Characterization Of Mechanical Behavior Research Articles

Experimental and modeling study of shear strength of unsaturated fine-grained soils with bi-modal water-retention characteristics

The mechanical behavior and strength characteristics of unsaturated fine-grained soils with dual-porosity are of crucial importance in geotechnical designs. Nanyang fine-grained soils have been selected as typical dual-porosity structure soils to perform experimental tests under a wide range of suction and different initial densities while studying its stress-strain-strength properties constitute the main scope of this study. Axial translation and vapor equilibrium techniques are jointly employed to apply a wide suction range. Our data suggest that soil behavior transits from strain-hardening with shear-induced contraction to strain-softening with shear-induced dilation as suction and density increase. By exploiting a bi-modal soil–water retention curve (SWRC) explicitly separating capillarity and adsorption mechanisms, the shear strength is allowed to be analyzed in the capillary suction stress-shear stress space. The strength envelop exhibits bi-linear characteristics. Building upon these findings, we propose a bi-linear shear strength criterion specifically for dual-porosity fine-grained soils. We utilize the obtained test data to evaluate existing strength criteria based on effective stress and dual stress variables that consider the bi-modal SWRC characteristics. The comparison indicates that the proposed bi-linear shear strength criterion can more reasonably represent the variation of shear strength under a wide range of suction for unsaturated dual-porosity fine-grained soils.

Dynamic behavior of polyethylene terephthalate (PET) foam under compressive loads: Experimental and numerical study

The behavior of PET foam under quasi-static and dynamic compressive loads is analyzed. An experimental study is performed to evaluate its mechanical behavior and energy absorption characteristics at different strain rates. Also, a numerical model is developed to reproduce the dynamic compression behavior of the PET foam. Differences between the properties obtained in the quasi-static and dynamic tests show that the strength, stiffness and energy absorption efficiency are dependent on strain rate. The evolution of the Poisson ratio with strain and strain ratio is studied. A decrease in the Poisson ratio is observed as the strain rate increases.

Investigating the Mechanical Deterioration Effect of Hard Sandstone Induced by Layer Structure under Uniaxial Compression

The deterioration of the surrounding rock at the tunnel bottom is a damage mechanics issue that occurs under disturbance load. To investigate the anisotropic characteristics of mechanical behavior and the AE response mechanism of layered sandstone, uniaxial compression tests and acoustic emission (AE) monitoring were conducted. The results show that the layer structure causes remarkable anisotropic characteristics in the wave velocities. The strain characteristics and mechanical parameters of layered sandstone exhibit obvious deterioration effects. The local strain and overall strain show a synergistic feature, with the local strain path being more complex and the deformation response being extremely sensitive. The peak stress and elastic modulus both exhibit V-type distribution rules, slowly decreasing first, then rapidly decreasing, and finally increasing rapidly, with the boundary points of the layer angle being 45° and 67.50°. The peak stress and elastic modulus show a nonlinear exponential correlation with the layer angle, and the sandstone belongs to the intermediate anisotropy level. The rupture pattern shows significant anisotropic characteristics, with the failure modes including tension failure, including tension failure I and tension failure Ⅱ, shear failure, and tension–shear composite failure. The fractal dimension shows a negative correlation with the layer deterioration effect. The AE activity exhibits a phased response characteristic to the aging deformation of layer structure. The more obvious the layer deterioration effect is, the longer the AE delay is. The AE intensity of tensile failure sandstone is generally greater than that of oblique shear failure.

Study on the formability of copper foils during multi-step micro deep drawing

In this work, the formability of copper foils was analyzed based on a series of multi-step micro deep drawing (MMDD) tests. The copper foils were annealed at temperatures ranging from 300 to 700 °C for 5 min, followed by tensile tests and electron backscatter diffraction (EBSD) tests for the exploration of mechanical behavior and microstructural characterization of annealed specimens. The results show that the as-received copper foils exhibit poor formability and cannot form micro cups during MMDD. When the annealing temperature attains 500 °C, a homogeneous microstructure was formed inside copper foils, enhancing the formability of materials and improving the surface quality of formed products. Nevertheless, both the elongation and tensile strength decrease dramatically due to the easy occurrence of incoordination deformation in coarse grain bands with further increase in annealing temperature to 700 °C. Consequently, marked wrinkling is generated on the surface of drawn cups and obvious thinning occurs at the nose radius region due to metal flow. In addition, the results show that the E texture component within the copper foils is favorable for MMDD. Overall, an optimal annealing temperature of 500 °C is obtained with improved formability of copper foils and forming quality of drawn cups.

