Tensile Mode Research Articles

On stress- and strain-temperature behavior of titanium nickelide with various grain/subgrain size

• The effect of grain/subgrain size of TiNi alloy on martensitic transformation and stress-temperature behavior is revealed. • The effect of the grain size on plasticity is ambiguous and depends on test temperature. • The phenomena of a two-stage shape recovery under heating is revealed. • Variation of pre-strain value permits the precise control of the finish temperature of shape recovery in a wide range. The effect of grain/subgrain size in the range of 0.13−9.0 μm on mechanical and shape recovery characteristics of Ti−50.8 at.%Ni alloy was studied at test temperatures from 77 K to 373 K using tensile and bending modes. The revealed regularities can be used for the precise control of the studied properties including applied tasks.

Experimental Study on Dynamic Tensile Properties of Macro-Polypropylene Fiber Reinforced Cementitious Composites

Using a high-speed photography system and a split Hopkinson pressure bar, macro-polypropylene fiber reinforced cementitious composites are tested to reveal the effects of the macro-polypropylene fiber volume fraction and loading rate on the dynamic tensile strength and failure mode. We also analyze the functional relationship between the dynamic tensile strength, loading rate, and fiber volume fraction, and study the splitting failure process using digital image correlation technology. The evolution law of the strain and displacement fields of the specimens is obtained, and the effect of the fiber volume fraction on the crack initiation strain value is quantitatively studied. The results show that the appropriate fiber content (1.5–2%) can significantly improve the dynamic tensile strength, while a higher fiber content (2.5%) leads to deterioration of the specimen. Adding macro-polypropylene fiber prevents the specimen from undergoing central tensile fracturing under dynamic loading, and distributes the impact load more evenly, thus improving the ability of the specimen to resist cracking.

Meso-Mechanical Simulation of the Mechanical Behavior of Different Types of Steel Fibers Reinforced Concretes

Introducing steel fibers into traditional concrete can improve its mechanical properties and crack resistance, but few studies have considered how the steel fiber shape and the bond-slip effect between fibers and matrix affect the mechanical behavior of concrete. This paper establishes a three-dimensional representative volume element (3D RVE) of steel fiber-reinforced concrete (SFRC) with random distribution, different shapes, and different interfacial strengths of steel fibers using Python, Abaqus and Hypermesh. Uniaxial tensile behaviors and failure modes of the SFRC are systematically simulated and analyzed. The results show that when the interfacial strength of steel fiber/concrete is changed from 1 to 3 MPa, the tensile strength of the SFRC increases accordingly. When the interfacial strength is greater than 3 MPa, it has no effect on tensile strength. Additionally, if the interfacial strength is 1 MPa, the tensile strength of the SFRC with end-hook steel fibers is increased by 7% when compared to the SFRC with straight steel fibers, whereas if the interfacial strength reaches 2.64 MPa (strength of pure concrete), the fiber shape has little effect on the tensile strength of the SFRC. Moreover, the simulation results also show that interfacial damage dominates when the interfacial strength is less than 1 MPa, and the crack propagation rate in the end-hook steel fiber-modified SFRC is lower than that in a straight steel fiber-modified SFRC. Therefore, this research reveals that using end-hook steel fibers can improve the strength of the SFRC under low interfacial strength, but the ideal strength of the SFRC can be achieved only by using straight fibers when the interfacial strength between steel fibers and concrete is relatively high.

Three-dimensional biomimetic reinforced chitosan/gelatin composite scaffolds containing PLA nano/microfibers for soft tissue engineering application

In the current study, we successfully prepared chitosan/gelatin composite scaffolds reinforced by centrifugally spun polylactic acid (PLA) chopped nano/microfibers (PLA-CFs). Herein, different amounts of PLA-CFs (0 %, 1 %, 2 %, 3 %, and 4 % w/v) dispersed in chitosan/gelatin solution were used. Morphological characterization of prepared scaffolds revealed that at the initial stage of adding PLA-CFs, the chopped fibers were localized at the wall of the pores; however, as the fiber load increased, aggregations of chopped-fibers could be seen. Also, mechanical evaluation of scaffolds in terms of compression and tensile mode showed that samples reinforced with 2 % PLA-CFs had enhanced mechanical properties. Indeed, its tensile strength increased from 123.8 to 247.2 kPa for dry and 18.9 to 48.6 kPa for wet conditions. Furthermore, the tensile modulus associated with both conditions increased from 2.99 MPa and 44.5 kPa to 6.43 MPa and 158.4 kPa, respectively. The results of cell culture studies also confirmed that the prepared composite scaffold exhibited appropriate biocompatibility, cell proliferation and migration. The cell infiltration study of the samples revealed that scaffolds reinforced with 2 % PLA-CFs had significantly better cell penetration and distribution compared with the control ones on both days (7 and 14).

