77,215 research outputs found
Effect of reconstituted method on shear strength properties of peat
Peat is an organic soil contains more than 75% organic content. Shear strength of the
soil is one of the most important parameters in engineering design, especially during
the pre-construction and post-construction periods, since used to evaluate the
foundation and slope stability of soil. Peat normally known as a soil that has very
low shear strength and to determine and understand the shear strength of the peat is
difficult in geotechnical engineering because of a few factors such as the origin of
the soil, water content, organic matter and the degree of humification. The aim of this
study was to determine the effective undrained shear strength properties of
reconstituted peat. All the reconstituted peat samples were of the size that passing
opening sieve 0.425mm, 1.000mm, 2.360mm and 3.350mm and were preconsolidated
at pressures of 50 kPa, 80 kPa and 100 kPa. The relationship deviator
stress- strain, σdmax and excess pore water pressure, Δu, shows that in both of
reconstituted and undisturbed peat gradually increased when confining pressure, σ’
and pre- consolidation pressure, σc increased. As a conclusion, the undrained shear
strength properties result obtained shows that the RS3.350 has higher strength than
RS0.425, RS1.000 and RS2.360. However, the entire reconstituted peat sample
shows the increment value of the shear strength with the increment of peat size and
pre- consolidation pressure. For comparison purposes, the undrained shear strength
properties result obtained shows that the reconstituted peat has higher strength than
undisturbed peat. The factors that contributed to the higher shear strength properties
in this study are segregation of peat size, pre- consolidation pressure, initial void
ratio and also the physical properties such as initial water content, fiber content and
liquid limit
Carburization and heat treatment to cause carbide precipitation in gamma/gamma prime-delta eutectic alloys
In an attempt to improve their longitudinal shear strength, several directionally solidified eutectic alloy compositions with minor element modifications were pact, carburized, and heat treated to provide selective carbide precipitation at the cell and grain boundaries. The directionally solidified Ni-17.8 Nb-6Cr-2.5Al-3Ta (weight percent) alloy was selected for the shear strength evaluation because it showed the shallowest delta-denuded zone at the carburized surface. The carburization-carbide precipitation treatment, however, did not appear to improve the longitudinal shear strength of the alloy
Shear strength properties of wet granular materials
We investigate shear strength properties of wet granular materials in the
pendular state (i.e. the state where the liquid phase is discontinuous) as a
function of water content. Sand and glass beads were wetted and tested in a
direct shear cell and under various confining pressures. In parallel, we
carried out three-dimensional molecular dynamics simulations by using an
explicit equation expressing capillary force as a function of interparticle
distance, water bridge volume and surface tension. We show that, due to the
peculiar features of capillary interactions, the major influence of water
content over the shear strength stems from the distribution of liquid bonds.
This property results in shear strength saturation as a function of water
content. We arrive at the same conclusion by a microscopic analysis of the
shear strength. We propose a model that accounts for the capillary force, the
granular texture and particle size polydispersity. We find fairly good
agreement of the theoretical estimate of the shear strength with both
experimental data and simulations. From numerical data, we analyze the
connectivity and anisotropy of different classes of liquid bonds according to
the sign and level of the normal force as well as the bond direction. We find
that weak compressive bonds are almost isotropically distributed whereas strong
compressive and tensile bonds have a pronounced anisotropy. The probability
distribution function of normal forces is exponentially decreasing for strong
compressive bonds, a decreasing power-law function over nearly one decade for
weak compressive bonds and an increasing linear function in the range of
tensile bonds. These features suggest that different bond classes do not play
the same role with respect to the shear strength.Comment: 12 page
Tensile & shear strength of porous dust agglomerates
Context.Within the sequential accretion scenario of planet formation, planets
are build up through a sequence sticking collisions. The outcome of collisions
between porous dust aggregates is very important for the growth from very small
dust particles to planetesimals. In this work we determine the necessary
material properties of dust aggregates as a function the porosity.
Aims: Continuum models such as SPH that are capable of simulating collisions
of macroscopic dust aggregates require a set of material parameters. Some of
them such as the tensile and shear strength are difficult to obtain from
laboratory experiments. The aim of this work is to determine these parameters
from ab-initio molecular dynamics simulations.
Methods: We simulate the behavior of porous dust aggregates using a detailed
micro-physical model of the interaction of spherical grains that includes
adhesion forces, rolling, twisting, and sliding. Using different methods of
preparing the samples we study the strength behavior of our samples with
varying porosity and coordination number of the material.
Results: For the tensile strength, we can reproduce data from laboratory
experiments very well. For the shear strength, there are no experimental data
available. The results from our simulations differ significantly from previous
theoretical models, which indicates that the latter might not be sufficient to
describe porous dust aggregates.
Conclusions: We have provided functional behavior of tensile and shear
strength of porous dust aggregates as a function of the porosity that can be
directly applied in continuum simulations of these objects in planet formation
scenarios.Comment: Accepted for publication in A&
Shear strength of metal - SiO2 contacts
The strength of the bond between metals and SiO2 was studied by measuring the static coefficient of friction of metals contacting alpha-quartz in ultrahigh vacuum. It was found that copper with either chemisorbed oxygen, nitrogen, or sulphur exhibited higher contact strength on stoichiometric SiO2 than did clean copper. Since the surface density of states induced by these species on copper is similar, it appears that the strength of the interfacial bond can be related to the density of states on the metal surface
Tensile and shear strength of adhesives
This experiment is conducted in a freshman-level course: Introduction to Engineering Materials. There are no prerequisites for the course although students should have some knowledge of basic algebra. The objectives are to tension and shear test adhesives and to determine the tensile and shear properties of adhesives. Details of equipment of procedure are given
Shear strength of fillet welds in aluminum alloy 2219
Fillet size is discussed in terms of theoretical or design dimensions versus as-welded dimensions, drawing attention to the inherent conservatism in the design load sustaining capabilities of fillet welds. Emphasis is placed on components for the solid rocket motor, external tank, and other aerospace applications. Problems associated with inspection of fillet welds are addresses and a comparison is drawn between defect counts obtained by radiographic inspection and by visual examination of the fracture plane. Fillet weld quality is related linearly to ultimate shear strength. Correlation coefficients are obtained by simple straight line regression analysis between the variables of ultimate shear strength and accumulative discontinuity summation. Shear strength allowables are found to be equivalent to 57 percent of butt weld A allowables (F sub tu.
Tribological properties of boron nitride synthesized by ion beam deposition
The adhesion and friction behavior of boron nitride films on 440 C bearing stainless steel substrates was examined. The thin films containing the boron nitride were synthesized using an ion beam extracted from a borazine plasma. Sliding friction experiments were conducted with BN in sliding contact with itself and various transition metals. It is indicated that the surfaces of atomically cleaned BN coating film contain a small amount of oxides and carbides, in addition to boron nitride. The coefficients of friction for the BN in contact with metals are related to the relative chemical activity of the metals. The more active the metal, the higher is the coefficient of friction. The adsorption of oxygen on clean metal and BN increases the shear strength of the metal - BN contact and increases the friction. The friction for BN-BN contact is a function of the shear strength of the elastic contacts. Clean BN surfaces exhibit relatively strong interfacial adhesion and high friction. The presence of adsorbates such as adventitious carbon contaminants on the BN surfaces reduces the shear strength of the contact area. In contrast, chemically adsorbed oxygen enhances the shear strength of the BN-BN contact and increases the friction
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