Mechanic of Advanced and Smart Materials

Abstract In this research, the effect of adding different percentages of graphene oxide to polyamide and the effect of different printing directions on the mechanical properties of 3D printed samples were investigated. At first, 0.3% and 0.7% of graphene oxide nanoparticles were mixed in the matrix. Pure and composite polymer samples with different percentages of graphene oxide were printed by stereolithography in three directions. The mechanical properties of the samples were evaluated using tensile, impact and hardness tests. A scanning electron microscope was used to check the fracture surfaces of the samples. The results of the mechanical properties tests indicate a decrease in strength with the addition of go nanoparticles. With the increase of graphene oxide nanoparticles, the strength of the parts decreased by 30%. On the other hand, there was a 12% difference in tensile strength in pure polymer samples, which reached 17% with the addition of nanoparticles. Microscopic investigations showed the formation of clusters of graphene oxide nanoparticles in the composite samples, which led to stress concentration and cracking. Based on this, the printing direction has a significant effect on the mechanical properties of the printed samples. Among the pure polymer samples, the sample printed in the flat direction and among the composite samples, the nanocomposites printed in the vertical direction showed the best mechanical properties. Adding graphene oxide nanoparticles to the resin and increasing the percentage of nanoparticles in the direction of printing on the edge led to a decrease in hardness compared to the pure polymer sample.

Abstract The self-driven movement of biped robots along an inclined surface is a topic that, despite its inherent complexities, has attracted the attention of many researchers. However, what distinguishes this research from similar works is the consideration of flexibility in the links that constitute such robotic systems. This assumption is not far-fetched, as in the transition phase (impact), the impulse force applied to the system significantly increases the likelihood of exciting vibrational modes. On the other hand, the bones involved in walking are enveloped by muscles, which have viscoelastic properties. Therefore, to achieve more accurate results, modeling the links with viscoelastic properties becomes inevitable. In the discussion of the autonomous movement of bipedal robots, the most important issue is determining the initial configuration of the robot so that the system can perform a periodic and stable motion solely under the influence of gravitational attraction. The highly unstable nature of the system under study, along with the vibrations created by the impact force resulting from the foot striking the inclined surface, constitutes one of the very serious challenges in the progress of this research. Nevertheless, this paper overcomes these challenges by presenting a completely systematic method with very strong mathematical frameworks. Finally, the effect of the intrinsic parameters of elastic links, including the modulus of elasticity and the Kelvin-Voigt coefficient, on the stability of the movement of such robotic systems is examined.

Abstract Cycloidal gearboxes are part of power transmission systems that use a cycloidal disk instead of an involute gear to transmit power. The use of cycloidal gearboxes is limited due to complicated profile shapes, difficulties in fabrication, and lack of data in the design process of industrial gearboxes. The special mechanism of cycloidal disks provides a high conversion ratio in small dimensions in cycloidal gearboxes. In this research, the design of a cycloidal gearbox will be discussed. Firstly, the mechanism of cycloidal gearboxes will be introduced and its advantages will be described, the operation mechanism and main components will be explained and then a cycloidal gearbox for conversion of 1500rpm into 32rpm (conversion ratio 47) will be designed according to basic equations. The designed gearbox is modeled in SolidWorks software and analyzed in finite element software (Ansys software). The finite element results show that the principal stress and shear stress of the cycloidal disk and other parts of the gearbox were in the safe region of the design criteria. In addition, the rotational speed of the gearbox is not constant due to the eccentricity of the input shaft, and the average rotational speed is calculated based on the finite element results and agrees with the design value.

Abstract Laminated composite materials are susceptible to damage, such as delamination, due to poor out-of-plane properties and inadequate adhesion at the layer interface. Using the interlayering method is an effective way to enhance resistance against delamination in these materials. However, interlayer synthesis methods have been limited and sometimes very expensive. Therefore, this study investigates the impact of novel 3D-printed polyvinyl alcohol (PVA) interlayers on the mode II interlaminar fracture toughness in glass/epoxy laminated composites. Notably, the interlayers feature a geometrical structure consisting of square cell shapes, allowing the filament to have an equal volume percentage to the resin in the interlayer. To achieve this, end-notch flexure specimens (ENF) were prepared, and the mode II interlaminar fracture toughness was calculated using the compliance-based beam method (CBBM). The specimens' crack growth resistance curve (R-curve) analysis revealed that using the desired 3D-printed interlayer increases the mode II interlaminar fracture toughness by 73%. Furthermore, the behavior of crack growth resistance in laminated composites reinforced with 3D-printed interlayer shows an increasing trend. The mode II fracture surface analysis of reinforced specimens demonstrates the influence of square cell shapes in creating shear hackles, increasing surface friction at the interface of laminated composite layers, crack pinning mechanism, and changing the direction of crack growth, ultimately leading to increased resistance to crack growth.