Revealing the microstructure evolution, deformation behavior and tensile properties of AZ31/AM60 dissimilar Mg alloy joints under different welding technologies

In this work, friction stir welding (FSW) and tungsten inert gas welding (TIG) were applied to prepare two kinds of dissimilar AZ31/AM60 Mg joints. The relationship between mechanical properties, deformation behavior, and microstructure characteristics of both joints was investigated. Microstructural characterization demonstrated that a significant grain orientation fluctuation occurred in the weld zone (WZ) of the FSW joint, but this was not obvious for the TIG joint. Compared with the base metals, the grain size of the FSW joint slightly decreased, but the grain of the TIG joint obviously coarsened. Locally strong texture appeared in the WZ of the FSW joint with a symmetrical distribution, while a random texture character occurred in the TIG joint. Furthermore, the WZ of the TIG joint possessed more and larger second phases than the FSW joint. Tensile tests indicated that both joints had equivalent yield strength (∼120 MPa) and ultimate tensile strength (∼255 MPa), but the elongation (9.0 %) of the FSW joint was lower than that of the TIG joint (12.1%). The similar strength originated from the higher Schmid factors (SFs) of basal slip and extension twinning in the WZ side of the FSW joint and the larger grain size and lower dislocation degree in the heat-affected zone of the TIG joint. The decreased elongation in the FSW joint was due to the apparent inhomogeneous deformation caused by significant SFs (basal slip) fluctuation, while the weaker SFs fluctuation and notable twinning behavior in the TIG joint contributed to the relatively higher elongation.

Use of nano-silica to improve the performance of LC3-UHPC: Mechanical behavior and microstructural characteristics

Ultra-high-performance concrete (UHPC) made of limestone calcined clay cement (LC3) exhibits excellent mechanical properties as well as good environmental friendliness. This paper studied the improving effect of nano-SiO2 on the mechanical properties and microstructure of LC3-UHPC. The experimental results show that the addition of nano-SiO2 demonstrates obvious advantages. The mechanical properties of LC3-UHPC are enhanced, and the frictional bond performance between steel fiber and cementitious matrix is also improved. The fiber/matrix bond strength is increased. A constitutive model describing the single fiber pullout behavior is established, and the values of related parameters are suggested. Besides, nano-SiO2 also refined the cementitious microstructure of UHPC and made the matrix denser. Based on the comprehensive analysis of mechanical properties and microstructural characteristics, the optimal content of LC3 and nano-SiO2 were proposed.

Mechanical behavior and fracture characteristics of high-temperature sandstone under true triaxial loading conditions

To understand the stability of deep underground engineering rocks at high temperatures, it is necessary to conduct comprehensive tests on the mechanical properties of the rocks. In this study, a series of true triaxial tests (TTT) were conducted on sandstones using a self-developed true triaxial testing system combined with XRD, FE-SEM and CT analyses. The study systematically examined the microstructural characteristics, physical phase behavior, deformation properties and internal fracture development of the sandstone before and after heat treatment. The results of the study show that sandstone has temperature-dependent true triaxial mechanical properties after heat treatment. The stress-strain characteristic curves of the post-peak portion from room temperature to 800 °C show a significant stress-reducing segment, indicating the presence of brittle behavior. In addition, when the temperature exceeds 1000 °C, the sandstone exhibits brittle-ductile change characteristics, with a peak stress threshold observed at 800 °C. Notably, the peak stresses corresponding to 800 °C increased by 84.5 %, 63.1 %, 47 %, and 49.8 %, respectively, compared with the room temperature intermediate principal stresses(IPS) ranging from 20 MPa to 50 MPa, respectively. Importantly, the linear Mogi-Coulomb criterion remains valid for the peak strength of the high-temperature sandstone, while the internal fracture damage pattern of the specimens shows an inverted "Y" or inverted "W" configuration. The internal fracture network of rock samples above 800 °C is more complex. Intergranular crack is the main form of microcracking. This experimental study on the mechanical properties of sandstone under the combined effects of high temperature and real triaxial stresses provides valuable guidance for the selection of sandstone parameters and safety evaluation of coal underground gasification roofs.

