Quasi-static Compressive Strength Research Articles

Effect of Ceramsite on the Dynamic Mechanical Properties of PVA Fiber Reinforced Cementitious Composite (PVA-FRCC)

The addition of ceramsite aimed to improve the toughness of high strength PVA-FRCC and reduce its weight. The quasi-static and dynamic compressive tests were carried out to obtain the compressive strength and the dynamic response of PVA-FRCC with the addition of ceramsite, respectively. The ceramsite can weaken the compressive strength of PVA-FRCC, the quasi-static compressive strength decrease with the increase of ceramsite volume fraction. With the increase of strain rate, the dynamic peak stress and critical compressive strain increase with different ceramsite volume fraction. At the same strain rate level, the dynamic compressive strength decrease with the increase of ceramsite volume fraction. The critical compressive strain of PVA-FRCC with 3% ceramsite volume fraction have the highest critical compressive strain at different strain rate.

Size-dependent compression deformation behaviors of high particle content B4C/Al composites

Abstract 55 vol.% B4C/Al composites reinforced with 3 μm and 20 μm particles respectively were prepared by squeeze casting. Effect of particle size on quasi-static and dynamic compression behaviors of the composites was investigated. The results show that the quasi-static compression strength of the composite with 3 μm particles is almost twice that of the composite with 20 μm particles. The reason is that the connectivity architectures of the composite with small particles are more stable than that of the composite with big particles due to the enhancement of in situ matrix by geometrically necessary dislocation. In addition, the dynamic compression strength and the fracture strain first increase with the increasing impact velocity and then decrease when the impact velocity is increased from 28 m/s to 33 m/s for the composite with 20 μm particles, and no similar phenomenon occurs for the composite with 3 μm particles. The size-dependent architecture stability of the connected reinforcement is the main contribution to the different dynamic deformation behaviors of the composites during adiabatic compression.

Determining the through-thickness properties of thick glass fiber reinforced polymers at high strain rates

The use of thick fiber reinforced polymer (FRP) laminates in composite armor and naval structures requires thorough characterization of the through-thickness properties of said laminates, both quasi-statically and at high strain rates. Specimens cut from an E-Glass/vinyl ester FRP were tested in compression both quasi-statically and dynamically using a split Hopkinson pressure bar (SHPB). The SHPB tests utilized a conical striker for pulse shaping, to reduce the variation in strain rate during the test. The quasi-static through-thickness compressive strength was 417 MPa, while the SHPB tests produced a strength of 462 MPa at an average strain rate of 5.1 × 102 s−1. A single HPB configured for spalling tests was used to determine the dynamic through-thickness tensile strength (interlaminar tension). The interlaminar tensile strength was 125 MPa at an average strain rate of 1.8 × 103 s−1.

Dynamic response of transparent ceramic MgAl 2O 4 spinel

The quasistatic and dynamic compressive strengths of transparent spinel (MgAl2O4) specimens with grain sizes of 0.4 and 1.4 μm are measured. The measured strengths and rate sensitivities of the spinel specimens are compared with another transparent ceramic material, AlON, with significantly coarser grains. The observed trends in rate sensitivities are consistent with micromechanical models that describe the dynamic failure of brittle solids under compression. Differences in observed crack speeds are also related to microstructural differences including grain size.

Quasi-static compressive strength of cement-based materials

Wet cementitious materials show a noticeable dependence on the rate of quasi-static loading. While dry cementitious materials are almost independent of loading rate in the quasi-static region, the mechanical strength of wet materials increases with increasing rate of loading. Therefore, the Abrams' formula for the static mechanical strength cannot provide reliable values with wet materials at higher rates and should be corrected. Some possibilities for its improvement have been discussed.

