Zur Beantwortung der Frage, wie sich die festigkeitssteigernden Effekte aus mehraxialer und dynamischer Druckbelastung in Beton überlagern wurde ein weltweit einzigartiger zweiaxialer Split-Hopkinson-Bar entwickelt. Es wurden umfangreiche Versuchsserien mit insgesamt mehr als 2500 Einzelversuchen durchgeführt. Ermittelt wurden dabei die ein- und zweiaxialen statischen und dynamischen Betondruckfestigkeiten zweier Betone der Druckfestigkeitsklassen C20/25 und C40/50. Die Versuchsergebnisse wurden hinsichtlich der Festigkeitsentwicklung in Abhängigkeit vom Spannungsverhältnis und der Dehnrate ausgewertet. Die Ergebnisse aus den zweiaxialen dynamischen Betondruckversuchen konnten als dreidimensionale Abhängigkeit der Spannungen in beiden Belastungsachsen von der Dehnrate für jede der beiden Betonsorten abgebildet werden. Aus den Ergebnissen wurde ein Ingenieurmodell für jede Betonsorte entwickelt, welches die Betondruckfestigkeitsentwicklung in Abhängigkeit vom Spannungsverhältnis und der Dehnrate beschreibt. Mit zunehmender Dehnrate wird die zweiaxiale Ergebniskurve um einen zusätzlichen, dynamischen Anteil der Festigkeitssteigerung vergrößert. Dabei kommt es aber nur zu einer teilweisen Überlagerung der beiden betrachteten festigkeitssteigernden Einflüsse. Eine Abschätzung der Größenordnung der jeweiligen Einflüsse aus Mehraxialität und hoher Belastungsgeschwindigkeit konnte durch eine entsprechend differenzierte Auswertung vorgenommen werden. Die Untersuchung der Bruchstücke der zerstörten Probekörper zeigte, dass die Verteilung der Partikelgröße stark von der Dehnrate abhängig ist. Im Gegensatz dazu hängt die Partikelgeometrie und die Form und Masse der entstehenden Kernbruchstücke vom Spannungsverhältnis ab.

Strain hardening cement-based composites (SHCC) and textile reinforced concrete (TRC) are two types of novel cementitious materials which can be used for strengthening structural elements against impact loading. Under tensile loading, these composites exhibit a strain hardening behavior, accompanied with formation of multiple cracks. The multiple cracking and strain hardening behavior yield a high strain and energy absorption capacity, thus making SHCC and TRC suitable materials for impact resistant structures or protective layers. The design and optimization of such composites for impact resistant applications require a comprehensive characterization of their behavior under various impact loadings. Specifically, the rate dependent behavior of the composites and their constituents, i.e. matrix, reinforcement, and their bond, need to be described. In the context of dynamic testing, SHCC, TRC and their constituents require customized experimental setups. The geometry of the sample, ductility of the material, the need for adapters and their influence on the measurements, as well as the influence of inertia are the key aspects which should be considered in developing the impact testing setups. The thesis at hand deals with the development process of various impact testing setups for both composite scale and constituent scale. The crucial aspects to be taken into account are discussed extensively. As a result, a gravity driven split-Hopkinson tension bar was developed. The setup was used for performing impact tension experiments on SHCC, TRC and yarn-matrix bond. Moreover, its applicability for performing impact shear experiments was examined. Additionally, a mini split-Hopkinson tension bar for high speed micromechanical experiments was designed and built. In the case of compressive loading, the performance of SHCC was investigated in a split-Hopkinson pressure bar. The obtained results, with focus on tensile experiments, were evaluated concerning their accuracy, and susceptibility to inertia effects. Full-field displacement measurement obtained by digital image correlation (DIC) was used in all impact experiments as a tool for visualizing and explaining the fracture process of the material in conjunction with the standard wave analysis performed in the split-Hopkinson bars.Moreover, the rate dependent behaviors of the composites were clarified with respect to the rate dependent behavior of their constituents.

Polymers are increasingly being used in engineering designs due to their favorable mechanical properties such as high specific strength, corrosive resistance, manufacturing flexibility. The understanding of the mechanical behavior of these polymers under both static and dynamic loading is critical for their optimal implementation in engineering applications. One such polymer utilized in a wide variety of applications from medical instrumentation to munitions is Polyetherimide, referred to as Ultem. This thesis characterizes both the static and dynamic mechanical behavior of Ultem 1000 through experimental methods and numerical simulations. Standard compression experiments were conducted on and MTS test frame to characterize the elastic-plastic behavior of Ultem 1000 under quasi-static conditions. The dynamic response of the material was investigated at very high strain rates using a custom built miniaturized Kolsky bar apparatus. The smaller Kolsky bar configuration was chosen over the conventional Kolsky device to increase the maximum capable strain rates and to reduce common experimental problems such as wave dispersion, friction, and stress equilibrium. Since a universal test standard for this apparatus is not available, the details of the design, construction, and experimental procedures of this device are provided. The results of the high strain rate testing revealed a bilinear relationship between the material yield stress and strain rate. This relationship was modeled using the Ree-Eyring two stage activation process equation.

