Compressive Stress-strain Response Research Articles

A review on fiber reinforced self compacting concrete addition with M-Sand

This review analyse the structural properties of the M-Sand addition with fiber reinforcerd Self Compacting concrete (SCC) is a high – execution solid that can traverse under its self-load to totally fill the structure work and self solidifies with no mechanical vibration. Comparison between the experimental results from the analysis exhibited that the proposed model provides satisfactorily predictions of ultimate compressive strength, failure strain, and stress-strain response. L-Box, U-Box, V-Funnel and J-Ring tests were performed to decide the properties of new concrete on both River sand and M sand. The properties of solidified cement on both R sand and M sand can likewise explored by leading the Flexural quality test. The test is directed after 28 days of restoring. The outcome of the review inferred that the Properties life time and workability of concrete.

High-temperature mechanical behavior of B2-ordered Ti–Mo–Al alloys

Compressive stress–strain responses of stoichiometric and off-stoichiometric B2-ordered Ti–Mo–Al alloys over the temperature range 973–1373 K were examined to investigate the effects of composition and temperature on the mechanical behavior. The Ti–Mo–Al alloys exhibited impressive yield strengths at elevated temperatures, e.g., 818 MPa for Ti50Mo35Al15 at 1073 K and 490 MPa for Ti50Mo25Al25 at 1273 K. Positive temperature dependence of yield strength was observed in Ti50Mo25Al25 below 1273 K but it had not been seen in either Ti60Mo25Al15 or Ti50Mo35Al15 throughout the test temperatures. Dislocation analyses of the compressed specimens indicated that the Ti–Mo–Al alloys primarily deformed via <111>slip. The mechanisms responsible for the variations of mechanical properties with composition and temperature are discussed by correlating with the antisite defects.

Compressive Stress–Strain Response of Concrete Exposed to Low Temperatures

Temperature is an important factor when considering the mechanical properties of engineering materials because they can change drastically as temperatures change. The research presented here is an experimental investigation to determine the changes in the compressive behavior of concrete that occur because of low exposure temperatures. The primary purpose of the research is the development of detailed experimental stress–strain relationships exposed to low temperatures, which remains a largely unexplored topic. A total of twenty-seven 101.6×203.2 mm concrete cylinders were tested in uniaxial compression at the University of New Brunswick. The specimens were exposed to temperature ranges from 20°C to −70°C to simulate extreme climatic temperatures and those obtainable in industrial storage facilities. The compression strain of specimens was obtained by using three-dimensional digital image correlation. The mechanical properties studied were the relative changes in compressive strength, modulus of elasticity, and peak strain attributable to temperature variations. Predictive equations and relationships for these properties with respect to temperature are presented and compared with the existing literature.

Ferroelastic properties and compressive stress-strain response of bismuth titanate based ferroelectrics

Ferroelectric materials have been widely studied for applications in numerous devices due to their controllable ferroelectric/ferroelastic properties under electric field or mechanical stress. Recently, a type of bismuth layer-structured ferroelectrics, W/Cr co-doped BIT ceramics, has attracted much attention due to its high Curie temperature, large spontaneous polarization, and particularly enhanced ferroelectric properties. Nevertheless, as a significant consideration for the reliability and durability of devices, the mechanical properties associated with ferroelastic behaviors of this type of ceramics are generally ignored. In this study, a type of W/Cr co-doped BIT ceramics with optimal chemical composition of Bi4Ti2·95W0·05O12.05+0.2 wt% Cr2O3 (BTWC) was synthesized via the solid-reaction technology. Ferroelastic domain structures and ferroelastic switching behaviors together with mechanical failure properties of the sintered ceramics were investigated in details. PFM observations reveal the existence of pseudo-90° and -180° ferroelastic domain structures in BTWC ceramics. The nonlinear deformation of stress-strain curve originates from ferroelastic domain switching induced by mechanical stress of sufficient magnitude. Moreover, the ferroelastic switching plays a significant role in improving the fracture toughness of BTWC ceramics. Additionally, the ceramics sintered at higher temperature are expected to exhibit a better ferroelastic switching behavior yet lower failure stress. The work can provide design consideration of loading conditions for practical applications of BTWC ceramics.

