Study of crystallinity and thermomechanical analysis of annealed poly(ethylene terephthalate) films

The objective of this article was the determination of the degree of crystallinity of a series of heat-set poly(ethylene terephthalate) (PET) films and their study by thermomechanical analysis (TMA) in order to elucidate a peculiar behaviour that takes place around the glass transition region. For this purpose, amorphous cast Mylar films from DuPont were annealed at 115 °C for various periods of time. Four methods were used to study the crystallinity of the samples prepared: differential scanning calorimetry (DSC), density measurements (DM), wide-angle X-ray diffraction (WAXD), and Fourier transform infrared spectroscopy (FT-IR). From the results obtained, the following conclusions are drawn: amorphous PET Mylar films can be crystallized in a degree of about up to 30% after thermal treatment for 30 min (cold crystallization) above glass transition temperature. When these semicrystalline samples are subjected to TMA, they show a two step penetration of the probe into them, which decreases with the increase of the degree of crystallinity. The first step of penetration was attributed to the shrinkage of the amorphous or semicrystalline sample, which takes place on the glass transition temperature, while the second step was attributed to the continuous softening of the sample, and the reorganization of the matter which takes place on heating run due to cold crystallization. © 2008 Elsevier Ltd. All rights reserved.

Seismic response of stone masonry spires: Analytical modeling

Stone masonry spires are vulnerable to seismic loading. Computational methods are often used to predict the dynamic linear elastic response of masonry towers and spires, but this approach is only applicable until the first masonry joint begins to open, limiting the ability to predict collapse. In this paper, analytical modeling is used to investigate the uplift, rocking and collapse of stone spires. General equations for static equilibrium of the spire under lateral acceleration are first presented, and provide a reasonable lower bound for predicting collapse. The dynamic response is then considered through elastic modal analysis and rigid body rocking. Together, these methods are used to provide uplift curves and single impulse overturning collapse curves for a complete range of possible spire geometries. Results are used to evaluate the historic collapse of two specific stone spires. © 2012 Elsevier Ltd.

Seismic response of stone masonry spires: Computational and experimental modeling

Analytical methods provide a global context from which to understand the dynamics of stone spires, but computational and experimental methods are useful to predict more specific behavior of multiple block structures. In this paper, the spire of St. Mary Magdalene church in Waltham-on-the-Wolds, UK, which was damaged in the 2008 Lincolnshire Earthquake, is used as a case study. Both a physical model and a discrete element computational model of the spire were created and used to investigate collapse under constant horizontal acceleration, impulse base motion, and earthquake ground motion. Results indicate that the global behavior compares well with analytical modeling, but local block displacements evident in DEM and experimental results also reduce the stability of the structure. In this context, the observed damage to St. Mary Magdalene church is evaluated and discussed. © 2012 Elsevier Ltd.

Modeling of soft clays response for seismic triggering of submarine slides

Submarine landslides pose considerable hazards to coastal communities and offshore structures. The difficulty and cost of obtaining undisturbed samples of offshore soils for determining material properties required for slope stability analyses contribute to the complexity of the problem. There are significant advantages in using a simplified model for the seismic response of submarine slopes, compatible with the limited amount of information that can be realistically gathered, but still able to capture the key elements of clay behavior. This paper illustrates the process of parameter determination and calibration of the SIMPLE DSS model, developed for the study of seismic triggering of submarine slope instabilities. The selection of parameters and predictions of monotonic and cyclic simple shear response are carried out for Boston Blue Clay, a marine clay extensively studied and with a large experimental database available in the literature. The results show that the simplified model is able to reproduce the important trends in the response of the soil, especially in accounting for the effect of the slope.

Centrifuge modeling of seismic liquefaction effects on adjacent shallow foundations

Shallow foundations built on saturated deposits of granular soils in seismically active areas are, regardless of their static bearing capacity, critical structures during seismic events. A single centrifuge experiment involving shallow foundations situated atop a liquefiable soil deposit has been performed to identify the mechanisms involved in the interaction between liquefaction-induced effects on neighboring shallow foundations. Centrifuge test results indicate that liquefaction causes significant settlements of footings, which are affected by the presence of neighboring foundations and can be extremely damaging to the superstructure. The understanding of these interaction effects is very important, mainly in densely populated urban areas. The development of high excess pore-pressures, localized drainage in response to the high transient hydraulic gradients, and earthquake-induced vertical motions to the footings are also important effects that are discussed to assist in enhancing current understanding and ability to predict liquefaction effects on shallow foundations. © 2014 Taylor & Francis Group.

