Uniaxial Compression Failure Research Articles

Determination of the effect of elevated temperatures on dynamic compressive properties of heterogeneous concrete: A meso-scale numerical study

In the present study, considering the internal heterogeneity of concrete, a meso-scopic simulation method was established to explore the dynamic compressive behavior of heterogeneous concretes at and after elevated temperature. In the meso-scale numerical model, the concrete was regarded as a tri-phase composite material consisting of aggregate, mortar matrix and the Interfacial Transition Zones (ITZs). Both the high-temperature degradation effect and the strain rate enhancement effect of the meso-components were taken into account. The simulation method involved two steps: (1) the heat conduction behavior was simulated initially; and (2) using the “result output” as “initial conditions”, the dynamic mechanical behavior of concrete was simulated. Based on the great agreement between numerical simulation results and the experimental observations, the dynamic uniaxial compression failure behavior and meso-scale failure mechanism of concrete at and after elevated temperature were studied. Furthermore, the effect of high temperature on the macroscopic dynamic compressive strength and elasticity modulus of concrete were revealed. The results indicate that the concrete specimen still shows significant strain rate effect at and after elevated temperature while the mechanical properties of concrete specimens after natural cooling further degenerates comparing with those at elevated temperature.

Experimental and numerical investigation of brittle sandstone specimens containing different shapes of holes under uniaxial compression

Defects, such as joints, fissures and holes, are common in natural rocks. These pre-existing defects have significant effects on the mechanical properties of rock masses. Researchers have performed several studies on jointed or fissured rocks; however, rock specimens with one hole of different shapes have not been studied systematically. In this research, the mechanical properties and cracking behaviors of specimens with a hole under uniaxial compressive loading are explored through laboratory experiments. The corresponding numerical simulations using two-dimensional particle flow code (PFC2D) are conducted and the force field distribution before and during cracking, which is significant for exposing the cracking mechanism but hard to be measured in laboratory tests, were captured. The results demonstrate that the shape of hole has a considerable impact on the uniaxial compression strength and failure mode but minimal effects on the elastic modulus. The force field distribution before crack initiation varies with the shape of the pre-existing hole, and differences primarily exist in the configuration of the pure tension triangle and the low force region. During compressive loading, the crack initiation and propagation are influenced by the force field distribution, which will be affected by the newly formed cracks in return. The macro-cracks, generated in the specimens with a hole under compression, can be assigned to two categories: tension-induced cracks and compression-induced cracks. The former type of crack is typically thin and comparatively orderly, and it generally propagates along the maximum loading direction. The latter type of crack is relatively disorderly and thick, and it typically forms from the coalescence of several short but thick cracks. The compression-induced crack is a mixture of tension and shear cracks whereas the tension-induced crack is a pure tension crack.

Multi-Scale Progressive Damage Model for Analyzing the Failure Mechanisms of 2D Triaxially Braided Composite under Uniaxial Compression Loads

Based on continuum damage mechanics (CDM), a multi-scale progressive damage model (PDM) is developed to analyze the uniaxial compression failure mechanisms of 2D triaxially braided composite (2DTBC). The multi-scale PDM starts from the micro-scale analysis which obtains the stiffness and strength properties of fiber tows by a representative unit cell (RUC) model. Meso-scale progressive damage analysis is conducted subsequently to predict the compression failure behaviors of the composite using the results of micro-scale analysis as inputs. To research the free-edge effect on the local failure mechanisms, meso-scale models of different widths are also established. The stress-strain curves obtained by numerical analysis are verified with the experimental data. Results show that fiber and matrix compression failure inside the fiber tows are the major failure modes of the composite under axial compression. For transverse compression, the dominated failure modes are recorded for matrix compression failure inside the fiber tows. It is also presented that the free-edge effect plays an important role in the transverse mechanical response of the composite, and the failure behaviors of the internal fiber tows are strongly influenced as well.

Compressive Strength and Block-Mortar Bond of a New-Type of Insulation Hollow Block

This paper mainly studies the mechanical properties of hollow block made from shale, coal gangue and sawdust. In China, shale is gradually used as substitute material for clay in the manufacture of sintered masonry materials. The research goal was to provide basis for the generalization and application of the fired shale hollow block through uniaxial compress compression test and failure mode under biaxial stress state. Results showed that the hollow block had reliable compressive strength and bond strength with lower density and good thermal insulation performance, meaning the feasibility of application in practical engineering.

