Combined Compression-shear Loading Research Articles

Shear strength and failure criterion analysis of steel fiber reinforced concrete exposed to elevated temperature under combined compression–shear loading

Shear strength and failure criterion analysis of steel fiber reinforced concrete exposed to elevated temperature under combined compression–shear loading

Acoustic emission and electromagnetic radiation of rock under combined compression-shear loading

This paper reports the use of inclined sandstone specimen in the uniaxial compression tests to achieve the combined compression and shear loading (CCSL) state. A series of CCSL tests are performed on the inclined specimens with an inclination angle of 0°, 3°, 5°, and 7°. Acoustic emission (AE) and electromagnetic radiation (EMR) during the failure process are monitored. The results show that the additional shear stress component caused by the inclined shape configuration of tested specimens has significant effects on the failure mode and mechanical properties. The increase of inclination causes the failure mode to transit from the axial splitting to shear failure, and decreases the peak strength and elastic modulus of the inclined specimens. The specimen inclination lowers the damage prior to the peak stress, but stimulates the damage development after the peak stress. EMR has better correlation with stress drop than AE. The 65% of the peak strength is defined as the stress threshold of rock failure. The inclination angle lowers stress threshold of rock failure and accelerates failure initiation

Dip effect on the orientation of rock failure plane under combined compression–shear loading

Shear failure often occurs in engineering rock mass (such as inclined pillar) in gently inclined strata. Prediction and characterization the orientation of shear failure plane is the foundation of rock mass engineering reinforcement. In this paper, sandstone samples are used to perform uniaxial and shear tests to obtain the basic mechanical parameters. Then, by employing the numerical method, the combined compression–shear loading tests were carried out for inclined specimens varied from 0° to 25° at an interval of 5°, to obtain the dip effect on the orientation of rock failure plane. The results show that the failure plane of rock changes with the change of dip angle of rock sample. Based on the Mohr–Coulomb criterion, the ultimate stress state of rock was characterized under combined compression–shear loading. The ultimate strength of rock is equal to the ratio of the stress circle radius of rock under combined compression–shear condition to the stress circle radius of rock under uniaxial compression condition, multiplied by the uniaxial compressive strength. The fracture angle of rock was defined under combined compression–shear loading. A theoretical model was developed for predicting the fracture angle. The developed model could be characterized by internal friction angle, dip angle of rock sample and Poisson's ratio. Finally, the numerical results of the fracture angle were analyzed, which are consistent with the predicted results of the model. The investigation shows that the rock fracture angle has a dip effect, which decreases with the increase of the inclination angle of the sample. The research results provide a new means to identify the potential failure plane of engineering rock mass, and lay a theoretical foundation for calculating the orientation of rock fracture plane.

Exploring the Cyclic Behaviour of URM Walls with and without Damp-Proof Course (DPC) Membranes through Discrete Element Method

Unreinforced masonry (URM) walls are common load-bearing structural elements in most existing buildings, consisting of masonry units (bricks) and mortar joints. They indicate a highly nonlinear and complex behaviour when subjected to combined compression–shear loading influenced by different factors, such as pre-compression load and boundary conditions, among many others, which makes predicting their structural response challenging. To this end, the present study offers a discontinuum-based modelling strategy based on the discrete element method (DEM) to investigate the in-plane cyclic response of URM panels under different vertical pressures with and without a damp-proof course (DPC) membrane. The adopted modelling strategy represents URM walls as a group of discrete rigid block systems interacting along their boundaries through the contact points. A novel contact constitutive model addressing the elasto-softening stress–displacement behaviour of unit–mortar interfaces and the associated stiffness degradation in tension–compression regimes is adopted within the implemented discontinuum-based modelling framework. The proposed modelling strategy is validated by comparing a recent experimental campaign where the essential data regarding geometrical features, material properties and loading histories are obtained. The results show that while the proposed computational modelling strategy can accurately capture the hysteric response of URM walls without a DPC membrane, it may underestimate the load-carrying capacity of URM walls with a DPC membrane.

