Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Youqi Wang / Ballistic performance of textile fabric is affected by numerous elements, such as fabric architecture, material property, and projectile characteristics. Near fiber-level microstructures of soft body armor composed of multi-layer Kevlar KM-2 fabrics are generated for numerical simulation. The modified digital element approach (DEA) is applied to determine the ballistic limit of textile fabrics against fragment simulating projectiles (FSP). Different from other numerical models, the DEA takes a considerable amount of fiber-level detail into consideration and models the fabric at filament-level. In this approach, fabric is an assembly of yarns weaved and relaxed into pre-arranged pattern; yarn is simulated as a bundle of digital fibers. When the number of digital fibers per yarn reaches the number of actual fibers per yarn, fiber-level simulation is achieved. The DEA model successfully simulates real scale multi-layer fabric impacted by spherical projectile and accurately predicted fabric displacement and failure mechanism. It was assumed that the digital fiber is fully flexible and its bending rigidity is negligible. Shear force was thus neglected. However, for projectiles with sharp edge(s), such as FSP, due to resultant shear force, fabric failure starts where it interacts with projectile edge. As a result, the numerical results derived from the previous DEA overestimated the impact strength of fabrics against projectiles with shape edges. Therefore, shear force and fiber bending rigidity must be considered. In the modified DEA approach, numerical tests are employed to determine the effective bending rigidity of digital fiber. A combined tension-shear failure model is then incorporated into the DEA in order to calculate the shear force applied to fibers. The 3-D microscope is applied to measure the radius of FSP along the edge. The surface of the FSP is meshed into triangle elements. A unique algorithm is developed and employed to search contacts between textile fabric and projectile of arbitrary shape. In this research, first, an overview of ballistic impact analysis is discussed; the previous DEA model used in simulating ballistic impact and penetration process is presented. Second, the modified DEA approach used in simulating arbitrary shape projectile perforation process is established and verified. The method of searching and calculating contacts between textile fabric and solid body projectile is explained. The convergence and accuracy of digital element mesh are investigated statistically using tension-shear failure model. Third, fabric shear force and fiber bending rigidity are investigated using tension-shear failure model. The effective digital fiber area moment of inertia is numerically determined. Fourth, standard ballistic tests of real scale multi-layer Kevlar KM2 fabrics are simulated using FSP. Numerical results are compared to high-resolution experimental test data. The modified DEA is validated.

Concrete’s great vulnerability against impact demonstrates significant risks of injury for workers and occupants in all building types, especially existing concrete structures in which protection measures were not originally integrated. Beside the social and economic costs directly associated with impact accidents, the reconstruction or replacement of buildings damaged by impact negatively affects the environment and resources. In response to the increasing public concern for safety and sustainability, the DFG Research Training Group GRK 2250 is formed with the core aim to develop significant improvements in the impact resistance of existing concrete buildings by applying thin strengthening layers made of innovative mineral-bonded composites. The introduction of textile-based high-performance reinforcement is highly instrumental in realizing the required functions of thin mineral-bonded strengthening layers. Novel