Mechanical behaviors of auxetic polyurethane foam at quasi-static, intermediate and high strain rates

We experimentally determined the uniaxial compressive stress-strain responses of an auxetic polyurethane (PU) foam at quasi-static (0.01/s), intermediate (1/s, 10/s and 745/s) and high (1430/s, 1870/s and 2290/s) strain rates. A hydraulically driven materials testing system (MTS) was used to perform the experiments at the strain rate of 0.1/s, 1/s and 10/s, while higher intermediate (745/s) and high strain-rate compressive loadings were introduced using long and regular Kolsky bars, respectively. The Poisson effect of the auxetic PU foam was also investigated during the experiments using a precision LED optical micrometer system (OMS) (0.01/s–10/s) or an ultra-high speed camera (745/s–2290/s). Our results show that the compressive stress-strain curves of the auxetic PU foam are non-linear and strain-rate sensitive. In all the experiments, the Poisson's ratio, with an initial negative value at small strains, progressively increased toward 0 as the specimen was further compressed. The strain-rate effect on the material's Poisson's ratio is also evident in our study, as the specimens subjected to high strain-rate loadings exhibited smaller negative Poisson's ratios (NPR) in absolute sense at small strains in comparing with those at quasi-static and intermediate strain rates.

Mechanical Response of Human Muscle at Intermediate Strain Rates.

We experimentally determined the tensile stress-strain response of human muscle along fiber direction and compressive stress-strain response transverse to fiber direction at intermediate strain rates (100-102/s). A hydraulically driven material testing system with a dynamic testing mode was used to perform the tensile and compressive experiments on human muscle tissue. Experiments at quasi-static strain rates (below 100/s) were also conducted to investigate the strain-rate effects over a wider range. The experimental results show that, at intermediate strain rates, both the human muscle's tensile and compressive stress-strain responses are nonlinear and strain-rate sensitive. Human muscle also exhibits a stiffer and stronger tensile mechanical behavior along fiber direction than its compressive mechanical behavior along the direction transverse to fiber direction. An Ogden model with two material constants was adopted to describe the nonlinear tensile and compressive behaviors of human muscle.

Effect of temperature on thermal, mechanical and morphological properties of polypropylene foams prepared by single step and two step batch foaming process

This study reports the influence of foaming temperature on morphological and thermo-mechanical characteristics of polypropylene (PP) foams prepared using two different methods of batch foaming at low saturation pressures. In the first method, involving single-step pressure-induced-foaming (PIF), the solid specimen was heated to different temperatures in a high-pressure vessel, and then saturated CO2 under pressure. Depressurization then led to foaming. In the second method, involving a two-step temperature-induced-foaming (TIF), the solid specimen was saturated with pressurized CO2 at room temperature for a specific period of time and then the CO2 laden specimen was immersed in hot glycerol bath at different temperatures for foaming. SEM micrographs of the fractured foamed specimens were employed for measurement of cell-size distribution. The average cell sizes ranged between 3 and 310 μm in specimens obtained using PIF, while in case of foams prepared by TIF, the cell sizes ranged between 30 and 70 μm. The cell sizes achieved in TIF are significantly smaller and more uniform as compared to those in PIF foams. The density (0.393–0.186 g cm−3) of PIF foams was seen to decrease with increasing foaming temperature; in contrast, in case of TIF the density remained more or less unchanged around 0.43–0.47 g cm−3 with changes in foaming temperature. The foamed specimens were characterized in uniaxial compression; the stiffness (elastic and collapse moduli) and compressive strengths of both the PIF and TIF foams were seen to decrease with increase in cell-size. The magnitude of plateau-regime stresses within the compressive stress-strain response showed strong correlation with the foam cell-wall thickness. The crystallinity of the foamed specimens was observed to decrease with increase in foaming temperatures. The thermal stability of both PIF and TIF foams in general showed improvement compared with the PP matrix.

The Impact Compressive Properties of 7075-T651 Aluminium Alloy over a Wide Range of Strain Rates and Temperatures

The mechanical properties of 7075-T651 Aluminium Alloy was studied under dynamic compressive loading over a wide range of strain rates from 600s−1 to 16000s−1 and the temperature range from 25°C to 400°C. A classic split Hopkinson pressure bar (SHPB) and a radiant-heating furnace are used for the experiment and measurement. Some improved test and data processing technique are used to get more accurate test result. It is found that the compressive stress-strain response is insensitive to the applied strain rate but depends on experimental temperature. The experiment results provide a good basis to build a more valid and accurate material models for 7075-T651 Aluminium Alloy.

