MIL-HDBK-17-3F Volume 3.Chapter 12-Lessons Learned C-17.Mechanical joint data bases should con- Practical occurrences can affect strength tain information pertaining to durability and durability. issues such as clamp-up,wear at inter- faces,and hole elongation.Manu- facturing permitted anomalies such as hole quality,edge finish,and fiber breakout also need to be evaluated. C-18.Use drilling procedures that prevent fi- Improper back side support or drilling pro- ber break out on the back side of the cedures can damage surface plies on the component. back side. C-19.Splice plate stresses should be lower Splice plates see less clamp up than the than the stresses in skins to prevent de- skin sandwiched in between,because of laminations bolt bending. C-20.The best bolted joints can barely exceed The strength reduction is caused by half the strength of unnotched lami- stress concentrations around the hole for nates. the fastener. C-21.Laminate percentages for efficient load Best range for bearing and by-pass transfer:.0°=30-50%；±45°=40-60%； strength. 90°=minimum of10%. C-22.Countersink depths should not exceed Deep countersinks result in degraded 70%of laminate thickness. bearing properties and increased hole wear. C-23.Fastener edge distance and pitch:Use Maximizes joint strength. 3.0D edge distance in direction of major load;use 2.5D +0.06 side distance.(D is diameter of fastener.) C-24.Gap between attached parts should not Large gaps cause excessive bolt bending. exceed 0.03 inch (0.8 mm)for non- non-uniform bearing stresses,and eccen- structural shim. tric load path. C-25.Any gap in excess of 0.005 inch should Minimizes interlaminar stresses due to be shimmed. clamp-up. C-26.Use "form-in-place"gaskets on carbon/ Prevents corrosion of aluminum. epoxy doors over anodized aluminum substructure.Allow for a seal thickness of0.010±0.005inch(-0.25±0.13mm) minimum. C-27.Use only titanium,A286,PH13-8 MO. Prevents galvanic corrosion. monel or PH17-4 stainless steel fas- tener with carbon/epoxy. C-28.Do not buck rivets in composite struc- The bucking force can damage the lami- ture. nate. 12-17MIL-HDBK-17-3F Volume 3, Chapter 12 - Lessons Learned 12-17 C-17. Mechanical joint data bases should con￾tain information pertaining to durability issues such as clamp-up, wear at inter￾faces, and hole elongation. Manu￾facturing permitted anomalies such as hole quality, edge finish, and fiber breakout also need to be evaluated. Practical occurrences can affect strength and durability. C-18. Use drilling procedures that prevent fi￾ber break out on the back side of the component. Improper back side support or drilling pro￾cedures can damage surface plies on the back side. C-19. Splice plate stresses should be lower than the stresses in skins to prevent de￾laminations. Splice plates see less clamp up than the skin sandwiched in between, because of bolt bending. C-20. The best bolted joints can barely exceed half the strength of unnotched lami￾nates. The strength reduction is caused by stress concentrations around the hole for the fastener. C-21. Laminate percentages for efficient load transfer: 0° = 30-50%; ±45° = 40-60%; 90° = minimum of 10%. Best range for bearing and by-pass strength. C-22. Countersink depths should not exceed 70% of laminate thickness. Deep countersinks result in degraded bearing properties and increased hole wear. C-23. Fastener edge distance and pitch: Use 3.0D edge distance in direction of major load; use 2.5D + 0.06 side distance. (D is diameter of fastener.) Maximizes joint strength. C-24. Gap between attached parts should not exceed 0.03 inch (0.8 mm) for non￾structural shim. Large gaps cause excessive bolt bending, non-uniform bearing stresses, and eccen￾tric load path. C-25. Any gap in excess of 0.005 inch should be shimmed. Minimizes interlaminar stresses due to clamp-up. C-26. Use “form-in-place” gaskets on carbon/ epoxy doors over anodized aluminum substructure. Allow for a seal thickness of 0.010 ± 0.005 inch (-0.25 ± 0.13 mm) minimum. Prevents corrosion of aluminum. C-27. Use only titanium, A286, PH13-8 MO, monel or PH17-4 stainless steel fas￾tener with carbon/epoxy. Prevents galvanic corrosion. C-28. Do not buck rivets in composite struc￾ture. The bucking force can damage the lami￾nate