مجله مهندسی مکانیک امیرکبیر
سال پنجاه و دوم شماره 5 (امرداد 1399)

In this paper, the elastic-plastic deformation response of cylindrical sandwich panels using ship hulls under the action of external blast loading has been obtained. It is assumed that the sandwich panel has simply supported boundary at all edges and consist of elastic orthotropic face sheets and a foam core layer with elastic-perfectly plastic behavior. Three-dimensional equations of motions based on the non-linear high-order theory have been used to describe the sandwich panel core deformations. The effects of various parameters including the panel span, core and facing thickness, pulse duration and maximum pressure on the plastic deformation of the core and sandwich panel facesheet fracture are studied. The results obtained from the present method are compared with finite element solutions using commercial software ANSYS and a good agreement among the results could be observed. It concluded that there is different blast resistant for sandwich panels with core pure elastic and elastic-plastic behavior. Also, it can be seen that inner facesheet of sandwich panels carried larger stresses than outer ones and causes panel fracture that for various foams occur in different place.

The present paper examines the experimental and numerical investigations of the behavior and initiation by development of the filament wound glass fiber/polyester composite cylinders under loading of the pressure between the by parallel rigid plates.For this purpose, composite cylinder samples were manufactured industrially in DIBA Fiberglass Corporation using a discrete filament winding method with winding angle equal to ±75 degree. The samples were pressurized by means of two parallel rigid plates according to ASTM D2412-02 standard. During the test, the behavior of the composite cylinder structure and initiation by development the damage in the cylinder were recorded at different stages of loading. In addition to performing experimental tests, numerical simulation was performed using ABAQUS commercial software. In order to take into account the effects of initiation by development of damage, the 3D Hashin damage model has been used. To apply Hashin’s three dimensional damage model, a UMAT subroutine coding procedure was conducted using Fortran 77 program. Mechanical properties and composite cylinder fracture strengths were obtained by measuring fiber and resin properties based on the relative standard and then separately by micro mechanical relations concerning the layers. In all test, experimental observations, including the level of failure due to loading and the cause of the occurrence of different mechanisms of damage, have been discussed. Comparison of the results of the experimental tests with the result of numerical simulation has a good agreement with each other. Therefore, the simulation has potential for predicting behavior of the composite cylinders under the loading conditions.

This research focuses on investigating the time-dependent behavior of polyamide 6 and using the generalized Maxwell model for prediction of this behavior. To achieve this goal, tensile specimens are manufactured via injection molding process and then are tested based on stress relaxation trials. Moreover, two specimens manufactured with different mold temperatures are tested to investigate the effect of the mold temperature on the time-dependent behavior of this kind of polymer. Finally, to evaluate the ability of generalized Maxwell model to predict the time-dependent behavior of polyamide 6 correctly, a finite element simulation is carried out via link between Moldflow and Abaqus software. In these simulations, the amount of warpage occurring in the specimen obtained from this model is compared with experimental finding. The results show that the mold temperature has a negligible effect on the time-dependent behavior of this polymer and also, there is a good agreement between simulation and experimental results of warpage with mean error of 13%. Therefore, the generalized Maxwell model is good enough to predict the time-dependent behavior of polyamide 6. On the other hand, this methodology can be used prior to making real parts to prevent the high cost of manufacturing

Different factors such as initial notch angle, notch depth, notch root radius, notch, specimen size, hammer geometry and striker velocity, and initial notch creation method (i.e. broaching and machining) influence the experimental determination of Charpy impact energy. Thus, the study of the influence of these parameters on Charpy fracture energy is important. In the present research, Charpy impact experiments are conducted on test specimens made from API X65 steel (used for gas transportation pipelines). The tests samples have standard size with different notch radius (within the range of 0.13 - 0.41 mm). By measurement of fracture energy, Charpy impact energy is determined as a function of variations of initial crack radius. Through having geometrical dimensions of the initial notch and considering the stated standard tolerance the aforementioned function allows the determination of measurement error of API X65 steel Charpy impact energy. Then, the test samples are modeled as 3D in ABAQUS using Gurson damage theory. The comparison of test and simulation results for different notch radius are presented in details and compared.