2D mesoscale modeling of compressive fracture in concrete using a mesh fragmentation technique

The computational prediction of the failure processes of concrete under compression is still a challenge. Several researchers have proposed mesoscale models to have a better understanding of the influence of the distinct phases of the concrete on the fracture process. In this sense, this work proposes an extension of the mesoscale model proposed by Rodrigues et al. (2016) to describe the complex failure behavior of concrete under compression. In the proposed 2D approach, two layers of interface elements are inserted into the standard finite element mesh to define the potential crack paths using the mesh fragmentation technique. Each layer is formed by a pair of high aspect ratio elements and is responsible for modeling the tensile or frictional shear failure behavior. According to this approach, the compressive failure is a consequence of the combination between tensile and shear failure modes in the mesoscopic scale. The use of these two damage models allows to represent the debonding (opening) between the aggregates and matrix due to local tensile stress concentration, i.e. the fracture propagation in mode-I, as well as the sliding process corresponding to the fracture propagation in mode-II. Furthermore, adopting adequate parameters, these models allow representing the friction condition between the concrete specimen and the steel loading plates. The failure behavior of compression tests with different specimen slenderness as well as the different friction restraints between loading platen and concrete specimen is predicted. The numerical results are compared qualitatively and quantitatively against the experimental results found in the literature, demonstrating that the proposed approach is able to describe the failure process of concrete in compression.

A unified regularized variational cohesive fracture theory with directional energy decomposition

In this paper, the cohesive fracture is revisited as an energy minimization problem. The energy functional is rigorously derived based on a pair of integral transformations and a novel directional energy decomposition method. The resulting description of the regularized crack is perfectly suitable for cohesive fracture. A well-defined crack direction is associated with each material point. The resulting constitutive relation shows that a damage-induced material orthotropy within the regularized crack is introduced in this theory, which is suitable for cohesive fracture. The proposed method can implement an arbitrarily given mixed-mode cohesive law. The tensile and shear fracture modes are covered in a unified manner and controlled by the tensile-to-shear strength ratio. These theoretical results are presented with detailed proofs and verified numerically by some representative examples involving tension, shear, and compression.

Remotely tuned multistate resistive switching in MoS2/NiMnIn thin film heterostructure for highly flexible ReRAM application

In this article, the Cu/MoS2/NiMnIn memory structure was fabricated over stainless steel substrate for flexible electronics applications. The bipolar resistive switching characteristics were observed in two different fabricated devices (i) without sulfur vacancies (D1) and (ii) with sulfur vacancies (D2) in MoS2 thin film. Three different resistance states such as the high resistance state (HRS), intermediate resistance state (IRS) and low resistance state (LRS) have been detected for the D2 memory device. It could be ascribed to the two filamentary models based on the movement of sulfur vacancies and the formation of Cu metallic filament with applied bias voltage. Moreover, the Ohmic and modified space charge limited conduction mechanisms clearly explain the current conduction in different resistance states of device D2. The fabricated MoS2 thin film-based memory structure exhibits stable resistive switching behavior with a high OFF/ON ratio of ∼3.6 × 103, good consistency of ∼3600 endurance cycles and excellent data retention capability up to 3000 s. Moreover, the remote tuning of device D2 was thoroughly investigated and an appreciable change in SET voltage was detected with external temperature and magnetic field. Additionally, the external magnetic field altered the switching states and enhanced the multi-bit data storage capability of the memory device. This can be ascribed to the effect of the Lorentz force on ionic movement in the presence of the external magnetic field. The mechanical flexibility of the memory structure was tested for 1000 bending cycles at various bending angles in both the tensile and compressive bending modes. Hence, the present study opens up new ways for the futuristic flexible device for high data storage and neuromorphic computing applications.

Flexible Investment Casting Wax Patterns for 3D-Printing: Their Rheological and Mechanical Characterizations.