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The principal aims of this research have been the development of photogrammetric techniques for the measurement of anisotropic deformation in uniaxially loaded cylindrical specimens. This has been achieved through the use of calibrated cameras and the application of edge detection and multiple view geometry. The techniques have been demonstrated at quasi-static strain rates, 10^-3 s^-1, using a screw-driven loading device and high strain rates, 10^3 s^-1, using Split Hopkinson Bars. The materials that have been measured using the technique are nearlyisotropic steel, anisotropic cross-rolled Ti-6Al-4V and anisotropic clock-rolled commercially pure Zr. These techniques allow the surface shapes of specimens that deform elliptically to be completely tracked and measured in situ during loading. This has allowed the measurement of properties that could not have been recorded before, including true direct stress and the ratio of transverse strains in principal material directions, at quasi-static and elevated strain rates, in tension and compression. The techniques have been validated by measuring elliptical prisms of various aspect ratios and independently measuring interrupted specimens using a coordinate measurement machine. A secondary aim of this research has been to improve the characterisation of the anisotropic mechanical properties of cross-rolled Ti-6Al-4V using the techniques developed. In particular, the uniaxial yield stresses, hardening properties and the associated anisotropic deformation behaviour along the principal material directions, have all been recorded in detail not seen before. Significant findings include: higher yield stresses in-plane than in the through-thickness direction in both tension and compression, and the near transverse-isotropy of the through-thickness direction for loading conditions other than quasi-static tension, where significant anisotropy was observed.

Carbon nanotubes, graphene and nano sized core shell rubber particles have all been extensively researched for their capability to improve mechanical properties of thermoset resins. However, there has been a lack of research on their evaluation for energy absorption in high velocity impact scenarios, and the fundamental mechanics of their failure mechanisms during highly dynamic stress transfer through the matrix. This fundamental research is essential for laying the foundation for improvement in ballistic performance in composite armor. In hard armor applications, energy absorption is largely accomplished through delamination between plies of the composite laminate. This energy absorption is accomplished through two mechanisms. The first being the elongation of the fiber reinforcement contained in the resin matrix, and the second is the propagation of the crack in between the discreet fabric plies. This research aims to fundamentally study the energy absorption characteristics of various nano-particles as reinforcements in thermoset resin for high velocity impact applications. Multiple morphologies will be evaluated through use of platelet, tubular and spherical shaped nano-particles. Evaluations of the effect on stress transfer through the matrix due to the combination of nano sized and micro scale particles of milled fiber is conducted. Three different nano-particles are utilized, specifically, multi-walled carbon nanotubes, graphene, and core shell rubber particles. The difference in surface area, aspect ratio and molecular structure between the tube, platelet and spherical nano-particles causes energy absorption through different failure mechanisms. This changes the impact performance of composite panels enhanced with the nanoparticle fillers. Composite panels made through the use of dispersing the various nano-particles iv in a non-contact planetary mixer, are evaluated through various dynamic and static testing, including unnotched cantilever beam impact, mixed mode fracture toughness, split-Hopkinson bar, and ballistic V50 testing. The unnotched cantilever beam testing showed that the addition of milled fiber degraded the impact resistance of the samples. Addition of graphene nano platelets unilaterally degraded impact resistance through the unnotched cantilever beam testing. 1.5% loading of MWCNT showed the greatest increase in impact resistance, with a 43% increase over baseline. Determining the critical load for mixed mode interlaminar shear testing can be difficult for composite panels that bend without breaking. An iterative technique of optimizing the coefficient of determination, R2 , in linear regression is developed for objectively determining the point of non-linearity for critical load. This allows for a mathematical method of determination; thereby eliminating any subjective decision of choosing where the data becomes non-linear. The core shell rubber nano particles showed the greatest strain energy release rate with an exponential improvement over the baseline results. Synergistic effects between nano and micro sized particles in the resin matrix during transfer of the stress wave were created and evaluated. Loadings of 1% milled carbon fiber enhanced the V50 ballistic performance of both carbon nanotube and core shell rubber particles in the resin matrix. However, the addition of milled carbon fiber degrades the impact resistance of all nano-particle enhanced resin matrices. Therefore, benefits gained from the addition of microsized particles in combination with nano-sized particles, are only seen in high energy impact scenarios with micro second durations. v Loadings of 1% core shell rubber particles and 1% milled carbon fiber have an improvement of 8% in V50 ballistic performance over the baseline epoxy sample for 44 mag single wad cutter gas check projectiles. Loadings of 1% multi-walled carbon nanotubes with 1% milled carbon fiber have an improvement of 7.3% in V50 ballistic performance over the baseline epoxy sample. The failure mechanism of the various nano-particle enhanced resin matrices during the ballistic event is discussed through the use of scanning electron microscope images and Raman spectroscopy of the panels after failure. The Raman spectroscopy data shows a Raman shift for the fibers that had an enhancement in the V50 performance through the use of nano-particles. The Raman band for Kevlar® centered at 1,649 cm-1 stemming from the stretching of the C==O bond of the fiber shows to be more sensitive to the residual axial strain, while the Raman band centered at 1,611 cm-1 stemming from the C-C phenyl ring is minimally affected for the CSR enhanced panels due to the failure mechanism of the CSR particles during crack propagation.