Compressive Mechanical Behavior Research Articles

Formation and mechanical properties of La–Al(–Ga)–C bulk metallic glasses with high content of carbon

Rare earth metal-based bulk metallic glasses (BMGs) containing metalloid element are synthesized in La–Al(–Ga)–C alloy system by copper mold casting. The high glass-forming ability (GFA) of the La–Al–C alloys revealed by the critical diameters up to 3mm could be due to the large difference in atomic size besides the strong bonding among the constituent elements. By partial substitution of Al in the La–Al–C alloy with similar element Ga, the La–Al–Ga–C BMGs exhibited enhanced GFA and the critical diameters were up to 6mm. The mechanical properties including compressive mechanical behavior, hardness and notch fracture toughness of the La-based BMGs are investigated. The La60Al30C10 BMG exhibits compressive fracture strength of nearly 1GPa, which is the highest for the La-based BMGs. The mechanisms for the formation and mechanical properties of the La–Al(–Ga)–C BMGs are discussed. The La–Al(–Ga)–C BMGs with high content of element C and high strength could be model materials for fundamental research.

Density dependent mechanical properties and structures of a freeze dried biopharmaceutical excipient – Sucrose

Knowledge of the mechanical behaviour of freeze dried biopharmaceutical products is essential for designing of products with physical robustness that will not to crack, crumble or collapse during processing or transportation. The compressive mechanical deformation behaviour for freeze-dried sucrose cakes has been experimentally studied from a relative density (ρf/ρs) of 0.01–0.30 using a novel in-vial indentation test. Cakes exhibited more open like structures at lower densities and more closed structures at higher densities with some faces being present at all densities, as confirmed by SEM. The reduced elastic modulus Ef/Es=0.0044(ρf/ρs)1 for all cake densities, indicating that face stretching was the dominant deformation mode assuming Gibson and Ashby’s closed cell model. This linear scaling for the reduced elastic modulus is in line with various theoretical treatments based on tetrakaidecahedral cells and other experimental studies. Consistently, the wall thickness to cell diameter ratio scaled ρf/ρs with a power constant of 1.05. The maximum crushing stress was given by σmax=3800(ρf/ρs)1.48 which agrees with a strut bending failure stress, assuming Gibson and Ashby’s open cell model. Overall, the freeze dried cakes behaved as neither classic closed cell nor open cell materials, with their compressive elastic moduli reflecting a closed cell elastic response whilst their failure stresses reflecting an open cell failure mode. It was concluded that the mechanical response of freeze dried cellular materials depends upon their complex cellular structures and morphologies, and they cannot be rationalised using simple limiting case models of open or closed cell solids.

Texture evolution and dynamic mechanical behavior of cast AZ magnesium alloys under high strain rate compressive loading

In this study, texture and compressive mechanical behavior of three cast magnesium alloys, including AZ31, AZ61 and AZ91, were examined over a range of strain rates between 1000 and 1400s−1 using Split Hopkinson Pressure Bar. Texture measurements showed that after shock loading, initial weak texture of the cast samples transformed to a relatively strong (00.2) basal texture that can be ascribed to deformation by twinning. Furthermore, increasing the aluminum content in the alloys resulted in increase in the volume fraction of β-Mg17Al12 and Al4Mn phases, strength and strain hardening but ductility decreased at all strain rates. Besides, it was found for each alloy that the tensile strength and total ductility increased with strain rate. By increasing the strain rate, the maximum value of strain hardening rate occurred at higher strains. Also, it is suggested that a combination of twinning and second phase formation would affect the hardening behavior of the cast AZ magnesium alloys studied in this research.

Nucleus Implantation: The Biomechanics of Augmentation Versus Replacement With Varying Degrees of Nucleotomy

Nucleus pulposus replacement and augmentation has been proposed to restore disk mechanics in early stages of degeneration with the option of providing a minimally invasive procedure for pain relief to patients with an earlier stage of degeneration. The goal of this paper is to examine compressive stability of the intervertebral disk after either partial nucleus replacement or nuclear augmentation in the absence of denucleation. Thirteen human cadaver lumbar anterior column units were used to study the effects of denucleation and augmentation on the compressive mechanical behavior of the human intervertebral disk. Testing was performed in axial compression after incremental steps of partial denucleation and subsequent implantation of a synthetic hydrogel nucleus replacement. In a separate set of experiments, the disks were not denucleated but augmented with the same synthetic hydrogel nucleus replacement. Neutral zone, range of motion, and stiffness were measured. The results showed that compressive stabilization of the disk can be re-established with nucleus replacement even for partial denucleation. Augmentation of the disk resulted in an increase in disk height and intradiskal pressure that were linearly related to the volume of polymer implanted. Intervertebral disk instability, evidenced by increased neutral zone and ranges of motion, associated with degeneration can be restored by volume filling of the nucleus pulposus using the hydrogel device presented here.

