Compressive Mechanical Behavior Research Articles

Dynamic mechanical properties and failure mechanism investigation of multiscale toughened basic magnesium sulfate concrete

The dynamic impact compressive properties of a novel whisker composite material (i.e., ultra-high toughness basic magnesium sulfate cement concrete, UHTBMSC) is investigated in this study. First, X-CT and scanning electron microscopy are used to characterize the three-dimensional distribution characteristics of two types of fibers in the UHTBMSC, as well as the microstructure. Second, the Hopkinson compression bar technique is used to investigate the dynamic impact compression behavior of UHTBMSC under different strain rates. Finally, a novel 3D random packing model of steel fibers (straight and hooked) is established, and the 3D mesoscopic numerical simulation of the dynamic impact compression behavior of UHTBMSC is performed. The results show that the steel fibers are crossed and evenly distributed in the UHTBMSC matrix, whereas needle-rod-like 5–1–7 whiskers appear in large quantities in the UHTBMSC. Dynamic impact compression results show that UHTBMSC is a rate-dependent material, and a mathematical relationship between strain rate and dynamic increase factor is established for UHTBMSC materials. The numerical simulation results agree well with the test results, indicating that the newly established 3D meso-model can be used to effectively analyze the dynamic compression mechanical behavior of UHTBMSC. In addition, the results confirm that UHTBMSC exhibits excellent resistance to dynamic impact compression, which is primarily attributed to the crack inhibition effects of 5-1-7 whiskers and steel fibers, thereby effectively improving the dynamic mechanical properties of UHTBMSC.

Design and evaluation of compressive properties of 3D-printed PLA stochastic open-cell foam

The deformation characteristics and mechanical behaviour of 3D-printed stochastic open-cell foam structures were experimentally studied under a quasi-static compression test. PLA foam specimens with irregular cell geometry, variable strut sections and prescribed relative density are constructed numerically using the Voronoi diagrams and prepared with fused deposition modelling. The design procedure allows controlling the strut topology easily, which makes the geometrical model suitable for studying the effect of local morphological characteristics on the mechanical performance of open-cell foam material. The effect of different morphological characteristics on the compressive mechanical behaviour of the fabricated PLA foam was examined in detail. Compression experiments prove that the mechanical properties are significantly dependent on the relative density and strut section shape. The main mechanical properties of the 3D-printed PLA foams for different cross-sectional shapes of struts were obtained via the energy-efficient method and expressed with the two common formulas existing in the literature.

Compressive mechanical behavior and failure of the pig bone rib and correlation to its morphological characteristics

The mechanical and failure properties of bones are well documented from a structural perspective. By contrast, less is known about those properties from the material and microstructural point of view. This study combines mechanical compression of pig bone rib slices, comprising both cortical and trabecular components, together with digital image correlation records. For monotonic loading, the three classical phases of the bone response, namely elastic, plateau/softening, and hardening are observed. The first phase is characterized by a uniform state of deformation which becomes heterogeneous in the following phases, through the appearance of well-defined domains. Failure is initiated in the trabecular bone at the interfaces between those domains, where the prevailing heterogeneous deformation indicates the operation of shear or uniaxial strain components. From a microstructural point of view, using micro-CT (computed tomography) it was noticed that sub-regions with relatively combined low BV/TV (bone material volume divided by total volume) and anisotropy, whose structure is oriented perpendicularly to the loading direction, are prone to failure at the interface between heterogeneously deforming domains. A globally similar behavior is reported for aluminum foams without cortical components.Repeated loading cycles reveal a previously un-noticed response of the bone, consisting of elastic shakedown without ratcheting, with diminishing hysteretic load-displacement loops, which indicate that most of the damage is achieved during the first loading cycle.The observations reported in this paper are believed to provide important physical evidence to be included in numerical models at the verification and/or validation stages.

Effect of the Load Application Angle on the Compressive Behavior of Al Honeycomb under Combined Normal-Shear Stress.

