Uniaxial Compressive Properties Research Articles

Quasi-static uniaxial compression and low-velocity impact properties of composite auxetic CorTube structure

Auxetic structures are gaining great attention due to their unique contraction deformation characteristics under compression and impact. In this paper, high performance carbon fiber-reinforced composites are used to fabricate the auxetic structure consist of corrugated sheets and tubes (CorTube). The quasi-static uniaxial compression and low-velocity impact properties of composite CorTube structure are explored. The response of the composite CorTube structures under quasi-static compression loads are analyze through a combination of theoretical analysis, simulations, and experimental tests. Additionally, drop-weight impact tests are conducted using a rigid impactor with a hemispherical head to examine the effects of impact energy levels, impact locations, and corrugated sheet thickness on the impact response of CorTube structure. Enhancing corrugated sheet-tube bonding via modified cross members and reducing tube crushing during quasi-static compression are notable findings. The results also highlight the remarkable auxetic properties of the composite CorTube under low-speed impact, and the impact resistance could be enhanced by increasing the corrugated sheet thickness and stiffness. Various failure modes were observed, including cracks, pits, tube crushing, and delamination. Significantly, peak-impacted specimens exhibited greater maximum displacement with lower peak impact forces. This study offers insights into the deformation and failure modes of auxetic CorTube structures under low-velocity impact.

Dynamic compressive behavior of steel fiber synergistically reinforced cellular concrete under high strain-rate loading

To better understand the reinforcement and toughness effects of steel fibers, a 75-mm split Hopkinson pressure bar (SHPB) device was used to test the uniaxial dynamic compression properties of steel fiber synergistically reinforced cellular concrete (SFSRCC) under high strain rates. The dynamic compression performance characteristics of the SFSRCC, including the stressstrain curve, dynamic strength, impact toughness and failure mode, were analyzed. The results showed that the dynamic strength, peak strain and impact toughness of SFSRCC increase with increasing strain rate. Compared with that of cellular concrete (SAP10S0), a higher steel fiber volume ratio corresponded to a greater enhancement in the dynamic performance characteristic indices of the SFRCC. The maximum increases were 138.4%, 180.0% and 280.0% for the DIF, peak strain, and impact toughness, respectively. The damage degree of the SFSRCC specimen decreased with increasing fiber content, and a larger area of residual "core retention" was observed, which indicated that the impact resistance of the SFSRCC with a high fiber content was improved. An empirical formula that can accurately characterize the dynamic strength increase factor (DIF) of SFSRCC with high strain rates was proposed, and the prediction results obtained by using the DIF of the SFSRCC were highly consistent with the test results, which confirmed its effectiveness. To further quantify the strain rate enhancement effect and fiber content for the reinforcement and toughening ability of SFSRCC, the relationships between the peak strength/peak strain/impact toughness and strain rate and between the DIF increment ratio/strain energy density increment ratio and fiber volume fraction were determined. In conclusion, the dynamic compression performance characteristics of SFSRCC can be enhanced by incorporating an appropriate quantity of steel fibers with a dynamic impact load.

Lightweight, hydrostatic pressure‐resistance, thermal insulating epoxy syntactic foam with a multiscale ternary structure for marine engineering application

AbstractThe study of lightweight epoxy syntactic foams is of great significance for the exploitation of marine resources. In this work, glass fibers reinforced epoxy hollow spheres (GFs‐EHS) were first prepared using a template method, and a lightweight three‐phase epoxy syntactic foam (LWTP‐ESF) with a multiscale ternary structure was prepared using a molding pressing method with epoxy resin as matrix, hollow glass microspheres (HGMs), and GF‐EHS as the lightweight fillers. The effect of HGMs content on the density, uniaxial compression properties, water absorption, and thermal conductivity of obtained LWTP‐ESF was evaluated. The results indicated that the density, uniaxial compression strength, and thermal conductivity of LWTP‐ESF were consistently decreased, while the water absorption was increased with the increase in HGMs content. The highest specific compression strength and lowest thermal conductivity of LWTP‐ESF could reach 52.77 ± 0.82 MPa·cm3/g and 0.113 ± 0.005 W/(m·K), respectively. Moreover, the effect of hydrostatic pressure on the water absorption and thermal conductivity of LWTP‐ESF were also systematically analyzed. This study provides a novel system and method to prepare lightweight epoxy syntactic foams, and the prepared composites have potential applications in the field of lightweight thermal insulation materials for marine.Highlights The composites with a multiscale ternary structure were designed. The composites possessed significantly lower density and thermal conductivity. The water absorption of composites under hydrostatic pressure was evaluated. The thermal conductivity of composites under hydrostatic pressure was evaluated. The water absorption mechanism and thermal insulation mechanism were proposed.

