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Proceedings Paper

Non-normal angle of incidence rain impact testing with whirling arm apparatus
Author(s): John A. Detrio
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Paper Abstract

Quantitative measurements of high speed rain drop impact damage to FLIR grade ZnS are reported for oblique angles of incidence. Specimens of ZnS and PMMA calibration witness pieces were tested at normal incidence and a 10 degree(s), 20 degree(s), 30 degree(s), and 45 degree(s) angle of incidence (AOI) as measured from the normal. The number of drop impacts on the PMMA increase slightly at the small angles over the value observed at 0 degrees. The density of impact events observed on the ZnS specimens increases more dramatically with small angles of incidence before dropping markedly at 30 degree(s) and 45 degree(s). Geometric considerations suggest a cos (theta) dependence. However, differences in air flow around the specimens may be responsible for the anomalous observations. The enhanced effects observed for the damage to the ZnS are not unique and support earlier observations by Gorham and Fields (Wear 41 (1977) 213 - 222). Measurements of the fracture stress also correlate with the angle of incidence. There is a reduction in strength at 10 degree(s) over normal incidence but thereafter the failure stress increases dramatically with increasing angle, which is indicative of a reduction in the magnitude of raindrop induced flaws. Specimens were tested at two velocities, 168 m/s and 210 m/s.

Paper Details

Date Published: 28 September 1994
PDF: 9 pages
Proc. SPIE 2286, Window and Dome Technologies and Materials IV, (28 September 1994); doi: 10.1117/12.187380
Show Author Affiliations
John A. Detrio, Univ. of Dayton (United States)


Published in SPIE Proceedings Vol. 2286:
Window and Dome Technologies and Materials IV
Paul Klocek, Editor(s)

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