A comparison of the compressive behavior of Al honeycomb under pure normal stress and combined normal-shear stress was analyzed in this work. The typical working stress of honeycomb is a compressive load along the direction parallel to the axis of the cells. However, the component can also undergo shear stresses during operation, which can cause premature failure. This work analyzes the mechanical behavior in compression by normal stress (0°) and in conditions of combined normal-shear stress (at 15° and 25°) using a special pair of wedges. The samples were obtained from a 3000 series Al alloy sandwich panel and tested according to the ASTM C365/C365M-22 standard. The different deformation modes of the cells in the combined compression were examined for three angles (0, 15°, and 25°). A theoretical model of combined compression was used to derive the normal and tangential components starting from the total stress-strain curves. A compression curve analysis was conducted at different angles θ, allowing for considerations regarding changes in strength, absorbed energy, and deformations. Overall, as the load application angle increased, both the shear resistance of the honeycomb and its tangential displacement up to densification increased, which is the opposite of what occurs in normal behavior. The cell rotation angle was calculated as the load angle varied. The rotation angle of the cell increased with the displacement of the crosshead and the application angle of the force.

Investigation of thermal and mechanical effects during electrically-assisted compression of CoCrFeNiW0.5 high entropy alloy

Electrically-assisted manufacturing (EAM) has many advantages than ambient temperature manufacturing and thermoforming for the building of hard-to-deform alloys. The EAM technique of High entropy alloys (HEAs), a newer alloy category, is an issue worth of research, especially the deformation mechanism in the process of EAM. In the paper, the electrically-assisted compressive mechanical behavior of CoCrFeNiW0.5 HEA composed of face centered cubic phase and μ phase precipitate was studied under current density and strain rate region of 0–40 A/mm2 and 0.0005 s−1-0.1 s−1, respectively. At high current density and strain rate, the reduction of yield stress is remarkable. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques were utilized to analyze the effect of current density on the flow stress behaviors and microstructure evolution under plastic deformation. The results show that the introduced electric current enhances the movement and annihilation of dislocations as well as dynamic recovery, resulting in the continuous decrease of flow stress. Additionally, we can clearly observed that the dislocation-free ring or some very low dislocation density regions around the μ phase precipitates, that's because μ phase precipitate can lead to severe lattice distortion and thus increase the electron scattering, and then the local high temperature appeared around the defect regions due to local Joule heating effect, which is recognized as the principal reason leading to the significant decrease of mechanical properties during electrically-assisted compression.

Axial Compressive Mechanical Behaviors of a Double-Layer Member

Axial Compressive Mechanical Behaviors of a Double-Layer Member

Compressive strength and elastic modulus of RBAC: An analysis of existing data and an artificial intelligence based prediction

In recent years crushing waste brick to produce recycled brick aggregates (RBAs) has become a viable solution for reducing environmental pollution and addressing the natural resource shortage in civil engineering. To promote the widespread use of the recycled brick aggregate concrete (RBAC) in construction, this study analyzes existing test results on the attributes of RBAs and the compressive mechanical behaviors of RBAC. The review results indicate significant differences and variabilities in the characteristics of RBAs compared to natural coarse aggregates and recycled concrete coarse aggregates. RBAs have the highest absorption capacity and crushing index among the three aggregates, leading to changes in the compressive failure mechanism and a decline in the mechanical properties of RBAC. Additionally, it is also observed that existing formulas do not adequately account for the deterioration of the compressive mechanical properties of RBAC. To tackle this problem, artificial intelligence (AI) approaches including artificial neural network and multigene genetic programming are utilized to develop precise models for predicting the compressive strength and elastic modulus of RBAC. It is found that RBAC’s these two mechanical indexes are mainly influenced by the standard strength of cement paste, water-to-cement ratio, sand-to-aggregate mass ratio, RBA replacement ratio and mass-weighted water absorption ratio of coarse aggregates. The AI models developed in this study accurately capture the trends of these factors and offer desirable predictive results.

Three-Dimensional Characterization of Polyurethane Foams Based on Biopolyols.

Two biopolyol-based foams derived from banana leaves (BL) or stems (BS) were produced, and their compression mechanical behavior and 3D microstructure were characterized. Traditional compression and in situ tests were performed during 3D image acquisition using X-ray microtomography. A methodology of image acquisition, processing, and analysis was developed to discriminate the foam cells and measure their numbers, volumes, and shapes along with the compression steps. The two foams had similar compression behaviors, but the average cell volume was five times larger for the BS foam than the BL foam. It was also shown that the number of cells increased with increasing compression while the average cell volume decreased. Cell shapes were elongated and did not change with compression. A possible explanation for these characteristics was proposed based on the possibility of cell collapse. The developed methodology will facilitate a broader study of biopolyol-based foams intending to verify the possibility of using these foams as green alternatives to the typical petrol-based foams.