Fundamental insights into the compressive and flexural response of binder- and aggregate-optimized ultra-high performance concrete (UHPC)

Ultra-high performance concrete (UHPC) mixtures demonstrating more than 150 MPa compressive strength and 20 MPa flexural strength are proportioned with commonly available cement replacement materials (30% or 50%, mass-based replacement levels) and steel fibers using a recently developed combined binder and aggregate optimization approach. The compressive (axial) stress-strain responses of the unreinforced and fiber-reinforced UHPC mixtures, along with the calculated volumetric strains, are used to define two critical stress states – viz., crack initiation and crack damage stresses. The crack damage stress, being the threshold value at which unstable crack propagation begins, is suggested to be used as the true strength of UHPC in structural design. The influence of matrix composition and fiber volume on these parameters is brought out, to better elucidate the influence of material design on properties. Digital image correlation (DIC) on unnotched beams under flexure is used to show the fundamental differences in the matrix properties that lead to differences in strain localization. The beneficial influence of fibers on strain localization in UHPC mixtures is also brought out.

Quantifying the Resistance to Dislocation Glide in Single Phase FeCrAl Alloy

The resistance to dislocation glide associated with slip systems {110} and {112} in single phase FeCrAl alloy is measured via micromechanical testing in a scanning electronic microscopy at room temperature. Two important factors, the shape and orientation of a pillar, are discussed with respect to the glide resistance and stress-strain response. Maximizing Schmid factor of one specific slip system while minimizing others is recommended in order to diminish obvious dislocations-induced hardening during in situ testing. Apparent Schmid factor analysis is conducted to select grains with preferred orientations. Two types of pillars with conventional cylindrical shape or dog-bone shape are tested under compression to estimate the resistance to dislocation glide and evaluate the effect of pillar shape on the compression stress-strain response. One dog-bone pillar is tested under tension to check the tension-compression isotropy. We find that the shape of a pillar to a smaller extent affects the measured resistance but strongly influences the stress strain response. Cylindrical pillars exhibit apparent hardening associated with early yielding due to stress or strain concentration at contact region, while dog-bone pillars show an obvious yielding and continuous shearing without hardening. The resistance is 220 MPa for slip system {110} and 230 MPa for slip system {112} . Finite element analysis is performed to account for the influence of pillar shape and contact condition on mechanical response. Furthermore, slip transmission across two high-angle grain boundaries is experimentally investigated and discussed with respect to the misorientation and the continuity of slips across GBs.

Compressive Mechanical Response of Porcine Muscle at Intermediate (100/s-102/s) Strain Rates

Compressive stress-strain response of porcine muscle was experimentally determined at intermediate strain rates (100/s-102/s) in this study. A hydraulically driven materials testing system with a dynamic testing mode was used to perform the compressive experiments on porcine muscle tissue with loading directions parallel and perpendicular to muscle fiber direction. Experiments at quasi-static strain rates were also conducted to investigate the strain-rate effects over a wider range. The experimental results show that, at intermediate strain rates, the porcine muscle’s compressive stress-strain responses are non-linear and strain-rate sensitive. The porcine muscle’s compressive mechanical response exhibits no significant difference between the two fiber orientation cases at quasi-static and intermediate strain rates. An Ogden model with two material constants was adopted to describe the rate-dependent compressive behavior of the porcine muscle.

A progressive damage model for 3D woven composites under compression

A progressive damage model is proposed to investigate the damage initiation and evolution of 3D woven composites under uniaxial compression at a micromechanical level. The typical compressive experiments were carried out. Based on the observations, the compression failure modes of 3D woven composites mainly include fiber kinking, transverse failure of fiber tow, matrix fracture, and interfacial debonding. The initial damage criteria are according to the physically based failure criteria for the fiber kinking, the Puck criteria for the transverse failure of fiber tow, and the maximum stress criterion for the matrix. The damage of fiber tow–matrix interfacial is simulated through cohesive contact. Particularly, the fiber’s initial misalignment angle is taken into account in the damage model. The simulated compression results agree well with the experimental ones. The compressive stress–strain response of the 3D woven composite is forecasted. The damage evolution of each constituent of the 3D woven composite is obtained. The results show that the influence of the fiber’s initial misalignment angle on the compression strength of the 3D woven composite needs to be considered.