Study on mechanical properties and failure mode of single-fissure sandstone discs under bi-directional linear loading

The tensile failure of discontinuous geological rock masses in underground spaces is an enduring issue in geotechnical engineering. Understanding the mechanical behaviour and failure characteristics of cracked rock under tension is vital for the safe practice of underground projects. In this study, bi-directional linear load tests were conducted on single-fissure sandstone discs under different stress ratios i (axial stress P1: lateral stress P2) = 1:1, 2:1, 3:1, 4:1, and ∞:1, with crack inclination angles α = 0°, 30°, 45°, 60°, and 90°. The specimens’ deformation characteristics, acoustic emission features, and microfracture characteristics were recorded using the digital image correlation (DIC), PIC-2 acoustic emission(AE) system, and the scanning electron microscopic (SEM). The results showed that the strength at α = 0° was not significantly different from that of intact discs. The AE results and test results indicated that the peak load and initiation load decreased when increasing α and i, and the initiation load approached the peak load. In addition, when the stress ratio was small(i ∼ 1:1), the failure mode of the specimens was mainly controlled by the lateral stress P2. As i increased, the constraint of the lateral stress weakened, and the final failure mode of the specimens was primarily determined by the crack inclination angles. Furthermore, fracture trajectories between adjacent load points were shear cracks, fractures along the axial load line were tensile cracks, and the failure between the end of the fissure and the axial load point was a tensile-shear mixed crack with tensile failure as the dominant mode. DIC displacement vector analysis and SEM results confirmed these failure characteristics. The findings provide a reference for underground support structures' design and safety maintenance.

Characterization of Microstructure and Mechanical Behaviour in Activated Tungsten Inert Gas Welded Dissimilar AA Joint of AA 5083 and AA 6061 Alloys

Characterization of Microstructure and Mechanical Behaviour in Activated Tungsten Inert Gas Welded Dissimilar AA Joint of AA 5083 and AA 6061 Alloys

Computational and experimental investigation of a new non equiatomic FCC single-phase Cr15Cu5Fe20Mn25Ni35 high-entropy alloy

The structural, mechanical, and thermal properties of a new non-equiatomic face-centered cubic (FCC) structured high entropy alloy (HEA) were examined computationally using density functional theory (DFT) calculations and validated experimentally. To identify potential single phase HEA candidates, the composition space of the CrCuFeMnNi alloy system, including 1451 alloys, was investigated using the CALculation of PHAse Diagrams (CALPHAD) method and Thermo-Calc software. The CALPHAD approach successfully predicted an FCC single-phase Cr15Cu5Fe20Mn25Ni35 alloy. Elastic constants and thermal properties of the Cr15Cu5Fe20Mn25Ni35 HEA were determined through DFT calculations using a 100-atom supercell. To validate the DFT calculations, HEA samples were prepared by the arc melting technique, and X-ray diffraction (XRD) analysis confirmed a single-phase FCC structure.The DFT calculated elastic constants values satisfied the Born stability conditions for stability of a cubic crystal structure. Pugh's theory indicated that this alloy exhibits ductility and metallic behavior due to its B/G ratio exceeding 1.75 and positive Cauchy pressure. Additionally, Poisson's ratio exceeded 0.26, further confirming its ductile nature. Experimental tests confirmed these findings by measuring bulk modulus, shear modulus, Young's modulus, and Poisson's ratio. The calculated CV values showed good agreement with experimental data at different temperatures. The linear coefficient of thermal expansion increased rapidly at lower temperatures before becoming linear. Both XRD as well as DFT calculations yielded similar lattice constant results for this HEA. These findings provide insights into various properties of the Cr15Cu5Fe20Mn25Ni35 HEA, including its structural stability, mechanical behavior and thermal characteristics.

Mechanical weakening behavior and energy evolution characteristics of shale with different bedding angles after microwave irradiation

