating the important role of the critical resolved shear stress relationship in the relative activity evolutions. Furthermore, the abnormally high strain of very few β grains was found, which was attributed to their severe rotations compelled by the neighboring pre-deformed α grains. The calculated pole figures, rotation axes, and compelled rotation behavior exhibited good agreement to the experimental results.

Faceting and Twin–Twin Interactions in {1121} and {1122} Twins in Titanium

Twin–twin interactions are an important component of the microstructural evolution of hexagonal close-packed metals undergoing plasticity. These interactions are prevalent because of the predominance of twinning due to limited easy slip modes. Despite their importance, the complexities of the atomic-scale behavior of interacting twins has limited robust characterization. Using interfacial defect theory, we developed a three-dimensional model of twin–twin interactions, double twinning and other complex interfacial reactions that occur between twins acting on different interface planes. Using molecular dynamics, {1122} and {1121} twins in titanium were activated and produced facets, twin–twin interactions and double twins that we characterized with our model. The results showed excellent agreement between the molecular dynamics results and the model. Surprisingly, some highly ordered and mobile boundaries can be produced by these complex reactions, which could provide important insights for higher scale models of plasticity.

Investigation of the deformation behavior of pure titanium with different self-consistent models

The mechanical properties of an annealed commercially pure Ti plate were investigated. Tension and compression tests were made at room temperature, and EBSD was used to characterize the initial and deformed microstructures. The visco-plastic self-consistent model with an empirical Voce hardening law was used to reproduce the material behavior. Several self consistent schemes (SCS) were used, and the simulated twin volume fractions, textures and plastic anisotropy (r-values) were compared with experimental data. The hardening of slip modes by twinning were taken into account by latent hardening coefficients. Only the Tangent SCS allows reproducing perfectly all the stress-strain curves, but the latent hardening for prismatic slip by tension twinning must be higher in compression than in tension. It is found that under compression, tension twinning and prismatic slip compete and impede each other, so tension twinning dramatically increases the critical resolved shear stress (CRSS) of all slip modes, which is modeled by a strong latent hardening. But under tension, tension twins grow in undeformed matrix and slightly increase the CRSS for prismatic slip, resulting in a low latent hardening. The Tangent SCS can also reproduce better the r-values. The deformed textures predicted by all the SCS except Secant are similar. Simulations show that the CRSS for pyramidal <c+a> slip is higher than the CRSS for basal slip.

Implications of ΔK‐Rratio in vacuum

AbstractIn this article we discuss the high vacuum implications on the role of positive load ratios (R = Pmin/Pmax) on the threshold ΔKthand fatigue crack growth (FCG) behavior in commercial alloys. It is experimentally observed that the ΔKthis independent ofRin vacuum. Also, for a given applied ΔK, FCG rate is weakly dependent ofRover the entire range of crack growth rates for several alloys. In addition, limited data on both short and long crack FCG in vacuum results fall within the same experimental scatter suggesting that a typical small crack FCG effect observed in lab air was insignificant or diminished in vacuum. A marginalR‐ratio effects on ΔKthin vacuum are seen for materials with different microstructures, yield strengths, elastic modulus, work hardening properties, and slip modes. The provided analysis and examples seem to imply that FCG in vacuum be primarily dependent on applied ΔK that comes from mechanical driving force. Possible mechanistic explanations are given.

A new insight into casing shear failure induced by natural fracture and artificial fracture slip

Casing deformation is often encountered due to hydraulic fracturing in the unconventional reservoir. Analysis of 3D seismic, microseismic and logging data shows that the casing shear failure is the primary casing failure mode during hydraulic fracturing. The casing deformation is closely related to the fracture system near the wellbore, but the mechanism and law behind this phenomenon are not completely clear. The slip mechanism of the fracture system and the characteristics of casing deformation were investigated to prevent casing deformation and identify the fracture with large slip distance. Based on the Mohr-Coulomb and maximum circumferential stress theory, the slip mode of natural fracture and the slip mechanism of artificial fracture were analyzed, respectively. Then, two numerical models were established to calculate the slip distance with finite fracture height and corresponding casing deformation. Furthermore, a monitoring model of casing deformation was presented based on microseismic data and real-time injection parameters. The result shows three slip modes in the fracture system crossing wellbore under different fluid pressures, including shear-slip under low fluid pressure, open-slip under medium fluid pressure and propagation-slip under high fluid pressure. The slip distance is associated with fracture length, fracture height, fluid pressure in the fracture and fracture angle. Hydraulic fracturing not only activates natural fractures and faults but also causes the slip of artificial fractures created by hydraulic fracturing, which is responsible for the casing shear deformation after fracturing and during production. The greater the stress deflection angle, the longer and higher the artificial fracture, the more likely the casing deformation in the fracturing section. Therefore, the scale of artificial fracture should be controlled during hydraulic fracturing. This study will provide guidance for predicting fracture slip distance and casing deformation prevention.

