- Joint overap should be sufficient to maintain the adhesive in shear mode, rather than in peel or cleavage. For example, when making a “clamshell” casing it is best to have the top piece insert into the bottom piece, rather than making a flat-to-flat joint.
- Bondline thickness can be kept relatively small; but there are some trade-offs. Epoxies and other two-part structurals have an optimum shear/tensile/compressive strength at a bondline thickness of about 0.1 mm. Deviating significantly below this thickness will cause a decrease in strength. However, if the joint is in peel/cleavage or a constrained geometry (insertion joint) with thermal cycling, a thicker bondline will be necessary to obtain optimum strength—perhaps as much as 0.4mm or so.
- Bond Overlap area can of course vary; because structural adhesives can be very strong, less bond overlap area is typically needed than with PSA type adhesives. However, again, extremely small overlaps may be more prone to allow the bond line to experience peel or cleavage forces.
- For both bondline thickness and overlap, FEA modeling can be a way to screen design options—being careful to obtain adhesive Stress/strain properties so the adhesive layer can be appropriately included in the model.
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