نشریه مهندسی مکانیک مدرس
سال بیست و سوم شماره 11 (آبان 1402)

In the current research, the effect of cutting depth and speed on surface topography, microhardness and microstructural changes in cross-sectional surface of turned parts under dry, wet, MQL and cryogenic cooling (CO2) conditions, on 304L stainless steel has been investigated. The main origin of surface topography defects was the formation of built up edge (BUE) on the cutting tool and its removal again. Also, the increase in cutting speed causes instability in the formation of BUE, as a result the volume of accumulated BUE decreases. Considering the improvement of surafce topography, in the order of priority, the efficiency of MQL, wet and cryogenic methods has been from the highest to the lowest compared to the dry method. the cross section of machined samples were prepared and it was observed that subsurface hardness of the samples decreases with the distance from the surface up to 34% and approaches the hardness of the bulk material. The hardness value in cross section of machined samples is directly related to the work hardening caused by severe plastic deformation on machined surface.With increase of cutting speed, the intensity of plastic deformation increases and the hardness under the surface increases. Different cooling and lubrication processes have a direct effect on thickness of the microstructural deformed layer. Under the highest value of cutting speed used in this research, the maximum reduction in thickness of the deformed layer of the microstructure in cryogenic and MQL conditions compared to the dry mode was equal to 62% and 28%, respectively

Thin-walled tubes play a significant role in increasing the energy absorption in energy absorbing systems. Holed thin-walled tubes are a suitable option for use in these systems due to the ease of production and the lack of geometry complexity. In this paper, a new geometric pattern for holed thin-walled cylindrical tubes made of aluminum alloy 6061 is presented, to improve the energy absorption characteristics. To this aim, the Taguchi design of experiment method has been used to find the optimal levels of the geometrical parameters of the tube to achieve the maximum energy-to-weight ratio and the minimum effective equivalent strain. The number of rows of holes, the number of holes in each row, the diameter of the small hole and the diameter coefficient of the small hole were considered as the geometric (input) parameters of the tubes. The initial crushing force, the total absorbed energy, the ratio of energy to weight and the ratio of the maximum initial force to the average force were compared for the optimal layouts. Examining the results showed that the arrangement of the holes in the middle with 3 rows of holes, 8 holes in each row, diameter of the small hole of 5 mm and the diameter coefficient of 1.2 (the large diameter is 6 mm) will lead to the best energy absorption result.

Ceramic materials are desirable in structural applications because of their strength at high temperatures, low thermal expansion, and excellent wear resistance. However, ceramic structures are generally brittle and will fail due to inherent flaws that can be introduced into the material through processing, handling, or while in service. In the strength test samples of ceramic materials, the observed strength depends on the sample volume and the test method, and the results have significant scattering. On the other hand, it is important to recognize the variability of the strength of ceramic materials for structural design, and in the design process, this variability usually requires a probability-based failure criterion, which, due to the brittle fracture of ceramics, usually uses the Weibull distribution to represent their strength. With the help of Weibull distribution, the concept of effective volume is defined and by using it, the strength of a test sample with a specific geometry and loading is predicted from another sample that has a different geometry and loading. In this research, the effective volume for a truncated cone under internal pressure has been derived analytically. With the effective volume for this configuration and a sufficient number of flexural strength tests with the help of small and low-cost flexural specimens, it is possible to predict the tensile strength of the ceramic truncated cone without conducting expensive tests. for a problem with a specific material property and dimensions, the effective volume was calculated numerically and it had a 3% error compared to the analytical value.

The purpose of this study is to develop a new surgeon assistant device applicable in open spinal fusion surgery to improve the accuracy of the entry point for pedicle screw insertion position.

We developed a new device named Surgeon Assistant Pedicle Detector (SA_PeD). SA_PeD detects and shows the accurate entry point for pedicle screw insertion to the surgeon, by using preoperative planning, registration and tracking phases.

The tests were made by eight operators and each of them on five vertebrae with two holes. The results show that the average position error is 0.52±0.26mm. Repeatability and reproducibility of device is also reported which is impressive. The device is also independent of the operator and has same result for all operators.

Considering that maximizing the accuracy, increases costs exponentially, so the device is cost effective in comparison to other expensive robotic and navigation systems and greatly reduces the number of errors. The device also occupies little space in the operating room and is easy to learn for the surgeon to use it.

This study examines the accuracy of three different methods for calculating the aerodynamic noise of the NACA-0012 airfoil in a homogeneous shear flow. The strength of flow vortices is crucial in aeroacoustic calculations, and it can be modeled more cost-effectively using the k-ω SST method or directly simulated up to 90% using large eddy simulation (LES) with higher cost. Additionally, a hybrid method called IDDES, which offers moderate accuracy and cost, is also considered in this research. The primary sources of noise generation identified are vortex shedding from the laminar boundary layer and its interference with the trailing edge, as well as Tollmien-Schlichting waves. Experimental data of the sound pressure level (SPL) in 1/3 octave is used to validate the accuracy of the methods. The results indicate that LES and IDDES show the closest agreement with the experimental data, with LES showing better accuracy. Furthermore, when studying the intensity of sound attenuation with distance, it is observed that the rapid attenuation of small vortices in LES leads to similar SPLs as IDDES after a distance of 1.2 meters. Moreover, since IDDES does not require strict regulations for creating a near-wall grid, it reduces the computing mesh by approximately 41% with less than 2 dB of error. This finding suggests that in similar applications, the IDDES method can be used as a suitable approximation instead of LES to expedite calculations and conduct parametric studies

In the present article, a survey is carried out on the parallelization of several iterative solvers of the system of linear equations resulting from the discretization of the Poisson equation using the finite difference method. In particular, the point and line Gauss-Seidel successive over-relaxation methods, as well as the conjugate gradient and stabilized biconjugate gradient methods are investigated. For the over-relaxation methods, the optimum over-relaxation coefficient is used. The parallelization is first carried out on a multi-core central processor using C++ programming language and the OpenMP library, and then for a graphics processing unit using CUDA programming language. The results show, for both the two-dimensional and three-dimensional equations, the conjugate gradient methods due to a smaller number of iterations, have less computation time. Comparing the execution time of the different methods shows that for an 8-core processing, speedups of about 10 and 5 are achieved for the two- and three-dimensional equations, respectively. Furthermore, using a graphics processing unit leads to speedups between 5 and 10 in comparison to the 8-core processing.