SAMPE Journal - September/October 2020 - 35

ORIGINAL EQUIPMENT BONDING
Before delving into the details of bonded repair, it
should be noted that secondary bonding is integral
to the original manufacture of nearly all composite
bicycle frames. In other words, the repair processes
described herein are like the original manufacturing methods. The oldest composite frame manufacturing method is tube-and-lug, wherein the
tubes and lugs (joints) of the frame are first individually formed and cured, then adhesively bonded to
form the complete frame assembly. The tube and
lug components may have complementary opposing surfaces -- such as tapers and step faces -- enabling seamless joints as described in1,2.
INSPECTION
In this case study, damage was visible on the surface of the top tube, as seen in Figures 1 and 2. By
visual inspection alone, it was not possible to discern whether the damage was purely cosmetic, or
structural.
The tap test (also known as the coin test or sonic test) was employed to check for structural damage of the top tube. A simple but effective method,
the tap test makes use of frequencies in the audible
range. It is performed by tapping the structure with
a coin or small hammer-like object and listening to
the response. A clear, sharp ring indicates a solid,
well-bonded composite laminate. A lower pitched
"thud" is indicative of damage. The tap test is reliable for detection of delaminations near the surface
of thin laminates (e.g., bicycle frame tubes)3. In this
case, sections of tube to the left and right of the visibly damaged area (circled in Figure 2) were tapped
to establish a baseline tone, which was a highpitched ring. The area with visible surface damage
produced a dull thud when tapped, indicating localized structural damage requiring repair. Based
on the damage location, it likely resulted from the
handlebars striking the top tube during a crash. It
should be noted that if the damaged area had responded with a clear, sharp ring when tapped, this
would indicate that the damage is most likely limited to the first ply. In this hypothetical scenario, the
structure could be repaired by an infusion method;
coating the damaged area with liquid epoxy and
allowing it to fill any near-surface cracks or delaminations by capillary action.

Figure 1. Carbon/epoxy composite mountain bike frame with
impact damage visible
on the top tube.

Figure 2. Visible surface damage on top
tube of composite
mountain bike. The
damage was sealed
with nail polish -- which
is visible at the surface
-- by the previous owner. Sealing the damage
at the surface does not
constitute a structural
repair if there is subsurface damage, however.

DAMAGE EVALUATION AND REMOVAL
If structural damage is detected by the tap test
(i.e., the structure responds with a "thud" when
tapped), the next step is to evaluate the extent of
the damage and remove damaged material. Determining the damage depth is critical. A light impact

w w w. s a m p e . o r g

S E P T E M B E R /O C TO B E R 2 0 2 0

SAMPE JOURNAL

http://aurora-polaris.com/eng/ http://www.sampe.org

SAMPE Journal - September/October 2020

Table of Contents for the Digital Edition of SAMPE Journal - September/October 2020