Research on Engineering Structures and Materials

347-353

Authors: Matheus de Lima Nunes, Mauro de Vasconcellos Real

Port structures are usually large and are subject to heavy loads such as the stresses caused by a port crane and other equipment used during a port operation. Therefore, for a meticulous analysis of the internal forces of the port structures, with the intention to optimize and turn more effective the design, is essential the use of computational tools and advanced mathematical methods, as, for example, the Finite Elements Method. The Porto Novo of the Port of Rio Grande moves millions of tons of materials per year, becoming one of the main ports in Brazil. Its structure has gone through two stages of modernization making it possible the use of larger and more efficient port equipment, operation with ships of greater load capacity, and more quantity of mooring berths available for simultaneous operation. This study will be intended to perform the computational modeling of the Public Wharf of Porto Novo of the Port of Rio Grande using the finite element method through the ANSYS software to estimate the axial loads of the wharf piles when a Mobile Port Crane is in port operation.

367-377

Authors: Vinícius Avila, Mauro Real, Márcio Moura

Bridges in Brazil are designed according to design code NBR 7188:2013 [1] and NBR 7187:2003 [2], in which the moving load model is composed of a three-axle vehicle. The configuration of the moving load model follows the pattern of an older version of the code, the NB-6 (1960). Despite the updating of load values, the present moving load model is not appropriate to represent the current traffic effects in Brazilian bridges. The dynamic effects induced by the moving load are taken into account by the impact coefficient, applied in the load model. The static values of the load model are obtained by multiplying its load by this coefficient. The objective of this work is to perform a dynamic analysis of bridge girders, to determine the dynamic effects, to compare with the static effects and to measure the accuracy of the impact coefficient. The results obtained for the beams, showed that for some cases, the impact coefficients had a good approximation to transform the static efforts into dynamic ones. However, in other cases, these coefficients did not show the same result. Through the study it was possible to identify that the impact coefficients provided in the code can be enhanced from new studies taking into account the dynamic analysis of loadings of Brazilian bridges.

393-402

Authors: Rodrigo Reis Amaral, Grégori da Silva Troina, Carolina Martins Nogueira, Marcelo Langhinrichs Cunha, Luis Alberto Oliveira Rocha, Elizaldo Domingues dos Santos, Liércio André Isoldi

The present article presents a geometric evaluation of stiffened plates employing the symmetry boundary condition. The computational models were developed in the software ANSYS, based on the Finite Element Method, using the SHELL281 finite element. As expected, the numerical simulations considering the symmetry demonstrated a gain in computational processing because of the possibility of developing the models in a quarter of a plate rather than simulating the entire plate, without accuracy loss. The geometric configurations are obtained through the application of Constructal Design. For this, some geometric parameters are varied (degrees of freedom) and others are kept fixed (restrictions). After that, these plates with different geometries are numerically simulated and their mechanical behaviors (deflection and stress) are compared to each other through the Exhaustive Search Technique. Then, it is possible to define the stiffened plate that has the best mechanical behavior. For this, a reference plate without stiffeners was used. In this plate part of its volume of material was transformed into stiffeners by reducing the thickness of the same, thus maintaining the value of the length and the value of the width as constants. The objective here is to determine the geometric configurations that minimize the maximum deflection and the maximum von Mises stress of the stiffened plates. The obtained results showed that, by transforming part of the volume of the reference plate into stiffeners, structural stiffness gains can be achieved in the stiffened plates when compared with the values of deflection and stress reached by the reference plate.

415-426

Authors: Conceição J.E.M. Fortes, Rute Lemos, Ana Mendonça, Maria Teresa Reis

This paper describes the two-dimensional (2D) physical model tests of a rock armor breakwater, performed at LNEC´s experimental facilities, under the framework of the HYDRALAB+ project. The aim of the present work was to evaluate damage evolution under future climate change scenarios, by using different damage evaluation techniques. The tested wave conditions simulated a storm sequence where two water levels (low water and high water) were considered, as well as an increase of the wave height. The water levels and the wave heights were chosen to simulate extreme events forecasted on climate change scenarios. Damage evaluation was based on the traditional counting method and on stereo-photogrammetric techniques. Test results are presented in terms of the damage parameter S and in terms of the percentage of removed armor units. The analysis is focused on the damage progression during the scale model tests, for the imposed storm sequence. The damage presents an oscillating behavior with two main damage areas corresponding to the active zones for each level, due to the variation of the water level between low-water and high-water. This behavior differs significantly from that found for the common storm sequences usually tested, where the water level does not change. Both measuring techniques lead to an intermediate damage of the cross-section breakwater. However, the damage parameter assessment with the stereo-photogrammetric technique allows a more versatile evaluation, since it is possible to characterize damage in representative zones of the cross- section.

