Local lithospheric stress distribution deduced by means of the total inversion algorithm and an objective classification method

New constraints on the seismotectonics and crustal structure of the Eastern Trans-Mexican Volcanic Belt based on local seismicity, focal mechanisms and a preliminary state of stress evaluation

Stable crack growth of axial surface flaws in pressure vessels

High strain rate constitutive and fracture characterization of AA7075-T6 sheet under various stress states

Using standard inversion algorithm, velocity and attenuation tomograms can show artifacts which compromise interpretation. These artifacts can be due to errors in borehole trajectory measurements, medium anisotropy, T<SUB>0</SUB> (initial time) or A<SUB>0</SUB> (initial amplitude) drifts. In order to cancel these artifacts, the error sources can be introduced as unknown parameters in inversion algorithms (Hollender, 1999). In this paper, we present results obtained with crosshole radar data, recorded in a limestone quarry. Using the appropriate algorithms, all the artifacts have been cancelled and tomograms show clearly subhorizontal structures in agreement with the quarry stratification. In our data set, results do not reveal significant trajectory error, and T<SUB>0</SUB> and A<SUB>0</SUB> drifts are low. However, the presence of a velocity and attenuation anisotropy appears clearly on the tomograms. In the case of attenuation tomograms, the high anisotropy rates could be explained by the cumulative effect of the partitioning of energy due to reflection and transmission mechanisms at interfaces, and medium anisotropy.

In order to know the local deformation and stress state near the contacting part of loaded tyre with the ground, a model case where a spherical balloon is compressed by two flat rigid plates from the opposite sides without friction, is analysed from the view-point of non-linear membrane theory. The so-called boundary layer solution is obtained. The local deformation and stress state can be explained by the boundary layer effect more precisely through the results of a nummerical example.

In this paper an experimental-numerical method, centred on flat-jack tests, is presented for the identification of local stress states and possibly deteriorated elastic properties of concrete in existing dams. It is shown herein that the synergistic combination of new pattern of flat-jack experiment, computer simulation of the test (by conventional finite elements) and inverse analysis allows to exploit experimental data more effectively than by the traditional procedure, and to achieve more information on material properties. In fact, at suitably chosen locations on the free surface of the monitored dam, all the components of local (plane) stress state and the elastic moduli in two orthogonal directions (including shear stiffness) can be estimated by the proposed method. The inverse problem in point is formulated as a sequence of two parameter identifications, i.e. as a bilevel (in the sense of Stackelberg) mathematical programming problem. The solution in a stochastic context is achieved by means of a modified Bayes technique, allowing to obtain, in a “batch” (non sequential) way, parameter estimates endowed with a covariance matrix which quantifies their degrees of confidence and correlations.

Despite great strides in developing physically motivated models for void growth, shape evolution and coalescence, a suitable treatment for void nucleation remains an open question. Accurate modeling of void nucleation is difficult within a Gurson-based framework due to the intrinsic assumption that the material does not contain any second-phase particles. Consequently, the nucleation models employed in these constitutive models are overly simplistic as the particle shape, composition, stress state and load-sharing are neglected, lumped into a single calibration parameter (Beremin 1981) or indirectly accounted for in a phenomenological manner (Chu and Needlman 1980). The lack of progress in developing physically sound nucleation models has not been for lack of effort but a result of the inherently complex nature of the nucleation process. Void nucleation is very difficult to capture experimentally since it is a relatively random and instantaneous event that cannot be captured in-situ without the aid of high resolution x-ray tomography. Additionally, the local stress state near a particle of interest is typically unknown, as well as the particle composition and mechanical properties. The nucleation mechanism can occur by debonding or particle cracking and is influenced by the particle size, shape, composition, distribution, strain rate and temperature. From an engineering perspective, one can clearly see the attraction in adopting a phenomenological nucleation model whose parameters can be adjusted to give good agreement with the experiment data. Nevertheless, there is ample opportunity to improve the physical foundation of the current nucleation models, especially in regards to percolation modeling.

Upon their cooling and solidification, significant thermal residual stresses can develop in short-fiber reinforced thermoplastics due to the mismatch in coefficient of thermal expansion between fiber and matrix. In this study we set out to investigate this effect numerically. The build-up of thermal residual stresses is modeled by expanding a well-established constitutive model, the Eindhoven glassy polymer (EGP) model, with thermal expansion. The experimentally measured thermal residual stresses can be described using an effective glass-transition temperature and a constant coefficient of thermal expansion without the need for complex equilibrium kinetics associated with the glass transition itself. Subsequently, the influence of thermal residual stress on the deformation behavior for a short-fiber reinforced thermoplastic is studied employing multi-fiber representative volume elements (RVEs) for different fiber-weight fractions. The micromechanical models are evaluated on the importance of thermal residual stresses on the local and nominal stress state. From these analyses it can be concluded that the thermal residual stresses should be accounted for when assessing the quantitative local stress state and are therefore essential when local mechanisms are studied. In contrast, thermal residual stresses are not required to capture the nominal transient stress–strain response.