The mechanical and rheological characterizations of flexible investment casting patterns capable of 3D printing are reported. The wax pattern was composed of microcrystalline hydrocarbon wax (DMW7478), Piccotex 75 (a copolymer of α-methyl-styrene and vinyl toluene with a 75/25 molar ratio, respectively) and Escorene (a copolymer of ethylene and vinyl acetate with a 72/28 mass ratio, respectively). It was found that in order to obtain a wax pattern with appreciable mechanical properties, the content of the microcrystalline hydrocarbon wax in these blends should not exceed 30% (m/m). Thus, a series of patterns with 28% (m/m) wax and varying Piccotex and Escorene contents spanning from 0 to 72% (m/m) was prepared. The dependence of the dynamic viscosities of the wax patterns on the composition was described using a stretched exponential model, whereas their variations with the temperature were interpreted in terms of the Arrhenius-Guzman equation. Furthermore, the slopes of the lines fitted to the viscosity versus temperature curves at the pour point decreased linearly with the Piccotex content. Non-Newtonian changes in the shear stress with the shear rate and shear stress crystallization were observed at temperatures near the pour points. The mechanical properties were evaluated using the uniaxial tensile mode and by three-point bending experiments. It was found that the stress (σ) versus the relative elongation (ε) curves can effectively be rendered by means of the standard linear solid (SLS) viscoelastic model. In addition, it was also established that the Young's modulus varied according to a sigmoid-type curve with the piccotex content, while the yield stress decreased linearly with the concentration of Piccotex. In addition, based on the spooling suitability and printability, the patterns were rated and it was found that the most appropriate wax pattern compositions for 3D printing were those which contained 30% (m/m) and 35% (m/m) Piccotex.

Failure modes in dual layer thickness Laser Powder Bed Fusion components using a novel post-mortem reconstruction technique

To exploit the design freedoms of Powder Bed Fusion, parameters can be varied within sub-volumes of components to achieve the optimal part for both service conditions and manufacturing productivity. This involves prioritising mechanical strength in areas of structural significance and high volumetric build rates in areas of low structural significance. In theory, a component with similar mechanical behaviour to that seen in standard Laser Powder Bed Fusion parts can be built in significantly less time and at a reduced cost. In practice however, the boundary between such regions is yet to be understood and discretising components into sub-volumes can induce interfacial defects. In this study, an in-depth analysis of interfaces between disparate layer thickness volumes in single components has been explored, to gain information vital to solving interface quality issues so that LPBF design freedoms can be fully exploited. A novel 3D reconstruction technique has been demonstrated to characterise transient plastic behaviour of interfacial pores post-fracture. This technique enables post-mortem evaluation of additively manufactured parts and tracking of pore deformation during subsequent mechanical testing. X-ray Computed Tomography (XCT) identified interfacial pores up to 170 µm Feret diameter, with a voxel resolution of 6 µm. Micro tensile testing with in-situ microscopy exhibited a real-time mechanical response, observing evidence that these interfacial defects lead to fracture at interface locations. The 3D reconstruction technique found that pores constricted 10.0 – 14.1% in the x direction and 10.3 – 14.6% in the y direction after fracture – normal to the loading direction. These findings contribute towards improving Additively Manufactured biomedical implants and airframe components with reduced time and cost. • LPBF components are discretised into sub-volumes with different layer thicknesses. • XCT revealed pores are introduced at the interface between sub-regions. • Interface plane orientation has a great effect on interfacial porosity. • Micro tensile failure modes are observed at the interfaces with in-situ microscopy. • A novel 3D pore reconstruction technique is demonstrated.

The influence of convex shoulder on tribological and mechanical behavior of FSLW of aircraft assembly technology

Regarding the challenges of welding for aluminum alloy, this research illustrates the influence of convex shoulder on mechanical and tribological behavior of friction stir lap welding of aircraft assembly technology. This research employs a spiral whirling needle convex shoulder, and the friction diffusion-welding test is carried out with 2024-T4 aluminum alloy sheets. Then the influence of the numbers of vortex-like needle convex shoulders on the cross-section morphology, material flow behavior, and mechanical properties are compared and analyzed. The experimental results show that there is no obvious bending phenomenon at the lapping interface under the action of a vortex-shaped stirring pin, and increasing the number of vortex-shaped structures is beneficial to increase the cross-sectional width of the nugget area. When the four vortex-shaped mixing needles are adopted, the effective lap width and fracture load of the lap joint with tensile fracture mode are greater than those with six vortex structures, respectively; the values are 11.74 mm and 17531.83 N.

Mechanical Evaluation of Salvage Fixation Techniques for a Lateralized Fibular Tunnel in Posterolateral Corner Reconstruction of the Knee.