Mechanical response and damage constitutive model of early-age cemented paste backfill after cyclic loading

During mining operations, cemented paste backfill (CPB) is damaged in real time by different loading gradient, loading rate and loading time. And there is variability in the degree of damage and destruction of CPB by different loading conditions. This paper carries out uniaxial compression and ultrasonic velocity tests to investigate the uniaxial compressive properties and damage characteristics of CPB after cyclic loading. The results show that when the loading rate is 1.3 mm min−1, the loading gradient is σ0.5 and the loading time is 300 s, the uniaxial compressive strength (UCS) of CPB at 3, 5 and 7 days of curing age is the maximum, and the values are 1.7335, 4.0325 and 6.5301 MPa, respectively. The value of ultrasonic velocity variation is exponentially related to that of UCS. The CPB dissipation energy (DE), elastic strain energy (ESE), and unit volume strain energy (UVSE) improved with curing age raising. Under the age of 3 d, 5 d and 7 d, the failure mode of CPB is X shear- X-conjugate shear - Y shear. The correction coefficient α and coefficient of compaction η were introduced, and the two-stage damage constitutive model of CPB after cyclic loading was constructed based on the Weibull distribution, with the model validated. The magnitude of the correction coefficient α affects the peak strength and the residual stress duration strain length of the model, and has less effect on the damage development. When the value of α ranges from 0.90 to 0.92, the model curve is closer to the test curve.

Experimental study of uniaxial compressive mechanical properties of rough jointed rock masses based on 3D printing

Abstract Roughness and inclination are important factors affecting the strength and deformation properties of jointed rock masses. Serrated joint specimens with varying joint roughness coefficient (JRC) and inclination angle were manufactured by 3D printing technique and cement mortar material. Then, uniaxial compression tests were performed for serrated joint specimens. The results show that when inclination angle equals 0° or 90°, the stress–strain curves of serrated joint specimens with various JRC values are basically the same and display a similar variation trend as that of the complete specimen, hence JRC presents a very little impact. When inclination angle varies from 30° to 60°, the stress–strain curves display a significant difference for various JRC values. Both the compressive strength and peak strain increase with the JRC value. With the increase in JRC value, the stress–strain curve exhibits a stress drop point, and with the further increase in JRC value, the stress drop point obviously delays or disappears directly. Variation in uniaxial compressive strength and deformation modulus with inclination angle is approximately U-shape for serrated joint specimens and displays typical anisotropic characteristics. Due to the variation in inclination angles and JRC values, failure modes of serrated joint specimens under uniaxial compression varies from splitting tensile or shear slip failure to compound tensile and shear failure. Rough serrated joint has a strengthening effect on the resistance ability to vertical load, and large roughness can effectively slow down the shear slip failure of jointed rock masses.

CDEM-Based Numerical Simulation of Uniaxial Compressive Mechanical Properties of Rocks

