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Surface Displacements (surface + displacement)

Distribution by Scientific Domains

Polymers and Materials Science	35%
Engineering	29%

Selected Abstracts

Fatigue damage analysis in a duplex stainless steel by digital image correlation technique

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2008
A. EL BARTALI
ABSTRACT Strain field measurements by digital image correlation today offer new possibilities for analysing the mechanical behaviour of materials in situ during mechanical tests. The originality of the present study is to use this technique on the micro-structural scale, in order to understand and to obtain quantitative values of the fatigue surface damage in a two-phased alloy. In this paper, low-cycle fatigue damage micromechanisms in an austenitic-ferritic stainless steel are studied. Surface damage is observed in real time, with an in situ microscopic device, during a low-cycle fatigue test performed at room temperature. Surface displacement and strain fields are calculated using digital image correlation from images taken during cycling. A detailed analysis of optical images and strain fields measured enables us to follow precisely the evolution of surface strain fields and the damage micromechanisms. Firstly, strain heterogeneities are observed in austenitic grains. Initially, the austenitic phase accommodates the cyclic plastic strain and is then followed by the ferritic phase. Microcrack initiation takes place at the ferrite/ferrite grain boundaries. Microcracks propagate to the neighbouring austenitic grains following the slip markings. Displacement and strain gradients indicate probable microcrack initiation sites. [source]

Finite element analysis of corner point displacements and stress intensity factors for narrow notches in square sheets and plates

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2000
L. P. Pook
It is possible to model a crack as a narrow parallel-sided notch with a semicircular tip. Surface displacements of narrow notches in the vicinity of a corner point where the notch tip intersects a free surface were investigated, using finite element analysis, for each of the three modes of crack tip surface displacement. Some reasonably accurate relevant stress intensity factors were determined by analysis of notch tip stresses. The extent of corner regions in which stress intensity measures, rather than stress intensity factors, dominate crack tip stresses was determined by analysis of the notch surface displacements and of relevant stress intensity factors. Under nominal Mode III loading corner point effects are local, but under nominal Mode I and nominal Mode II loadings they are a combination of local and global effects. Volterra distorsioni are useful in the description of crack, and narrow notch, surface displacements under load. [source]

Surface displacements due to batter piles driven in cross-anisotropic media

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2008
Cheng-Der Wang
Abstract This article derives the closed-form solutions for estimating the vertical surface displacements of cross-anisotropic media due to various loading types of batter piles. The loading types include an embedded point load for an end-bearing pile, uniform skin friction, and linear variation of skin friction for a friction pile. The planes of cross-anisotropy are assumed to be parallel to the horizontal ground surface. The proposed solutions are never mentioned in literature and can be developed from Wang and Liao's solutions for a horizontal and vertical point load embedded in the cross-anisotropic half-space. The present solutions are identical with Wang's solutions when batter angle equals to 0°. In addition, the solutions indicate that the surface displacements in cross-anisotropic media are influenced by the type and degree of material anisotropy, angle of inclination, and loading types. An illustrative example is given at the end of this article to investigate the effect of the type and degree of soil anisotropy (E/E,, G,/E,, and ,/,,), pile inclination (,), and different loading types (a point load, a uniform skin friction, and a linear variation of skin friction) on vertical surface displacements. Results show that the displacements accounted for pile batter are quite different from those estimated from plumb piles, both driven in cross-anisotropic media. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Solifluction processes in an area of seasonal ground freezing, Dovrefjell, Norway

PERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2008
Charles Harris
Abstract Continuous monitoring of soil temperatures, frost heave, thaw consolidation, pore water pressures and downslope soil movements are reported from a turf-banked solifluction lobe at Steinhøi, Dovrefjell, Norway from August 2002 to August 2006. Mean annual air temperatures over the monitored period were slightly below 0°C, but mean annual ground surface temperatures were around 2°C warmer, due to the insulating effects of snow cover. Seasonal frost penetration was highly dependent on snow thickness, and at the monitoring location varied from 30,38,cm over the four years. The shallow annual frost penetration suggests that the site may be close to the limit of active solifluction in this area. Surface solifluction rates over the period 2002,06 ranged from 0.5,cm yr,1 at the rear of the lobe tread to 1.6,cm yr,1 just behind the lobe front, with corresponding soil transport rates of 6,cm3,cm,1 yr,1 and 46,cm3,cm,1 yr,1. Pore water pressure measurements indicated seepage of snowmelt beneath seasonally frozen soil in spring with artesian pressures beneath the confining frozen layer. Soil thawing was associated with surface settlement and downslope soil displacements, but following clearance of the frozen ground, later soil surface settlement was accompanied by retrograde movement. Summer rainfall events caused brief increases in pore pressure, but no further soil movement. Surface displacements exceeded maximum potential frost creep values and it is concluded that gelifluction was an important component of slow near-surface mass movements at this site. Temporal and spatial variations in solifluction rates across the area are likely to be considerable and strongly influenced by snow distribution. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Finite element analysis of corner point displacements and stress intensity factors for narrow notches in square sheets and plates

