Triaxial Stress State Research Articles

Experimental study on the effective stress law and permeability of damaged sandstone under true triaxial stress

The effective stress law and the permeability play a notable role in dealing with the gas-solid coupling problem of porous media . The key parameter to quantify the influence of pore pressure to effective stress is the effective stress coefficient α ij . However, current relevant researches are mainly focused on the pore elastic flow characteristics in the elastic stage or hydrostatic pressure under conventional triaxial stress state, which are difficult to reflect the actual formation stress condition. To this end, the present study was conducted to investigate the influence of induced damage on the effective stress coefficient and the permeability of sandstone under true triaxial stress. The results showed that the effective stress coefficient and the permeability were closely related to the damage evolution and fracture propagation . α ij exhibited obvious anisotropy, α 1 was larger than α 2 and α 3 , and α 3 > α 2 appeared in the horizontal direction. α ij increased with increasing the fracture density and opening, even greater than unity. Increasing the initial horizontal stress could reduce α ij under the damage state. The elastic modulus E ij also exerted anisotropy during loading, E 1 basically exhibited an increasing trend followed by a decrease as the axial strain increased, E 2 and E 3 were continue to degrade with increasing the axial strain. Loading the deviatoric stress could cause damage, which induced the initiation and propagation of microcracks , and in turn led to the nonlinear stress-strain relationship and volume expansion of the rock, so the permeability increased, and it had increased sharply before reaching the peak strength. Under the influence of σ 2 , α ij first increased and then decreased with increasing the intermediate principal stress coefficient b under the damage stage. The porosity effect also affected the relationship between α ij and the permeability related to the induced damage, and α ij revealed an increasing trend as the permeability increased. • Effective stress coefficient a ij increases with fracture growth, even beyond unity. • a ij and E ij exhibit anisotropy with loading. a 1 is the largest, and a 3 > a 2 . • Increasing the horizontal stress can reduce a ij related to the induced damage. • a ij first decreases and then increases with increasing b under the damage state. • a ij increases with the increase in permeability attributed to the induced damage.

Experimental Investigations of Al-Cr3C2 Composite Preform Densification and Deformation

This investigation on strain hardening, densification and workability of the Sintered aluminium- Chromium Carbide composition of (Al-Cr3C2 of 2, 4 and 6%) preforms subjected to upsetting were investigated in this research. Industrial practitioners needed the workability data and densification mechanisms to plan and envisage the failure strains. In the current study, under triaxial stress state conditions Al-Cr3C2 preform with primary preform densities and various aspect ratios were compressed. Strain hardening, densification behaviors of aluminium- Chromium Carbide be investigated by gradually increasing the load till the fracture occurs. The outcome of adding Cr3C2 to Al and the impact of aspect ratio on formability was also extensively investigated. We looked at the parameters of stress ratio, instant varying strain rate, work hardening exponent, instantaneous density coefficient and densification attained.

Vertical velocity at hydrostatic and anisotropic stresses

Sonic and dipole wireline tools measure Vp and Vs along the vertical direction. The state of stress in the subsurface is predominantly anisotropic, while most laboratory experiments measuring the dynamic elastic properties are conducted under hydrostatic stress. The question we ask is whether such laboratory experiments provide the velocities that are close to those measured in the vertical wellbore where the stresses are anisotropic. To address this question, we conducted ultrasonic pulse transmission experiments on several room-dry rock samples. The comparison was made between the P- and S-wave velocities obtained at pure hydrostatic loading conditions and those at a smaller hydrostatic stress with added axial stress, so that the total stress along the axis of a cylindrical plug was the same as under pure hydrostatic loading. These differences were significant in the extreme case of only 1 MPa hydrostatic confining stress with the axial stress increasing up to 40 MPa. However, as the hydrostatic (confining) stress increased, the differences between the velocities along the axis of the sample became smaller and smaller. For example, at 1 MPa confining and 30 MPa axial stress, the relative difference in Vp was about 10%, while that in Vs was about 20%. However, at 10 MPa confining stress, these differences became about 3% and 6%, respectively, and further decreased as the confining stress increased. This means that even at strong in-situ contrasts between the vertical and horizontal stresses, the results of laboratory hydrostatic experiments can be used for in-situ velocity estimates. These results also appear to be consistent with a theoretical model that predicts the directional velocities at any triaxial stress conditions from those measured versus hydrostatic stress.

