Uniaxial Compressive Loading Research Articles

3D FE analysis of bored pile- pile cap interaction in sandy soils under axial compression- parametric study

In this research study, a 3D elasto-plastic finite element was used to analyze the influence and the interaction between the bored concrete pile, pile cap, and surrounding ground under uniaxial compression load, using ABAQUS finite element software. Mohr-Coulomb plasticity model was used to simulate sand elements while the pile was modeled as elastic material with a modulus, Ep. The contact between pile and adjacent sand was simulated using contact pair with surface-to-surface type of interaction. Different sand properties and pile length / diameter (L/D) ratios were considered in the analysis. Pile cap bearing pressure (qcap), side shear stress (fside), tip bearing pressure (qtip), deformation, and stresses and strains around the pile were investigated. The results show that for the same soil, as L/D ratio increases qcap decreases. Moreover, the results show that for the same L/D ratio, qcap decreases as the soil modulus (Es) increases and qtip decreases slightly with the increase in Es whereas for the same Es, qtip increases with the increase in L/D ratio. The major contribution in the capacity of capped bored pile under compression loading is devoted to qtip. As L/D increases, the contribution of qtip increases. Furthermore, qtip increases as the relative stiffness, Es/Ep increases.

Cyclic compressive behavior of hook-end steel and macro-polypropylene hybrid fiber reinforced recycled aggregate concrete

One widely accepted strategy is to add fiber into recycled aggregate concrete (RAC) to improve compressive strength. Few existing investigations have focused on the cyclic compressive behavior of hybrid fiber reinforced recycled aggregate concrete (HFRRAC). A total of eighteen groups of prismatic specimens with different fiber combinations and recycled coarse aggregate (RCA) replacement rates were conducted under cyclic compression to investigate the mechanical properties of hooked-end steel and macro-polypropylene hybrid fiber reinforced recycled aggregate concrete. Results indicate that specimens under cyclic loading fail similarly to those subjected to monotonic loading. The envelope curve of the cyclic stress-strain curve for HFRRAC closely resembles the corresponding monotonic stress-strain curve. RCA replacement rates and fiber combinations do not significantly affect plastic strain and stress deterioration. Fibers added to specimens mitigate stiffness degradation and improve hysteretic energy dissipation. The proposed constitutive equations can be used to describe the cyclic compressive behavior of HFRRAC. The fibers improve the density and structure of mortar and aggregate-paste interfaces from the microstructure morphologies. The fracture mechanisms of HFRRAC were also studied using mesoscale numerical models under uniaxial compression loading. The cohesive zone model is suitable for simulating the compressive behavior of HFRRAC. Numerical specimens fail in mixed fracture modes, primarily mode II fractures.

Self-sensing study of stress in low-doped carbon fiber reinforced hydraulic concrete

As an intrinsically self-sensing material, carbon fibre concrete has promising applications in structural health monitoring. Investigating the long-term stability of carbon fibre concrete in terms of resistivity changes under the influence of factors such as ageing effects and environmental conditions can help assess its feasibility for long-term monitoring applications. In this paper, the specimens were designed based on the variables of carbon fibre admixture (0.05 vol%, 0.08 vol%, 0.1 vol%) and carbon fibre length (3 mm, 6 mm, 9 mm, 12 mm), and the DC four-electrode method was used to study the self-sensing of low admixture carbon fibre reinforced hydraulic concrete containing coarse aggregate (5–20 mm) under long age (180d) in order to analyze the resistivity change law when it was loaded under long age condition. The results show that the fraction of resistivity change during loading (in compression and flexure) is low for all specimens in the long-age condition, but the resistivity change is consistent with its internal change. Uniaxial compressive cyclic loading in the elastic phase, each specimen exhibits a piezoresistivity under each loading cycle, while the material's own resistance under bending loading increases irreversibly as the loading progresses. In addition, for the flexural toughness evaluation test of fibre concrete, an adjustable deflection test device is designed based on existing codes, which can effectively solve the drawback of the existing bracket for fixing the deflection test instrument in the span, which needs to know the type of instrument in advance and then reserve the through-holes that can be clamped to the instrument.

