Sh. Abolhasani , F. Fallah, Javad Akbari,
Volume 19, Issue 1 (1-2019)
Abstract
By increasing the level of public awareness, more recyclable and natural materials are used. The aim of this research was to fabricate natural fiber reinforced composites and to investigate the effects of fiber length (5mm and 9mm), fiber mass percent (5%, 10%, 12.5%, and 15%), and fiber surface treatment on tensile, flexural, and water absorption properties of the fabricated composite. The experiments were designed, by the Taguchi method. In this research, epoxy resin and kenaf fiber have been used. Tensile, flexural and water absorption tests were performed on the samples. The highest values were 37.67 MPa for tensile strength, 4.94 GPa for tensile modulus, 31.78 MPa for flexural strength, and 6.05 GPa for flexural modulus. The lowest percentage of water absorption was 0.3%. Alkali treatment improved tensile, flexural, and water absorption properties. The optimum of fiber mass percent was 12.5% to maximize tensile strength, tensile modulus, and flexural strength, 10%to maximize flexural modulus, and 5% to minimize water absorption. Except for the tensile modulus, the effect of fiber length on the mechanical properties of the composite is observed to be less pronounced than the other two factors. To maximize the tensile modulus, the fiber length is better to be 9 mm. In this study, the values obtained for the tensile strength and tensile modulus of the fabricated composite are more than the ones in the previous works. Finally, the strength and tensile modulus obtained experimentally were compared with the ones obtained via two micro-mechanical models, modified rule of mixture, and modified Halpin-Tsia model.
A.r Ghasemi, H. Khabaz Kashani,
Volume 19, Issue 1 (1-2019)
Abstract
In this research, the analysis of the effects of circular hole and thermal cycle fatigue on the mechanical properties in multi-layer polymer composite reinforced with nanoparticles are investigated. First, multi-walled carbon nanotubes with 0.1% weight fraction of nanoparticles are added to the epoxy resin ML506. The. In order to homogenize particle in the resin, it is mixed with a magnetic stirrer for 30 minutes. The material is placed in an ultrasonic device for 40 minutes to homogenize the resin and nanoparticle completely. The resin reinforced with glass fibers constitute symmetric cross ply laminates stacking sequence [02/902]s, and nanocomposite samples are made with hand layup method. In this study, open-hole specimens with diameter of 2 and 4mm are investigated. To study the thermal cycles, nanocomposite samples of 3 levels of thermal cycles including 0, 180, and 360 cycles were investigated. The samples are exposed to a temperature range of 0 to 100oC. After that, the specimens undergo tensile testing. Using the tensile test, the modulus of elasticity and tensile strength are compared for the different thermal cycles and the diameter of the holes. By increasing the number of thermal cycles, the tensile strengths of nanocomposite samples are not significantly changed. Also, with increasing the diameter of the hole, the tensile strength is decreased. The elasticity modulus with increasing thermal cycles for all specimens have been minimal changes. Also, a linear regression model was developed, using MINITAB software for strength and elastic modulus in terms of number of thermal cycles and diameter to width ratio.
K. Osouli-Bostanabad, A. Tutunchi , M. Eskandarzade , A. Kianvash ,
Volume 19, Issue 2 (2-2019)
Abstract
Incidence of breaks and leakages in fluid transportation pipes is a common issue in Iran. Depending on the type of pipes and environmental conditions, the breaks in the pipes may be caused by different factors, including mechanical damages, internal or external corrosions, failures, or applied stresses. In the repair of damaged pipes, there are several strategies for rebuilding and implementing the pipeline, most of which are replacing the entire exhausted pipe, using weld clamps and using composite patches. In recent years, the use of composite patches has been accepted as a low-cost, permanent, and standard method for different pipe sections with the least interruption in transportation. In the present study, the boding strength of glass fibers-reinforced epoxy composite patches on a structural steel substrate were investigated and optimal conditions of achieving enhanced adhesion strength of composite patches on the steel substrate were determined, using the Tagochi method at various curing temperatures and times. In this regard, the tensile and shear strength of epoxy, cyanoacrylate, and methacrylate-based glues as three kinds of appropriate polymers for bonding the epoxy composite on the steel substrates were tested. The mechanical strength measurements and fractured interfaces evaluations using a scanning electron microscopy (SEM) revealed that the methacrylate-based glue has the better adhesion strength to the steel substrate.