A multiscale study on the structural and mechanical properties of the luffa sponge from Luffa cylindrica plant

Cellular materials that are often observed in biological systems exhibit excellent mechanical properties at remarkably low densities. Luffa sponge is one of such materials with a complex interconnecting porous structure. In this paper, we studied the relationship between its structural and mechanical properties at different levels of its hierarchical organization from a single fiber to a segment of whole sponge. The tensile mechanical behaviors of three single fibers were examined by an Instron testing machine and the ultrastructure of a fractured single fiber was observed in a scanning electronic microscope. Moreover, the compressive mechanical behaviors of the foam-like blocks from different locations of the sponge were examined. The difference of the compressive stress–strain responses of four sets of segmental samples were also compared. The result shows that the single fiber is a porous composite material mainly consisting of cellulose fibrils and lignin/hemicellulose matrix, and its Young׳s modulus and strength are comparable to wood. The mechanical behavior of the block samples from the hoop wall is superior to that from the core part. Furthermore, it shows that the influence of the inner surface on the mechanical property of the segmental sample is stronger than that of the core part; in particular, the former׳s Young׳s modulus, strength and strain energy absorbed are about 1.6 times higher. The present work can improve our understanding of the structure–function relationship of the natural material, which may inspire fabrication of new biomimetic foams with desirable mechanical efficiency for further applications in anti-crushing devices and super-light sandwich panels.

Microstructures and Crackling Noise of AlxNbTiMoV High Entropy Alloys

A series of high entropy alloys (HEAs), AlxNbTiMoV, was produced by a vacuum arc-melting method. Their microstructures and compressive mechanical behavior at room temperature were investigated. It has been found that a single solid-solution phase with a body-centered cubic (BCC) crystal structure forms in these alloys. Among these alloys, Al0.5NbTiMoV reaches the highest yield strength (1,625 MPa), which should be attributed to the considerable solid-solution strengthening behavior. Furthermore, serration and crackling noises near the yielding point was observed in the NbTiMoV alloy, which represents the first such reported phenomenon at room temperature in HEAs.

Morphological and Compressional Mechanical Properties of Freeze-Dried Mannitol, Sucrose, and Trehalose Cakes

A novel mechanical compression test has been developed which allows cake mechanical properties to be assessed quantitatively, and can be applied to fragile and moisture-sensitive freeze-dried (FD) cakes within the vials without sample preparation. FD mannitol, sucrose, and trehalose cakes, prepared from 5% aqueous solutions, exhibited linear compressive elastic behavior for small strains with apparent moduli of 25, 148, and 207 kPa, respectively. These materials exhibited brittle cracking/crushing failure of the cells over a wide strain range, with low crushing stresses from 11to 31 kPa for 0.15-0.25 strain. This technique is sensitive to differences in freezing conditions for sucrose formulations and the moisture content of sucrose cakes. The test highlights the rapid changes in cake mechanical properties occurring when moisture-sensitive excipients such as sucrose are briefly exposed to ambient humidity. Using established models for the compressive mechanical behavior of closed cellular solids, a method for predicting cell wall thickness is demonstrated. Three FD formulations gave predicted wall thicknesses of 1.1-1.6 μm, consistent with scanning electron microscopy (SEM) images obtained. SEM determined that unit cell dimensions for all formulations were similar and it was concluded that if all other factors were identical, excipient choice plays a minor role in determining the pore shape/morphology.