Inverse Finite Element Approach to Identify the Post-Necking Hardening Behavior of Polyamide 12 under Uniaxial Tension.

Finite-element (FE) simulations that go beyond the linear elastic limit of materials can aid the development of polymeric products such as stretch blow molded angioplasty balloons. The FE model requires the input of an appropriate elastoplastic material model. Up to the onset of necking, the identification of the hardening curve is well established. Subsequently, additional information such as the cross-section and the triaxial stress state inside the specimen is required. The present study aims to inversely identify the post-necking hardening behavior of the semi-crystalline polymer polyamide 12 (PA12) at different temperatures. Our approach uses structural FE simulations of a dog-bone tensile specimen in LS-DYNA with mesh sizes of 1 mm and 2 mm, respectively. The FE simulations are coupled with an optimization routine defined in LS-OPT to identify material properties matching the experimental behavior. A Von Mises yield criterion coupled with a user-defined hardening curve (HC) were considered. Up to the beginning of necking, the Hockett–Sherby hardening law achieved the best fit to the experimental HC. To fit the entire HC until fracture, an extension of the Hockett–Sherby law with power-law functions achieved an excellent fit. Comparing the simulation and the experiment, the following coefficient of determination could be achieved: Group I: > 0.9743; Group II: > 0.9653; Group III: > 0.9927. Using an inverse approach, we were able to determine the deformation behavior of PA12 under uniaxial tension for different temperatures and mathematically describe the HC.

Comparative Study of Shear Fracture between Fe-based Amorphous and Ultrafine-grained Alloys Using Micro-tensile Testing

Micro-tensile tests were employed to clarify the post-plastic-instability behavior in the shear fractures of specimens with the dimensions of 18×25×50 µm3 made from iron-based amorphous (AM) and ultrafine-grained (UFG) alloys. The AM specimen yielded by localized shear bands with an inclination angle of ~52° with respect to the loading axis, followed by sliding off almost throughout the entire specimen thickness. Micro-tensile and micro-shearing tests revealed that the Mohr failure envelope of the AM specimens could be described by a quadratic equation rather than a linear equation. Therefore, the sliding-off process is assisted by the applied normal stress, which suggests that it is caused by free-volume coalescence. For the UFG specimen, yielding set in by shear band formation with an inclination angle of ~45° with respect to the loading axis, following the Tresca criterion. Necking after shear band diffusion formed a triaxial stress state, which resulted in a final shear fracture plane via void coalescence in the UFG specimens. Voids formed along the intersection of the primary shear bands with secondary shear bands during the necking process. This indicates that the deviation of the shear fracture plane in the UFG specimen was determined by the strain development process. A comparison of the post-plastic-instability behavior between the AM and UFG specimens suggests that the external control of triaxial stress conditions is key to improving the formability of AM specimens.

Interpretation of mechanical and biodegradation behaviour of municipal solid waste

An advanced constitutive model for MSW (municipal solid waste) is proposed in this study to consider biodegradation and overconsolidation jointly based on sub-loading surface plasticity. A reference line, namely the BNCL (biodegradation-independent normally compression line), is introduced to quantify the total biodegradation time and overconsolidation state of MSW. Under unchanged stress level, the void ratio change due to biodegradation is interpreted as the change of overconsolidation. An isotropic stress–strain-biodegradation constitutive model is then proposed by considering biodegradation-dependent deformation through overconsolidation parameter. The current yield surface and the reference yield surface are introduced for assessing the effect of overconsolidation (biodegradation has been included). The isotropic model is then extended to a triaxial stress state in the space of mean effective stress, deviator stress and biodegradation variable. The performance of the constitutive model is discussed through various scenarios and validated by using experimental data from the literature.

Experimental study on deformation and fracture characteristics of coal under different true triaxial hydraulic fracture schemes

