Stress field

About: Stress field is a research topic. Over the lifetime, 11926 publications have been published within this topic receiving 226417 citations.

Contribution of gravitational potential energy differences to the global stress field

Abstract: SUMMARY Modelling the lithospheric stress field has proved to be an efficient means of determining the role of lithospheric versus sublithospheric buoyancies and also of constraining the driving forces behind plate tectonics. Both these sources of buoyancies are important in generating the lithospheric stress field. However, these sources and the contribution that they make are dependent on a number of variables, such as the role of lateral strength variation in the lithosphere, the reference level for computing the gravitational potential energy per unit area (GPE) of the lithosphere, and even the definition of deviatoric stress. For the mantle contribution, much depends on the mantle convection model, including the role of lateral and radial viscosity variations, the spatial distribution of density buoyancies, and the resolution of the convection model. GPE differences are influenced by both lithosphere density buoyancies and by radial basal tractions that produce dynamic topography. The global lithospheric stress field can thus be divided into (1) stresses associated with GPE differences (including the contribution from radial basal tractions) and (2) stresses associated with the contribution of horizontal basal tractions. In this paper, we investigate only the contribution of GPE differences, both with and without the inferred contribution of radial basal tractions. We use the Crust 2.0 model to compute GPE values and show that these GPE differences are not sufficient alone to match all the directions and relative magnitudes of principal strain rate axes, as inferred from the comparison of our depth integrated deviatoric stress tensor field with the velocity gradient tensor field within the Earth's plate boundary zones. We argue that GPE differences calibrate the absolute magnitudes of depth integrated deviatoric stresses within the lithosphere; shortcomings of this contribution in matching the stress indicators within the plate boundary zones can be corrected by considering the contribution from horizontal tractions associated with density buoyancy driven mantle convection. Deviatoric stress magnitudes arising from GPE differences are in the range of 1–4 TN m−1, a part of which is contributed by dynamic topography. The EGM96 geoid data set is also used as a rough proxy for GPE values in the lithosphere. However, GPE differences from the geoid fail to yield depth integrated deviatoric stresses that can provide a good match to the deformation indicators. GPE values inferred from the geoid have significant shortcomings when used on a global scale due to the role of dynamically support of topography. Another important factor in estimating the depth integrated deviatoric stresses is the use of the correct level of reference in calculating GPE. We also elucidate the importance of understanding the reference pressure for calculating deviatoric stress and show that overestimates of deviatoric stress may result from either simplified 2-D approximations of the thin sheet equations or the assumption that the mean stress is equal to the vertical stress.

Stress field associated with the rupture of the 1992 Landers, California, earthquake and its implications concerning the fault strength at the onset of the earthquake

Abstract: We investigate the space and time history of the shear stress produced on the fault during the 1992 Landers earthquake. The stress is directly calculated from the tomographic image of slip on the fault derived from near-source strong motion data. The results obtained shed some light on why the earthquake rupture cascaded along a series of previously distinct fault segments to produce the largest earthquake in California in over 40 years. Rupture on the 30 km long northernmost segment of the fault was triggered by a large dynamic increase of the stress field, of the order of 20 to 30 MPa, produced by the rupturing of the adjacent fault segments. Such a large increase was necessary to overcome the static friction on this strand of the fault, unfavorably oriented in today's tectonic stress field. This misorientation eventually led to the arrest of rupture. The same mechanism explains why rupture broke only a small portion of the Johnson Valley fault on which the earthquake originally started, before jumping to an adjacent fault more favorably oriented. We conclude from these results that the dynamic stress field could not sustain and drive the rupture along the strongly misoriented NW-SE strands of the preexisting fault system. Instead, the dynamic stress field produced new fractures favorably oriented in a N-S direction and connecting parts of the old fault system.

A converging channel rheometer for the measurement of extensional viscosity

Abstract: The development of an extensional rheometer for polymer solutions is described. The test section is a converging channel through which a test fluid is pushed at high Reynolds numbers, and several pressure drops along the channel are measured with flush-mounted transducers. The high Reynolds numbers ensure a core flow of purely extensional motion and the channel is shaped to produce a constant rate of extension. Analysis of the stress field shows that the pressure drop is equal to the normal stress difference τzz - τrr in the core, plus other terms which are calculated. The calculations are based on an analytical solution for inelastic power-law fluids, and the calculations were verified by finite element computations. Extensional viscosity measurements were made for a solution of a copolymer of PMMA in an organic solvent. The data show that extensional viscosity increases with extensional rate to about the 3/2 power and, at a fixed extensional rate, extensional viscosity increases roughly as the total fluid strain.

A new methodology based on X-ray micro-tomography to estimate stress concentrations around inclusions in high strength steels

Abstract: This work aims at improving the calculation of stress fields around non-metallic inclusions in high strength bearing steels. A new methodology is proposed, based on: (i) the determination of 3D morphologies of inclusions by X-ray micro-tomography imaging; (ii) the characterization of the mechanical properties of the inclusion by nano-indentation, and (iii) finite element (FE) calculations of the stress concentration induced by the inclusions. The methodology is applied to a calcium aluminate inclusion with cavities, located in a Hertzian stress field. The stress concentration appears to be strongly dependent on the orientation of the inclusion-cavity considered. The stress concentration fields obtained from realistic 3D shapes are compared to those obtained from simplified shapes of inclusions.