Compression Tests Of Specimens Research Articles

Extraction and Testing of Miniature Compression Specimens From Bearing Balls Subjected to Rolling Contact Fatigue

Extraction and testing of miniature compression specimens from localized regions of components affected by rolling contact fatigue loading can provide significant insight into material degradation. Current ASTM standards for compression testing of cylindrical specimens become too stringent and difficult to achieve when specimen size is reduced to around 1 mm in diameter. The tolerances for surface flatness, parallelism of the loading surfaces, and the perpendicularity between the axis and the loading surfaces play crucial roles in the resulting stress-strain curves under uniaxial compression loading. In this manuscript, a systematic study is performed to quantify the influence of the above geometric parameters on the stress-strain response. Based on the analysis, the allowable geometric tolerances of miniature cylindrical specimens for a valid compression tests are recommended. The analysis results are validated and the usefulness of the method is demonstrated on miniature specimens extracted from the rolling contact fatigue affected regions of high strength M50 bearing balls. The yield stress within the rolling contact fatigue affected region is shown to increase by over 12%.

A prompt procedure for prediction of strength in artificially cemented soft soils

The focus of this paper is to present a new evaluation method for strength gain in very soft soils when using cementation as a means of improvement. This test procedure was created due to great difficulty encountered in molding specimens for compression and tensile tests in very soft clays and silts. The test consists in the measurement of the maximum force applied to embed a flat base rod into a soil mass using high sensibility dynamometric rings. The maximum pressure (maximum force divided by the flat base rod area) recorded up to 30 mm embedding of the rod into the soil mass is adopted as reference and has been shown to have direct linear correlation to Brazilian tensile tests. A correlation was set to a range of different materials encouraging its use in engineering practice. The main advantages of the proposed test are the easiness to mold specimens, the option of carrying out multiple tests in a single specimen and the possibility of carrying out tests outside the laboratory environment.

天日乾燥浄水汚泥の縮減性と最適含水比条件下での安定処理効果

Sludge treatment at the water purification plant is classified into solar drying and pressure dehydration. Compared with the latter, the former can reduce an expense required for a device and facilities. On the other hand, the former has disadvantages in that the retrievement of sludge is after approximately one year because the drying rate of sludge including a large quantity of water depends on a season or the weather.We firstly performed a simple loading test to promote the water-reducing of sludge which was dried in the sun. In this experiment, we laid the sludge of nearly 460% water content onto geotextile fixed in a container of 100mm inside diameter, and added the normal stress of 0.10MN/m2 from 0.05MN/m2 for 24 or 48 hours. Water contents after the unloading have decreased to about 260% due to synergy of load and geotextile for the drainage promotion. This difference of the water content was almost corresponding to three months solar drying period. We secondly examined the bearing capacity and strength characteristics of specimens made by adding stabilizers into the sludge which was dried to nearly optimum water content. The results of California Bearing Ratio test, unconfined compression test and box shear test indicated that CBR value, unconfined compressive strength and shear strength all increased with lapse of the days, regarding the specimens cured in water upon the neck of air. The consequence that the strength developed in proportion to the common logarithm of curing days was also obtained, from the unconfined compression test of specimens cured only in air for 90 days.As above, it can be considered that shortening a solar drying period to heighten the desludging frequency contributes to an improvement in the operating ratio of air drying bed and a cyclic utilization of resources.

Phenomenological and chemomechanical modeling of the thermomechanical stability of liquid silicone rubbers

In this article, we present the constitutive models taking into account the stability of liquid silicone rubber's. We propose the phenomenological large strain viscoelastic material model and the enhanced chemomechanical model. The phenomenological model is calibrated to the experimental investigations probing the thermomechanical behavior of liquid silicone rubber's, while the chemomechanical model uses kinetic theory, to calculate the changes of mechanical properties in time. The proposed chemomechanical model employs: chemical reaction kinetics, statistical mechanics and microstructural based Bergström-Boyce material model. Viscoelastic material property changes resulting from e.g. the variation of crosslink density are computed using the Arrhenius equation. The material model is validated by comparison with results of compression tests of specimens aged in 125 and 175 °C non-loaded and under stress of 0.48 MPa. We achieve 96% compliance for investigated temperature and pressure range. The good agreement with the experimental data, demonstrates that chemomechanical modeling framework provides a useful tool for the prediction of the stability of liquid silicone rubbers and the lifetime of vibration isolators.

