Nomenclature ................................................... vi
Abstract ........................................................ x
Kurzfassung ................................................... xii
1 Introduction ............................................... 1
1.1 Background ................................................. 1
1.2 Objective and Aims ......................................... 2
2 Literature Review .......................................... 5
2.1 Behaviour of Composite Structures under Impact ............. 5
2.1.1 High Velocity Impact ................................ 5
2.1.2 Fibre Reinforced Polymers ........................... 7
2.1.3 Impact Damage Mechanisms ............................ 8
2.1.4 Damage Tolerance ................................... 12
2.2 Effects of Preloads ....................................... 12
2.2.1 Loads and Strength ................................. 12
2.2.2 Effects of Preloads in the Elastic Regime .......... 14
2.2.3 Experimental Studies ............................... 16
2.2.4 Analytical and Numerical Approaches ................ 21
2.3 Damage and Failure Models for Composites .................. 23
2.3.1 Mesoscale Laminate Model ........................... 24
2.3.2 Ply Models ......................................... 24
2.3.3 Delamination Models ................................ 26
2.3.1 Interaction between Ply and Delamination Damage .... 30
2.3.2 Strain Rate Effects ................................ 32
2.3.3 Implicit and Explicit Solving Algorithms ........... 34
2.4 Conclusion and Thesis Structure ........................... 35
3 Experimental Investigation ................................ 39
3.1 Experimental Methodology .................................. 39
3.1.1 Materials and Specimens ............................ 39
3.1.2 Impactor ........................................... 41
3.1.3 Preload Scenarios .................................. 41
3.1.4 Test Setup ......................................... 44
3.1.5 Test Matrix ........................................ 46
3.1.6 Non-destructive Testing ............................ 47
3.2 Results and Discussion .................................... 49
3.2.1 Visible Damage ..................................... 49
3.2.2 Internal Damage .................................... 51
3.2.3 Energy Dissipation ................................. 54
4 Numerical Approach ........................................ 55
4.1 Intra-ply Damage and Failure .............................. 55
4.1.1 Ply Model Numerical Implementation ................. 55
4.1.2 Maximum Damage and Element Elimination ............. 62
4.1.3 Ply Model Input Parameters ......................... 64
4.1.4 Ply Model Out-of-plane Behaviour ................... 67
4.2 Delamination Damage ....................................... 69
4.2.1 Cohesive Zone Model ................................ 69
4.2.2 Cohesive Stiffness and Density ..................... 70
4.2.3 Crack Propagation Strength ......................... 73
4.3 Selection of Representative Sub-laminates ................. 76
4.4 Model Assembly ............................................ 79
4.5 Modelling Preloads ........................................ 81
4.6 Friction .................................................. 82
5 Validation of the Numerical Approach ...................... 85
5.1 Plate Deformation ......................................... 85
5.2 Prediction of Delamination Damage ......................... 87
5.3 Prediction of Intra-ply Damage ............................ 93
5.4 Energy Absorption ......................................... 95
5.5 Conclusion ................................................ 95
6 Discussion of Preload Effects ............................. 97
6.1 Change of Damage Mechanisms ............................... 97
6.1 Load Distribution Resulting from Preloads ................ 103
6.2 Deformation Behaviour and Contact Force .................. 105
7 Conclusion and Outlook ................................... 111
7.1 Conclusion ............................................... 111
7.2 Future Research .......................................... 113
Appendices .................................................... 117
Appendix A: Numerical Impact Simulation ....................... 117
Appendix B: Preload Fixture ................................... 118
References .................................................... 119
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