Stress field

Attention is here focused on the implementation of a coupled BEM–FEM procedure employing the BE method for the modelling of the near-crack region and the FEM for the far-field, where no singularities in the stress field are expected to arise. The symmetric variational version of the BE method is utilized, allowing to obtain a final linear system endowed with a symmetric matrix. With respect to 3D linear elastic fracture mechanics, the code developed is used to evaluate stress intensity factors for some benchmarks and simulate fracture propagation.

The model of inclined seam excavation is established acc ording to the deformation characteristics of inclined seam and the principles of FEA. It carried out numerical s imulation method to research rock mass movement, surface subsidence and distribution of stress, which simulated excavat ion with the ANSYS software, at the same time the basi c characteristics of rock movement and the correlative par ameters of surface subsidence are obtained. The ANSYS software can not only compute the deformation mechanism of surface subsidence, but also draw up the distribution contours of stress, the distribution contours of horizontal displace and vertical subsidence. The computing model visuall y displays the deformation and stress distribution of the o verburden rock board, coal strata and lower rock board. The deformation mechanism of surface subsidence provides a refe rence for inclined seam excavation under the building. The underground excavation of mine is the huge and complex system eng...

A detailed analytical and experimental investigation is presented to understand the dynamic fracture behavior of functionally graded materials (FGMs) under mode I and mixed mode loading conditions. Crack-tip stress, strain and displacement fields for a mixed mode crack propagating at an angle from the direction of property gradation were obtained through an asymptotic analysis coupled with a displacement potential approach. This was followed by a comprehensive series of experiments to gain further insight into the behavior of propagating cracks in FGMs. Dynamic photoelasticity coupled with high-speed photography was used to obtain crack tip velocities and dynamic stress fields around the propagating cracks. Birefringent coatings were used to conduct the photoelastic study due to the opaqueness of the FGMs. Dynamic fracture experiments were performed using different specimen geometries to develop a dynamic constitutive fracture relationship between the mode I dynamic stress intensity factor (K ID ) and crack-tip velocity ( ${\mathop a\limits^ \cdot }$ ) for FGMs with the crack moving in the direction of increasing fracture toughness. A similar ${\mathop a\limits^ \cdot }$ -K ID relation was also obtained for matrix material (polyester) for comparison purposes. The results obtained show that crack propagation velocities in FGMs were about 80% higher than the polyester matrix. Crack arrest toughness was found to be about 10% lower than the value of local fracture toughness in FGMs.

ABSTRACT The first-order South American intraplate stress field was modeled through a finite element analysis to evaluate the relative contribution of plate boundary forces and intraplate stress sources. The finite element mesh consisted of 3100 nodes in a network of 5993 equal-area triangular elements which provided a spatial resolution of about 1° at the equator. An important aspect of our modeling is the inclusion of topographic forces due to the cooling oceanic lithosphere along the Mid-Atlantic Ridge (e.g., ridge push), the continental margins along the east coast of Brazil and Argentina, and the elevated continental crust (e.g., the Andean Cordillera). Predicted intraplate stresses for two representations of the western collisional boundary forces are evaluated: pinned collisional boundaries and applied collisional boundary forces. Constraint for the modeling was provided by information about the orientation of the maximum horizontal compressive stress, SHmax, provided by 217 stress indicators from the World Stress Map Project as well as by SHmaxmagnitude estimates and torque information from previous investigations. Our modeling results demonstrate that the first-order features of the observed stress field can be explained with simple tectonic models which balance the torque acting on the plate either with a fixed western margin or drag forces applied along the base of the plate. The predicted intraplate stress field is characterized by a nearly uniform E-W SHmax orientation throughout most regions of the plate, with stress magnitudes generally less than 20 MPa averaged over a 100-km-thick lithosphere. Significant perturbation of this regional stress field occurs in the western part of the plate in response to forces associated with the high topography of the Andes. Although the magnitude of the collisional boundary forces acting along the western margin remains poorly constrained, we estimate a plausible upper bound on the force per unit length acting along the Peru-Chile Trench to be about 2.5×1012 Nm-1. While some of our models are consistent with a driving basal drag to balance the torques acting on the plate, the magnitude of the drag torque is small compared to the contribution from other sources of stress such as the ridge push force.

 Mount Rainier is one of the most seismically active volcanoes in the Cascade Range, with an average of one to two high-frequency volcano-tectonic (or VT) earthquakes occurring directly beneath the summit in a given month. Despite this level of seismicity, little is known about its cause. The VT earthquakes occur at a steady rate in several clusters below the inferred base of the Quaternary volcanic edifice. More than half of 18 focal mechanisms determined for these events are normal, and most stress axes deviate significantly from the regional stress field. We argue that these characteristics are most consistent with earthquakes in response to processes associated with circulation of fluids and magmatic gases within and below the base of the edifice.Circulation of these fluids and gases has weakened rock and reduced effective stress to the point that gravity-induced brittle fracture, due to the weight of the overlying edifice, can occur. Results from seismic tomography and rock, water, and gas geochemistry studies support this interpretation. We combine constraints from these studies into a model for the magmatic system that includes a large volume of hot rock (temperatures greater than the brittle–ductile transition) with small pockets of melt and/or hot fluids at depths of 8–18 km below the summit. We infer that fluids and heat from this volume reach the edifice via a narrow conduit, resulting in fumarolic activity at the summit, hydrothermal alteration of the edifice, and seismicity.

... 15,1985; accepted February 13,1986) Abstract Boullier, AM, Li geois, JP, Black, R., Fabre, J., Sauvage, M. and Bertrand, JM, 1986. ... Saharan belt, resulting from oceanic closure and oblique collision between the West-African Craton and the Tuareg-Nigerian shields around 600 ...

Sommario Scopo principale del presente lavoro è di analizzare e descrivere lo schema di funzionamento e lo stato tensionale di accoppiamenti albero mozzo realizzati per serraggio e presenti nelle sospensioni anteriori motociclistiche. Sono stati analizzati sia gli accoppiamenti tra il trapezio ed il gambale della sospensione (morsetti trapezio), realizzati mediante l'impiego di una o due viti di serraggio, sia gli accoppiamenti tra la gamba ed il perno ruota (morsetti gamba), con una vite di serraggio. Il modello di calcolo proposto per tali accoppiamenti è stato determinato utilizzando analisi agli elementi finiti in appoggio alla teoria classica di De Saint Venant, per ottenere un fattore teorico di concentrazione delle tensioni presente sul mozzo dovuto alla presenza di discontinuità geometriche, come le lamature ed i fori di alloggiamento delle viti. Il risultato principale consiste nel disporre di un modello di calcolo completo che permette di progettare, verificare ed ott...

This work examines experimentally how a viscous incompressible liquid modifies the behavior of a granular bulk in avalanche. A large and a small laboratory flume of identical length-to-width ratio have been constructed to initiate granular avalanche. Two types of monatomic spheres were used, preserving the ratio between the particle diameter and the flume width, with or without water to prepare

A closed-form stress plasticity solution is presented for gravitational and earthquake-induced earth pressures on retaining walls. The proposed solution is essentially an approximate yield-line approach, based on the theory of discontinuous stress fields, and takes into account the following parameters: (1) weight and friction angle of the soil material, (2) wall inclination, (3) backfill inclination, (4) wall roughness, (5) surcharge

... b) Source locations of induced microseismic events and compos-ite focal mechanisms for cluster events. ... towards a better understanding of the physical processes related to induced microseismicity at reservoir or ... Passive Seismic Monitoring of Natural and Induced Earthquakes ...