Influence of multi-walled carbon nanotubes on the residual performance of concrete exposed to high temperatures

Residual mechanical properties of lightweight concrete (LWC) and normal strength concrete (NSC) containing multi-walled carbon nanotubes (MWCNTs) after exposure to high temperatures are presented. Mechanical properties such as compressive strength (f’c,T), tensile strength (f't,T), stress-strain response, compressive toughness (Tc) and mass loss of the analyzed formulations were studied and have been elaborately discussed. A heating ramp of 5 °C per minute was selected to expose the cylindrical specimens to target temperatures up to 800 °C. The test data indicated that the inclusion of nano-reinforcements in concrete can significantly improve the residual mechanical properties. Morphological changes in microstructure, crack formation and interfacial interaction between aggregate and mortar were studied using scanning electron microscopy (SEM). Furthermore, the data obtained from high temperature material property tests were utilized to develop mathematical relationships for expressing residual mechanical properties of CNTs modified concrete as a function of temperature.

Aluminum foam sandwich with density-graded open-cell core: Compressive and flexural response

We created a density-graded, open-cell, aluminum foam core sandwich (AFS) by joining, alternately arranged Al sheets and three different relative density (ρ* = 7%, 29%, and, 42%) foams using a zinc filler. A defect free, lamellar, α + η microstructure was observed in the foam/facesheet joint interface. Vickers microhardness and nanoindentation of the joint revealed higher hardness in the Zn filler compared to foam struts and sheets. The density-graded AFS showed a staggered compressive stress-strain response and its energy absorption increased by up to 607% compared to as-received (7% ρ*) foam core AFS. Three-point bend testing of the density-graded AFS showed indentation, foam strut bending, core shear and interface debonding as major failure mechanisms. Our results show that density-grading of foam core by introducing different relative density foam layers is a viable method to tailor the mechanical response of AFS.

Relationship of compressive stress-strain response of engineering materials obtained at constant engineering and true strain rates

In this study, a Johnson–Cook model was used as an example to analyze the relationship of compressive stress-strain response of engineering materials experimentally obtained at constant engineering and true strain rates. There was a minimal deviation between the stress-strain curves obtained at the same constant engineering and true strain rates. The stress-strain curves obtained at either constant engineering or true strain rates could be converted from one to the other, which both represented the intrinsic material response. There is no need to specify the testing requirement of constant engineering or true strain rates for material property characterization, provided that either constant engineering or constant true strain rate is attained during the experiment.

Experimental investigation on the compressive behavior of short‐term preloaded carbon fiber reinforced polymer‐confined concrete columns

Strengthening of concrete columns with fiber reinforced polymer sheets provides a good improvement to the existing structural members in terms of load and strain capacity due to the properties of the composite jacket. A proper knowledge of the load–strain response of the composite members is necessary to design retrofitting intervention of existing structures; however, so far the available design methods do not allow to take into account the effect of the possible presence of service loads on the compressive behavior of the reinforced columns. An experimental investigation on the compressive behavior of preloaded circular concrete columns reinforced with carbon fiber reinforced polymer was carried out to determine the load and deformational capacity of confined concrete subjected to short‐terms loads. Nineteen compression tests were performed to underline the difference respect to the standard compressive stress–strain response of the confined specimens. The results indicate that the compressive behavior seems to be not particularly influenced by the preloading. As the preloading level increases, ultimate axial load and axial strain do not have significant change respect to the test performed without preloading; however, the load–strain response of the confined concrete is affected by a reduction of the secant stiffness.

