مجله مهندسی مکانیک
پیاپی 141 (بهمن و اسفند 1400)

A Bone fracture often happens due to an accident and old age. Broken bones are fixed by connection elements that is mounting on the drill holes. So many attempts have been done to reduce thermal necrosis and drilling force. To predicate thermal necrosis and drilling force, Finite Elements Modeling (FEM) has been considerably utilized recently. In this study, bone drilling has been simulated by commercial DEFORM/3D. This software has a special module in machining process. So, it is user friendly, easier, and faster than other FE software. Due to the anisotropy of the bone, The Hill equation was used to define the material properties. Rotational speed and Feed rate as two inputs were changed in three levels, a total of 32 =9 tests were designed and its simulation was performed in three dimensions and compared with experimental tests. The results of computer simulations and experimental experiments have shown high agreement. The error rate between the experimental and simulation values was a maximum of 10% for force and 7% for temperature.

Shape memory polymers are a type of smart materials that can recover their original shape when exposed to external stimuli including temperature, magnetic field, light, and electric field. One of the most widely used of these polymers is thermalresponsive shape memory polymers. These polymers have advantages such as a high percentage of shape recovery and low cost and using them results in reducing complex mechanisms that lead to reducing the weight and volume of the systems. Thermalresponsive shape memory polymers have been used in many fields, including medicine, robotics, mechanics, and aerospace and have led to great changes. This paper aims to study thermal-responsive shape memory polymers behavior and their different applications. In fact, by investigating the thermomechanical cycle, constitutive models, different kinds of shape memory effect, different applications, their future, and challenges of these polymers including low recovery force and its solution and preparation of various tables from recent researches, these materials have been comprehensively studied. Due to the unique properties of these polymers and the effort to overcome their limitations, they will become a candidate for many self-assembled mechanical actuators in the future.

After the initial design of turbomachinery, optimization is the main goal of engineers in this field. The first step is to parameterize the geometric variables of the blade shape and the next step is to implement it in stochastic optimization algorithms. In this research, a combination of sweep, lean, dihedral and end bend is used for the parameterization of the rotor and stator blades of a transonic single-stage axial compressor. The genetic algorithm is used in conjunction with numerical simulations, using finite volume method, implemented in an automated multiobjective optimization platform. Amongst the optimization benefits, performed with the aforementioned parameterization methods, is the displacement of the normal shock wave towards the trailing edge and reduction of the intensity of the bow shock wave at the leading edge of the rotor blades and also reduction of the flow separation area in the stator blade, can be pointed out. These changes led to an increase in the isentropic efficiency of the compressor by 3% and in the total pressure ratio by 1%, at the design point. Also, the mass flow rate increased and the choked flow effect was decreased, compared with the initial design. In this research, simultaneous effect of the use of the mentioned geometric parameterization methods on the optimization results is considered, which has not been performed in previous studies.

 Since the nuclear energy has been recognized as a useful energy, the subject of structure, operation and safety and environmental protection have also been important. In the nuclear reactors, one of the most dangerous accidents that can occur is the loss of coolant accident, that the most important of these events is the guillotine breaking in cold or hot leg coolant, which, this will melt the reactor core if it is not stopped. This paper presents one of the most dangerous accidents in reactor containments known as Loss of Coolant Accident in its worst condition which is called Large Break Loss of Coolant Accident. The specific type of large Break Loss of Coolant Accident is Double Ended Cold Leg break which means totally guillotine type of break in cold leg pipe. This modeling is performed in Multi-volume method in Advanced Pressurized water reactor which is one of the most sophisticated safe reactors that has ever been built. The conservation mass ,energy and momentum equations have been used in this modeling and the modeling software applied in our analysis is MATLAB, and the results are compared with the Advanced Pressurized-1000 water reactor safety, security and environmental reports.

Diaphragm pressure sensors are used in various industries. Much research has been done to optimize and improve the quality of these sensors. This paper investigates "sensitivity" as a critical variable in diaphragm pressure sensors based on MEMS technology. Aperture geometry is one of the most influential variables in the sensitivity of a diaphragm sphygmomanometer, which in addition to sensitivity, can affect other variables such as operating range, sensor accuracy, dimensions, and even price. To increase the performance and sensitivity of pressure sensors, the sensor aperture was simulated in AbaqusFEA software, and while validating the computational solver, different geometries were evaluated. The results showed that the circular diaphragm has the best performance. Then the effect of corrugations on the surface of the diaphragm was investigated, and different forms of waves were simulated. The results showed that creating a circular wave with a radius of 15 μm at the end of the diaphragm surface increases the sensor's sensitivity by 18%.

In this paper, a pair of non-circular gear reducers consisting of a triangular driver gear and a pentangle driving gear was designed and fabricated. By determining the design parameters, two-dimensional and three-dimensional models of both gears were drawn using the software. Then, the movement of the gears was simulated and analyzed in the software. With the confirmation of the angular velocity and angular acceleration results, both gears were manufactured by the additive manufacturing process. The results revealed that the design method presented in this paper guarantees the functional accuracy of non-circular gears. The gears were assembled correctly and their movement was correct. Moreover, by selecting precise input parameters the production of non-circular gears using the additive manufacturing process has led to the achievement of a tolerance range ±0.02 mm and has prevented them from stepping along the thickness.

Tractor-trailer robot is a kind of mobile robots used to carrey heavy loads. So, load carrying capacity of such robots is an appealing subject which has not been considered up to now. In this article, load carrying capacity of the tractor-trailer mobile robots is investigated using the nonlinear optimal control theory. In point-to-point motion of the tractor-trailer robot, an advanced algorithm based on the indirect solution of the nonlinear optimal control is presented to calculate load carrying capacity of the tractor-trailer robot. Formulation of the optimal control is performed by considering the nonlinear dynamic and nonholonomic equations of the robot as constraints of the problem. Then, by presentation of an advanced iterative algorithm, load of the robot is gradually increased and in each step, optimal conditions are considered as a set of coupled nonlinear differential equation and solved. Load carrying capacity of the tractor-trailer robot is calculated at the final step of the algorithm with consideration of saturation of actuators. Then, the simulation of the tractor-trailer point-to-point motion is performed and the load carrying capacity obtained. The results demonstrate the capability of the proposed algorithm to calculate the load carrying capacity of the tractor-trailer robots and can be applicable for various missions.

Due to the risks of pressure vessels testing and need for random vibration test for qualification space tanks, identifying and proposing standard and valid testing procedure is the most important goal of this study. Due to various vessels tank types, detailed vibration test process is not reported in any aerospace standard, clearly, also study the famous standards like: ISO, AIAA, MIL and ECSS proof this fact. According to the vibration tests risks and importance of pressure vessels, in this article, the technical points of standards and valuable articles have been summarized to propose a proper vibration test procedures with safety and accuracy considerations. Reviewing the valid test methods leads to a vibration test procedure classification in the form of a flowchart. So, with this classification and with available equipment and test limitations considerations, random vibration test of space pressure vessels could be selected with the minimum coast and probable risks levels which are based on a valid universal process.