The use of magnesium and its alloys, as the lightest structural materials, to decrease the weight, improve the fuel efficiency and reduce the greenhouse gas emissions has significantly increased in the automotive and aerospace industries in recent years. However, magnesium alloys are commonly used as die casting products. The current application of wrought magnesium alloy products is limited because of their poor ductility at room temperature due to the formation of a strong texture and restricted active deformation modes in wrought magnesium products. Moreover, to support the application of magnesium alloys in automobile and airplane components, their dynamic mechanical response must be determined to evaluate their behavior during impact events such as car crash and bird strike in airplanes. Therefore, in this research study, the dynamic mechanical behavior of magnesium alloys at high strain rates was investigated. The effects of initial texture, composition, strain rate and grain size on the deformation mechanism were also determined. Split Hopkinson Pressure Bar was used to investigate the dynamic mechanical behavior of the magnesium alloys. Texture analysis on the alloy prior and after shock loading was done using X-ray diffraction. Scanning electron microscopy was used to study the microstructural evolution in the alloys before and after shock loading. Chemical analysis and phase identification were done by energy dispersive spectroscopy and X-ray diffraction analysis, respectively. Additionally, twinning type and distribution was determined by means of orientation imaging microscopy whereas dislocation types and distribution was determined using transmission electron microscopy. A visco-plastic self-consistent simulation was used to corroborate the experimental textures and possible deformation mechanisms. The dynamic mechanical behavior of cast AZ and AE magnesium alloys with different chemistries was investigated at strain rates ranging between 800 to 1400 s-1 to determine the effects of composition on the response of the alloys to shock loading. It was found that an increase in the aluminum content of the AZ alloys increased the volume fraction of β-Mg17Al12 and Al4Mn phases, strength and strain hardening but, on the other hand, decreased the ductility and twinning fraction, particularly extension twinning fraction, for all the investigated strain rates. In addition, increasing the strain rate resulted in considerable increase in strength of the alloys. Texture measurements showed that shock loading of the AE alloys resulted in development of a stronger (00.2) basal texture in samples with higher content of yttrium at the investigated strain rates. Increasing the yttrium content of the cast AE alloys decreased twinning fraction but increased dislocation density and volume fraction of the Al2Y second phase. As a result, the tensile strength and ductility of the alloys increased which is an interesting result for high-strain rate applications of AE alloys in comparison to AZ alloys. The dynamic mechanical behavior of rolled AZ31B and WE43 magnesium alloys were also studied at strain rates ranging between 600 to 1400 s-1. A strong (00.2) basal texture was observed in all shock loaded AZ31B samples. It was also observed that increasing the strain rate led to an increase in strength and ductility, but to a decrease in twinning fraction. A high degree of mechanical anisotropy was found for all investigated strain rates so that the lowest strength was registered for the samples cut along the direction parallel to the rolling direction. Furthermore, it was found that at high strain rates, fine-grained AZ31B alloy exhibits better ductility and strength compared to coarse-grained alloy. However, the hardening rate of coarse-grained alloy was higher. In the case of rolled WE43 alloy, it was found that the strength and ductility increased and twinning fraction decreased with increase in strain rate. Furthermore, another effect of increase in strain rate was the higher activation of pyramidal <c+a> slip systems. In addition, degree of stress and strain anisotropy is low particularly at higher strain rates, which is mainly related to the weak initial texture of the samples due to the presence of rare earth elements. Furthermore, strength and ductility were found to decrease with increasing grain size, while twinning fraction, activity of double and contraction twins and strain hardening rate increase with increasing grain size. In both AZ31B and WE43 alloy, the presence of <c+a> dislocations was confirmed at high strain rates using ‘g.b’ analysis confirming activation of pyramidal <c+a> slip systems during dynamic shock loading.