An Investigation on the Interfacial Transition Zone of Lightweight Aggregate Concrete

The technique of linking the SEM photographs taken around the interfacial transition zone area is applied to observe the development of hydration products for lightweight aggregate and paste at the different curing ages. This research first determines the mixture proportions of the two types of concrete specimens with different aggregate unit weights. The lightweight aggregate used is the sludge kilned aggregate from Shihmen reservoir. The very small SEM samples to be observed are taken from the concrete compressive test specimens and must include both aggregate and paste. The research then observes the hydration products (such as CH, C-S-H) of calcium ion and the pozzolanic reaction on the samples. Finally it assesses if the aggregate will produce ion exchange with cement and generate the hydration products. The hydration products on either side of the interface with a range of 100μm are observed using 2000x magnification. From the results, it is found that (1) the development of hydration products of the lightweight aggregate concrete is similar to that of the normal-weight aggregate concrete, (2) the failure at the 91 days age is that the lightweight aggregate is sheared, (3) the bond stress of aggregate and paste is controlled by hydration products of paste, (4) the aggregate has not interacted with cement paste to produce hydration products, and (5) the development of hydration products proves that the amount of binder used in the concrete specimen will affects its compressive strength.

Mechanisms of toughness improvement in Charpy impact and fracture toughness tests of non-heat-treating cold-drawn steel bar

In this study, toughness properties of a non-heat-treating cold-drawn bar were examined by Charpy impact test and fracture toughness test, and the toughness enhancement mechanisms were clarified in relation with microstructure. As the thickness of pearlite bands decreased after the cold drawing, the Charpy impact energy of the cold-drawn bar was higher than that of the as-rolled bar, which could be reasonably explained by the thin sheet toughening. On the other hand, thin pearlite bands negatively affected the fracture toughness because of the decreased spacing between crack or void initiation sites inside the fracture process zone in front of the pre-fatigued crack tip. The Charpy impact test data could also be correlated with the absorbed energy of the dynamic compressive test specimen whose orientation was matched with the hammer impact direction of the Charpy impact test, although the Charpy impact and dynamic compressive test specimens had a notched body and a smooth body, respectively.

Compressive Behavior of Spark Plasma Sintered CNT Reinforced Al2124 and Al6061 Nanocomposites

In the present study, compressive behavior of CNT reinforced Al2124 and Al6061 nanocomposites was investigated. The powders were sonicated for 30 minutes then ball milled at 200 rpm for 1 hour under argon environment. The ball milled slurry was dried and again was milled under same conditions for 15 min to disperse the agglomerated particles. The prepared powders were spark plasma sintered at 35 MPa and 450oC. Sintered specimens with final dimensions of 6 mm diameter and 12 mm length were used as standard specimens for compression tests carried out at a compression rate of 0.5 mm/min. The effect of CNT addition on the compressive modulus, percentage compression, and compressive strength was investigated.

Overview of the testing activities on ITER sub-scale pre-compression rings

Abstract After a first RD one of them was used as base composite material to manufacture different sets of specimens for shear, compression and non destructive tests (NDT). Then, five other mock-ups were manufactured following ENEA VPI process and three using WW technique by two different industrial companies. The rings were tested in ENEA Frascati in a dedicated hydraulic testing machine consisting of 18 radial actuators working in position control with a total load capability of 1000 tons. The complete testing campaign consisted of six ultimate tensile strength (UTS) tests and four stress relaxation (SR) tests. The tests demonstrated that the composite (S2 glass-epoxy) is a valid and viable solution for the ITER pre-compression rings (non conductive, non magnetic, capable to work at high stress level without relaxation). UTS tests showed an overall average ultimate strength of 1550 MPa (mean hoop stress in the cross section) and a constant hoop modulus to failure of all the mock-ups. Stress relaxation tests did not show any significant relaxation at different stress levels and durations.

