Joining of thirty three percent by weight random carbon fibre reinforced low density polyethylene using variable frequency microwave

[Abstract]: This paper extends the range of applications for Variable Frequency Microwave facilities (VFMF) (2 – 18 GHz) to joining thirty three percent by weight carbon fibre reinforced low density polyethylene composite [LDPE/CF (33%)]. With a given power level, the composite was exposed to various exposure times to microwave irradiation. The primer or coupling agent used was 5-minute two-part adhesive containing 100% liquid epoxy and 8% amine, ie Araldite. Bond strengths of the joints were lap shear tested and results were compared with those obtained using fixed frequency (2.45 GHz) microwave processing. The VFMF was operated under software control, which provided automatic data logging facilities. The maximum lap shear strength of joint was 230 N/cm2 using variable frequency microwave facility while that obtained by fixed frequency microwave configuration was only 150 N/cm2. The former was found to be 53% stronger than the latter

Preliminary results on literature review skills of students doing capstone projects

[Abstract]: A survey was carried out to investigate literature review skills of students doing their final year research projects. This survey was given before intervention to their literature review skills. Their literature review skills revealed by this survey were compared with that of a post-intervention survey, which was in turn compared with the literature review skills revealed in their intermittent reports. From the pre- and post-intervention surveys, it seems that the intervention workshops work and the percentage of students understanding how to conduct a literature review has improved from 11% to 78%. However, the intervention was not so successful if the literature review knowledge revealed by the project appreciation was compared with that of pre-intervention survey

Joining of thirty three percent by weight random glass fibre reinforced polystyrene using variable frequency microwave

[Abstract]: This paper extends the range of applications for Variable Frequency Microwave (VFM) (2 – 18 GHz) facilities to joining thirty three percent by weight glass fibre reinforced polystyrene composite [PS/GF (33%)]. With a given power level, the composite was exposed to various exposure times to microwave irradiation. The primer or coupling agent used was 5-minute two-part adhesive containing 100% liquid epoxy and 8% amine, i.e. Araldite, which was more readily microwave reactive than the composite itself. Bond strengths of the joints were lap shear tested and results were compared with those obtained using fixed frequency (2.45 GHz) microwave processing. The VFMF was operated under software control, which provided automatic data logging facilities. The maximum lap shear bond strength of joint was 430 N/cm2 using variable frequency microwave facility while that obtained by fixed frequency microwave configuration was only 331 N/cm2. The former is nearly 30% stronger than the latter

Permittivity measurement of thermoplastic composites at elevated temperature

[Abstract]: The material properties of greatest importance in microwave processing of a dielectric are the complex relative permittivity Epsilon = Epsilon' - jEpsilon'', and the loss tangent, tan Delta = Epsilon'/Epsilon''. This paper describes two convenient laboratory based methods to obtain Epsilon', Epsilon'' and hence tan Delta of fibre-reinforced thermoplastic (FRTP) composites. One method employs a microwave network analyser in conjunction with a waveguide transmission technique, chosen because it provides the widest possible frequency range with high accuracy. The values of the dielectric constant and dielectric loss of glass fibre reinforced (33%) low density polyethylene, LDPE/GF (33%), polystyrene, PS/GF (33%), and Nylon 66/GF (33%), were obtained. Results are compared with those obtained by another method using a high-temperature dielectric probe

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Multi-messenger Observations of a Binary Neutron Star Merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ∼ 1.7 {{s}} with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of {40}-8+8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 {M}ȯ . An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ∼ 40 {{Mpc}}) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ∼ 9 and ∼ 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.</p

Contrast joints of glass-fibre with carbon-fibre reinforced polystyrene composite bonded by microwave irradiation

[Abstract]: This paper contrasts the loss tangent, durability of reinforcement and the lap shear strengths of 33 percent by weight random glass fibre reinforced polystyrene matrix composite [PS/GF (33%)] with 33 percent by weight random carbon fibre reinforced polystyrene matrix composite [PS/CF (33%)] bonded using microwave irradiation. Fixed (2.45 GHz) and variable (2 – 18 GHz) frequency microwave (VFM) facilities are used to bond the two composites. With a given power level, the composites were exposed to various exposure times to microwave irradiation. The primer or coupling agent used for joining the glass-fibre-reinforced composite was 5-minute two-part adhesive, Araldite. No filler was used in joining the carbon-fibre-reinforced composite. The lap shear strengths of PS/GF (33%) obtained by FFM facility and VFMF are higher than those of PS/CF (33%). In all cases, the PS/CF (33%) absorbed too much microwave irradiation and this damaged the material (Ku et al., 2000c)

Productivity improvement of composites processing through the use of industrial microwave technologies

This paper starts with the characteristics and advantages of microwaves processing. The shortcomings of fixed frequency, typically at 2.45 GHz were also mentioned. On account of this, the newly developed variable frequency microwave (VFM) fabrication was mentioned and adopted in place of the fixed frequency process. Two cases of fixed frequency microwave processing of materials were described; the characteristics, pros and cons of each case was mentioned and commented. Two cases of processing materials using variable frequency microwave facility (VFMF) were mentioned; the advantages and limitations of each case were discussed. The microwave processing of materials provides improved mechanical, physical and electrical properties with much reduced processing time. Furthermore, variable frequency microwave processing is more superior to its fixed frequency counterpart except that the cost of the facilities of the former is much higher than the latter at this point in time but it appears that the price will drop in the coming ten years

Risks involved in curing vinyl ester resins using microwaves irradiation

[Abstract]: Preliminary studies have been carried out to cure vinylester particle reinforced resins in microwaves to reduce shrinkage of the composites. The results were encouraging. With an exposure time of 35 to 40 seconds and a power level of 180 W, the shrinkage of 50 ml and 200 ml composite samples, flyash particulate reinforced vinylester resin, approached zero percent. Despite the success, there are risks in the process of curing the vinylester resins by microwave irradiation. The styrene vapour emitted from the resins is harmful to human beings and becomes an inhalation hazard. In addition, the styrene vapour in the cavity of the microwave oven may be ignited arcing within the oven. Alternatively, arcing from the high voltage (HV) transformer behind the oven cavity may ignite vapour leaking from the cavity. Even if this does not happen, the concentration of the styrene vapour in the oven cavity is high may lead to explosions. Another risk is posed by the hardening agent, methyl ethyl ketone peroxide (MEKP), which undergoes an exothermic reaction when irradiated with microwaves and could spontaneously ignite. However, if the usual rate of 1-2% of it is used in hardening the resin, most of its dangerous properties will disappear (Sweet, undated). MEKP is itself poisonous and has to be handled with care