Compliant Sticky Foot

The design focus is to make a foot that is optimized for the use of an adhesive, be it SuperGlue, some other type of WetAdhesion, or the inherent stickiness of the material.

Development will be listed in reverse chronological order.

Related TWiki Links

• SuperGlue

• AdhesionModels

• WetAdhesion

Adhesive Joint Design Considerations

-- KevinHufford - 07 May 2004

The following basic adhesive joint design considerations are taken from two articles on http://www.specialchem4adhesives.com (free registration required): "How Joint Design Affects Adhesive Joint Strength" and "Why Adhesives Fail".

These general considerations are for standard applications of commercial adhesives (continous bond surface); a foot with discrete points of adhesive contact or some type of WetAdhesion may behave differently.

• Design the joint to stress the adhesive in shear.

• Minimize peel and cleavage stresses.

• Distribute the stress uniformly.

• Generally, rigid adhesives are better in shear, and flexible, tough adhesives are better in peel.

• The stiffer the adherend with respect to the adhesive, the more uniform the stress distribution in the joint and the higher the bond strength.

• The higher the Et (modulus x thickness) of the adherend, the less likely the deformation during load and the stronger the joint.

• The adhesive bondline thickness is not a strong influence on the strength of the joint.

• More important characteristics are a uniform joint thickness and void free adhesive layer.

Meeting Notes 05/06/04

-- KevinHufford - 07 May 2004

MarkCutkosky put forth the following major point to consider in design:

Use compliance to distribute the force optimally across the surface of the foot.

Minimize Peel:

• Pure tensile load (High stress concentrations at perimeter of contact because of Poisson shrinkage)

• Non-perpendicular load

Possible Ideas:

• Segmented Pad to distribute force

• We want to be able to push into the surface to adhere

• N "strings" adhered to the surface would work in tension, but would preclude pushing into the surface and wouldn't work in shear

• Put CompliantStickyFoot only on front feet and have rear feet provide resistance to shear?

• Flared Tip to minimize stress at edges of adhesion

-- KevinHufford? - 07 May 2004