Hollow Cylindrical Specimens Research Articles

Micro-scale modeling of saturated sandy soil behavior subjected to cyclic loading

Liquefaction induced damage to the built environment is one of the major causes of damage in an earthquake. Since Niigata earthquake in 1964, it has been popularly recognized that the liquefaction induced ground failures caused severe damage in various forms such as sand boiling, ground settlement, lateral spreading, landslide, etc. Since then, understanding the mechanism of liquefaction phenomena became very important to take measures against the liquefaction induced ground failures. To understand the mechanism of liquefaction, it is important to consider the soil as an assemblage of particles. A continuum approach may fail to explain some of the phenomena associated with liquefaction. Discrete approach, such as distinct/discrete element method (DEM), is an effective method that can simulate the mechanism of liquefaction and associated phenomena well at the microscopic level. In this study, a new three-dimensional DEM model is developed to study the liquefaction and its associated phenomena. The hollow cylindrical torsion test under undrained condition, which replicates the ground condition before and during the earthquake well, is simulated using the newly developed model. A vertical strip from the hollow cylindrical specimen is considered in the study and the boundaries in the tangential direction are numerically connected to simulate the continuity in tangential direction. The liquefaction study is carried out by strain control shearing at the top while keeping the bottom plate fixed. The cyclic mobility, which is observed in saturated sands when subjected to cyclic shearing, is predicted by the proposed model. The effect of particle rotation on the development of dynamic pore water pressure is also investigated using the model. Also, sand boiling is simulated using the proposed model.

Influence of Bond Coat Roughness on Life Time of APS Thermal Barrier Coating Systems under Thermo-Mechanical Load

The influence of the bond coat roughness on the life time of air plasma-sprayed (APS) thermal barrier coating systems (TBCs) was investigated under thermo-mechanical (TMF) load. The TBC system was applied on hollow cylindrical specimens made of the single crystal super alloy CMSX-4 in the orientation with a MCrAlY-bond coat. Two different values of the bond coat roughness were investigated. In order to study the influence of the thicknesses of the thermally grown oxide layer (TGO), the specimens were isothermally oxidized at 1000 °C for a long term prior to the TMF experiments. The thermo-mechanical experiments show a higher number of cycles-to-failure for TBCs corresponding to an increase of the bond coat roughness. Furthermore, it could be demonstrated that a certain TGO thickness is needed to produce a total delamination of the top coat in the TMF experiments. This minimum thickness varies with the surface roughness of the bond coat and the TMF cycle's phase shift and strain range. Crack initiation and crack propagation were investigated by microscopical analyses, for example, SEM and EDX. Therefore most of the experiments were completed before a total delamination of the top coat occurred. On the basis of these investigations, crack initiation and crack propagation under thermo-mechanical load were described systematically.

Effect of Specimen Size on Quasi-Elastic Properties of Toyoura Sand in Hollow Cylinder Triaxial and Torsional Shear Tests

Abstract Quasi-elastic deformation properties of dry, dense Toyoura sand were experimentally investigated by triaxial and torsional shear tests on hollow cylindrical specimens of medium sizes (outer diameter Do=20 cm, inner diameter Di=16 or, 12 cm, and height H=30 cm) and small size (Do=10, Di=6, H=20 cm). In addition to the conventional external measurements, strains were measured locally by the newly developed pin-type local deformation transducers. The effect of specimen size on locally measured Young’s modulus Ez was insignificant. On the other hand, the locally measured values of shear modulus Gzθ with the small size specimen revealed lower reproducibility as compared with those measured with the medium size specimens, suggesting that larger specimen size is preferred in evaluating the small strain shear modulus in torsional shear tests on hollow cylindrical specimens. It was also inferred from the test results that, irrespective of the specimen size, effect of end restraint at the top cap and pedestal is significant on the externally measured values of Gzθ.

A nonlinear elastic analysis of static stress and lateral pressure coefficient for granular Couette systems

Whether or not the classical theory of elasticity is valid for static granular matter is a basic question of granular physics. We present in this work stress distributions inside hollow cylindrical (Couette geometry) specimens， calculated with the nonlinear elastic equations recently reported in literature. Most of these results can be experimentally measured， and are useful for clarifying the basic question by testing the applicability of the nonlinear elastic equations to granular matter. Moreover they can also be used for analyzing the lateral pressure coefficient of interest in soil engineering.