Hydraulic fracturing techniques are often applied to form permeability enhancement zones near boreholes and/or wellbores in tight low-permeability reservoirs to improve their extraction efficiency. As conventional hydraulic fracturing techniques often generate high breakdown pressure and induced seismic potential, novel alternative production enhancement techniques (such as pulse hydraulic pressurization) have been proposed. However, their applicability requires further verification. Therefore, this study conducted hydraulic fracturing tests of coal under three test schemes: conventional hydraulic fracturing (CHF), stepwise pressurization hydraulic fracturing (SPHF), and stepwise pulse pressurization hydraulic fracturing (SPPHF), considering the true triaxial stress state of an actual coal seam. The results showed that the breakdown pressure of coal decreased with an increase in the horizontal stress difference (σ2-σ3). Moreover, the pulse pressurization produced more intergranular fractures and caused a large number of particles to be conducted as a stress concentrator at the fracture tip spalling, which promoted the unstable propagation of fractures, which decreased the breakdown pressure of coal. The abnormally high breakdown pressure in the SPHF experiments is likely due to the obstruction of high σ2 to the fracture propagation rate and fluid injection, which intensifies the fluid hysteresis effect and the stable fracture development and expansion during the pressure-maintaining stage, thus increasing the breakdown pressure. To describe the relationship between the variation in the breakdown pressure and fracture evolution characteristics, we introduced the equivalent characteristic length l and established a breakdown pressure prediction model based on the tensile stress criterion, which shows effective prediction of the breakdown pressure in different test schemes. Anisotropic principal strain appeared under different injection schemes. During the CHF and SPHF experiments, fluid injection deformed the σ1 direction by compression and the σ3 direction by expansion. In the σ2 direction, the deformation transitioned from expansion at a low stress level to compression at a high stress level. The deformation in the σ2 direction was always compressive in the SPPHF experiments. Continuous and pulse pressurizations can promote the deformation and fracture development. For the fracture morphology, the coal in the CHF experiments was dominated by a single tensile fracture, and macroscopic shear fractures were formed in the SPHF and SPPHF experiments owing to the continuous stimulation of fluid pressure to the bonding of particles and the weak surface structure, such as bedding and cleats during the pressure maintenance and pulse, and the fragmentation effect was significant and accompanied by obvious particle spalling.

Multiaxial Damage Ratio Strength Criteria for Fiber-Reinforced Concrete

Based on the damage ratio strength theory, a dimensionless damage ratio strength criterion for fiber-reinforced concrete (FRC) under true triaxial stress states was established under the assumption of small strains. Based on the experimental data of steel fiber–reinforced concrete (SFRC), polypropylene fiber–reinforced concrete (PFRC), hybrid fiber–reinforced concrete (HFRC), and steel fiber–reinforced high-performance lightweight concrete (SFRHLC), parameters for the damage ratio criterion were recommended. The damage ratio values were verified by SFRC experimental results under uniaxial, biaxial, and triaxial loading conditions, and the damage ratio values of SFRC under uniaxial tension, uniaxial compression, and biaxial equal compression stress conditions were compared with those of plain concrete. The true triaxial damage ratio strength criterion can be reduced to the conventional triaxial criterion and biaxial criterion, and the corresponding simplified strength criteria were proposed. The proposed dimensionless six-parameter criterion agrees well with the experimental results of the aforementioned materials for true triaxial, conventional triaxial, and biaxial loading conditions. Compared with the strength criteria in other studies, the proposed criterion can accurately represent the strength characteristics of FRC.

Experimental investigation of timber samples under triaxial compression conditions

Timber is re-emerging as a prominent structural material in construction due to its sustainability and aesthetic features. Timber is increasingly used in composite elements made along with steel and concrete. In the composite elements, timber is subjected to a triaxial confined stress state. However, the characteristics of timber under triaxial stress state are not well understood. An experimental campaign was carried out to characterise the triaxial confined behaviour of timber samples. Two types of timbers (soft and hardwood) were used in the experimental campaign. The selected timber samples were subjected to confined and unconfined axial compression loading conditions. In total, 50 samples were tested with five different lateral confining pressures (unconfined, 3, 5, 8 and 12 MPa). The experimental results are presented in terms of compressive strengths and axial compression stress-strain curves. The experimental data obtained was used to define the critical parameters of confined timber, such as confined strength, strain at peak stress and stress-strain behaviour. Test results demonstrate that the confinement pressure improves the strength and ductility, and the conventional Mohr-Coulomb criterion can be used to represent the confined timber strength and strain evolution. Finally, based on the data gathered, a suitable constitutive model to characterise the stress-strain behaviour of timber under the triaxial confined stress-state is proposed. This model is similar to the constitutive models typically used for concrete, mortar and rock under confined stress state. However, differences are highlighted in timber in terms of strength gain and ductility.