impact-resistant 3D reinforcement is developed on the basis of the innovative 3D cellular weaving technology in this dissertation. Woven 3D cellular structures are characterized by outstanding and customizable mechanical characteristics, owning to the flexible incorporation of elements with different materials and geometries both in in-plane and out-of-plane directions. Based on a systematic and partly iterative development process, impact-resistant woven 3D cellular reinforcements containing impact-load-oriented elements and impact-appropriate material combination are successfully designed and optimized. On the one hand, a series of experiments are conducted to capture the working mechanism of woven 3D cellular structure in mineral-bonded composites loaded under impact, and to understand the effects of critical structure features. On the other hand, feasible weave patterns and effective technological solutions are worked out and implemented to enable a reliable and low-damage manufacturing process. Through a series of impact experiments, it can be strongly evidenced that the developed 3D cellular reinforcement pronouncedly enhances the load bearing capacity, ductility and energy dissipation of mineral-bonded composite undergoing impact, thus, remarkably enhances its impact resistance. The development of impact-resistant woven 3D cellular reinforcements in this dissertation introduces a completely new and unique class of textile-based reinforcement for concrete, as well as mineral-bonded composites, with numerous benefits over the presently available reinforcing structures. A major advantage of the novel 3D cellular reinforcement is the capability to activate and exploit multiple energy dissipation mechanisms using both material and structure properties, through which remarkable impact resistance can be obtained. Thanks to a high degree of versatility and flexibility in material combination and structure design, in combination with a high degree of automation and flexibility of the weaving technology, impact-resistant woven 3D cellular reinforcement that is highly customized to specific impact scenarios can be produced with a significant time and cost efficiency. Furthermore, impact-resistant woven 3D cellular reinforcements possess an integral 3D architecture that ensures a high structure stability, allowing for a speedy casting process with a high placement-accuracy. On that basis, a reasonable production cost and a stable performance of designed functions can be obtained. The successful development of impact-resistant woven 3D cellular reinforcement essentially facilitates the successful creation of high-performance mineral-bonded strengthening layers, through the use of which the impact resistance of existing concrete structures, thus, their sustainable use, significantly enhances.:1 INTRODUCTION AND MOTIVATION 1 2 LITERATURE REVIEW 7 2.1 Fundamentals of concrete and reinforced concrete 7 2.1.1 Normal concrete 7 2.1.2 Structural concrete family 10 2.1.3 Steel reinforced concrete 11 2.1.4 Concrete and reinforced concrete under impact loading 14 2.1.5 Fiber-based reinforcing materials for concrete 18 2.1.6 Fiber reinforced concrete 21 2.1.7 Textile reinforced concrete 22 2.2 Two-dimensional textile concrete reinforcements 24 2.2.1 Welded metal wire mesh 24 2.2.2 Expanded metal mesh 25 2.2.3 Woven 2D reinforcing structures 25 2.2.4 Warp knitted 2D reinforcing structures 27 2.2.5 Stitched 2D reinforcing structures 28 2.2.6 Adhesively-bonded 2D reinforcing structures 29 2.2.7 Discussion of 2D reinforcing structures 30 2.3 Three-dimensional textile concrete reinforcements 33 2.3.1 Assembled 3D reinforcing structures 33 2.3.2 Woven 3D reinforcing structures 34 2.3.3 Warp knitted 3D reinforcing structures 35 2.3.4 Stitched 3D reinforcing structures 36 2.3.5 Adhesively-bonded 3D reinforcing structures 36 2.3.6 Discussion of available 3D reinforcing structures 36 2.4 Woven 3D cellular structures 