Coatings are used in different industries in order to improve the surface properties in components and instruments. In some situations, such as improving the wear resistance of an instrument, brittle coatings have been considered. Dominant failure mode in these structures is crack initiation and propagation. So, investigating the fracture behavior of these structures is in great importance. In this paper, discrete element method (DEM) is used to simulate the crack initiation and propagation in coating/substrate structures. This method has a great ability to predict damage initiation and propagation in structures. For this purpose, a DEM solver code is written by authors. Brittle elastic behavior is considered in coating and substrate and the effect of elastic mismatch in constituents of structure and the coating thickness in damage initiation and propagation were investigated. The results showed that in structures in which coating stiffness is less than substrate stiffness, in the case of low thickness of coating, damage appears as crack initiation and propagation into the substrate but, by increasing the coating thickness, crack grows into or parallel to interface. In structures in which the coating stiffness is greater than substrate stiffness, no matter to the coating thickness, crack grows to the substrate.

In recent years, shape memory alloys, specially NiTi, as a group of smart materials, have received more attentions in industrial applications. Martensitic phase transformation in shape memory alloys is the most important factor in their unique behavior. In this paper, the formation of stress induced martensite phase in the crack tip of superelastic NiTi (50.8% Ni) samples was investigated by using the DIC method. In particular, SEC specimens were subjected to fatigue mechanical loading, then the crack length and also displacement fields at the crack tip of specimens were measured by DIC technique. Control of the crack length was performed using a high magnification camera during the fatigue test. In the following, stress intensity factors were calculated according to ASTM standard E647-15. Obtained results from the fracture analysis show that fatigue threshold values are decreased with increasing the load ratio (R). In the present paper, for a load ratio of R=0.05, during the crack propagation, the fatigue threshold value is 〖∆K〗_th=17 MPa√m, while stress intensity factor is estimated about 35 MPa√m before the final failure. Also, as a new method in observation of the phase transformation, DIC pictures indicated the formation of stress induced martensite at the specimens crack tip.

Today, because of widespread faults in metallic pipes such as internal and external corrosion, hard deformability, abundant deposition arising from much roughness on internal parietal and profuse salt absorption and high pressure drop because of internal surface roughness, weightiness and installation difficulties and low lifetime etc. the tendency to use polymer pipes in transfer pipelines, industrial, marine, drilling and agricultural zones has increased. Examine the rate of damage the plastic tubes reinforced with the glass fiber under internal pressure from different angles, which might be defeated under creep phenomenon in long term, has not receive the attention to a large extend. Therefore, in the present research, it has been tried to simulate the fracture by Tsai-Wu, Hashin criterions and also the crack inlet opening with J-integral criterion in this pipes with different layering at internal pressure using finite element method and ABAQUS software. This research results show that the fibers under compressive and tensile stress and the resin of tube has not fractured by tensile stress, but the fracture has occurred in the resin of composite tubes that were under pressure. According to the yielded results, the fracture index is less than one for each of ten layers, when layering angle varies from [(30)] to[(60)], but the fracture index is more than one, layering decoration for[(70)], [(80)] and [(90)] of composite tubes has been fractured. However, the value of stress intensity factor was immediately decreased for layering decoration angle of [(55)], but this factor has improved when layering angle increased.

Cold expanded holed plates are widely used in bolted joints which are subjected to clamping force. Previous studies on the effect of clamping force together with cold expansion on the fatigue behavior of the bolted joints revealed that the size of cold expansion has great influence on the fatigue durability of these joints due to the increase of the possibility of fretting fatigue occurrence. For better understanding this phenomenon, it is necessary to have detailed information about the effect of cold expansion on frictional force evolution during fatigue loading and the resulting stress field around the stress concentration zone. Therefore, in this paper, fretting fatigue testing apparatus was designed and fabricated for conducting fretting fatigue tests on the cold expanded specimens. Moreover, finite element simulation was used for evaluation of the residual stress distribution due to cold expansion and its effect on the fretting fatigue behavior of the joint. SWT multiaxial fatigue parameter was engaged for comparing the fatigue durability of the test specimens. The obtained results indicated that the cold expansion process reduces the stress concentration effect near the hole edge while it increases the possibility of fretting fatigue occurrence by generating tensile residual stress at areas away from the hole edge.