Application of SAR interferometry to a large thrust deformation: the 1999 Mw= 7.6 Chichi earthquake in central Taiwan

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2004
C. P. Chang
SUMMARY Application of the interferometric method to four ERS2-SAR images acquired before and after the 1999 Chichi earthquake has allowed determination of the coseismic surface displacement in the footwall area of the Chelungpu fault. The interferometric results revealed a relative shortening in the round trip distance between the radar antenna and the ground of the footwall side of Chelungpu fault, during the earthquake. This shortening progressively increased from the west to the east and reaches the maximum amount of approximately 26 cm near the central segment of the Chelungpu fault. Our interferometric results have been precisely examined using a dense GPS network in the investigated area. We mapped the GPS coseismic measurements into the radar line of sight and implemented a forward simulation of SAR interferogram from this synthesized result to control our unwrapping performance. In this study, these two observations are compared with a 3-D dislocation model of the fault. Finally, a deformation analysis based on our interferometric result has indicated that a segment with irregular deformation behaviour can be distinguished in the footwall area of the Chelungpu fault. This segment may result from either the influence of inherited basement faults or the presence of a structural terrace that provide local opportunities for superficial deformation. [source]

Finite element analysis of corner point displacements and stress intensity factors for narrow notches in square sheets and plates

Viscoelastic,afterslip concurrence: a possible mechanism in the early post-seismic deformation of the Mw 7.6, 1999 Chi-Chi (Taiwan) earthquake

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004
Shyh-Yang Sheu
SUMMARY Observed coseismic data as well as 97 days of post-seismic GPS data for the Chi-Chi earthquake are used as constraints in the modelling of crustal evolution using the 3-D finite-element method. First, the coseismic GPS data are used to justify the use of the elastic earth model and the source rupture model. Subsequently, the most likely rheological model is determined by analysing several modelled time-dependent displacements for various viscosity structures. The range of viscosities of the lower crust in central Taiwan is determined in advance from laboratory measurements and the long-term strain rate. The estimated viscosity of 5.0 × 1017 Pa s seems to be very low and a relaxation time of 116 days seems very short, but the latter approximates the GPS measurement of 86 days. Since earlier studies have indicated that both the viscoelastic response model and the afterslip model may affect post-seismic deformation, we compare theoretical surface displacements for each of the two models that we evaluate. The results reveal that there is little doubt that while neither of these models alone is able to predict the GPS measurements well in a 97-day period, the combination of the two models improves the predictions considerably. We conclude that the afterslip mainly dominated Chi-Chi post-seismic deformation in the rupture area while the viscoelastic model did so elsewhere. [source]

On the use of dislocations to model interseismic strain and stress build-up at intracontinental thrust faults

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2001
J. Vergne
Summary Creeping dislocations in an elastic half-space are commonly used to model interseismic deformation at subduction zones, and might also apply to major intracontinental thrust faults such as the Main Himalayan Thrust. Here, we compare such models with a more realistic 2-D finite element model that accounts for the mechanical layering of the continental lithosphere and surface processes, and that was found to fit all available constraints on interseismic and long-term surface displacements. These can also be fitted satisfactorily from dislocation models. The conventional back-slip model, commonly used for subduction zones, may, however, lead to a biased inference about the geometry of the locked portion of the thrust fault. We therefore favour the use of a creeping buried dislocation that simulates the ductile shear zone in the lower crust. A limitation of dislocation models is that the mechanical response of the lithosphere to the growth of the topography by bending of the elastic cores and ductile flow in the lower crust cannot be easily introduced. Fortunately these effects can be neglected because we may assume, to first order, a stationary topography. Moreover, we show that not only can dislocation models be used to adjust surface displacements but, with some caution, they can also provide a physically sound rationale to interpret interseismic microseismicity in terms of stress variations. [source]

Displacement and stress distributions under a uniform inclined rectangular load on a cross-anisotropic geomaterial

