Search results for "CREEP"
showing 10 items of 167 documents
The influence of strain rate and presence of dispersed second phases on the deformation behaviour of polycrystalline D2O ice
2018
ABSTRACTThis contribution discusses results obtained from 3-D neutron diffraction and 2-D fabric analyser in situ deformation experiments on laboratory-prepared polycrystalline deuterated ice and ice containing a second phase. The two-phase samples used in the experiments are composed of an ice matrix with (1) air bubbles, (2) rigid, rhombohedral-shaped calcite and (3) rheologically soft, platy graphite. Samples were tested at 10°C below the melting point of deuterated ice at ambient pressures, and two strain rates of 1 × 10−5 s−1 (fast) and 2.5 × 10−6 s−1 (medium). Nature and distribution of the second phase controlled the rheological behaviour of the ice by pinning grain boundary migratio…
Microstructure and fabric development in ice: Lessons learned from in situ experiments and implications for understanding rock evolution
2014
Abstract In this contribution we present a review of the evolution of microstructures and fabric in ice. Based on the review we show the potential use of ice as an analogue for rocks by considering selected examples that can be related to quartz-rich rocks. Advances in our understanding of the plasticity of ice have come from experimental investigations that clearly show that plastic deformation of polycrystalline ice is initially produced by basal slip. Interaction of dislocations play an essential role for dynamic recrystallization processes involving grain nucleation and grain-boundary migration during the steady-state flow of ice. To support this review we describe deformation in polycr…
Deformation of melt-bearing systems—insight from in situ grain-scale analogue experiments
2005
Abstract The deformation behaviour of partially molten rocks was investigated using in situ analogue experiments with norcamphor+ethanol, as well as partially molten KNO 3 +LiNO 3 . Three general deformation regimes could be distinguished during bulk pure shear deformation. In regime I, above ca. 8–10 vol.% liquid (melt) fraction ( ϕ bulk ), deformation is by compaction, distributed granular flow, and grain boundary sliding (GBS). At ϕ bulk ϕ bulk (regime III), grains form a coherent framework that deforms by grain boundary migration accommodated dislocation creep, associated with efficient segregation of remaining liquid. The transition liquid fraction between regimes I and II ( ϕ LT ) dep…
Shear banding mechanism of plastic deformation in LiF irradiated with swift heavy ions
2012
The effect of ion irradiation on the behavior of plastic deformation at micro- and nanoindentation on (001) face of LiF has been investigated. The irradiation was performed using heavy ions (U, Au, Ti and S) with energy in the range from 3 MeV to 2 GeV at fluences up to 5x1013 ions/cm2. In non-irradiated LiF, the indentation produces dislocation gliding on the {110} planes along the and directions. At high fluence irradiation, the resource of the dislocation slip along the preferable directions becomes exhausted due to immobilization of dislocations by radiation defects and their aggregates. The present study demonstrates the change of the mechanism of plastic deformation from homogenous di…
Cataclastic solution creep of very soluble brittle salt as a rock analogue
1998
Until about the late 1960s, macroscopically ductile deformation of quartz was seen as a microscopically cataclastic process by most geologists (cf. the origin of the name ‘mylonite’). Undulatory extinction, subgrains, recrystallised grains and even crystallographic preferred orientations were interpreted as due to water-assisted brittle deformation processes. Nowadays, by contrast, the occurrence of these optical microstructures is considered as conclusive and unequivocal evidence for dislocation creep. The abundance of these microstructures in naturally deformed rocks lead to the conclusion that dislocation creep is the most important ductile deformation mechanism within the Earth’s crust.…
Forest Fragmentation Increases Nest Predation in the Eurasian Treecreeper
2004
We used long-term breeding data to monitor the influences of fragmentation and habitat composi- tion at different spatial scales on the reproductive success of Eurasian Treecreepers (Certhia familiaris) breeding in nest boxes. We collected data from the same forest patches (2.7-65.1 ha in size) during seven breeding sea- sons. Nest predation varied considerably over the years and was the primary cause of nesting failure (mean annual rate of 21.6 ± 12.8%). Nest predation explained most of the variation in fledgling production during the study period. Landscape-level fragmentation (radius of 500 m from territory center) affected nest predation more than did fragmentation on the territory scal…
Conceptual design of prestressed slab bridges through one-way flexural load balancing
2013
In this paper a study on prestressed concrete slab bridges is presented. A design philosophy based on the concept of load balancing through prestressing is proposed in order to minimize the effects of delayed deformations due to creep. Aspects related to the stress redistribution inside these bridges for time-dependent phenomena are analyzed and discussed, by applying the principles of aging linear visco-elasticity. Prestressing is seen as an equivalent external load which counterbalances the permanent loads applied to the bridge, nullifying the elastic deflections due to sustained loads, and thus avoiding the related delayed deformations. An optimization of the structural behavior through …
Serviceability and Ultimate Safety Checks of SegmentalConcrete Bridges through N-M and M-V Interaction Domains
2015
In current engineering practice, safety checks on serviceability and determinations of ultimate limit states of segmental bridges built by cantilevering are generally performed, either considering separately the contributions of axial force N, bending moment M, and shear force V, or considering the interaction effects through approximate expressions supplied by building codes. During construction stages and service life, the interaction between internal forces can be of fundamental importance in establishing the actual degree of structural safety and, for this reason, a different philosophy for performing checks in segmental bridges is proposed in this paper, plotting N-M and M-V interactio…
The influence of time-dependent phenomena in segmental construction of concrete cable-stayed bridges
2011
Construction stages of a cable-stayed bridge are characterized by a sequence in which geometric configuration, restraints and consequently stress and strain patterns vary many times till the final arrangement is achieved. When construction of concrete bridges is made by cantilever method the influence of time-dependent phenomena becomes significant. In this study an evaluation of stay stressing procedures is given by taking into account creep and shrinkage in cantilever construction of concrete cable-stayed bridges. A methodology of stay stressing is proposed with the final target of reaching the desired geometric configuration. Comparison with classical analyses performed by backward metho…
Risk evaluation and creep in conventional conductors caused by high temperature operation
2008
The advent of electricity market deregulation, the increased operating and overload temperatures of transmission line conductors have caused concern among TSOs (Transmission System Operators) and DSOs (Distribution System Operators) about the effect of elevated temperatures on conventional bare conductors of existing line. Nowadays building new lines is very difficult cause of increased costs to obtain rights of way, public intervention, etc.... Cost and lead times required to place new lines into service are now increased and the business in electric market is reduced for the limited possibility of transmission. Therefore, utilities are attempting to gain as much capacity as possible modif…