Assessment of the compressive mechanical behavior of injection molded E-glass/polypropylene by mechanical testing and X-ray computed tomography

Nowadays, thermoplastic composite materials are considered among the most promising ones as they are gaining the interest of many industrial sectors due to their eco-friendly features such as their recyclability and their low-cost demand while being produced in high volumes. Among the most concerning issues regarding the injection molded, short fiber-reinforced composites are the fiber distribution, the fiber orientation, and their effect on the overall mechanical performance. In the present work, the effect of the injection molding on the compressive properties is investigated experimentally. In this context, compressive mechanical tests have been conducted in a range between subzero and elevated temperatures using specimens oriented parallel and perpendicular to the injection direction. In addition, X-ray computed tomography is implemented for characterizing some crucial features such as the fiber volume fraction, in local and global scale, and the orientation of the fibers through the thickness and length of the material. The results revealed a different compressive mechanical behavior between the two specimen categories in all the testing temperatures. In addition, the results obtained by the nondestructive testing revealed a significant variation of the fiber content locally and a notable difference between distinct zones through the thickness.

Mechanical behavior of Fe80P20/α-Fe amorphous/nanocrystalline composites studied by molecular dynamics simulations

In this paper, the compression mechanical behavior of Fe80P20/α-Fe amorphous /nanocrystalline composites (ANCCs) with grain diameters (d) from 0 to 6 nm was studied by molecular dynamics simulations. The peak strength (τp) increases with increasing d from 0 to 6 nm, while the flow strength (τs) increases with increasing d from 0 to 5 nm, then decreases with further increasing d to 6 nm. As a result, the composite with d = 5 nm exhibits the highest normalized difference (Δτ/τp, where Δτ = τp – τs) indicating its good plasticity. In order to reveal the effect mechanism of nanocrystalline size on deformation behavior, the atomic shear strain at different levels was analyzed. Besides, the amorphization of α-Fe phase during deformation was investigated by common neighbor analysis. The result is helpful for improving the mechanical properties of Fe-based ANCCs by strict controlling of heat treatment process to adjust the nanocrystalline size.

Compressive mechanical properties and dynamic behaviour of origami-inspired tri-directional auxetic metastructure

This study investigates the compressive properties of origami-inspired metastructures in the three directions and compares them with the conventional two-dimensional (2D) double arrow structure. Quasi-static crushing experiments of the 2D double arrow specimens are first conducted and the test results are used to calibrate the finite element model. With the calibrated numerical model, the compressive strength and tri-directional auxeticity of the origami-inspired metastructures and the conventional 2D double arrow structure are numerically investigated under quasi-static and dynamic crushing. As compared to the 2D double arrow structure, the origami-inspired metastructure shows larger transverse contraction deformation owing to its more obvious tri-directional auxeticity, and exhibits more isotropic crushing resistance in the three directions. In addition, the localized impact resistance performances of the origami-inspired metastructures are examined and compared with the 2D double arrow structure. The maximum indentation depth of the origami-inspired metastructure can reach up to 40% less than that of the 2D double arrow structure, indicating its superior impact resistance performance and great potential for impact-resistant applications.

Effects of elevated temperature and water re-curing on the compression behavior of hybrid fiber reinforced concrete

Over the past decades, the effect of elevated temperatures on the mechanical properties of concrete has received significant attention because of the importance for fireproof design, safety evaluation and repair of fire damaged constructions. However, very few researches have been dedicated to the consequences of water re-curing of a thermally damaged concrete. In this paper, the effect of elevated temperatures and water re-curing on the mechanical response of two hybrid fiber reinforced concretes was investigated. For the first hybrid reinforced mix, long hooked-end and medium hooked-end steel fibers were adopted, as well as high strength short wave shaped steel fibers. In the second mix, polypropylene fibers substituted the short-wave shaped steel fibers. The mechanical behavior in compression was studied by measuring the stress-strain response. The elevated temperatures above 200 °C decreased: Young's modulus, compressive strength and toughness of the hybrid fiber reinforced concretes. The stable crack growth stage was reduced with the increase of the temperature above 200 °C, with an extension of the unstable crack growth stage for both kinds of hybrid fiber reinforced concrete. Water re-curing partially recovered Young's modulus, compressive strength, toughness, and extended the stable crack growth. An existing model was modified for predicting the stress-strain response of thermally damaged hybrid fiber reinforced concrete.

