مجله مهندسی مکانیک
پیاپی 146 (آذر و دی 1401)

Travelling Wire Electro Chemical Spark Machining (TW-ECSM) is one of the newest machining processes that has the potential to machine advanced materials such as glass, quartz, silicon nitride, various composites and ceramics, and has the factors of creating complex cavities in materials. Forging is used, especially in the aerospace industry, to produce turbine assemblies, jet engine parts, and nozzles. The Studies show that the combined methods applied to model and optimize the TW-ECSM process are reasonable. In this research, a second-order linear regression mathematical model has been used to predict the rate of chip removal during machining operations and surface roughness and their effective interactions. Then, using the Sobol statistical analysis method, various differences including voltage, wire feeding speed, electrolyte density and thickness of the work piece on the material removal rate and surface roughness have been obtained. The results obtained from the sensitivity analysis show that the voltage has the greatest effect on the chip removal rate and the wire feeding speed has the greatest effect on the surface roughness.

In this paper, a weighing system with an electromagnetic force restoration is introduced. The systems are widely used in industry and especially in research laboratories. These sensors have a shorter response time compared to the strain gauge load cells. This feature of the sensors has made it suitable for dynamic weighing. In addition, EMFR systems operate independently of the elastic component in measurement. This feature eliminates effects such as fatigue of the elastic structure in the measurement. The proposed weighing system is designed based on the structure of two levers and has 3 mechanical, electrical, and electromagnetic parts. The measuring capacity of the proposed weighing system is 1 kg and its accuracy is 1 gr. In this system, a leaf flexure hinge has been used, which has increased the sensitivity of the system by 5 and 2 times compared to the hyperbolic type and circular type flexure hinges, respectively. The mechanical part of the system is integrally made of steel alloy, and the electromagnetic compensator consists of a coil with a ferrite core and the displacement can be detected through an optical switch.

The applications of reinforced composites and heterogeneous solid materials have been widely developed in different fields of aerospace and mechanical engineering. In this research, the necessity of using non-destructive methods in identifying possible damages in composite materials is pointed out. In addition, the acoustic emission method is described and compared with other non-destructive evaluation methods. It is stated that acoustic emission is a dynamic diagnosis method which can instantly show discontinuities in a structure under tension. The nature of acoustic emission signals is mentioned as an electrical signal. Finally, it is concluded that the best method to check the delamination and fiber damage in composite laminates is the acoustic emission method.

Improving the specialized problem solving skill is necessary for solving specialized problems at work because the correct and timely solution of work problems increases productivity and prevents its possible corresponding damages. Improving this skill is necessary for all people with any job, especially people with academic education in all fields of study. Machine design is one of the most important specializations of mechanical engineering and mechanical engineering of biosystems which students need to learn it well during their studies. Due to the high importance of specialized problem-solving skill, the necessity of proper implementation of the design process to solve various problems, and the effective role of education in improving this skill, the purpose of the present research is to review various materials in the field of teaching the design of machine elements with a focus on problem solving skill. In addition to teaching a suitable textbook, solving the home works of the textbook, and writing tests, teaching the design of machine elements requires five main components including 1. Idea generation, 2. Safety considerations, 3. Design of the day, 4. Improving designers’ responsibility, and 5. Conducting a project. Considering these cases in the educational course, a strong foundation and an important stimulus is provided for students to enter real design and product manufacturing with a problem solving approach.

In this paper, buckling analysis of a composite sandwich panel used in payload fairing structure is done and effects of various parameters on the structure buckling are investigated using finite element method. To this end, first, finite element model is validated for an aluminum honeycomb core and carbon/epoxy facesheets by the experimental results presented in literatures. Then, the effect of various parameters such as the core and facesheets thicknesses, material and structure of core, hybrid composite facesheets and facesheets layouts on the critical buckling load of panel is investigated. The composite panel is modeled as a 1/16th sector of thin cylindrical shell and is meshed using 6 mm linear cubic elements. The panel is considered without initial geometrical imperfections and cracks. According to the results, panel with hybrid facesheets consisting of titanium alloy and carbon/epoxy has the best buckling strength, 78% increase in critical buckling load compared to the basic panel.

Increasing welfare level in human societies, especially in big cities, has caused an increase in energy consumption, especially electric energy. One of the major uses of electrical energy in our country is in the field of cooling, which has taken a significant share of the network's peak load in recent years. One of the solutions that today's energy policymakers in the world use as an effective and efficient tool in energy management is energy production based on the method of simultaneous production of electricity, heat and cooling (or in short, simultaneous production). Simultaneous production is the combined production of two or more forms of energy (such as electrical, thermal and refrigeration energy) from a simple primary source (such as chemical energy of different fuels). The main purpose of this study is to examine the existing CCHP systems in Iran and the world, which includes the types of primary drivers used and foreign and domestic companies active in this field.