مجله مهندسی مکانیک
پیاپی 147 (بهمن و اسفند 1401)

Many arrangements are available for placing cylinders with respect to each other. Some arrangements of circular cylinders include side-by-side, tandem, and staggered at different angles. Thus, in the present study, the drag coefficient at three cylinders, A, B and C with diameters of 15.5, 21.3 and 31 mm at different angles (0°, 5°, 10°, 22.5°, 45°,67.5° and 90°) in L/D=2 and 4 at various Reynolds numbers (14700<Re<48000) is experimentally investigated. The results showed that the drag coefficient is completely dependent on the diameter of cylinders and the L/D ratio. The variation of drag coefficient in L/D = 2 is less dependent on the Reynolds number changes at different angles. Also, by increasing the diameter of the downstream cylinder, the effect of the Reynolds number on the drag coefficient was reduced. The drag coefficient in L/D = 4 is less sensitive to the angle changes except for the zero degree angle.

In this article, the Mori-Tanaka micromechanical approach is used to obtain the elastic and piezoelectric properties of a hybrid composite with a polyamide matrix and reinforced with piezoelectric particles of lead zirconate titanate and carbon nanotubes. Modeling consists of two steps, first, the effect of carbon nanotube distribution in the polyamide matrix is calculated, In the next step, the obtained results were used to calculate the addition of piezoelectric particles. The model has been validated with experimental results and previous studies. the increase in the volume fraction of piezoelectric particles causes an increase in the elastic and shear moduli and piezoelectric constants. Modeling for uniform and non-uniform distribution of carbon nanotubes has been done. The results show that by adding carbon nanotubes, the elastic moduli and piezoelectric constants increase. Also, the agglomeration of carbon nanotubes reduces these modules.

Energy harvesting from wasted energy in the environment in order to run lowpower electronic devices is one of the common methods to use renewable energy. The main purpose of this technology is to provide sources of electrical energy in remote places and also to charge energy storage devices such as capacitors and batteries. The present study compares the harvested power from two electromagnetic energy harvesting systems with linear and non-linear spring (in two condition: COMSOL software and experimental results) which are vibrated by the human motion The innovation of this research is the spring that use in the energy harvesting system, which has linear spring on the one hand and is affected by non-linear spring on the other hand, as well as the validation of the simulation results using the design experimental system.

In this research, using R410a coolant in cooling the cutting edge of the tool and comparing it with the traditional fluid of soapy water, the life of the tool and the wear rate of the cutting edge of the tool were investigated. The wear rate of high speed steel (HSS) tool in steel cutting (ck45) 1045 at cutting speeds of 15, 25, 40, and 55 meters per minute, cutting depths of 0.5, 1, and 1.5 mm and feed rate of 0.05, 0.12, and 0.2 mm /rev was investigated in two modes of liquid cooling, soapy water and R410a coolant. The obtained results show that cooling with R410a coolant, due to its high cooling power and better control of the temperature of the cutting area compared to the soapy water fluid in the machining process, has reduced the amount of tool wear and can be used as one of the suitable cooling fluids. Based on the minimum amount of tool wear in different conditions, by using R410a coolant, the cutting speed can be increased by 60% from 25 m/min to 40 m/min. Also, in the most optimal mode, the amount of tool wear is improved up to 20 times, and at a cutting speed of 40/min, the cutting depth is 1 mm and the feed rate is reduced from 400 to 20 micrometers.

Solid-state welding and processing methods will be an alternative to joining lightweight metals that cannot be welded using conventional fusion welding processes. After three decades after its invention, FSW is the first choice in joining high-strength aluminum alloys with an application in automotive and aerospace. The process is also capable of joining other alloys too. Due to the success of FSW, it was considered for more complicated applications and joining high-strength alloys. It should be noted that FSW is not the only successful rotary friction-based solid-state welding process. In recent years, friction hydro-pillar processing (FHPP) which is successful in repairing surface and body cracks and defects of different steel grades is also very interesting. In the present study, main rotary friction-based welding and processing methods are introduced and discussed in two major classes including friction stir welding and friction hydro-pillar processing.

A nanoparticle or an infinitesimal particle is usually defined as a particle of matter that has a diameter between 1 and 100 nanometers (nm). The properties of nanoparticles often differ significantly from larger particles of matter. Nanoparticles show different dislocation mechanics, which together with their unique surface structure, lead to different mechanical properties from bulk materials. Nowadays, by adding nanoparticles, the mechanical properties of composites are improved. Due to their small size, nanoparticles increase the surface area between the base material and the reinforcement and therefore improve the mechanical properties. The type of nanoparticle used, dimensions, weight percentage and the way of nanoparticle distribution are determining factors in improving mechanical properties. In the present study, while presenting the concepts related to nanocomposite, the effect of five different nanoparticles on the common mechanical properties considered by structural designers is investigated. The results show that the addition of nanoparticles up to a certain weight percentage improves the properties, and more than that amount sometimes has the opposite effect, one of the reasons for which is the clumping of nanoparticles.