Revisiting deformation anisotropy of ω-variants via microcompression of β oriented Ti85Nb15 alloy

The disperse-precipitated ω has a significant strengthening effect on metastable β-titanium (Ti) alloys. The (211)β[1¯11]β/(2¯11)β[111]β slip systems are massively activated during plastic deformation. However, the interaction of the four-equivalent crystallographic ω variants with these slip systems has not been investigated. Here, we revisit the evolvement of the internal ω-precipitate via systematically exploring the compressive mechanical behavior of <110>β-oriented Ti85Nb15 micropillars. Firstly, the four ω-variants show the strong deformation anisotropies. Secondly, this deformation anisotropy is pertinent to the interaction with dislocations. Dislocations originating from the β-matrix can continuously across the ω1-variant, but have no ability to across the ω2 variant. The accumulation of dislocations in the interface of ω2/β leads to severe local stress concentrations that ultimately prompts the dismemberment of ω2. Finally, we confirmed by first-principles calculations that the proliferation of ω1-variant owing to the reorientation of ω2-variant, that is, ω2→ω1, rather than a dissolution-reprecipitation mechanism, ω2→β→ω1. These findings are beneficial for a comprehensive understanding of the deformation mechanism of the ω-variants in metastable β-Ti alloys.

Quantitative Analysis of Mechanical Strength of Three-Phase Rigid Polyurethane Foam Composites Immersed with Water

The mechanical properties of rigid polyurethane foam (PUF) will be significantly affected because of the existence of water when applied in dam repair and road maintenance. The related studies generally consider the effects of water and matrix on the mechanical properties of rigid PUF. However, PUF is a three-phase composite consisting of water, air, and matrix in practical engineering. Its mechanical properties are subject to the combined effects of these three composites at the same time. In this case, an improved three-phase viscoelastic model was proposed to quantify the effects of water, air, and matrix on the compressive mechanical behavior of rigid polyurethane foam immersed in water (WRPF). Based on the improved viscoelastic model and piecewise method, a compressive strength prediction model of WRPF was developed to describe the change of WRPF’s compressive strength during the full-service life. Then uniaxial compression tests and electron microscope tests were conducted to verify the rationality of the model. Results show that water and air have reinforcing effects on the compressive property of WRPF in the short-term, unsaturated absorption stage. In contrast, water has weakening effects on its compressive property in the long-term, saturated stage. Finally, at different stages of water absorption, a semitheoretical and empirical formula was developed from the prediction model and the experimental data from compressive tests.

Out-of-plane compressive mechanical properties of square-twist origami folded-stable state

Origami structures are widely favored by engineering applications due to their reconfigurable characteristics and controllable mechanical properties. The square-twist (S-T) origami, featured with typical folded stability, has a broad application prospect. However, researchers usually focus on how the S-T folded-stable configuration is formed and affected by critical designing factors, lacking attention to its out-of-plane mechanical properties. Here, the mechanical properties of out-of-plane compression for the S-T origami in folded-stable state with zero neutral angle are revealed. A finite element compression model of the prestressed S-T origami folded-stable state is established and verified by compression experiments on the typical S-T origami. With the finite element model, the three-stage out-of-plane compressive mechanical behavior of typical S-T origami folded-stable state caused by facet contact and facet-substrate contact is discovered. By investigating the effects of different geometric and material parameters on the out-of-plane compressive mechanical properties for S-T origami folded-stable state, it is found that the self-contact situation of the S-T origami folded state significantly affects its out-of-plane compressive mechanical behavior. The influence of various filling materials in the S-T origami folded-stable state on its out-of-plane compressive mechanical behavior is discussed, highlighting the feasibility of our design in the flexible protection and related applications.