437-446

Authors: Marcelo Langhinrichs Cunha, Emanuel da Silva Diaz Estrada, Grégori da Silva Troina, Elizaldo Domingues dos Santos, Luiz Alberto Oliveira Rocha, Liércio André Isoldi

This work is a feasibility study of a Genetic Algorithm (GA) based geometric optimization of stiffened plates subjected to transverse loads. For that, the Constructal Design method was used in order to define the search space, aiming to minimize the stiffened plate’s central deflection, while keeping the total volume of material constant. The number of longitudinal Nls and transverse Nts stiffeners and the relation hs/ts, the ratio between the height and the thickness of the ribs, were considered as degrees of freedom of the studied optimization problem. In order to estimate the displacement field of the plate reinforced with stiffeners, the Finite Element Method (FEM) was used through the ANSYS® Mechanical APDL software. For the verification, the results obtained in the present study were compared with those obtained by Troina (2017), which used Exhaustive Search (ES) as optimization technique. The results indicated that is more efficient using GA than ES since the former requires the analysis of a lesser amount of cases in order to determine the optimal geometric configuration; there being reductions of up to 47,09% on the number of simulations.

213-231

Authors: H. Ersen Balcıoğlu

Natural fibers are a good alternative as economically since they are readily available in fibrous form and can be extracted from plant leaves at very low costs. However, they have lower strength values than synthetic fibers due to their deficiencies in material structure. In this respect, many studies have been carried out by researchers to increase the strength of natural fibers. In this study, mechanical properties, Izod impact toughness, and Shore D hardness behavior of silicon carbide (SiC) filled natural fiber reinforced laminated composites were investigated. In this context, natural jute/epoxy laminated composites were reinforced in different ratios (3%, 6%, and 9%) with SiC powders having different grain size (4.5μ, 9.3μ and 53μ). The test results were compared with the results of unfilled jute/epoxy composites in order to better understand the effects of the fill percentage and grain size on mechanical strength. The produced laminated composites were tested under tensile, compression and impact loads. Scanning Electron Microscopy (SEM) was also performed to analyze the mechanisms of damage of the specimens. The test results showed that the SiC particle size and the percentage of reinforcement were effective on the mechanical behavior of the composite material.

249-261

Authors: Engin Burgaz, Okan Gencoglu, Mert Goksuzoglu

Carbon black reinforced natural rubber (NR)/butadiene rubber (BR), NR/styrene-butadiene rubber (SBR) and NR/BR/SBR composites were prepared by using two types of BR with highly linear chain structure (higher viscosity and molecular weight) and branched chain structure (lower viscosity and molecular weight). NR/BR composite consisting of BR with higher viscosity has the highest fatigue strength. Damping factors of NR, NR/SBR and NR/BR/SBR composites as a function of frequency were systematically compared at constant temperatures of -40, 0, 25 and 60°C. Based on dynamic mechanical analysis (DMA) results, the elasticity of NR/carbon black composite improves, its heat buildup character and tan d decreases with the addition of BR. The addition of 20 phr BR to NR/SBR composites provides 4-5 times better fatigue strength due to the decrease of tan d. Lastly, using a higher viscosity BR in carbon black filled NR or NR/SBR is quite favorable in terms of using these composites as anti-vibrational rubber bushings in automotive applications where high fatigue resistance and lower damping factor are important criteria.

279-298

Authors: Sinan Kutluay, Orhan Baytar, Ömer Şahin

Toluene is the primary material in chemical process industries and is often used as a raw material in the production of many chemicals and as a solvent in many engineering processes. In this study, the material of char, which is used as an adsorbent, was produced from almond shells. The adsorption process of gas-phase toluene onto char was investigated using a laboratory-scale fixed-bed reactor under atmospheric pressure. The structure of the char was characterized by BET and FTIR. The influences of adsorption parameters such as nitrogen (N2) flow rate as the gas-phase toluene carrier, char amount, gas-phase toluene concentration at the inlet and the adsorption temperature on both the adsorption capacity and adsorption efficiency were examined. It was found that the adsorption of the gas-phase toluene onto char could be well represented by the pseudo-second-order kinetic model. Equilibrium isotherm data were analyzed by the Langmuir and Freundlich isotherm models and the results indicated that the adsorption process was described well by the Langmuir isotherm model. The maximum monolayer adsorption capacity (qmax) of the char was determined as 15.42 mg g-1 for 303 K. Thermodynamic parameters such as ΔG° = -7.93 kJ mol-1, ΔH°= -17.18 kJ mol-1, ΔS°= -0.013 kJ mol-1 K-1 showed that the adsorption process was spontaneous, exothermic and physical. The results showed that the material of char produced from almond shells could be used as a biosorbent to remove the material of gas-phase toluene from various industrial and natural sources through the adsorption method.