Nowadays, the increase in axial load and speed in railway transportation systems has increased the amount of pressure applied to the surface and energy loss, and has caused severe wear of turnout profiles, especially in turnout intersections. One of the major financial and physical losses to the country's railway is the train derailment in the turnout intersections. As mentioned above, due to the importance of turnout in this study, it has been tried to study the role of damages caused by turnout wear of railway system and explain the necessity for such research in this regard, particularly in Iran, by studying this phenomenon and examining the ruling theories as well as collecting information. In fact, these studies are the starting point for a more precise investigation into this phenomenon. In the following, the movement of train on a turnout is simulated in the "Universal Mechanism" software and the amount of force applied to the turnout and the wear energy is extracted. Furthermore, the effect of different parameters such as speed, axial load, friction coefficient, arc radius, and turnout profile on the rate of wear will be investigated. Then the turnouts are modeled on CATIA software and the forces extracted from the Universal Mechanism simulation are exerted to the turnout in the FEM software, and the stress, strain and deformation of the turnouts are investigated.

In this paper, an approximate solution based on the Rayleigh’s method is sought to analyze the vibration behavior of Euler-Bernoulli cracked beam resting on an elastic foundation. The modeling of the elastic foundation is implemented using the Winkler elastic spring theory and the stiffness factor of the elastic spring is specified corresponding to material characteristics of the elastic foundation. The Dirac’s delta function is used to apply the crack opening mode in the equation of the Rayleigh in which the factor of this function can be identified in terms of the stiffness factor of an equivalent rotational spring by considering material and geometric parameters of the crack. In the present analysis, explicit relationships are originally established to obtain the natural frequency in three boundary conditions of simply supported-simply supported, clamped-free and clamped-clamped. In this method, the natural frequency of the first mode is determined as the ratio of the maximum enriched potential energy and the maximum kinetic energy. Based on these relationships, the effects of the crack depth, the crack position and the elastic foundation on the response of natural frequency of the beam are investigated. The results of the analysis demonstrate that increasing the crack depth decreases the natural frequency of the beam containing the crack; while the elastic foundation increases the natural frequency of the cracked beam. The comparison of the results of proposed relationships with those of full modeling of the structure in Abaqus software shows a great accuracy of the present analysis.

In this study, static and vibration analyses of cylindrical piezoelectric structures by means of superelements are targeted. In this regard, the cylindrical superelement is modified in order to be used in analysis of hollow cylinders made of piezoelectric materials. At first, the cylindrical superelement, which was previously defined in the literature, is introduced. Next, the calculation of stiffness and mass matrices of piezoelectric structures in finite element (FE) analysis is briefly reviewed, and then, a piezoelectric cylindrical superelement is developed. In order to verify the accuracy of the defined element, two case studies are analyzed by means of the superelement, and the results are compared with the ones obtained by a commercial FE software. At the end, the piezoelectric superelement is further modified to be used in static and vibration analyses of hollow cylinders which are made of functionally graded piezoelectric materials (FGPM). Also in this case, two classical problems are analyzed with the defined element. In both piezoelectric and FGPM cases, the results shows appropriate compatibility with the ones obtained by the conventional elements.

