Adhesive Layer Thickness and Porosity Criteria for Bonded Joints.

摘要

This inventigation is concerned with two aspects of the effects of imperfections in adhesive bonds. These imperfections are nonuniform thickness and porosity (or, in the extreme case, flaws). Both cause redistribution of the load transfer with respect to that for nominally perfect bonds. A thorough treatment of induced of induced peel stresses in structural joints and test coupons is included because the growth of bond flaws is known to be associated more with peel stresses than shear stresses in the adhesive. The report covers both the ductiel adhesives most suitable for subsonic transport aircraft and the brittle adhesives needed for supersonic military aircraft. The first major section of the report discusses the effects of adhesive layer thickness variation,iwth particular emphasis on the ends of bonded overlaps where peak load transfer inevitably occurs. The second major topic is that of flaws and porosity; and it is shown that adhesive bonded joints are far more tolerant of such naturally occurring imperfections than is generally recognized. The final subject is that of peel stresses induced in the adhesive layer due to eccentricities in load path. While it is known that such peel stresses can be very detrimental to the life of bonded joints, it shown here that it is often quite simple to eliminate them from structurally proportioned joints.