Free machining alloys containing soft immiscible phases in the aluminium (Al) matrix, like lead (Pb) and bismuth (Bi), are of great industrial interest. Typical applications in automotive industry are components requiring very high machinability, such as braking pistons and antiblocking system (ABS) housings. Presence of soft immiscible phases is giving their machining properties to this class of alloys. These phases melt due to localised heat build-up generated by machining process and induce chips breaking. Such type of alloys offers best in class performance when the soft phase is uniformly distributed in the Al matrix. The main objective of this work was to develop a method to tailor the distribution of the immiscible phase particles in the final solidified structure of DC cast billets in order to provide enhanced machinability while keeping low levels of Pb and/or Bi additions. As a consequence, another objective of this study was to improve recyclability of such alloys as well as to reduce their environmental impact. Three categories of Al-Pb alloys and different solidification paths were studied: hypermonotectic Al-3Pb, monotectic Al-1.2Pb and industrial hypo-monotectic free machining alloy containing both Pb and Bi. A newly developed melt conditioning combines mechanical, thermal and chemical treatments to obtain a very fine and uniform distribution of the immiscible phase droplets and eliminate compositional heterogeneities. The effect of these new melt treatments on microstructure was evaluated. For the soft phase droplets size was reduced and distribution becomes finer and more homogeneous under the individual effect of each of the treatments and optimum results obtained with the combination of them. These new melt treatments affect not only the nucleation of the Pb/Bi droplets, enhancing their heterogeneous nucleation but reduces considerably the Marangoni motion and Stokes sedimentation reducing therefore the droplet coalescence and restricting their growth. As a consequence of this improved microstructure, mechanical properties and machining performance were enhanced considerably. The results from this study provide a promising new microstructure with a fine and uniform distribution of droplets.

No description available.

Diplodia tip blight is an important disease of pines, especially Scots pine Christmas trees in Kentucky. The hypothesis for my thesis work was that D. pinea could be acquired and transmitted on the tools during annual shearing of the Christmas trees. Samples taken from tools after shearing on two different Christmas tree farms in Kentucky in 2005 and 2006 yielded D. pinea colony forming units, but in very low quantities; typically less than 10 CFUs per collection. Diplodia-associated dieback from the sheared tips was never found in the field, suggesting that transmission and subsequent infections were not occurring via these sheared tips. Controlled infections indicated that a minimum of 100 spores was necessary to create symptomatic infections on sheared tips. Lysolandamp;reg; Disinfectant Spray did not remove D. pinea from tools when sprayed on them after shearing, but it did effectively prevent spore germination in vitro. Observations of Diplodia lesion development on one Scots pine Christmas tree farm in Kentucky during the springs of 2006 and 2007 suggested that D. pinea infections occurred primarily via the bases of needle bundles on elongating shoots. The most likely source of inoculum was dead infested pine tissues within and beneath the canopy. The use of a protectant fungicide may have resulted in an observed dramatic decrease of disease on this farm.

Novel approaches to the determination of material properties and damage parameters of fibre-matrix composites using inverse analysis are presented. In inverse analysis system identification techniques are used to update some form of mathematical model (normally a FE model) using data from an over-determined number of tests. Initially, pultruded GFRP box-section beams are subjected to a quasi-static impact or bending crush. The results of the impact tests are presented to corroborate those in the literature that have been obtained using simpler geometries such as flat plates. In the first form of inverse analysis, a model-updating approach is applied to progressive tearing damage in pultruded composite box-section beams. The difference between empirical data (from a programme of three-point bend tests) and a FE model is minimised by a genetic algorithm to produce an optimal solution. The solution is in the form of a FE model that can be subsequently analysed to determine the structural integrity of the damaged specimen. Secondly, a unidirectional composite disc from the same GFRP pultruded section is analysed in diametral compression to both verify and improve the validity of the diametral compression test in determining the material properties. Coupons are cut from damaged specimens and test results are presented. The strain distribution within the disc is compared to known laminate theory in order to process data obtained by speckle-shearing interferometry. Finally, speckle-shearing interferometry is used to characterise the response of the pultruded box-section exhibiting progressive tearing damage. Out-of-plane displacement-gradient data is used to determine and characterise damaged regions or flaws. The differences between the need to perform it programme of unequivocal static tests and the collection of full-field optical data are highlighted. It is shown that the shearing interferometry approach is the superior method.