Numerical Modeling of Rock Blocks with Nonpersistent Rough Joints Subjected to Uniaxial Compressive and Shear Loadings

Characterizing the mechanical behavior of jointed rocks is important to understand the behavior of structures in rock masses. Jointed rocks can be composed of persistent and nonpersistent joints where the impact of nonpersistent joints requires careful consideration for an accurate rock mass mechanical characterization. Most previous investigations into nonpersistent jointed rocks focused on joints with smooth surfaces, and a few experimental studies focused on nonpersistent rough joints and nothing specific has been reported numerically. Therefore, this study investigated several synthetic jointed rocks with nonpersistent rough joints numerically under uniaxial compressive and shear loadings. The PFC2D-based synthetic rock mass (SRM) approach was adopted to assess the impact of bridge angle (γ) and length (L), joint roughness coefficient (JRC), and normal stress (σn) on the shear strength (τn) and cracking in jointed rocks with nonpersistent rough joints. In addition, the impacts of γ, L, JRC, and joint inclination (θ) on the uniaxial compressive strength (UCS or σcm), elastic modulus (Em), and failure pattern in the jointed blocks were examined numerically. First, several numerical models were developed and verified by the laboratory data, followed by an extensive parametric study to assess the effects of the defined parameters further. The effects of JRC and σn on τn were more pronounced than γ and L due to the formation of interlocking cracks, which could cause significant shear resistance during shear loading. In addition, the numerical results under axial loading revealed that an increase in θ could reduce the deformation modulus and the value of the other parameters, in particular the JRC, could lead to an increase in the strength of jointed samples.

Particle-matrix debonding with Strength-Differential effects

In this work the onset of failure caused by particle-matrix debonding in aluminum alloy 2090-T3 and magnesium alloy AZ31 under either overall uniaxial plane strain tension or compression load is studied numerically using a unit cell model. Especially for magnesium AZ31, experiments show a significant difference in the tensile-compressive yield stresses, the so-called Strength-Differential-effect (SD-effect). This SD-effect cannot be captured by any isotropic yield function and only by recent anisotropic yield functions. To accurately model AA 2090-T3 and magnesium AZ31 the general yield function by Yoon et al. (2014) is adopted in addition to the isotropic von Mises plasticity yield function and the anisotropic yield function of Hill (1948). The numerically predicted strain at which void nucleation initiates is generally found to be larger for magnesium AZ31 than for AA 2090-T3. However, depending on the orientation of the principal axes of plastic anisotropy this void nucleation strain varies significantly. This holds true for both materials, but the void nucleation strain of AA 2090-T3 in compression is numerically predicted to be practically identical whether or not isotropic or anisotropic plasticity is considered. In tension the void nucleation strain of AA 2090-T3 based on anisotropic plasticity is found to be more than double the strain obtained by von Mises plasticity. The numerically predicted void nucleation strain of magnesium AZ31 is significantly affected by the yield function adopted. For the von Mises yield function the value of the void nucleation strain is in between the predictions based on the anisotropic yield functions. For both tension and compression, the yield function of Yoon et al. (2014) results in the largest void nucleation strain, whereas the yield function of Hill results in the smallest strain value. This holds true for all five orientations of the principal axes of plastic anisotropy investigated.

Stress–Strain Model for Geopolymer Mortar under Active Confinement

A stress–strain model is developed for geopolymer mortar subjected to uniaxial compressive loading with active confinement. The model was developed using the triaxial test carried out on cylindrical geopolymer mortar samples cast with different weight percentages of slag and fly ash. The samples were tested under four levels of confining pressures (i.e., 0, 5, 10, and 15 MPa) to study the effect of confining pressure on peak stress, peak strain, volume change, modulus of elasticity, and Poisson’s ratio. The stress–strain behavioral model for geopolymer mortar together with the functional relationship for model parameters with confinement ratios is developed. The developed strain–strain model shows good agreement with the experimental results. Further, the modulus of elasticity and Poisson’s ratio are linearly varied with confining pressure. Also, the normalized volumetric strain factor increases linearly with the compressive strength. The obtained experimental results demonstrate significant improvement in strength and ductility due to confinement for geopolymer mortar.