311-320

Authors: Neslihan Deveci Duranay, Nazlı Çaycı

In this study, it was aimed to produce solid fuel by applying torrefaction process to agricultural wastes, left in the field (usually left to decay) after harvest or post-cultivation period. An eggplant stalk left in the field as an agricultural waste after production period was used in the study. The torrefaction process was applied to the original plant parts cut in certain lengths, and also to the pellets prepared from the same plant. The torrefaction experiments were performed in a pyrex glass reactor placed inside a vertical cylindrical refractory chamber, through which resistance wires are passed. The torrefaction process was performed in N2 atmosphere at the operation temperatures of 220, 260 and 300oC. The proximate and elemental analyses of the solid product were performed. Besides, the energy yield was determined by measuring the higher heating values (HHV) of the original sample and solid product. Depending on torrefaction temperature ıt was determined a decrease in the solid product yield, an increase in the yields of liquid and gas products. While the volatile matter content of the solid product was decreased, it was found that the rate of fixed carbon increased. It was also determined that elemental carbon ratio increased and oxygen ratio decreased as a result of the torrefaction process. It was detected that the higher heating value of the biomass increased with rising torrefaction temperature and 65.58% of the energy that contained has been maintained at severe (300ᴼC) torrefaction conditions.

99-105

Authors: Ebru Baser, Alper Incesu, Sedef Sismanoglu, Ali Gungor

Aluminum silicon alloys are the most preferred alloys for industrial applications due to their ease of production and lightness. It is important to improve the mechanical properties of these materials in order to increase their usage. Wear properties are one of these mechanical properties that can be improved. In this present investigation, 3 different artificial aging durations; 2hrs, 4 hrs, 8 hrs aging at 200 °C were applied after solution heat treatment for 4 hrs. at 540 °C to the AlSi8Cu3Fe alloy. Microstructural analysis, mechanical tests were applied to understand the effect of aging parameters on wear performance and also hardness values of AlSi8Cu3Fe alloy. According to the results obtained from tests and analyzes, the highest wear resistance was reached on the 4 hrs. aged sample.

115-125

Authors: Ahmet C. Tatar, Halil B. Kaybal, Hasan Ulus, Okan Demir and Ahmet Avcı

Epoxy based fiber reinforced composites are widely utilized in aerospace applications due to mechanical properties, thermal stability and, chemical resistance. However, it is known that materials become brittle and due to the poor crack resist restricts their applications in cryogenic engineering applications. The purpose of this paper is to experimentally investigate the cryogenic temperatures’ effect on the low-velocity impact (LVI) test of composite laminates. In addition, the effect of matrix modification in the studied composites was investigated. The LVI tests were conducted at RT (room temperature), 0 °C, -50 °C, -150 °C and -196 °C (liquid nitrogen temperature) on the composite laminates to measure influence on their energy absorption capacity. LVI tests performed according to ASTM-D-7136 standard under 10, 20 and 30 J impact energy levels. The results show that the contact forces and energy absorption capacities are improved by adding SiO2 nanoparticles into the epoxy matrix. The absorbed energy at cryogenic temperatures is increased by 24.87% from 18.1 J of pure epoxy resin to 22.7 J of modified epoxy. For the purpose of comparison, the LVI properties of composites at room temperature (RT) are also investigated. It is noted that the energy absorption capacity is not higher at cryogenic temperatures than that at RT for the modified and neat epoxy composites. Moreover, the peak contact forces are reduced in low-temperature conditions.

137-146

Authors: Serkan Islak, Uğur Çalıgülü, Husain R.H. Hraam, Cihan Özorak, Vahdettin Koç

In this study, Cu–Mo composite coatings were produced on copper substrate by plasma spray technique. Electrical conductivity, microstructure and wear properties of the composite coatings were investigated. Microstructure and phase composition of the coatings were examined by using optical microscopy (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The microhardness experiments were also performed by using a microhardness machine. The electrical conductivity properties of the coatings were evaluated with eddy current instruments. Wear tests were performed by pin-on-disc method. Although the electrical conductivities of the coatings are very small compared to the substrate, it has been determined that the coatings exhibit very good tribological property and high hardness in comparison to the substrate.

