نشریه مهندسی مکانیک مدرس
سال بیست و سوم شماره 8 (امرداد 1402)

The roll forming of an asymmetrical channel section is associated with a twisting defect, but this defect also occurs in a symmetrical section whose holes are asymmetrical. Therefore, first, a finite element model was presented to investigate the process. By designing the full factorial method, the important factors affecting the twisting defect and the effect of each during the cold roll forming process have been investigated. In the end, it was concluded that the thickness of the sheet and the diameter of the holes are the most important factors affecting the twisting defect. It was concluded that the greater the difference in the diameter of the holes on both sides of the channel, the higher the amount of twisting defect. For the forming angle of 45 degrees, by increasing the thickness of the sheet from 2 mm to 3 mm, the twist angle of the piece increased from 1.5 degrees to 2.5 degrees. According to the behavior of the metal, a series of experimental tests were designed and the effect of the hole diameter factor on this defect was determined. Appropriate matching of experimental and numerical results indicates reliable and verifiable numerical results.

Freezing is a common issue in blowers, wind turbines and flying vehicles. This phenomenon has a great impact on reducing aerodynamic performance, increasing noise pollution and imposing extra load on the structure. In this article, the effect of freezing on the aerodynamic and aeroacoustic performance of the Naka-0012 airfoil has been studied. Transient and three-dimensional Navier-Stokes equations have been used for aerodynamic prediction. Sound wave is calculated using Fox-Williams and Hawkins equations. Simulation of eddies has been done using LES method and WALE subgrid scale model. First, all calculation methods have been validated using experimental data. Then the effect of freezing on airfoil performance has been studied. Flow vortices have been studied and sound production mechanisms corresponding to these vortices have been identified. The results show that freezing reduces the lift force by 9.7% and increases the drag force by 3.8 times. In the range of maximum human hearing sensitivity (one to five kHz), the average amount of sound increase is around 9 dB, which is a significant amount in terms of noise pollution. The increase in sound caused by freezing can be used to identify and deal with this phenomenon faster and reduce its risks.

In the present research, classic micromechanical methods and their application as constitutive models in conjugation with incremental theory were developed. Using the modified Eshelby model, the Eigen strain concept in polymeric composite, and a modified form of self-consistent model the elastic properties of nanocomposites were predicted. Also, the stress-strain behavior of elastomer nanocomposites was calculated and validated by the experimentally determined ones. The results showed that the new model can predict the stress-strain behavior of elastomer nanocomposite at different particle volume fractions.

Advances in many engineering fields depend on materials with appropriate properties. The use of metal-matrix composites is rapidly growing as a suitable alternative to conventional materials due to their strength-to-weight ratio, resistance to wear and creep, etc. Machining of metal-based composites is a difficult task due to the presence of very abrasive reinforcing particles in its based metal. Therefore, it is necessary to investigate the factors affecting these materials. In this research, a methodical study has been conducted to investigate the effect of the parameters of spindle  speed, feed rate, depth of cut and the percentage of reinforcing particles on the behavior of cutting force and tool wear using experimental design methods, modeling and statistical sensitivity analysis methods. . Detailed analysis of behaviors has been done by providing statistical regression equations and optimization by Deringer's method and E-Fast-Sensitivity Analysis. According to the obtained results, the cutting depth had the greatest effect on the machining force. Also, cutting speed with 77%, advance rate with 9% percent and cutting depth and weight percent of reinforcing particles with 7% percent are other parameters affecting tool wear in the milling process of this composite.

The proper method for jointing Carbon fiber reinforced polymers (CFRP) to aluminum, which causes uniform stress distribution, more suitable fatigue performance and weight reduction, is adhesive bonded joint. In adhesive bonding, the interface of adhesives and adherent are sensitive areas for the initiation and propagation of failure. In order to eliminate surface contamination, adherents must be surface treated. In this research, the effect of the functional pattern of laser surface treatment on the strength of aluminum/composite adhesive bonded joint in the mode I fracture has been investigated. At first, laser surface treatments were performed throughout the specimen in order to find the parameters of the laser device that increase the strength of the adhesive bonding by creating a suitable surface quality. After that, the functional pattern of laser surface treatment with the appropriate parameters for ablation and cleaning of the adhesive surface is done. The results show a 15.5% increase in the critical strain energy release rate of the mode I for the all-over laser surface treatment specimen compared to the sanding method. Meanwhile, with the functional pattern of laser surface treatment, the critical strain energy release rate of the mode I has increased by 5.9% and 22.4% compared to all-over laser surface treatment and sanding, respectively. Examining the fracture surface of the specimen shows the delay in crack growth in the specimen of the functional pattern with changes from the adhesive failure to the fiber tearing, which has improved the strength of the adhesive bonding.

In this article, the numerical and experimental investigation of the effect of ultrasonic waves on the heat transfer rate with an increase of the wave amplitude is discussed. Numerical modeling determines the possibility of the investigation of the ultrasonic wave’s effects on fluid flow distribution and heat transfer. For this purpose, a cylindrical tank is considered inside which a spiral heater is placed at a fixed height in the water. In addition, ultrasonic transducers are considered as circular plates under the bottom of the tank. In order to simulate, the ANSYS Fluent software is used and the modeling is accomplished in two stages before and after ultrasonic excitation. To validate the numerical results, they are compared with those of the experiments. For this purpose, an experimental setup is prepared witch consists two coaxial cylinders, a spiral heater kept at a certain height in the water, and five transducers attached to the bottom of the tank. Both experimental and numerical results show that the convection heat transfer coefficient increases with the use of ultrasonic waves with a discrepancy of nearly 4% between the results. By increasing the heat transfer coefficient, the heater surface temperature decreases. The discrepancy between the measured and calculated temperature is about 5%. The velocity and temperature distributions obtained from the numerical results show that using ultrasonic waves enhance the fluid flow mixing which in turn increases the convection heat transfer. The higher the amplitude of the ultrasonic wave, the higher the heat transfer coefficient will result.