Numerical simulation of effect of reclaimed asphalt pavement on damage evolution behavior of self-compacting concrete under compressive loading

The preparation of self-compacting concrete (SCC) using reclaimed asphalt pavement (RAP) to replace part of natural coarse aggregate can realize efficient recycling of resources and have achieved good economic benefits. However, the mechanism of the effect of RAP on the mechanical properties of concrete is still not clear. Therefore, a discrete element model (DEM) of SCC with different RAP contents is established. The bonding characteristics between RAP and cement paste were considered and the crushable aggregate was generated to improve the model reliability. Based on the DEM, the influence of RAP on mechanical behavior and failure mode of SCC under uniaxial compression load was analyzed. The results indicated that RAP significantly affects the total number and growth character of microcracks. The microcracks appear earlier and the total crack number decreases with RAP content ranging from 0% to 100%. Cracks are more curved and formed network damage with RAP content increase. Furthermore, the simulation result shows that RAP affects concrete's crack type under compression load. This study helps to understand effects of RAP on the damage evolution behavior of SCC and the related mechanism.

Experimental Study on the Sulfuric Acid Corrosion Resistance of PHC Used for Pipe Pile and NSC Used in Engineering

In order to compare and investigate the sulfuric acid corrosion resistance of concrete for PHC pipe piles and two kinds of concrete commonly used in engineering, acid accelerated corrosion tests were conducted on specimens with three different strength grades of C30, C50, and C80 in a sulfuric acid solution with pH ≈ 0.85. The appearance of the specimens was observed, and the changes in mass loss percentage, corrosion depth, and stress–stain curves under uniaxial compressive loading were calculated and obtained with the corrosion time. From the comparison of corrosion depth and mass loss percentage of the concrete specimens with three different strength grades of C30, C50, and C80, it was found that the higher the strength grade of the concrete, the more severe the corrosion degree. The shapes of the stress–strain curves of three different strength grades of concrete specimens were basically the same. As the corrosion time was prolonged, the peak stress and the elastic modulus of concrete decreased. From the perspective of long-term corrosion, C80 specimens had a relatively smaller percentage of peak stress loss and a stronger resistance to peak stress loss. The research results provide references for the durability design of concrete structures and the prediction of concrete’s service life in a sulfuric acid environment.

Mechanical behavior of the cellular concrete and numerical simulation based on meso-element equivalent method

The novel cellular concrete with millimeter-size isolated spherical pores can greatly reduce the transportation cost of concrete coarse aggregate in the construction of facilities on remote islands, which utilizes spherical saturated SAP (Super-Absorbent Polymer) presoaked in seawater in situ. The mechanical property of this cellular concrete is an important basis for its engineering application. The purpose of this paper is to present a numerical method to understand more fully and efficiently its mechanical properties. According to the characteristics of meso-component of this cellular concrete, the meso-element equivalent model is improved, in which statistical homogenization method is used to substitute Voigt equivalence method. Based on the elastic damage constitutive model, uniaxial compression numerical tests are carried out on random meso-elements, and the parameters of damage constitutive model related to the porosity are obtained. On this basis, the random specimen model is divided into meso-elements of the same size, and the equivalent mechanical properties are given to the elements according to their porosities. The effectiveness of the numerical simulation method is verified by comparing with the actual test results, and it can reflect the damage process during uniaxial compressive loading.

Failure characteristics and the law of the energy evolution of granite with different pre-crack inclination angles under uniaxial compression loading

