Effects of manufacturing defects on the mechanical properties of carbon fibre reinforced polyethersulphone laminates

The effects of defects on the mechanical properties of carbon fibre reinforced polyethersulphone laminates have been measured. The defects studied were cut fibre plies, omission of polymer films and local delamination produced by the inclusion of foreign matter. Of these it was found that only cut plies had a significant detrimental effect on the strength of a laminate. For specimens with two cut plies, the failure stress, tensile, flexural and compressive in the remaining continuous plies was the same as in the defect-free material, provided that the cut plies were widely separated. However the failure stresses were 15–18% lower in the continuous plies in the specimens containing two cut plies which were more closely spaced and in specimens containing four cut plies.     

Absorption of silicone fluid in a silicone elastomer

Measurements have been made of the absorption properties of a silicone fluid in a silicone elastomer, Aircast 3700, at temperatures between 0 and 150 °C. It was found that the diffusivity could be described by Arrhenius' law. The saturation fluid content was 20% at 0 °C, decreasing to 17% at 120 °C. The swelling was large, up to 26% at saturation, and approximately equalled the volume of fluid absorbed. A reverse thermal effect was observed and an attempt has been made to explain it.     

RTO: An overview and assessment of current practice

The practice of implementing real-time optimization (RTO) using a rigorous steady-state model, in conjunction with model predictive control (MPC), dates back to the late 1980s. Since then, numerous projects have been implemented in refinery and chemical plants, and RTO has received significant attention in the industrial and academic literature. This history affords us the opportunity to assess the impact and success of RTO technology in the process industries. We begin with a discussion of the role RTO serves in the hierarchy of control and optimization decision making in the plant, and outline the key steps of the RTO layer and the coordination with MPC. Where appropriate, we point out the different approaches that have been used in practice and discuss the success factors that directly relate to the success of RTO within an organization. We also discuss alternative approaches that have been used to alleviate some of the challenges associated with implementing RTO and which may be appropriate for those unwilling to commit to the traditional RTO approach. Lastly, we provide suggestions for improvement to motivate further research.     

Effect of clay content, homogenization RPM, pH, and ultrasonication on mechanical and barrier properties of fish gelatin/montmorillonite nanocomposite films

The effect of clay content, homogenization RPM, and pH on the mechanical and barrier properties of fish gelatin/nanoclay composite films was investigated. The addition of 5% nanoclay (w/w) increased the tensile strength from 30.31 ± 2.37 MPa to 40.71 ± 3.30 MPa. The 9 g clay/100 g gelatin film exhibited the largest improvements in oxygen and water barrier properties. Oxygen permeability decreased from 402.8 × 10⁻⁶ ± 0.7 × 10⁻⁶ g m/m² day atm to 114.4 × 10⁻⁶ ± 16.2 × 10⁻⁶ g m/m² day atm and the water vapor permeability decreased from 31.2 × 10⁻³ ± 1.6 × 10⁻³ ng m/m² s Pa to 8.1 × 10⁻³ ± 0.1 × 10⁻³ ng m/m² s Pa. The XRD and TEM observation suggested that the ultrasonication treatment (30 min at 40% output) resulted in exfoliation of the silicates.     

Self-implantation energy and dose effects on Ge solid-phase epitaxial growth

The effects of implantation energy and dose on Ge solid-phase epitaxial growth kinetics were studied using (0 0 1) Ge substrates self-implanted at energies of 20-150 keV and doses of 1 × 10¹⁴−2 × 10¹⁵ cm⁻². All implants produced a continuous amorphous layer, which was crystallized by annealing at 330 °C for 22-176 min. At lower doses, the growth velocity was implant energy-independent while at higher doses the growth rate tended to decrease with decreasing implant energy. The decrease in growth velocity with energy at higher doses is discussed in terms of possible implantation-induced stresses altering growth kinetics.     