N. Cheraghi , M. Lezgy-Nazargah, E. Etemadi ,
Volume 19, Issue 3 (3-2019)
Abstract
In this study, a three-dimensional (3D) Peano series solution is presented for the dynamic analysis of functionally graded (FG). Layered magneto-electro-elastic (MEE) plates resting on elastic foundations with considering imperfect interfacial bonding and the interfacial imperfection is modeled using a generalized spring layer method. Regardless of the number of layers, the equations of motion, Gauss’ equations (for electrostatics and magnetostatics), and the boundary and interface conditions are satisfied exactly. In this method, no assumptions on deformations, stresses, magnetic and electric fields along the thickness direction are introduced. Finally, the governing partial differential equations are solved using state-space method. The proposed formulation is validated through comparison with other available results. Effects of a two-parameter elastic foundation, gradient index, bonding imperfection, applied mechanical and electrical loads on the dynamic response of the functionally graded magneto-electro-elastic (FGMEE) plate are discussed The obtained exact solution can be used to assess the accuracy of the theorems for layered FGMEE plates and validating finite element codes.
Sh. Adami, O. Rahmani, P. Ghasemi,
Volume 19, Issue 4 (4-2019)
Abstract
Today, sandwich structures are being used in many applications. Understanding the behavior of these structures and their properties is necessary for proper and optimum design. Because of thin face sheet and low stiffness of foam core, sandwich beams are very sensitive when exposed to local loading. Due to their structure, carbon nanotubes (CNT) have excellent mechanical properties, which improve the mechanical properties of the polymer when added to polymer matrix. In this article, the indentation behavior of sandwich structure is studied experimentally and theoretically. ABAQUS software is used for modeling the indentation behavior of sandwich beam. Elastic modulus of epoxy resin reinforced with CNT with different weight fractions is obtained with use of Mori-Tanaka theory and also by fabrication and testing of the composite specimens. Results show that adding CNT up to 0.3 %wt improve the elastic modulus of composite, while weight fraction of CNT more than 0.3% decrease the mechanical properties. Finally, the results obtained from the analytical solution and ABAQUS modeling were compared with the results obtained from experimental tests of indentation of sandwich structures. An acceptable agreement was observed between the results.
H. Khajeh Arzani, A.r. Kabiri Ataabadi, Y. Chaparian,
Volume 19, Issue 6 (6-2019)
Abstract
The preference of fiber–metal laminate over metal and composite in lots of In the present study, the main goal is to investigate an idea for impact resistance improvement of laminates under high-velocity impact by numerical analysis and experiment. Due to the existence of various types of mechanisms for dissipating kinetic energy of projectile in contact with the target, in this research, it has been concentrated on one of them and by adding a rubber layer into AL/GL/GL/AL laminate, it has been allowed more bending to the aluminum layer thereby offering higher dissipating kinetic energy and increased special perforation energy. Materials used in this study are 2024-T3 aluminum alloy, woven glass/epoxy prepreg and Nitrile butadiene rubber (NBR). All of the tests have been done by a high-speed gas gun in Tarbiat Modarres University and numerical analysis is done with Ls Dyna software. With numerical analysis, it is possible to achieve results such as contact force and different energies variations during the impact of the projectile cannot be achieved by The results show that by adding a rubber layer into the laminates, the aluminum layer bend more so more kinetic energy can be dissipated from the projectile. Hence, special perforation energy and ballistic velocity are increased
A. Ebrahimzadegan, A. Mohammadpour Fattahi,
Volume 19, Issue 7 (7-2019)
Abstract
Carbon nanotubes have special importance due to unique properties as an amplifier phase. In this paper, the effect of multiwall carbon nanotubes on water absorption and fatigue life of poly methyl methacrylate is investigated. To this end, nanocomposites based on polymethyl methacrylate, containing 0-1.5 weight percentage of multiwall carbon nanotubes are produced with screw and injection molding process. The morphology was studied, using scanning electron microscopy. Microscopic images examination showed that carbon nanotubes have been well released in the field of polymer. The fatigue testing of each of the prototypes was carried out under identical conditions. Based on the results of fatigue test, nanocomposite fatigue strength containing 0.5% carbon nanotubes increased than base polymer. Also, based on the results of water absorption test, the existence of multiwall carbon nanotubes in polymer field decreased absorption water of the samples.