Study on Failure Difference of Hard Rock Based on a Comparison Between the Conventional Triaxial Test and True Triaxial Test

The study on the failure difference of deep hard rock based on the comparison between conventional and true triaxial tests can help us better understand the fracture processes and failure characteristics of the deep rock mass. Therefore, this article carries out a comparative analysis of the failure of hard rock under conventional and true triaxial stress states. Within the scope of this study, it is found that the brittle–ductile transformation properties can be intuitively reflected in the rock stress–strain curve and failure mode. The brittle–ductile transition point of rock can also be determined by the difference between peak and residual strengths. The rock failure strength increases with the increase of σ2, the peak strain decreases with the increase of σ2, the stress drop of the post-peak curve becomes more obvious with the increase of σ2, and the rock tends toward Class II brittle failure after the peak with the increase of σ2. When σ3 is relatively high, the rock fracture angle increases with the increase of σ2 with obvious regularity. Compared with conventional triaxial stress conditions, the differential stress-induced anisotropy failure is the biggest difference in rock fracture characteristics between true and conventional triaxial stress states. This study can supply useful references to the study of failure properties of hard rock under complex stress states.

Strength characteristics of brittle rocks under multi-stage intermediate principal stress loading

A series of single-stage true triaxial compression (TTC) tests and multi-stage intermediate principal stress (σ2) loading tests were carried out on three types of brittle rock specimens in this study to examine the influence of σ2 and the validity of obtaining strength parameters by using a multi-stage loading method under true triaxial stress conditions. There exists a critical σ2 at which the rock strength attains its ultimate value under both loading conditions. Under the same σ3 level, the critical σ2 is much smaller under the multi-stage σ2 loading compared with under the single-stage TTC. The test results also show that the strength determined under multi-stage σ2 loading is much smaller than that determined under single-stage TTC. The strength difference can attain 39%. A lower strength is measured under multi-stage σ2 loading because the local fracture plane induced by true triaxial stress is parallel to the σ2, and the strength of the rock specimen containing this type of local fracture plane is not affected by σ2. On the contrary, rock damage accumulates during multiple loading and unloading cycles. The current testing results indicate that the multi-stage loading test is not suitable for determining the strength envelope of brittle rock under true triaxial conditions.

Mechanical Behavior and Fracture Characteristics of Rock with Prefabricated Crack under Different Triaxial Stress Conditions

In this study, the compression failure test of rock with prefabricated fractures under different true triaxial conditions is carried out by using the true triaxial electro-hydraulic servo test system. The traditional large number of fracture laws with prefabricated fissures are merged and attributed to the induction of intermediate principal stress. The test results show that the direction of σ2 has a significant effect on the deformation characteristics of the prefabricated fractured rock. The internal crack expansion direction is more random and the crack distribution is more extensive and complex under uniaxial and conventional triaxial conditions. Under biaxial and true triaxial conditions, the crack propagation direction is clearly along the σ2 direction. This shows that the development process of internal cracks in rocks tend to the direction of σ2. Further, the failure mechanism of rock with prefabricated cracks is analyzed based on theory. It is found that the intermediate principal stress direction plays a very important role in inducing the direction of rock crack propagation. According to the unified idea, the fracture analysis of fractured rock is summed up as true triaxial theory, and the results are consistent with the experimental results. This provides a new perspective for the study of rock fracture mechanics, and provides an important basis for the analysis of surrounding rock fracture mechanism of underground engineering.

Correction of the stress–strain curve for 2024 aluminum alloy after necking using the new surface strain method

Nowadays, many studies concerning plasticity and numerical simulations indicate that the true stress–strain curve plays a prominent role in the analysis of metal deformation. Hence, a new method is considered to correct the stress–strain curve based on image processing. Since the axial stress mainly becomes triaxial in the neck zone, the relationship obtained from the engineering stress–strain curve is not reliable in terms of authenticity and accuracy. Accordingly, correcting this relationship is highly advantageous and necessary. Due to the triaxial state of stress in the plastic area, longitudinal and surface strains are calculated through image processing and the correction coefficient of the stress–strain curve is obtained based on them. The equation of the stress–strain curve is based on the Hollowman relation until the onset of necking and then becomes almost linear. The finite element method (FEM) is employed for validating the obtained results. Since the corrected stress and strain equation is linear, the objective function of optimization is considered. This optimization is based on minimizing the difference between the three diameters values of the specimen, which are observed through experiment and FEM. Besides, a statistical method with the help of the genetic algorithm is employed to minimize this difference. As a result, an optimal equation is predicted for the 2024 aluminum based on the stress–strain curve of the error rate. Finally, a comparison is made between the results obtained from the surface strain method and the results obtained from the classical methods of Bridgman and Davidenkov, and a good agreement is observed between them.