Cracks affect the strength of rock masses and eventually threaten their stability in engineering. In order to study the fracture characteristics and mechanical properties of cracked rocks, uniaxial compression tests of pre-cracked granite samples with a central circular through hole were carried out by using MTS816 rock mechanics testing system. The inclination angles of different pre-cracks are 0°, 15°, 30°, 45°, 60°, 75°, and 90° respectively, and the influence of the crack stop hole near the crack tip on the failure behavior of pre-cracked samples is also considered. The results indicate that, compared with the intact sample, the peak strength of pre-cracked samples decreases significantly and is related to the pre-crack inclination angle. The failure mode of the sample varies with the pre-crack inclination angle, and the crack stop hole near the crack tip also has a certain influence on the crack growth to a certain extent. However, in terms of failure mode and its transformation law, the influence of central circular through hole and crack stop hole can be ignored. Generally speaking, the larger the inclination angle of the pre-crack, the more the total energy required for failure of the sample, and the more the stored elastic strain energy. Before the peak strength, the elastic strain energy of the sample is greater than the dissipated energy, after the peak strength, the dissipated energy gradually exceeds the elastic strain energy due to energy conversion. It is found that the pre-crack reduces the energy storage capacity of the sample, and the total energy is ultimately dominated by sample integrity. The dissipated energy rate increases first, then decreases, and finally increases again, the inflection points are the end of micro-crack closure and the peak strength, respectively. The crack stop hole changes the law of energy evolution to a certain extent, which can improve the ability of rocks to accumulate energy when designed at an appropriate position, so as to improve its load-bearing capacity in a certain range. The results display the mechanical properties of pre-cracked granite samples under uniaxial compression and are conducive to its application in engineering.

Mechanical Characterisation and Simulation of the Tensile Behaviour of Polymeric Additively Manufactured Lattice Structures

BackgroundThe mechanical properties of lattice structures have been primarily investigated using uniaxial compression loads. Particularly for polymers, tensile properties are rarely considered because of the difficulties of defining a suitable specimen design in which the fracture occurs within the gauge length.ObjectiveThis work proposes a novel formulation to obtain a specimen for the tensile test with a gradation of the lattice density at the interface with the bulk portion, which realises a uniform stress distribution. The aim is to combine a localisation of the fracture in the gauge length with a specimen geometry accomplishing the EN ISO 527 standard and analyse the correlation between the mechanical performance and the defects induced by the process on such thin structures.MethodsThe formulation is experimentally and numerically (FEM) tested by designed specimens with different cell topology, cell size, strut diameter, and number of cells in the sample thickness. Also, results from uniaxial compression tests are used to validate the tensile properties. The specimens are manufactured in different orientations in the building volume by laser powder bed fusion with Polyamide 12. The effects of the pores morphology, distribution, and inherent anisotropy are investigated using X-ray computed tomography analysis. This data is also used to tune a numerical model.ResultsThe numerical analysis showed a uniform stress distribution; experimentally, the fracture is localised inside the gauge length in respect of the ISO standard. Remarkably, among the different strut-based architectures, the elongation at break is, in the best case, 50% of the corresponding bulk material, while the tensile strengths are comparable. Vertical printed specimens exhibited a slight decrease in tensile strength, and the elongation at break was lower than 50% compared to the counterparts built along the horizontal orientation. Modifying the numerical model according to process-related dimensional deviations between the actual and the nominal structures significantly improved the numerical results. The remaining deviation highlighted the incorrectness of modelling the lattice material from the bulk properties.ConclusionDensity gradation is a reliable approach for describing the tensile behaviour of polymeric lattice structures. However, the lower amount of porosity and the different shape in the lattice led to a different material mechanical performance with respect to the corresponding bulk counterpart. Therefore, for polymeric lattice structures, the relationship between process-design-material appears crucial for correctly representing the structure behaviour.

Investigation on the multimodal failure characteristics of cement mortar under uniaxial compression loading