Microwave irradiation, as a novel, clean, and efficient rock-breaking technology, can be employed in shale gas exploitation to address the challenges of low fracture efficiency and environmental pollution. Therefore, it is essential to investigate the physico-mechanical properties of shale under microwave irradiation. Firstly, samples with different bedding angles (0°, 30°, 60°, and 90°) were subjected to microwave irradiation at a power of 1 kW and frequency of 2.45 GHz for durations of 0, 20, 40, 60, and 80 s. Additionally, measurements of mass, P-wave velocity, and porosity were taken before and after microwave irradiation, followed by uniaxial compression testing using acoustic emission (AE). The results demonstrated that with increasing microwave irradiation duration, the P-wave velocity and mass of shale gradually decreased, exhibiting anisotropic behavior for the P-wave velocity. The highest degree of weakening (24.75%) was observed for shale at 0°, while the lowest (7.03%) occurred at 90°. Both uniaxial compressive strength and elastic modulus weakened gradually. Notably, USC displayed more significant weakening at 30° and 60°. The energy evolution pattern revealed increasing dissipated energy and decreasing brittleness index, enhancing anisotropy with duration, particularly at 60°. Moreover, AE captured the transition of failure mode from tensile splitting to tensile-shear failure. The results indicated the significant and anisotropic weakening effect of microwave irradiation on shale. The increase in porosity and permeability also provided preliminary evidence for the enhanced permeability ability of shale, resulting in reduced hydraulic fracturing pressures and decreased environmental pollution. Furthermore, the changes of most parameters revealed threshold effect of microwave irradiation duration, which can be classified as weak or strong depending on whether it occurs before or after 40 s. Therefore, attention should be paid to the threshold conditions of microwave irradiation duration to achieve efficient extraction. This research provided initial theoretical support for microwave-assisted shale gas exploitation.

Characterization of mechanical behavior of different types of masonry with a detailed investigation of full-field strain using digital image correlation

This article presents an experimental study on the mechanical characterization of three different types of masonry: burnt clay bricks, fly ash bricks, and autoclaved aerated concrete (AAC) blocks, with a detailed focus on strain distribution and failure mechanism. The specimens were subjected to direct and diagonal compression loading, and the stress–strain curves and failure modes were studied. Digital image correlation (DIC) was used to obtain full-field strain data, allowing for detailed analysis of failure mechanisms, tracking of crack propagation, and examination of other intricate details. The DIC analysis showed that in burnt clay brick and fly ash brick masonry, failure under compression was initiated by the tensile splitting of the brick, while in AAC block masonry, it was initiated by the tensile splitting of the mortar. Additionally, the study identified that the failure modes under diagonal compression were different for each type of masonry, with bed joint sliding being the dominant failure mode in fly ash brick and AAC block masonry. In contrast, the failure mode in burnt clay brick masonry was due to vertical splitting along the loaded diagonal. In the diagonal compression test, the shear strain along both diagonals was negligible, and principal strain directions were observed to be aligned along the two diagonals.

Mechanical Behavior and Wear Characteristics of a Conform Extruded C18150 (Cu-Cr-Zr Alloy) Rod

The demand level of Cu-Cr base alloys is on the top notch from miniature parts to large parts based on their mechanical, metallurgical, chemical, and electrical properties. Due to these, the processing of Cu-Cr-Zr alloys for the betterment of those properties has been a prospect for researchers. Commonly, Cu-Cr alloys are manufactured through the conventional extrusion process at the industrial level. However, conventional extrusion processes have some limitations, specifically regarding grain size refinement and accompanying strength. To avoid such a problem, the conform extrusion process is inculcated for the Cu and Al alloys extrusion. In the present study, C18150 copper rods were extruded from the feed stock rod of 12.5 mm to 10 and 8 mm in diameter through the conform extrusion process; however, no posttreatment and artificial aging have been made to the extrudates. The extrudates of C18150 rods were tested mechanically and microstructurally. Significant mechanical properties improvement has been observed as the diameter decreased to a certain dimension. Same phenomenon is also observed in the microstructural and hardness case. Wear test results also followed the similarity with that of mechanical properties.

Investigation of mechanical behavior, AE and EMR characteristics of rocks under compression-shear loading via variable-angle shear tests

The surrounding rocks of underground engineering are usually subjected to the coupling of compressive and shear stresses. The mechanical characteristics of underground geomaterials subjected submitted to compression-shear loading have received considerable attention recently. The complex response arises from the microstructure redistribution under high in-situ stress and the resulting fracture behaviors at multiaxial stress states. Understanding the compression-shear behavior and failure mechanism of rocks is of essential importance for mechanical characterization and construction safety in deep underground engineering applications. In this study, variable-angle shear tests are conducted for cubic sandstone samples to investigate damage evolution under compression-shear loading, and the acoustic emission (AE) and electromagnetic radiation (EMR) are simultaneously monitored to record crack development. The mechanical behaviors of rock with AE and EMR responses in variable-angle shear tests with shear angle of 30°, 45° and 60° are analyzed. Then, correlation between AE and EMR is evaluated. Damage evolution of the rock specimen is described based on AE and EMR energy. Fractal dimension and b-value of AE and EMR time series are calculated to further reveal the microscopic crack mechanism of rocks. The results suggest that the continuous decline of fractal dimension and b-value of AE and EMR can act as the precursor of rock failure.

