Liz Girvan

Effect of autoclave induced low-temperature degradation on the adhesion energy between yttria-stabilized zirconia veneered with porcelain.

OBJECTIVE To investigate the effect of autoclave induced low-temperature degradation on the adhesion energy between yttria-stabilized zirconia veneered with porcelain. METHODS The strain energy release rate using a four-point bending stable fracture test was evaluated for two different porcelains [leucite containing (VM9) and glass (Zirox) porcelain] veneered to zirconia. Prior to veneering the zirconia had been subjected to 0 (control), 1, 5, 10 and 20 autoclave cycles. The specimens were manufactured to a total bi-layer dimension of 30 mm × 8 mm × 3 mm. Subsequent scanning electron microscopy/energy dispersive spectrometry, electron backscatter diffraction and X-ray diffraction analysis were performed to identify the phase transformation and fracture behavior. RESULTS The strain energy release rate for debonding of the VM9 specimens were significantly higher (p<0.05) compared to the Zirox specimens across all test groups. Increasing autoclave cycles lowered the strain energy release rate significantly (p<0.05) from 18.67 J/m(2) (control) to the lowest of 12.79 J/m(2) (cycle 10) for only the VM9 specimens. SEM analyses showed predominant cohesive fracture within the porcelain for all cycle groups. XRD analysis of the substrate prior to veneering confirmed a tetragonal to monoclinic phase transformation with increasing the number of autoclave cycles between 5 and 20. The monoclinic phase reverted back to tetragonal phase after undergoing conventional porcelain firing cycles. EBSD data showed significant changes of the grain size distribution between the control and autoclaved specimen (cycle 20). SIGNIFICANCE Increasing autoclave cycles only significantly decreased the adhesion of the VM9 layered specimens. In addition, a conventional porcelain firing schedule completely reverted the monoclinic phase back to tetragonal.

Protecting the extremities of military personnel: fragment protective performance of one- and two-layer ensembles

In order to provide protection from fragmenting ballistic threats, combat body armour contains multiple layers of fabric. The garment covers the torso, but may provide (removable) protection to the upper arms, neck and groin. Such garments are thick, stiff, impede movement and increase the thermophysiological loading of the dismounted soldier. Examination of wound locations from recent conflicts has suggested it would be advantageous to provide protection to the extremities. Current modular systems can be expanded with strap-on coverings to the arms and legs, but this further exacerbates the mass, mobility and thermal problems already observed. Soldiers already wear coverings on their arms and legs in the form of a combat uniform, and the provision of a hierarchical protection system incorporated in the existing uniform has been discussed. Not all areas of the body would be protected to the same level. In the current work, the fragment protective capabilities of one or two layers of commercially available para-aramid woven fabric. Specifically, 1.1 g chisel-nosed fragment simulating projectile V50 data were obtained. The aim was to establish whether the incorporation of such one or two layers of para-aramid woven fabric into current combat clothing could provide a level of fragment protection with only a minimal associated increase in stiffness, mass and thermal resistance. Post-failure analysis was conducted to investigate inter-layer interaction and failure mechanisms. This work suggests that the use of one- and two-layer para-aramid woven fabric layers incorporated into clothing could offer some protection against wounding to the extremities from fragments.

Effect of domestic laundering on the fragment protective performance of fabrics used in personal protection

UK Armed Forces wear items of clothing that incorporate fragment protective fabrics (Tier 1 Pelvic Protection) and other items of clothing are under development (e.g. Improved Under Body Armor Combat Shirt). The long-term robustness of such garments is of interest. In this paper four candidate fabrics (knitted silk, ultra-high molecular weight polyethylene felt, para-aramid felt and a woven para-aramid) were investigated. The effect of laundering on 0.24 g chisel-nosed fragment simulating projectile ballistic protective performance was measured on packs containing the candidate fabrics that were representative of clothing layers. Changes in the physical properties (mass, thickness, dimensional change) of candidate fabrics were measured. The ballistic protective performance of two candidate fabrics was unaffected by laundering; for the other two fabrics improved performance was measured. The masses of the specimen packs was unaffected by laundering; however, the thickness of all fabrics increased, relative to dimensional change.

Identifying the source of bullet wipe: a randomised blind trial

ObjectiveTo assess the usefulness of scanning electron microscopy and energy dispersive x-ray spectroscopy in matching bullet wipe to the bullet.HypothesisBullet wipe can be used to match a bullet type to a crime scene.

Degradation of military body armor due to wear: Laboratory testing:

Personal armor, including body armor, is protective clothing designed to either absorb or deflect attacks that would usually be fatal to an individual. These attacks include, but are not limited to, slashing, bludgeoning, stabbing and ballistic threats. In the UK, body armor is worn by police officers for their shift; however, military personnel (particularly when based overseas) may wear body armor continuously for much longer time periods. Thus, the effect of wear due to use on the performance of body armor is of interest. Testing of body armor after actual use is problematic for several reasons including, but not limited to, (i) access to such items and (ii) a lack of knowledge of exactly what the body armor has been exposed to. Thus the use of laboratory testing to understand degradation of body armor is of interest to many agencies. Additionally, laboratory testing allows for the effect of variables to be investigated independently of each other, as well as in combination. The effect of inter-layer wear between apparel items and/or among layers of fabric within apparel does not appear to be systematically explored in the literature. In this paper, the effect of wear on (i) the tensile strength and (ii) the fragment protective performance of fabrics packs containing a para-aramid woven fabric typical of those used to manufacture body armor was investigated.

Effect of a cordless retraction paste material on implant surfaces: an in vitro study

Cordless retraction paste material for gingival retraction in implant dentistry has recently become of interest to the clinician. However, few studies have been conducted on the use of retraction pastes and their possible interaction with implant surfaces. This in vitro study evaluated the effect of a cordless retraction paste material, Expasyl® (Acteon), on TiUnite® (Nobel Biocare) implant surfaces. Three areas of the fixtures were evaluated before and after contact with the retraction paste using scanning electron microscopy to evaluate changes in surface topography and energy-dispersive spectroscopy to identify any surface chemistry modifications. Alteration of the initial surface after exposure to Expasyl® was identified, with the implant collar showing the most changes.