학술논문
Effect of Non-uniformity on Time-of-Flight Measurement of Critically Refracted Longitudinal Waves for Stress Evaluations of Carbon Composite Materials.
Document Type
Article
Source
Subject
*STRESS waves
*TIME-of-flight measurements
*CARBON composites
*MATERIALS testing
*ULTRASONIC waves
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Language
ISSN
0732-8818
Abstract
Acoustoelasticity is an inexpensive and reliable technique for measuring stresses in mechanical structures, provided the influencing factors are controlled. However, ultrasonic waves propagating inside solid bodies are affected by temperature, roughness, differences in microstructure, defects, and others. Non-uniformity is one of the most influential characteristics as it is difficult to evaluate. In this study, experiments were performed to assess the time-of-flight (TOF) of critically refracted longitudinal (Lcr) waves traveling in different regions of a unidirectional carbon-epoxy sample with allowable manufacturing non-uniformities using transducers of 1 MHz and 3.5 MHz to vary the depth of propagation. A phased array system (PAS) with transducers of 5 and 10 MHz was used to identify the regions with non-uniformities in the structure through the signal-to-noise ratio (SNR) and B-Scan images. The material under test is a unidirectional composite bar made of carbon fibers (HexTow® AS4) pre-impregnated with epoxy matrix (HexPly® 8552). The investigation shows that the TOF of the Lcr wave and the SNR results can be linearly related, for an optimized configuration. Therefore, the influence of non-uniformities can be removed from TOF using SNR values. Based on the results, a coupled PAS-Lcr ultrasonic system is proposed to measure stress in composites, including those with non-uniformities. [ABSTRACT FROM AUTHOR]