The present work focuses on the structure-property relationships of particulate-filled thermoplastics and thermoplastic elastomer (TPE). In this work two thermoplastics and one TPE were used as polymer matrices, i.e. amorphous bisphenol-A polycarbonate (PC), semi-crystalline isotactic polypropylene (iPP), and a block copolymer poly(butylene terephthalate)-block-poly(tetramethylene glycol) TPE(PBT-PTMG). For PC, a selected type of various Aerosil® nano-SiO2 types was used as filler to improve the thermal and mechanical properties by maintaining the transparency of PC matrix. Different types of SiO2 and TiO2 nanoparticles with different surface polarity were used for iPP. The goal was to examine the influence of surface polarity and chemical nature of nanoparticles on the thermal, mechanical and morphological properties of iPP composites. For TPE(PBT-PTMG), three TiO2 particles were used, i.e. one grade with hydroxyl groups on the particle surface and the other two grades are surface-modified with metal and metal oxides, respectively. The influence of primary size and dispersion quality of TiO2 particles on the properties of TPE(PBT-PTMG)/TiO2 composites were determined and discussed. All polymer composites were produced by direct melt blending in a twin-screw extruder via masterbatch technique. The dispersion of particles was examined by using scanning electron microscopy (SEM) and micro-computerized tomography (μCT). The thermal and crystalline properties of polymer composites were characterized by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The mechanical and thermomechanical properties were determined by using mechanical tensile testing, compact tension and Charpy impact as well as dynamic-mechanical thermal analysis (DMTA). The SEM results show that the unpolar-surface modified nanoparticles are better dispersed in polymer matrices as iPP than polar-surface nanoparticles, especially in case of using Aeroxide® TiO2 nanoparticles. The Aeroxide® TiO2 nanoparticles with a polar surface due to Ti-OH groups result in a very high degree of agglomeration in both iPP and TPE matrices because of strong van der Waals interactions among particles (hydrogen bonding). Compared to unmodified Aeroxide® TiO2 nanoparticles, the other grades of surface modified TiO2 particles are very homogenously dispersed in used iPP and TPE(PBT-PTMG). The incorporation of SiO2 nanoparticles into bisphenol-A PC significantly increases the mechanical properties of PC/SiO2 nanocomposites, particularly the resistance against environmental stress crazing (ESC). However, the transparency of PC/SiO2 nanocomposites decreases with increasing nanoparticle content and size due to a mismatch of infractive indices of PC and SiO2 particles. The different surface polarity of nanoparticles in iPP shows evident influence on properties of iPP composites. Among iPP/SiO2 nanocomposites, the nanocomposite containing SiO2 nanoparticles with a higher degree of hydrophobicity shows improved fracture and impact toughness compared to the other iPP/SiO2 composites. The TPE(PBT-PTMG)/TiO2 composites show much better thermal and mechanical properties than neat TPE(PBT-PTMG) due to strong chemical interactions between polymer matrix and TiO2 particles. In addition, better dispersion quality of TiO2 particles in used TPE(PBT-PTMG) leads to dramatically improved mechanical properties of TPE(PBT-PTMG)/TiO2 composites.

In recent years, nanofiller-reinforced polymer composites have attracted considerable interest from numerous researchers, since they can offer unique mechanical, electrical, optical and thermal properties compared to the conventional polymer composites filled with micron-sized particles or short fibers. With this background, the main objective of the present work was to investigate the various mechanical properties of polymer matrices filled with different inorganic rigid nanofillers, including SiOB2B, TiOB2B, AlB2BOB3B and multi-walled carbon nanotubes (MWNT). Further, special attention was paid to the fracture behaviours of the polymer nanocomposites. The polymer matrices used in this work contained two types of epoxy resin (cycloaliphatic and bisphenol-F) and two types of thermoplastic polymer (polyamide 66 and isotactic polypropylene). The epoxy-based nanocomposites (filled with nano-SiOB2B) were formed in situ by a special sol-gel technique supplied by nanoresins AG. Excellent nanoparticle dispersion was achieved even at rather high particle loading. The almost homogeneously distributed nanoparticles can improve the elastic modulus and fracture toughness (characterized by KBICB and GBICB) simultaneously. According to dynamic mechanical and thermal analysis (DMTA), the nanosilica particles in epoxy resins possessed considerable "effective volume fraction" in comparison with their actual volume fraction, due to the presence of the interphase. Moreover, AFM and high-resolution SEM observations also suggested that the nanosilica particles were coated with a polymer layer and therefore a core-shell structure of particle-matrix was expected. Furthermore, based on SEM fractography, several toughening mechanisms were considered to be responsible for the improvement in toughness, which included crack deflection, crack pinning/bowing and plastic deformation of matrix induced by nanoparticles. The PA66 or iPP-based nanocomposites were fabricated by a conventional meltextrusion technique. Here, the nanofiller content was set constant as 1 vol.%. Relatively good particle dispersion was found, though some small aggregates still existed. The elastic modulus of both PA66 and iPP was moderately improved after incorporation of the nanofillers. The fracture behaviours of these materials were characterized by an essential work fracture (EWF) approach. In the case of PA66 system, the EWF experiments were carried out over a broad temperature range (23~120 °C). It was found that the EWF parameters exhibited high temperature dependence. At most testing temperatures, a small amount of nanoparticles could produce obvious toughening effects at the cost of reduction in plastic deformation of the matrix. In light of SEM fractographs and crack opening tip (COD) analysis, the crack blunting induced by nanoparticles might be the major source of this toughening. The fracture behaviours of PP filled with MWNTs were investigated over a broad temperature range (-196~80 °C) in terms of notched impact resistance. It was found that MWNTs could enhance the notched impact resistance of PP matrix significantly once the testing temperature was higher than the glass transition temperature (TBgB) of neat PP. At the relevant temperature range, the longer the MWNTs, the better was the impact resistance. SEM observation revealed three failure modes of nanotubes: nanotube bridging, debonding/pullout and fracture. All of them would contribute to impact toughness to a degree. Moreover, the nanotube fracture was considered as the major failure mode. In addition, the smaller spherulites induced by the nanotubes would also benefit toughness.

