Development of nondestructive non-contact acousto-thermal evaluation technique for damage detection in materials.
This paper presents the development of a new non-contact acousto-thermal signature (NCATS) nondestructive evaluation technique. The physical basis of the method is the measurement of the efficiency of the material to convert acoustic energy into heat, and a theoretical model has been used to evaluate this. The increase in temperature due to conversion of acoustic energy injected into the material without direct contact was found to depend on the thermal and elastic properties of the material. In addition, it depends on the experimental parameters of the acoustic source power, the distance between sample and acoustic source, and the period of acoustic excitation. Systematic experimental approaches to optimize each of the experimental variables to maximize the observed temperature changes are described. The potential of the NCATS technique to detect microstructural-level changes in materials is demonstrated by evaluating accumulated damage due to plasticity in Ti-6Al-4V and low level thermal damage in polymer matrix composites. The ability of the technique for macroscopic applications in nondestructive evaluation is demonstrated by imaging a crack in an aluminum test sample.
A Review on Detecting and Characterizing Damage Mechanisms of Synthetic and Natural Fiber Based Composites
The damage to composite structures caused by impact events is one of the most critical behaviors that inhibit the widespread application of composite material. As the application of synthetic and natural based composite material increases over time, improved knowledge of composite damage in areas such as automotive and aerospace is exceedingly necessary. It is important to study and understand the damage mechanism of composite structures to produce effective designs. The failure caused by damage in structural design can result in unintended consequences. Extensive research has been conducted to detect impact damage in synthetic fiber. There are various methods to identify and characterize the damage. This article provides a comprehensive review of recent literature focusing on the broader scope of impact damage and incipient thermal damage of synthetic and natural fiber-based composites. In this report, the available research is reviewed by considering all aspects related to damage in composite materials, particularly the work done on detecting and characterizing damage mechanisms of synthetic and natural fiber-based composites.
Über den Einfluß thermisch angeregter Schallwellen auf die plastische Deformation
ZusammenfassungUnter Annahme eines plausiblen Wirkungsquerschnitts einer Versetzung für Streuung von Schallwellen wird gezeigt, daß die durch diese Streuung erzwungene Reibung unter normalen Bedingungen maximale Versetzungsgeschwindigkeiten von nur etwa 1/10 Schallgeschwindigkeit zuläßt. Es wird auf einen Zusammenhang zwischen der durch thermisch angeregte Wellen erzeugten mittleren Schubspannung und der Schmelztemperatur eines Metalls hingewiesen. Dieser Zusammenhang ist identisch mit der bekanntenLindemannschen Formel.