Numerical Simulation on Uniaxial Compression Failure of A Roof Rock–Coal–Floor Rock Composite Sample with Coal Persistent Joint

Geological dynamic hazards during coal mining can be induced by the structural instability of a composite structure of roof rock, coal and floor rock layers, whereas the joint in coal plays a vital role in the corresponding structural instability. In this paper, the effects of coal persistent joint on the uniaxial compression failure of a roof rock–coal–floor rock composite sample were analyzed using PFC2D software. The results show that with an increase of included angle $$\alpha$$ between the loading direction and coal persistent joint plane, the uniaxial compressive stress (UCS) and peak strain of the composite sample decreased firstly and then increased. The change of elastic modulus was not obvious with $$\alpha$$ . The UCS and peak strain at $$\alpha$$ of 45° were the smallest. Additionally, the coal bodies in composite samples were mainly destructed as a shear failure. The roof or floor rock presented a tensile failure or no damage. And four failure patterns were observed for composite samples after failure, i.e., inverted V-shaped shear failure in coal and tensile failure in roof or floor rock, M-shaped shear failure in coal and tensile failure in floor rock, shear failure along the joint plane in coal and tensile failure in roof and floor rocks, shear failure along partial joint plane without obvious damage for roof or floor rock.

Study on the Progressive Failure Characteristics of Coal in Uniaxial and Triaxial Compression Conditions Using 3D-Digital Image Correlation

To investigate the progressive failure process of coal, a series of uniaxial and triaxial compression tests were conducted and a novel 3D digital image correlation instrument with six cameras combined with a special transparent pressure cell was used for the strain measurement. The stress thresholds of coal were obtained in uniaxial and triaxial compression. The energy evolution during the compression was discussed, coupled with the crack volumetric strain. The field strain of the whole specimen surface and crack propagation at different stress levels were described to study the progressive failure mechanism of coal. The average stress level of crack initiation and crack damage of coal in uniaxial compression are 43.75% and 63.03%, while that in the triaxial compression are 74.53% and 89.84%, respectively. The dissipation energy evolution corresponds to the crack volumetric strain, while the elastic energy release leads to flake ejection and coal failure. The crack evolution and localization of coal indicated the progressive failure process that the coal sample undergoes in tension failure in uniaxial compression and in tension-shear failure in triaxial compression. The findings of this study can serve as a reference to understand the failure process of coal and improve the stability and safety of mining engineering.

Effect of joint angle in coal on failure mechanical behaviour of roof rock–coal combined body

Geological dynamic hazards during coal mining can be caused by the structural instability of a composite system of roof rock and coal layers, and joints in coal play a vital role in this structural instability. In this paper, uniaxial compression simulation tests on roof rock–coal combined bodies with a single joint at different angles in coal were conducted using PFC2D software. In particular, the effects of joint angle on the uniaxial compressive strength (UCS), acoustic emission (AE) and failure characteristics in a combined body were analysed. The results show the following. (1) The joint in coal causes a decrease in the UCS and crack initiation stress, and has promoting effects on the AE occurrence of the combined body. With an increase in the included angle α between the loading direction and joint plane direction, the UCS, AE occurrence time and crack initiation stress first decrease and then increase, presenting ‘V-shaped’ curves. The UCS and crack initiation stress at α of 45° are the lowest, and the AE occurrence time at α of 30° is the earliest. (2) The AE characteristics at α of 0°, 75° and 90° are basically consistent with those of the intact combined body, whereas at α between 15° and 60°, the intensity and frequency of AE events in the macro-failure stage are reduced by the joint in coal. (3) The failure of the combined body mainly occurs within the coal, whereas no apparent failure is observed for the roof rock. Only when α is between 15° and 45°, the roof rock near the bedding plane is destroyed by crack propagation in the coal. (4) Three typical failure modes (i.e. V-shaped shear failure cutting across the coal, shear failure partly along the joint plane direction and shear failure along the joint plane direction) are found for combined bodies with a single joint in coal.