Considering that global energy resources are decreasing, energy harvesting from environment has become more important. One of the most important methods of power scavenging from environmental vibrations is energy harvesting using piezoelectric materials, and researchers have recently focused on optimizing this type of energy harvesters. In this paper, the effect of decreasing beam width on the amount of harvested energy from an oscillating piezoelectric cantilever beam is investigated using experimental and numerical methods. In this study, one of the newest piezoelectric materials called EAPap cellulose has been utilized. At first, a fixed-width beam was investigated, and then two beams with half-width of the initial beams, were analyzed in series and parallel connections with the same boundary conditions, and in the next stage, the unit cantilever was divided into three equal parts and serial and parallel states of these beams have been investigated and the results are compared with laboratory data. It is seen that if the width of a beam is divided into several equal parts and some beams with fewer width and series connection are utilized, amount of harvested energy is significantly greater than the initial beam.

Quartz crystal is a piezoelectric material and due to the inverse piesoelectric effect, applying an AC voltage to this crystal makes the crystal to vibrate. The natural frequency of these forced vibrations varies with the application of mechanical stresses, and temperature change in the crystal. In this article, a digital resonator force sensor was designed and simulated. This new force sensor has two working mode. In the first mode, the sensitivity of the sensor to the applied force is maximum, and in the second mode, the temperature error of the sensor is reduced. The sensor output in these working modes was simulated by a numerical-mathematical model. The model was verified by experimental data in previous literature. The effect of force azimuth angle, and length of loading edges at the crystal, were evaluated on both working modes. The possibility of making measurements in two working modes leads to the increase of measurement resolution, by increase in sensitivity, and also the increase of measurement accuracy, by decreasing the thermal error on the sensor.

In this study, nonlinear dynamics of non-classical Kirchhoff plate is analyzed for the first time and the region of chaotic behavior is predicted and controlled by designing the robust adaptive controller. Virtual displacement principle is employed to derive the governing equation of Kirchhoff micro-plate resting on nonlinear elastic foundation. In the governing equation, von Karman geometrical nonlinearity and couple stress theory is considered. Solving the eigen value governing equation for fully simply supported boundary conditions, results are validated. Next, Galerlkin method considering harmonic excitation of first mode is used to derive micro-plate forced vibration equation. Regardless of modal interaction, the chaos threshold is then investigated. Homoclinic orbits of unperturbed system is plotted and stable and unstable manifold transversely cut that is criteria to predict chaos according to Melnikov’s method is studied. Using maximum Lyapunov exponents numerical method, size-dependent chaos is also locally identified. Phase portrait, Poincare mapping and time response are plotted for different values of size ratios and the important effect of size on the chaotic behavior of micro-plats is presented. The results of this study show that chaos in the micro-plats is size dependent and using the non-classical theories to analyze the chaos of micro-plats is necessary. Subsequently, designing the robust adaptive fuzzy controllers, chaotic vibrations are completely eliminated from the system and the robust adaptive fuzzy controller is introduced as an effective method for controlling chaos in these systems. Results of this research can be used in the production process, optimization and control of nanoelectromechanical systems.

A Spherical Parallel Mechanism (SPM) is used to rotate a body around a fixed point. Using type synthesis, different kinematic arrangements can be obtained for the robot with three degrees of rotational freedom. The most commonly used structure for this robot is the 3-RRR kinematic architecture which is an overconstrained parallel mechanism and causes several problems of mounting the mechanism, but has the advantage of having high rigidity thus a good accuracy. In this paper two non-overconstrained architectures 3-RRS and 3-RSR that are extracted from the type synthesis are compared with overconstrained one from accuracy point of view based on joint clearance. First, a method to obtain a model of moving platform pose (position and orientation) error based on joint clearance is introduced which leads to a standard convex optimization problem. Then maximum values of six components of the pose error are computed in more than 1000 different configurations within their workspace. It is shown that this displacement is configuration dependent. The obtained results revealed that the 3-RRR SPM has better position accuracy while in the case of orientation, the 3-RRS SPM has lowest maximum error between SPMs under study in the prescribed workspace. It can be concluded that non-overconstrained structures can be used instead of the overconstrained structure. Finally, a comparison was made between the performance indices and the method presented in this paper and results showed that the kinematic sensitivity index is most consistent with the accuracy of the robot.

