| Danial Norjidi |
TWO keynote presentations were delivered yesterday following the opening of the 6th Brunei International Conference on Engineering and Technology (BICET 2016) and the 9th Asean Civil Engineering Conference (9th ACEC) at Universiti Teknologi Brunei (UTB).
The BICET keynote presentation was delivered by Professor Chen Zhong, Professor of Materials Science and Engineering at Nanyang Technological University, Singapore.
Professor Chen’s research interest includes: coatings and engineered nanostructures for clean energy, environmental and other functional surface applications; and mechanical behaviour of materials, encompassing mechanics and fracture mechanics of bulk, composite and film materials, material joining as well as experimental and computational mechanics of materials.
His presentation was entitled ‘Towards mechanically icephobic coatings: from the science to engineering.’
Icephobicity is the ability of a solid surface to repel ice or prevent ice formation due to a certain topographical structure of the surface.
In his presentation, he spoke on what he called the ‘Inter Tropical Convergence Zone (ITCZ).’ He explained that the ITCZ is a belt of low pressure which circles the Earth generally near the Equator where the trade winds of the Northern and Southern Hemispheres come together.
Professor Chen Zhong. – PHOTOS: AZROL AZMI
“Aircraft flying through an active ITCZ will probably encounter some or all the hazards such as icing, turbulence, lightning and wind shear.”
He then posed what he called the “fundamental science questions behind icephobicity”.
He noted that ice forms from water freezing, and therefore water contact with solid surfaces (wetting states) is an important issue. He also noted that if water can roll off quickly before freezing occurs, ice will not form. However, ice inevitably forms at very low temperatures, and as such the adhesion should be low enough for easy removal.
Speaking on the development of new coatings that are icephobic, he shared the limitations of existing coatings, noting that they suffer from one or more of the following: high cost/poor scalability; low mechanical resistance and durability; and poor UV resistance.
He said that for practical applications, the developed coating should be: of low cost in materials and coating process; easily applied to a large are and complex shape; and processable at low temperatures. Solution-based spray/spin/brush coating methods are thus highly feasible, he added.
Professor Chen also shared that future challenges for the technology include the development of coating that is transparent, anti-UB and even self-healing.
In his conclusion, he shared that low surface energy is the most essential requirement for icephobicity.
Icephobicity can be enhanced by surface nanostructure favouring air trapping. Another notable finding is that not all super hydrophobic surfaces, as indicated by the water contact angle at room temperatures, can remain water repellent at low temperatures.
He also shared that anti-icing performance is closely correlated with low surface energy coupled with rough surface and the wetting mode of the Cassie-Baxter Model at lower temperatures. Finally, he added that engineering considerations usually pose more constraints and challenges when reaching for a practical solution.
Professor Takashi Matsumoto.
Meanwhile, the 9th ACEC keynote presentation was delivered by Professor Takashi Matsumoto, Professor in Engineering and Policy for Sustainable Development at Hokkaido University, Japan.
Professor Matsumoto’s research interest is in the maintenance and durability of bridges and structures with the help of fracture mechanics and micromechanics. His focus is on the theoretical modelling of fracture and fatigue mechanisms of composite materials and structures.
His presentation yesterday was entitled ‘Long-term Management of Bridges – Fatigue Analysis of RC Bridge Deck Slabs.’
He began by sharing information on Japan’s civil infrastructure, noting that there are 686,332 roadway bridges. He noted that in 10 years, the number of bridges that are 50 years or older will account for 43 percent of all bridges, while in 20 years they will account for 67 percent of all bridges.
Professor Matsumoto then spoke on deteriorations in steel structures, noting fatigue and corrosion as causes. Deteriorations in concrete structures include fatigue, freeze-thaw, chloride attack and alkali silica reaction.
He spoke on what he called “fatigue problems of structures in Japan”. He noted that reinforced concrete (RC) bridge deck slabs and steel bridge deck slabs are repeatedly under heavy traffic loads. This, he said, can influence pavement and endanger driving vehicles, and may even lead to collapse.
The professor then shared the “stages of RC slab fatigue”. The first stage sees one-way cracks, while the second stage is two-way cracks. The third stage sees a grid of cracks, while the fourth and final stage is the collapse of the slab.
He went on to explain that a fatigue fracture is a “time-dependent fracture”, where there is “crack propagation and the final fast fracture under cyclic stress below static strength level”.
He also touched on a concept he called “Bridging Stress Degradation”. On this, it was stated in the presentation that “Bridging stress rapidly decreases in the early stage of cyclic loading,” adding that it “promotes crack propagation under cyclic loading”.
On fatigue crack propagation in concrete, he said in his presentation, ‘Cracks propagate even under constant amplitude loading because of bridging stress degradation.’
Professor Matsumoto then spoke on ‘Ultra High Performance Fibre Reinforced Concrete’ (UHPFRC) and how it can be used to repair RC slabs.
He explained that UHPFRC is “dense, impermeable, strong, strain-hardening in hardened state and flowable, segregation-resistant and thixotropic in fresh state”.
The post Professors discuss icephobic coatings, long-term bridge management appeared first on Borneo Bulletin Online.