| Summary: | This thesis presents a study of the effects of surface colour, surface finish and dent
shape on the visual inspection reliability of 3D surface indentations common in shape
to those produced by impact damage to carbon fibre reinforced epoxy laminates.
Falling weight (2.5kg) apparatus was used to produce impact damage to non-painted,
non-mesh Hexcel AS4/ 8552 carbon fibre reinforced plastic (CFRP) laminates and
painted AS4/ 8552 laminates containing bronze mesh and glass fabric lightning strike
protection layers. Ø20 mm and Ø87 mm hemispherical tip impacts to painted 17ply
and 33ply laminates at varying energy levels typically produced circular shaped,
smoothly contoured, rounded sectional profiles with an absence of surface breaking
cracks.
Sectional profiles through coordinate measuring (CMM) data of the impact dents
were described using a set of geometric variables. Identifying relationships between
impact energy and the geometric variables allowed the typical sectional profile
through impact damage dents from Ø20 mm and Ø87 mm hemispherical tips on 17ply
and 33ply painted CFRP laminates to be calculated for energies between 5J to 80J.
Calculated sectional profiles typical of impact damage dents to CFRP laminates were
reconstructed as simple revolved shapes using 3D computer aided design (CAD)
models. The 3D CAD models were computer numerical control (CNC) machined into
3mm Plexiglas panels to produce facsimiles of hemispherical impact damage dents on
CFRP laminates.
Facsimile specimen sets of sixteen 600 mm x 600 mm panels were produced in gloss
and matt grey, white and blue finishes. Each set contained the same 32 different sized
machined dents representing Ø20 mm and Ø87 mm hemispherical tip impact damage
to 17ply & 33ply painted CFRP laminate. Each facsimile specimen set was combined
with similarly finished unflawed (dent free) panels. 64 panels in each colour/ finish
were presented for 5 seconds in a randomised order to a minimum of 15 novice
participants in a visual inspection task lasting approximately 25 minutes.
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A set of corresponding visual inspection experiments were performed in which
physical specimens were replaced by digitally projected actual size photorealistic
images of the machining CAD data. Comparisons between the results of the physical
and virtual specimen trials revealed differences in detectability for similarly sized
dents.
The detection results obtained from visual inspection of physical specimens
demonstrated that the detectability of dents similar to those caused by higher (>40J)
energy impacts from a Ø87 mm hemispherical tip was less than that of the dents
caused by lower energy (<20J) impacts from Ø20 mm tips. However, larger
subsurface delamination area was demonstrated by the higher energy Ø87 mm
impacts than lower energy Ø20 mm impacts on 150 mm x 100 mm coupons of the
same thickness laminate. The results of these experiments imply that detectability of
dents caused by larger diameter objects at higher energies cannot be assumed to be
greater than that of lower energy impacts from smaller diameter objects.
The detection results demonstrate that detectability by visual inspection cannot be
assumed the same for an impact dent on different surface colours and finishes. In
general terms, the highest numbers of dents returning >90% detection were observed
on grey specimens and the highest number of dents returning 0% detection were
observed on matt blue specimens. The difference in detection rates for similarly sized
dents on a gloss and matt finish was least on grey coloured specimens and greatest on
blue coloured specimens.
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