A fracture mechanics approach to the failure of graphite in laboratory tests

Laboratory tests show that for some graphites the calculated stress at failure exceeds the tensile strength in uniform tension by an amount which depends on the test considered and increases with the severity of the stress gradient. Fracture mechanics has been applied to bend, internal pressure and diametral compression tests to investigate whether it can provide a consistent failure criterion for graphite in situations where stress gradients are important. A finite element method of analysis has been used to compute the stress distributions in specimens containing cracks of various lengths, from which energy release rates and stress intensity factors have been derived. The results indicate that there is not constant effective inherent crack size which can be employed with a constant critical stress intensity factor K _IC to predict the failure conditions in the three tests considered. However, assuming a constant K _IC, a relationship has been found between the effective inherent crack size responsible for failure and the maximum stress gradient in a specimen, which may be of value in developing a fracture criterion for practical purposes.

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Résumé On montre par des essais de laboratoire que, dans le cas de certains graphites, la contrainte calculée à la rupture dépasse la tension de rupture en traction uniforme d'une quantité qui dépend de l'essai et qui s'accroit avec la sévérité du gradient de contrainte. La mécanique de rupture a été appliquée à des essais de flexion, de pression interne et de compression diamétrale, afin de se rendre compte si elle pourrait fournir un critère de rupture significatif pour le graphite pour les cas où les gradients de contraintes sont importants. Une méthode d'analyse par éléments finis a été appliquée au calcul des distributions des contraintes dans des éprouvettes comportant des fissures de différentes longueurs. On en a tiré les taux de relaxation de l'énergie de déformation et les facteurs d'intensité des contraintes. Les résultats montrent qu'il n'y a pas de dimensions effectivement constantes de fissure susceptible d'être associée à un facteur d'intensité des contraintes constant K _IC pour prédire la rupture dans les trois essais envisagés. Toutefois, en supposant une valeur constante pour K _IC, on a pu établir une relation entre la dimension effective de la fissure provoquant la rupture et le gradient maximum de contrainte dans l'éprouvette. Cette constatation peut être intéressante pour développer un critère de rupture correspondant à des problèmes pratiques.

     

Treating Pseudomonas cepacia meningitis with trimethoprim-sulfamethoxazole

An infant with neonatal meningitis caused by Pseudomonas cepacia responded promptly to treatment with trimethoprim-sulfamethoxazole (Bactrim) after other abtibiotics had failed. Pseudomonas cepacia has proven to be resistant to most of the commonly used antibiotics.     

Study of the variables affecting pressure drop and temperature rise in blow molding dies

The extrusion head systems for both pipe and blow molding were analyzed theoretically and relationships derived between pressure drop and temperature rise for various materials at different flow rates and die restrictions. Because of the complexity of the geometry involved, the die was segmented into several sections axially and momentum and energy equations for these sections were solved with the help of IBM 360. The floating boundary conditions were used in order to take into account the nature of the flow phenomenon involved. To complement and support this theoretical work, rigid polyvinyl chloride (PVC) bottle compounds were used to obtain extrusion data on a 3½ inch extruder with several different die sizes. A good agreement was found between the predicted versus experimental data. Results showed that temperature rise in the die systems in significant and that neglecting it would result in a gross error in the calculated pressure drop. Based on this work, a simplified version of the theoretical equation was developed to serve as an engineering tool in estimating pressure drop and stock temperature for a given material where extreme accuracy is not essential. Results of the engineering equation which contains several empirical constants correlate well with the data and support the theoretical effort.     

Antioxidant effects in PVC plasticized with DIDA

Antioxidants such as bisphenol A (BPA) have long been recommended for retention of physical properties on oven-aging of PVC plasticized with certain plasticizers. We have shown how BPA inhibits oxidative fragmentation of plasticizers such as diisodecyl adipate (DIDA) and thus decreases apparent volatility, and how it improves retention of modulus, elongation, and low temperature flexibility. Low concentrations are more beneficial than either zero or high concentrations, especially on longer aging. At higher concentrations, although the plasticizer is retained in the PVC, it becomes less efficient at low temperature, and low-temperature flex is impaired while elongation is preserved. DIDA exudes during oven-aging unless oxidation occurs to prevent it. When BPA is present, exudation is worst at the most efficient concentrations of antioxidant. This appears to be the normal incompatibility of DIDA at 105°C which is permitted by the antioxidant. On oxidation, the dielectric constant of DIDA rises into the 4–8 range, signifying compatibility with PVC, and the DIDA does not exude.