| Autor: |
Barnard, Dan, Margetan, Frank J., Chiou, C.-P., Herman, Aaron, Pavel, Brittney, Chakrapani, Sunil K. |
| Předmět: |
|
| Zdroj: |
AIP Conference Proceedings; 2015, Vol. 1650 Issue 1, p1256-1265, 10p, 4 Diagrams, 5 Graphs |
| Abstrakt: |
In this paper we discuss nondestructive testing of five varieties of transparent armor panels fabricated from layers of glass, polymer and adhesive. The emphasis is on characterizing fabrication anomalies, such as lack of uniform layer thickness, rather than on damage detection. We report measurements of sound speed and attenuation on single-layer specimens of the polymer and the two types of glass used in the panels. We then discuss the results of various nondestructive studies of the panels, beginning with 225 KHz air-coupled ultrasonic testing (ACUT) and 5-MHz ultrasonic immersion testing. For all panels ultrasonic through-transmission C-scans reveal interesting patterns of signal amplitude and time-of-flight variations. These are traced to lateral changes in adhesive thickness within the panels. For one panel, adhesive sound speed, attenuation and density are deduced by analyzing UT immersion pulse/echo and pitch/catch data. Adhesive thickness variations manifest themselves differently in the two types of ultrasonic inspections. At the immersion inspection frequency adhesive attenuation dominates, so regions with thicker adhesive always have the smallest throughtransmitted response. At ACUT frequencies reverberation echoes within the adhesive layer superimpose with echoes from other sound paths, and an increase in adhesive thickness can result in either an increase or decrease in through-transmitted amplitude. A simple model to account for such signal superposition is developed and found to be in qualitative agreement with the results of the ACUT inspections. The adhesive thickness variations cause the surfaces within the panel to be nonplanar, leading to stresses on the various layers. We demonstrate the use of Terahertz-ray (T-ray) electromagnetic inspection to map the surface undulations of the thin glass outer layer in one of the panels. Bending stresses are estimated from the undulations and, at some locations, found to be at or near the levels that would cause fracture. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
|