Posterolateral corner (PLC) reconstruction of the knee involves precise drilling of a single tunnel from anterolateral to posteromedial in the fibular head (FH) to ensure adequate graft fixation. Misplacement of the tunnel in a too lateral or too superior trajectory can lead to cortical breach and inadequate graft fixation. To (1) determine the mechanical consequence of a lateralized FH tunnel in PLC reconstruction and (2) compare the mechanical strength of 3 salvage fixation techniques for a lateralized FH tunnel. Controlled laboratory study. Sawbones models of a uniform density were utilized. FH tunnels (7-mm diameter) were drilled from anterolateral to posteromedial in positive controls (lateral cortex thickness, 7.6 ± 0.7 mm) to represent an improperly placed FH tunnel at risk of lateral cortical breach. For negative controls and salvage experimental groups, FH tunnels were drilled from anterolateral to posterolateral (lateral cortex thickness, 2.7 ± 0.9 mm). Three salvage fixation techniques were compared: suture anchor fixation, tunnel redrilling, and nitinol staple fixation. Samples (n = 5 per group) underwent uniaxial tension testing, and the ultimate tensile strength (UTS) and mode of failure were recorded. Data were analyzed using the 1-sample t test and nonparametric 1-sample Wilcoxon signed-rank test. The negative control group had a 4-fold lower mean UTS relative to the positive control group (1.49 ± 0.17 vs 6.25 ± 1.98 MPa; P < .01) and exhibited failure through the lateral cortex and tunnel. Nitinol staple fixation improved the mean UTS by >16 times compared with the negative control group (24.06 ± 6.49 vs 1.49 ± 0.17 MPa; P < .01). Suture anchors and tunnel redrilling exhibited similar UTS and mode of failure to those of negative controls. Reinforcement of a thinned lateral FH cortex with a single nitinol staple improved graft fixation strength in a sawbones model. A lateralized FH tunnel can be a common intraoperative pitfall during PLC reconstruction. Salvage of a thinned lateral FH cortex with a single nitinol staple may reduce the risk of cortical breach and graft failure.

Experimental and statistical exploring for mixed-mode (I&II) fracture behavior of cement emulsified asphalt mortar under freeze–thaw cycles and aging condition

This study has been investigated the effect of freeze–thaw cycles and aging condition on the pure mode I, pure mode II and mixed-mode I/II fracture resistance of Cement Emulsified Asphalt Mortar (CEAM). The experiments were conducted on SCB specimens designed with 16 randomized mix designs with different cement contents (C), asphalt-to-cement ratios (A/C), and water-to-cement ratios (W/C) using the d-optimal response surface methodology. The specimens were divided into three groups: control specimens (n = 144), aged specimens (n = 144), and specimens subjected to 1, 3, 5, and 10 freeze–thaw cycles (n = 576). The experiments were performed in three modes of loading: pure tensile (I), pure shear (II), and mixed-mode tensile-shear (I/II). To assess the impact of freeze–thaw and aging damage on fracture properties, the Fracture Energy Ratio (FER) was defined as the ratio of fracture energy of the damaged/conditioned specimen to that of the corresponding control specimen. Then, a number of statistical models were developed for the relationship between FER and mix design variables (A/C, W/C, and C). The results showed that the application of freeze–thaw cycles reduced the fracture energy of CEAM in all three modes. The independent variable with the greatest impact on fracture energy changes was A/C for the pure tensile mode, and C for the pure shear mode and the mixed-mode tensile-shear. The initial freeze–thaw cycles were found to have a greater impact on fracture energy than later cycles. Also, freeze–thaw cycles are more detrimental in reducing mode II fracture energy than mode I and mixed-mode I/II fracture energies and therefore have a more damaging impact on the pure shear fracture properties of CEAM. Aging also reduced the fracture energy of CEAM in all three modes; an effect that was most greatly influenced by the amount of asphalt in the mortar composition. Aging had a greater impact on mode I fracture energy than mode II and mixed-mode I/II fracture energies.