A. Jamshid, N. Vahdat Azad,
Volume 19, Issue 8 (8-2019)
Abstract
In this study, flutter of functionally graded carbon nanotube (FG-CNT)-reinforced composite wing carrying a distributed patch mass is analyzed and presented. Wing is modeled by a rectangular plate with cantilever boundary conditions in supersonic flow. To evaluate the displacement fields of the moderately thick plate, First-order shear deformation theory (FSDT) and chebyshev polynomials series are applied. In supersonic airflow simulation effect, the first-order piston theory was used and differential equation governing the system was adapted, using the Hamilton principle. In this study, 4 different types of CNT are considered through the thickness. CNT distribution patterns are as uniform, decreasing, decreasing-increasing, and increasing-decreasing. Finally, the effects of size, mass, and location of the distributed patch mass as well as various CNT distributions and fiber orientation angle in a two-layer anti-symmetric composite on flutter boundaries were studies. In comparisons with the results of previous studies, a good agreement is observed. The results showed that the flutter boundary reduced with increasing mass ratio and increased in longer length of added mass. By increasing orientation's angle of CNT fiber of anti-symmetric composite, the flutter boundary is raised and has different behavior for different distribution patterns.
T. Shojaee , B. Mohammadi , R. Madoliat ,
Volume 19, Issue 8 (8-2019)
Abstract
The optimal design of multilayer substrates containing the cutout under compression is very important to achieve maximum buckling resistance in comparison with structural weight, especially in aerospace structures. In this study, buckling and post-buckling behavior of composite laminated plates with orthogonal and symmetrical layup containing the cutout with different diameters has been investigated experimentally, semi-analytically, and numerically. To study the buckling of the composite plate with cutout semi-analytically, a finite strip method is developed. A finite element method was used for numerical analysis. The required material parameters for modeling were obtained from standard tests. The results of the current study show that the size of diameter of cutout does not have considerable effect on elastic rigidity of plate, but the buckling load significantly decreases by increasing cutout diameter. Also, buckling load and elastic rigidity of plate are considerably increased by increasing the number of composite layers. The thickness of plate has more effect on buckling load than the diameter of hole. Studies show that there is a good match between the results of buckling behavior derived from semi-analytical and finite element methods with experimental results.
S. Maleki, A. Andakhshideh, A. Seyfi,
Volume 19, Issue 8 (8-2019)
Abstract
One of the applications of composite materials in the oil and gas industry is to repair worn metal pipelines. Calculating the strain energy release rate of the first failure mode is an important criterion for testing the bond strength and predicting the failure of these types of structures. In this paper, the rate of strain energy release during crack growth in bonding a composite patch to a steel substrate is investigated. In this regard, using the theory of elastic beam first, a new method is proposed to calculate the thickness of the metal and composite for Unlike Double Cantilever Beam (UDCB). This is due to the fact that the standard for experimental test procedure of strain energy release rate (ASTM-D5528) is for symmetric double cantilever beams. In this study, samples are fabricated from composite consisting of unidirectional fiberglass/ epoxy resin with harder in the upper and steel in the lower half of the beam. After sample fabrication, the strain energy release rate of UDCB and Asymmetric Unlike Double Cantilever Beam (AUDCB) are calculated experimentally. In addition, for the separation of first and second failure modes in symmetric and asymmetric samples, finite element simulation based on the virtual crack closure technique is presented. This analysis is to qualify the accuracy of the proposed equation for the thickness of unlike beams to achieve the first failure pure mode of symmetric samples. Also, it calculates the contribution of the first and second modes of failure in the strain energy release rate of AUDCB samples.
