On the Use of Dent Depth as an Impact Damage Metric for Thin Composite Structures

Abstract

The damage resistance of thin composite structures was investigated experimentally. Specifically, surface damage in the form of dent-depth measurements are compared with internal damage states obtained by the X-radiography technique to better understand the implications of "barely visible impact damage" (BVID). Impact and quasistatic tests were conducted on plate and shell graphite/epoxy specimens between 0.804 mm and 2.412 mm thick in a [45n/10n], layup configuration. Damage was measured via visual, transducer, and X-ray methodologies. No correlation was found between internal (nonvisible) damage from the X-ray data and measured characteristics of the surface damage, specifically the depth of the dent. The results indicate that the use of dent depth as a metric can be misleading, particularly in that no dent depth can be found in some cases where substantial subsurface damage exists. Other examples are given wherein substantial (relative to other specimens) dent depths are measured with no corresponding internal damage. In previous work, peak force was found to correlate the resulting internal damage for both shell and plate specimens. However, dent depth shows no such general trend or correlation with peak force. This, coupled with previous damage tolerance work, places into question the use of dent-depth for thin (less than 2.4 mm, or 0.10") composite plate and shell structures in current damage tolerance methodologies.