karen abrinia

Problem statement: 

One of the most critical issues in architectural design is form, which has become more complicated in computational design. To overcome such problems nowadays, digital manufacturing methods such as additive manufacturing could be used. For a long time, concrete has been considered one of the primary materials in architecture. In recent decades, concrete 3D printing has made significant progress and practical samples such as pedestrian bridges, residential units, and urban furniture have been made with this technology. One of the most important advantages of 3D printing is the creation of complex geometries including curved surfaces. In 3D concrete printing, due to its large scale, some defects of the printed surfaces, such as the staircase effect are more visible. One of the methods that could be used to make the final finish of the printed surface smoother and closer to the original digital design is the application of curved (non-flat) layering in the production process. This method could produce surfaces with a better finish only by intervening at the software level and using the existing hardware.

This paper seeks to investigate the methods presented in the additive manufacturing of cementitious materials and attempts to find their advantages and limitations in published articles.

In this review article, the documentary data collected from published scientific documents like articles, books, and theses, have been analyzed using a descriptive-analytical method.

Three main methods in additive manufacturing of concrete materials have been investigated, and the advantages and limitations of each have been listed. The main challenges for additive manufacturing of concrete in the three categories: properties of printable concrete, supporting structures for concrete printing, and the presence of cold joints were investigated, and finally, the methods presented for the construction of curved surfaces with 3D concrete printing technology were mentioned.

Dental implants are one of the restoration methods used to revitalize the function of a lost tooth. The natural tooth has a unique structure and composition that enable it to withstand mastication loads at different rates and angles of applying load in the wet and warm environment of the mouth. To simulate such behavior, the structure, material, and parameters of the design (implant diameter and length, abutment connection, etc.) in the dental implants are under unremitting study. A favorable dental implant should have sufficient strength and ultimate fatigue life on behalf of minimum displacement. It should be wear-resistant to keep the crown profile on the occlusal surface and remain in touch with other teeth. In the review, the effect of the usage of additive manufacturing on the quality of the 3D printed dental implant parts and important guidelines of design, have been studied and analyzed. Collected results are, based on finite element studies and experimental, empirical, and statistical investigations.

In recent decades, the use of metal matrix composites and functionally graded materials for achieving a combination of mechanical and physical properties has increased. In this research, an in-situ centrifugal casting method was used to make the samples. The primary composite used in this method was Al-15wt.% Mg2Si. In situ prepared functionally graded samples were successfully manufactured at 1000, 1300, and 1700 rpm rotational speeds. Optical microscopy was used to examine the microstructure of the samples, and a Vickers hardness tester was used to examine the mechanical properties. The cross-section of the fabricated samples was divided into two parts, the reinforced and the matrix parts. Porosity increased as a destructive parameter in the reinforced area. The hardness increased as the volume fraction of particles in the reinforced area was increased. Also, hardness increased in the chilled zone due to the fine-grains and trapped particles in that area. Solutionizing heat treatment was performed for the fabricated samples. By observing the microstructure, there was no change in the placement trend of the primary particles, but the morphology of the primary and eutectic Mg2Si particles were changed. Hardness increased after heat treatment while its gradient did not change.

Nowadays, with increasing environmental pollution and damages that threaten the health of the community, a lot of research is being conducted on reducing the emission from transportation sector as one of the main sources of total worldwide emissions. It is confirmed that one of the ways to reduce emission is to switch from fossil-based fuels to more environmentally benign fuels. Among the options, electric vehicles (EVs) have proven themselves as one of the best options. In this research study, a solar-based EV which is developed and built at University of Tehran is studied.  The environmental impacts assessment along with the energy consumption of this solar-electric vehicle is investigated

An efficient procedure is presented for the evaluation of solid oxide fuel cell (SOFC) anode microstructure triple phase boundary length (TPBL). Triple phase boundary- the one that is common between three phases of the microstructure- has a great influence on the overall efficiency of SOFC because all electrochemical reactions of anode take place in its vicinity. Therefore, evaluation of TPBL for virtual or experimental 3D microstructures is essential for comparison purposes and the optimization processes. In this study, first, an algorithm is proposed to distinguish between percolated and non-percolated clusters for each of the phases. Then, another algorithm is used to determine the value of TPBL for all percolated clusters of three phases. Also, a procedure based on thermal and diffusion analogy is presented to assess the tortuosity of porous and solid phases. Finally for a virtual microstructure, percolated clusters, active and total TPBL and tortuosity are calculated and discussed.

Ironing is a conventional metal forming process for producing thin walled cans with uniform thickness components manufactured from deep drawn cups. The most important drawback of the conventional ironing is the lower thickness reduction ratio (TRR) causes needing annealing process and multi stage ironing. Recently, a new ironing process named constrained ironing was presented by the current authors to achieve an extra TRR to solve the conventional ironing problems. This process that is based on the compressive stresses makes it possible achieving high TRR without interruption for additional processing such as multi-stage ironing and annealing. In this paper, FEM simulation was performed to investigate the effective parameters. The simulation results showed that process the process load increases with increasing the friction coefficient. Also, the state of the stresses is fully compressive in constrained ironing process while it is tensile in the conventional ironing method. Thus, compressive stress components minimize formability problems, and higher thickness reduction ratio is achievable in the new ironing method. Also, experimental results showed that the tensile strength and hardness increased after constrained ironed of the deep drawn cup.