The physical condition and durability of cement-based structures can easily decrease after years of operation due to exposure to severe scenarios associated with internal defects, aggressive usage, and continuous load changes. Therefore, accurately assessing such infrastructures is essential for ensuring safety and serviceability and preventing hazards. In this study, an experimental investigation of the multimodal failure characteristics of cement mortar with various sand contents at different uniaxial compressive loading rates was conducted. Specifically, the multimodal failure characteristics include three main categories: mechanical properties (e.g., compressive strength), one-dimensional signals (e.g., micro-vibration and electromagnetic radiation), and two-dimensional videos/images (e.g., crack propagation trajectory). A geophysical acquisition and a high frame rate camera were employed to simultaneously record the micro-vibration, electromagnetic radiation and crack propagation videos of the cement specimens in a uniaxial compression test. Based on the computer vision technique and the feature pyramid network (FPN), an automatic pixel-level crack segmentation method was proposed to extract cracks of each critical moment in the fracture video. Then, the fractal dimension and crack area were calculated to quantitatively depict the crack propagation trajectory. Finally, the stress drop, micro-vibration, electromagnetic radiation, and crack propagation trajectory characteristics were analysed and discussed. The experimental results indicate the following. (1) The FPN offers a practical way to identify cracks in structures of cement-based materials at the pixel-level. (2) The micro-vibration, electromagnetic radiation, and crack propagation trajectory exhibit good consistency. In particular, the area and fractal dimension of cracks positively correlate with the stress drop of cement under compression loading. (3) The peak and cumulative energy values of micro-vibration and electromagnetic radiation tend to increase as the sand content increases when subjected to the same loading rate.

Buckling Analysis of Porous Functionally Graded Plates

This study investigated the buckling behavior of Porous Functionally Graded Material (PFGM) plates. The present model assumes unevenly distributed porosity along the plate thickness and the use of the novel hyperbolic shear deformation functions and hyperbolic tangent and secant thickness stretching functions. In the present work, a porous Functionally Graded (FG) plate was analyzed by the principle of virtual work in order to understand the buckling behavior under uniaxial and biaxial compressive loading. The Rayleigh quotient method was applied to find the critical buckling load. The mesh convergence was investigated on a Finite Element (FE) model, and the accuracy of the results was compared with the prior research. The results of the proposed model match reasonably well with the ones of the published literature. Thorough parametric studies were performed to investigate the effect of porosity on the critical buckling load of the PFGM plate.

Mechanical responses of buoyant bio-inspired foamed concrete structures

This work proposes a new type of lightweight cellular foamed concrete (FC) inspired by natural cellular structures with controllable mechanical properties for different prefabricated engineering applications. The 3D printed formworks are inspired by the lattice structure and triply periodic minimal surface (TPMS) architectures, including gyroid and primitive prototypes. These 3D printed sacrificial thermoplastic Polylactic Acid (PLA) formworks were then infiltrated with two types of foamed concrete with different densities of 600 kg/m3 and 800 kg/m3 and subjected to uniaxial compressive loadings. Furthermore, the X-ray computed tomography (CT) scan was conducted on the prefabricated structures to further observe the PLA-foamed concrete contact region and to investigate the air void characteristics. Numerical simulation was employed for further investigation on the structural performance and failure mechanism of three bio-inspired structures (TPMS-Primitive, -Gyroid, and strut-based lattice). By both numerical and experimental investigations, the gyroid cellular structure yields the highest compressive capacity, followed by the primitive and lattice structures, respectively. Furthermore, based on the X-ray micro-CT scan, the bio-inspired architecture of the moulds showed a significant effect on the size and distribution of air voids, which highly influenced the compressive strength of the infiltrated foamed concrete.

Influence of Pretreatment Methods on Compressive Performance Improvement and Failure Mechanism Analysis of Recycled Aggregate Concrete.