PRACTICAL EFFECTIVE STRESS-STRAIN MODEL OF SAND CONSIDERING CYCLIC MOBILITY BEHAVIOR

A practical effective stress-strain model of sand is presented in which only the soil parameters directly obtained from a common site investigation and a laboratory test, i.e., G-γ, h-γ curve and liquefaction curve, are used as input parameters. A key mechanism simulating liquefaction and cyclic mobility behavior is modeled based on the accumulated damage concept for pore pressure generation with a generalized hardening model for shear behavior. The proposed model can simulate reasonably well the stress strain behavior of hollow cylindrical specimens subjected to earthquake loading.

Interpretation of torsional shear results for nonlinear stress–strain relationship

AbstractTorsional tests are frequently used in material testing to determine shear stress–strain relationships. In the tests, torque is applied to a solid or hollow cylindrical specimen, whose twist angle is recorded as the response. While the raw test results are readily available in terms of torque–twist sets, converting them into intrinsic stress–strain relationships is not always straightforward, owing to the nonlinear stress–strain behavior and the non‐uniform radial distribution of the stress and strain fields. It follows that the approaches currently used to interpret torsional data are essentially empirical based.The present paper addresses this data interpretation issue from a more rigorous perspective. The paper includes two parts: the first part concerns hollow cylindrical specimens under torsion, where an analytical‐based recursive procedure is developed; and the second part deals with solid torsional specimens, for which an analytical solution given by Nadai is directly employed. Examples pertaining to these two cases are examined and the resulting shear stress–strain curves are compared with those based on a number of popular empirical methods. The proposed analytical approaches can serve as a benchmark for checking the accuracy and validity of those empirical propositions. It is worth noting that, for brittle materials exhibiting softening behavior, only the analytical method gives the correct interpretation. Copyright © 2007 John Wiley & Sons, Ltd.

Development of a galling resistance test method with a uniform stress distribution

In this study, a new galling test method is presented along with results from a pilot testing program. The pilot program was performed on type 303 stainless steel. The new testing configuration consists of two concentrically aligned hollow cylindrical specimens loaded along their longitudinal axes. The specimens are held in alignment using a custom made alignment pin. The pin maintains concentricity between the mated surfaces while enabling the contact interface to self-align. The resulting contact surface is in the shape of an annulus and has a uniform stress distribution. The new testing configuration eliminates the stress concentration that exists in the ASTM G98 Standard Test Method for Galling Resistance of Materials. The results of this study show that the galling wear phenomena do not transition from non-galled to galled at a single value. Galling is shown to be stochastic in nature.

Evaluation of self-welding susceptibility of an austenitic stainless steel (alloy D9) in sodium

Self-welding susceptibility of a 15Cr–15Ni–2Mo titanium-modified austenitic stainless steel (alloy D9), in both annealed and 20% cold-worked conditions, have been evaluated in flowing sodium at 823 K for 2160 and 4320 h under contact stress of 9.4 MPa. Tests were performed on flat-on-flat geometry of hollow cylindrical specimens under compression. One pair of 20% cold-worked alloy D9 vs. 20% cold-worked alloy D9 specimens tested for 4320 h was self-welded for which the breakaway shear force was measured. Scanning electron micrographs of the self-welded region showed that portions of the original interface no longer existed. The paper discusses the experimental set-up installed in the sodium loop test facility and the results of self-welding susceptibility studies on this material.

Deformation-induced martensite formation during cyclic deformation of metastable austenitic steel: Influence of temperature and carbon content

To study the influence of the parameters carbon content, temperature and total strain amplitude on the deformation-induced martensite formation in metastable 301 austenitic steel, hollow cylindrical fatigue specimens were carburized and decarburized in methane–hydrogen gas mixtures. Fatigue experiments were carried out in a temperature range between RT and T = −100 °C while monitoring the fraction of deformation-induced martensite versus the number of cycles by means of a magneto-inductive ferrite sensor. The results show that deformation-induced martensite formation leads to pronounced cyclic hardening. A certain amount of accumulated plastic strain is necessary and a threshold value of the plastic strain amplitude must be exceeded to trigger martensitic transformation. The effect of the carbon content and/or the temperature on the formation of α′ martensite is very strong in such a way that high carbon concentrations and elevated temperatures stabilize the austenite phase.