Cartilage responses to a novel triaxial mechanostimulatory culture system

Experimental measurement of bovine caudal annulus fibrosus (AF) biaxial stress-strain states for unloaded motion segments and those loaded in flexion combined with axial compression. To measure AF biaxial stress-strain states for motion segments free of external loads and those loaded in flexion combined with axial compression. In vitro, cyclically loaded flexion is associated with the complete rupture of the AF in acute cases. However, currently little is known about the tissue-level stress and strain states in this damaging load configuration. Surface strains of the posterior annulus were measured, during loading of intact bovine caudal motion segments in flexion combined with axial compression, using the unloaded motion segment as a reference. Planar annulus specimens were excised from the motion segments, and the measured strains from the unloaded and flexed intact discs were applied to the excised specimens in a planar biaxial stress-strain device to determine the stress state in each condition. The annulus strain state of the flexed disc was input into a previously developed nonlinear strain energy function with additive terms that directly represent the structural features of the AF. The AF posterior surface strain for motion segments in flexion combined with compression was -0.1087 (circumferential) and 0.1051 (axial) on average. This strain state corresponded to average biaxial stresses in the annulus of 0.046 MPa (circumferential) and 0.224 MPa (axial). The planar AF specimens contracted after sectioning, resulting in small negative strains. In the absence of external loads on a motion segment, the annulus was approximately in a state of equibiaxial tensile stress. The theoretical analysis indicated that collagen crosslinks store a greater portion of the strain energy than the matrix or collagen fibers. In flexion combined with compression, the posterior AF stress state is biaxial and is much larger in the axial direction in bovine caudal discs.

How pore pressure changes affect stress and strain in fault zones with complex internal structure – Insights from hydromechanical modelling

The propensity for dynamic earthquake triggering is thought to depend on the local stress state and amplitude of the stress perturbation. However, the nature of this dependency has not been confirmed within a single crustal volume. Here, we show that at Sierra Negra volcano, Galápagos Islands, the intensity of dynamically triggered earthquakes increased as inflation of a magma reservoir elevated the stress state. The perturbation of short-term seismicity within teleseismic surface waves also increased with peak dynamic strain. Following rapid coeruptive subsidence and reduction in stress and background seismicity rates, equivalent dynamic strains no longer triggered detectable seismicity. These findings offer direct constraints on the primary controls on dynamic triggering and suggest that the response to dynamic stresses may help constrain the evolution of volcanic unrest.

To research the local stress state of the polyline pretensioned beams, the 3-D nonlinear finite element model is established by FEA software ANASYS. The results show that the existence of the inflection point on the prestressed reinforcement is the main reason of local stress distribution, and the corner radius R is the primary influential factor of the local stress distribution phenomenon. Then, the variation law of the stress and stress distribution by the corner radius R is illustrated clearly. With the increasing of R, the maximum local stress has decreased, and the stress distribution curve has increasingly become smoothly and gently. Considered the variation law of local stress and various of construction requirement in engineering practice, R=600mm is selected as the optimal radius. This research lays a good foundation for the further researches and wide applications of the polyline pretensioned beams.

Technical Briefs The Local Stress State at a Sharp Corner of an Expanding Inclusion Celina Go´mez, Celina Go´mez Department of Civil Engineering, Northwestern University, Evanston, Ill. 60201 Search for other works by this author on: This Site PubMed Google Scholar John Dundurs John Dundurs Department of Civil Engineering, Northwestern University, Evanston, Ill. 60201 Search for other works by this author on: This Site PubMed Google Scholar Author and Article Information Celina Go´mez Department of Civil Engineering, Northwestern University, Evanston, Ill. 60201 John Dundurs Department of Civil Engineering, Northwestern University, Evanston, Ill. 60201 J. Appl. Mech. Mar 1982, 49(1): 229-231 (3 pages) https://doi.org/10.1115/1.3162009 Published Online: March 1, 1982 Article history Received: May 1, 1981 Revised: September 1, 1981 Online: July 21, 2009

Seismic fragility assessment of Balvano (Potenza, Italy) pre and post 1980 Irpinia's earthquake