Research on Engineering Structures and Materials

431-445

Authors: K R Yellu Kumar, Adnan Qayoum, Shahid Saleem, Fasil Qayoom Mir

The current study involves a computational investigation on the cooling of the combustion chamber liners in a gas turbine engine. Effusion cooling is a high-efficiency, lightweight and low-cost cooling system widely used in combustion chamber liners nowadays. The effect of blowing ratio and effusion hole injection angle on adiabatic effectiveness is investigated. The simulations are carried using COMSOL Multiphysics 5.4 with the standard k- ε turbulence model. A 3D computational model consisting of mainstream duct, effusion plate and effusion holes has been incorporated for the analysis. The blowing ratios used in the study are 0.25, 0.5, 1, 1.25 and 1.5 at constant density ratio of 1.0 for different injection angles of 30° and 60°. The simulation results show a strong dependence of adiabatic effectiveness on the blowing ratios. For low blowing ratios the adiabatic effectiveness in effusion hole region is high on account of coolant being attached to the surface. On the contrary, for high blowing ratios the adiabatic effectiveness is low near the effusion holes region. In the downstream region of effusion holes the adiabatic effectiveness raises for high blowing ratios. In addition, it has been observed that injection angle of 30o provides better adiabatic effectiveness compared to injection angle of 60o. The velocity and temperature profiles are investigated to demonstrate the behavior of coolant flow on the effusion surface and the influence on adiabatic effectiveness. This study concludes that the proper selection of blowing ratio and injection angle improves combustion chamber’s efficiency and lifetime.

463-490

Authors: Nitin Kumar, Michele Barbato, Erika L. Rengifo-López, Fabio Matta

Finite element (FE) simplified micro-modeling techniques are commonly used to investigate and predict the mechanical behavior of masonry structures because they provide a good compromise between accuracy and computational cost. These FE techniques generally discretize masonry structural elements into expanded masonry units and zero-thickness interface joints of assumed known locations. These joints correspond to actual masonry joints and to preferential cracking surfaces, which are often placed vertically in the middle of the expanded masonry units to simulate the cracking mechanisms that are typically observed in masonry bricks and blocks. Three different versions of simplified micro-models (SMMs) are widely used in the literature to model the response of masonry walls and assemblies: SMMs with rigid, elastic, and elasto-plastic constitutive models for the expanded masonry units. All SMMs are based on the hypothesis that the masonry inelastic behavior and cracking are concentrated along the pre-defined zero-thickness interface joints. The hypothesis is often satisfied for ordinary masonry, in which masonry units are generally stronger than the masonry joints, i.e., mortar and unit-mortar interface. However, this hypothesis is not always satisfied for historical masonry with units of irregular shapes or for earth block masonry, in which masonry units and masonry joint can have similar mechanical properties. This paper highlights the capabilities and limitations of SMM techniques by comparing the experimentally-measured and numerically-simulated response of ordinary and earth block masonry walls, for which well-documented experimental results are available in the literature. It is found that SMMs can properly reproduce the mechanical behavior of masonry when the masonry units are significantly stronger than the masonry joints; however, SMMs produce poor estimates of the mechanical response when this hypothesis is not satisfied. This finding highlights the need to develop more general FE models to investigate the mechanical behavior of different masonry materials and construction techniques, as well as to identify the parameters controlling the cracking patterns and the conditions under which SMM techniques can be accurately use.

519-533

Authors: Megha Bhatt, Sandip A. Vasanwala

The 3rd revision of IS: 4998 i.e. 2015 edition adopted a limit state method of design for RC chimney and gave a new model of stress-strain relationship for concrete and steel. RC chimneys are tall cantilever columns having thin-walled hollow circular sections and subjected to axial compression resulting from self-weight and bending moment resulting from lateral forces. It has been seen that there are many disparities between the stress-strain relationship of these materials adopted by IS: 4998 – 2015 and other well-established design standards. This paper compares and discusses these disparities in terms of strength, ductility factor and energy absorption with the help of plotted moment-curvature charts. For the comparison, design recommendations of IS: 4998 – 2015, CICIND 2011, ACI: 307 – 08 are used. Moment-curvature curves are plotted using the major two conditions of the section i.e. yielding of tension reinforcement and crushing of concrete in compression. It is obtained from the study that CICIND 2011 gives higher results for all parameters, namely strength, ductility factor and energy absorption.

