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Adhesive Joint Design
Modern epoxies and cyanoacrylates are very strong adhesives that can
be utilized with poor joint design. These materials can be used in a
tension application somewhat successfully. Traditional adhesives and
especially ceramic adhesives have good compressive strength and very
poor tensile or flexural strength. Thus adhesive joints should be
designed so that a large part of the joint line is in compression when
typical loads are applied to the part.
Butt joints where a part is simply resting on another puts the entire
joint line in tension when a tipping force is applied, making it a poor
design for a ceramic adhesive. Looking to typical wood joinery is a good
reference for good ceramic adhesive joint design. The use of tongue in a
groove, a mortise and tenon, and the joint having a dowel pin can be
used to direct the forces into compression when force is applied to the
joint. Once again it is best if the materials have a similar coefficient
of expansion and the dowel pins if used should be made of the same
material as the majority of the joint material. Another tactic is to
make a part (splint), which surrounds the joint and can then be further
enhanced by pinning to the main parts. The dowel pins and splints are
very useful when repairing an existing part that has broken. Placing
small splints and dowel pinning them to the main part will result in a
robust repair.
Some repairs will be best made by using the most ancient method of
wrapping the area in the high temperature cloth or ceramic paper and
causing a “cast” to be formed around the part. The ceramic adhesive
is used to solidify the wrapping into a solid hard mass. |
