Sarah V. Hainsworth

The effect of the substrate on the mechanical properties of TiN coatings

TiN coatings are commonly used in industry to impart improved friction and wear performance. It is widely recognised that the substrate plays an important role in determining the mechanical properties and wear resistance of such coatings. TiN coatings are usually applied to hard tool steels where there is substantial load support from the substrate. However, there are many applications where it may be desirable to apply the coatings to substrates with lower hardness or stiffness values than the conventional, hard tool-steel substrates that are commonly used. Coatings can still be effectively used in these applications. However, it is then critical to understand the transitions between where the deformation is contained solely in the coating and where it is a combination of coating/substrate properties that are important in determining the overall mechanical response of the system. This paper therefore reports on a systematic investigation of the effect of the substrate on the mechanical response using a range of mechanical testing techniques. A TiN coating was deposited using ion-assisted PVD onto a number of substrates with differing combinations of modulus and hardness [i.e. a range of Youngs modulus (E) to yield stress (Y) E/Y ratios]. The mechanical properties of these coatings have been investigated using nanoindentation, microindentation and scratch testing, and the deformation was observed using scanning electron microscopy. In the microindentation tests, nested cracks were observed around the indentations. In the nanoindentation tests, the indentation response was found to be plasticity-dominated, with little evidence of cracking. The scratch tests showed that the scratch response was controlled by plastic deformation in the substrate, and that the friction coefficient increased as the depth of penetration into the sample increased. For the coatings here, it was observed that the indentation depth/coating thickness ratio required for the deformation to be contained within the coating was less than the usual t/10 ratio.

Cutting crime: the analysis of the “uniqueness” of saw marks on bone

Witness marks produced on bone by the use of saws have traditionally been examined using stereomicroscopy. The marks are typically found on the kerf wall or floor and give important information about the implement that made them. This paper describes a new approach to the analysis of witness marks left on kerf walls and floors from crimes involving dismemberment. Previously, two types of marks have been identified: deep furrows formed during the pull stroke and fine striations formed on the push stroke. These types of striation allow the class of saw to be identified, but not an individual saw. With the advent of environmental scanning electron microscopy (ESEM), insulating materials can now be examined without the need for conductive coatings to be applied. This allows materials to be examined at higher magnifications than those available with stereomicroscopy. Here we report on a new, third type of striation that is visible at higher magnifications on ESEM images. These striations are formed from the imperfections on the cutting teeth of saws and give real possibilities of uniquely identifying whether or not a particular saw was used to cause the mark. In blind trials conducted on sawing of nylon 6.6, different individual saws could be successfully identified even if different people used the saw. We discuss ways in which these results can be extended to bone and how this may assist in the investigation of the act of dismemberment.

Airway wall geometry in asthma and nonasthmatic eosinophilic bronchitis

Background:  Variable airflow obstruction and airway hyperresponsiveness (AHR) are features of asthma, which are absent in nonasthmatic eosinophilic bronchitis (EB). Airway remodelling is characteristic of both conditions suggesting that remodelling and airway dysfunction are disassociated, but whether the airway geometry differs between asthma and nonasthmatic EB is uncertain.

The role of micro-computed tomography in forensic investigations☆

The use of micro-CT within forensic practice remains an emerging technology, principally due to its current limited availability to forensic practitioners. This review provides those with little or no previous experience of the potential roles of micro-CT in forensic practice with an illustrated overview of the technology, and the areas of practice in which micro-CT can potentially be applied to enhance forensic investigations.

How sharp is sharp? Towards quantification of the sharpness and penetration ability of kitchen knives used in stabbings.

Stabbing is the most common method for violent death in the UK. As part of their investigation, forensic pathologists are commonly asked to estimate or quantify the degree of force required to create a wound. The force required to penetrate the skin and body by a knife is a complex function of the sharpness of the knife, the area of the body and alignment with cleavage lines of the skin, the angle of attack and the relative movement of the person stabbing relative to the victim being stabbed. This makes it difficult for the forensic pathologist to give an objective answer to the question; hence, subjective estimations are often used. One area where some degree of quantification is more tractable is in assessing how sharp an implement (particularly a knife) is. This paper presents results of a systematic study of how the different aspects of knife geometry influence sharpness and presents a simple test for assessing knife sharpness using drop testing. The results show that the radius of the blunt edge at the tip is important for controlling the penetration ability of a kitchen knife. Using high-speed video, it also gives insight into the mechanism of knife penetration into the skin. The results of the study will aid pathologists in giving a more informed answer to the question of the degree of force used in stabbing.

