Mohammad Hossein Sadeghi’s research while affiliated with Tarbiat Modares University and other places

This study investigates the design and optimization of a porous hip implant to mitigate stress shielding. Initially, the focus was on determining the elastic modulus of a three-dimensional auxetic structure, primarily in the y-direction. Various methods—numerical, analytical, and experimental—were used to assess the elastic properties. Additive manufacturing was employed to create samples, which were then tested for their elastic properties through compression testing. The results revealed a strong correlation between the elastic modulus values obtained from simulations and experimental tests in the y-direction. To further enhance the implant’s performance and reduce stress shielding at the implant-bone interface, a gradient structure was introduced. This gradient design progressively increases the elastic modulus away from the bone contact surfaces, aligning closely with the bone’s modulus at the interface. The elastic modulus of this gradient structure was computed using Abaqus software and validated through analytical methods in MATLAB, with a minimal 4.8% difference between the two approaches, demonstrating high agreement. The application of a genetic algorithm enabled the creation of a porous hip implant tailored to minimize stress shielding throughout its structure. This innovative approach, integrating numerical, analytical, and experimental techniques with gradient structures, holds promise for improving hip implant performance and enhancing patient outcomes by reducing stress-shielding complications.

Ultrasonic welding (USW) of thermoplastic composites is considered as an interesting joint technique, which can be cost-effective due to its short welding time. The paper focuses on studying the effect of USW current on strength and quality of welding. In this paper, the welding of thermoplastic unidirectional prepregs glass/polyamide 6 composites laminate with stacking sequence of (0/90/+45/−45/−45/+45/90/0) is conducted by USW. A flat energy director is used to concentrate the interface heat. To examine the interface microstructure, the current-time graph was utilized during welding processes, and the relationship between such interface events, consumed current, weld strength, weldability, and weld quality is fully investigated. Based on the results, the highest welding strength and welding quality of thermoplastic composites can be obtained when the energy director and the first layer of the composite are completely melted and no disorder is observed in the fibers. In addition, the highest joint strength equals to 24.46 MPa, which is obtained after 1830 ms welding time.

In this study, experimental and numerical methods have been used in order to obtain the elastic modulus of the gradient structure with auxetic unit cells (negative Poisson’s ratio). Stress shielding is the most significant issue at the bone-implants interface. The difference in elastic modulus between bone and implant provides stress shielding. The development of mechanical properties in the porous structure can provide opportunities to resolve this mechanical properties mismatch between bone and implant. In this study, firstly, the uniform auxetic unit cells with negative Poisson’s ratio were introduced, and their mechanical properties were investigated by numerical and experimental methods in the x and y direction, and the results were verified. Then, numerical methods were used to achieve the uniform distribution of the elastic modulus in the gradient structure. Therefore, in the gradient structure, the elastic modulus in the outermost layer (assumed the contact surface with the bone) is considered lower to reduce the stress shielding at the bone-implant contact surface. In the next layers approaching the center of gradient structure, the elastic modulus is increased gradually in order to increase the mechanical properties of the whole porous structure. It is noted that the difference in elastic modulus between two contact layers is approximately 15% to reduce stress shielding. The results showed that stress shielding could be reduced by using the gradient structure. In addition, using negative Poisson’s ratio unit cells can establish good surface contact between the bone and implant.

This study investigates the laser-assisted turning (LAT) of AISI 4340 hardened steel (∼52 HRC). Despite the various advantages of this process for machining hard materials, the issues related to the machined surface integrity remain the most important challenge. The laser heating used in this process substantially affects the surface integrity characteristics of the workpiece and its mechanical properties. Therefore, it is important to understand, predict, and optimize the workpiece's heat effects at various regions. Due to the complexity of the process, experimental investigations alone cannot reveal thorough information of various phenomena involved. Therefore, a reliable finite element model has been developed to predict the effect of various process input parameters on the metallurgical changes of the machined workpieces. Since general-purpose finite element codes cannot predict the phenomena of interest, three user-defined subroutines have been developed to capture surface integrity parameters such as heat-affected zone, hardness variations of the machined surface, and white layer formation. The developed FE model consists of three parts: mechanical model, thermal model, and coupled thermo-mechanical model. The results of the FE models are verified with experimental data, and a good agreement has been observed. The effect of various process parameters on the surface integrity characteristics of the workpiece has been studied in detail. It has been observed that the laser scanning speed, laser power, and undeformed chip thickness have the most significant influence on the metallurgical effects on the workpiece, respectively.