A strategic research area today is development of polymericproducts made from renewable sources. The ways of utilizingrenewable sources studied in this thesis are using 1)prepolymers obtained by steam treatment of wood and 2) monomersobtainable by fermentation of agricultural products. Novel hemicellulose-based hydrogels were prepared by usingprepolymers obtained from steam treatment of spruce.Hemicellulose was first modified with well-defined amounts ofmethacrylic functions. Hydrogels were then prepared by radicalpolymerization with 2-hydroxyethyl methacrylate orpoly(ethylene glycol) dimethacrylate to form hydrogels. Theradical polymerization reaction was carried out in water usinga redox initiator system. The hydrogels were in generalelastic, soft and easily swollen in water. Frequency sweeptests indicated that the hydrogel system displayed prevailingsolid-like behavior. Comparison of the hemicellulose-basedhydrogels with pure poly(2-hydroxyethyl methacrylate)-basedhydrogels showed that it was possible to preparehemicellulose-based hydrogels with properties similar to thoseof pure poly(2-hydroxyethyl methacrylate)-based hydrogels. Polyester-based materials were prepared by using themonomers 1,3- propanediol and succinic acid obtainable byfermentation. α,ω-Dihydroxyterminatedoligomeric polyesters produced by the thermal polycondensationof 1,3-propanediol and succinic acid were chain-extended toobtain sufficiently high molecular weight. Depending on thechain-extension technology adopted, poly(ester carbonate)s orpoly(ester urethane)s were obtained. In the case of poly(estercarbonate)s, the chain-extended products ofα,ω-dihydroxyterminated oligomeric copolyesters werealso produced using 1,3-propanediol/1,4-cyclohexanedimethanol/succinic acid mixtures toimprove thermal and mechanical properties. Segmented poly(esterether carbonate)s fromα,ω-dihydroxyterminated oligo(propylenesuccinate)s and poly(ethylene glycol) were also synthesized toincrease the hydrophilicity. Molecular weights and polydispersity were analyzed by SECfor all materials. Their structures were also identified by NMRspectroscopy (1H NMR and 13C NMR). All characterizations werein agreement with the proposed structures. Thermal parameterswere characterized by DSC. Tensile testing anddynamic-mechanical tests were performed and in additionpreliminary processing trials were carried out in some cases.The results demonstrate the feasibility of using monomersderived from renewable sources to build up new polymericstructures endowed with a variety of physical and mechanicalproperties.

<p>A strategic research area today is development of polymericproducts made from renewable sources. The ways of utilizingrenewable sources studied in this thesis are using 1)prepolymers obtained by steam treatment of wood and 2) monomersobtainable by fermentation of agricultural products.</p><p>Novel hemicellulose-based hydrogels were prepared by usingprepolymers obtained from steam treatment of spruce.Hemicellulose was first modified with well-defined amounts ofmethacrylic functions. Hydrogels were then prepared by radicalpolymerization with 2-hydroxyethyl methacrylate orpoly(ethylene glycol) dimethacrylate to form hydrogels. Theradical polymerization reaction was carried out in water usinga redox initiator system. The hydrogels were in generalelastic, soft and easily swollen in water. Frequency sweeptests indicated that the hydrogel system displayed prevailingsolid-like behavior. Comparison of the hemicellulose-basedhydrogels with pure poly(2-hydroxyethyl methacrylate)-basedhydrogels showed that it was possible to preparehemicellulose-based hydrogels with properties similar to thoseof pure poly(2-hydroxyethyl methacrylate)-based hydrogels.</p><p>Polyester-based materials were prepared by using themonomers 1,3- propanediol and succinic acid obtainable byfermentation. α,ω-Dihydroxyterminatedoligomeric polyesters produced by the thermal polycondensationof 1,3-propanediol and succinic acid were chain-extended toobtain sufficiently high molecular weight. Depending on thechain-extension technology adopted, poly(ester carbonate)s orpoly(ester urethane)s were obtained. In the case of poly(estercarbonate)s, the chain-extended products ofα,ω-dihydroxyterminated oligomeric copolyesters werealso produced using 1,3-propanediol/1,4-cyclohexanedimethanol/succinic acid mixtures toimprove thermal and mechanical properties. Segmented poly(esterether carbonate)s fromα,ω-dihydroxyterminated oligo(propylenesuccinate)s and poly(ethylene glycol) were also synthesized toincrease the hydrophilicity.</p><p>Molecular weights and polydispersity were analyzed by SECfor all materials. Their structures were also identified by NMRspectroscopy (1H NMR and 13C NMR). All characterizations werein agreement with the proposed structures. Thermal parameterswere characterized by DSC. Tensile testing anddynamic-mechanical tests were performed and in additionpreliminary processing trials were carried out in some cases.The results demonstrate the feasibility of using monomersderived from renewable sources to build up new polymericstructures endowed with a variety of physical and mechanicalproperties.</p>

Organic hybrid composites based on carboxylated nitrile rubber and nylon-12 reinforced with mercerized and diisocyanated lignocellulose residue (LCR) was prepared. The influence of the LCR on the viscoelastic properties of these organic hybrids was investigated by dynamic mechanical analysis and thermal analysis (differential scanning calorimetry (DSC)). It is found that either the position of the damping peak was shifted to higher values or the intensity of the damping peak was significantly increased with LCR. These results could imply that the LCR enhanced the damping properties of the composites. The thermal stability of the composites was evaluated with the mean values obtained using thermogravimetrical analysis. The decomposition rate was investigated using differential thermal gravimetry. The crystallization behavior of the prepared composites was checked by DSC.