Predicting compressive strength and behavior of ice and analyzing feature importance with explainable machine learning models

Building and using ice-related models is challenging due to the complexity of the material. A common issue, shared by both material models and (semi-)empirical approaches, is estimating unknown input parameters such as compressive strength. This is often done with additional empirical formulas which have drawbacks, e.g., they are based on a limited amount of data. Regarding material modeling, a strongly related problem is the prioritization of effects to include in the model. This is mostly done based on a subjective mix of knowledge, model purpose, and experimental studies limited to that purpose, which risks overlooking effects or interaction of effects, and limits transferability of material models to other scenarios.To tackle these issues, a hybrid approach of domain knowledge and explainable machine learning was used. A large ice test database was compiled to train machine learning models to predict compressive strength and behavior type. The machine learning models’ predictions were more accurate than existing empirical or analytical approaches and can thus be used as an alternative, though less straightforward, tool for such predictions. Further, the SHAP explainable AI method was applied to the predictions. Impact rankings of experimental parameters and interaction effects between parameters were analyzed and discussed in terms of ice mechanics. Top features were strain rate, triaxial stress state, temperature, and loading direction, but impact rankings were highly dependent on prediction target and type of ice. Few interaction effects were found. The approach adds objectivity to the prioritization of effects for material modeling and generated further insights into ice mechanics. It is also considered useful for other natural materials or generally when there is more data than knowledge.

Experimental investigation on hard rock fragmentation of inserted tooth cutter using a newly designed indentation testing apparatus

This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus. This apparatus was designed to realize a triaxial loading and indentation test of cylindrical specimens using inserted tooth cutter. The boreability and crushing efficiency of granite rock was investigated by analyzing the change rules of the thrusting force, penetration depth, characteristics of chippings and failure patterns. Several quantitative indexes were used to evaluate rock boreability in this investigation. The granite rock samples all had a chiselled pit and a crushed rock core. Under initial stress conditions, only flat-shape chippings were stripped from the rock surface when the thrusting force reached 20 kN. The rock cutting special energy had a close correlation with the initial stress conditions and inserted tooth shape. Moreover, a thrusting force prediction model was proposed in this paper. The contribution of this study is that for the first time the influence mechanism of the initial triaxial stress conditions on rock fragmentation is investigated using an inserted tooth and the newly designed testing apparatus. This study has a crucial importance for practical underground hard rock crushing in geoengineering.

Transition from necking to cavitation driven tertiary creep with length scale in constrained ductile metal joints

This study investigates the effect of length scale on the tertiary creep behavior of elastically constrained ductile metal joints. Creep tests were performed in tension on Sn–Cu joints of thicknesses ranging from 1.4 mm to 170 μm. Sn being more creep compliant as compared to Cu undergoes creep deformation, whereas Cu remains in the elastic state. The overall creep rate and the amount of strain accumulated during the tertiary creep decreased with reduction in joint thickness. This was accompanied by a reduction in the extent of lateral contraction, especially near the fracture surfaces of the joints. Fractographs revealed a transition in the mode of creep failure from pure necking in thick joints to cavitation along with constrained necking in thin joints. A joint size dependent tertiary creep model incorporating necking and cavitation was developed to explain the observed transition in tertiary creep behavior and final failure. The model captures the effects of both joint size dependent triaxial stress state and a decrease in the size of the necking ligament with reduction in joint size. Overall, the decrease in strain accumulated during tertiary creep is attributed to smaller size of the neck and higher triaxiality in thin joints, which enhances the strain due to cavity growth and reduces that due to necking as the joint thickness reduces.