Understanding the mechanical properties of rock is of great significance for the development of unconventional reservoirs. However, a large number of bedding makes the mechanical laws of rock unclear. To investigate the effect of bedding properties on the uniaxial mechanical properties of rock, the coal model containing bedding is developed based on the continuous–discontinuous method, and the effect of bedding angle, bedding strength, bedding number, and loading rate on the uniaxial mechanical properties of rock is investigated. The failure morphology, stress–strain evolution, peak stress, and fracture degrees are analyzed and discussed in detail. The reliability of the numerical model in this paper has been verified by comparison with the indoor experiments. The results show that when the bedding angle is 0°, the peak stress of the rock is maximum, 8.16 MPa, and when the bedding angle is 90°, the fracture degree of the rock is maximum, 3.74%. For the different bedding strengths, the peak stress first decreases linearly with the decrease of the bedding strength. The peak stress barely varies when the bedding strength is less than 0.5 MPa. The fracture degree of the rock shows a nonlinear increase with the increase in bedding strength. For different bedding numbers, the activation of the bedding is not related to the bedding number. The loading speed also has a great influence on the mechanical properties of rock. With the increase in loading rate, the difficulty of bedding activation gradually increases, and the complexity of fractures gradually increases. This study aims to further improve the understanding of the effect of bedding properties on the uniaxial mechanical properties of rock.

Experimental Study on the Effect of High Temperature on the Physical and Mechanical Properties of Sandstone with Different Bedding Angles

As a typical sedimentary rock, the number of beddings in the horizontal direction of sandstone is far greater than that in the vertical direction, leading to its physical and mechanical properties showing obvious anisotropy with changes in bedding angle. After high temperature exposure, bedding damage further transforms the change rule of the physical and mechanical properties of sandstone with the bedding angle. This study tested the appearance, wave velocity, uniaxial compression, and conventional triaxial compression properties of sandstone with five bedding angles before and after high temperature exposure. The results show that (1) the longitudinal wave velocity, shear wave velocity, elastic modulus, and cohesion decreased, while the internal friction angle increased slightly. At the same temperature, when the dip angle of sandstone was 30° or 60°, the mechanical properties were optimal, and when the dip angle was 45°, the mechanical properties were the worst. (2) High temperature increases the development degree of micropores and microfractures in the sandstone bedding plane and matrix, thus increasing the anisotropy degree of the physical and mechanical properties of sandstone with different bedding angles. (3) With increasing temperature, the rock samples gradually transitioned from brittle failure to ductile failure. Sandstone with a bedding angle of 0° presented splitting failure that vertically penetrated the bedding plane at different temperatures. Sandstone with dip angles of 30° and 40° presented shear failure that penetrated the matrix and bedding plane. A failure plane along the bedding plane appeared at the end. Sandstone with dip angles of 60° and 90° was more prone to failure along the bedding plane, showing shear failure along the bedding plane and tensile failure along the bedding plane, respectively.

Uniaxial compressive mechanical properties and stress–strain model for roller-compacted concrete with initial damage subjected to freeze–thaw cycles

Roller compacted concrete (RCC) often remains in a damage state as a result of improper vibrating compaction control, which makes it more susceptible to the action of freezethaw (FT) cycles in cold regions and thus results in the degradation of mechanical behaviors. In this paper, the influences of initial damage and FT cycles on the physical and mechanical behaviors of RCC were systematically examined through physical tests, including FT cycle tests, pore structure tests and uniaxial compressive tests. An in situ vibrating compaction procedure was employed in the experiment to accurately replicate the field compaction process for RCC under laboratory conditions, and the dynamic elasticity modulus (DEM) was adopted as the non-destructive testing (NDT) index to quantify the initial damage caused by improper RCC construction control. The results indicated that the higher values of initial damage and FT cycles exhibited a greater influence on the frost resistance and pore structure distribution. Remarkable attenuation of compressive strength and elastic modulus and an increase in peak strain were observed to occur in RCC when the initial damage degree exceeded 0.1 and the number of FT cycles exceeded 75. Finally, the uniaxial compressive stressstrain model was established through segmented linear regression analysis based on the Weibull-Lognormal model. The proposed model was validated to be effective and reasonable in predicting the mechanical properties of RCC under the combined effects of initial damage and FT cycles.

