The low frequency corrosion fatigue performance of some surgical implant alloys: with reference to stress concentration, environmental factors and the behaviour of mild steel

A review of the literature on corrosion fatigue and fatigue testing is followed in this work by an analysis of the variables involved and of the various mechanisms which have been advanced. Particular reference is made to the corrosion fatigue of surgical implant alloys. An experimental programme was devised to be particularly relevant to the environmental variations possible in implant/body systems. A multi-specimen, reverse-bend, strain facility was designed and produced for this research. Small smooth specimens were tested at a 'walking pace' of 1.7 Hz. A multi-channel, mini-potentiostat was also designed and produced for electrochemical studies during corrosion fatigue. Scanning and transmission electron microscopy was used to examine fracture surfaces. The corrosion fatigue performance of some alloys (stainless steel type 316, titanium 130 and 318) currently used for surgical implants has been evaluated. A comparative study of the performance of mild steel, a material which has in the past been used for implants, was also made. A series of experiments was conducted to simulate normal conditions with a 0.17M saline solution buffered at pH 6.5. Some extreme conditions were also investigated at pH 1.5 and pH 11.5. In order to evaluate the comparative influence of saline, additional experiments were conducted in air and in distilled water for each material.A considerable number of metal/environment combinations was thereby investigated, involving corrosion fatigue in both the passive-state and the active state. Since it is common place for some implants to be drilled for fitting, a further series of experiments was conducted using specimens containing a drilled hole. The influence of such stress concentrating features was thus established for each material. The behaviour of mild steel in all the environments tested, and that of S316 in pH 1.5 saline was described using a single model for interaction between stress concentration and corrosion during fatigue. A different model was found to represent the behaviour of all the other metal/environment combinations tested. The two models were seen to represent, respectively, activestate corrosion fatigue and fatigue under passive state conditions. The drilling of holes in mild steel and T130 showed a small stress concentration effect. No such effect was produced with holes in stainless steel. By contrast, however, the drilling of a hole in T318 resulted in a dramatic reduction in the fatigue limit: a reduction of the order of 50% was obtained in both distilled water and saline solutions. Unlike other materials S316 produced a wide scatter band of results in saline pH 6.5. This was attributed to a naturally fluctuating corrosion potential indicative of an irregular film breakdown and repair. This was attributed to a naturally fluctuating corrosion potential indicative of an irregular film breakdown and repair. The results are generally discussed and the evidence produced shows that the use of S316 for surgical implants cannot be recommended because of poor resistance to corrosion fatigue at low pH. T130 was superior in this respect. However, T318 showed the best resistance to corrosion fatigue even allowing for the drastic reduction in performance with a drilled hole

Electronic detection of weak spectrum links

Recording spectroscopic data by digital and analog electronic systems - Detection of weak spectrum line

A theoretical study of the gamma-ray scattering technique for measuring atmospheric density Final report

Theoretical modeling study of gamma ray scattering technique for measuring atmospheric densit

Photoelectric Detection of Weak Spectrum Lines

Photoelectric detection of weak spectral lines by application of digital and gated filter electronic devices to optical spectrometr

Mathematical model predictions and optimization study of the gamma ray atmospheric density sensor

Mathematical model predictions and optimization study of gamma ray atmospheric density senso

Experimental verification of gamma ray atmospheric density sensor mathematical model predictions

Experimental verification of mathematical model performance predictions for gamma ray atmospheric density sensor

POVERTY AS A CHALLENGE TO WEALTH IN HOMER’S ODYSSEY

This article examines the ways in which poverty, as a condition, and as represented by poor individuals, poses a challenge to wealthy, elite characters in the Odyssey. Great, almost revolutionary, changes took place in Greece in the eighth century BC, when the Odyssey was most likely composed. The audience of the epic, it is argued, comprised both wealthy, elite and poor, non-elite persons. The bases of wealth and poverty in the Odyssey were land, or the lack of it.  Reflecting the instability of the eighth century, the Odyssey repeatedly presents a fall into poverty as a very real, challenging possibility for wealthy individuals. In the epic, the presence of poverty in their midst, as represented by the ‘beggar’ (Odysseus in disguise), tests the humanity and compassion of the characters whom he meets. The suitors fail the test, reacting with cruelty and contempt to the poor man. Eumaios and Penelope rise to the challenge, showing pity and generosity of spirit. The Odyssey thus indicates that moral goodness is independent of wealth and status, and thatpity and compassion are the appropriate responses to the poor

Performance of thermal control tape in the protection of composite materials

The selection of materials for construction of long duration mission spacecraft has presented many challenges to the aerospace design community. After nearly six years in low earth orbit, NASA's Long duration Exposure Facility (LDEF), retrieved in January of 1990, has provided valuable information on both the nature of the space environment as well as the effects of the space environment on potential spacecraft materials. Composites, long a favorite of the design community because of a high strength-to-weight ratio, were flown in various configurations on LDEF in order to evaluate the effects of radiation, atomic oxygen, vacuum, micrometeoroid debris, and thermal variation on their performance. Fiberglass composite samples covered with an aluminum thermal control tape were flown as part of the flight experiment A0171, the Solar Array Materials Passive LDEF Experiment (SAMPLE). Visual observations and test results indicate that the thermal control tape suffered little degradation from the space exposure and proved to be a reliable source of protection from atomic oxygen erosion and UV radiation for the underlying composite material

Solitary Waves in Discrete Media with Four Wave Mixing

In this paper, we examine in detail the principal branches of solutions that arise in vector discrete models with nonlinear inter-component coupling and four wave mixing. The relevant four branches of solutions consist of two single mode branches (transverse electric and transverse magnetic) and two mixed mode branches, involving both components (linearly polarized and elliptically polarized). These solutions are obtained explicitly and their stability is analyzed completely in the anti-continuum limit (where the nodes of the lattice are uncoupled), illustrating the supercritical pitchfork nature of the bifurcations that give rise to the latter two, respectively, from the former two. Then the branches are continued for finite coupling constructing a full two-parameter numerical bifurcation diagram of their existence. Relevant stability ranges and instability regimes are highlighted and, whenever unstable, the solutions are dynamically evolved through direct computations to monitor the development of the corresponding instabilities. Direct connections to the earlier experimental work of Meier et al. [Phys. Rev. Lett. {\bf 91}, 143907 (2003)] that motivated the present work are given.Comment: 13 pages, 10 figure