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2009
Cheng-Der Wang
Abstract In practical engineering, an applied rectangular area load is not often horizontally or vertically distributed but is frequently inclined at a certain angle with respect to the horizontal and vertical axes. Thus, the solutions of displacements and stresses due to such a load are essential to the design of foundations. This article yields the analytical solutions of displacements and stresses subjected to a uniform rectangular load that inclines with respect to the horizontal and vertical axes, resting on the surface of a cross-anisotropic geomaterial. The planes of cross-anisotropy are assumed to be parallel to the horizontal ground surface. The procedures to derive the solutions can be integrated the modified point load solutions, which are represented by several displacement and stresses elementary functions. Then, upon integrations, the displacement and stress integral functions resulting from a uniform inclined rectangular load for (1) the displacements at any depth, (2) the surface displacements, (3) the average displacements in a given layer, (4) the stresses at any depth, and (5) the average stresses in a given layer are yielded. The proposed solutions are clear and concise, and they can be employed to construct a series of calculation charts. In addition, the present solutions clarify the load inclinations, the dimensions of a loaded rectangle, and the analyzed depths, and the type and degree of geomaterial anisotropy profoundly affect the displacements and stresses in a cross-anisotropic medium. Parametric results show that the load inclination factor should be considered when an inclined rectangular load uniformly distributed on the cross-anisotropic material. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Surface displacements due to batter piles driven in cross-anisotropic media

A ,-coordinate three-dimensional numerical model for surface wave propagation

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2002
Pengzhi Lin
Abstract A three-dimensional numerical model based on the full Navier,Stokes equations (NSE) in , -coordinate is developed in this study. The , -coordinate transformation is first introduced to map the irregular physical domain with the wavy free surface and uneven bottom to the regular computational domain with the shape of a rectangular prism. Using the chain rule of partial differentiation, a new set of governing equations is derived in the , -coordinate from the original NSE defined in the Cartesian coordinate. The operator splitting method (Li and Yu, Int. J. Num. Meth. Fluids 1996; 23: 485,501), which splits the solution procedure into the advection, diffusion, and propagation steps, is used to solve the modified NSE. The model is first tested for mass and energy conservation as well as mesh convergence by using an example of water sloshing in a confined tank. Excellent agreements between numerical results and analytical solutions are obtained. The model is then used to simulate two- and three-dimensional solitary waves propagating in constant depth. Very good agreements between numerical results and analytical solutions are obtained for both free surface displacements and velocities. Finally, a more realistic case of periodic wave train passing through a submerged breakwater is simulated. Comparisons between numerical results and experimental data are promising. The model is proven to be an accurate tool for consequent studies of wave-structure interaction. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Elastic Indentation Response of Float Glass Surfaces

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010
Andrea M. Muller
Instrumented Hertzian indentation was used to evaluate the reduced elastic modulus and cone-crack initiation forces for the as-received surfaces of commercial float glasses. Custom-built indentation equipment with the capability of acoustic emission detection was used to monitor continuously the load and depth of penetration at the microscopic scale for forces up to 1 kN. Equipment verification was performed using a reference material, GE 124. The air and tin surfaces of commercial soda,lime,silica and borosilicate float glasses were tested to determine any difference in indentation response for the elastic and fracture behavior of as-received surfaces. Information obtained from the analysis of the load,displacement curves and from the visual inspection of the indentation sites was used to determine the elastic modulus, and the conditions for the onset of cone cracking as a function of surface roughness. The reduced modulus results were verified using additional equipment that allowed the in situ observation of the contact area during loading and unloading. The results showed that there was no difference in the reduced modulus data for the air and tin surfaces for the range of surface displacements studied. The same conclusions were found for cone-cracking loads on as-received surfaces but tests on abraded surfaces showed that the tin surfaces had slightly more resistance to cone cracking than the air surfaces. [source]

Remote sensing of permafrost-related problems and hazards

PERMAFROST AND PERIGLACIAL PROCESSES, Issue 2 2008
Andreas Kääb
Abstract Modern remote sensing techniques can help in the assessment of permafrost hazards in high latitudes and cold mountains. Hazard development in these areas is affected by process interactions and chain reactions, the ongoing shift of cryospheric hazard zones due to atmospheric warming, the large spatial scales involved and the remoteness of many permafrost-related threats. This paper reviews ground-based, airborne and spaceborne remote sensing methods suitable for permafrost hazard assessment and management. A wide range of image classification and change detection techniques support permafrost hazard studies. Digital terrain models (DTMs) derived from optical stereo, synthetic aperture radar (SAR) or laser scanning data are some of the most important data sets for investigating permafrost-related mass movements, thaw and heave processes, and hydrological hazards. Multi-temporal optical or SAR data are used to derive surface displacements on creeping and unstable frozen slopes. Combining DTMs with results from spectral image classification, and with multi-temporal data from change detection and displacement measurements significantly improves the detection of hazard potential. Copyright © 2008 John Wiley & Sons, Ltd. [source]