Eccentric Compression Behaviors of Self-Compacting Concrete-Filled Thin-Walled Steel Tube Columns.

For the sake of solving sustainability issues and analyzing the complicated service force states, eccentric compression experiments on self-compacting concrete-filled thin-walled medium-length steel tube columns with a circular cross-section were carried out in the present study. Thereafter, the influence of the eccentric ratios and the wall thickness factors on the mechanical behavior and failure characteristics of both the eccentrically loaded and axially loaded columns was comprehensively analyzed. Finally, prediction formulas for the ultimate load of the columns under eccentric compression were proposed, and a comprehensive comparison of the ultimate loads between the predicted values and experimental values was also conducted. The results indicated that the typical failure characteristics of the eccentrically loaded columns presented lateral deflection together with buckling, while the axially compressed columns displayed expansion and rupture at local positions. Moreover, the ultimate loads of the eccentrically loaded columns decreased by 43.0% and 34.5% in comparison to the columns under axial compression, with the wall thickness factor decreasing from 116.7 to 46.7, respectively. Meanwhile, the ratios of the ultimate loads calculated using design codes to the tested values were in the range of 0.70~0.90, which demonstrated that the design codes could predict the ultimate loads conservatively. Additionally, the ratios of the ultimate loads calculated using the proposed formulas to the tested values were within the range of 0.99~1.08, implying that the proposed formulas were more accurate than the design codes. At the same time, the initial stiffness of the columns under eccentric compression was correspondingly lower than that of the columns undergoing axial compression. The lateral deflections along the height of the columns were almost symmetrical at different loading levels. This study could provide a meaningful approach for designing columns and facilitate their application in civil industry.

Buckling of non-Lévy-type rectangular thick plates:New benchmark solutions in the symplectic framework

The third-order shear deformation theories (TSDTs) are frequently employed to enhance the accuracy of mechanical behavior characterization for thick plates. However, the analytic buckling solutions based on the TSDTs are rare due to the major challenge in mathematical treatments. This study introduces an analytic symplectic superposition method to derive new benchmark buckling solutions of TSDT-based rectangular thick plates with non-Lévy-type boundary conditions (BCs), which are inaccessible using conventional analytic approaches. The governing equations are formulated in the Hamiltonian system. The symplectic framework-based mathematical techniques are manipulated, which shapes the characteristic of the method that a rational derivation is realized without any predetermined solution forms. The comprehensive buckling load factors and mode shapes of fully clamped plates and their variations are given, all of which are verified through comparison with the finite element method as well as literature results. Utilizing the obtained solutions, a comprehensive parametric analysis is conducted to elucidate the effects of BC, thickness-to-width ratio, and aspect ratio on critical buckling load factors. A comparison study is made between the results by the TSDT and those by the Kirchhoff theory and the first-order shear deformation theory, which demonstrates the superior accuracy of the former. The proposed rigorous framework offers a rational route to obtaining more benchmark buckling solutions.

A Fractional Creep Constitutive Model Considering the Viscoelastic-Viscoplastic Coexistence Mechanism.

In order to improve the accuracy and universality of the nonlinear viscoelastic-plastic mechanical behavior characterization method of asphalt mixture, a new criterion for the division of the creep process of materials was established based on the strain yield characteristics, and the coexistence mechanism of Viscoelastic-Viscoplastic strain was proposed in the subsequent yield phase; then, a viscoelastic element was constructed in the form of a parallel connection of two fractional viscoelastic elements based on fractional calculus theory, and its mathematical equations were derived; with novel viscoelastic elements, a constitutive model characterizing the whole creep process of asphalt mixtures was developed and its analytical expression was derived. The laboratory short-term creep test of Cement and Asphalt Mortar (CA mortar) and the simulation test data of asphalt mixtures from the references were used to verify the constitutive model. The results show that the creep constitutive model of asphalt mixture established in this paper has excellent fitting accuracy for different phases of the creep process of asphalt mixture under different stress levels, where the minimum fitting correlation values R2 for CA mortar, asphalt mixture (applied to pavement engineering), and asphalt sand are 0.9976, 0.981, and 0.979, respectively. Therefore, this model can be used to provide a theoretical reference for the study of the characterization of the mechanical behavior of asphalt materials.

