Development and measurement of stress in polymer coatings

This paper reviews stress development mechanisms and stress measurement techniques for polymer coatings. Most polymeric coatings shrink during and after solidification due to chemical reaction, solvent evaporation, phase separation, or some combination thereof. Coating adhesion, however, prevents shrinkage from occurring freely; this frustration of in-plane shrinkage leads to a tensile stress in the plane of the coating. At the same time, stress accumulates, it may be relaxed by processes such as molecular motion. The measured stress at any time is the result of the competition between stress buildup from frustrated shrinkage and stress relief from relaxation. Accumulation of stress is a problem because it can lead to defects such as cracks. An understanding of stress development in various types of polymeric coating systems will lead to strategies for material selection, process optimization, and defect elimination. In this paper, background on stress development is provided, followed by an overview of stress measurement methods for polymer coatings. The remainder of the paper focuses on stress development during the drying and curing of polymer coatings, drawing many examples from previous stress measurement studies.     

Investigation into the formation and mechanical properties of a bioactive material based on collagen and calcium phosphate

A biomaterial composite was formed by the room-temperature precipitation of calcium phosphate (in the form of brushite) on to collagen. It was found that the addition of 1 mM O-phosphoserine (Ser P) causes the morphology of the brushite crystals to change from large plates to small needles. An increase in the surface coverage and weight fraction of brushite incorporated into the collagen was observed. The mechanical properties of this composite were tested in the wet state. The ultimate tensile strength (UTS) was 45 MPa compared with 34 MPa for the wet collagen. Osteoblastic differentiation was promoted on the surface of the material and new bone formed.     

Preimplantation adoption: establishing pregnancy using donated oocytes and spermatozoa

The experience of transferring embryos produced through in-vitro fertilization (IVF) utilizing donated oocytes and spermatozoa is described. Recipients (n = 28; aged 38-59 years) received oral micronized oestradiol and i.m. progesterone and were synchronized to donors undergoing ovarian stimulation. Reasons for selecting therapy included advanced reproductive age (> 42 years; n = 21) or hypergonadotrophic hypogonadism (n = 7), combined with severe male factor infertility in 23 couples. Five women were single and without partners. Oocytes were fertilized by cryopreserved spermatozoa designated for use by the recipient. Up to five embryos were transferred transcervically. Supernumerary embryos were cryopreserved. A total of 36 aspirations produced 15.6 +/- 7.3 oocytes per retrieval. In 10/36 cycles (27.8%), embryos were available for cryopreservation. Using fresh embryos, the overall pregnancy rate was 38.9% (14/36), clinical pregnancy rate 33.3% (12/36), and ongoing/delivered pregnancy rate 30.6% (11/36). Three ongoing pregnancies were later established by transferring cryopreserved embryos. Adjusting for these events, the per aspiration overall pregnancy rate per retrieval was 47.2%, clinical pregnancy rate 41.7%, and ongoing/delivered pregnancy rate 38.9%. Implantation rates per individual embryo transferred were 16.6% following fresh embryo transfer. A viable pregnancy was achieved by 14 of 28 women (50% cumulative pregnancy rate). We conclude that using donor oocytes and donor spermatozoa is efficacious and allows couples of whom both members suffer from severe gamete abnormalities and single functionally agonadal women an effective means of achieving pregnancy.     

Fuzzy modelling and estimation of economic relationships

A modelling strategy based on the application of fuzzy logic is shown to provide a powerful and efficient method for the estimation of non-linear and linear economic relationships. The procedure is particularly suitable for the estimation of ill-defined systems in which there is considerable uncertainty about the nature and range of key input variables. In addition, no prior knowledge is required about the form of the underlying relationships, and trend, cyclical and irregular components of the model can all be estimated in a single pass. The potential benefits of the fuzzy logic approach are illustrated using a model of real-wage behaviour in the United States over the period 1960-1995. The results suggest that the relationships in the model are basically non-linear.     

An infrared heat source for temperature control of a smallmicroscope flow bath

A simple, inexpensive, and easily installed infrared heat source with temperature controller for small superfusion baths used in electrophysiologic experiments is described. The output of a thermal sensor in the bath is amplified and sent to a feedback circuit which in turn controls the voltage supplied to a tungsten/halogen bulb focused on the bath. Fluctuation from the set point is no more than 0.2 degrees C with good fluid level control. Judging from the lack of change in the cardiac action potential duration, heart cells do not preferentially absorb infrared radiation.     

Niagara Cantilever

The first modern metal cantilever bridge in the United States, using erection methods that were to be utilized in most future cantilever bridges, was by C. C. Schneider across the Niagara Gorge in 1883. The Niagara, saw in order, John Roebling’s Railroad Suspension Bridge, Samuel Keefer’s Honeymoon Suspension Bridge, Edward Serrell’s Lewiston-Queenston Suspension Bridge, Schneider’s cantilever, Leffert Buck’s arch bridge at the falls as well as Buck’s arch built under Roebling’s suspension bridge. Schneider’s bridge had a useful life of over 40 years during a period when rolling stock on the railroads was increasing rapidly. The speed of erection of a new style bridge coupled with its performance makes it one of the most innovative and significant bridges built in the world at the time.     

Analysis of Surface Tension from Aerodynamic Levitation of Liquids

Aerodynamic levitation allows contactless diagnostics of very high-temperature liquid properties. Liquids can be metals or inorganic compounds, and the levitation gas may have any composition. Temperature limitation is dependent on the heating power and radiative properties of the samples, with 3000°C possible for oxides. Surface-tension measurement is based on previous theories, which relate it to specific vibrations of the drop. Rotation and precession of liquid drops are specific aspects of aerodynamic levitation, and their effects are quantified here. Experimental examples for nickel and alumina are also shown and compared with results from previous experiments, when available.     

Thermal and thermomechanical effects in dry sliding

Whenever friction occurs in dry sliding of mechanical components, mechanical energy is transformed into heat through surface and volumetric processes in and around the real area of contact. This frictional heating, and the thermal and thermomechanical phenomena associated with it, can have a very important influence on the tribological behavior of the sliding components, especially at high sliding velocities. Significant developments in the study of these phenomena are reviewed in this paper. Among the topics reviewed are mechanisms of frictional heating and the distribution of heat during sliding friction, the measurement and analysis of surface and nearsurface temperatures resulting from frictional heating, thermal deformation around sliding contacts and the changes in contact geometry caused by thermal deformation and thermoelastic instability, and the thermomechanical stress distribution around the frictionally heated and thermally deformed contact spots. The paper concludes with a discussion of the influence of the thermal and thermomechanical contact phenomena on wear, thermocracking and other modes of failure of sliding mechanical components.     

Dislocation substructure inin situ deformed foils of niobium-8 to 10 at % vanadium alloy

The development of dislocation substructure in foils of niobium-8 to 10 at % vanadium alloy deformedin situ in the tensile stage of the microscope is presented to substantiate earlier observations presented in Part 1. The results of direct observation of the formation of straight dislocations, dislocation loops and loop debris are presented. In addition, the behaviour of cracks in foils containing hydrogen is compared with that observed in the absence of the interstitial. Through thein situ observations, the mechanism of embrittlement of niobium-rich vanadium alloys in the presence of hydrogen presented in Part 1 is substantiated.