In-sodium self-welding susceptibility evaluation of chromium-plated 2.25Cr-1Mo steel with Inconel 82 weld metal

The self-welding susceptibility of Cr-plated 2.25Cr-1Mo steel with Inconel 82 weld metal, with and without Cr-plating, has been evaluated in flowing sodium at 823 K for three and six months under contact stress of 3.0 MPa. Tests were performed on flat-on-flat geometry of hollow cylindrical specimens under compression. No self-welding was observed in either test for either material combination. Scanning electron micrographs of the tested specimens showed no damage in the surface. The paper discusses the experimental set-up and the results of self-welding susceptibility studies on these material combinations.

Double cracking in brittle cylindrical specimens subjected to quenching

A series of quench tests on hollow cylindrical specimens made of the machinable ceramic, Pyrophyllite, has been performed. The specimens consistently fractured with two diametrically opposite longitudinal cracks. Finite element analysis indicates that the primary crack occurred at the stage when the strain energy of the cylinder reached its maximum during the thermal transient process, while the secondary crack was caused by stress waves generated following the primary crack. This is supported by experimental observation of the time of fracture and the crack morphology. The work reported here helps to shed light on the fracture criterion for brittle cylindrical components under transient thermal and dynamic loadings.

Constitutive behaviour of high-performance ferrocement under axial compression

The increased utility of ferrocement for stressed skin surfaces such as domes, arches, funicular shells etc, necessitated further research and development for better performance. The aim of the current paper is to develop an analytical model for predicting the stress–strain behaviour of an improved ferrocement, based on the experimental results. The results of 144 hollow cylindrical specimens tested under strain control rate of loading are presented. The increase in strength and strain of ferrocement are used in formulating the constitutive relation.

Effects and interactions of temperature and stress-level related damage on permeability of concrete

The objective of this study is to investigate damage-temperature-stress level-permeability interactions in structural concrete. The tests are performed on hollow cylindrical concrete specimens, subjected to compressive loading and temperature up to 150 °C. The results emphasize that at stress levels lower than 80% of the peak stress, the variation of permeability is small and it is slightly influenced by the stress. As a matter of fact, the permeability under load is smaller than the permeability measured after unloading. As the load exceeds 80% of the peak stress, micro-cracking increases rapidly, causing an increase of the permeability and a greater sensitivity to the applied load, i.e. a noticeable difference between the permeability measured under load and after unloading, the first becoming greater than the latter. In the post-peak phase the increase of permeability is much larger due to significant crack width growth. The increase of permeability with the applied load seems to be greater with temperature, inducing further alterations of concrete and dilation of the porous structure of the material. Finally, the experimental results seem to agree with the format of coupled evolution of the permeability due to damage and temperature assumed by Gawin et al. [D. Gawin, C.E. Majorana, B.A. Schrefler, Numerical analysis of hygro-thermal behaviour and damage of concrete at high temperature, Mechanics of Cohesive-Frictional Materials 4 (1999) 37–74.].

Nucleation and growth of small fatigue cracks in filled natural rubber under multiaxial loading

This paper presents and discusses observations of crack nucleation and small crack growth in a filled natural rubber compound subjected to multiaxial loading. A hollow cylindrical specimen was used in which simultaneous axial and shear strains are produced. The loading path types investigated include axial, torsion, proportional axial-torsion, and non-proportional axial-torsion loadings. It is shown that cracks appear and grow in a particular orientation during a typical fatigue test. The nature and evolution of these cracks with applied cycles were studied by direct observation. The observed failure plane behavior is compared to predictions based on the calculated cracking energy density. Effects of crack closure, load phase angle, crack density, and crack face shearing (mode II), as well as aspects that distinguish between “nucleation” and “growth” processes in rubber are discussed.