Compression-shear performance of steel fiber reinforced rubber concrete

Rubber powder can be produced from waste tires through processing and its inclusion in concrete, either with steel fiber or alone, has been shown to improve impact and shear toughness and reduce environmental pollution. However, the mechanical behaviors and failure criteria of steel fiber reinforced rubber concrete (SFRRC) under combined compression-shear loading, which is essential for structural application, is lacking. This study investigates the compression-shear properties of SFRRC, considering steel fiber and rubber powder content, and compressive stress ratio. The effects of these parameters on shear strength, shear peak displacement, and shear toughness were analyzed. Results indicate that as the compressive stress ratio increases, SFRRC's failure pattern changes from tensile failure to compression-shear failure when k ≥ 0.4, exhibiting ductile failure. The equivalent initial energy density increases with rubber powder content, while equivalent shear residual toughness increases after the peak value, but shear strength and peak displacement decrease. With the addition of steel fiber, initial shear strength, peak displacement, and equivalent residual strength increase. A calculation criterion for compression-shear strength was proposed, with theoretical values matching well with experimental values.

Fracture behaviours of sustainable multi-recycled aggregate concrete under combined compression-shear loading

Fracture behaviours of sustainable multi-recycled aggregate concrete under combined compression-shear loading

Revealing the interlaminar shear failure behavior of unidirectional laminate under combined compression–shear loads

Due to the coupling effects between stresses in different directions, the mechanical behavior of an advanced composite material under multiaxial loading is extremely complex. In this study, the influence of through-thickness compressive stress on the interlaminar shear performance of a carbon fiber-reinforced composite was experimentally investigated. Hollow cylindrical unidirectional laminate specimens were fabricated to conduct combined compression–shear tests, and the fracture morphologies of the specimens were characterized to reveal their failure behavior. The results indicate that a moderate compression load significantly enhanced the shear properties of the laminate by inhibiting crack propagation and improving the friction effect. The shear strength and modulus of a laminate specimen subjected to combined stresses improved up to a maximum of 76% and 231%, respectively, over those of an equivalent specimen subjected to pure shear. However, as the applied through-thickness load approached the compressive strength of the laminate, the specimen shear capacity began to decline owing to the transition of fracture mechanisms. Indeed, the specimens exhibited mixed failure modes corresponding to the different stress states, which were induced by the combined effects of through-thickness compressive and shear stresses. As the applied through-thickness compressive stress increased, the dominant failure mode of the laminate specimen changed from fiber–matrix debonding to fiber shearing and then to fiber breakage, resulting in various shear performances.

Mechanical properties of multi-recycled aggregate concrete under combined compression-shear loading

The mechanical properties and strength failure criteria of multi-recycled aggregate concrete (multi-RAC) under combined compression and shear loading states are investigated in this paper. The peak shear strength, peak shear displacement, and failure patterns are compared under different regeneration cycles and normal compressive stress ratios. The results reveal that both the peak shear strength and peak shear displacement increase with the increased normal stress ratio. The shear failure pattern with higher severity corresponds to more spalling powder and debris deposited on the shear fracture surface. When the regeneration cycles of coarse aggregate increase, the peak shear strength decreases and the descending trend become more evident with the higher vertical compressive stress ratio. Under the normal compressive stress, contact friction strength is the dominant component of peak shear strength among the cohesive strength, contact friction strength, and shear dilation strength. Based on different stress expressions, three compression-shear failure criterion models considering the regeneration cycles of coarse aggregate under planar stress state were established for RAC. The stress invariance failure criterion model and octahedral stress failure criterion model in quadratic parabolic functional form can provide high prediction accuracies.

Experimental Study of Yield Surface in Polypropylene Considering Rate Effect: Stress Path Dependence.

In order to investigate the yield surface evolution of polypropylene (PP) under dynamic impact and the relationship between yield surface parameters and the strain rate, five shear-compression specimens (SCSs) with different inclination angles are designed and produced to explore the yield behavior of PP under dynamic loading. Dynamic combined stress loading paths with different compression-shear ratios are achieved by the split Hopkinson pressure bar (SHPB). The evolution laws of the compressive stress and shear stress in the measurement region during the PP SCS compressive deformation process are analyzed. In terms of mechanical response, PP under combined compression-shear loading is of visco-elasticity plasticity and its deformation undergoes a three-stage transition, namely “unyield→yield→failure”. The yield characteristics of PP are found to be affected not only by the hydrostatic pressure but also by the stress path. According to the Hu–Pae yield criterion, the dynamic yield surface and model parameters of PP are obtained, and the relationship between the yield surface and the strain rate is ascertained. These findings contribute to deepening the research on the mechanical response characteristics of PP-based materials.