Strain rate sensitive compressive response of gelatine: Experimental and constitutive analysis

Gelatine is widely used as a soft tissue simulant in physical surrogates for the human body. Historically, gelatine has been used to evaluate penetrating impacts and, more recently, to evaluate blunt impact and blast loading effects on soft tissue. There is a need for material characterisation data across a wide range of strain rates, and appropriate constitutive relationships that can be used in models, particularly finite element models, to accurately predict the response of gelatine under various loading conditions. In this study, dynamic experiments were conducted using a split Hopkinson pressure bar and quasi-static tests performed on gelatine to investigate its compressive stress-strain response at both quasi-static and dynamic rates of deformation. The experimental results show that gelatine exhibits rate-sensitive and nonlinear behaviour. The Zhu-Wang-Tang constitutive model can adequately describe the rate-sensitive compressive behaviour of gelatine as good agreement was found between experimental results and model prediction.

Multiscale structural characterization of methyltriethoxysilane-based silica aerogels

A series of methyltriethoxysilane-based silica aerogel monoliths were prepared by ambient pressure drying with various volume ratios of water to ethanol (R). The pore volumes and average pore sizes of silica aerogels were obtained by Barrett–Joyner–Halenda (BJH) method from nitrogen adsorption–desorption isotherms. The stress–strain curves of the cylindrical aerogel specimens were measured by performing uniaxial compressive tests. The particle size distributions and the average particle sizes of silica aerogels were also evaluated based on scanning electron microscopic observations. The experimental data revealed that the average particles size increased from 0.115 to 3.08 μm as R varied from 0.7 to 1.5, and that the silica aerogels exhibited two characteristic types of the compressive stress–strain responses. By proposing a multiscale structural model to describe microstructures of silica aerogels, a structural parameter, defined as the slenderness L/D of the cube column length L and the average particle diameter D, was related to the specific volume and the BJH volume of the silica aerogel monoliths, as well as the specific volume of silica. Accordingly, the two types of the compressive stress–strain responses may be distinguished by the critical value (L/D)c.

High-strain-rate plastic deformation and fracture behaviour of Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy at room temperature

To study the plastic deformation and fracture behaviour of Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy under high strain rate loading conditions, a series of dynamic compression tests on Ti-55511 alloy have been performed at constant strain rates ranging from 350 s−1 to 2900 s−1 by means of split Hopkinson pressure bar technique at room temperature. The different strain and strain rate loading conditions are realized by changing the length and velocity of the striker bar, and high intensive localized shear region is induced in Ti-55511 alloy. The dynamic compression stress-strain response, strain rate hardening effect and strain rate sensitivity, and the fracture behaviour are discussed. The experimental results demonstrate that: The strain rate hardening effect and strain rate sensitivity of Ti-55511 alloy are apparent; Brittle shear bands form at high strain rate loading conditions, and the formation of a shear band does not mean the occurrence of phase transformation; Collapse of the specimens occurs along a plane inclined at an angle of about 45° to the compression axis at room temperature for both quasi-static and dynamic compression loading; The shear-compression zone and tension-shear-compression zone coexist in the fracture surface, and collapse of the specimens is attributed to shear failure mechanism for Ti-55511 alloy under compression loading at room temperature.

Monotonic Stress–Strain Behavior of Steel Rebars Embedded in FRP-Confined Concrete Including Buckling

Fiber-reinforced polymer (FRP) confining jackets offer an attractive solution for the seismic retrofit of RC columns. For the accurate prediction of strength and ductility of FRP-confined RC columns, it is necessary to understand interactions between the FRP jacket and the RC column at all deformation levels under seismic loading. In particular, when the transverse steel reinforcement consists of widely spaced steel stirrups or spirals, the longitudinal steel reinforcing bars (rebars) are likely to develop buckling deformations despite the lateral support provided by the FRP-confined concrete. This paper presents a theoretical study into the buckling behavior of longitudinal steel rebars embedded in FRP-confined concrete subjected to monotonic axial compression. In the theoretical model, a beam-on-elastic foundation idealization is used, where the steel rebars are laterally supported by elastic springs representing the FRP-confined cover concrete. To evaluate the stiffness of the elastic springs, a curved beam model is proposed. Predictions from the theoretical model are compared with test results, demonstrating the reliability of the theoretical model. A parametric study is then presented to examine the influence of three key factors (i.e., spring stiffness, yield strength of steel, and slenderness ratio of rebar) on the overall compressive stress–strain response of laterally supported steel rebars. Finally, an empirical compressive stress–strain model considering the effect of buckling deformation is proposed for steel rebars embedded in FRP-confined concrete subjected to monotonic axial compression and validated through comparisons with the test results.