Effects of Diatomite–Limestone Powder Ratio on Mechanical and Anti-Deformation Properties of Sustainable Sand Asphalt Composite

Diatomite has gained more and more interest as a new resource, since it has potential as a favorable alternative to mineral filler in the construction of asphalt pavement compared with ordinary limestone powder. In this paper, the mechanical and anti-deformation properties of sand asphalt composites with various proportions of diatomite were investigated by a uniaxial compression failure test, a uniaxial compression repeated creep test, and a low-temperature splitting test in order to determine the optimal replacement content of ordinary limestone powder. Five groups of sand asphalts with various volume ratios of diatomite to limestone (0:1, 0.25:0.75, 0.5:0.5, 0.75:0.25, and 1:0) were determined by the simplex-lattice mixture design (SLD) method. The results reveal that the compression strength, anti-deformation properties, and low-temperature crack resistance of sand asphalts are improved through the use of diatomite. Furthermore, the optimal ratio (0.327:0.673) of limestone to diatomite is determined by the SLD method, according to secant modulus and creep strain results.

Features of Uniaxial Compression Failure of Brittle Rock Samples with Regard to Grain Characteristics

The results are presented for uniaxial compression testing of brittle rock samples; their failure occur in the form of columnar cracking along the axis of applying the force. Test results are compared with characteristic quantities determining tensile strength. Sample failure is modeled with regard for grain characteristics, which makes it possible to estimate the ratio of compression strength to tensile strength.

Study of Experiment on Rock-like Material Consist of fly-ash, Cement and Mortar

Study the uniaxial compression test of rock-like material consist of coal ash, cement and mortar by changing the sand cement ratio, replace of fine coal, grain diameter, water-binder ratio and height-diameter ratio. We get the law of four factors above to rock-like material’s uniaxial compression characteristics and the quantitative relation. The effect law can be sum up as below: sample’s uniaxial compressive strength and elasticity modulus tend to decrease with the increase of sand cement ratio, replace of fine coal and water-binder ratio, and it satisfies with power function relation. With high ratio increases gradually, the uniaxial compressive strength and elastic modulus is lower, and presents the inverse function curve; Specimen tensile strength decreases gradually with the increase of fly ash. By contrast, uniaxial compression failure phenomenon is consistent with the real rock common failure pattern.

Updated Smoothed Particle Hydrodynamics for Simulating Bending and Compression Failure Progress of Ice

In this paper, an updated Smoothed Particle Hydrodynamics (SPH) method based on the Simplified Finite Difference Interpolation scheme (SPH_SFDI) is presented to simulate the failure process of ice. The Drucker–Prager model is embedded into the SPH code to simulate the four point bending and uniaxial compression failure of ice. The cohesion softening elastic–plastic model is also used in the SPH_SFDI framework. To validate the proposed modeling approach, the numerical results of SPH_SFDI are compared with the standard SPH and the experimental data. The good agreement demonstrated that the proposed SPH_SFDI method including the elastic–plastic cohesion softening Drucker–Prager failure model can provide a useful numerical tool for simulating failure progress of the ice in practical field. It is also shown that the SPH_SFDI can significantly improve the capability and accuracy for simulating ice bending and compression failures as compared with the original SPH scheme.

Numerical simulation of macro-meso mechanical behaviours of sandstone containing a single open fissure under uniaxial compression

By employing the improved rigid block spring method, the failure process of a sandstone example containing a single open fissure under uniaxial compression is modelled. In this method, the intact rock is considered as an assemblage of rigid polygonal blocks. Macro mechanical behaviours are governed by mechanical properties of interfaces between two neighbouring blocks. In the local scale on interfaces, both tensile splitting failure and shearing sliding failure are considered. Micro properties are obtained by a calibration procedure against the stress–strain curve of intact rock under uniaxial compression in the lab. Influences of fissure inclination and length on the uniaxial compression strength (UCS) and failure modes are discussed. Comparisons between numerical simulations and laboratory tests are presented. The growth process of micro-cracks is studied and the mechanism of micro-crack propagation is studied through analysis on the displacement evolution. Some conclusions are drawn: numerical results generally agree well with those from lab tests; the UCS of fissured rock is lower than the intact one; the UCS first goes down then goes up as inclination increases, but decreases gradually as fissure length increases; the micro failure modes are governed mainly by tensile splitting failures.