Constitutive model for fibre reinforced composites with progressive damage based on the spectral decomposition of material stiffness tensor

Complex nature of the fibre reinforced composites, their non-homogeneity and anisotropy make their modelling a challenging task. Although the linear – elastic behaviour of the composites is well understood, there is still a significant uncertainty regarding prediction of damage initiation, damage evolution and material failure especially for a general loading case characterised with triaxial state of stress or strain. Consequently, simplifying assumptions are often unavoidable in development of constitutive models capable of accurately predicting damage. The approach used in this work uses decomposition of the strain energy based on spectral decomposition of the material stiffness tensor and an assumption that each strain energy component represent free energy for a characteristic deformation mode. The criteria for damage initiation are based on an assumption that the damage corresponding to a deformation mode is triggered when the strain energy for that mode exceeds a specified critical limit. In the proposed model the deformation modes are not interacting at continuum scale due to orthogonality of the eigenvectors, i.e. the stiffness tensor symmetry. Damage and its evolution are modelled by reduction of the principal material stiffness based on the effective stress concept and the hypothesis of strain energy equivalence. The constitutive model was implemented into Lawrence Livermore National Laboratory (LLNL) Dyna3d explicit hydrocode and coupled with a vector shock Equation of State. The modelling approach was verified and validated in a series of single element tests, plate impact test and high velocity impact of hard projectile impact on an aerospace grade carbon fibre reinforced plastic. The model accurately predicted material response to impact loading including the test cases characterised by presence of shock waves, e.g. the plate impact test. It was also demonstrated that the model was capable of predicting damage and delamination development in the simulation of the high velocity impact tests, where the numerical results were within 5% of the post impact experimental measurements.

Transformation yield surface of nanocrystalline NiTi shape memory alloy

Molecular dynamics (MD) simulation is used for investigating mechanical behavior and phase transformation in nanocrystalline NiTi shape memory alloy (SMA) under complex stress states, including uniaxial, biaxial and triaxial stress states. The simulation results indicate that tension-compression asymmetry occurs in terms of transformation strain, critical transformation stress, dissipation energy density, martensite variant and martensite domain. This asymmetry is mainly aroused by the fact that transformation strains under the stress states with tensile loading in the major deformation direction are larger than the counterparts under the stress states with compressive loading in the major deformation direction for most crystallographic orientations. The phase transformation stresses in complex stress states strictly comply with neither the Von Mises criterion without considering tension-compression asymmetry nor the Bouvet and Patoor criteria considering tension-compression asymmetry. Consequently, a new transformation yield criterion on the basis of Bouvet and Patoor criteria is proposed in the present work to precisely describe the transformation stress anisotropy of nanocrystalline NiTi SMA under complex stress states.

Unsaturated wetting deformation characteristics of a granite rockfill under rainfall conditions

Rainfall-induced unsaturated wetting deformation has been one of the main sources of postconstruction deformations of rockfill structures. An experimental study is presented of the unsaturated wetting deformation characteristics of a weakly weathered granite rockfill under different triaxial stress conditions and rainfall intensities investigated by a modified triaxial apparatus equipped with the newly developed rainfall simulator. Results show that the wetting deformation of rockfill materials occurs at a relatively small water content; when the rockfill reaches a critical wetting point (i.e., the effective water content), additional water does not produce more deformations. It is shown that the tested rockfill material has an effective water content of <6.89%, with a corresponding effective degree of saturation of <17.26%. Moreover, the unsaturated wetting deformation can be classified into two components: the instantaneous wetting deformation that occurs during rockfill wetting and exhibits properties of parallelism and the wet-state creep deformation that occurs time-dependently after the rockfill is wetted and shows features similar to those of general creep deformation, suggesting that unsaturated wetting can be considered as a generalized load. Finally, by introducing the two-stage wetting deformation model, the experimental curves of axial strain and volumetric strain against time were well predicted.

Experimental study on the shear‐slip characteristics of natural fractures in shale reservoirs

AbstractThe injection of high‐pressure fluid and the propagation of hydraulic fractures (HF) can impact the stress state of natural fractures (NF) in shale reservoirs, which will lead to shear slip in NF that are in a critical stress state. However, the NF mechanics response mechanism during hydraulic fracture (HF) approximation has not been well investigated, especially under triaxial stress and injection conditions. This work focuses on the NF shear‐slip characteristics during HF through experimental investigation. Each shale sample contains a single rough NF in the tests, and high‐pressure fluid is injected through a pre‐drilled hole at the top of the sample. Meanwhile, the deformation (axial deformation and radial deformation), axial stress, and injection pressure of the sample during the experiment were recorded in real‐time. The experimental results show that the NF will initiate in tension or shear mode during the HF approaching process, and the fracture will produce shear slip in both initiation modes. In addition, the deviator stress, confining pressure, hydraulic fracture approach angle, and fracture surface roughness all affect the degree of shear slip in natural fractures (NF). The results further reveal the mechanical response mechanism of NF during hydraulic fracturing and provide a reference for optimizing hydraulic fracturing process measures.