The ballistic performance was investigated with rigorous testing of the new armor steel alloy, a tempered variant and a benchmark material. Mechanical testing included Hopkinson pressure bar tests, high temperature, notched tests and standard quasi-static tensile tests. The combination of a commercial prototype cast steel and ballistic testing with NATO standard soft projectiles allowed a uniquely practical perspective when comparing results. The ballistic test procedure reported the same minimum thickness values, for STANAG level 1 kinetic energy threats, than the suggested values of the manufacturer and comparison to the new alloy was thus established. Dynamic material characterization is only accurate within the testing range. Using a single material model to predict critical strength and failure over large strain-rate and temperature ranges is only possible if the material response is consistent. A few scaling problems during specimen testing resulted in a challenging data set with subsequent numerical characterization difficulty. Ballistic performance was however found to correlate well with high strain-rate tensile tests. / Thesis (MEng)--University of Pretoria, 2017. / Materials Science and Metallurgical Engineering / MEng / Unrestricted

With the introduction of fragment protective fabrics into combat clothing, there was a need to understand the effect of laundering on the performance of these fabrics. This thesis investigated the effect of typical laundering regimes on selected ballistic protective fabrics representative of those suitable for clothing applications. This study presents evidence that knitted silk and felted ultra-high molecular weight polyethylene retained their ballistic protective performance after laundering. The para-aramid fabrics showed significant improvement from laundering. The dimensional stability of the selected fabrics was affected by laundering and the effect was cumulative. The damage imparted to the fibres was determined to be due to mechanical wear. This mechanical wear was significantly increased when the fabrics were wet. This was due to the water increasing the friction between fibres during the laundering process. The fabrics investigated were shown to be suitable for use in fragment protective clothing, and were more robust than was generally considered.

The optimisation of compressor stage aerofoil and fan blade design remains an important area of titanium alloy research and development for aerospace gas turbines. Such research has important implications for critical and sensitive component integrity and efficiency. In particular, a better understanding of how deformation twinning interacts with microstructural features in titanium alloys is required, because such twinning facilitates plastic deformation at a higher strain rate than dislocations. To investigate this behaviour, commercial purity titanium and the titanium alloy Ti–6Al–4V were subjected to ballistic impact testing at room temperature with a high strain rate of 10³s⁻¹. In addition, a detailed analysis was conducted of three manufacturing processes of Ti–6Al–4V (wt. %) that are likely to cause deformation twinning: metallic shot peening, laser shock peening and deep cold rolling. The results presented in this thesis have furthered the understanding of the role of deformation twinning in the plastic deformation of α-phase titanium. Key findings of the research include the characterisation of deformation twinning types and the conditions that favour certain deformation twinning types. From the analysis of the ballistic testing of commercial purity titanium, the first definitive evidence for the existence of {112‾4} twinning as a rare deformation twinning mode at room temperature in coarse-grained commercial purity titanium is presented. In addition, the ballistic testing results of the Ti–6Al–4V alloy highlighted very different deformation twinning characteristics. Commercial purity titanium deformed plastically by a combination of {101‾2} and {112‾1} tensilve twinning and {112‾4} and {112‾2} compression twinning modes. By contrast, the deformation twinning of Ti–6Al–4V was limited to only the {101‾2} and {112‾1} tensile twinning modes. The two tensile deformation twinning types have very different morphologies in equiaxed fine grained Ti–6Al–4V. {112‾1} deformation twins span multiple grain boundaries and {101‾2} deformation twins reorient entire grains to a twinned orientation. This observation provides evidence for whole grain twinning of equiaxed fine grained Ti–6Al–4V by {101‾2} twinning. Grain boundary interactions between various deformation twinning types and alpha phase grain boundaries in commercial purity titanium and Ti–6Al–4V are reported and analysed. In commercial purity titanium {101‾2} as well as other deformation twinning types were observed interacting across alpha phase boundaries and higher angle alpha phase grain boundaries. The analyses of the manufacturing processes of Ti–6Al–4V highlight the very different dislocation and deformation twinning structures in surfaces processed by these techniques. A notable feature of material processed by laser shock peening is the almost complete absence of deformation twinning, contrasting with the frequent observation of extensive deformation twinning observed in the material processed by metallic shot peening and deep cold rolling. Therefore, the findings suggest that there is a strain rate limit above which deformation twinning is suppressed. The implications of this research are that a better understanding of the conditions that that favour certain deformation twinning types or propagation behaviours will enable more accurate plasticity modelling and better alloy design. This is important for the design and the manufacturing of titanium components and the high strain rate deformation to which titanium components in aerospace gas turbines can be subjected because of bird strike, foreign object debris ingestion or fan blade failures.

