FRACTURE DESIGN CRITERIA FOR STRUCTURAL ADHESIVE BONDING‐PROMISE AND PROBLEMS

Authors:
  • WBWillard D. Bascom
    Willard D. Bascom
  • RCRobert L. Cottington
    Robert L. Cottington
  • CTCarter O. Timmons
    Carter O. Timmons
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Abstract
The joining of load bearing structures using organic resin adhesives is an established technology in aircraft, spacecraft, and automobile construction and is being considered in ship construction; especially for hydrofoil and other advanced craft. The failure analysis of structural adhesive joints must be based on fracture criteria since these joints fail by linear elastic brittle fracture. Accordingly, the Navy has supported work over the past decade on developing an adhesive fracture test methodology and data base. Recent work at the Naval Research Laboratory (NRL) had demonstrated that fracture testing of structural adhesive joints is fundamentally more complex than the fracture testing of monolithic structures. Specifically, there is a very strong bond thickness effect; and more importantly, testing must be done under combined stress conditions. Opening‐mode (cleavage) tests alone are not sufficient. A study of the adhesive fracture behavior of structural adhesives has established why this additional testing is necessary. Work remains to be done on developing analytical relationships for the effect of joint geometry on adhesive fracture behavior.

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