Axial mechanical behavior of innovative inter-module connection for modular steel constructions

Modular steel construction (MSC) is a construction mode where volumetric modules are prefabricated in a factory and assembled on-site to form permanent buildings. Inter-module connections are critical to the integrity and robustness of modular steel constructions (MSCs). In this paper, the mechanical behavior of a typical corner inter-module connection under axial tensile and compressive loads was investigated. A tensile test of the inter-module connection was carried out to investigate their axial tensile behavior. The refined numerical model was established, calibrated against the test results and then used to simulate the axial tensile and compressive mechanical behaviors of the inter-module connection. The effects of key design parameters on the axial load-displacement responses of the connection, including the bolt gasket thickness, the bolt diameter and the preload were investigated. The inter-module connection was shown to exhibit excellent load-carrying capacity under axial compression and adequate performance under tension. In terms of tensile resistances, the bolt gasket thickness and the bolt diameter were shown to be the critical parameters, while the section size of the modular columns dominated the compressive load-carrying capacity. Through geometrical parameters correlation analysis, a simplified piecewise polynomial axial load-displacement model with different stiffnesses in tension and compression was employed for predicting the axial load-displacement relationship. The proposed model was shown to be capable of accurately capturing the axial resistance characteristics of the connection while maintaining simplicity, and is therefore recommended for use to represent the axial behavior of the inter-module connection in global frame modelling.

Compressive Mechanical Behavior of Partially Oxidized Polyvinyl Alcohol Hydrogels for Cartilage Tissue Repair.

Polyvinyl alcohol (PVA) hydrogels are extensively used as scaffolds for tissue engineering, although their biodegradation properties have not been optimized yet. To overcome this limitation, partially oxidized PVA has been developed by means of different oxidizing agents, obtaining scaffolds with improved biodegradability. The oxidation reaction also allows tuning the mechanical properties, which are essential for effective use in vivo. In this work, the compressive mechanical behavior of native and partially oxidized PVA hydrogels is investigated, to evaluate the effect of different oxidizing agents, i.e., potassium permanganate, bromine, and iodine. For this purpose, PVA hydrogels are tested by means of indentation tests, also considering the time-dependent mechanical response. Indentation results show that the oxidation reduces the compressive stiffness from about 2.3 N/mm for native PVA to 1.1 ÷ 1.4 N/mm for oxidized PVA. During the consolidation, PVA hydrogels exhibit a force reduction of about 40% and this behavior is unaffected by the oxidizing treatment. A poroviscoelastic constitutive model is developed to describe the time-dependent mechanical response, accounting for the viscoelastic polymer matrix properties and the flow of water molecules within the matrix during long-term compression. This model allows to estimate the long-term Young's modulus of PVA hydrogels in drained conditions (66 kPa for native PVA and 34-42 kPa for oxidized PVA) and can be exploited to evaluate their performances under compressive stress in vivo, as in the case of cartilage tissue engineering.

Experimental and Simulation Analysis on the Mechanical Behavior of 3D‐Enhanced Al‐Based Tetrahedral Lattice Materials

Herein, the compressive mechanical behavior of novel 3D tetrahedral lattice materials is investigated by ways of experimental, numerical, and analytical methods with a good performance of accuracy. Samples with varied length–diameter ratios are fabricated through 3D printing combined with investment casting method. The compressive behavior, deformation characteristic, and energy property of the lattice materials are comprehensively recorded and analyzed with respect to the geometric parameter and compression directions. It is observed that the length–diameter ratio exhibits a significant influence on the mechanical performance and energy absorption of the materials, that is, the lower the length–diameter ratio, the higher the relative density, strength, and energy absorption. Good agreements are observed among the experimental, numerical, and analytical results within a relative acceptable error. Moreover, the mechanical properties and deformation characteristics of lattice materials depend on compression directions to a great extent. In addition, the novel tetrahedral lattice materials with reasonable relative density present superior performance features compared with the other cellular materials.

Meso-scale modeling of the compressive mechanical behavior of concrete by a RVE-based BEM formulation

A 2 D Boundary Element Method (BEM) formulation, based on the representative volume element (RVE) concept, simulates the mechanical behavior of experimentally tested concrete under compression. A step-by-step parametric identification is presented. Considering different modeling for the fracture process at ITZ (Interfacial Transition Zone), the experimental results are captured when this phenomenon is modeled only around bigger aggregates. Besides, the size and quantity of the aggregates do not have great influence on the concrete mechanical behavior and the insertion of porosity in the mortar domain is very important. The proposed numerical model is efficient, robust, and accurate.

Hot Compression Mechanical Behavior of Solution Heat-Treated and Pre-aged Mg–Zn–Gd–Er Alloys

Hot Compression Mechanical Behavior of Solution Heat-Treated and Pre-aged Mg–Zn–Gd–Er Alloys