Mechanical properties, flexural behaviour, and ductility characteristics of fibre-reinforced geopolymer mortar

This study aims to explore the potential of ambient-cured geopolymer as a substitute for ordinary Portland cement (OPC)-based mortar. However, due to their brittle nature, geopolymer materials require reinforcement to enhance ductility. To address this, an experimental program was conducted to investigate the effects of adding polypropylene (PP) and micro steel (MS) fibers to fiber-reinforced geopolymer mortar (FRGM) at volume fractions of 0%, 0.5%, 1%, and 1.5%. The ternary blended geopolymer mortar consisting of fly ash (FA), and ground granular blast furnace slag (GGBS), along with a novel pozzolan called eco-processed pozzolan (EPP) was investigated. The present study assessed the hardened properties of the FRGM, including compressive strength, splitting tensile strength, modulus of elasticity (MoE), ultrasonic pulse velocity (UPV), and the compressive strength of the material when exposed to elevated temperatures. The aim of this study was also to investigate the load–deflection response in terms of deflection, load, flexural strength, and toughening mechanisms; and also, the bonding between the fibers and the mortar matrix was examined using field emission scanning electron microscopy (FESEM). The results indicated that including 0.5% PP fibers and up to 1.5% MS fibers marginally improved compressive strength and MoE. The corresponding increments in splitting tensile strengths were 5% and 134%, respectively. The addition of fibers improved the fracture parameters of the FRGM. The inclusion of both MS and PP fibers significantly enhanced post-cracking flexural and toughness energy. At deflection L/150, MS fiber mixes exhibited 4–5 times higher toughness energy than PP fiber mixes, and also its evidently observed in the FESEM micrographs. The incorporation of 1.5% fiber volume to non-fibrous mix resulted in an improvement of 43.2 N.m. and 10.1 N.m. in toughness (T150) for MS and PP mixes, respectively. At an elevated temperature of 600 °C, the FRGM specimens gained a massive reduction in compressive strength, with the maximum result being at 87% for 1.5PP and 71% for 0.5MS. Overall, the MS fiber-reinforced geopolymer mixes exhibited superior performance as compared to PP fibers.

Finite element analysis of the mechanical properties of sheet- and skeleton-gyroid Ti6Al4V structures produced by laser powder bed fusion

Additive manufacturing, and laser powder bed fusion (L-PBF) in particular, can produce complex geometric components with high resolution, and is very suitable for manufacturing lightweight triple periodic minimal surface (TPMS) structures to achieve lightweight. With regard to the two forms of the same structure, most of the previous studies focused on sheet-TPMS, but lacked the understanding of the difference between skeleton-TPMS and sheet-TPMS structures. In order to explore the characteristics of these two structures and provide theoretical support for the development of lightweight structure design, this paper compares the manufacturing performance and defect distribution of skeleton-gyroid (GSK) and sheet-gyroid structures (GSH). It employs high-precision finite element analysis (FEA) prediction and experimental verification to compare comprehensively the mechanical properties, failure behavior and energy absorption characteristics of the two structures. The results show that, compared to GSK, the larger specific surface area of GSH leads to more unmelted powder and draping adhesion, without affecting its higher stiffness and strength. Moreover, the more stable failure mode of GSH leads to more gentle stress platform stage and superior energy absorption performance. The results predicted by simulation are highly consistent with the experimental results. This improved understanding allows better prediction of the mechanical properties of the specimens using the Gibson–Ashby theory, which can reduce the experimental cost and time, and improve the resource consumption of TPMS structural performance research. This study can open new possibilities for the design and application of TPMS structures.

Mechanical behavior and failure characteristics of double-layer composite rock-like specimens with two coplanar joints under uniaxial loading

To study the combined action of joints and bedding plane on crack evolution of flawed layered rock masses, uniaxial compression tests and digital image correlation (DIC) tests were carried out on double-layer composite rock-like specimens with multi-inclination two coplanar joints under different bedding angles. Based on the experimental results, the existence of bedding plane and joints performs a significant effect on characteristics of stress-strain curves and strength parameters. The failure modes are divided into four different types. The existence of bedding plane inhibits the coalescence of cracks in rock bridge area, and the variation of bedding angle affects the crack propagation path and failure mode transition greatly. For specimens with bedding angle of 30° and 45°, the larger the joint angle, the less the influence of bedding plane on failure characteristics. Besides, a new tensile crack type which initiates from the bedding plane and is easier to propagate in the upper layer was observed.