4,570 research outputs found
Development of Stresses in Cohesionless Poured Sand
The pressure distribution beneath a conical sandpile, created by pouring sand
from a point source onto a rough rigid support, shows a pronounced minimum
below the apex (`the dip'). Recent work of the authors has attempted to explain
this phenomenon by invoking local rules for stress propagation that depend on
the local geometry, and hence on the construction history, of the medium. We
discuss the fundamental difference between such approaches, which lead to
hyperbolic differential equations, and elastoplastic models, for which the
equations are elliptic within any elastic zones present .... This displacement
field appears to be either ill-defined, or defined relative to a reference
state whose physical existence is in doubt. Insofar as their predictions depend
on physical factors unknown and outside experimental control, such
elastoplastic models predict that the observations should be intrinsically
irreproducible .... Our hyperbolic models are based instead on a physical
picture of the material, in which (a) the load is supported by a skeletal
network of force chains ("stress paths") whose geometry depends on construction
history; (b) this network is `fragile' or marginally stable, in a sense that we
define. .... We point out that our hyperbolic models can nonetheless be
reconciled with elastoplastic ideas by taking the limit of an extremely
anisotropic yield condition.Comment: 25 pages, latex RS.tex with rspublic.sty, 7 figures in Rsfig.ps.
Philosophical Transactions A, Royal Society, submitted 02/9
Viscoplastic constitutive models for zero-thickness interface elements, formulation and applications
An energy-based work-softening visco-plastic model for zero-thickness interface elements has been developed as an extension of an existing elastic-perfectly-viscoplastic formulation. In the inviscid limit the model also collapses into a well-established fracture mechanics-based elasto-plastic model. The new model is verified satisfactorily for common loading cases at interfaces such as pure tension (mode I) opening, and shear-compression (mixed-mode) sliding, with results that in the long term match the predictions of the fracture mechanics inviscid model
Viscoplastic constitutive models for zero-thickness interface elements, formulation and applications
An energy-based work-softening visco-plastic model for zero-thickness interface elements has been developed as an extension of an existing elastic-perfectly-viscoplastic formulation. In the inviscid limit the model also collapses into a well-established fracture mechanics-based elasto-plastic model. The new model is verified satisfactorily for common loading cases at interfaces such as pure tension (mode I) opening, and shear-compression (mixed-mode) sliding, with results that in the long term match the predictions of the fracture mechanics inviscid model.Postprint (published version
Experimental investigation of the elastoplastic response of aluminum silicate spray dried powder during cold compaction
Mechanical experiments have been designed and performed to investigate the
elasto-plastic behaviour of green bodies formed from an aluminum silicate spray
dried powder used for tiles production. Experiments have been executed on
samples obtained from cold compaction into a cylindrical mould and include:
uniaxial strain, equi-biaxial flexure and high-pressure triaxial
compression/extension tests. Two types of powders have been used to realize the
green body samples, differing in the values of water content, which have been
taken equal to those usually employed in the industrial forming of traditional
ceramics. Yielding of the green body during compaction has been characterized
in terms of yield surface shape, failure envelope, and evolution of cohesion
and void ratio with the forming pressure, confirming the validity of previously
proposed constitutive models for dense materials obtained through cold
compaction of granulates.Comment: 17 pages; Journal of the European Ceramic Society, 201
Numerical analysis of rapid drawdown: applications in real cases
In this study, rapid drawdown scenarios were analyzed by means of numerical examples as well as modeling of real cases with in situ measurements. The aim of the study was to evaluate different approaches available for calculating pore water pressure distributions during and after a drawdown. To do that, a single slope subjected to a drawdown was first analyzed under different calculation alternatives, and numerical results were discussed. Simple methods, such as undrained analysis and pure flow analysis, implicitly assuming a rigid soil skeleton, lead to significant errors in pore water pressure distributions when compared with coupled flow-deformation analysis. A similar analysis was performed for the upstream slope of the Glen Shira Dam, Scotland, and numerical results were compared with field measurements during a controlled drawdown. Field records indicate that classical undrained calculations are conservative but unrealistic. Then, a recent case of a major landslide triggered by a rapid drawdown in a reservoir was interpreted. A key aspect of the case was the correct characterization of permeability of a representative soil profile. This was achieved by combining laboratory test results and a back analysis of pore water pressure time records during a period of reservoir water level fluctuations. The results highlight the difficulty of predicting whether the pore water pressure is overestimated or underestimated when using simplified approaches, and it is concluded that predicting the pore water pressure distribution in a slope after a rapid drawdown requires a coupled flow-deformation analysis in saturated and unsaturated porous media.Peer ReviewedPostprint (published version
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Buried shallow fault slip from the South Napa earthquake revealed by near-field geodesy.
Earthquake-related fault slip in the upper hundreds of meters of Earths surface has remained largely unstudied because of challenges measuring deformation in the near field of a fault rupture. We analyze centimeter-scale accuracy mobile laser scanning (MLS) data of deformed vine rows within ±300 m of the principal surface expression of the M (magnitude) 6.0 2014 South Napa earthquake. Rather than assuming surface displacement equivalence to fault slip, we invert the near-field data with a model that allows for, but does not require, the fault to be buried below the surface. The inversion maps the position on a preexisting fault plane of a slip front that terminates ~3 to 25 m below the surface coseismically and within a few hours postseismically. The lack of surface-breaching fault slip is verified by two trenches. We estimate near-surface slip ranging from ~0.5 to 1.25 m. Surface displacement can underestimate fault slip by as much as 30%. This implies that similar biases could be present in short-term geologic slip rates used in seismic hazard analyses. Along strike and downdip, we find deficits in slip: The along-strike deficit is erased after ~1 month by afterslip. We find no evidence of off-fault deformation and conclude that the downdip shallow slip deficit for this event is likely an artifact. As near-field geodetic data rapidly proliferate and will become commonplace, we suggest that analyses of near-surface fault rupture should also use more sophisticated mechanical models and subsurface geomechanical tests
An elastoplastic analysis of a uniaxially loaded sheet with an interference-fit bolt
The stresses and strains in a uniaxially loaded sheet with an unloaded interference-fit bolt were calculated by an elastoplastic finite-element analysis. The material properties represented a 7075-T6 aluminum alloy sheet and a steel bolt. The analysis considered the two ideal cases of no slip and no friction at the bolt-sheet interface for a single combination of bolt diameter, interference level, and cyclic loading. When the bolt was inserted, the sheet deformed plastically near the hole; the first tensile load cycle produced additional yielding, but subsequent cycles to the same level caused only elastic cyclic stresses. These stresses together with fatigue data for unnotched specimens were used to estimate crack initiation periods and initiation sites. The cases analyzed with interference-fit bolts were predicted to have crack initiation periods which were about 50 times that for a clearance-fit bolt. Crack initiation was predicted to occur on the transverse axis at a distance of about one radius from the hole
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