Finite Size and Speciment Thickness Influence in Acousto-Ultrasonic NDE

Acousto-ultrasonics (AU) uses a pair of transducers to characterize distributed damage in composite plates. A transducer placed normal to the surface creates resonances which propagate as plate waves. Once the receiving transducer picks up the signal, simple analysis techniques, such as the zeroth or first moment of the power spectrum, are applied to create a Stress Wave Factor (SWF). The SWF is then used to quantify the damage state of the composite once the system has been properly trained

The Influence of Finite-size Sources in Acousto-ultrasonics

This work explores the effects that the finite normal axisymmetric traction loading of an infinite isotropic plate has on wave propagation in acousto-ultrasonics (AU), in which guided waves are created using two normal incidence transducers. Although the work also addresses the effects of the transducer pressure distribution and pulse shape, this thesis concentrates on two main questions: how does the transducer's diameter control the phase velocity and frequency spectrum of the response, and how does the plate thickness relate to the plate's excitability? The mathematics of the time-harmonic solution and the physical principles and the practical considerations for AU wave generation are explained. Transient sources are modeled by the linear superposition of the time-harmonic solutions found using the Hankel transform and they are then compared to experimental data to provide insight into the relation between the size of the transducer and the preferred phase velocity

Heritability of pain catastrophizing and associations with experimental pain outcomes: a twin study

This study used a twin paradigm to examine genetic and environmental contributions to pain catastrophizing and the observed association between pain Catastrophizing and cold-pressor task (CPT) outcomes. Male and female monozygotic (n = 206) and dizygotic twins (n = 194) torn the University of Washington Twin Registry completed a measure of pain catastrophizing and performed a CPT challenge, As expected, pain catastrophizing emerged as a significant predictor of several CPT outcomeS, including cold-pressor Immersion Tolerance, Pain Tolerance, and Delayed Pain Rating. The heritability estimate for pain catastrophizing was found to be 37% with the remaining 63% of variance attributable to unique environmental influence. Additionally, the Observed associations between pain catastrophizing and CPT outcomes were not found attributable to shared genetics or environmental exposure, which suggests a direct relationship between catastrophizing and experimental pain. outcomes. This Study is the first to examine the heritability of pain catastrophizing and potential processes by which pain catastrophizing is related to experimental pain response

Thermal Quantitative Sensory Testing in Fibromyalgia Patients

Publisher Copyright: © 2015 by Marija Mihailova. Copyright: Copyright 2015 Elsevier B.V., All rights reserved.Fibromyalgia (FM) is a chronic disorder manifested by diffuse musculoskeletal pain, fatigue, sleep, and emotional disturbance. The disorder is probably associated with dysfunction of C and A delta peripheral nerve fibres. Thermal quantitative sensory testing (QST) was used to analyse thinly myelinated A delta fibres and nonmylinated C fibres, which function in the nociceptive sensory system, and the spinothalamic pathway. The observation that FM pain has neuropathic nature increased the value of QST as an additional diagnostic tool. The research group included 51 patients. Somatic symptoms were assessed using the Fatigue Severity Score (FSS), Fibromyalgia Impact Questionnaire (FIQ) and American College of Rheumatology (ACR) 2010 year diagnostic criteria. QST was performed by using thermal stimulus at wrist and feet. QST results were compared with 20 non-FM controls matched for age and sex. FM patients showed significant alteration of thermal perception and pain threshold compared with that in healthy controls, which demonstrated possible neuropathic pain nature in FM patients. Changes were more expressed in warm perception and heat pain threshold, which probably indicates that in FM patients C fibres are more damaged and warm perception and warm pain threshold are more sensitive, which may be used as FM diagnostics. We also found statistically significant negative correlations between warm and cold perception thresholds and between heat and cold pain thresholds, reflecting central sensitization or a defective pain inhibitory system.publishersversionPeer reviewe

Influence of stacking sequence on scattering characteristics of the fundamental anti-symmetric Lamb wave at through holes in composite laminates

This paper investigates the scattering characteristics of the fundamental anti-symmetric (A(0)) Lamb wave at through holes in composite laminates. Three-dimensional (3D) finite element (FE) simulations and experimental measurements are used to study the physical phenomenon. Unidirectional, bidirectional, and quasi-isotropic composite laminates are considered in the study. The influence of different hole diameter to wavelength aspect ratios and different stacking sequences on wave scattering characteristics are investigated. The results show that amplitudes and directivity distribution of the scattered Lamb wave depend on these parameters. In the case of quasi-isotropic composite laminates, the scattering directivity patterns are dominated by the fiber orientation of the outer layers and are quite different for composite laminates with the same number of laminae but different stacking sequence. The study provides improved physical insight into the scattering phenomena at through holes in composite laminates, which is essential to develop, validate, and optimize guided wave damage detection and characterization techniques.Martin Veidt and Ching-Tai N