The time lag between deformation process and seismic activity in El Hierro Island during the eruptive process (2011–2014): a functional phased approach

On 10 October 2011, a submarine eruption occurred in El Hierro island. Thus, the eruptive process in the Canary islands was reactivated after 40 years of inactivity. The main objective of this work is to evaluate, using Functional Data Analysis, how the surface deformation phenomenon explains the seismic–volcanic activity in the island. The GNSS-GPS data are from the FRON (GRAFCAN) station, located in Frontera. These data measure, each 4 h, the distance between the FRON station and the reference station LPAL (La Palma island) from August, 2010 to December, 2013. In this study a functional correlation measure is employed to establish the relation between the deformation curve and the curve of cumulative energy released. The period of time analysed has been divided into four phases to avoid the mix of phenomena. For each phase, the correlation measure and the time lag between deformation curve and the curve of cumulative energy released have been estimated. These values show a strong relation between these curves. With respect to time lag period, the only significant lag, of about 1 month, occurred in Phase 1, which was after a long period without seismic activity. The later phases had very short, insignificant, lags. After a long period without seismic and volcanic activity in El Hierro island, the time lag between the deformation process and the beginning of the seismic activity takes approximately 1 month. In a similar situation a method to predict in real time the beginning of the seismic activity is proposed. This method, based on the changes produced in the derivative curves when there is a rapid descent in the deformation curve, could activate a warning system approximately 13 days before the beginning of seismicity.

The Domain of Portevin-Le Chatelier Effect in Al-3Mg Alloy

An Al-3Mg (wt. %) alloy was studied after equal channel angular pressing and subsequent cold rolling. The mechanical behavior of the alloy in the temperature range from 223 K to 373 K (from –50°C to 125°C) at strain rates 2.1×10–1 – 5.2×10–5 s–1 was investigated. The analysis of stress-strain curves was performed to determine the conditions of manifestation of the Portevin – Le Chatelier (PLC) effect in investigated alloy. The deformation curve at a temperature of 298 K (25°C) and a strain rate of 1×10–3 s–1 is characterized by instability of plastic flow in contrast to the deformation curves obtained under other studied strain rate/temperature conditions. Stress oscillations at the necking stage were observed at high temperatures (>323 K (50°C)) and lower strain rates (1×10–4 s–1 and 5.2×10–5 s–1) forming the left border of the PLC effect domain. In general, deformation curves are characterized by the absence of stress serrations during the uniform elongation.

Numerical description of the viscoelastic properties of low- and high-filled elastomeric nanocomposites

In this work, an analytical solution is found for the change in the dissipative (inelastic) part of the stress tensor at a constant rate of uniaxial loading of the material within the framework of a new thermodynamic model of the behavior of viscoelastic materials. At the same time, a fairly accurate coincidence of the theoretical curve constructed on the basis of the obtained solution with the experimental results was demonstrated. For this, uniaxial tests with nested loading cycles were carried out for samples of low- and high-filled elastomeric nanocomposites with various fillers. At each section of loading and unloading, time holdings were set, which made it possible to neglect the temporal processes taking place in the material, this makes it possible to experimentally find the equilibrium deformation curve. The resulting equilibrium curve can be described using the elastic potential. Having determined the equilibrium (elastic) and finding the dissipative (inelastic) parts of the stress tensor, the viscoelastic response of the considered elastomeric materials was described with high accuracy.

Ultrasonic rate changes bytension of the Fe-Cr-Ni alloy at 180-318 K

Investigations of the mechanical characteristics and changes in the propagation velocity of ultrasound (Rayleigh waves) during plastic deformation of the Fe-Ni-Cr alloy in the temperature range 180 ≤ T ≤ 318 K. The implementation of the method for measuring the velocity of Rayleigh waves consisted in the periodic generation of rectangular pulses with a duration of 100 ns at the input of the radiating piezoelectric transducer and registration of the wave passed through the sample by means of a receiving piezoelectric transducer connected to a digital oscilloscope. It was found that a decrease in the temperature of the alloy under study changes not only the type of the deformation curve under uniaxial tension, but also changes the character of the dependence of the ultrasound velocity on deformation and stresses associated with the growth of the martensitic α'-phase formed as a result of γ-α'- phase transformation.