155-165

Authors: Bedriye Ucpinar Durmaz, Ayse Aytac

The aim of the present work was to investigate the effect of glycerol (GLY) concentration on the properties of poly (vinyl alcohol) (PVA)/casein (CAS) blend films. The films were prepared by solution casting method at the different concentrations of GLY. The structural, mechanical, thermal, barrier and hydrophilic-hydrophobic properties of the films were determined by various methods. The structural analysis indicated that there were some interactions between the components. Tensile test results release that tensile strength of the film decreased with the addition of GLY while strain at break values increased. According to thermogravimetric analysis (TGA) results, the GLY included films exhibited lower thermal stability than GLY-0 film. The residual weight decreased by increasing GLY content. The contact angle measurements showed that all films were hydrophilic structure. Also, the water vapor barrier property of the GLY-0 film was developed with the addition of GLY.

175-188

Authors: Mehmet Akçair, Melih Savran, Levent Aydın, Ozan Ayakdaş, Savaş Öztürk, Nilay Küçükdoğan

Stacking sequence design and optimization of 64 layered symmetric-balance graphite/epoxy laminated composite have been performed. The optimization problems aim to find the optimum stacking sequence maximizing the critical buckling load by single objective optimization approach. Differential Evolution (DE) and Simulated Annealing (SA) optimization algorithms are proposed to solve the problems. The effect of the aspect ratios (a/b) and in-plane biaxial compressive loading ratios (Nx/Ny) on critical buckling load are investigated. In order to see the effect of discrete increments of fiber orientation angle on critical buckling load, 1°, 5°, 15°, 30° and 45° fiber angle increments are also considered. The results show that (i) the proposed algorithms DE and SA exhibit comparable performance in terms of critical buckling load when compared Genetic algorithm (GA) and Generalized pattern search algorithm (GPSA), (ii) DE and SA find distinct stacking sequence configurations in terms of buckling load for the same laminated structure design problems.

13-32

Authors: Vebil Yıldırım

In this study exact free vibration analysis is performed for thick-walled hollow spheres made of an isotropic and homogeneous linear elastic material. Equation of motion in terms of Lame constants is derived from the field equations of elasticity, and then solved analytically with the help of spherical Bessel’s functions. This existing solution technique is extended to several boundary conditions. For each classical boundary condition, the characteristic free vibration equation is presented in closed forms. After verifying the present results with the available literature, variation of the dimensionless natural frequencies with respect to the boundary conditions and the sphere aspect ratio (outer radius/inner radius) are examined. To show the direct use of the present results, some of which are originals, a case study for a metal-matrix composite is originally studied. This composite material is formed by a perfect dispersion of either single-walled carbon-nanotubes (SWCNT) or multi-walled carbon-nanotubes (MWCNT) within an Aluminum (AL) metal matrix so that the resulting composite is still to have both isotropy and homogeneity properties. Elastic properties of the composite are computed by using the simple mixture rule and Halpin–Tsai equations.

43-74

Authors: M.G. Sobamowo

The wide range of applications of cooling fins are evident in heat transfer enhancements for various thermal systems and also, for the control and prevention of thermal damages in mechanical and electronic equipment. In this work, nonlinear thermal behaviour of convective-radiative cooling fin with convective tip and subjected to magnetic field is analyzed using Galerkin finite element method. The numerical solutions are verified by the exact analytical solution of the linearized models using Laplace transforms method. Based on the numerical investigations, it is established that increase in Biot number, convective, radiative and magnetic parameters increase the rate of heat transfer from the fin and consequently improve the efficiency of the cooling fin. Also, the study shows that for a relatively short cooling fin operating for prolonged periods of time or steady state, the adiabatic/hypothetical condition (or negligible heat transfer) at the tip can be assumed without any significant loss in accuracy or equality as compared to the convective condition at the tip. However, for a long cooling fin of finite length operating in a transient state, especially for short period of time, the assumption of insulated tip produces significant different results as compared to the results of the convective tip. Therefore, for transient thermal studies of fins, the assumption that no heat transfer takes place at the fin tip should be taken with caution for a long cooling fin of finite length operating within a relatively short period of time. It is hope that the present study will enhance the understanding of transient thermal response of the solid fin under various factors and fin tip conditions.