Compression-shear performance and failure criteria of seawater sea-sand engineered cementitious composites with polyethylene fibers

• Tests on the compression-shear performance of seawater sea-sand ECC were performed. • Seawater sea-sand ECC under the combined loading shows ductility failure mode and high shear strength. • Failure law is reflected by the criterion based on octahedral stress or stress invariant. • The failure criterion of seawater sea-sand ECC could be applied in future structural analysis. Seawater sea-sand engineered cementitious composites (SS-ECC) with polyethylene (PE) fibers holds wide application prospects. However, the understanding on its mechanical behaviors and failure criteria under combined compression-shear loading, which is essential for structural application, is lacking. The object of this research is to obtain the mechanical performance and establish the corresponding failure criteria of SS-ECC under combined loading. The influences of fiber content and normal stress ratio on failure modes, shear strength, peak shear displacement and shear strength components were analyzed. SS-ECC under combined loading exhibited ductile failure mode. Shear strength increased significantly with the increasing normal stress ratio, while increased slightly with higher fiber content. The effects of fiber content and normal stress ratio on the combined compression-shear behaviors were clarified. Further, the failure criteria based on octahedral stress and stress invariant were proposed for describing the failure law of SS-ECC under combined loading. This research lays the groundwork for understanding the mechanical performance of SS-ECC under combined compression-shear loading and preparing its application in structural members.

A numerical prediction of failure probability under combined compression-shear loading for unidirectional fiber reinforced composites

Microbuckling (MB) is the dominant failure mode in unidirectional fiber reinforced polymers (FRPs) under predominantly compression loads. MB is highly sensitive to material imperfections and nonlinear material behavior. Material imperfections are spread in the form of fiber misalignment in the volume of the material. Because of high sensitivity of MB failure to the fiber misalignment, the MB strength shows uncertainty. It has been shown in the literature that the nature of the misalignment in FRPs is correlated random, where the misalignment of a fiber depends on the other fibers in its surroundings. To represent the misalignment in numerical models for the prediction of MB strength while preserving the spatial correlation information, the spectral representation method is employed in this investigation. For this purpose spectral densities were calculated for measured distributions of the fiber misalignment using computed tomography scans on specimens. This information was subsequently used to generate realistic distributions of the fiber misalignment in numerical modeling of FRPs for prediction of MB strength. Quantification of uncertainty in MB failure is essential for reliable design practices. Therefore, the current investigation aims for a probabilistic prediction of MB failure under axial compression and combined compression-shear loads. Different model series, each containing a large number of realizations, were developed based on spectral densities calculated from the measurements of the fiber misalignment from different specimens. The resulting distributions of strengths under the axial compression load case from these model series are compared and a suitable model series was chosen for further analysis. The stress–strain response under different combinations of combined compression-shear loads is discussed. A comparison of numerically predicted strengths against experimentally obtained results under the axial compression loads is included. Since the sizes of the model and the experimental specimen were different, this comparison was performed on the basis of a scaling law for the compression strength. Finally, the numerically determined probabilistic failure envelopes in stress and strain spaces are presented with lower percentiles of distributions of failure. The failure enveloped are also compared against classical failure criteria from the literature to highlight the limitations of the classical criteria.

Experimental determination of a probabilistic failure envelope for carbon fiber reinforced polymers under combined compression–shear loads

The compressive strength of fiber reinforced composites is sensitive to material imperfections. Material imperfections are spread in the volume in an apparently random manner in the form of fiber misalignment, resulting in non-deterministic strength in compression dominated load cases. The main factors dictating failure under compression dominated loads are the fiber misalignment and the nonlinear material behavior. To enable reliable failure prediction, a quantification of the strength uncertainty is required. Therefore, the current investigation considers different experimental aspects of the problem such as measurements of the fiber misalignment and the material characterization. To implement combined compression–shear loading, a newly in-house developed combined loading fixture was used. A statistically significant number of specimens was tested under aforementioned load cases. Macroscopic images of the failed specimens and a micrograph of the fracture surface are shown to provide evidence of microbuckling failure mode under combined compression–shear loads. Using the experimental strain measurements, a probabilistic failure envelope in strain space is presented. Results of the axial compression load case are interpreted in the context of the notion of the effective misalignment angle using an analytical model. A failure envelope in stress space is derived using an analytical solution for the combined compression–shear load cases and the effective global misalignment angle calculated from the measurements. Applied far field stresses of different load cases are compared, and a visual depiction of the strain localization phenomenon leading to microbuckling failure using digital image correlation is presented.