Mechanical Properties and Microstructural Behavior of Uniaxial Tensile-Loaded Anisotropic Magnetorheological Elastomer

Magnetorheological elastomers (MREs) are well-known for their ability to self-adjust their mechanical properties in response to magnetic field influence. This ability, however, diminishes under high-strain conditions, a phenomenon known as the stress-softening effect. Similar phenomena have been observed in other filled elastomers; hence, the current study demonstrates the role of fillers in reducing the effect and thus maintaining performance. Anisotropic, silicone-based MREs with various carbonyl iron particle (CIP) concentrations were prepared and subjected to uniaxial tensile load to evaluate high-strain conditions with and without magnetic influence. The current study demonstrated that non-linear stress–strain behavior was observed in all types of samples, which supported the experimental findings. CIP concentration has a significant impact on the stress–strain behavior of MREs, with about 350% increased elastic modulus with increasing CIP content. Microstructural observations using field emission scanning electron microscopy (FESEM) yielded novel micro-mechanisms of the high-strain failure process of MREs. The magnetic force applied during tension loading was important in the behavior and characteristics of the MRE failure mechanism, and the discovery of microcracks and microplasticity, which was never reported in the MRE quasi-static tensile, received special attention in this study. The relationships between these microstructural phenomena, magnetic influence, and MRE mechanical properties were defined and discussed thoroughly. Overall, the process of microcracks and microplasticity in the MRE under tensile mode was primarily formed in the matrix, and the formation varies with CIP concentrations.

Compressive and Tensile Fracture Failure Analysis of Asphalt Mixture Subjected to Freeze–Thaw Conditions by Acoustic Emission and CT Scanning Technologies

The cracking of bitumen pavement in seasonal frozen areas has direct and significant influences on its properties. In order to study the compressive and tensile fracture failure features of basalt fiber-reinforced asphalt mix after freeze–thaw (F-T) treatment, the load–displacement curves under the compression and tensile modes of asphalt mixture after F-T conditions were tested. As a real-time detection means, acoustic emission (AE) was used for testing asphalt mix under compression and tensile load modes. X-ray computed tomography (CT) was employed to represent and evaluate the interior void in F-T conditions. The results showed that, as F-T conditions continue, the compressive and tensile strength of the specimens at different temperatures decreases. The amplitude and count of AE signals with the time history of load level show different characteristics of change in various intervals. AE signal indirect parameters reveal that under compressive and tensile load modes there is a gradual deterioration of performance for asphalt mix due to the coupling interactions between tensile and shear cracks. The asphalt mixtures have different behavior in F-T conditions, which are attributable to interior meso-void characteristics based on CT analysis. This study is limited to the type and loading mode of asphalt mixture in order to quantitatively predict the performance of asphalt mixture.

Buckling behavior and damage mechanism analysis of fiber-reinforced shape memory polymer composites

Shape memory polymer composites (SMPCs) are emerging as an attractive material for space deployable structures due to their variable stiffness, programmable deformation, high packing ratio, and controllable deployment. However, the research on the deformation behaviors and damage mechanisms of SMPC was scarce. The buckling behaviors and damage mechanisms of out-of-plane buckling and in-plane buckling of fiber-reinforced SMPC were investigated in this study. The expression and evolution law of strain energy and key parameters of fiber buckling were studied. The effects of material parameters and size parameters on damage mode and critical damage curvature were analyzed quantitatively. It was found that in-plane buckling was more likely to occur without external constraints. The damage modes of in-plane buckling are classified as delamination, matrix cracking and fiber tensile fracture. Out-of-plane buckling is more susceptible to damage and has one more fiber buckling fracture damage mode than in-plane buckling. When the fiber volume content is below a certain value, only fiber tensile fracture damage mode will appear, regardless of the thickness. Delamination is more likely to occur in cases of out-of-plane buckling, and matrix cracking is more frequent in cases of in-plane buckling. Subsequently, the correctness of the theoretical analysis was verified by the bending test. The theoretical analysis in this study provides a theoretical foundation for SMPCs-based structural design.

Oil Palm Fibers Micromechanics: Anisotropic Behavior

ABSTRACT The anisotropic behavior of oil palm fibers (OPF) was investigated using finite element models, which were used to fit experimental data from stalk and mesocarp oil palm fibers under different tensile deformation modes. The experimental results showed damage to oil palm fibers due to deformation, viscoelastic behavior from reduced stress at fixed strain, as well as anisotropic behavior from tensile-twisting tests. In this work, the finite element models were improved from the previous works on the fiber mechanics by including Fung orthotropic and Prony series viscoelastic functions. The developed single-element finite element model agreed with experimental tensile data under cyclic, stress-relaxation, and step-relaxation modes. The modeling parameters from the single element model and information from the experimental work were then used to simulate the deformation of a virtual fiber obtained from µ-CT analysis, as well as its composite model.