M. Soroush , K. Malekzadehfard, M. Sharavi ,
Volume 19, Issue 9 (9-2019)
Abstract
This paper introduces the initiation and evolution of interlaminar and intralaminar damage in the laminated composite plate under high-velocity impact with the finite element model. Damage in composite layers and delamination between layers are defined based on progressive damage model and cohesive zone modeling. Interlaminar and intralaminar damage initiation are predicted with Hashin criterion and traction-separation law and the damage evolution is predicted with reducing the value of stiffness based on fracture toughness energy that is available in ABAQUS. In this study, needed parameters for the finite element model such as fracture toughness energy are measured experimentally with some tests such as CT and DCB. The finite element model is valid with a velocity comparison of the impactor after impact in experimental impact test with 160J and the numerical simulation. The low percent difference between the experimental and numerical impact results is achieved and thus the needed parameters for simulation is extracted correctly. The present paper introduces a validated, accurate and low-cost finite element model with damage consideration and perforation of impactor for a laminated composite under the high-velocity impact that needed parameters could be measured experimentally.
A.r. Taherzadeh-Fard, M. Javanbakht, M. Karevan,
Volume 19, Issue 9 (9-2019)
Abstract
In the present study, the effect of graphite nano platelet (GNP) as a filler on the vibrational properties of the epoxy EP411 DSM matrix was studied. For this purpose, GNP-epoxy composites samples were fabricated with 0-5 wt.% of GNPs using the solution mixing method. Free and forced vibrations tests on the cantilever composite specimens were conducted. Based on the free vibration results, the structural damping loss factor η was obtained as a function of the GNP loading. It was found that η
decreases as the GNP wt.% increases and reaches to the lowest value at 0-3 wt.% of GNP content, and
increases as the GNP loading increases and reaches to the value at 3-5 wt.% of GNP. Also, the frequency response function (FRF) around the second vibration mode was obtained for the neat epoxy. The Rayleigh damping coefficients were calculated employing the free and forced vibration results. The results revealed a nonlinear dependence of damping ratio η on the natural frequency of the neat epoxy. A representative volume element (RVE) incorporating 0-5 wt.% of GNPs was generated and the vibrational properties were numerically simulated. The modeling results were compared with those obtained from the experiment to verify whether the basic assumptions had been chosen properly.
F. Nazari, M.h. Abolbashari, Seyed Mahmoud Hosseini,
Volume 19, Issue 10 (10-2019)
Abstract
Shape memory alloys (SMAs) are a new generation of smart materials which was the subject of researches in recent years. In this study, SMAs are employed to improve the vibrational and structural behavior of composite beams. A numerical solution was presented for natural frequency analysis of the clamped-clamped beam and the obtained results were validated with results of available references. Two main goals were followed in this study: first, analysis the influences of effective design parameters of embedded SMA wires on natural frequencies of composite beams and second, optimal design of SMAs to improve the vibrational and structural behavior of composite beam. In the first step, the effect of design parameters of shape memory alloy wires including the number and the diameter of wires on natural frequencies and total mass of structure was studied. In the second step, maximization of the first natural frequency of the structure and minimization of the total weight of the structure was the objective function of multi-objective optimization process which was performed by employing the genetic algorithm and weighted sum optimization approach. The obtained results of optimization processes confirmed the high efficiency of the proposed approach to improve the vibrational and structural properties of Shape memory alloys composite beam.