Mechanical Properties and Energy-Absorption Capability of a 3D-Printed TPMS Sandwich Lattice Model for Meta-Functional Composite Bridge Bearing Applications

This paper reports on a proposed novel 3D-printed sandwich lattice model using a triply periodic minimal surface (TPMS) structure for meta-functional composite bridge bearings (MFCBBs). It could be implemented in bridge systems, including buildings and railway bridges. A TMPS structure offers a high performance to density ratio under different loading. Compared to typical elastomeric bridge bearings with any reinforcements, the use of 3D-printed TPMS sandwich lattices could potentially lead to a substantial reduction in both manufacturing cost and weight, but also to a significant increase in recyclability with their better mechanical properties (compressive, crushing, energy absorption, vibration, and sound attenuation). This paper shows predictions from a numerical study performed to examine the behaviour of a TPMS sandwich lattice model under two different loading conditions for bridge bearing applications. The validation of the modelling is compared with experimental results to ensure the possibility of designing and fabricating a 3D-printed TPMS sandwich lattice for practical use. In general, the compressive experimental and numerical load–displacement behaviour of the TPMS unit cell are in excellent agreement within the elastic limit region. Moreover, its failure mode for bridge bearing applications has been identified as an elastic–plastic and hysteretic failure behaviour under uniaxial compression and combined compression–shear loading, respectively.

Shear strength and failure criterion of carbon fiber reinforced coral concrete under combined compression-shear stresses

With the rapid development of the marine industry, the wide application potential of coral concrete (CC) in the construction of islands has been identified. Adding carbon fiber (CF) into CC can improve its mechanical properties and further expand its application scope. Many concrete members, such as corbels, expressways, and deep beams, are usually subjected to combined compression-shear loading during service. This study investigated the shear strength of carbon fiber reinforced coral concrete (CFRCC) under combined compression-shear stresses. A total of 162 specimens with six CF dosages (0.0%, 0.3%, 0.6%, 0.1%, 1.5%, 2.0%), six normal stress ratios (0.0, 0.1, 0.2, 0.4, 0.6, 0.8), and three concrete strength grades (C20, C30, C40) were designed to carry out the test. The results show that with the increase in the normal stress ratio, the spalling of concrete along the main shear crack and the friction trace on the shear failure surface are increasingly apparent, and the shear strength also increases. The addition of CF can diminish the spalling of concrete and improve the shear strength, and the optimum CF dosage is approximately 1.5%. As the uniaxial compressive strength increases, the shear strength increases approximately linearly. Based on the test results, the failure criteria for CFRCCs under compression-shear stresses are proposed and show a good agreement with the test results.

An improved material model for loading-path and strain-rate dependent strength of impacted soda-lime glass plate

The main purpose of this work is to develop a macro material constitutive model for inorganic glass response description under impact conditions. Firstly, the quasi-static and dynamic strength of soda-lime glass was obtained through uniaxial compression and combined compression-shear loading tests. The strain-rate and loading-path dependence of glass strength was observed from these experimental results. An improved model of impacted soda-lime glass plate was proposed based on the JH-2 model including the loading-path influence through an additional factor as a function of the Lode parameter. In commercial code Abaqus, the improved model is implemented through a user-defined material subroutine. Additionally, simulation of the static test, SHPB test, and impact test on glass specimens respectively is conducted to validate the model with updated material constants. The comparisons illustrate that the improved model of soda-lime glass provides better accuracy and efficiency predictions of glass responses at various loading conditions.

Experimental Investigations on Creep Behavior of Coal under Combined Compression and Shear Loading

The creep behavior of rock has received much attention for analyzing the long-term response and stability of underground rock engineering structures. Numerous studies have been carried out on the creep properties of various rocks under pure compression conditions. However, little attention has been paid to the creep behavior of rocks in a combined compression-shear loading state. In this work, a novel combined compression and shear test (C-CAST) system was used to carry out inclined uniaxial compression tests and creep tests for various inclination angles (0°, 5°, 10°, and 15°). The results revealed that the peak strength of the coal decreased with the inclination angle of the specimen, which could provide the basis for setting up a creep test scheme. Multistage compression-shear creep tests were carried out on specimens with different inclination angles. Based on the analysis of the creep test data, the creep behavior of the coal in a combined compression-shear state was studied. It was found that the specimen inclination affected the time-dependent deformation, long-term strength (LTS), and time to failure. Compared with the specimen under pure compression, the inclination specimens tend to produce large shear strain with time, while they were more prone to shear failure. The reduction of the long-term strength was closely associated with the increase of the specimen inclination angle when the angle was more than 5°. Moreover, the ratio of the peak strength to the LTS was not affected by the specimen inclination, which is considered an inherent characteristic. We anticipate that the results obtained will assist in pillar design and long-term stability analysis.