Mechanical behaviors of GFRP tube confined recycled aggregate concrete with sea sand

An experimental program was undertaken to study the mechanical behaviors of glass fiber-reinforced polymer (GFRP) tube confined recycled aggregate concrete with sea sand (GRACSS) under the axial compression. Two different parameters were mainly considered: recycled coarse aggregates (RCA) replacement percentage (0, 100%) and type of sand (sea sand, river sand). Typical influences of RCA and sea sand on the strength, the deformation and the load–deformation curve of GRACSS were investigated. The test results showed that the failure pattern of GRACSS was similar to that of GFRP tube confined ordinary concrete (GCOC). The strength of GRACSS decreased with an increasing RCA replacement percentage, while sea sand could reduce the negative effect of RCA. It is also found that the peak deformation of GRACSS increased with the increasing RCA replacement percentage whereas with decreasing sea sand chloride ion (Cl–) content. The stiffness of the specimen was obviously influenced by the concrete type. Research findings indicated that the axial load-deformation curve of GRACSS can be divided into elastic-plastic and hardening stages. An analytical expression was proposed to calculate the load-deformation curve of GRACSS. Finally, the finite element method (FEM) was applied to study the effects of outer tube thickness, concrete strength, RCA replacement percentage and Cl– content in sea sand on the mechanical behaviors (strength and deformation) of GRACSS.

Calibration of CDM-Based Creep Constitutive Model Using Accelerated Creep Test (ACT) Data

In conventional creep testing (CCT) a specimen is subject to constant load and temperature for a long-duration until creep rupture occurs. Conventional testing can be costly when considering the number of experiments needed to characterize the creep response of a material over a range of stress and temperature. To predict long-term creep-rupture properties, the time-temperature-stress superposition principle (TTSSP) approach has been employed where stress and/or temperature is applied at an elevated level; the result of which are extrapolated down to low stress and/or temperature conditions. These methods have been successful in predicting minimum-creep-strain-rate (MCSR) and stress-rupture (SR) but suffer from an inability to predict the creep deformation curve or account for changes in deformation mechanisms or aging that occurs at long-duration. An accelerated technique, termed the Stepped isostress method (SSM) allows the accelerated testing of materials to determine their creep deformation response. Unlike TTSSP tests, the SSM test employs a single specimen where the stress is periodically step increased until rupture. The SSM creep deformation curve is processed (time and strain shifted) to produce an accelerated creep deformation curve that represent the creep deformation curve at the initial stress level in SSM. A processing procedure for metals has yet to be developed. The research objective of this study is to develop a processing procedure for SSM test data using a creep-damage constitutive model. Triplicate SSM tests were conducted on Ni-based superalloy Inconel 718 at 650°C with stress being periodically increased until rupture. Triplicate CCT tests were conducted at the initial stress level of the SSM tests. The Sine-hyperbolic (Sinh) creep-damage model was employed in this study. The Sinh creep-damage constitutive model is based on coupled creep strain rate and damage evolution equations; where both rates are dependent on the current state of damage. Calibration is two-step: analytical and numerical optimization. Each stepped creep deformation curve is tackled quasi-analytically to determine MCSR and SR related material constants and accumulated damage. The damage accumulated at the end of each step was then passed onto subsequent steps to calibrate the MCSR, rupture prediction, and damage evolution. Numerical optimization was applied to optimize model constants involved in the creep strain constitutive equations in order to generate best-fitted Sinh creep deformation curves. The Sinh model predictions were compared to the SSM and CCT data. The Sinh model satisfactorily predicts the SSM data and thus the calibrated material constants provides a good estimate of rupture found in the CCT data. Calibration using SSM data reduces the number of tests needed to calibrate a model; significantly reducing costs. A single SSM test replaces numerous creep tests at different stresses.

Simplified Mathematical Model to Predict Response of Ferrocement-Lgs Composite Wall to In-Plane Loading

Ferrocement-LGS (Light Gauge Steel) composite construction is recently proposed novel form of construction as a substitute to traditional RCC framed construction. In this construction form, walls of the building behave more or less like a shear wall in resisting in-plane lateral loads. The present paper attempts to propose a simplified mathematical model for obtaining response of composite wall under in plane lateral loading. As first part of present work, in-plane force deformation behavior of Ferrocement-LGS composite wall panel is predicted through FEM analysis (ANSYS). This force deformation curve was employed to estimate equivalent spring parameters of simplified mathematical model (ETABS) of composite walls. The simplified mathematical model saves significant computational efforts in predicting the in-plane response compared to the traditional FEM model without compromising the accuracy.