Active Slip Mode Analysis of an Additively Manufactured Ti-6Al-4V Alloy via In-Grain Misorientation Axis Distribution

Selective laser-melted (SLM) Ti-6Al-4V alloy was quasi-statically compressed in the transverse and longitudinal directions at a strain rate of 1 × 10−3 s−1 at room temperature. The twinning, in-grain misorientation axis (IGMA) distribution and active slip modes of individual grains in the deformed SLM Ti-6Al-4V alloy were studied in detail via transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). The α’/α phase was textured with the c-axis oriented either at ~45° or perpendicular to the building direction (BD). A combined analysis of the IGMA distribution and Schmid factor revealed that the prismatic &lt;a&gt; slip or pyramidal slip was easily activated in the soft grains with their c-axes perpendicular to the BD (or the loading direction) in the longitudinal compressed sample, while slip was hardly activated in the transverse compressed sample due to the lack of soft grains. Prismatic &lt;a&gt; slip with IGMA around &lt;0001&gt; Taylor axis also occurred in {10–11} twins. The observations revealed that the prismatic &lt;a&gt; slip played a key role in accommodating the external strain and, thus, well explained the anisotropy of mechanical properties in the SLM Ti-6Al-4V alloy.

Temperature-dependent cyclic deformation behavior of CoCrFeMnNi high-entropy alloy

We compare the low-cycle fatigue behavior of a CoCrFeMnNi high-entropy alloy at room-temperature (RT) and 550 °C. The cyclic response at 550 °C manifests no cyclic softening, presence of serrated flow and reduced fatigue life compared to that at RT. Microstructural investigations show that distinctly from the dominating wavy slip at RT, dislocations planar slip complements wavy slip at 550 °C. The unexpected planar slip at 550 °C is ascribed to the increase of stacking fault width, likely due to Suzuki segregation. Furthermore, dislocation slip mode evolution with both strain amplitude and cycle number at 550 °C is revealed.

Mechanical behavior of thin CoCrFeNi high-entropy alloy sheet under laser shock peening

It is a challenge to optimize the mechanical performance of high entropy alloys (HEAs). Here, we obtain yield strength enhancement along with considerable tensile ductility of CoCrFeNi HEA by laser shock peening (LSP). The surface hardness of the material is also increased significantly by 40% after LSP. Based on microstructure analysis, it is observed that the grain refinement and the mixed deformation mode of dislocation slip and deformation twin are the main strengthening mechanisms after being treated by LSP. This study demonstrates an effective method for tailoring the mechanical properties of HEAs.

Frictional controls on the seismogenic zone: Insights from the Apenninic basement, Central Italy

Crustal seismicity is in general confined within the seismogenic layer, which is bounded at depth by processes related to the brittle-ductile transition (BDT) and in the shallow region by fault zone consolidation state and mineralogy. In the past 10-15 years, high resolution seismological and geodetic data have shown that faulting within and around the traditional seismogenic zone occurs in a large variety of slip modes. Frictional and structural heterogeneities have been invoked to explain such differences in fault slip mode and behaviour. However, an integrated and comprehensive picture remains extremely challenging because of difficulties to properly characterize fault rocks at seismogenic depths. Thus, the central-northern Apennines provide a unique opportunity because of the integration of deep-borehole stratigraphy and seismic reflection profiles with high resolution seismological data and outcrop studies. These works show that seismic sequences are limited within the sedimentary cover (depth < 9-10 km), suggesting that the underlaying basement plays a key-role in dictating the lower boundary of the seismogenic zone.Here we integrate structural data on exhumed outcrops of basement rocks with laboratory friction data to shed light on the mechanics of the Apenninic basement. Structural data highlight heterogeneous and pervasive deformation where foliated and phyllosilicate-rich rocks surround more competent quartz-rich lenses up to hundreds of meters in thickness. Phyllosilicate horizons deform predominantly by folding and foliation-parallel frictional sliding whereas quartz-rich lenses are characterized by brittle signatures represented by extensive fracturing and minor faulting. Laboratory experiments revealed that quartz-rich lithologies have relatively high friction, μ≈0.51, velocity-strengthening to neutral behaviour, and elevated healing rates. On the contrary, phyllosilicate-rich (muscovite and chlorite) lithologies show low friction, 0.23 <μ < 0.31, a marked velocity strengthening behaviour that increases with increasing sliding velocity and negligible rates of frictional healing.Our integrated approach suggests that in the Apenninic basement deformation occurs along shear zones distributed on thickness up-to several kilometres, where the frictionally stable, foliated, and phyllosilicate-rich horizons favour aseismic deformation and therefore confine the depth of major earthquake ruptures and the seismogenic zone.