Impact of damaged external polymeric layer on axial compressive response of flexible pipes

A fully three-dimensional finite element model was developed in order to study the axial compressive response of flexible pipes. The model is parameterized and features five layers, with emphasis on the layers responsible for reacting to axial loads. Tensile armor instability may occur in the form of lateral buckling and radial buckling, also known as “birdcaging”, which is influenced by several parameters, including defects on the layers that are supposed to restrain and protect the tensile armor, more specifically, the external polymeric layer. By being the outermost layer, the external sheath is responsible for keeping the pipe watertight and it is the most likely to sustain damage from launching, collision from vessels, anchors or ice structures and even damage caused by sea creatures. This article focuses on the effect of damage on the external polymeric layer on the tensile armor instability failure modes and uses a finite element model to simulate that phenomenon. For that purpose, the outermost layer was deliberately damaged with cuts on a key position. The cut dimension is parameterized for this analysis and the results will show that, if the flexible pipe is equipped with a high strength layer and the differential pressure is not taken into account, the external polymeric layer will not play an effective part on protecting the tensile armor layers from instability. However, it may influence the triggering of the instability on a specific position of the pipe.

Mixed mode-I/II fatigue performance of Cement Emulsified Asphalt Mortar: Experimental and statistical analysis at intermediate temperature

This study has investigated fatigue life of Cement Emulsified Asphalt Mortar (CEAM) under mixed-mode I/II loadings at the intermediate temperature. For this investigation, SCB specimens of 16 randomized mixture designs with different cement contents (C), asphalt-to-cement ratios (A/C), and water-to-cement ratios (W/C) were prepared and subjected to the cyclic mixed tensile-shear loading with Me = 0, 0.5, 1.0 at three frequencies of 2, 4 and 8 Hz. The results were analyzed using the d-optimal response surface method and revealed that for all three loading modes, the fatigue life increased with increasing C and A/C. The CEAM also showed a longer fatigue life in the pure shear mode than in the pure tensile mode. The difference between the fatigue life of mode I and II was found to be increasing with the increase in cement content and loading frequency. Increasing the loading frequency increased the fatigue life of the mortar in all three modes.

Tensile behavior of cruciform stubs with four bolts per row

SummaryThe stiffened top‐and‐seat angle connection is widely used in earthquake‐prone areas, and additional tensile bolts on angles' column leg effectively improve its bending behavior. However, such design and construction are not governed by any regulations. It is urgent to figure out the mechanical behavior and develop accurate theoretical methods. Based on the component method, this paper first conducted an experimental study on the extracted cruciform stubs with four bolts per row. It compared the tensile properties and damage modes for different thicknesses. After that, the further parametric analysis compared the impact of stub thickness, bolt arrangement, and whether or not the bolt was pretensioned after validation. Stub thickness and bolt gauge were observed with a greater impact than the bolt distance on the plastic resistance. Furthermore, a prediction model for the plastic resistance of the cruciform stub with four bolts per row is proposed by integrating approaches for classic stiffened and unstiffened angles.

Tensile mechanical properties and AE characteristics of shale in triaxial Brazilian splitting tests

Under the high temperature and high stress geological environment, how the physical and mechanical properties of deep shale reservoirs will change has become a hot research issue. Based on the Confined Brazilian Test, this paper improves a test method for the tensile strength of shale under triaxial conditions with a simple specimen fixture and convenient specimen preparation and performs a high confining pressure (0–60 MPa) Brazilian splitting test on Longmaxi Formation shales. The stress-displacement curve records the deformation and failure of shale. Acoustic emission technology (AET) detects the evolution process of fractures and further identifies failure modes. 3D optical scanning system reconstructs the fracture morphology. The results show that the maximum tensile strength of the shale specimens in the triaxial condition is increased by 58.5% relative to direct tensile strength. As the confining pressure gradually increases to 60 MPa, the specimen enters the stress state of compressed in three directions, the tensile failure mode gradually transitions to shear failure mode via tensile-shear composite failure mode, and the fracture angle gradually increases. The AE signal in triaxial conditions mainly shows a leap trend. The appearance of AE signal with high peak frequency can be used as a reference for micro-fracture initiation. The presence of shear fractures increases the roughness of the shale main fracture surface, and this effect diminishes as the confining pressure increases. This study can provide a reliable theoretical basis for the optimal design of hydraulic fracturing in deep shale gas reservoirs.