Mechanical properties and micro characterization of coal slime water-based cementitious material-gangue filling: A novel method for co-treatment of mining waste

With the improvement of coal mining depth and mechanization level, the difficulty of coal slime water (CSW) disposal increases. The preparation of cementitious materials with CSW can not only solve the disposal problems, but improve the structural stability and mechanical properties of coal gangue (CG) piles as a cementitious material. At the same time, it realizes the cooperative resource utilization of mining waste and reduces environmental pollution. In this study, it is proposed to prepare high water contained coal slime water-based cementitious material (CSCA) with 6 types of additives to bond CG particles and improve mechanical properties. Study on property of compressive strength CSCA-CG (CGSB) show that five factors (f1-f5) influence the property order as: calcination temperature of CG (f5) > CG particle size distribution (f4) > ratio of CG and CSCA (f1) > additives content (f2) > volume of water glass (f3). The optimal experimental parameters were that f5 calcined at 800 °C for 30 min, f4 with 0 ∼ 0.18 mm (6 %), 0.18 ∼ 2 mm (24 %) and 2 ∼ 5 mm (70 %), f1 of 4:1, f2 of 5 %, and f3 with 3 ml. The mechanical experiments shows that the uniaxial compressive strength of aged 28 d could reach 1.48 MPa, and results of variable angle shear test at 50°showed that principal stress of 1.26 MPa and shear strength of 1.45 MPa were obtained. The CGSB prepared with by non-calcined CG has better plastic deformation ability and less strength loss after peaking. The reason for improved uniaxial compressive mechanical properties of CGSB with calcined CG are suggested as following: densifying the structure of CG, strengthening the hydration process of cementitious materials, and promoting the growth of calcium alumina structure. Therefore, it is suggested that this study provides new ideas for CSW-CG co-disposal and provides a reference solution for mechanical property optimization.

INFLUENCE OF GRAPHENE NANOPLATELETS ON MECHANICAL AND THERMO-MECHANICAL PROPRTIES OF GLASS/EPOXY COMPOSITES

The current work focuses on the influence of graphene nanoplatelets (GPs) on the mechanical and thermo-mechanical properties of unidirectional glass/epoxy (GE) composites. GE and GP-GE composites are fabricated using the hand lay-up method followed by compression molding. Different percentages of GPs used in the fabrication of GP-GE composites are (0.1, 0.3, 0.5, and 0.7) w/% by weight of the epoxy. Tests are conducted to experimentally evaluate the uniaxial compressive properties and the coefficient of linear thermal expansion (CLTE) in the direction of fibers. Tests are also conducted to study the thermo-mechanical properties such as storage modulus (E’) and loss modulus (E’’). The variation in the storage modulus and loss modulus is measured from 15 °C to 125 °C, using a dynamic mechanical analyzer (DMA) while the CLTE is measured using a dialatometer. The results indicate that the compressive as well as thermo-mechanical properties increase with the addition of GPs up to 0.5 % and then they decrease. The addition of GPs has no effect on the CLTE of the GE composites in the fiber direction.

Attack resistance mechanism, uniaxial compressive mechanical properties and meso-simulation of high-performance concrete exposed to brine in salt lake for 10 years

The study investigated the corrosion resistance, corrosion micro-mechanisms, and the uniaxial compression stress–strain constitutive relationship of high-performance concrete (HPC) specimens subjected to long-term brine corrosion in an underground salt lake environment (Xining, China), which possesses a salt content of 180894.5mg/L. A three-dimensional random aggregate concrete meso-model was established considering the mesostructural characteristics of concrete. The mechanical behavior of HPC was assessed using the LS-DYNA software platform. The findings indicated that both the compressive strength and the dynamic elastic modulus of HPC demonstrated a pattern of initial increase, followed by a decrease, with extended brine exposure. Nevertheless, after 10 years of exposure to salt lake brine, the compressive strength of the HPC samples was still considerably greater than their original strength, with minimal evident corrosion damage to the concrete. Physical and chemical corrosion products formed exclusively in the spherical pores created by the air-entraining agent within the shallow layer of HPC, without notable micro-cracks or spalling. The HPC specimens exposed to brine for ten years under uniaxial compression load exhibited typical characteristics of splitting failure. In addition, the results from the mesoscopic numerical simulations aligned well with the experimental findings. The study shows that the three-dimensional random aggregate concrete mesoscopic model can simulate the uniaxial compressive mechanical behavior of HPC specimens under long-term corrosion conditions.