M. Mohammadi, J. Jafari Fesharaki,
Volume 19, Issue 10 (10-2019)
Abstract
This study aims to investigate the ability of ultrasonic method by using critically refracted longitudinal (LCR) wave for measuring stress in the elastic phase of an iron-base alloy and a an equation includes of acoustoelastic constant was provided. For this purpose, extract detail of metal alloy components was achieved by use of quantometer analysis testing and . In order to send and receive the LCR wave into the samples, the investigation leads to design a unique type of ultrasonic fixture. The fixture was made based on Snell’s law that only in one part. In the next step, different amounts of stress were applied to the specimens by using a uniaxial tensile testing machine and record stress-strain curve data. To this end, more than three metal samples were used in the study. Measurement of longitudinal applied stress by ultrasonic method was done by using 2MHz probes based on Acoustoelasticity theory and close to the surface of the samples. After conducting the experimental tests, the results indicated that there was a significant relation between stress and time of flight and wave speed in the elastic phase of the used sample. Every material has a unique acoustoelastic constant that can determine stress value by having times of flight wave. The conclusions of the study provide a gradient of a line that known as an acoustoelastic constant. Finally, by comparing the results of the used method with other researchers results, findings showed that there were good agreements between them which shows the good capability of acoustoelasticity theory in the measurement of stress.
M. Gholami, A. Hassani, H. Afrasiab, M. Kazemiyan,
Volume 19, Issue 12 (12-2019)
Abstract
Biodegradable polymers have widespread usages in the biomedical field, such as stents, sutures, scaffolds, and implants. Due to the importance of behavior of these materials exposed to environmental effects, whether in nature or the human body, extensive researches have been carried out in the last decade that most of them are experimental results and very few are theoretical results. These researches have mainly been performed for specific loading and temperature conditions and so on. For this purpose, in addition to validating the theoretical and empirical relationships derived through the experimental results, the effects of more complex conditions can be considered using the finite element method and numerical solution. In this paper, an analytical relationship extraction method has been presented, as well as the abilities and weaknesses of biodegradable polymers have been investigated by presenting the experimental results of biodegradable polymers. A numerical and finite element analysis is also provided to analyze the behavior of biodegradable polymers. The theoretical analysis and numerical simulation of biodegradable polymers have been carried out using the neo-Hookean hyperelastic model. First, the relationship of stress, versus the stretch has been derived using the strain energy of neo-Hookean material. Next, by assuming a degradation parameter, changes in the properties of the material exposed to environmental effects, according to the time in Abaqus Umat subroutine have been applied to the model. Finally, the accuracy of the simulation has been studied by a comparison between the experimental results and theoretical analyses with numerical solutions.
M. Najafi, H. Ahmadi, G.h. Liaghat,
Volume 20, Issue 2 (1-2020)
Abstract
Human being has always been looking for optimal use of his surrounding materials that has been able to invent various structures through getting inspired by nature. Some of these structures are lattice structures. Due to their lower weight, high compressive strength and high stiffness, lattice structures are widely used in various applications, including energy absorbers. A new type of lattice structure is auxetic structures that have a negative Poisson’s ratio due to their geometric structure. This characteristic has caused auxetic structures to have unique properties such as shear strength, indentation resistance, and high-energy absorption. In this study, the experimental and numerical investigation of in-plane uniaxial quasi-static loading on three auxetic structures and one non-auxetic structure have been conducted. The specimens have three different auxetic geometries including re-entrant, arrowhead and anti-tetra chiral and one honeycomb geometry that is non-auxetic. The specimens have been manufactured using additive manufacturing technology (3D printing). Experimental results were compared with finite element simulation results, which were in a good agreement. As expected, auxetic structures showed a much better performance in energy absorption compared to the honeycomb structure. So that the energy absorption of the arrowhead structure was 161% higher than the honeycomb structure.