The utilization of recycled aggregate can avert the squandering of resources and the destruction of the environment. Nevertheless, there exists a slew of old cement mortar and microcracks on the surface of recycled aggregate, which give rise to the poor performance of aggregates in concrete. In this study, for the sake of ameliorating this property of recycled aggregates, the surface of the recycled aggregates is covered with a layer of cement mortar to compensate for the microcracks on the surface and reinforce the bond between old cement mortar and aggregates. In order to demonstrate the influence of recycled aggregate by different cement mortar pretreatment methods, this study prepared natural aggregate concrete (NAC) and concretes with recycled aggregate after the wetting pretreatment (RAC-W) and cement mortar pretreatment (RAC-C), and conducted uniaxial compressive strength tests on different types of concrete at different curing ages. The test results indicated that the compressive strength of RAC-C at a 7 d curing age was higher than that of RAC-W and NAC, and the compressive strength of RAC-C at a 28 d curing age was higher than RAC-W but lower than NAC. The compressive strength of NAC and RAC-W at a 7 d curing age was about 70% of that at a 28 d curing age, and the compressive strength of RAC-C at a 7 d curing age was about 85-90% of that at a 28 d curing age. The compressive strength of RAC-C increased dramatically at the early stage, while the post-strength of the NAC and RAC-W groups increased rapidly. The fracture surface of RAC-W mainly occurred in the transition zone between the recycled aggregates and old cement mortar under the pressure of the uniaxial compressive load. However, the main failure of RAC-C was the crushing destruction of cement mortar. With changes in the amount of cement added beforehand, the proportion of aggregate damage and A-P interface damage of RAC-C also changed accordingly. Therefore, the recycled aggregate pretreated with cement mortar can significantly improve the compressive strength of recycled aggregate concrete. The optimal amount of pre-added cement was 25%, which is recommended for practical engineering.

A combined experimental–numerical modelling approach for self-crack monitoring in conductive cementitious materials

This study proposes an innovative methodology by combining experimental testing and numerical modelling for self-evaluating the crack development of conductive cementitious materials based on piezoresistivity. Cube specimens enhanced with carbon black nanoparticles were subjected to cyclic and uniaxial compression loads individually for evaluating their piezoresistivity behaviour and analysing the crack sensing mechanism. A discrete element model (DEM) was utilised to extract crack development information which was correlated with resistivity variation in experiments for damage quantification. Acoustic emission was also utilised for the validation of resistivity-based crack monitoring. It was found that electrical resistivity started to rise at a relatively early stage of compression process, followed by an increasing rise before the specimen reached its peak strength and then a rapid surge when the specimen started to lose its load-bearing capacity. The results prove that the proposed approach can monitor crack development of conductive cementitious materials from a micro scale through resistivity variation and more precisely describe the damage accumulation. The study also demonstrates that DEM is capable of capturing failure mechanism of cementitious materials.

Mechanical behaviour and fracture evolution of coal specimens containing an over‐excavated hole: Experimental study and numerical modelling

AbstractUtilising a series of mechanically over‐excavated cavities along borehole is a novel technique for enhancing the permeability of soft coal seams and, consequently, gas drainage. The evolution of cracks induced by a wide range of pressure‐relief around an over‐excavated hole is intrinsically complex. In this study, the mechanical behaviour and crack evolution of the specimens containing an over‐excavated hole under uniaxial compression loading were studied by experimental and 3D numerical simulation. The results indicated that the peak strength and elastic modulus of the specimens gradually decrease with increasing cavity diameter and length, which is also verified by the numerical simulation. The inclusion of cylindrical cavities in over‐excavated holes results in reduced crack initiation stress and a greater degradation of peak stress and elastic modulus, despite having an equivalent volume to the ellipsoidal cavity. This is likely attributed to the difference in stress concentration between the cylindrical and ellipsoidal cavities. The crack propagation process can be classified into four stages based on the acoustic emission (AE) event counts, initial crack compaction, stable crack propagation, unstable crack propagation and post‐peak failure stage. The two AE indices, rise angle and average frequency value, demonstrated that the failure is dominated by tensile crack and gradually transformed to shear crack. Stress redistribution is essential in the initiation and propagation of cracks. Tensile stress concentration leads to cracks forming at the top and bottom of the hole, which propagate in the direction of loading. Compressive stress concentration results in shear cracks forming at the left and right sides of the hole, which propagate diagonally. The failure pattern of the specimen is ultimately determined by a combination of tensile and mixed crack propagation. The experimental and numerical results contribute to a deeper understanding of the crack evolution mechanism of coal seams with over‐excavated holes.