Experimental and modeling research on compression-shear behavior of carbon fiber reinforced coral concrete

With the accelerating development of oceanic resources, the broad application potential of coral concrete (CC) on islands and reefs has been identified. Incorporating carbon fiber (CF) into CC improves its mechanical properties and further expands its application scope. Moreover, many concrete members usually suffer combined compression-shear loading during service. Thus, this work focus on the compression-shear behavior of carbon fiber reinforced coral concrete (CFRCC). Combined compression-shear test results show that the compression-shear failure process can be divided into four stages. The peak shear displacement, peak shear stress, and initial shear stiffness increase are significantly influenced by the normal stress ratio, CF dosage, and concrete strength grade. Secondly, a compression-shear damage model considering the influences of normal stress ratio, CF dosage, and concrete strength is proposed. By comparison, this model is proved to be effective for simulating the shear behavior of CFRCC under combined compression-shear stresses.

Investigation of Dip Effect on Uniaxial Compressive Strength of Inclined Rock Sample by Experimental and Theoretical Models

The strength of rock under combined compression and shear loading has been paid more and more attention, but still lacks a theoretical model that incorporates both compression–shear characteristics and influence of dip angle to estimate the strength of the rock. This work is aiming to solve the issue by combining experimental and theoretical methods. First, in the laboratory, 112 rock samples with different sizes were applied to obtain the dip effect characteristics of strength via combined compression–shear tests. The ratio of compression–shear strength to uniaxial compression strength is called the compression–shear coefficient, which is used to characterize the degree of dip effect. Second, according to the compression–shear load characteristics of inclined rock samples, a strength model was established considering both compression–shear characteristics and dip angle by the Mohr–Coulomb failure theory. This strength model is an extension of the Mohr–Coulomb criterion and was verified by experimental data. The verification results are consistent with experimental results. Finally, the mechanism of dip effect on strength was explained from the resistance to the sliding and stress path of the rock sample. The results show that the dip effect is an inevitable strength weakening characteristic of rock materials under combined compression–shear loading. Compared with the vertical rock sample loaded under pure pressure, the resistance to the sliding of inclined rock samples decreases and the stress path is changed, which reduces the ability of the rock sample to resist external loads, resulting in the decrease of strength.

Microcrack fracturing of coal specimens under quasi-static combined compression-shear loading

Abstract Coal pillars are usually loaded under combined compression-shear stresses at underground coal mines. Their long-term stability is critical to the utilization of underground structures, such as underground reservoirs at coal mines. In this study, a modified rock property testing system was used to explore the mechanical properties of coal specimens under quasi-static combined compression-shear loading conditions. The acoustic emission technique was applied to investigating the microcrack fracturing of coal specimens at various inclination angles. The experimental results show that specimen inclination has remarkable effects on the microcrack initiation, microcrack damage and ultimate failure of the coal specimen. The failure mode of the coal specimen tends to transit from axial splitting to shear failure with increasing specimen inclination, and its peak strength is closely associated with the microcrack damage threshold. In practice, it is recommended to consider coal strength under combined compression-shear loading when using empirical pillar strength formulae so that the effect of pillar inclination can be included.

Mechanical responses and failure mechanism of hydrostatically pressurized rocks under combined compression-shear impacting

Accurately characterizing the mechanical responses and failure mechanism of hydrostatically pressurized rocks under combined compression-shear impacting are of great significance for construction safety in deep underground engineering. Using a split Hopkinson pressure bar (SHPB) modified with axial and radial confining systems, oblique cylindrical specimens with different hydrostatic confining pressures of 7, 14, 21 and 28 MPa are tested under loading rates varying from 1200 to 3200 GPa/s. The dynamic force equilibrium of the oblique specimen in the triaxial SHPB tests can be satisfied by using the pulse shaping techniques. A complementary discrete element method (DEM) simulation is conducted to describe the failure behaviours of hydrostatically confined rocks under combined compression-shear loading. The experimental and numerical results show the effects of confining pressure and loading rate on the compression-shear impact responses and failure mechanism of rocks. Under different hydrostatic confinements, both the dynamic compressive and shear strength of rocks increase linearly with equivalent stress rate, while the rate of increase slows as confinement increases. Post-mortem examination of recovered specimens and the DEM simulation show that the failure pattern of hydrostatically pressurized rocks under compression-shear impacting changes from two parallel shear bands with small inclination to a single shear band along the short diagonal of oblique specimen as confinement increases. Fragmentation analysis shows that the rocks are more fragmented under a higher loading rate and that confinement enlarges the average fragment size and its distribution range.