Influence of Loading System Stiffness on Post-peak Stress–Strain Curve of Stable Rock Failures

It is well known from laboratory testing that the rock failure process becomes unstable in a soft test machine due to excessive energy released from the machine. Great efforts had been devoted to increasing the loading system stiffness (LSS) of laboratory test machines to ensure that the post-peak stress–strain curve of rock can be obtained for underground rock engineering design. A comprehensive literature review on the development of stiff test machines reveals that because of the differences in the manufacturing arrangement of the test machines, LSS values of the test machines used for rock property testing are always finite and vary in a large range, and the influence of LSS on stable rock failure is less understood. A FEM-based numerical experiment is carried out to study the influence of LSS on the stress–strain curves of stable rock failure in uniaxial compression, with a focus on the post-peak deformation stage. Three test machine loadings including idealized rigid loading, platen loading, and frame–platen loading with finite LSS are considered, and the simulation results are analyzed and compared. The modeling results obtained from the simulations indicate that even if the LSS value is large enough to inhibit unstable rock failure, as long as LSS is finite, it has an influence on the post-peak stress–strain curve of rock. It is revealed that because the input energy supplied by the external energy source to drive the stable rock failure process is affected by the finite LSS of a test machine, the post-peak descending slopes of the stress–strain curves are all steeper than the post-peak descending slope obtained under an ideal loading condition of infinite LSS. An insight from this numerical experiment is that it might be more feasible to develop laboratory test machines with variable LSS that can match the local mine stiffness in the field for rock property testing.

Fragmentation of an advanced ceramic under ballistic impact: Mechanisms and microstructure

In this paper, the impact-induced fragmentation of a commercially available hot-pressed boron carbide is explored. Fragmentation has been noted previously by many authors to be important in the impact performance of advanced ceramics, and so this paper seeks to provide some of the first near-complete and detailed measurements of individual fragment size and shape distributions available in the literature. Fragment size and shapes are quantified using methods developed in previous papers by the authors, and results reveal that two distinct fragmentation mechanisms exist as a consequence of the impact failure of boron carbide: one mechanism that creates small fragments that is associated with the coalescence of fractures originating from carbonaceous defects in the material, and one that creates larger fragments that is associated with structural failure (e.g., radial and circumferential cracking). While these mechanisms are similar to those noted for uniaxial compressive failure, results presented here highlight the importance of fragment shape as a consequence of impact failure. Namely, results indicate that both blocky and shard fragments are formed during impact into a boron carbide plate. Blocky and shard fragment types span across both the small and large fragmentation mechanisms. Using Scanning Electron Microscopy, blocky fragments were found to be associated with the predominant growth of cracks parallel to the impact direction, while shard fragments contain fracture surfaces that are associated with crack growth and coalescence in a direction perpendicular to the impact direction. The shards are, thus, believed to be a consequence of structural bending. No amorphous features were found on any blocky or shard fragments observed in this study (determined using Raman Spectroscopy), suggesting brittle fracture may be the dominant mechanisms that creates the shard fragments. Altogether, the implications of these results is that one can control fragment size and shape by controlling the carbonaceous defects population in boron carbide. This should help in the design of next-generation advanced ceramics for personal protection.

The Mesh and Height Effects of Rock Sample Failure in Uniaxial Compression by Statistical Damage Method

Due to presence of flaws in intact rock such as cracks and voids, rock failure associated with damage evolution becomes significantly discontinuous and difficult to describe. Based on the Weibull function and plastic criterion of Drucker–Prager, a statistical damage method has been implemented by finite element method. Laboratory testing has been conducted to verify in the method and to obtain the mechanical parameters of rock, which show good agreement with the results of the numerical simulation. For studying the size effects of mesh and sample height, appropriate numerical simulations were carried out in the uniaxial compression. The study results show that the failure pattern and strength of rock sample are greatly influenced by the size of mesh and sample height. Smaller the mesh size or more height of rock sample, the lower is the peak and residual is the strength of the rock, moreover failure pattern gradually changes from tensile failure to the shear failure.