Analysis of the Strain and Stress Fields of Cardboard Box during Compression by 3D Digital Image Correlation

Corrugated boards with small flutes appear as good alternatives to replace packaging folding boards or plastic materials due their small thickness, possibility of easy recycling and biodegradability. Boxes made up of these materials have to withstand significant compressive loading conditions during transport and storage. In order to evaluate their structural performance, the box compression test is the most currently performed experiment. It consists in compressing an empty container between two parallel plates at constant velocity. Usually it is observed that buckling phenomena are localized in the box panels, which bulge out during compression [1]. At the maximum recorded compression force, the deformation localises around the box corners where creases nucleate and propagate. This maximum force is defined as the quasi-static compression strength of the box. The prediction of such strength is the main topic of interest of past and current research works. For example, the box compression behaviour of boxes was studied by Mc Kee et al. [2] and Urbanik [3], who defined semi-empirical formula to predict the box compression strength, as well as by Beldie et al. [4] and Biancolini et al. [5] by finite element simulations. But comparisons of these models with experimental results remain rather scarce and limited.

Investigating Silica Nanoparticle Effect on Dynamic and Quasi-static Compressive Strengths of Glass Fiber/Epoxy Nanocomposites

The research is aimed to investigate the compressive strengths of glass/epoxy nanocomposites, containing various loadings of spherical silica nanoparticles. Through a sol—gel technique, the silica particles with a diameter of 25 nm were exfoliated uniformly into the epoxy resin. Subsequently, by inserting the silica—epoxy mixture into the unidirectional glass fiber through a vacuum hand lay-up process, the glass fiber/epoxy composite laminates with 10, 20, and 30 wt% of silica nanoparticles were fabricated. Quasi-static and dynamic compression tests were conducted on the brick composite specimens with fiber orientations of 0°, 5°, 10°, 15°, and 90° using a hydraulic MTS machine and a split Hopkinson pressure bar, respectively. Observations on the failure specimens indicated that for fiber orientations less than 15°, the fiber microbuckling is the dominant failure mechanism. On the other hand, for the 90° samples, the out-of-plane shear failure is the main failure mechanism. In addition, it was denoted that as the silica contents increase, the compressive strengths of the glass/epoxy composites are improved accordingly. The enhancing mechanism in the compressive strengths can be properly explicated using the microbuckling model.

High strain-rate behavior of ice under uniaxial compression

In the present study, a modified split Hopkinson pressure bar (SHPB) is employed to investigate the dynamic response of ice under uniaxial compression in the range of strain rates from 60 to 1400 s −1 and at initial test temperatures of −10 and −30 °C. The compressive strength of ice shows positive strain-rate sensitivity over the range of strain rates employed; a slight influence of ice microstructure is observed, but it is much less than that reported previously for ice deformation under quasi-static loading conditions [Schulson, E.M., IIiescu, D., Frott, A., 2005. Characterization of ice for return-to-flight of the space shuttle. Part 1 – Hard ice. NASA CR-2005-213643-Part 1]. Specimen thickness, within the range studied, was found to have little or no effect on the peak (failure) strength of ice, while lowering the test temperature from −10 to −30 °C had a considerable effect, with ice behaving stronger at the lower test temperature. Moreover, unlike in the case of uniaxial quasi-static compression of ice, the effect of specimen end-constraint during the high rate compression was found to be negligible. One important result of these experiments, which may have important implications in modeling ice impacts, involves the post “peak-stress” behavior of the ice in that the ice samples do not catastrophically lose their load carrying capacity even after the attainment of peak stress during dynamic compression. This residual (tail) strength of the damaged/fragmented ice is sizable, and in some cases is larger than the quasi-static compression strength reported for ice. Moreover, this residual strength is observed to be dependent on sample thickness and the strain rate, being higher for thinner samples and at higher strain-rates during dynamic compression.

