Mechanic of Advanced and Smart Materials

Abstract Hybrid composite of aluminum base reinforced with alumina and graphite particles was prepared by vortex casting method along with centrifugal casting and its tribological behavior was investigated. The wear test was performed with a sliding speed of 60 cm/s and a force of N30. The results showed that by adding graphite and alumina to the aluminum base, the abrasion resistance of the hybrid composite increased. The amount of graphite in the hybrid composite had a great effect on the wear rate, and adding it to an optimal amount leads to a decrease in the wear rate and its further increase leads to an increase in the wear rate. With the presence of alumina particles, the hardness decreased less and the wear resistance increased. The Al-Al2O3-Gr hybrid composite showed a much better wear rate than the base alloy as well as the Al-Gr composite. Al-Gr composite had a higher wear rate than the base alloy due to the high amount of graphite and the absence of alumina particles. The scanning electron microscope investigations of the wear surfaces showed that in the base alloy, the wear mechanism is a combination of adhesive, scraping, and indentation mechanisms, while in composites, the dominant wear mechanism is scratching and indentation.

Abstract The purpose of the levitation process is to neutralize the gravitational force on the sample with the help of a non-contact force and levitate the sample in the air without contacting the secondary surfaces. The benefits of eliminating the contact of a substance with external surfaces have led to the attention of the levitation process. Considering that among the levitation methods, ultrasonic levitation is the only method that can be applied to materials with different physical properties and geometries, levitation of the material in the liquid phase can also be done with the help of this method. The potential of ultrasonic levitation of liquids for use in cases such as pharmaceuticals, biology, controlling the structure of matter, etc., has led to several types of research in the field of improving the conditions of this process. In this article, an attempt has been made in the first part to review the theory and analytical relationships of the ultrasonic levitation process, and then in the second part, the studies conducted in the field of improving the conditions of the levitation process and the factors affecting it have been examined. Finally, the future of research in this field has been looked at.

Abstract Phononic crystals are advanced structures which are created by repetition of inclusions in an elastically different host material. The distinguishing feature of these materials is the existence of a band gap. complete band gap is a frequency range that the phononic crystal prevents the propagation of elastic or acoustic waves in all directions whose frequency is in that range. Due to the feature of band gap, phononic crystals are suitable for managing the propagation of elastic waves. In this research, two-dimensional phononic crystal structures have been investigated. In order to reach the optimal band gap, many works have been done on the phononic crystal structures. In this article, the above efforts have been investigated including rotation of non-circular inclusions, adding an inclusion to the primary unit cell, changing the type of lattice and the shape of the inclusion, hybrid phononic crystal, nested phononic crystal, heterostructure phononic crystal, hierarchical phononic crystal and the use of Smart materials.

Abstract The aim of this article is to select material for the components of the quadrotor drones with a time-variable structure. Although the use of a time-variable structure provides the capability to maneuver along various paths and exhibit diverse functionalities, dimensional changes may lead to component failures due to loads, vertical forces, and drag forces from the motors. Therefore, in the design process, in addition to considering weight and cost, parameters related to the durability and load-bearing capacity of the robot's structure must be examined. There are various criteria for selecting suitable materials for construction, and in this regard, the effectiveness of each criterion is specified in the design tables. Ultimately, the optimal materials for use are identified. The results indicate that by selecting Aluminum 7075-T6 and ABS+ Filament materials, the deformation of the drone's body under maximum motor loads is minimal, and the factors of weight and total cost are also optimized.

Abstract In this research, the induction of high-frequency alternating stresses in steel parts using an alternating magnetic field has been investigated experimentally. This treatment, in addition to the induction of alternating stresses, can increase the temperature of the part and facilitate the release of residual stresses. Residual stresses caused by the welding process in the area around the weld line are a good example of the applications of this method. This method is very fast, and it can be used for small or large parts without space limitations. Also, the necessary equipment can be prepared easily at low costs.

In this study, a small coil with an iron core was used to induce the magnetic field, and a simple and cheap electric board was used to create an oscillating current in the coil. The electric board employs a high-frequency electronic switch in a DC circuit to generate a rectangular waveform voltage. The obtained experimental results show that the steel part can resonate at frequencies close to the first longitudinal natural frequency or its subharmonics, and in this case, normal stresses in the order of 100 MPa are induced in the part. By upgrading the electrical equipment prepared in this research, it is possible to increase the induced stresses several times. Hence, employing appropriate equipment, the high-frequency magnetic induction method can be used as an alternative method for stress relief of welded joints.

Abstract Due to the effect of environmental conditions on the behavior of materials, in this research, the effect of acidic environment on the flexural modulus and fracture toughness of glass fiber/vinyl ester composite multilayers at different temperatures under second mode loading has been investigated. The samples were placed at 25°C and 80 °C for different periods of time in acidic environmental conditions. The experimental results show that different environmental conditions, especially at a temperature of 80 °C, have a significant effect on the behavior of composite samples. The load-displacement diagrams and fracture toughness of the samples have been investigated in different time intervals. The experimental results show that at the temperature of 25°C, the maximum load as well as the interlayer fracture toughness increases at the beginning and then decreases. Also, at around 80 °C, after 250 days, more than 50% of the fracture toughness value was observed. The scanning electron images (SEM) of the mechanisms of damage and crack growth over time showed that fiber breakage and separation of fibers from the resin occur at the fracture surface of the samples.

Abstract Miniature robots are being developed today and are used to monitor electrical equipment and medical matters such as drug delivery or minimal intervention. Polymeric robots that have been presented for this purpose are compatible with the environment and have good performance, but they have the possibility of changing the limited diameter. A new generation of flexible and soft robots have emerged that work based on metallic fluids. Ultra-thin deformation and passage through confined spaces make it possible to avoid damaging surrounding biological tissues. The efficiency of these robots also depends on the environment. Meanwhile, hybrid robots based on elastomer-metal have been introduced, which are flexible like slime and have the ability to control stiffness with magnetic field like magnetorheological fluid. In this article, the construction of nano-magnetic slime robot is explained and some of its physical and rheological properties are reported, and some of its applications are investigated by experimental tests.