Physiological and degenerative loading of bovine intervertebral disc in a bioreactor: A finite element study of complex motions

Intervertebral disc (IVD) degeneration and regenerative therapies are commonly studied in organ-culture experiments with uniaxial compressive loading. Recently, in our laboratory, we established a bioreactor system capable of applying loads in six degrees-of-freedom (DOF) to bovine IVDs, which replicates more closely the complex multi-axial loading of the IVD in vivo. However, the magnitudes of loading that are physiological (able to maintain cell viability) or mechanically degenerative are unknown for load cases combining several DOFs. This study aimed to establish physiological and degenerative levels of maximum principal strains and stresses in the bovine IVD tissue and to investigate how they are achieved under complex load cases related to common daily activities.The physiological and degenerative levels of maximum principal strains and stresses were determined via finite element (FE) analysis of bovine IVD subjected to experimentally established physiological and degenerative compressive loading protocols. Then, complex load cases, such as a combination of compression + flexion + torsion, were applied on the FE-model with increasing magnitudes of loading to discover when physiological and degenerative tissue strains and stresses were reached.When applying 0.1 MPa of compression and ±2–3° of flexion and ±1–2° of torsion the investigated mechanical parameters remained at physiological levels, but with ±6–8° of flexion in combination with ±2–4° of torsion, the stresses in the outer annulus fibrosus (OAF) exceeded degenerative levels.In the case of compression + flexion + torsion, the mechanical degeneration likely initiates at the OAF when loading magnitudes are high enough. The physiological and degenerative magnitudes can be used as guidelines for bioreactor experiments with bovine IVDs.

Elemental and experimental analysis of modified stent's structure under uniaxial compression load

Additive manufacturing has enabled the fabrication of lightweight complex metamaterials that possess high energy absorption and impact resistance properties. Stents, a typical 3D auxetic material, have significant self-expanding behavior, and their mechanical properties can be finely tuned over a wide range. In this study, we systematically analyzed three distinctive elastic-plastic regions using experimental, numerical simulations, and theoretical analysis, focusing on investigating the energy absorption capability of a designed structure by varying tessellated unit cell numbers in two section views in X- and Y-direction. Two batches of 5 specimens each were 3D printed using FDM techniques. The results showed that designing a self-expanding stent with innovative capabilities was possible, with the yield stress ranging between 1.5 MPa and 2.0 MPa and extended effective elastic moduli derived from the deformation mode of tessellated unit cells. The maximum energy absorption for all structures ranged between 7.1J and 18J, with similar capabilities observed for the designed stents. However, increasing unit cells along the X-direction resulted in a significant increase in SEA, while the Y-direction remained unchanged. Therefore, these structures have a significant influence on areas requiring energy absorption. In addition, they are the ideal class of energy absorbers for cushioning applications. Furthermore, their energy-absorption capacity can be easily tailored to meet specific end-use requirements by varying their structural parameters using unit cell tessellation.

Experimental study on compressive behaviors and meso-scale structure of SFRFC based on CT scanning technique

Due to the excellent characteristic of lightweight, foam concrete shows great potential in civil and mining engineering fields, such as prefabricated roofs and supportive materials for tunnels. However, inherent porosity not only reduces the density of foam concrete but also the strength, which greatly limits its application in engineering structures. In this study, the foam concrete reinforced by steel fibers (SFRFC) is proposed, and a detailed experimental study is conducted to investigate the influence of steel fibers and porosities on the physical and mechanical properties of SFRFC. Firstly, 17 groups of SFRFC specimens with different steel fiber content (0, 0.5, 1, 1.5, 2 and 2.5%) and different foam content (0, 40, 50, 60, 70, 80%) are fabricated, and the mechanical properties under uniaxial compressive loading are tested. Secondly, CT scanning technique is adopted to investigate the distribution of steel fiber and pores in the prepared specimens at the meso-scale level and clarifies their interaction at the meso-scale level; Thirdly, the formula which takes porosity and steel fiber content as variables, is established to predict the compressive strength of SFRFC and provides references for the design and engineering application of SFRFC. According to the results of uniaxial compressive test, it can be concluded that steel fibers play an important role in improving the compressive properties of SFRFC, especially the compressive strength and energy absorption. The increase of Steel fibers will reduce the proportion of foam pores in SFRFC and make the pore size distributions polarized according to the X-CT test results. Based on the empirical models commonly used for different materials, we obtain the best formulas for predicting the porosity and compressive strength of SFRFC.