Choice of shearing time is one of the major management decisions for a wool-producing Merino flock and affects many aspects of wool production and sheep health. Previous studies have investigated the effect of shearing on only a few of these factors at a time, so that there is little objective information at the flock level for making rational decisions on shearing time. This is particularly the case for flocks that lamb in spring, the preferred time in south-eastern Australia. / A trial was conducted in a self-replacing, fine wool Merino flock in western Victoria, from January 1999 to May 2004, comparing ewes shorn annually in December, March or May. Within each of these shearing times, progeny were shorn in one of two different patterns, aligning them with their adult shearing group by 15–27 months of age. / Time of shearing did not consistently improve the staple strength of wool. December-shorn ewes produced significantly lighter and finer fleeces (average 19.1 μm, 3.0 kg clean weight), whereas fleeces from March-shorn ewes were heavier and coarser (19.4 μm, 3.1 kg). Fleeces from ewes shorn in May were of similar weight to fleeces from March-shorn ewes (3.1 kg), but they were of significantly broader diameter (19.7 μm). In young sheep, beneficial changes in some wool characteristics for each shearing group were offset by undesirable changes in others. / Shearing ewes in March or May, and weaners in March, May or June, significantly increased the risk of post-shearing mortality about three- and four-fold, respectively, compared to unshorn sheep. Substantial, highly significant associations in young sheep between post-weaning mortality, bodyweight and growth rate were also quantified using various survival analysis techniques. For example, the lightest 20% of weaners at weaning contributed 31% of all deaths in the year following weaning, and increasing average growth rate over summer and autumn from 250 to 500 g/month reduced the risk of death by 74%. These results could be used to develop supplementary feeding systems that efficiently reduce weaner mortality, which is a significant animal welfare issue in many Australian Merino flocks. / Mortality effects were incorporated into estimates of the total value of wool produced by the different shearing times between birth and culling at 6¼ years of age. Using median historical (1991–2006) wool prices, shearing ewes in March and their progeny first in June, or October (weaner)-December (ewe) shearing produced the greatest total value of wool ($111/head). March (weaners)-March (ewes) shearing had a wool value of $107/head and December (weaners)-December (adults) shearing $103/head. May-shorn ewes produced the smallest value of wool, irrespective of whether their progeny were first shorn in May or July ($93–96/head). / No shearing time consistently improved all animal health measures. May-shorn ewes had significantly more fleece rot in late autumn than the other shearing groups (odds ratio 2.5) and were up to 0.4 condition score lighter during winter, although they had a lower cost of dag (average $0.64/head) and significantly less breech strike risk in spring, compared to December-shorn ewes (odds ratio 0.18). December-shorn ewes had the greatest cost of dag ($1.50/head). March-shorn ewes had an intermediate cost of dag ($1.03/head) but significantly less breech strike than May-shorn ewes (odds ratio 0.38).Overall, December and March shearing were shown to be appropriate alternatives for a self-replacing Merino flock in south-eastern Australia, whereas May was an undesirable shearing time.