Compressive and hydration behavior of steel fiber-reinforced concrete under high geothermal environment

The unique challenges presented by high geothermal environments in tunnel construction are becoming increasingly evident, particularly in the context of the high geothermal conditions in western China. In this paper, the uniaxial compressive properties, and stress–strain relations of steel fiber-reinforced concrete (SFRC) in high geothermal environment are studied. The effects of the volume fraction of steel fiber (0.5%/1.0%/1.5%/2.0%) and the heat damage temperature (40 °C/60 °C) on the peak stress, peak strain, and the stress–strain curve of SFRC under uniaxial compression are analyzed. The results show that the fracture and spalling of concrete around the main crack increase due to the heat damage after uniaxial compression test. Compared to 20 °C, the peak stress, bending strength, and limit flexural toughness of SFRC significantly decrease (45.9%, 29.5%, and 72.1%, respectively) after 60 days of exposure to a high geothermal environment of 60 °C. Moreover, while the addition of steel fiber can enhance the peak strain and limit flexural toughness of concrete, the decline in peak stress and bending strength of SFRC becomes more pronounced as the duration of heat damage increases. Based on the P-K hydration kinetics model, the ettringite content in cement without an accelerator is determined to decrease by 66.35% after 28 days of hydration at 60 °C, indicating in the change of the concrete's material properties.

Enhancing the strain-hardening performance of ultra-high performance concrete by tailoring matrix toughness and fiber parameters

Ultra-high performance concrete (UHPC) features high strength but a relatively low tensile strain capacity. Matrix, fiber parameters and their interaction are the controlling factors, which need careful designation to enhance the tensile performance of UHPC. In this research, different fiber parameters, e.g., fiber shapes, fiber aspect ratios, fiber hybridization and crumb rubber are utilized to tailor fiber parameters and matrix toughness to improve the tensile properties of UHPC. Systematic investigations were carried out to obtain the uniaxial tensile, compressive, fracture toughness and single-crack tension properties of UHPC. Results show that the tensile properties of UHPC could be largely improved by adjusting the fiber parameters and matrix toughness, in which the incorporation of crumb rubber demonstrates the most predominant effect in enhancing both tensile strength and strain capacity. The tensile strain capacity and crack number of developed UHPC reach 5585 με and 18, respectively, which are almost twice as the values of referred UHPC. The fracture toughness of developed UHPC ranges from 4.01 to 6.17 MPa·m1/2, approaching that of metals and alloys. The methods used in this work provide potential methods for more efficient improvement of the tensile performance of UHPC.

Correlations between Uniaxial Compressive Strength and Dynamic Elastic Properties for Six Rock Types

The assessment of the behavior of the ground is highly critical for any geotechnical and geological projects. Uniaxial compressive strength (UCS) is an essential mechanical parameter for any rock mass characterization, whereas the elastic properties of rocks help us understand the deformational behavior of the rocks. However, the determination of these parameters is challenging, time-consuming, destructive, and expensive and requires a skilled workforce. In contrast, the dynamic elastic properties require P-wave velocity (VP), S-wave velocity (VS), and density (ρ) for calculation, which are easy, quick, nondestructive, and cost-effective to determine. Therefore, in this paper, to understand the behavior of different rocks, UCS has been correlated with the dynamic elastic properties, including dynamic bulk modulus (KD), dynamic shear modulus (GD), dynamic Young’s modulus (ED), and dynamic Poisson’s ratio (µD) for carbonate, serpentinite, shale, sandstone, volcanite, and ignimbrite rocks incorporated from the databases of eight previous studies. Based on the lithology, different correlation equations have been proposed to predict the UCS from dynamic elastic properties using simple regression (SR) analysis. From SR analysis, it was observed that the coefficient of correlation (R) values depended on the type of rock. The R-values for the overall rocks, including all six rock types, for different correlations, were observed to be inferior to the R-values obtained on the basis of lithology. The principal component analysis (PCA) reduced the dimension of the data sets, and the trendline obtained for each rock type was observed to be dependent on the lithology. Moreover, descriptive statistics were also used to validate the lithological control for six different rock types.

