MIL-HDBK-17-3F Volume 3.Chapter 12-Lessons Learned D-5.When there is no need for repair,as in Load transfer is performed without drilling missiles and unmanned aircraft.bond- holes for fasteners. ing permits extremely high structural ef- ficiencies to be obtained.even on thick structures. D-6.Proper surface preparation is a "must"- Maintaining joint strength in service is beware of "cleaning"solvents and peel very dependent on the condition of the plies.Mechanical abrasion is more reli- surfaces to be bonded. able. D-7.Laminates must be dried before per- Heat applied to the laminates during re- forming bonded repairs. pair can cause any moisture present to vaporize and cause blisters. D-8.Adherend overlaps must not go below Key to durability of bonded joints is that specified minimums. some of the adhesive must be lightly stressed to resist creep. D-9.Bonded overlaps are usually sized to Elevated temperature and moisture de- survive hot/wet environmental condi- grade the strength and stiffness of the tions adhesive. D-10.Bonded joint strength can also be de- The brittleness of the adhesive limits joint graded by cold environment where ad- strength. hesive is brittle D-11.Taper ends of bonded overlaps down to Minimizes induced peel stresses that 0.020 inch (0.51 mm)thick with a would cause premature failures. 1-in-10 slope. D-12.Adhesives work best in shear,are poor Joint must be designed to minimize out- in peel,but composites are even of-plane stresses. weaker in interlaminar tension. D-13.Design of simple,uniformly thick (for Provides a bonded joint with good near quasi-isotropic carbon/epoxy) strength capability. bonded splices is very simple.Use 30 t overlap in double shear,80 t overlap for single-lap joints,1-in-50 slope for scarf joint. D-14.Design of stepped-lap joints for thick Complex stress states in stepped-lap structure needs a nonlinear analysis joints.Nonlinear adhesive characteristics. program. D-15.Adhesives are well characterized by This test provides ample data for analysis thick-adherend test specimen,generat- of joints critical in shear. ing complete nonlinear shear stress- strain curve. D-16.For highly loaded bonded joints a co- Very efficient joint design. cured,multiple step,double sided lap is preferred. 12-19MIL-HDBK-17-3F Volume 3, Chapter 12 - Lessons Learned 12-19 D-5. When there is no need for repair, as in missiles and unmanned aircraft, bond￾ing permits extremely high structural ef￾ficiencies to be obtained, even on thick structures. Load transfer is performed without drilling holes for fasteners. D-6. Proper surface preparation is a "must" - beware of "cleaning" solvents and peel plies. Mechanical abrasion is more reli￾able. Maintaining joint strength in service is very dependent on the condition of the surfaces to be bonded. D-7. Laminates must be dried before per￾forming bonded repairs. Heat applied to the laminates during re￾pair can cause any moisture present to vaporize and cause blisters. D-8. Adherend overlaps must not go below specified minimums. Key to durability of bonded joints is that some of the adhesive must be lightly stressed to resist creep. D-9. Bonded overlaps are usually sized to survive hot/wet environmental condi￾tions. Elevated temperature and moisture de￾grade the strength and stiffness of the adhesive. D-10. Bonded joint strength can also be de￾graded by cold environment where ad￾hesive is brittle. The brittleness of the adhesive limits joint strength. D-11. Taper ends of bonded overlaps down to 0.020 inch (0.51 mm) thick with a 1-in-10 slope. Minimizes induced peel stresses that would cause premature failures. D-12. Adhesives work best in shear, are poor in peel, but composites are even weaker in interlaminar tension. Joint must be designed to minimize out￾of-plane stresses. D-13. Design of simple, uniformly thick (for near quasi-isotropic carbon/epoxy) bonded splices is very simple. Use 30 t overlap in double shear, 80 t overlap for single-lap joints, 1-in-50 slope for scarf joint. Provides a bonded joint with good strength capability. D-14. Design of stepped-lap joints for thick structure needs a nonlinear analysis program. Complex stress states in stepped-lap joints. Nonlinear adhesive characteristics. D-15. Adhesives are well characterized by thick-adherend test specimen, generat￾ing complete nonlinear shear stress￾strain curve. This test provides ample data for analysis of joints critical in shear. D-16. For highly loaded bonded joints a co￾cured, multiple step, double sided lap is preferred. Very efficient joint design