Ice-templating, znm tak© jako freeze-casting, je relativnÄ jednoduchou, levnou a velmi univerzln­ technikou pro vrobu por©zn­ch keramickch struktur s ­zenou mikrostrukturou. Takto pipraven© keramick© struktury jsou pouity pro vrobu hybridn­ch keramickch kompozit, nebo jako biokeramick© scaffoldy. Hybridn­ keramick© kompozitn­ materily jsou zaloeny na napodobovn­ p­rodn­ch/ biologickch materil. Hlavn­m c­lem je napodobit v p­rodÄ se vyskytuj­c­ zhouevnauj­c­ mechanismy t­m, e por©zn­ keramick© struktury jsou po slinut­ naputÄny polymern­mi materily. Hlavn­m probl©mem pi vrobÄ por©zn­ch keramickch vzork s velkmi rozmÄry, pomoc­ metody ice-templating, je dosaen­ ­zen©ho rstu ledovch krystal v cel©m objemu vzorku. Aby tedy bylo mon© z­skat velk© keramick© vzorky s dobe definovanou lamelrn­ strukturou je teba proces ice-templatingu velmi pesnÄ kontrolovat. Biologick aktivita biokeramickch materil zvis­ na kombinaci fyzikln­ch a chemickch charakteristik, kter© silnÄ souvisej­ s jejich mikrostrukturou. Porozita scaffold mus­ bt vzjemnÄ propojen a velikost­ pr dostateÄnÄ velk pro spÄn rst kostn­ tknÄ v cel©m objemu implanttu. Prezentovan disertaÄn­ prce je zamÄena na problematiku zvÄtovn­ rozmÄr keramickch vzork pipravench pomoc­ metody ice-templating, vytvoen­ v­cerovov© porozity uvnit vzork a vrobu hybridn­ch keramickch kompozit pro balistickou ochranu. Keramick© suspenze pro ice-templating byly spÄnÄ pipraveny z rznch prk (zejm©na hydroxyapatitu a oxidu hlinit©ho s rznm plnÄn­m keramick©ho prku od 7,5 obj.% do 45 obj.%. Byl tak© studovn vliv aditiv na utven­ lamelrn­ drsnosti a mezilamelrn­ch pemostÄn­. V souÄasnosti je zkoumn dopad tÄchto strukturn­ch prvk na vsledn© mechanick© vlastnosti. Hybridn­ kompozity oxid hlinit/polymer byly spÄnÄ navreny a pipraveny z destiÄek z oxidu hlinit©ho pipravench metodou ice-templating s d©lkou lamel a 70 mm a rznch polymern­ch pryskyic. Byla testovny mechanick© vlastnosti hybridn­ch kompozit oxid hlinit/polymer a vsledky ukzaly, e ice-templating je robustn­ metodou pro vrobu hybridn­ch kompozit keramika-polymer s dobrm pomÄrem pevnost/hustota. Avak balistick© testy hybridn­ch kompozit oxid hlinit/polymer odhalily, e vÄtina kompozit vytvoench v rmci t©to prce nebyla schopna ÄinnÄ zastavit stely s prbojnm jdrem. Ukzalo se, e kombinace procesu ice-templating a nep­m©ho 3D tisku umouje vrobu biokeramickch scaffold pro kostn­ nhrady z hydroxyapatitu s v­cerovovou porozitou, co by se mohlo ukzat jako prospÄn© pro vvoj bioaktivn­ch vysoce por©zn­ch scaffold se zvenou biologickou aktivitou. Ice-templating tak© vznamnÄ ovlivnil zmÄnu fzov©ho sloen­ bÄhem slinovn­ hydroxyapatitovch vzork.