Prospects in the application of a frontally curable epoxy resin for cured-in-place-pipe rehabilitation

Photocurable acrylates and vinyl esters are among the most commonly used resins in cured-in-place-pipe (CIPP) rehabilitation technology, as they impart excellent thermomechanical properties in composite pipes. In the quest for achieving a higher energy efficiency of the photo-curing process in CIPP, the frontal polymerization technique is a viable alternative that requires a lower irradiation dosage coupled with exceptionally high curing speeds and depths. Herein, for the first time, we report the application of frontal polymerization in the rehabilitation of underground pipes using a newly developed frontally curable epoxy-based resin (Trelleborg Self-Curing*). The neat resin is characterized for degree of cure, glass transition temperature, and mechanical properties via FTIR, DMA, and tensile tests, respectively. In a comprehensive way, the properties are benchmarked against commercially available acrylate (Trelleborg Light Cure*) and vinyl ester (Trelleborg Rapid Cure*) resins to evaluate their applicability for CIPP. The results show a higher glass transition temperature and final monomer conversion for the frontally cured resin, which cures significantly faster than the reference resins under the same irradiation conditions. In proof-of-concept trials, the newly developed resin successfully cures polymeric liners in a PVC host pipe with 100% water tightness and without losing its structural integrity. Results from ring stiffness tests for cured composite pipes additionally show that liners cured with Trelleborg Self-Curing* resin pass the minimum required Young's modulus for non-pressure drainage pipes as per ASTM F1216. Thus, frontally curable epoxy-based resins are a promising and competitive alternative to acrylates and vinyl esters in CIPP.     

Quantifying risks in a supply chain through integration of fuzzy AHP and fuzzy TOPSIS

Risk is inherent in almost every activity of supply chain management. With the ever-increasing push for efficiency, supply chains today are getting more and more risky. Adding to the difficulty of dealing with these risks is the amount of subjectivity and uncertainty involved. This makes analytical examination of the situation very difficult, especially as the amount of information available at a particular time is not sufficient for such an analysis. Thus a supply chain risk index, which captures the level of risk faced by a supply chain in a given situation, is the need of the hour. This study is an effort towards quantifying the risks in a supply chain and then consolidating the values into a comprehensive risk index. An integrated approach, with a fuzzy analytical hierarchy process (AHP) and a fuzzy technique for order preference by similarity to the ideal solution (TOPSIS) as its important elements, has been used for this purpose. Fuzzy values in this study help in capturing the subjectivity of the situation with a final conversion to a crisp value which is much more comprehensible. A case study is used to illustrate the proposed methodology.     

Dynamic analysis and nonlinear simulation of aircraft flat spin

Abstract

In this paper we investigate the dynamic characteristics of flat spin of a fighter aircraft in open-loop configuration. The aircraft model under study is of the multi-role fighter configuration co-sponsored by China and Pakistan. The aerodynamic model used in the study is in the form of look-up tables that have been developed from rotary balance steady coning and oscillatory coning motion wind tunnel data. The set of all possible equilibrium spin states is numerically computed for various values of control settings using eighth-order aircraft equations of motion. Results from dynamical systems theory are applied to investigate local stability characteristics of aircraft around steady spin state. The complete set of dynamic modes of aircraft in spin is evaluated and mode content in each of the motion variable is determined using modal decomposition. This analytical technique is complemented by performing numerical simulations to investigate flat spin dynamic features. The methodology is applied to investigate dynamic behavior of two flat spins: right flat spin at 72.1° and much flatter left spin at 84.4°. The presented work provides insight into the global overview of aircraft flat spins as a function of various control settings, and their dynamic characteristics and it can facilitate the designing of flight control laws for spin recovery/prevention.     

On the structural and physicochemical properties of gamma irradiated UHMWPE/silane hybrid

This study has been carried to investigate the influence of gamma rays on the structural and physicochemical properties of UHMWPE/silane hybrid. UHMWPE was mixed with vinyltriethoxysilane (VTES) and compression molded sheets were irradiated at different doses of gamma rays. Fourier transform infrared spectroscopy indicated the formation of siloxane linkages in hybrids, which were found to be shifted towards lower wave number upon irradiation. The X-ray diffraction patterns showed significant increase in the percentage crystallinity of hybrid upon gamma irradiation, especially at 65 kGy absorbed dose. Scanning electron micrographs showed good consolidation and compaction with no surface defects. Moreover, the rough topography was changed to smooth ripple-like appearance upon γ-irradiation. Thermal analysis revealed that irradiated hybrids exhibited higher onset thermal degradation temperature, peak melting temperature, and crystalline lamellae thickness compared with the water treated hybrid. In addition, the tensile testing confirmed an increase of 41% and 133% in yield strength and Young's modulus in 100 kGy irradiated hybrid respectively than that of water treated hybrid. We hope that the irradiated UHMWPE/silane hybrids can be used in various high-strength applications such as total joint replacements, pickers for textile machinery, lining for coal chutes and dump trucks.     

Management of natural gas resources and search for alternative renewable energy resources: A case study of Pakistan

Energy usage in Pakistan has increased rapidly in past few years due to increase in economic growth. Inadequate and inconsistent supply of energy has created pressure on the industrial and commercial sectors of Pakistan and has also affected environment. Demand has already exceeded supply and load shedding has become common phenomenon. Due to excessive consumption of energy resources it would become difficult to meet future energy demands. This necessitates proper management of existing and exploration of new energy resources. Energy resource management is highly dependent on the supply and demand pattern. This paper highlights the future demands, production and supply of energy produced from natural gas based on economic and environmental constraints in Pakistan with special emphasis on management of natural gas. An attempt has been made by proposing a suitable course of action to meet the rising gas demand. A mechanism has been proposed to evaluate Pakistan's future gas demand through quantitative analysis of base, worst and best/chosen option. CO₂ emission for all cases has also been evaluated. The potential, constraints and possible solutions to develop alternative renewable energy resources in the country have also been discussed. This work will be fruitful for the decision makers responsible for energy planning of the country. This work is not only helpful for Pakistan but is equally important to other developing countries to manage their energy resources.     

Effect of Surface Roughness on Laser Induced Nonlinear Optical Properties of Annealed ZnO Thin Films

Variation of nonlinear optical properties with surface roughness of ZnO thin films deposited on corning glass substrates at different annealing temperature(TA) was reported.The films were characterized by X-ray diffraction(XRD),UV-Vis-NIR transmission and single beam z-scan technique using second harmonics of Nd:YAG laser.Surface morphology of the samples was investigated by atomic force microscopy(AFM).Surface roughness was found minimum(8.4 nm) for ZnO sample annealed at 450 ℃.The nonlinear optical properties(NLO) were found to be dependent on surface roughness and the highest value of third order nonlinear susceptibility(χ～(3)=4.3×10～(-7) esu) was obtained for ZnO at TA 450 ℃.