An Investigation on the Interfacial Transition Zone in Concrete Using SEM

The technique of linking the SEM (Scanning Electron Microscopy) photographs taken around the interfacial transition zone area is applied to observe the development of hydration products for aggregate and paste at the different curing ages. This research first chooses the aggregate with clay properties not containing the calcium ion, and then observes the hydration products (such as CH, C-S-H) of calcium ion on the aggregate. Finally it assesses if the aggregate will produce ion exchange with cement and generate the hydration products. The very small samples to be observed are taken from the concrete compressive test specimen and must include both aggregate and paste. They are wiped with alcohol to have better pictures before shooting SEM. Initially, the interface of aggregate and paste is sought using 2000x magnification. However, the hydration products on either side of the interface with a range of 50 μm are observed using 10000x magnification. From the results, it is found that aggregate has not interacted with cement paste to produce hydration products and the bond stress of aggregate and paste is controlled by hydration products of paste.

Deformation Modulus of Fly Ash Modified with Lime and Gypsum

Deformation modulus of fly ash is one of the most important mechanical properties generally used in different design problems and also as an input parameter to sophisticated numerical techniques employed to assess the response of different structures resting on fly ash fill or embankment made of fly ash. Deformation modulus is usually expressed in terms of compressive strength. This paper presents the deformation modulus of fly ash modified with lime alone or in combination with gypsum at different strain levels. The values of deformation modulus obtained from both unconfined compression test and unconsolidated undrained triaxial test results are presented herein. The specimens for unconfined compression test and for undrained triaxial tests were cured up to 90 and 28 days, respectively. The effects of addition of lime (4–10%) and gypsum (0.5 and 1.0%) on the deformation modulus of class F fly ash are highlighted. With addition of lime and gypsum, the class F fly ash achieved the deformation modulus in the range of 190 MPa in UCS test and up to 300 MPa in triaxial test specimens tested under all round pressure of 0.4 MPa. Based on the present test results empirical relationships are developed to estimate deformation modulus of modified fly ash from unconfined compressive strength and relationships between initial tangent modulus and secant modulus at different strain levels are also developed.

Experimental investigation on the lateral compression in the foam-filled circular tubes

This paper investigates the effect of polyurethane foam-filler on the lateral plastic deformation in the circular tubes under radial quasi-static loading, experimentally. For this purpose, the specimens were prepared with five different diameters and thicknesses. For each constant diameter of specimens, several tubes with different lengths were prepared. All geometrical groups of specimens in the lateral compression tests (flattening) were used in empty and polyurethane foam-filled conditions. The effect of length, diameter and wall thickness of tubes on the lateral load, energy absorption and the specific absorbed energy were studied. The experimental results show that the polyurethane foam-filler increase the energy absorption capability of tubes and furthermore the increment of the energy absorption in thinner tubes is more than thicker specimens. Results show that using the polyurethane foam in the circular tubes under the lateral compression works as an excellent filler.

Numerical Study on Effects of Rock Bridge Angle in Uniaxial Compression Test

Numerical specimens with two pre-existing flaws is established by using particle flow code PFC2D and by changing the relative position of the pre-existing flaws different rock bridge angle is obtained. Though the uniaxial compression test of specimens with different rock bridge angle , it can be found that rock bridge angle have a great impact on the mode of crack propagation of specimen. The different relative position between the two pre-existing flaws led to different levels of stress shielding effect under the axial force, and it is most likely to damage when the two pre-existing flaws are about overlap.