553-567

Authors: Afreen Nissar, M. Hanief, Fasil Qayoom Mir

Used engine oil is a high pollutant material as it contains extremely toxic contaminants accumulated during operation. These contaminants if disposed improperly can not only cause extensive damage to the environment but also affect all living organisms. To tackle this rising problem the engine oil can be recycled by recovery of its base oil and reused for various purposes. Since the cost of recycling is comparatively much lower than production from crude oil, so recycling can prove to be a preferable alternative source as crude oil reserves are getting depleted. In this research study, SAE 5W30 was collected from the vehicle where it had been used for about 3000 miles operation and the collected oil was then subjected to various recycling methods. The recycled oils obtained undergo various tests for quality check comparison by Rheometer, FTIR Spectrometer, Oil Densitometer and Flash Point Tester. From the results obtained it was clearly observed that the acid/clay treatment method fetched superlative results. The degree of viscosity reduction (%) in acid/clay treatment method was found to be 95.077% which was significantly greater than other methods. Also, different engine oil samples were analyzed and compared for contamination by FTIR spectroscopy which can assist in condition monitoring of the vehicle engine.

583-602

Authors: P.N. Ojha, Pranay Singh, Brijesh Singh, Abhishek Singh, Piyush Mittal

With the increase in strength, concrete explodes spontaneously at failure creating a serious safety hazard. Researchers are actively looking for methods to arrest the cracks in concrete and design a higher strength concrete that fails in a more ductile fashion. Fiber-reinforced concrete has emerged as one of the solutions to this problem. This paper presents findings from the experimental investigation conducted to compare the fracture behavior of plain and fiber-reinforced high strength concrete of varying compressive strength. Six different concrete mixes were prepared with w/b ratios of 0.47, 0.36, and 0.20 resulting in average compressive strength of 36, 52, and 92 MPa. Each mix consists of two variations, first without fiber and second with 1% of steel fiber by volume. The mixes were tested for their strength and fracture Behavior using various standard codes and recommendations. From the Load-deflection and Load-CMOD (Crack Mouth Opening Displacement) curves obtained from the study, Fracture parameters like Fracture energy, Stress intensity factor, energy release rate, and Characteristic length is evaluated and compared for plain and Steel fiber reinforced concrete. It was found that adding steel fiber significantly improves the fracture properties of the concrete of different compressive strengths. By adding 1% of steel fiber in the high-strength concrete, the average fracture energy increased by 850%, 770%, and 450% respectively for the concrete with compressive strength of 36, 52, and 92 MPa. Other parameters also show a very significant improvement suggesting fiber reinforcement as a suitable choice to prevent brittle failure and increase the fracture performance of high strength concrete.

615-632

Authors: Badrinarayan Rath

Nowadays road construction is rapidly increasing on-demand to meet several medium and long terms development programs. A huge amount of natural resources, types of machinery and fuels are used in road construction. Using material resources and fuel an efficient manner, reducing in emission of greenhouse gases and controlling various impacts on the environment are important tasks in the road construction industry. In the present research, several environmental impacts related to the construction of asphalt paved highways in Ethiopia have been determined using the Life Cycle Assessment Approach for common pavement materials and construction activities. A deep focus has been given towards the extraction and processing of sand and gravel for preparation of base and sub-base; transportation of these input raw materials; consumption of fuels by various road construction machinery; direct or indirect emissions of carbon dioxide and other pollutants to atmosphere etc. Various suitable methods have been used to calculate the impacts of raw materials, fuel and machinery on various categories such as global warming potential, ozone depletion potential, terrestrial acidification potential, freshwater eutrophication, freshwater ecotoxicity etc. From the investigation, it has been suggested to use recycled materials for substituting gravel as base or sub-base materials and biodiesel for substituting diesel in the transportation trucks and dumpers. These types of new recycled materials may greatly help in assisting the evaluation of sustainable pavement construction. The present case study may help for potential changes in asphalt pavement construction to improve environmental sustainability.