Evaluation of the tribological properties of DLC for engine applications

Diamond-like carbon (DLC) coatings are used in automotive engines for decreasing friction and increasing durability. There are many variants of DLC films which provide a wide range of mechanical, physical and tribological properties. The films can be extremely hard (>90 GPa), give low coefficients of friction against a number of counterfaces and exhibit low wear coefficients. The films are often considered to be chemically inert. The properties of DLC films depend to a large degree on the relative proportions of graphitically- (sp2) and diamond-like (sp3)-bonded carbon but the inclusion of elements such as hydrogen, nitrogen, silicon, tungsten, titanium, fluorine and sulphur can dramatically change their tribological response. Two different types of DLC, a WC/C amorphous hydrogenated DLC (WC/C a-C : H) coating and an amorphous hydrogenated DLC (a-C : H) have been investigated. The mechanical and tribological properties have been evaluated by nanoindentation, scratch and wear testing and friction testing in an instrumented cam–tappet testing rig. The deformation mechanisms and wear processes have been evaluated by scanning electron and atomic force microscopy. The results show that the harder a-C : H film was more wear resistant than the softer WC/C a-C : H film and performed better in the cam–tappet testing rig.

Perimortem trauma in King Richard III: a skeletal analysis

BACKGROUND Richard III was the last king of England to die in battle, but how he died is unknown. On Sept 4, 2012, a skeleton was excavated in Leicester that was identified as Richard. We investigated the trauma to the skeleton with modern forensic techniques, such as conventional CT and micro-CT scanning, to characterise the injuries and establish the probable cause of death. METHODS We assessed age and sex through direct analysis of the skeleton and from CT images. All bones were examined under direct light and multi-spectral illumination. We then scanned the skeleton with whole-body post-mortem CT. We subsequently examined bones with identified injuries with micro-CT. We deemed that trauma was perimortem when we recorded no evidence of healing and when breakage characteristics were typical of fresh bone. We used previous data to identify the weapons responsible for the recorded injuries. FINDINGS The skeleton was that of an adult man with a gracile build and severe scoliosis of the thoracic spine. Standard anthropological age estimation techniques based on dry bone analysis gave an age range between 20s and 30s. Standard post-mortem CT methods were used to assess rib end morphology, auricular surfaces, pubic symphyseal face, and cranial sutures, to produce a multifactorial narrower age range estimation of 30-34 years. We identified nine perimortem injuries to the skull and two to the postcranial skeleton. We identified no healed injuries. The injuries were consistent with those created by weapons from the later medieval period. We could not identify the specific order of the injuries, because they were all distinct, with no overlapping wounds. Three of the injuries-two to the inferior cranium and one to the pelvis-could have been fatal. INTERPRETATION The wounds to the skull suggest that Richard was not wearing a helmet, although the absence of defensive wounds on his arms and hands suggests he was still otherwise armoured. Therefore, the potentially fatal pelvis injury was probably received post mortem, meaning that the most likely injuries to have caused his death are the two to the inferior cranium. FUNDING The University of Leicester.

Time-dependent changes in the mechanical properties of diamond-like carbon films

Abstract A number of workers have reported the degradation of hydrogenated diamond-like carbon films at elevated temperatures — generally graphitisation rapidly occurs at temperatures above 250°C. However, changes in properties due to structural relaxation at lower temperatures have been much less well studied. The residual stress measured in an ion-beam-assisted diamond-like carbon (DLC) film is much greater just after deposition than when remeasured some months later. Nanoindentation measurements on DLC films produced by ion-beam-assisted deposition and plasma-assisted chemical vapour deposition have been made within a few weeks of coating and then repeated after allowing the coatings to age for several years. There is a reduction in both the hardness and the Youngs modulus of the coating. These results are discussed in light of the structure of DLC and how this changes during ageing.

The morphologies and compositions of depleted uranium particles from an environmental case-study

Abstract Uraniferous particles from contaminated environmental samples were analysed by scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDXA) and microfocus extended X-ray absorption fine structure (μEXAFS) spectroscopy. The particles of interest are uranium oxides, which were released into the environment by the combustion of scrap depleted uranium (DU) metal at a factory in Colonie, New York, USA. Most of the identified particles appear to have primary, ‘as emitted’ morphologies; some have evidence of minor dissolution, including corrosion pitting. Polycrystalline and often hollow microscopic spheres were identified, which are similar to particles produced by DU munitions impacting armoured targets. They are attributed to the autothermic oxidation of melt droplets. The compositions of the analysed spheres are dominated by UO2+x with variable amounts of U3O8, two of the least soluble and least bioaccessible phases of U. These particles, collected from dusts and soils, have survived more than 25 y in the terrestrial environment. This study further supports the case for using Colonie as an analogue for battlefield DU contamination.

Forces Required for a Knife to Penetrate a Variety of Clothing Types

In stabbing incidents, it is usual for the victim to be clothed and therefore a knife penetrates both clothes and skin. Clothes (other than leather) have been thought to make little difference to the penetration force. However, there is little quantitative data in the literature. In this study, a range of clothes have been tested, either singly or in layers of, for example, T‐shirt and shirt, to quantify the additional force required when clothes are present. A materials testing system has been used to test the penetration force required to stab through clothes into a foam–silicone rubber skin simulant. The results show that the force required can be significantly different, particularly when layers of clothing are penetrated. A cotton t‐shirt adds c. 8 N to the penetration force, while a T‐shirt and jacket can add an additional 21 N. The results allow a more quantitative assessment of forces required in stabbing.