Evolution of surface morphology of thermo-mechanically cycled NiCoCrAlY bond coats

We investigate morphological surface instabilities on bond coat surfaces of thermal barrier coatings, induced due to thermo-mechanical loading. Experimental results of hollow circular cylindrical specimens, consisting of a directionally solidified superalloy (IN 100 DS) coated with a NiCoCrAlY bond coat, show that the morphological instabilities are strongly dependent on the load conditions. In particular, the morphological instabilities develop during thermal cycling with a thermal gradient over the cylinder wall, whereas the surface remains smooth for thermal cyclic conditions without a gradient. Furthermore, if a cyclic, axial tensile force is applied (synchronized with the thermal cycling), the morphological instabilities become aligned with the axial direction. We discuss a model, quantified by finite element simulations, capturing this behavior and elucidating the thermo-mechanical response.

Zusammenhang zwischen fortschreitender Schädigung, Temperatur und Permeabilität des Betons: Experimentelle und numerische Untersuchungen / Coupling between Progressive Damage, Temperature and Permeability of Concrete: Experimental and Numerical Study

Article Zusammenhang zwischen fortschreitender Schädigung, Temperatur und Permeabilität des Betons: Experimentelle und numerische Untersuchungen / Coupling between Progressive Damage, Temperature and Permeability of Concrete: Experimental and Numerical Study was published on August 1, 2006 in the journal Restoration of Buildings and Monuments (volume 12, issue 4).

Strain Localization in Combined Axial-Torsional Testing on Kaolin Clay

A series of combined axial-torsional tests were performed to study the 3D mechanical behavior of kaolin clay in an undrained condition. Using the digital image analysis technique, discrete local deformation of the surface of a hollow cylindrical specimen under loading was recorded. A linear interpolation method was used to generate a continuous deformation and strain field of the specimen based on the recorded discrete local deformations. Evolution of shear band was vividly visualized and recorded during the loading process for various inclinations of major principal stress. The theory of strain localization on continuous bifurcation was briefly reviewed and applied to the Mohr-Coulomb model, and a single hardening model incorporating the concept of loading-history-dependent plastic potential was developed by the writers. The largest critical plastic modulus and orientation of the shear bands were predicted by using the theoretical solution. Significant disagreement was observed between the experimental results and theoretical predictions related to the initial occurrence of strain localization and the inclination of fully developed shear bands.

Single Hardening Elasto-Plastic Model for Kaolin Clay with Loading-History-Dependent Plastic Potential Function

The effect of principal stress rotation on the mechanical behavior of Kaolin clay is investigated using combined axial-torsional tests on hollow cylindrical specimens. The yielding behavior and failure criteria are found to be strongly dependent on the principal stress rotation angle (β) and plastic work. A unique plastic potential function determined solely by the current stress state is not sufficient to model the plastic flow observed in these experiments. Therefore, a single hardening elasto-plastic model that includes a loading-history-dependent plastic potential function is proposed for normally consolidated Kaolin clay subjected to principal stress rotation. A general methodology for incorporating history dependency in modeling complex elasto-plastic behavior of cohesive soils is presented along with comparisons of model predictions with experimental data.

Interaction Curve for High Performance Ferrocement in Biaxial State of Tension

abstractFerrocement′s attribute as a thin reinforced concrete and laminated cement based composite enables numerous applications where strong and tough protective shell is needed. It is used in the construction of cylindrical and spherical shells as liquid retaining structures. The stress condition at a point in such shell structures is biaxial state of tension-tension. A study on the behaviour of ferrocement in biaxial state is important for establishing a rational design. The authors carried out a full-fledged investigation on ferrocement under different biaxial stress conditions. The present investigation deals with the study of ferrocement in biaxial tension-tension based on hollow cylindrical specimens. An interaction curve is proposed to estimate the strength of ferrocement in biaxial tension-tension. The relationship between octahedral normal and shear stress is also presented.

Engineering Properties of Wet-Pluviated Hollow Cylindrical Specimens

Abstract A hollow cylinder apparatus was used to study some engineering properties of hollow cylindrical sand specimens prepared using the wet-pluviation technique. The refined specimen preparation method had good repeatability. Wet pluviation produced inherently cross-anisotropic specimens, with the initial level of anisotropy reducing with decreasing initial void ratio. The variation in the initial void ratio of the sand specimens was related to the volume of the specimens. The stress-strain responses under isotropic consolidation were not significantly affected by the small variations in the initial void ratios that occurred for a target initial specimen volume. The levels of membrane penetration recorded for the different specimens were independent of the applied cell confining pressure, and the amount of membrane penetration compared well with other experimental studies.