Experimental study on uniaxial compressive properties and damage evolution of basalt fiber reinforced concrete after being subjected to high temperature

The study investigated basalt fiber reinforced concrete (BFRC) for failure characteristics after being subjected to high temperatures under uniaxial compression. Twenty-five sets of cylindrical BFRC specimens were carried out under different basalt fiber (BF) content and temperature. Based on 3D digital image correlation (3D-DIC) and acoustic emission (AE), the effects of temperature and volume content of BF on the compressive mechanical properties, damage evolution and failure mode of BFRC are analyzed. The results indicate that the proper volume content (0.26%) of BF can improve the compressive strength of concrete. Generally, the uniaxial compressive strength of BFRC decreases with increasing temperature. The internal and external damage evolution trend of BFRC is basically the same, which can be divided into pore compaction stage, stable crack growth stage and unstable crack growth stage. The proper volume content (0.26%) of BF reduces the degree of BFRC damage. The increase in the volume content of BF leads to an increase shear cracks proportion in BFRC, and the failure mode of the main crack gradually changes from tension-shear failure to shear failure. Conversely, the increase in temperature increased the degree of BFRC damage. The internal and external failure modes of BFRC are basically the same. At 20 °C, the failure of concrete without basalt fiber is mainly tensile crack. With the increase of temperature, the main failure mode is tension-shear failure.

Effect of isothermal annealing temperature on microstructure and mechanical properties of Cu45Zr45Ag7Al3 amorphous alloy

Bulk amorphous alloys, as a material with broad application prospects, are highly expected in many cutting-edge applications. However, its plastic deformation relies on highly localized shear bands, resulting in brittle fracture characteristics of materials with low plastic strain as a whole. Therefore, strengthening and toughening of amorphous alloys is one of the key topics in the research of amorphous applications. In this paper, the effects of different isothermal annealing temperature on the microstructure and uniaxial compression properties of Cu45Zr45Ag7Al3 amorphous alloy were studied by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that Cu10Zr7, AlCu2Zr, Cu8Zr3 and Al2Zr phases precipitated successively from the amorphous alloy matrix with the increase of annealing temperature, and the fracture strength and plastic strain increased first and then decreased; At an isothermal annealing temperature of 741 K, the precipitated nanocrystalline Cu10Zr7 phase can improve the fracture strength of the alloy; when the annealing temperature rises to 746 K, the strength of the alloy decreases slightly, but the plasticity increases; with the continuous increase of annealing temperature, the plasticity of the alloy decreases and the strength continues to increase; As the annealing temperature continues to increase, the fracture strength of the alloy decreases, exhibiting significant brittle fracture characteristics.

Study on mechanical properties and damage mechanism of recycled concrete containing silica fume in freeze–thaw environment

In order to study the uniaxial compressive mechanical properties and damage evolution of recycled aggregate concrete (RAC) containing silica fume (SF) under freeze–thaw cycles, the RAC with SF replaced partial cement was prepared. The replacement rates were 0% and 9%. The RAC were subjected to 0, 50, 75, 100, 125 freeze–thaw cycles and uniaxial compression tests. The microstructure, micro-crack propagation process and reaction products were observed by acoustic emission (AE) and scanning electron microscope (SEM). The statistical damage theory was used to explore the mesoscopic damage evolution mechanism of RAC. The results showed that the peak stress and modulus of elasticity of the specimen tended to decrease, the peak strain and mass loss rate gradually increased with the increase of the number of freeze–thaw cycles(N). The compressive strength of RAC with S = 0% decreases from −41.52MPa to −11.23MPa when N increases from 0 to 125. The addition of SF produced additional volcanic ash reactions, resulting in an increase in ettringite (AFt), which reduces the porosity of RAC and is able to increase the compressive strength at different N significantly. Compressive strength increases by 21.84% and 12.06% at N = 0 and 125, respectively. Considering the existence of two mesoscopic damage modes of fracture and yield, the deformation failure mechanism of RAC was analyzed from the perspective of effective stress. The all five characteristic parameters characterizing the mesoscopic damage show significant regular change with increase of the number of cycles. The relationship between the macroscopic mechanical properties of RAC and the mesoscopic damage mechanism was established by analyzing the evolution law for the characteristic parameters.