Abstract This paper proposes an approach for the exact solution of the transverse free vibration of exponential axially functionally graded material (AFGM) Timoshenko beams with concentrated tip masses and general boundary conditions. Initially, by utilizing the governing equilibrium equations of a Timoshenko beam, the main differential equation for the free vibration of the AFGM Timoshenko beam is obtained. Then, the beam deformation function is achieved by solving the governing equation of the beam vibration exactly. Subsequently, by applying the boundary conditions, the constant coefficient matrix of the beam becomes available. By making the determinant of the constant coefficients zero, the characteristic equation of the system and consequently, the beam's natural frequencies are obtained. It is noteworthy that the final relation is presented so that it can be used to find the exact frequencies of homogeneous and inhomogeneous Euler-Bernoulli, Rayleigh, and shear beams, too. Numerical examples demonstrate the accuracy of the results obtained by the proposed method. In the next section of the paper, the effect of the exponential gradient index, elastic end supports, concentrated tip mass, rotational inertia of the concentrated mass, and thickness-to-length ratio on the natural frequencies and mode shapes of the Timoshenko beam is investigated. The results show that the exponential gradient index, boundary conditions, concentrated tip mass, and thickness-to-length ratio play an influential role in the dynamic behavior of AFGM beams.

Abstract The use of metal-based composite materials, especially aluminum composites, has found wide applications in various industries such as automotive, aerospace, military, etc., due to their favorable mechanical properties, high strength-to-weight ratio, and high wear resistance and hardness. On the other hand, these mechanical properties and high hardness and wear resistance, which is due to the presence of reinforcing particles such as silicon carbide in these composites, makes them difficult to machine, so that only special tools and blades, such as polycrystalline diamond tools, can machine these composites optimally. The findings from this study can be valuable in optimizing the turning process of aluminum-based metal matrix composites.

In this study, the effects of four input parameters - cutting speed, feed rate, feed force in the X direction, and feed force in the Z direction - on the output parameter of tool wear rate in the dry turning process of A359 aluminum alloy metal matrix composite reinforced with 20 vol.% of silicon carbide particles using polycrystalline diamond tools were investigated.

The numerical investigation of the effect of each of the four input parameters on the output parameter was done using the E-fast statistical sensitivity analysis method, which has high speed in quantitative and qualitative data analysis. The results showed that the parameters of feed force in X direction, feed rate, feed force in Z direction, and cutting speed have 88%, 8%, 3%, and 1% effect on tool wear, respectively.

Abstract Given the increasing use of nanotechnologies in human life and the significance of nano-electromechanical systems, this paper investigates the buckling and post-buckling behavior of Euler-Bernoulli (EB) composite beams (CB) reinforced with graphene nanoplatelets (GPLs), considering the nonlocal strain gradient theory (NSGT). Initially, the elastic properties of the nanocomposite reinforced with GPLs were calculated using the rule of mixtures and the Halpin-Tsai (HT) micromechanical model. Subsequently, the governing equations (GE) for the EB beam were derived using the virtual work principle, the NSGT, and the von Kármán (VK) strain field. These equations were analytically solved, and the achieved findings were checked against those found in existing studies, showing excellent agreement. Finally, the effects of varying the weight fraction and distribution of GPLs in the composite, changes in nonlocal parameter (NP) and strain gradient (SG) parameter, as well as the ratio of beam's length to beam’s thickness, on the critical buckling load were examined and as a results for a constant weight fraction, the critical buckling load is highest in the X pattern, followed by the U and O patterns.

Abstract Advanced oxidation processes (AOP), based on the formation of highly reactive radicals, are able to degrade many emerging organic environmental contaminants such as tetracycline (TC) in wastewater. In peroxymonosulfate(PMS)-advanced oxidation process(AOP), the presence of a Heterogeneous catalyst is required. Among of them, perovskite( as an advanced material) is promising due to its tunable composition in cationic positions and structural stability. In this research, LaMnO3 perovskite nanocatalyst was synthesized by sol-gel method via complex agents. the LaMnO3 nanoparticles were successfully prepared, as proven using different spectroscopic techniques including XRD, FESEM, EDS, BET, XPS and TG/DTG. Finally, the performance of LaMnO3 nanoparticles in degrading tetracycline in water during advanced oxidation process for PMS activation was investigated. The results shows that this method is very good for treatment of wastewater containing this dangerous pollutant. It is shown the tetracycline pollutant in the wastewater can be reduced from 25 and 50 ppm by 62.7% and 70.2%.