Bloodstain pattern analysis is used in the investigation of a crime scene to infer the impact velocity and size of an impacting droplet and from these, the droplet’s point and cause of origin. The final pattern is the result of complex fluid dynamic processes involved in the impact and spreading of a blood drop on a surface with variable surface properties such as wettability and porosity. An experiment has been designed to study these processes and the resulting patterns for the case of a single Newtonian droplet impacting an inclined surface with variable roughness and wetting properties. An experimental apparatus, including a droplet generator, has been designed to produce droplets on-demand, and that impact an interchangeable surface. In addition, a blood-simulant liquid has been developed as a replacement for performing tests with real blood. With this apparatus and blood simulant, fluid dynamics concepts, such as contact line motion and wetting behavior are examined in the context of parameters of interest to the forensics community. These include eccentricity, spread factor and the number of spines formed on impact. The effect of varying dimensionless parameters including Reynolds number, Weber number and Laplace number, the angle of impact and surface properties is examined. Correlations are developed for predicting conditions at the point of impact from those observed later, as would be available to a forensics examiner, and the accuracy of the predictions developed in this thesis are evaluated.

In order to estimate the oxygen fugacity of Hawaiian lavas I have measured the ferric/ferrous ratios of samples from the 1984 eruption of Mauna Loa volcano and from the ongoing (1983-2017) Puu Oo eruption of Kilauea volcano. Fifteen samples were studied from the 21 day Mauna Loa eruption and 86 samples, erupted between 1983 and 2004, of the 34 year long Kilauea eruption. Both studies show that, in order to obtain reliable estimates of oxygen fugacity when, where, and how basaltic lava is sampled is of critical importance. Water-quenched lavas and spatter sampled at, or near vents, are less oxidized than water-quenched samples taken from open flow channels several kilometers away from the vent, or from slowly-cooled solidified flows. Additionally, samples of water-quenched lava traveling in lava tubes are less prone to oxidation than lava flowing in open channels, with oxygen fugacities similar to those of near vent quenched samples. The oxidation state of the rapidly quenched near vent or lava tube samples is at or below magnetite-wüstite (MW). This contrasts with the oxidation state of previously reported values for Hawaiian lavas, which are closer to fayalite-magnetite-quartz (FMQ) or nickel-nickel oxide (NNO). From this I conclude that the initial oxygen fugacity of Hawaiian parental magmas is close to MW and not FMQ, and that previous estimates of the oxidation state of Hawaiian magmas, based on data from solidified lava flows, were too high. This implies that the plume source of both Mauna Loa and Kilauea magmas is also close to MW, but not as reduced as the mantle source of mid-ocean ridge basalts.

The causes of errors in the angle of impact calculation were investigated including the surface type, falling velocity and the method used to fit an ellipse to a bloodstain. As had been cited previously the angle of impact was generally underestimated, especially at acute angles and the reason for this was determined to be due to an overestimation of the length of a bloodstain. The surface type was found to significantly affect the accuracy of an angle of impact calculation and as the falling velocity increased, the angle of impact calculation became more accurate. High-speed photography was used to further investigate the formation of bloodstains on surfaces. It was found that the formation of the bloodstain varied depending on the surface type and the angle of the surface. Bloodstain pattern analysis involves the application of scientific techniques to reconstruct events that resulted in a bloodstain pattern. The position of the blood source in three-dimensional space is a fundamental element of this application. Currently little is known about the methods used by bloodstain pattern analysts to select bloodstains when determining the region of origin. Fourteen analysts worldwide were surveyed in order to ascertain this information. It was found that the methods used were variable and were often not based on scientific research. Research was therefore undertaken into bloodstain selection and in particular, which bloodstains should be selected for a region of origin analysis. As a result of these experiments, two sets of selection criteria were established, one for use when the region of origin is being calculated manually and one for when directional analysis is being used.

The causes of errors in the angle of impact calculation were investigated including the surface type, falling velocity and the method used to fit an ellipse to a bloodstain. As had been cited previously the angle of impact was generally underestimated, especially at acute angles and the reason for this was determined to be due to an overestimation of the length of a bloodstain. The surface type was found to significantly affect the accuracy of an angle of impact calculation and as the falling velocity increased, the angle of impact calculation became more accurate. High-speed photography was used to further investigate the formation of bloodstains on surfaces. It was found that the formation of the bloodstain varied depending on the surface type and the angle of the surface. Bloodstain pattern analysis involves the application of scientific techniques to reconstruct events that resulted in a bloodstain pattern. The position of the blood source in three-dimensional space is a fundamental element of this application. Currently little is known about the methods used by bloodstain pattern analysts to select bloodstains when determining the region of origin. Fourteen analysts worldwide were surveyed in order to ascertain this information. It was found that the methods used were variable and were often not based on scientific research. Research was therefore undertaken into bloodstain selection and in particular, which bloodstains should be selected for a region of origin analysis. As a result of these experiments, two sets of selection criteria were established, one for use when the region of origin is being calculated manually and one for when directional analysis is being used.

Cold laps are defined as micro-lack of fusion defects at the weld toe more or less parallel to the surface of the parent plate. These defects are known to negatively influence the fatigue properties of weldments. Previous studies suggest that cold lap formation can not be avoided completely in Gas Metal Arc Welding (GMAW). Therefore, a better understanding of formation mechanisms is imperative to be able to minimize the number and size of these defects. The main objective of this work has been to provide a more comprehensive understanding of cold laps, including categorising, characterisation and defining the most significant factors for formation. GMAW was used to produce welds that were investigated by metallographic methods using light optical microscopy, scanning electron microscopy and energy dispersive spectrometry. A novel classification of cold laps was introduced and three types of cold laps were identified: spatter cold laps, overlap cold laps and spatter-overlap cold laps. It was shown that cold laps are partially or fully filled by oxides. The most common oxides are manganese silicon oxides which were concluded to be formed primarily by oxidation of droplets. The presence of oxides was found to significantly increase the tendency to form spatter cold laps as well as overlap cold laps. Particularly for overlap cold laps, it was found that the depth (in transverse direction of weld) is reduced when welding in a non-oxidising environment. Welding on blasted surfaces increased the cold lap formation by entrapment of gas. The droplet and base metal temperatures were also found to be significant factors in cold lap formation. For overlap cold laps the occurrence frequency decreased with increased preheating temperature of the base metal. Mechanisms of overflowing resulting in overlap cold laps were discussed based on an extensive literature review. Several phenomena are believed to contribute to overflow including Rayleigh instability, the balance of forces, transfer of lateral momentum by droplets and an outward Marangoni fluid flow of the weld pool. The present studies suggest that cold lap formation can be suppressed by ensuring that the welding process (arc) is as stable as possible and by welding on a preheated work piece in a non-oxidising environment.

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