Stabilization of Gob-Side Entry with an Artificial Side for Sustaining Mining Work

A concrete artificial side (AS) is introduced to stabilize a gob-side entry (GSE). To evaluate the stability of the AS, a uniaxial compression failure experiment was conducted with large and small-scale specimens. The distribution characteristics of the shear stress were obtained from a numerical simulation. Based on the failure characteristics and the variation of the shear stress, a failure criterion was determined and implemented in the strengthening method for the artificial side. In an experimental test, the distribution pattern of the maximum shear stress showed an X shape, which contributed to the failure shape of the specimen. The shear stress distribution and failure shape are induced by a combination of two sets of shear stresses, which implies that failure of the AS follows the twin shear strength theory. The use of anchor bolts, bolts, and anchor bars enhances the shear strength of the artificial side. When this side is stable, the components can constrain the lateral deformation as well as improve the internal friction angle and cohesion. When the AS is damaged, the components prevent the sliding of broken blocks along the shear failure plane and improve the residual strength of the artificial side. When reinforced with an anchor bar, the AS is still stable even after mining operations for three years.

Strength, Deformability and X-ray Micro-CT Observations of Deeply Buried Marble Under Different Confining Pressures

In this research, a series of triaxial compression experiments and X-ray observations were conducted to explore the strength, deformability and internal damage mechanism of deeply buried marble. The results show that an increase in confining pressure results in obvious brittle–ductile transition characteristics of deeply buried marble. The Young’s modulus of the marble increased nonlinearly with increasing confining pressure. The peak and residual strength of the marble exhibit a clear linear relationship with the confining pressure, which can be described by the linear Mohr–Coulomb criterion. The sensitivity of the residual strength on the confining pressure was clearly higher than that of the peak strength. After uniaxial and triaxial compression failure, marble specimens were analyzed using a three-dimensional X-ray micro-CT scanning system. Based on horizontal and vertical cross-sections, the marble specimen is mainly dominated by axial splitting tensile cracks under uniaxial compression, but under confining pressure, the marble specimen is mainly dominated by a single shear crack. To quantitatively evaluate the internal damage of the marble material, the crack area and aperture extent for each horizontal cross-section were calculated by analyzing the binarized pictures. The system of crack planes under uniaxial compression is more complicated than that under triaxial compression, which is also supported by the evolution of the crack area and aperture extent. Finally, the brittle–ductile transition mechanism of the marble is discussed and interpreted according to the proposed conceptual models.

An Experimental and Numerical Study on Mechanical Behavior of Ubiquitous-Joint Brittle Rock-Like Specimens Under Uniaxial Compression

Rock engineers often encounter materials with a large number of discontinuities that significantly influence rock stability. However, the strength and failure patterns of ubiquitous-joint rock specimens have not been examined comprehensively. In this study, the peak uniaxial compressive strength (UCSJ) and failure patterns of ubiquitous-joint rock-like specimens are investigated by combining similar material testing and numerical simulation using the two-dimensional particle flow code. The rock-like specimens are made of white cement, water, and sand. Flaws are created by inserting mica sheets into the fresh cement mortar paste. Under uniaxial compressional loading, the failure patterns of ubiquitous-joint specimens can be classified into four categories: stepped path failure, planar failure, shear-I failure, and shear-II failure. The failure pattern of the specimen depends on the joint-1 inclination angle α and the intersection angle γ between joint-1 and joint-2, while α strongly affects UCSJ. The UCSJ of specimens with γ = 15° or 30° shows similar tendencies for 0° ≤ α ≤ 75°. For specimens with γ = 45° or 60°, UCSJ increases for 0° ≤ α ≤ 30° and decreases for α > 30°. For specimens with γ = 75°, the UCSJ peaks when α = 0° and increases for 60° ≤ α ≤ 75°. The numerical and experimental results show good agreement for both the peak strength and failure patterns. These results can improve our understanding of the mechanical behavior of ubiquitous-joint rock mass and can be used to analyze the stability of rock slopes or other rock engineering cases such as tunneling construction in heavily jointed rock mass.

Mixed-mode fracture modeling with smoothed particle hydrodynamics

In this work, we describe a coupled Drucker–Prager and Grady–Kipp SPH framework in order to simulate mode I, mode II and mixed mode failure under the same formulation. This framework is then applied to study failure in uniaxial compression of gypsum samples containing a single angled flaw.To validate the model, results are compared with the experimental analysis and shows good agreement, where fracture initiation positions and angles are well represented. This trend of agreement continues beyond initiation, through to propagation, and finally post-failure behavior.The methodology and results shown here describe a powerful tool for study of fracture mechanics.

Shale uniaxial compressive failure property and the affecting factors of UCS.

Shale uniaxial compressive failure property and the affecting factors of UCS.