MIL-HDBK-17-3F Volume 3.Chapter 12-Lessons Learned C-6.Common errors in composite bolted Does not maximize the strength of the joints are to use too few bolts,space laminate. them too far apart,and to use too small a diameter. C-7.Rated shear strength of fasteners does Bolt diameter is usually governed by the not usually control the joint design. need not to exceed the allowable bearing stress in the laminate. C-8.The peak hoop tensile stress around Keeping the laminate tensile strength high bolt holes is roughly equal to the aver- requires keeping the bearing stress low. age bearing stress. C-9.Maximum torque values should be con- Avoids crushing the composite trolled,particularly with large diameter fasteners. C-10.Bolt bending is much more significant in Composites tend to be thicker(for a given composites than for metals. load)and more sensitive to non-uniform bearing stresses(because of brittle failure modes. C-11.Optimum w/d ratio for multi-row bolted Maximizes joint strength. joints varies along length of joint.w/d 5 at first row to minimize load transfer. w/d 3 at last row to maximize transfer. w/d =4 for intermediate bolts. C-12.Stainless steel fasteners in contact with Prevents galvanic corrosion. carbon should be permanent and in- stalled wet with sealant. C-13.Use a layer of fiberglass or Kevlar Prevents corrosion of aluminum. (0.005 inch(0.13 mm)minimum)or ad- hesive with serim on faying surfaces of carbon epoxy panels to aluminum. C-14.Bolt stresses need careful analysis,par- Bolt failures are increasingly becoming ticularly for the effects of permissible the“weak link”with current high strength manufacturing parameters,for example, composite materials. hole perpendicularity (+10),shimming. loose holes. C-15.Bolted joint data bases should include Establishes that failure modes remain the full range of all permitted design fea- consistent and that there are no detrimen- tures. tal interaction effects between design pa- rameters. C-16.The design data base should be suffi- For proper verification of analytical accu- cient to validate all analysis methods racy. over the entire range permitted in de- sign. 12-16MIL-HDBK-17-3F Volume 3, Chapter 12 - Lessons Learned 12-16 C-6. Common errors in composite bolted joints are to use too few bolts, space them too far apart, and to use too small a diameter. Does not maximize the strength of the laminate. C-7. Rated shear strength of fasteners does not usually control the joint design. Bolt diameter is usually governed by the need not to exceed the allowable bearing stress in the laminate. C-8. The peak hoop tensile stress around bolt holes is roughly equal to the aver￾age bearing stress. Keeping the laminate tensile strength high requires keeping the bearing stress low. C-9. Maximum torque values should be con￾trolled, particularly with large diameter fasteners. Avoids crushing the composite. C-10. Bolt bending is much more significant in composites than for metals. Composites tend to be thicker (for a given load) and more sensitive to non-uniform bearing stresses (because of brittle failure modes. C-11. Optimum w/d ratio for multi-row bolted joints varies along length of joint. w/d = 5 at first row to minimize load transfer, w/d = 3 at last row to maximize transfer, w/d = 4 for intermediate bolts. Maximizes joint strength. C-12. Stainless steel fasteners in contact with carbon should be permanent and in￾stalled wet with sealant. Prevents galvanic corrosion. C-13. Use a layer of fiberglass or Kevlar (0.005 inch (0.13 mm) minimum) or ad￾hesive with serim on faying surfaces of carbon epoxy panels to aluminum. Prevents corrosion of aluminum. C-14. Bolt stresses need careful analysis, par￾ticularly for the effects of permissible manufacturing parameters, for example, hole perpendicularity (±10°), shimming, loose holes. Bolt failures are increasingly becoming the “weak link” with current high strength composite materials. C-15. Bolted joint data bases should include the full range of all permitted design fea￾tures. Establishes that failure modes remain consistent and that there are no detrimen￾tal interaction effects between design pa￾rameters. C-16. The design data base should be suffi￾cient to validate all analysis methods over the entire range permitted in de￾sign. For proper verification of analytical accu￾racy