Mechanical characterization of glass fibre–epoxy composite material for ITER pre-compression rings

Pre-compressions rings have been designed to improve the ITER magnets structural support. They are made of high strength unidirectional S-2 glass fibres wound in an epoxy matrix. In order to obtain very high strength properties, ENEA developed and characterized this composite with a high volumetric glass content (∼68%). Benefits of this solution include high strength, no interference with magnet fields and long expected service life. This work illustrates the mechanical characterization of the material used to manufacture the rings. At first, linear specimens were produced to perform tensile and creep tests. Then, reduced scale ring mock-ups have been fabricated and tested in ENEA Fusion-Laboratories. One ring was used for the machining of several specimens for compression and shear tests. Standard and non standard specimens were machined from different geometric directions (longitudinal, radial and transversal with reference to the fibre–glass direction) and tested at room temperature and at liquid nitrogen (77 K) temperature to complete characterization with compression and shear tests. The experimental campaign has been carried out following as close as possible the related ASTM standards in order to evaluate material strength, Young and shear moduli. Test results showed high mechanical strength of the composite in fibre–glass longitudinal direction but lower values in transversal direction.

A measurement method for piezoelectric material properties under longitudinal compressive stress–-a compression test method for thin piezoelectric materials

We introduce a new compression test method for piezoelectric materials to investigate changes in piezoelectric properties under the compressive stress condition. Until now, compression tests of piezoelectric materials have been generally conducted using bulky piezoelectric ceramics and pressure block. The conventional method using the pressure block for thin piezoelectric patches, which are used in unimorph or bimorph actuators, is prone to unwanted bending and buckling. In addition, due to the constrained boundaries at both ends, the observed piezoelectric behavior contains boundary effects. In order to avoid these problems, the proposed method employs two guide plates with initial longitudinal tensile stress. By removing the tensile stress after bonding a piezoelectric material between the guide layers, longitudinal compressive stress is induced in the piezoelectric layer. Using the compression test specimens, two important properties, which govern the actuation performance of the piezoelectric material, the piezoelectric strain coefficients and the elastic modulus, are measured to evaluate the effects of applied electric fields and re-poling. The results show that the piezoelectric strain coefficient d31 increases and the elastic modulus decreases when high voltage is applied to PZT5A, and the compression in the longitudinal direction decreases the piezoelectric strain coefficient d31 but does not affect the elastic modulus. We also found that the re-poling of the piezoelectric material increases the elastic modulus, but the piezoelectric strain coefficient d31 is not changed much (slightly increased) by re-poling.

Effect of Vanadium Addition at a Rate of 0.1% on the Mechanical Characteristics, Microstructure, and Microhardness of Al-Cu Casted Alloys

Due to essential need of Al-Cu alloys in different applications such as aerospace and automotive industries, and the mechanical characteristics of Al-Cu alloys being weak; the effect of vanadium addition at a rate of 0.1% on the mechanical behavior, microhardness, and microstructure have been investigated. The effect of upsetting process -cold work- on the microstructure, microhardness has been also investigated. Three set of alloys namely; Al, Al-9%Cu, and Al-9%Cu-0.1%V were prepared. The specimens for microstructure, microhardness and compression tests were machined. The mechanical tests were performed to investigate the effect of vanadium addition and the effect of upsetting process. It was found that the 0.1% vanadium addition resulted in grain refinement of Al-9% Cu alloys of about 32.3 %, furthermore, and extra refining resulted after upsetting process by 44.2 %. On the other hand, the microhardness of Al-9%Cu enhanced by 54.1 %, and the valuable result was a 422.8 % enhancement in the microhardness of Al-9%Cu-0.1%V alloy after upsetting process compared to pure Al.

Shear behaviour in numerical triaxial compression tests by 3D fluid-coupled DEM: a fundamental study on mechanisms of landslide initiation

Shear behaviour in triaxial compression tests was numerically examined by 3D fluid-coupled DEM in a fundamental study on the mechanisms of landslide initiation. Changes in pore-water pressure because of undrained compression were calculated by introducing a measurement sphere surrounding a ball which represented the soil particles. The pore-water pressure was assigned to the measurement sphere as the product of the changes in volumetric strain and modulus of compressibility of water, and resulting flow due to the pressure differences among neighbouring measurement spheres was given on the basis of Darcy's law. Specimens for the numerical triaxial compression tests were prepared with wide ranges of initial void ratio by use of samples with three different grain-size distributions. In the loose specimens, positive pore-water pressure build-up and subsequent liquefaction were numerically reproduced. In contrast, in the dense specimens, negative pore-water pressure was observed, showing upgrade of soil structure. For the medium specimens, phase transformation, which is a typical characteristic of granular soils, was successfully reproduced. Although steady-state lines were found for each sample on a diagram, there was a gap at a specific initial void ratio. Although the angles of internal friction were inversely proportional to the initial void ratio in both the undrained and drained tests in the medium to dense specimens, the observed angles of internal friction were smaller than the particle-to-particle friction angle. This result may be attributable to the fact that the balls could not form the complicated soil structures created in reality by particles with complex shapes.