In this paper, an upper bound analysis for novel backward extrusion has been presented. Initially deformation zone has been divided to four separated regions and an admissible velocity field for them has been suggested. Then total power in this process has been calculated for every region and extrusion force has been gained. Moreover investigation of relevance of extrusion force and process powers (friction, deformation, velocity discontinuity) with process parameters has been revealed better understanding in load estimation and process efficiency in this method. Finite element analysis by DEFORMTM3D has been done for validation of upper bound results. Upper bound analysis showed, increasing of initial billet diameter enhances extrusion force by nonlinear relation. In addition big billet size remodels novel backward extrusion to conventional backward extrusion and it proves lower requirement extrusion load in novel backward extrusion in comparison with conventional backward extrusion. Moreover Increasing of first region’s thickness in this process diminishes extrusion force by exponential relation and no considerable change in extrusion force can be seen in a particular thickness domain. Investigation of process parameters in power efficiency shows that bigger extruded part’s diameter creates critical condition in process efficiency because of high friction power. But increasing of thickness enhances power efficiency. Finally upper bound analysis results have a good agreement with FEM.

Spin-bonding is a method for fabrication of bilayer tubes based on flow-forming process. This new method is a process with high potential in production of seamless thin-walled tubes. Utilizing this process, aluminum tube (as the inner layer or clad layer) has been bonded into steel tube (as the outer layer) to fabricate tubular laminate composites. As important parameters for creating a suitable bond, effects of thickness reduction, initial aluminum thickness and strength on bonding strength were investigated. The bond strength was evaluated by peel test and the peeled surfaces were examined using scanning electron microscopy (SEM). The results indicated that thickness reduction has great influence on strength and quality of the bond. After a threshold reduction (about 35%) the bond strength increases rapidly with the amount of deformation, until it approaches the weaker metal strength, and samples fracture from the base metal in the peel test. Approaching the strength of the two metals and decreasing the initial thickness of the clad layer, with a high amount of deformation increased the bonding strength. Fracture surface images showed that the surface fraction of bonding area was increased when deformation increased. It was also increased with the reduction of the initial thickness of the clad layer and when the strength of the two layers approached each other. Additionally, distribution and shape of the fracture area changed from a disordered fibril structure to approximately straight area, with an increase in the deformation.

In this paper, a new forward extrusion process is proposed for producing large-diameter tubular components. At the beginning of the process, a round billet is located in the container and then extruded into a preliminary die with three bean-shaped holes forcing a hole in the original billet. The material is then entered into another die with a diverging and converging surfaces designed to weld the material and decrease the tube thickness. Material flow behavior, applied strain and the required process load were predicted using finite element (FE) simulations. The results showed that the new extrusion process had three important advantageous namely a lower process load and a container with a smaller diameter while applying much higher plastic strain compared to the conventional methods.

Incremental Sheet Metal Forming (ISMF) is based on localized plastic deformation. In this process, a hemispherical-head tool, controlled by a CNC milling machine, shapes a sheet metal according to a defined path. Study of the forming force is one of the most important topics in this process. Increasing of vertical step size, tool diameter, wall angle and sheet thickness together with using of high strength sheet metals and lightweight alloys, leads to an increase in the forming force. In this paper, the performance of a novel forming process, named Ultrasonic Vibration assisted Incremental Sheet Metal Forming (UVaISMF) has been investigated. The procedure of design, manufacture and test of vibratory forming tool, is presented. The occurrence of longitudinal mode and resonance phenomenon has been confirmed by the results of modal analysis and experimental test. Furthermore, the effect of ultrasonic vibration on the vertical component of forming force and spring-back has been studied. Aluminium sheet of grade Al 1050-O is used as a work material. Experimental results obtained from straight groove test, indicate that ultrasonic excitation of forming tool, will reduce the average of vertical component of forming force and spring-back in comparison to conventional process.

The current study conducted a finite element (FE) and experimental investigation on tubular channel angular pressing as a noble severe plastic deformation technique for producing ultrafine grained and nanostructure tubular components. To examine the effects of the TCAP process on the strain distribution and deformation behavior, FE simulations were employed. The FE results demonstrated that equivalent plastic strain of 2.1-2.9 was developed after applying one pass TCAP. Analytical investigations were carried out to calculate the accumulated strain during the process. Tube thinning in the early stages of the process was observed as a result of tensile circumferential strains but this could be compensated for by the back pressure effect resulting from the next shear zones and also compressive circumferential strain resulting from decreasing the tube diameter. Microstructural observations showed significant grain refinement after one pass TCAP on AZ91 magnesium alloy at 300 ºC. Microhardness measurements demonstrated increasing hardness to 78 HV from the initial value of 51 HV.

In the present paper, the deformation zone of the ECAE (Equal Channel Angular Extrusion) process was investigated using the upper bound theorem. For this purpose, the shape of the streamlines in the deformation zone was assumed to be cubic Bezier curves. Then, the force required for the ECAE process was optimized with regard to the parameters defining the shape of streamlines by the upper bound theorem. By using of these streamlines, equivalent stain induced through one pass of the ECAE was calculated and the shape of the dead metal zone was determined. The influence of different friction conditions on the deformation field was studied. The force applied through the process was determined by optimizing an upper bound solution and was compared with other works including experimental and theoretical data. Also using this comparison, it was seen that the difference between the theoretical and experimental value for the force was reduced in the present method.