The first systematic analysis of 3D rapid prototyped poly(ε-caprolactone) scaffolds manufactured through BioCell printing: the effect of pore size and geometry on compressive mechanical behaviour and in vitro hMSC viability

Novel additive manufacturing processes are increasingly recognized as ideal techniques to produce 3D biodegradable structures with optimal pore size and spatial distribution, providing an adequate mechanical support for tissue regeneration while shaping in-growing tissues. With regard to the mechanical and biological performances of 3D scaffolds, pore size and geometry play a crucial role. In this study, a novel integrated automated system for the production and in vitro culture of 3D constructs, known as BioCell Printing, was used only to manufacture poly(ε-caprolactone) scaffolds for tissue engineering; the influence of pore size and shape on their mechanical and biological performances was investigated. Imposing a single lay-down pattern of 0°/90° and varying the filament distance, it was possible to produce scaffolds with square interconnected pores with channel sizes falling in the range of 245–433 µm, porosity 49–57% and a constant road width. Three different lay-down patterns were also adopted (0°/90°, 0°/60/120° and 0°/45°/90°/135°), thus resulting in scaffolds with quadrangular, triangular and complex internal geometries, respectively. Mechanical compression tests revealed a decrease of scaffold stiffness with the increasing porosity and number of deposition angles (from 0°/90° to 0°/45°/90°/135°). Results from biological analysis, carried out using human mesenchymal stem cells, suggest a strong influence of pore size and geometry on cell viability. On the other hand, after 21 days of in vitro static culture, it was not possible to detect any significant variation in terms of cell morphology promoted by scaffold topology. As a first systematic analysis, the obtained results clearly demonstrate the potential of the BioCell Printing process to produce 3D scaffolds with reproducible well organized architectures and tailored mechanical properties.

Compressive properties of nanoparticle modified epoxy resin at different strain rates

Epoxy resins often exhibit high strength yet are often brittle, especially at high strain rates. Block copolymer modified epoxy resins have generated significant interest since it was demonstrated that the combination could lead to nanostructured thermosets through the self-assembly of the block copolymer. Such nanostructured epoxies exhibit increased ductility without the significant loss in yield strength exhibited by traditional rubber-modified epoxies. In this study, the effect of different nanoscale additives on the compressive yield strength of a model epoxy resin has been studied. In the first case, a block copolymer styrene-b-butadiene-b-polymethylmethacrylate (SBM) was added to the model epoxy resin. In the second case, carbon nanotubes (CNTs) were added. In the final case, both additives were mixed simultaneously with the epoxy resin. The compressive mechanical behavior of these materials has been investigated over a wide range of strain rates (0.001–3500s−1). The yield behavior was found to fit the cooperative yield model proposed by Fotheringham and Cherry.

Flexural and compressive mechanical behaviors of the porous titanium materials with entangled wire structure at different sintering conditions for load-bearing biomedical applications

The entangled titanium materials with various porosities have been investigated in terms of the flexural and compressive mechanical properties and the deformation and failure modes. The effect of the sintering parameters on the mechanical properties and the porosity reduction has been comprehensively studied. The results indicate that both the flexural and compressive mechanical properties increase significantly as the porosity decreases. In the porosity range investigated the flexural elastic modulus is in the range of 0.05–6.33GPa, the flexural strength is in the range of 9.8–324.9MPa, the compressive elastic modulus is in the range of 0.03–2.25GPa, and the compressive plateau stress is in the range of 2.3–147.8MPa. The mechanical properties of the entangled titanium materials can be significantly improved by sintering, which increase remarkably as the sintering temperature and/or the sintering time increases. But on other hand, the sintering process can induce the porosity reduction due to the oxidation on the titanium wire surface.

Experimental Research of Foamed Ceramic Composite under Dynamic Loading Using SHPB

The Split Hopkinson Pressure Bar (SHPB) is used to investigate the dynamic compressive mechanical behavior of a new foamed ceramic composite under impact loading. The stress versus strain curves are obtained under high strain rates. The test results are considered to be able to assure conformability of the tests, validate the stress equilibrium assumption, and show that the stress versus strain curves of foamed ceramic composite display strain hardening effect and damage softening effect as brittle materials. Meanwhile the curve includes short plateau region while no densification region.

An experimental investigation on the effect of strain rate on the behaviour of bare and foam-filled aluminium honeycombs

The effects of strain rate (in low-strain rate regime) on the compressive mechanical behaviour of bare and foam-filled honeycomb structures are experimentally investigated in this paper. Empirical tests show that unlike the existing theoretical formula for bare hexagonal honeycombs, the mean crushing strength of these structures is highly dependent on the strain rate, as an increase of the strain rate yields an increase in the mean crushing strength of up to 40% in some specimens. This effect would be less considerable when it comes to the case of foam-filled panels. The results also indicate that the strain rate has no effect on the densification strain but could change the plane of deformation and increase the number of folds, and consequently decrease their wavelengths.