The compressive response of carbon fiber composite pyramidal truss sandwich cores

Abstract Pyramidal truss sandwich cores with relative densities in the range 1 – 10 % have been made from carbon fiber reinforced polymer laminates using a snap-fitting method. The measured quasi-static uniaxial compressive strength increased with increasing from 1 to 11 MPa over the relative density range investigated here. A robust face-sheet/truss joint design was developed to suppress truss – face sheet node fracture. Core failure then occurred by either (i) Euler buckling () or (ii) delamination failure () of the struts. Micro-buckling failure of the struts was not observed in the experiments reported here. Analytical models for the collapse of the composite cores by Euler bucking, delamination failure and micro-buckling of the struts have been developed. Good agreement between the measurements and predictions based on the Euler buckling and delamination failure of the struts is obtained. The micro-buckling analysis indicates this mechanism of failure is not activated until delamination is suppressed. The measurements and predictions reported here indicate that composite cellular materials with a pyramidal micro-structure reside in a gap in the strength versus density material property space, providing new opportunities for lightweight, high strength structural design.

Role of porosity in controlling the mechanical and impact behaviours of cement-based materials

This work deals with the influence of porosity on the tensile, the compressive and the impact behaviours of two fine cementitious mortars—one with silica fume and one without. The addition of silica fume is shown to change the pore size distribution. The mix without silica fume is characterized by porosity at the scale of the grains of fine sand (approximately 100 μm), while silica fume addition results in a more porous matrix with pore sizes of millimetre-length size. The mortar with silica fume shows a higher quasi-static compressive and flexural strength whereas the mix without silica fume is observed to be less compressible (by irreversible reduction of volume) under heavy confinement pressure (quasi-oedometric tests) and shows better ballistic performance. A numerical simulation of the impact tests employing the Krieg, Swenson and Taylor model, which accounts for both deviatoric and volumetric inelastic behaviour of the material, was undertaken using the data from quasi-oedometric tests. These calculations follow the experimental results and confirm the influence of the macroscopic porosity on the impact performance of cement-based materials.

Influence of powder particle size distribution on complex viscosity and other properties of acrylic bone cement for vertebroplasty and kyphoplasty

For use in vertebroplasty and kyphoplasty, an acrylic bone cement should possess many characteristics, such as high radiopacity, low and constant viscosity during its application, low value of the maximum temperature reached during the polymerization process (T(max)), a setting time (t(set)) that is neither too low nor too high, and high compressive strength. The objective of this study was to investigate the influence of the powder particle distribution on various properties of one acrylic bone cement; namely, residual monomer content, T(max), t(set), complex viscosity, storage and loss moduli, injectability, and quasi-static compressive strength and modulus. It was found that the formulations that possessed the most suitable complex viscosity-versus-mixing time characteristics are those in which the ratio of the large poly(methyl methacrylate) beads (of mean diameter 118.4 microm) to the small ones (of mean diameter 69.7 microm) was at least 90% w/w. For these formulations, the values of the other properties determined were acceptable.

Quasi-static and high cycle fatigue strength of brick masonry

Quasi-static and high cycle fatigue tests have been conducted on brick masonry test specimens under laboratory dry, wet and submerged test conditions. The relatively low compressive strengths of the bricks and mortar used to manufacture the test specimens were intended to be representative of the type of bricks and mortar likely to be encountered in relatively old masonry arch bridges. The quasi-static test results indicate that the compressive strength of brick masonry increases with an increase in the compressive strength of the mortar, and decreases with an increase in the degree of saturation. The compressive strength of brick masonry, based on assumed linear no tension stress distributions, increases with an increase in the load eccentricity or stress gradient. Approximately 20% of the apparent increase in compressive strength due to load eccentricity can be attributed to non-linear material behaviour, resulting in non-linear no tension stress distributions in the mortar joints. The high cycle fatigue tests on laboratory dry, wet and submerged test specimens indicate that the fatigue strength of brick masonry depends upon the induced stress range, the mean or maximum induced stress and the quasi-static compressive strength of the brick masonry under similar loading conditions. A lower bound fatigue strength curve for laboratory dry, wet and submerged brick masonry is proposed.