Sh. Amini Nejad, G.h. Majzoobi, S.a.r. Sabet,
Volume 20, Issue 2 (1-2020)
Abstract
In this research, the effect of strain rate on the tensile behavior of the graphene/epoxy nanocomposites was investigated. The specimens were prepared for 0.05, 0.1, 0.3 and 0.5 wt.% graphene oxide and were subjected to tensile tests at different strain rates. The experimental results showed that the maximum improvements in the tensile strength, the modulus, and nanocomposite were 9%, 16%, and 0.1 wt.%, respectively. Also, the results indicated that the epoxy and its nanocomposites were sensitive to the strain rate. The rate sensitivity decreased with the increase of the graphene weight percentages. Moreover, it was shown that by increasing the strain rate, the tensile strength and modulus for pure epoxy were improved by 15.8% and 16.8%, respectively. In this study, the appropriateness and applicability of the Johnson-Cook material model for describing the stress-strain relation of the nanocomposites were examined by a combined experimental-numerical-optimization technique. The numerical simulations were carried out using Abaqus commercial program and the optimizations were performed using the Surrogate modeling. The results showed that the Johnson-cook model is not accurate at very low strain rates. However, the accuracy of the model was remarkably improved by increasing the graphene weight percentage or increasing strain rate.
A. Firouzian-Nejad, M. Ghayour, S. Ziaei-Rad,
Volume 20, Issue 3 (2-2020)
Abstract
This study introduces a new lay-ups of bi-stable hybrid composite laminate (BHCL) which consists of 90° unidirectional composite laminas in the upper and lower layers and metallic strips distributed along with the middle layer of 0° unidirectional composite laminas in the middle layer. The static characteristics of the laminates were investigated using the finite element (FE) method and were experimentally validated. The two stable configurations of laminate have identical curvatures with opposite signs. The curvature direction of the proposed BHCLs does not change during snap-through between stable states. This feature will give the engineers more freedom to design morphing structures with desired specifications. The effect of the width, thickness, and material properties of the strips and laminate side length on the static characteristics of the laminate were numerically investigated using the finite element method through Abaqus software. Several BHCLs with different materials, lay-up and dimension were fabricated for verification of the results. The curvatures, out of plane displacement, and the static snap-through load of the laminates were determined experimentally and compared with the results of the finite element method. A good qualitative and quantitative agreement was observed between the FE and the experimental results. The results show that it is possible to adjust residual curvature and load-carrying capability by changing the width, thickness, and material of the strips and laminate geometry.
S.a. Azimi, V. Momeni, M.h. Alaei , A. Mirzaei, M. Rezvani Nasab, M. Ramezani Nezhad, A.h. Mohamadian,
Volume 20, Issue 3 (2-2020)
Abstract
In this research, the effect of adding clay Nanoparticles on increasing the lifetime of glass/epoxy composites under hydrothermal conditions has been investigated. For this purpose, samples containing 3 Vol.% of clay Nanoparticles and samples without clay Nanoparticles in resin epoxy has been manufactured for the fabrication of specimens of the tensile test using hand lay-up and vacuum bag. The specimens were placed under the hydrothermal condition of 90% humidity and 75 °C temperature for 500 hours in the incubator and were tested for tensile properties. The results show that addition of clay Nanoparticles decreases the strength of the composite by 21.39% in the newly produced samples while in a long time, these particles slow down the process of composite degradation, so that in the same environmental conditions, the strength of specimens containing clay Nanoparticles is 9% higher than the specimens without clay Nanoparticles.
S.m. Mahoori, M.e. Golmakani, A. Tavasoli Farshe,
Volume 20, Issue 4 (4-2020)
Abstract
In this research, the mechanical behavior of composites made with polyethylene matrix and wood powder reinforcement have been investigated. In order to improve the mechanical properties, the wood powder has been added to polyethylene at three levels of 30, 40 and 50 wt.%. The material was mixed using an internal mixer Haake and then the material was removed from the mixer and was granulated by a crushing machine. Finally, the granules were molded using an injection molding machine and tensile test specimens were made according to ASTM D638 standard and bending test specimens were made according to ASTM D790 standard. After preparing the specimens, a tensile and flexural test performed on them. The results of the mechanical tests show that the amount of elastic modulus increased with increasing the amount of wood powder so that the highest amount of elastic modulus was observed in the specimens containing 50 wt.% wood powder. Also, the highest strength in the tensile test was observed at the level of 30 wt.% of the wood weight and the highest flexural strength was in the 50% level of wood weight. Also, mechanical tests were simulated using Abaqus software.