Experimental and modeling study of dynamic mechanical properties of cement paste, mortar and concrete

Understanding the strain rate effects on cement-based materials are important for accurately modeling concrete structure damage to high-velocity impact and blast loads. This paper reports experimental results of the strain rate effect on paste, mortar and concrete. A pulse-shaped split Hopkinson pressure bar (SHPB) was employed to determine the dynamic compressive mechanical responses and failure behavior of paste, mortar and concrete under valid dynamic testing conditions. Quasi-static experiments were conducted to study material strain rate sensitivity. Strain rate sensitivity of the materials is measured in terms of the stress–strain curve, elastic modulus, compressive strength and critical strain at peak stress. Empirical relations of dynamic increase factor (DIF) for the material properties are derived and presented. A compressive constitutive model with strain rate and damage effects was modified to accurately describe the dynamic compressive stress–strain curves of the materials.

Description of the mechanical behavior of different thermoset composites reinforced with Manicaria saccifera fibers

This work describes for the first time the flexural and compression mechanical behavior of Manicaria saccifera fibers–polymer matrix composites. These lignocellulosic fibers are obtained from a palm of natural occurrence at the Amazon region. Specifically here the fibrous natural mat that protects the fruits’ palm is used. The results obtained are comparable to the data from other lignocellulosic fiber–polymer matrix composites, demonstrating the feasibility of using Manicaria saccifera fibers as reinforcement. The wear behavior of the composites was also analyzed and their use as parquet floor is pointed out as a possibility.

Polyurethane foams based on modified tung oil and reinforced with rice husk ash II: Mechanical characterization

Viscoelastic polyurethane (PU) foams based on modified tung oil, ethylene glycol and polymeric MDI, and reinforced with rice husk ash (RHA), were prepared by a free-rise pouring method and characterized in terms of density, compression and dynamic mechanical behavior. The density of foams ranged between 50 and 90 kg/m3, depending on the position of the sample with respect to the foam rise direction and filler content. As revealed by dynamic mechanical tests, the foams exhibited two different and broad thermal transitions, the temperature of their maxima depending on filler concentration. Compression modulus, compressive strength and storage modulus increase as foam density increases but decreases as rice husk ash concentration increases due to the detrimental changes induced by the filler in the foam cellular structure. However, densification strain exhibits the opposite behavior, indicating that reinforced foams can sustain slightly higher deformations without collapsing, probably due to a reduced reactivity of the components induced by the filler.

Effect of Nano Silica on Mechanical Properties and Durability of Normal Strength Concrete

AbstractNano technology is an emerging field of interest for civil engineering application. Among the nano materials presently used in concrete, nano-silica possess more pozzolanic nature. It has the capability to react with the free lime during the cement hydration and forms additional C-S-H gel giving strength, impermeability and durability to concrete. Present paper investigates the effects of addition of nano silica in normal strength concrete. Three types of nano-silica in the form of nano suspension having different amount of silica content have been investigated. Mix design has been carried out by using particle packing method. X-Ray diffraction (XRD) analysis has been carried out to find the chemical composition of control concrete and nano modified concrete. Further, experimental investigations have been carried out to characterize the mechanical behaviour in compression, tension and flexure. It has been observed that the addition of nano-silica in normal strength concrete increased the compressive strength and decreased the spilt tensile strength and flexural strength. Also, Rapid chloride permeability test (RCPT) has been conducted to know the chloride permeability of control concrete, nano modified concrete, and nano coated concrete. It has been observed that the chloride permeability is less for nano coated concrete.