Aluminium applications can be found in the vast majority of industries – particularly the automotive, aerospace and building sectors. Light weight, good corrosion resistance, high strength with good machining and weldability has led 6xxx series alloy to be the most widely used for extrusion products. Semi-continuous direct-chill (DC) casting is a well established process and the most widely used in the production of wrought aluminium extrusion billets. The techniques have continuously evolved since its invention in the 1930s. To ensure high productivity and a quality billet by DC casting, grain refiners are added during casting prior to solidification. It is efficient, cost effective and considered optimized in modern production techniques. However, some problems still persist, for example, macrosegregation, centerline cracking, porosity, hot tearing, etc. For surface finish critical products, particles in added grain refiners may cause surface defects during downstream processing. Additions of grain refiners are also not desirable for recycling of the end use products. As a novel DC casting technology, the melt conditioned DC casting (MC-DC) technology is developed to achieve uniform fine equiaxed grains without deliberate additions of grain refiners. The MC-DC process is implemented by submerging a rotor-stator high shear device into the mould assembly of a conventional hot-top vertical DC caster. In this work, the fundamentals of MC-DC process has been investigated by studying the flow patterns in the sump using computer modelling in combination with thermal field measurement and delineation of the sump profile. Followed is the microstructural evolution of the MC-DC castings. Then the formation of Fe-bearing intermetallics which are critical to the arrangement of homogenisation treatment are presented. The grain refining mechanism by MC-DC is due to enhanced heterogeneous nucleation on dispersed oxides and grain fragments by intensive melt shearing, in combination with dendrite fragmentation and transportation in a uniform temperature and solute field. By optimising MC-DC parameters, alleviation of macrosegregation can be achieved even compared with DC-GR castings. Another finding is the correlation between grain structure and the distribution of the Fe-intermetallic particles. It has been demonstrated that equiaxed dendritic grains with fine secondary dendritic arm spacings achieved in MC-DC are preferred rather than finer granular grains in grain refined material. MC-DC also promotes the formation of α- Fe-bearing intermetallics. All these offer the potential for the reduction of homogenisation practices currently required as part of the DC process.

The thesis solves the design of tools for pressing round eyelet 10 mm diameter from steel sheet of DX51 0,5 mm thick. The ring is produced on the press LENA 25 C. Based on a literary study of shearing, expanding and neck drawing, a tool was developed that combines the hole punching of the sail and expanding of the ring end. The study of the circle edge appearance on SSM 3-E stereo microscope and the measurement of wall thickness using the ATOS Core 80 was performed. A simulation of the strain on the press was performed. The proposed tool was experimentally verified as working.

The thesis presents a proposal of production of a molded part from the aluminum alloy of group 2024 (dural). Based on the theoretical study and the requirements of the company was designed a cutting tool with a rounded edge for cutting the unfolded shape of the part on the eccentric press LEN 40 C. A new forming tool from textite material for fluid press Quintus QFC was designed. The parts of the cutting tool were designed primarily from normalized (purchased) parts. Manufactured punch and shearing die are made of commonly available tool steels and processed on the attached drawings. The result of the thesis is a recommendation to invest in a specialized workplace for the production of a unfolded shape and reduction of laboriousness adjusting after forming.

The master’s thesis presents a design for the technology of manufacture of a chandelier hinge from the material ČSN 42 3005 (Cu99.5) with a sheet thickness of 0.5 mm. Due to the spherical shape of the part and the series 40 000 parts per year, the technology of deep drawing was chosen for two drawing operations, while the redrawing is performed by reverse deep drawing. Due to the nature of the component, the additional technology is shearing. The manufacturability of the part was verified using numerical simulation in the PAM-STAMP software. The forming process is performed using three forming tools on three different presses. For the first, combined tool, an LE 160C eccentric press is used. A hydraulic press ZHO100 is applied in the second tool for the reverse drawing, and finally, an eccentric press LEK160 is applied for the shearing in the third operation. With the selected profit value of 25 %, the final price for the component was set at CZK 104.17. The turning point occurs after reaching 16 248 parts.

The thesis solves the efficient production of the sheetmetal cover. The new technological procedure will save two manufacturing operations deep drawing. The deep drawing of the cylindrical vessel with a flange and its following calibration in accordance with the design documentation was choosed. The last stage of the deep drawing is the construcion of the circular cut-out and its bending. By doing so the final shape of the cover will be reached.