37 2.5 Conclusion based on literature review 37 3 RESEARCH AIMS AND OBJECTIVES 39 4 PRELIMINARY INVESTIGATION INTO IMPACT BEHAVIOR OF MINERAL-BONDED COMPOSITE REINFORCED WITH WOVEN 3D CELLULAR STRUCTURE 41 4.1 Introduction 41 4.2 Materials under investigation 43 4.2.1 Reinforcement - Reference woven 3D cellular structure 3DWT Ref 43 4.2.2 Matrix - Fine-grained concrete Pagel TF10 44 4.2.3 Comparing reinforcement - Warp knitted 2D structure 2D BZT2 44 4.3 Specimen labeling 45 4.4 Methodology of small-scale plate impact test 46 4.4.1 Specimen preparation 46 4.4.2 Test setup 47 4.5 Preliminary small-scale plate impact test results 47 4.6 Summary and conclusion of preliminary investigation 58 4.7 Derivation of requirements and procedure for developing impact-resistant woven 3D cellular reinforcement 59 5 DEVELOPMENT OF STRUCTURE SYSTEMATICS FOR IMPACT-RESISTANT WOVEN 3D CELLULAR REINFORCEMENT 63 5.1 Fundamentals of woven 3D cellular structure 64 5.1.1 Conventional woven structure 64 5.1.2 Elements of woven 3D cellular structure 65 5.1.3 Formation principles of woven 3D cellular structure 66 5.1.4 Variation possibilities within woven 3D cellular structure 68 5.2 Design concept of mineral-bonded strengthening layers against impact 71 5.3 Requirements for impact-resistant woven 3D cellular reinforcement 73 5.4 Two-plane woven 3D cellular reinforcements 77 5.4.1 Two-plane woven 3D cellular reinforcements with biaxial grids 77 5.4.2 Two-plane woven 3D cellular reinforcements with triaxial grids 81 5.4.3 Two-plane woven 3D cellular reinforcements with quadriaxial grids 82 5.5 Three-plane 3D cellular reinforcements 83 5.6 Material variation 85 5.6.1 Double yarns 85 5.6.2 Hybrid yarns 86 5.7 Selected impact-resistant woven 3D cellular reinforcements for realization and investigation 86 6 DEVELOPMENT OF WEAVE PATTERN FOR IMPACT-RESISTANT WOVEN 3D CELLULAR REINFORCEMENT 89 6.1 Introduction 89 6.2 Two-plane reference structure 3DWT Ref 90 6.3 Two-plane double yarn structure 3DWT DbWi 92 6.4 Three-plane structure 3DWT DbLyr 93 6.5 Two-plane pyramid structure 3DWT Pyr 95 7 DEVELOPMENT OF TECHNOLOGICAL SOLUTIONS FOR THE MANUFACTURE OF IMPACT-RESISTANT WOVEN 3D CELLULAR REINFORCEMENT 101 7.1 3D cellular weaving technology 101 7.2 Manufacture of two-plane double yarn structure 3DWT-DbWi 107 7.3 Manufacture of three-plane structure 3DWT-DbLyr 108 7.4 Manufacture of two-plane pyramid structure 3DWT-Pyr 112 8 TENSILE BEHAVIOR OF SHCC CONTAINING IMPACT-RESISTANT WOVEN 3D CELLULAR REINFORCEMENT 117 8.1 Quasi-static tension tests 117 8.1.1 Specimen preparation 117 8.1.2 Test setup 118 8.1.3 Quasi-static tension test results 119 8.2 High-speed tension tests 126 8.2.1 Specimen preparation 126 8.2.2 Test setup 126 8.2.3 High-speed tension test results 127 9 ENHANCEMENT OF IMPACT-RESISTANT WOVEN 3D CELLULAR REINFORCEMENT 131 9.1 Concept of enhanced impact-resistant 3D cellular reinforcement 131 9.2 Weave pattern development of enhanced impact-resistant reinforcement 3DWT Pyr Hyb 134 9.3 Manufacture of enhanced impact-resistant reinforcement 3DWT Pyr Hyb 136 9.3.1 Material selection 136 9.3.2 Carbon rovings impregnation 142 9.3.3 Steel wires straightening and preshaping 142 9.3.4 Weaving and realized structure 143 10 PERFORMANCE OF MINERAL-BONDED STRENGTHENING LAYER WITH IMPACT-RESISTANT WOVEN 3D CELLULAR REINFORCEMENT 147 10.1 Tensile behavior of SHCC reinforced with 3DWT Pyr Hyb 147 10.1.1 Specimen preparation 147 10.1.2 Quasi-static tension test results 148 10.1.3 Dynamic tension test results 154 10.2 Impact behavior of SHCC reinforced with 3DWT Pyr Hyb 157 10.2.1 Materials under investigation 157 10.2.2 Small-scale plate impact test results 159 10.3 SHCC reinforced with 3DWT Pyr Hyb as strengthening layer on the impacted side of concrete core 169 10.4 Summary and conclusion of the performance investigation on mineral-bonded strengthening layer reinforced with 3DWT Pyr Hyb 173 11 CONCLUSIONS AND RECOMMENDATIONS 175