This thesis is concerned with the extended finite element method (XFEM) for deformation analysis of three-dimensional heterogeneous materials. Using the "enhanced abs enrichment" the XFEM is able to reproduce kinks in the displacements and therewith jumps in the strains within elements of the underlying tetrahedral finite element mesh. A complex model for the micro structure reconstruction of aluminum matrix composite AMC225xe and the modeling of its macroscopic thermo-mechanical plastic deformation behavior is presented, using the XFEM. Additionally, a novel stabilization algorithm is introduced for the XFEM. This algorithm requires preprocessing only.

Für die lösbare Verbindung von Bauteilen aus Polymerwerkstoffen sind Direktver-schraubungen das kostengünstigen Fügeverfahren. Nachteilig sind allerdings die durch das viskoelastische Verhalten der Polymerwerkstoffe bedingte zeit- und tem-peraturabhängige Abnahme der Vorspannkraft und deren weitere Beeinflussung durch den Wärmeausdehnungsunterschied von Polymerwerkstoff und Metall. Ziel der Arbeit ist es, durch den gekoppelten Einsatz von Experiment und FE-Simulation den Einfluss von Zeit und Temperatur auf die Vorspannkraft bei Direktverschraubungen in Polymerwerkstoffen zu beschreiben. Der Tubus aus Polymerwerkstoff, der auf-grund der Faserorientierung inhomogen und anisotrop ist, wird ortsaufgelöst unter-sucht, und hierauf aufbauend werden die lokalen Werkstoffparameter für die FE-Analyse ermittelt. Die FE-Analyse der Direktverschraubung selbst wird experimentell anhand des Vorspannkraftverlaufs sowie der Oberflächendeformation überprüft. Beim betrachteten Verbindungssystem ist deutlich zu beobachten, dass der Vor-spannkraftabbau hauptsächlich im Bereich der Entlastungsbohrung bis zu einer be-stimmten Einschraubtiefe stattfindet.

The broad engineering applications of polymers and composites have become the state of the art due to their numerous advantages over metals and alloys, such as lightweight, easy processing and manufacturing, as well as acceptable mechanical properties. However, a general deficiency of thermoplastics is their relatively poor creep resistance, impairing service durability and safety, which is a significant barrier to further their potential applications. In recent years, polymer nanocomposites have been increasingly focused as a novel field in materials science. There are still many scientific questions concerning these materials leading to the optimal property combinations. The major task of the current work is to study the improved creep resistance of thermoplastics filled with various nanoparticles and multi-walled carbon nanotubes. A systematic study of three different nanocomposite systems by means of experimental observation and modeling and prediction was carried out. In the first part, a nanoparticle/PA system was prepared to undergo creep tests under different stress levels (20, 30, 40 MPa) at various temperatures (23, 50, 80 °C). The aim was to understand the effect of different nanoparticles on creep performance. 1 vol. % of 300 nm and 21 nm TiO2 nanoparticles and nanoclay was considered. Surface modified 21 nm TiO2 particles were also investigated. Static tensile tests were conducted at those temperatures accordingly. It was found that creep resistance was significantly enhanced to different degrees by the nanoparticles, without sacrificing static tensile properties. Creep was characterized by isochronous stress-strain curves, creep rate, and creep compliance under different temperatures and stress levels. Orientational hardening, as well as thermally and stress activated processes were briefly introduced to further understanding of the creep mechanisms of these nanocomposites. The second material system was PP filled with 1 vol. % 300 nm and 21 nm TiO2 nanoparticles, which was used to obtain more information about the effect of particle size on creep behavior based on another matrix material with much lower Tg. It was found especially that small nanoparticles could significantly improve creep resistance. Additionally, creep lifetime under high stress levels was noticeably extended by smaller nanoparticles. The improvement in creep resistance was attributed to a very dense network formed by the small particles that effectively restricted the mobility of polymer chains. Changes in the spherulite morphology and crystallinity in specimens before and after creep tests confirmed this explanation. In the third material system, the objective was to explore the creep behavior of PP reinforced with multi-walled carbon nanotubes. Short and long aspect ratio nanotubes with 1 vol. % were used. It was found that nanotubes markedly improved the creep resistance of the matrix, with reduced creep deformation and rate. In addition, the creep lifetime of the composites was dramatically extended by 1,000 % at elevated temperatures. This enhancement contributed to efficient load transfer between carbon nanotubes and surrounding polymer chains. Finally, a modeling analysis and prediction of long-term creep behaviors presented a comprehensive understanding of creep in the materials studied here. Both the Burgers model and Findley power law were applied to satisfactorily simulate the experimental data. The parameter analysis based on Burgers model provided an explanation of structure-to-property relationships. Due to their intrinsic difference, the power law was more capable of predicting long-term behaviors than Burgers model. The time-temperature-stress superposition principle was adopted to predict long-term creep performance based on the short-term experimental data, to make it possible to forecast the future performance of materials.