Designing inclusive interfaces through user modeling and simulation

Elderly and disabled people can be hugely benefited through the advancement of modern electronic devices, as those can help them to engage more fully with the world. However, existing design practices often isolate elderly or disabled users by considering them as users with special needs. This article presents a simulator that can reflect problems faced by elderly and disabled users while they use computer, television, and similar electronic devices. The simulator embodies both the internal state of an application and the perceptual, cognitive, and motor processes of its user. It can help interface designers to understand, visualize, and measure the effect of impairment on interaction with an interface. Initially a brief survey of different user modeling techniques is presented, and then the existing models are classified into different categories. In the context of existing modeling approaches the work on user modeling is presented for people with a wide range of abilities. A few applications of the simulator, which shows the predictions are accurate enough to make design choices and point out the implication and limitations of the work, are also discussed. © 2012 Copyright Taylor and Francis Group, LLC.

Modeling natural sounds with modulation cascade processes

Natural sounds are structured on many time-scales. A typical segment of speech, for example, contains features that span four orders of magnitude: Sentences ($\sim1$s); phonemes ($\sim10$−$1$ s); glottal pulses ($\sim 10$−$2$s); and formants ($\sim 10$−$3$s). The auditory system uses information from each of these time-scales to solve complicated tasks such as auditory scene analysis [1]. One route toward understanding how auditory processing accomplishes this analysis is to build neuroscience-inspired algorithms which solve similar tasks and to compare the properties of these algorithms with properties of auditory processing. There is however a discord: Current machine-audition algorithms largely concentrate on the shorter time-scale structures in sounds, and the longer structures are ignored. The reason for this is two-fold. Firstly, it is a difficult technical problem to construct an algorithm that utilises both sorts of information. Secondly, it is computationally demanding to simultaneously process data both at high resolution (to extract short temporal information) and for long duration (to extract long temporal information). The contribution of this work is to develop a new statistical model for natural sounds that captures structure across a wide range of time-scales, and to provide efficient learning and inference algorithms. We demonstrate the success of this approach on a missing data task.

Modeling cyclic behavior of lightly overconsolidated clays in simple shear

Assessment of seismic performance and estimation of permanent displacements for submerged slopes require the accurate description of the soil's stress-strain-strength relationship under irregular cyclic loading. The geological profile of submerged slopes on the continental shelf typically consists of normally to lightly overconsolidated clays with depths ranging from a few meters to a few hundred meters and very low slope angles. This paper describes the formulation of a simplified effective-stress-based model, which is able to capture the key aspects of the cyclic behavior of normally consolidated clays. The proposed constitutive law incorporates anisotropic hardening and bounding surface principles to allow the user to simulate different shear strain and stress reversal histories as well as provide realistic descriptions of the accumulation of plastic shear strains and excess pore pressure during successive loading cycles. (C) 2000 Published by Elsevier Science Ltd. | Assessment of seismic performance and estimation of permanent displacements for submerged slopes require the accurate description of the soil's stress-strain-strength relationship under irregular cyclic loading. The geological profile of submerged slopes on the continental shelf typically consists of normally to lightly overconsolidated clays with depths ranging from a few meters to a few hundred meters and very low slope angles. This paper describes the formulation of a simplified effective-stress-based model, which is able to capture the key aspects of the cyclic behavior of normally consolidated clays. The proposed constitutive law incorporates anisotropic hardening and bounding surface principles to allow the user to simulate different shear strain and stress reversal histories as well as provide realistic descriptions of the accumulation of plastic shear strains and excess pore pressures during successive loading cycles.

Modeling mode i fracture of bitumen films

The fracture behavior of thin films of bitumen in double cantilever beam (DCB) specimens was investigated over a wide range of temperature and loading rate conditions using finite-element analysis. The model includes a phenomenological model for the mechanical behavior of bitumen, implemented into a special-purpose finite-element user material subroutine, combined with a cohesive zone model (CZM) for simulating the fracture process. The finite-element model is validated against experimental results from laboratory tests of DCB specimens by comparing measured and predicted load-line deflection histories and fracture energy release rates. Computer simulation results agreed well with experimental data of DCB joints containing bitumen films in terms of peak stress, fracture toughness, and stress-strain history response. The predicted "normalized toughness," G=2h, was found to increase in a power-law manner with effective temperaturecompensated strain rate in the ductile region as previously observed experimentally. In the brittle regime, G=2h is virtually constant. The model successfully captured the ductile and brittle failure behavior of bitumen films in opening mode (tension) for stable crack growth conditions. © 2013 American Society of Civil Engineers.