High Strain Rate Responses and Failure Analysis in Polymer Matrix Composites – An Experimental and Finite Element Study

Compressive properties and failure analysis of unidirectional and plain weave S2-glass/vinylester composites under high strain rate (HSR) loading have been investigated using the Split Hopkinson Pressure Bar (SHPB) technique. A systematic experimental approach has been adopted in this work to identify the damage progression at various stress levels and the strain rate effects on composites. The classical SHPB apparatus has been incorporated by a wave-trapping mechanism to apply a predetermined level of impact loading and to restrict the repeated loading. This facilitates identification of the microstructural damage progression during the loading period. The stress–strain responses at various strain rates in all three principal directions are investigated and the relevant failure modes are also identified by microscopic examinations. The quasi-static compressive strength, the strain to failure, and the elastic moduli are compared with SHPB test results to determine the shift in the failure mechanism. The compressive strength and failure strain for both unidirectional and plain weave composites are observed to be rate dependent. Such rate dependencies of compressive response are analyzed and correlation between the failure modes and the rate effects on composites are established. Finally, a three-dimensional transient finite element analysis (FEA) has also been carried out for unidirectional composites under high strain rate loading in order to have a thorough understanding of the failure mechanisms. Loads are applied in thickness, fiber and transverse of fiber directions and corresponding stress contours are simulated. The FEA prediction of the stress–strain behavior in all the three principal directions of loading correlates well with the high strain rate experimental results.

Dynamic properties of nitrogen alloyed 1045 iron-carbon-steel

A new high-pressure melting process enables nitrogen addition to ferritic Fe-C-alloys. A commercial-grade steel alloy, 1045, was cast under elevated nitrogen pressure, resulting in solid solution (austenite, ferrite, and martensite) and a porous microstructure. The retained high nitrogen concentrations in the Fe-C-alloy resulted in a substantial improvement in both quasistatic and dynamic compression strength. Using Planar-Plate-Impact-Technique (PPI) together with a VISAR and Split-Hopinson-Pressure-Bar-Technique (SHPB) the dynamic properties have been determined in the strain rate regime 10 3 s -1 - 10 6 s -1 . With the PPI-Technique the Hugoniot-Elastic-Limit and the spall strength as well as the U S -U p and the stress-strain relation have been determined. An unusual strong slope of the U S -u p -relation and a very low spall strength have been observed for both nitrogen contents. In this paper, the properties of the Fe-C-N alloy with these two nitrogen contents will be compared to those of nitrogen alloyed austenitic steels.

Optimized warm peening of the quenched and tempered steel AISI 4140

Using a modified air blast shot peening machine with an upgraded air flow heater system, warm peening at 20≤ T≤410 °C was feasible. An optimized peening temperatures of about 320 °C was identified for quenched and tempered steel AISI 4140 by analyzing the stability of the shot peening induced residual stress states during cyclic loading. Additionally, the quasi-static surface compressive yield strength as well as the cyclic surface yield strength of optimally peened states were determined from residual stress relaxation tests. At these peening temperatures, the Bauschinger effect common in quenched and tempered steels was overcompensated by dynamic and static strain aging effects resulting in stabilized dislocation structures. Finally, the effect of warm peening on the fatigue behavior at alternating bending will be discussed.

