Thermal analysis of friction stir welding process and investigation into affective parameters using simulation

Mahmoud Abbasi,Behrouz Bagheri,Rasoul Keivani 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.2

Friction stir welding (FSW) as an efficient solid state joining process has numerous applications in industries. Temperature distributionanalysis through simulation not only brings the possibility to characterize the microstructure of different zones, but also enables one tosave cost and energy as optimum welding variables are obtained with less concern. In the present study, the temperature distributionduring the friction stir welding (FSW) process of AA6061-T6 was evaluated using finite element method (FEM). Since experimentalmeasurements cannot be readily made in the weld region, it is difcult to understand physics in the stir zone of the welds without simulation. Abaqus software was applied to model the parts and simulate the process of welding, while Johnson-Cook law utilized to evaluatethe effect of strain rate and generated heat. FE-results were verified by experimental results. The comparisons revealed a good compatibilitybetween the results. The effect of probe shape on temperature distribution was also studied. It was found that spherical pins result inthe highest temperatures at workpieces with respect to cylindrical and tapered pins. Additionally, it was concluded that more heat is generatedin workpieces as pin angle increases.

Application of the GTN model to predict the forming limit diagram of IF-Steel

Mahmoud Abbasi,Mohammad A. Shafaat,Mostafa Ketabch,Davoud F. Haghshenas,Mohammad Abbasi 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.2

Forming limit diagrams (FLDs) are extensively used in industries, particularly the auto industry. The establishment of these diagrams using a predictive approach can lead to reduction in both cost and time. In the present work, Gurson-Tvergaard-Needleman (GTN), a porosity-based model, was used to predict the FLD of an interstitial-free steel via finite element simulation. Optimum values of the GTN model were obtained by applying a response surface methodology (RSM) based on central composite design. Results show that RSM is a good method for an appropriate determination of the GTN model parameters, such as initial void volume fraction, effective void volume fraction, critical void volume fraction, and final void volume fraction. