MIL-HDBK-17-3F Volume 3.Foreword Table of Contents 7.5.2.3 Ground hail... ,51 7.5.2.4 Lightning......... 51 7.5.2.5 Handling and step loads.52 7.5.2.6 Exposed edges..... 52 7.5.3 Test issues.......... 52 7.5.4 Analysis methods-description and assessment....................................52 7.6 DURABILITY (DAMAGE INITIATION).............. 52 7.6.1 Introduction.… 52 7.6.2 Life factor approach........... 53 7.6.3 Load enhancement factor approach..........55 7.6.4 Ultimate strength approach. 56 7.6.5 Spectrum truncation....... 57 7.6.6 Durability certification.. 57 7.6.7 Influencing factors.. .57 7.6.8 Design issues and guidelines......................... 57 7.6.9 Test issues.… 58 7.6.10 Analysis methods-description and assessment.... 58 7.7 DAMAGE GROWTH UNDER CYCLIC LOADING............... 58 77.1 Influencing factors. 58 7.7.2 Design issues and guidelines.........60 773 TeSt SSUeS60 7.7.4 Analysis methods-description and assessment.. 60 7.7.4.1 Large through-penetration damage......... 60 7.7.4.2 Single delaminations and disbonds..... 60 7.7.4.2.1 Delamination growth ........... ..60 7.7.4.3 Impact damages. 60 7.7.4.4 Cuts and gouges...... 60 7.8 RESIDUAL STRENGTH............................ 61 7.8.1 Influencing Factors 61 7.8.1.1 Relationships between damage resistance and residual strength................. 61 7.8.1.2 Structure with impact damage...... 61 7.8.1.2.1 Material effects..... 61 7.8.1.2.2 Interlaminar toughness effects...62 7.8.1.2.3 Stacking sequence effects.62 7.8.1.2.4 Laminate thickness effects....... 4 7.8.1.2.5 Through-thickness stitching.. 64 7.8.1.2.6 Sandwich structure.64 7.8.1.2.7 Impact characteristic damage states.....................64 7.8.1.2.8 Residual strength -compressive/shear loads......................................68 7.8.1.2.9 Residual strength -tensile loads......... 69 7.8.1.2.10 Stiffened panels.. 69 7.8.1.3 Structure with through-penetration damage.................................71 7.8.1.3.1 Stitched skin/stiffener panels.....82 7.8.2 Design issues and guidelines...8 7.8.2.1 1Stacking sequences....................................................................82 7.8.2.2 Sandwich structure......................... 82 7.8.3 Test issues.... .83 7.8.3.1 Impact tests on coupons............. ..83 7.8.3.2 Impact tests on stiffened panels.83 7.8.3.3 Impact tests on sandwich panels.... ,83 7.8.3.4 Tests for large through-penetration damage to stiffened panels .....................84 7.8.3.5 Tests for large through-penetration damage to sandwich panels....................84 7.8.4 Analysis methods-description and assessment............. 4 7.8.4.1 Large through-penetration damage.......................84 7.8.4.1.1 Reduced singularity (Mar-Lin)model. 92 7.8.4.1.2 Strain softening laws..103 xiMIL-HDBK-17-3F Volume 3, Foreword / Table of Contents xi 7.5.2.3 Ground hail ...................................................................................................... 51 7.5.2.4 Lightning .......................................................................................................... 51 7.5.2.5 Handling and step loads .................................................................................. 52 7.5.2.6 Exposed edges................................................................................................ 52 7.5.3 Test issues ..................................................................................................................... 52 7.5.4 Analysis methods - description and assessment........................................................... 52 7.6 DURABILITY (DAMAGE INITIATION) ..................................................................................... 52 7.6.1 Introduction .................................................................................................................... 52 7.6.2 Life factor approach ....................................................................................................... 53 7.6.3 Load enhancement factor approach.............................................................................. 55 7.6.4 Ultimate strength approach............................................................................................ 56 7.6.5 Spectrum truncation....................................................................................................... 57 7.6.6 Durability certification..................................................................................................... 57 7.6.7 Influencing factors.......................................................................................................... 57 7.6.8 Design issues and guidelines ........................................................................................ 57 7.6.9 Test issues ..................................................................................................................... 58 7.6.10 Analysis methods - description and assessment........................................................... 58 7.7 DAMAGE GROWTH UNDER CYCLIC LOADING................................................................... 58 7.7.1 Influencing factors.......................................................................................................... 58 7.7.2 Design issues and guidelines ........................................................................................ 60 7.7.3 Test issues ..................................................................................................................... 60 7.7.4 Analysis methods - description and assessment........................................................... 60 7.7.4.1 Large through-penetration damage................................................................. 60 7.7.4.2 Single delaminations and disbonds................................................................. 60 7.7.4.2.1 Delamination growth ............................................................................. 60 7.7.4.3 Impact damages .............................................................................................. 60 7.7.4.4 Cuts and gouges.............................................................................................. 60 7.8 RESIDUAL STRENGTH........................................................................................................... 61 7.8.1 Influencing Factors ........................................................................................................ 61 7.8.1.1 Relationships between damage resistance and residual strength .................. 61 7.8.1.2 Structure with impact damage ......................................................................... 61 7.8.1.2.1 Material effects...................................................................................... 61 7.8.1.2.2 Interlaminar toughness effects.............................................................. 62 7.8.1.2.3 Stacking sequence effects .................................................................... 62 7.8.1.2.4 Laminate thickness effects.................................................................... 64 7.8.1.2.5 Through-thickness stitching .................................................................. 64 7.8.1.2.6 Sandwich structure ............................................................................... 64 7.8.1.2.7 Impact characteristic damage states .................................................... 64 7.8.1.2.8 Residual strength - compressive/shear loads...................................... 68 7.8.1.2.9 Residual strength - tensile loads.......................................................... 69 7.8.1.2.10 Stiffened panels..................................................................................... 69 7.8.1.3 Structure with through-penetration damage .................................................... 71 7.8.1.3.1 Stitched skin/stiffener panels ................................................................ 82 7.8.2 Design issues and guidelines ........................................................................................ 82 7.8.2.1 Stacking sequences......................................................................................... 82 7.8.2.2 Sandwich structure .......................................................................................... 82 7.8.3 Test issues ..................................................................................................................... 83 7.8.3.1 Impact tests on coupons.................................................................................. 83 7.8.3.2 Impact tests on stiffened panels ...................................................................... 83 7.8.3.3 Impact tests on sandwich panels..................................................................... 83 7.8.3.4 Tests for large through-penetration damage to stiffened panels ..................... 84 7.8.3.5 Tests for large through-penetration damage to sandwich panels.................... 84 7.8.4 Analysis methods - description and assessment........................................................... 84 7.8.4.1 Large through-penetration damage................................................................. 84 7.8.4.1.1 Reduced singularity (Mar-Lin) model.................................................... 92 7.8.4.1.2 Strain softening laws ........................................................................... 103