Toughening mechanisms in novel nano-silica epoxy polymers

A crosslinked epoxy polymer has been modified by the addition of nano-silica particles. The particles were introduced via a sol-gel technique which gave a very well dispersed phase of nanosilica particles which were about 20 nm in diameter. The glass transition temperature was unchanged by the addition of the nano-particles, but both the modulus and toughness were increased. The fracture energy increased from 100 J/m2 for the unmodified epoxy to 460 J/m2 for the epoxy with 13 vol% of nano-silica. The microscopy studies showed evidence of debonding of the nano-particles and subsequent plastic void growth of the epoxy polymer. A theoretical model of plastic void growth was used to confirm this mechanism

Vascular Communications of the Hand in Patients Being Considered for Transradial Coronary Angiography Is the Allen’s Test Accurate?

ObjectivesThe purpose of this study was to assess the accuracy of the Allen’s test (AT) in predicting hand ischemia in patients undergoing transradial coronary angiography.BackgroundPatients with poor vascular communications between the radial artery (RA) and ulnar artery (UA), as indicated by an abnormal AT, are usually excluded from transradial coronary angiography to avoid ischemic hand complications.MethodsOver a four-month period, patients undergoing coronary angiography were screened for AT time. Circulation in the RA, UA, principal artery of the thumb (PAT), and thumb capillary lactate were measured before and after 30 min of RA occlusion.ResultsFifty-five patients were studied (20 normal, 15 intermediate, 20 abnormal). Three patients with an abnormal AT were excluded, owing to absence of detectible flow in the distal UA. Patients with an abnormal AT were all men, had a larger RA (3.4 vs. 2.8 mm; p <0.001), and smaller UA (1.9 vs. 2.5 mm; p <0.001), compared with patients with a normal AT. After 30 min of RA occlusion in patients with abnormal AT, blood flow to the PAT improved (3.2 to 7.7 cm/s; p <0.001) yet remained reduced relative to patients with normal AT (7.7 vs. 21.4 cm/s; p <0.001. Thumb capillary lactate was elevated in patients with an abnormal AT (2.0 vs. 1.5 mmol/l; p = 0.019).ConclusionsAfter 30 min of RA occlusion, patients with an abnormal AT showed significantly reduced blood flow to the thumb and increased thumb capillary lactate (compared with patients with a normal AT) suggestive of ischemia. Transradial cardiac catheterization should not be performed in patients with an abnormal AT

The effectiveness of patch repairs to restore the impact properties of carbon-fibre reinforced-plastic composites

The present paper studies the low-velocity impact testing of carbon-fibre reinforced-plastic (CFRP) pristine and patch-repair CFRP panels. Firstly, the effect of repeated impacts on the pristine CFRP damage growth is considered at impact energies of 7.5, 10.5 and 30 J. Secondly, such tests lead to a single-sided, patch-repair panel being manufactured by removing a 40 mm diameter central hole, to act as the ‘damaged area’, from the parent CFRP panel and then adhesively-bonding a circular CFRP patch-repair over the hole so generated. Various diameters and thicknesses for the CFRP patch-repair are employed and, in some cases, a CFRP circular plug is also used to fill the hole created by removal of the parent composite. The measured load versus time, and load versus displacement, traces are compared. Further, the extent and location of any interlaminar damage, i.e. delaminations between the plies of the CFRP, caused by the impact event are mapped using an ultrasonic C-scan technique. It is shown that single-sided patch repairs can be very effective in restoring the impact performance of damaged CFRP panels

A facile way to produce epoxy nanocomposites having excellent thermal conductivity with low contents of reduced graphene oxide

A well-dispersed phase of exfoliated graphene oxide (GO) nanosheets was initially prepared in water. This was concentrated by centrifugation and was mixed with a liquid epoxy resin. The remaining water was removed by evaporation, leaving a GO dispersion in epoxy resin. A stoichiometric amount of an anhydride curing agent was added to this epoxy-resin mixture containing the GO nanosheets, which was then cured at 90 C for 1 h followed by 160 C for 2 h. A second thermal treatment step of 200 C for 30 min was then undertaken to reduce further the GO in situ in the epoxy nanocomposite. An examination of the morphology of such nanocomposites containing reduced graphene oxide (rGO) revealed that a very good dispersion of rGO was achieved throughout the epoxy polymer. Various thermal and mechanical properties of the epoxy nanocomposites were measured, and the most noteworthy finding was a remarkable increase in the thermal conductivity when relatively very low contents of rGO were present. For example, a value of 0.25 W/mK was measured at 30 C for the nanocomposite with merely 0.06 weight percentage (wt%) of rGO present, which represents an increase of *40% compared with that of the unmodified epoxy polymer. This value represents one of the largest increases in the thermal conductivity per wt% of added rGO yet reported. These observations have been attributed to the excellent dispersion of rGO achieved in these nanocomposites made via this facile production method. The present results show that it is now possible to tune the properties of an epoxy polymer with a simple and viable method of GO addition. A

Characterization Of Epoxy-Coated Oxide Films Using Acoustic Microscopy

An adhesive joint consisting of aluminum adherends bonded with an epoxy adhesive is composed of three main layers. The adherends are usually a few millimeters thick with a layer of epoxy adhesive between one and three hundred microns thick between them. The surfaces of the adherends are typically pre-treated to produce a thin film of porous aluminum oxide, which has a honeycomb-like structure. The epoxy adhesive may then penetrate into these honeycomb cells or pores. The resulting layer between the adhesive and adherend is therefore a micro-composite and it is typically of the order of one micron in thickness. The use of the surface pre-treatment is a major factor in increasing the durability of the adhesive joint when it is exposed to water. Additionally, joints which have been in use for some time, especially ones which have been subject to environmental attack, usually experience a failure along the plane of this film. Therefore, characterization of this epoxy/oxide interlayer is very important in understanding adhesive joints and how they are affected by environmental factors. Unfortunately, not much is known about their mechanical properties

Tough Nanoparticle-Modified Polymers

Abstract: A crosslinked epoxy polymer has been modified by the addition of nano-silica particles. The particles were introduced via a sol-gel technique which gave a very well dispersed phase of nano-silica particles which were about 20 nm in diameter. The glass transition temperature was unchanged by the addition of the nanoparticles, but both the modulus and toughness were increased. The fracture energy, G Ic , increased from 100 J/m 2 for the unmodified epoxy to 460 J/m 2 for the epoxy with 20 wt. % of nano-silica. The microscopy studies showed evidence of debonding of the nanoparticles and subsequent plastic void growth of the epoxy polymer. A theoretical model of plastic void growth was used to confirm this mechanism. The cyclic-fatigue behaviour of the epoxy polymers has also been studied and the fatigue properties were clearly enhanced by the presence of the nano-silica particles. Indeed, it was found that the values of the strainenergy release rate at threshold, G th , from the cyclic-fatigue tests increased steadily as the toughness, G Ic , also increased, i.e. as the concentration of nanosilica particles was increased