The present paper is conducted to develop a new structure of an electromagnetic pump capable of controlling the magnetic field in a rectangular channel. Common electromagnetic pumps do not create uniform velocity profiles in the cross-section of the channel. In these pumps, an M-shape profile is created since the fluid velocity in the vicinity of the walls is higher than that in its center. Herein, the arbitrary velocity profiles in the electromagnetic pump are generated by introducing an arrayed structure of the coils in the electromagnetic pump and implementing 3D numerical simulation in the finite element software COMSOL. The dimensions of the rectangular channel are 5.5 × 150 mm ² . Moreover, the magnetic field is provided using a core with an arrayed structure made of low-carbon iron, as well as five couples of coils. 20% NaoH solution is utilized as the fluid (conductivity: 40 S/m). The arrayed pump is fabricated and experimentally created an arbitrary velocity profile. The pressure of the pump in every single array is 12 Pa and the flow rate is equal to 3375 mm ³ /s. According to the results, there is a good agreement between the experimental test carried out herein and the simulated models. Article highlights This is the first time that the idea of arrayed electromagnetic pump is presented. This pump uses a special arrayed core with coils; by controlling the current of each coil and the direction of the currents, the magnetic field under the core could be adjusted. By changing the magnetic field at any position in the width of the channel, the Lorentz force alters, which leads to different velocity and pressure profiles. Using COMSOL multiphysics software, the electromagnetic pump was simulated in real size compared to the experimental model. Subsequently, the simulation model was verified and different velocity profiles were generated by activation and deactivation of different coils. The pressure and velocity curves and contours were extracted. The experimental setup was manufactured and assembled. NaOH solution was utilized as the fluid. Afterwards, different modes of coil activations were investigated and the pressure and velocity profiles of the pump were calculated.

A Correction to this paper has been published: https://doi.org/10.1007/s00170-021-07852-3

In recent years, new materials such as titanium, nickel alloys, and high-strength steels have been widely used in medical, nuclear, and other industries. Since the manufacturing of different components from these materials has always been associated with the machining process, the use of hard machining in their production is unavoidable. The short life of the cutting tool, the poor quality of the machined surfaces, and the long machining time are some of the challenging issues involved in the traditional machining of these materials. Therefore, researchers have investigated new machining techniques to increase the efficiency and quality of produced parts. Thermal-assisted machining, especially laser-assisted machining is one of the promising methods of machining difficult-to-machine materials. However, this process faces some challenges in terms of the achievable surface integrity of the machined surfaces. This research studies the effect of cutting and thermal parameters on the surface roughness in the laser-assisted turning (LAT) process of AISI 4340 hard steel with a hardness of 560 HV. The results illustrated that by selecting a proper combination of process parameters, the damage caused by the heat penetration into the workpiece can be minimized and the advantages of LAT can be benefited from.

Magnetic pumps received considerable attention because of their very low turbulence and their independence from moving components. Such pumps have a higher lifetime and lower maintenance costs compared to mechanical pumps. In the past centuries, it developed many types of fluid pumps for different fields of application. In the industry of magnesium melting, magnetic pumps have been considered. This pump, which follows the Lorentz law, leads to imposing the pressure in the melt following the right-hand rule by simultaneously applying the magnetic field and the orthogonal electric current on the electrically conductive fluid. The effective parameters in the design of the magnetic pump include the input dimensions of the channel (length and width), the size of the magnetic field, and the electrical current applied to the conductive fluid. The simultaneous presence of three physics in a magnetic pump has made it difficult for experimental and numerical investigations. In this study, the simulation of the magnetic pump was examined in a three-dimensional manner, and the simultaneous solving of three physics. Pumping and melt displacement were performed by applying a 0.26 T magnetic field in a channel with input dimensions of 100 mm × 10 mm and an electrical current of 200 A to the Salt water fluid. The speed of the fluid has been obtained through applying a Lorentz force of 0.25 m/s and a 60 Pa pump pressure.

Direct-drive friction welding of ASTM A106 and AISI 4140 steel tubes has been investigated both experimentally and numerically. A remeshing technique was implemented to accurately simulate highly distorted flashes during the FE simulation. The results revealed that the circumferential thermal expansion led to a higher contact pressure at the inner diameter of the interface and consequently, inner flashes were formed up to 18% larger than the outer ones. The maximum temperature was also located at the outer diameter of the interface in the first moments of the process, then it moved towards the center of the section where there was a balance between the higher slipping rate at the outer section and greater pressure at the inner section of the joint. Validation tests showed the capability of the FE model in terms of temperature, flash cross-section, and axial shortening with the maximum difference of 18.6%.

In this research, the effects of high speed milling on the main surface integrity characteristics, including surface roughness and topography, microhardness, white layer thickness, and surface chemical composition of Ti-6Al-4V were empirically studied. Totally, 18 experiments were carried out using a full factorial design of experiments method in the presence of minimum quantity lubricant. The results showed that by using high speed milling, it is possible to reach the surfaces with a higher quality and surface roughness of approximately 0.2 μm. Also, it was discovered that the microhardness variation with cutting speed has a dual nature. The maximum microhardness was obtained at the cutting speed of 375 m/min and the feed rate of 0.08 mm/tooth, which showed a 57% increase compared with the bulk material. In addition, by using the cutting speed of 450 m/min, the depth of heat-affected layer and work hardening effects declined up to 75% in comparison with the cutting speed of 300 m/min.