Degradation of Polycarbonate Properties Under Thermal Aging

Journal of Failure Analysis and Prevention - The aim of this paper is to characterize the thermal aging effect near the glass transition temperature of polycarbonate (PC) at different hold time....     

Interfacial damage on fatigue‐loaded textile–rubber composites

To reach admissible lifetime expectancy, unidirectional textile–rubber composites must show a strong interface. Usually, it is achieved by coating the textile with Resorcinol–Formaldehyde–Latex (RFL). To evaluate fatigue impact on interfacial properties, composites with or without RFL are tested at different numbers of loading cycles and characterized through peel tests, dynamic mechanical analysis (DMA), scanning electron microscopy and energy‐dispersive X‐rays, and nanoindentation. For composites with RFL, the results indicate two main mechanisms for damaging: propagation of pre‐existing fibrillar microcracks at the rubber/RFL interface completed by adhesive debondings at the RFL/textile interface. At first, the propagation of fibrillar microcracks is correlated with decrease of global composite peeling resistance and contribution of interphase to DMA damping. Then, RFL/textile debondings become critical. They are highlighted with a change of peeling failure surface and could be explained by RFL hardening, highlighted by nanoindentation. This questions the choice for RFL as a sustainable adhesive for composites under fatigue loading. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41346.     

Repair and Restoration of the Optical Properties of Sandblasted Glasses By Silica-Based Sol-Gel Coatings

The damage provoked by sand storms in Sahara desert to windscreen of vehicles and solar mirrors is a problem. Different solutions have been proposed, one of them is the application of polymeric coatings, but they rapidly degrade. In this work, we have deposited silica-based sol-gel coatings including silica nanoparticles onto sandblasted glasses. The glasses were eroded by sandblasting varying the projected sand mass and the incidence angle to obtain different surface states. The eroded samples were coated by dipping with a silica layer to correct the defects induced by sandblasting and restore the optical transmission. The damage increases with increasing projected mass and the impact angle. The optical transmission decreases with increasing damage. In extreme conditions, optical transmission falls from 91.5% to 68.6%. The deposition of silica-based layers containing SiO₂ colloidal nanoparticles promotes the repairing of sandblasting defects. A strong decrease of roughness to values similar to those of as-received glass is related with the increasing of the optical transmission up to levels permitting of windscreens and solar mirrors. Transmittance measurements showed a remarkable improvement in all cases, whatever the projected sand mass or the impact angle. For highly degraded samples, the transmission increases from 68.6% to 91.4%, an improvement of near 23%.     

Influence of curing conditions on durability of alkali-resistant glass fibres in cement matrix

Glass fibres in concrete material often increase the flexural strength. However, these fibres when in contact with cement are altered by alkali reactions due to the presence of portlandite. This study presents the results of investigation to show the effect of curing conditions on the durability of alkali-resistant glass fibres in cement matrix. Test results show that even alkali resistant fibres treated with zirconium oxide present the same degradation phenomenon. They also show that the nature of the cement has a large influence on the protection of the fibres: the Portland CEM II is less damaging than the CEM I. The substitutions of a part of cement by silica fume gave no substantial improvements to the mechanical strength of the glass fibre reinforced cement (GFRC). However, the observed microstructures in the samples show that the degradation is weakened with the addition of silica fumes. The analytical techniques used in this study are scanning electron microscope (SEM) and X-ray diffraction.     

Obstacle's effects and their location inside the square cavity on the thermal performance of Cu–Al2O3/H2O hybrid nanofluid

The current study focuses on the effect of obstacles and their positioning within the square cavity (L = H) on heat exchange. This work considers heating the cavity's bottom wall to a steady, high temperature. The top wall of the cavity is adiabatic, while the two vertical side walls are cooled. Four cases are explored under these conditions: the first case is a square-shaped cavity holding a square-shaped obstacle h = l = 0,15 L, while the other three cases, respectively, each include two, three, and four square obstacles. The cavity was filled with Cu–Al₂O₃/H₂O hybrid nanofluid with a volume fraction φ = 0.03. Numerical results for laminar and stationary flow regimes with Rayleigh numbers 10⁴ ≤ Ra ≤ 10⁶. The finite volume approach solves the governing equations numerically. The findings show that the number of square obstacles within the square-shaped cavity significantly impacts heat exchange and hybrid nanofluid flow. The second example, with two square obstacles, improves heat exchange more than other cases with one to four barriers. In the second example, the obstacle location at the plane Y = 0.25H is suitable and helps boost heat transmission of the hybrid nanofluid. The ideal obstacle position in the fourth scenario, which has four square barriers, is at the plane Y = 0.75H.     

A numerical investigation of the effect of sinusoidal temperature on mixed convection flow in a cavity filled with a nanofluid with moving vertical walls

The aim of this study is to investigate numerically the effect of sinusoidal temperature on mixed convection flow in a cavity filled with nanofluid and moving vertical walls by using a new temperature function, where thermal heating takes the form of the sinusoidal temperature; and could be found in various natural processes and industries such as solar energy, and cooling of electronic components. The heating is concentrated in the center and then distributed to both ends at different values of Rayleigh numbers, Reynolds numbers, and volumetric fractions of nanoparticles ranging from 1.47 × 10³ to 1.47 × 10⁶, 1 to 100, and 0 to 0.1, respectively. The impact of nanoparticle size on thermal characteristics and hydrodynamics was considered and evaluated. From the results, the volume fraction concentration of nanoparticles affects the flow shape and thermal performance in the case of a constant Reynolds number. Moreover, the effect of nanoparticles decreases with the increase of the Reynolds number. Besides this, with increasing the volume percentage of nanoparticles, the rate of heat transmission increases. It is worth noting that the presence of nanoparticles results in height convective heat transfer coefficient. On the other hand, the thickness of thermal boundary layers decreases with increasing Rayleigh number. The current investigation found that the (sinusoidal) temperature change significantly affects heat transfer.     

Design of grasping methodologies for rotational assembly components

This article describes a design methodology for grasping assembly components. Three heuristics are developed. The first determines feasible grasping configurations based on component geometric information. The second heuristic determines feasible grasping configurations by including gripper functional attributes. The third heuristic generates the final set of grasping configurations by including the area available for grasping a component. An interactive program written in Fortran 77 is developed to capture the user inputs, and a sample application is described. The methodology does not assume an initial feeding state of the component to the robot. The grasping configurations generated (if more than one) provide the designer with alternate feasible feeding methods.