In recent years, there has been much interest in the use of automatic dynamic ball balancers to balance the rotors with varying imbalances. An automatic dynamic ball balancer is a device that can automatically compensate the variable imbalances of a rotor in certain working conditions without having to stop the rotating equipment. Ball-spring autobalancer is a new type of automatic ball balancers which has two main advantages over the traditional ones, i.e. it causes the rotor vibration amplitude at the transient state to be small and it has a wider balanced stable region. Bearings are one of the most important mechanical components due to their considerable influence on the dynamic behavior and stability of the rotary systems. In previous studies, the dynamic behavior and stability of the rotor with isotropic bearings equipped with a Ball- spring autobalancer has been analyzed. However in practice, the bearings have generally anisotropic behavior due to manufacturing process. In this study, the dynamics and stability of a rotor with anisotropic bearings equipped with a Ball-spring autobalancer are investigated via the multiple scales method for the first time. The results show that the anisotropic bearings do not impair the main advantages of the Ball-spring autobalancers, and as the anisotropic parameter increases the balanced stable region decreases.

Due to stochastic noises, modeling uncertainties and nonlinearities in low-cost inertial measurement units (IMUs), the positioning error of Strap-down Inertial Navigation Systems (SINS) are increased exponentially. So, SINS is integrated with aiding navigation systems like a Global Navigation Satellite System (GNSS) by using an estimation algorithm to obtain an acceptable positioning accuracy. In urban area the GNSS signal may be obstructed because of tall trees and buildings. Therefore, in the paper a novel constrained adaptive integration algorithm is developed for integration the SINS/GNSS. In this algorithm, the velocities constraints in body frame in addition to altitude constraints based on a barometer data are firstly developed, and then a constrained estimation algorithm is designed based on the proposed constraints. In addition a fuzzy type 2 algorithm is used to calculate the estimator parameters based on vehicle maneuvers. The real vehicular tests are used for implantation and validation of the proposed algorithm. The experimental results indicate that, the proposed adaptive constrained estimation algorithm enhanced the estimation accuracy of the SINS steady states.

Quadrotors have high energy consumption due to their inherent structure, hence minimization of their energy consumption play a crucial role in terms of enhancing their operational range and flight time. In this paper, optimal control based on a minimum-energy trajectory planning algorithm of a quadrotor has introduced between two certain points to maximize operation time. To do this, first, dynamic equations of quadrotor and Brushless motor are derived. Energy consumption of quadrotor is introduced as a cost function and the minimum energy path is determined using optimal control theory. To satisfy constraints, all of them are combined with a Hamiltonian equation using Lagrange multiplier. Finally, simulation results are compared with results of conventional trapezoidal velocity profile which shows energy saving up to 4% compared with conventional trapezoidal velocity profile. Also, results reveal that the influence of operation time is far more than path length on energy consumption. In order to verify the validity of the simulation results, they are compared with the results of an experimental model which is consisting Brushless motor, sensor and, control board. As well as using simulation results in different situations, a mathematical equation was extracted among path length, operation time and energy consumption which can be useful to estimate the maximum flight range or operation time considering the amount of energy of the battery.

This paper proposes an optimal method for eradicating cancer, such that it can not be relapsed. The major issue, is that the tumor free equilibrium point at the end of chemotherapy is still unstable. Mathematically, it means that when the chemotherapy is stopped, the trajectory of the system moves away from the tumor free equilibrium point and the tumor cells starts increasing. To overcome this problem, we can either restart the process of chemotherapy or try to stabilize the equilibrium. In this article the dynamics of the system is changed around the tumor free equilibrium point by the use of vaccine therapy and the chemotherapy pushes the system to the domain of attraction of the desire point. For optimal chemotherapy, two objective functions optimized simultaneously in order to minimize the size of tumor as well as the side effects of the anticancer drug on the patients’ body. After removing the chemotherapy, the cancer does not relapse due to change in the dynamics of the system. Simulation results show that by applying this method, the cancer cells population approaches to zero even after cessation of chemotherapy for a long time.