Scale Effect on Uniaxial Compressive Properties of the Outburst-Prone Coal.

Coal is a naturally discontinuous, heterogeneous, and anisotropic brittle material. The uniaxial compressive strength of coals is significantly affected by the sample size-dominated microstructure of minerals and fractures. The scale effect of the mechanical properties of coal is a bridge connecting the mechanical parameters of laboratory-scale coal samples and engineering-scale coal. The scale effect of coal strength is of great significance in explaining the fracturing law of the coal seam and reveal the mechanism of coal and gas outburst disaster. The uniaxial compressive strength of outburst-prone coal samples with different scale sizes was tested, the variation law of uniaxial compressive strength with increasing scale was analyzed, and the mathematical models of both were constructed. The results show that the average compressive strength and elastic modulus of outburst coal decrease exponentially with the increase in scale size, and the decrease rate is reduced. The average compressive strength of the tested coal samples decreased from 10.4 MPa for size 60 × 30 × 30 mm3 to 1.9 MPa for scale 200 × 100 × 100 mm3, which decreases by 81.4%.

Effect of Sulfate Crystallization on Uniaxial Compressive Behavior of Concrete Subjected to Combined Actions of Dry–Wet and Freeze–Thaw Cycles

This study focuses on the influence of salt crystallization from sodium sulfate on uniaxial compressive properties of concrete subjected to the coupling action of dry–wet cycles and freeze–thaw cycles. Eight groups of concrete specimens with different concentrations of sodium sulfate solution (CSSS) and different numbers of drying and wetting cycles (NDWC) were designed. Three groups of specimens with different numbers of freezing and thawing cycles (NFTC) exposed to same dry–wet cycles and same sulfate concentration were prepared to study the effects of combined environmental conditions. Salt crystallization from sodium sulfate was generated under a cyclical dry–wet time ratio of 3:1. Scanning electron microscopy and X-ray diffraction analysis were used to analyze reaction products of sulfate and concrete matrix. The results show that under single sulfate dry–wet cycles, with the increase of CSSS and NDWC, the uniaxial compressive strength of concrete degrades as a parabola and corresponding strain increases as a parabola, except for the linear increase of CSSS strain. Subjected to the combined action of sulfate dry–wet cycles and freeze–thaw cycles, it shows that the uniaxial compressive strength of concrete decreases as a parabola with the increase of NFTC, but corresponding strains have no obvious variation. The sulfate salt attack in advance greatly accelerates the deterioration of specimens after freeze–thaw cycles. The common dimensionless predication model of stress–strain relationship of concrete subjected to the combined action of dry–wet cycles and freeze–thaw cycles has been established.

Theoretical study on uniaxial compressive mechanical properties of three-dimensional graphene

Combining molecular dynamics (MD) simulations and continuum modeling, the uniaxial in-plane compressive properties of honeycomb three-dimensional (h3D), triangle-like 3D (t3D) and non-equilateral hexagon 3D (nh3D) graphene are investigated to elucidate configuration-property relationships, and the constitutive relations of three kinds of 3D graphene are derived to evaluate the compressive mechanical properties. Based on theoretical and MD simulation results, it is found that the compressive stress-strain responses of 3D graphene can be divided into five stages. The compressive mechanical properties and deformation mechanisms of each stage are different. When 3D graphene is compressed, graphene sidewalls undergo rotations, bending and buckling deformations, collapses. Because graphene sidewalls of h3D graphene are prone to undergo buckling deformations, there is large locking strain in h3D graphene. For t3D and nh3D graphene, their high plateau stress is attributed to unique configurations. Moreover, we also find that with increasing graphene sidewall width, Young's modulus and plateau stress of 3D graphene gradually decrease. In addition to the above investigations, the energy absorption mechanisms and compression-unloading stress-strain curves of 3D graphene are also studied. It is found that there are extraordinary compression-recovery properties and energy absorption capacities in 3D graphene. Finally, the selection criteria of 3D graphene are proposed.