Experimental Study of Post-Fire Behavior of Steel Fiber Reinforced Ceramsite Concrete Filled Steel Tubes

The axial compressive mechanical behavior of steel fiber reinforced ceramsite concrete filled steel tubes (noted as SFR-CCST) after exposure to fire are experimentally studied. Effect of furnace temperature, dosage of steel fiber in specimens on the post-fire mechanical performance of the specimens after exposure to fire was especially discussed. The results show that all the specimens of SFR-CCST have higher post-fire bearing capacity and better plastic deformation, and there was no obvious descending segment in the load-strain curves of the most specimens after exposure to fire. It was concluded that the furnace temperature applied to the specimens and dosage of steel fiber in the specimens of SFR-CCST has some effect on the post-fire mechanical performance of the ceramsite concrete-filled steel tubes after exposure to fire, and the dosage of steel fiber of 0.5% has the most effect on the post-fire performance of lightweight aggregate concrete filled steel tubes after exposure to fire.

Effect of salt crystallization ageing on the compressive behavior of sandstone blocks in historical buildings

Sandstone building stones are important in the building elements of Portuguese monuments, particularly in the western and southern regions. Alveolization due to salt crystallization was the most important degradation pattern found in the old sandstone façades of buildings in the village of Atouguia da Baleia. Because weathering progressively increases porosity in stones, experimental research was conducted on the most porous variety of sandstone, which is similar to the type of stones found in the façades of ancient buildings in that village. An automatic salt crystallization accelerated ageing chamber was developed. Monotonic and cyclic uniaxial compressive tests were carried out on samples after sodium chloride crystallization ageing tests had been performed, in order to assess the compressive mechanical behavior of sandstone during accelerated ageing. The results of stress–strain compression diagrams showed a clear decreasing trend in the values of mechanical parameters during the salt crystallization ageing progress. The difference in compressive strength values between monotonic and cyclic compression also decreases with as salt crystallization ageing progresses. A predictive equation that correlates the compressive strength of sandstones with salt crystallization ageing cycles is proposed.

Quasi-static and dynamic compressive mechanical properties of engineered cementitious composite incorporating ground granulated blast furnace slag

The ground granulated blast-furnace slag (GGBS) has been widely used as a supplementary cementitious material in concrete production due to its lower heat of hydration, ability to gain strength over a longer period, superior performance against chemical attacks, and lower environmental impact. Four Engineered Cementitious Composite (ECC) mixtures with 50%, 60%, 70% and 80% substitution amounts of GGBS were prepared and their dynamic compressive mechanical behavior had been investigated by using a split Hopkinson pressure bar (SHPB) system at strain rates ranging from 84.8 to 184.6s−1. The corresponding quasi-static compressive responses of GGBS–ECC were also studied experimentally for contrasting with their dynamic tests. The objective of using GGBS to replace fly ash in ECC was to obtain higher quasi-static compressive strength and dynamic load-carrying capacity. The dynamic compressive stress–strain curves did not show residual strength behavior as that in the quasi-static stress–strain curves. ECC incorporating GGBS exhibited strain rate dependence. The peak stress increased and the peak strain decreased with the increase of strain rates. The toughness ratio under quasi-static compression was lower than that of dynamic compression according to the proposed method in this study. The toughness ratio under dynamic compression showed a slight increase with the GGBS content increasing. The strain rate had little influence on the toughness ratio.

Hydration-induced reinforcement of rigid polyurethane–cement foams: mechanical and functional properties

Mechanical and functional properties of a newly proposed hybrid foam based on rigid polyurethane foam and Portland cement for application in the building field are herein reported. The hybrid is characterized by the co-continuity of the two phases, hydrated cement and polyurethane, which cooperate in a synergistic way to the properties of the resulting material. Furthermore, the closed-cell foam structure gives the material properties typical of porous materials: in particular, the hybrid foam evidences thermal insulation, sound absorption and acoustic insulation, high impact energy and low density typical of polymeric foams. At the same time, the hybrid foam exhibits water vapor permeability, improvement of thermal stability, high compressive mechanical behavior, and adhesion to concrete and mortars typical of inorganic binders such as cement. The materials were obtained by mixing cement powder with polyurethane foam precursors, i.e., methylene di(phenyl-isocyanate), polyol polyether and catalysts, and silicone surfactants. Water was used as blowing reagent. The resulting compounds were foamed in flat closed molds. The cement phase was then allowed to hydrate in accelerated conditions, i.e., in water at 60 °C for 72 h. Mechanical, morphological, and functional characterization showed that the hydrated cement particles interacted with each other, forming an inorganic network within the polymeric matrix (co-continuity), thus “hydration-induced reinforcement of polymer–cement” hybrid foam, in contraposition with the term “composite foam.”