Analysis of active islanding detection techniques for grid-connected inverters systems

&lt;span&gt;An island is a section of the electrical grid that contains producing assets and loads that are separated from the main grid and powered by these generators, such as solar systems, with voltage and frequency maintained at nominal levels. It's worth noting that the concept of islanding is linked to time. When the inverter detects an isolated grid activity for a particular period of time, the inverter is compelled to decouple from the general grid, according to the criteria that dictate the working principle of a photovoltaic (PV) systemThis paper presents research and comparisons of the main islanding detection techniques for single-phase systems based on various structures, as well as a comparison of the improvement of the traditional islanding detection method using three different methods (active frequency drift (AFD), slip mode phase shift (SMS) and Sandia frequency shift (SFS)). Under normal and abnormal operating conditions, a comparison of these three examined improvements was made. Additionally, physical security information management (PSIM) software simulation results are generated to test the performance and effectiveness of the effective technique plan.&lt;/span&gt;

Plastic deformation mechanisms that explain hot-rolling textures in Nickel–Titanium

Plastic deformation of B2 Nickel Titanium is usually attributed to {110}〈001〉 slip and {114}〈221〉 deformation twinning. The most commonly observed hot-worked texture of these alloys, is defined by a {111}〈uvw〉 gamma fiber and {hkl}〈110〉 partial alpha fiber. A Visco-Plastic Self Consistent (VPSC) model was used to establish relationships between microscopic slip and twin activity with the observed macroscopic hot-rolling texture. This knowledge will better aid in modeling NiTi austenite plasticity. Since the primary slip modes in NiTi do not have five independent slip systems, and deformation that can be accommodated by twinning is limited, multiple deformation modes must contribute to NiTi ductility. It is shown that {110}〈001〉 slip, {100}〈001〉 slip and, {114}〈221〉 twin deformation modes need to be active simultaneously to explain the observed textures. The relative CRSS ratios and hardening parameters were varied to study the effect of the deformation modes on the various texture components. Textures observed below 723 K and at less than 80% rolling reduction were simulated with deformation primarily accommodated on the {110}〈001〉 slip mode and {114}〈221〉 twinning mode. Textures observed at temperatures greater than 903 K and greater than 80% rolling reductions were captured in the simulations that included all three deformation modes. Activity on the {100}〈001〉 slip mode strongly correlated with the {110}〈110〉 texture component observed at high temperatures.

Cross-effects of loading rate and cumulative fault slip on pre-seismic rupture and unstable slip rate of laboratory earthquakes

The fact that the same fault may host different rupture or slip modes was partly attributed to the change in strain rate of the fault in previous studies. However, contradictory observations were obtained in the previous experimental studies, that is, the loading rate can promote or inhibit the rapid instability of faults. Although the two opposite effects of the loading rate were separately explained in the previous studies, the contradiction remains unresolved. Based on an experiment conducted on a granodiorite sample, we use the cumulative fault slip to quantitatively describe the slip-driven changes in fault properties and study the cross-effects of loading rate and cumulative fault slip on the pre-seismic rupture speed, unstable slip rate, and friction coefficient drop of the laboratory earthquakes (stick-slip events). The experimental results show that under the same loading rate, the exponential propagating rupture speed, the unstable slip rate, and the friction coefficient drop of the stick-slip events increase with increasing cumulative fault slip. As a result, the loading rate has opposite effects on the exponential propagating rupture speed, the unstable slip rate, and the friction coefficient drop under different amounts of the cumulative fault slip. This provides an explanation for the observation contradiction that the loading rate can promote or inhibit the rapid instability of the fault. The experimental results also reveal that the steady rupture speed is approximately proportional to the loading rate but weakly depends on the cumulative fault slip. Finally, the significance of the experimental results for understanding the earthquake and faulting mechanics is discussed.