Dynamic behavior of concrete at high strain rates and pressures: I. experimental characterization

Understanding the behavior of concrete and mortar at very high strain rates is of critical importance in a range of applications. Under highly dynamic conditions, the strain-rate dependence of material response and high levels of hydrostatic pressure cause the material behavior to be significantly different from what is observed under quasistatic conditions. The behavior of concrete and mortar at strain rates of the order of 10 4 s −1 and pressures up to 1.5 GPa are studied experimentally. The mortar analyzed has the same composition and processing conditions as the matrix phase in the concrete, allowing the effect of concrete microstructure to be delineated. The focus is on the effects of loading rate, hydrostatic pressure and microstructural heterogeneity on the load-carrying capacities of the materials. This experimental investigation uses split Hopkinson pressure bar (SHPB) and plate impact to achieve a range of loading rate and hydrostatic pressure. The SHPB experiments involve strain rates between 250 and 1700 s −1 without lateral confinement and the plate impact experiments subject the materials to deformation at strain rates of the order of 10 4 s −1 with confining pressures of 1–1.5 GPa. Experiments indicate that the load-carrying capacities of the concrete and mortar increase significantly with strain rate and hydrostatic pressure. The compressive flow stress of mortar at a strain rate of 1700 s −1 is approximately four times its quasistatic strength. Under the conditions of plate impact involving impact velocities of approximately 330 ms −1, the average flow stress is 1.7 GPa for the concrete and 1.3 GPa for the mortar. In contrast, the corresponding unconfined quasistatic compressive strengths are only 30 and 46 MPa, respectively. Due to the composite microstructure of concrete, deformation and stresses are nonuniform in the specimens. The effects of material inhomogeneity on the measurements during the impact experiments are analyzed using a four-beam VISAR laser interferometer system.

REACTION SYNTHESIS/DYNAMIC COMPACTION OF TITANIUM CARBIDE AND TITANIUM DIBORIDE

Titanium carbide and titanium diboride were synthesized by self-propagating combustion reactions and densified by a high-speed forging technique, in which a hammer strikes the hot and porous ceramic (T - 2O0O0C) at velocities in the range 5 - 15 m/s. Compacts with densities higher than 96% of the theoretical density and diameters close to 10 cm were produced by this method. Optical and scanning electron microscopy of the consolidated material were carried out, revealing a grain size of approximately 44 pm for Tic and 15 pm for TiB2; these grains were equiaxed, indicating that crystallization (or recrystallization) occurred after the densification process. The quasistatic and dynamic compressive strengths were established and compared to those of hot-pressed material produced by CERCOM. For TiB2, the strengths were approximately 1.8 GPa, while for Tic the quasistatic (109 S-') and dynamic (102 S-') strengths were 1.7 and 2.2 GPa, respectively.

Effects of the Sequence of Measuring Nondestructive Deformation and Specific Gravity on the Quasi-Static Compression and Impact Strength of Eggs from White Leghorn Hens

Two experiments were done to determine if the types of shell measurement and the order in which they were obtained could influence the egg shell strength results. All possible sequences involving specific gravity (SG) and/or nondestructive deformation (or neither) followed by a destructive test, impact or quasi-static compression fracture, were considered. Each of the 10 sequences was applied to 45 eggs in each of two experiments. Both impact and compression fracture showed significant differences (P<.01) among sequences, mainly because sequences involving deformation generally produced lower fracture measurements. There was no evidence that SG influenced subsequent measurements nor that it was affected by previous deformation measurements. The results were generally consistent across the two experiments.

The Effects of Storage Duration on Nondestructive Deformation, Quasi-Static Compression Strength, Impact Fracture Strength, and Specific Gravity of Eggs from White Leghorn Hens

Three experiments were done to determine the effects of storage duration on egg shell strength. Groups of 30 to 48 eggs were stored in air in vinyl plastic bags at 10 C for up to 21 days after oviposition. Quasi-static compression fracture force, specific gravity (SG), and egg weight in air and in water tended to decrease with time, while impact fracture force tended to increase. These trends were consistent across experiments. Nondestructive deformation, however, appeared to decrease in one experiment and increase in another. The SG was lower when measured by the flotation procedure than by Archimedes’ principle. Because egg weight changed at the same rate in air and in water, the decrease in SG can be attributed to the loss in weight. The changes in compression and impact fracture strength of the eggs indicated that material and structural properties of the shell were influenced by the length of storage.