Flow Behaviour of Commercial Purity Titanium Subjected to Equal Channel Angular Pressing

Commercial purity Ti was subjected to equal channel angular pressing (ECAP) for up to three passes at 400oC using a die with die angle of 120o. Compression testing of the ECAP specimens was carried out to determine the subsequent flow behavior. Two types of compression test specimen orientations, one parallel to the axis of ECAP and the other at 45o to the axis of the ECAP, were prepared from the specimens subjected to ECAP. Anisotropy in flow behaviour (as indicated by values of strength co-efficient, K and strain hardening exponent, n) was observed. The strain hardening rates were also calculated from the experimentally determined flow curves for the specimens tested in compression in the two orientations. The results have been interpreted in terms of the strain path change parameter between the two deformation steps (ECAP and compression). Strain hardening behaviour and microstructure evolution is discussed in terms of strain path change parameter. Specimens compressed in the direction parallel to the ECAP direction had lower strain hardening exponents while exhibiting higher initial flow stresses. The strain hardening rates were lower for specimens compressed at 45o to the ECAP direction compared to specimens compressed parallel to the ECAP direction.

Investigation on Seismic Properties of Load-Bearing Masonry Walls in Chinese Historical Buildings

Masonry walls resist most of the lateral loads in some Chinese historical architecture. To investigate the seismic properties of these load-bearing masonry walls, blocks in a typical Chinese old building undergoing retrofit are reserved. Compressive test specimens and wall panel specimens are constructed using these blocks and lime mortar. Mixing of the lime mortar is similar to that used in the old building. Material tests and pseudo-static tests are then performed. The damage modes and hysteretic curves of the wall panel specimens are studied. The test results are expanded through computer simulation. Some characteristics of the load-bearing masonry walls are summarized based on the test and simulation results. The proposed methodology and results can be referred to in further researches on seismic properties of historical masonry architectures.

Measurement of resistance curves in the longitudinal failure of composites using digital image correlation

This paper presents a new methodology to measure the crack resistance curves associated with fiber-dominated failure modes in polymer–matrix composites. The crack resistance curves not only characterize the fracture toughness of the material, but are also the basis for the identification of the parameters of the softening laws used in the numerical simulation of fracture in composite materials. The proposed method is based on the identification of the crack tip location using Digital Image Correlation and the calculation of the J-integral directly from the test data using a simple expression derived for cross-ply composite laminates. It is shown that the results obtained using the proposed methodology yield crack resistance curves similar to those obtained using Finite Element based methods for compact tension carbon–epoxy specimens. However, it is also shown that, while the Digital Image Correlation based technique mitigates the problems resulting from Finite Element based data reduction schemes applied to compact compression tests, the delamination that accompanies the propagation of a kink-band renders compact compression test specimens unsuitable to measure resistance curves associated with fiber kinking.

発泡剤不使用の摩擦攪拌法によるアルミニウム合金ダイカストを用いたポーラスアルミニウムの圧縮特性

Porous aluminum was fabricated without the use of a blowing agent by friction stir processing using the gases contained in ADC12 aluminum alloy die-casting plates. The compressive properties of the obtained porous aluminum were investigated. It was shown that a compressive test specimen with a porosity of approximately 70% was obtained that had pores with a relatively small area and high sphericity. Porous aluminum fabricated without the use of a blowing agent exhibited brittle fracture at a relatively high plateau stress and high absorption energy compared with those of ALPORAS.