MIL-HDBK-17-3F Volume 3.Chapter 12-Lessons Learned A-27.Skin ply drop-offs should not occur Provides a better load path and fit-up be- across the width of spars,rib,or frame tween parts. flange. A-28.In areas of load introduction there Balanced and symmetric pairs of t45 should be equal numbers of +45 and plies are strongest for in-plane shear -45 plies on each side of the mid-plane. loads which are common at load introduc- tion points. A-29.A continuous ply should not be butt- Introduces a weak spot in the load path. spliced transverse to the load direction. A-30.A continuous ply may be butt-spliced Eliminates the possibility of a weak spot parallel to the load direction if coincident where plies are butted together. splices are separated by at least four plies of any orientation. A-31.The butt joint of plies of the same orien- Minimizes the weak spot where plies are tation separated by less than four plies of butted together. any direction must be staggered by at least 0.6 inch (15 mm). A-32.Overlaps of plies are not permitted. Plies will bridge a gap,but must joggle Gaps should not exceed 0.08 inch (2 over an overlap. mm). 12.3.1.1 Sandwich design B-1.Facesheets should be designed to mini- Thin skin honeycomb structure is very mize people induced damage during han- susceptible to damage by harsh handling. dling or maintenance of component. B-2.When possible avoid laminate buildup on Minimizes machining of the core. the core side of the laminate. B-3.Core edge chamfers should not exceed Prevents core collapse during cure cycle. 20(from the horizontal plane).Larger angles may require core stabilization. Flex core is more sensitive than rigid core B-4.Use only non-metallic or corrosion resis- Prevents core corrosion tant metal honeycomb core in composite sandwich assemblies. B-5.Choice of honeycomb core density should Prevents crushing of the core. satisfy strength requirements for resisting the curing temperature and pressure dur- ing bonding or cocuring involving the core.3.1 PCF (50 g/m)is a minimum for non-walking surfaces. 12-14MIL-HDBK-17-3F Volume 3, Chapter 12 - Lessons Learned 12-14 A-27.Skin ply drop-offs should not occur across the width of spars, rib, or frame flange. Provides a better load path and fit-up be￾tween parts. A-28.In areas of load introduction there should be equal numbers of +45° and -45° plies on each side of the mid-plane. Balanced and symmetric pairs of ±45° plies are strongest for in-plane shear loads which are common at load introduc￾tion points. A-29.A continuous ply should not be butt￾spliced transverse to the load direction. Introduces a weak spot in the load path. A-30.A continuous ply may be butt-spliced parallel to the load direction if coincident splices are separated by at least four plies of any orientation. Eliminates the possibility of a weak spot where plies are butted together. A-31.The butt joint of plies of the same orien￾tation separated by less than four plies of any direction must be staggered by at least 0.6 inch (15 mm). Minimizes the weak spot where plies are butted together. A-32.Overlaps of plies are not permitted. Gaps should not exceed 0.08 inch (2 mm). Plies will bridge a gap, but must joggle over an overlap. 12.3.1.1 Sandwich design B-1.Facesheets should be designed to mini￾mize people induced damage during han￾dling or maintenance of component. Thin skin honeycomb structure is very susceptible to damage by harsh handling. B-2.When possible avoid laminate buildup on the core side of the laminate. Minimizes machining of the core. B-3.Core edge chamfers should not exceed 20° (from the horizontal plane). Larger angles may require core stabilization. Flex core is more sensitive than rigid core. Prevents core collapse during cure cycle. B-4.Use only non-metallic or corrosion resis￾tant metal honeycomb core in composite sandwich assemblies. Prevents core corrosion B-5.Choice of honeycomb core density should satisfy strength requirements for resisting the curing temperature and pressure dur￾ing bonding or cocuring involving the core. 3.1 PCF (50 g/m3 ) is a minimum for non-walking surfaces. Prevents crushing of the core