Influence Of Stress Changes Research Articles

High-temperature creep rupture behavior of dissimilar welded joints in martensitic heat resistant steels

The creep rupture behavior and microstructure changes of dissimilar welded joints of two types of martensitic heat resistant steel F92 and Co3W2, under a creep testing of 115–200 MPa and 873–893 K, were investigated. Fracture position and mode change from transgranular ductile fracture in parent F92 to intergranular brittle fracture in the fine grain heat affected zone (type IV cracking) near F92, with the drop of applied stress. Microstructural degradation resulted from creep with respect to dislocation density decrease, precipitates coarsening, dislocation cells, microvoids, macroscopic secondary cracks, and fracture surface morphology are researched based on detailed experimental results. The creep rupture data are analyzed employing Norton’s power law, Monkman–Grant relation, creep damage tolerance, and Larson–Miller parameter. Main creep damage micromechanisms are analyzed with the aid of calculated and experimental data. The extrapolating creep rupture stress for a creep life of 100,000 h are obtained and the influence of stress change and temperature change on creep life are compared in terms of calculated normalized creep life growth rate.

Wyznaczanie maksymalnego modułu ścinania popiołów składowanych na składowisku mokrym

The design of above-ground ash storage sites requires an assessment of the safety performance of the structure (GEO). This is usually done by using finite elements methods, for which the geotechnical parameters measured in the range of small deformations should be provided. The paper compares the results of the maximum shear modulus obtained on the basis of laboratory and field tests. This parameter is derived from the theory of elasticity and is a measure of the material’s reaction to external loads in the range of small deformations (10–6–10–3%). The analysis of the results assumes that the range of low deformations corresponds to the response of the soil to the applied external loads. The paper presents the dependence of the maximum shear modulus on the effective stress and void ratio obtained on the basis of tests in a triaxial cell with piezoelectric elements. To determine Gmax in situ, SASW/CSWS methods were used to measure the velocity of acoustic waves generated from the ground surface. The authors’ many years of experience prove that determining the parameters of stiffness of a medium in the range of small deformations is essential for assessing the behavior of the material under the influence of stress changes. Ash stored in the form of post-bonded suspension has a high shear strength and the results of small strain stiffness tests should form the basis for determining the parameters for numerical methods for resistance and stability calculations.

Tidally induced variations in vertical and horizontal motion on Rutford Ice Stream, West Antarctica, inferred from remotely sensed observations

AbstractTo better understand the influence of stress changes over floating ice shelves on grounded ice streams, we develop a Bayesian method for inferring time‐dependent 3‐D surface velocity fields from synthetic aperture radar (SAR) and optical remote sensing data. Our specific goal is to observe ocean tide‐induced variability in vertical ice shelf position and horizontal ice stream flow. Thus, we consider the special case where observed surface displacement at a given location can be defined by a 3‐D secular velocity vector, a family of 3‐D sinusoidal functions, and a correction to the digital elevation model used to process the SAR data. Using nearly 9 months of SAR data collected from multiple satellite viewing geometries with the COSMO‐SkyMed 4‐satellite constellation, we infer the spatiotemporal response of Rutford Ice Stream, West Antarctica, to ocean tidal forcing. Consistent with expected tidal uplift, inferred vertical motion over the ice shelf is dominated by semidiurnal and diurnal tidal constituents. Horizontal ice flow variability, on the other hand, occurs primarily at the fortnightly spring‐neap tidal period (Msf). We propose that periodic grounding of the ice shelf is the primary mechanism for translating vertical tidal motion into horizontal flow variability, causing ice flow to accelerate first and most strongly over the ice shelf. Flow variations then propagate through the grounded ice stream at a mean rate of ∼29 km/d and decay quasi‐linearly with distance over ∼85 km upstream of the grounding zone.

Monte Carlo Simulation of Stress-Associated Scattering Attenuation from Laboratory Ultrasonic Measurements

Abstract Seismic coda waves scattered by small‐scale heterogeneities contain information on stress changes of the medium, because of changes in the physical state of materials. Based on the ultrasonic measurements under different stresses for a cylindrical sandstone sample, we investigate the influence of stress changes on ultrasonic S ‐coda attenuation and aim to characterize its stress/frequency‐dependent pattern. Considering the complexity of ultrasonic coda waveforms measured from finite‐size rock samples in laboratory experiments, the Monte Carlo simulation is employed to synthesize ultrasonic envelopes, which act by incorporating the effect of multiple scatterings and boundary reflections on coda waves. The optimal simulation parameters, estimated by minimizing the residual between the observed and synthesized envelopes, indicate that the rock sample under study presents moderate heterogeneities. The relationship between attenuation and stress is similar for direct and coda S waves and remains stable in the range of high‐effective stresses around 30–60 MPa, with less stress sensitivity. Enhanced attenuation for both types of waves occurs at lower‐effective stresses, but with coda attenuation much faster and stronger, presenting a quite different nonlinear behavior with respect to stress. Coda attenuation increases drastically at extremely low‐effective stresses below 15 MPa because of the increase in rock compliance, showing much greater sensitivity to high‐pore pressure than intrinsic attenuation. This study improves our understanding of the mechanism of ultrasonic coda attenuation and its scaling dependence on stress and frequency.

Pattern of stress change and its effect on seismicity rate caused by M s8.0 Wenchuan earthquake

We use five published source models to calculate the Coulomb failure stress changes induced by the M s8.0 Wenchuan earthquake, and analyze the association between stress changes and the subsequent earthquakes. Based on the analysis of uncertainties resulting from source models, we determine the stress changes on nearby faults caused by the Wenchuan earthquake. Moreover, we focus on the seismicity rate change as a function of time on every fault under the influence of stress changes. The results indicate that the spatial distributions of aftershocks correlate well with the regions where stress is calculated to increase using the related models. The largest lobes of dropped stress lie in the west and east sides of source fault. The largest lobes of increased failure stress close to southern and northern ends of the source fault extend into the whole source failure plane. In addition, another region of increased stress lies in the Wenchuan-Yingxiu zone close to the southern segment of source fault, where a large number of aftershocks have occurred. And subsequent earthquakes seem to extend to even more remote distances; therefore, this area also has a high risk of seismic hazard. We find that the positive stress changes on nearby faults imposed by the Wenchuan earthquake produce an encouraging effect on seismicity rate. The effect is most significant on the Pengxian-Guanxian fault and Qingchuan fault, the value of seismicity rate maintains two times greater than the value before the mainshock for the next hundred years on these faults, and the time needed for the aftershock rate to recover to the pre-mainshock seismicity rate can reach up to 800–900 yr. The influence is not significant on the western Qinling fault, the Longquanshan fault, the Xianshuihe fault, the Yulongxi fault, the Anninghe fault, the Minjiang fault, and the Aba fault. Compared with the seismicity rate on these faults before the mainshock, the aftershock rate is raised by less than two times, and the time of perturbation duration is not long. The stress changes on the Fubianhe fault and Huya fault are negative, which reduce the seismicity for the next thousand years. Under the influence of stress changes caused by the Wenchuan earthquake, both Pengxian-Guanxian fault and Qingchuan fault have a high risk of earthquake occurrence.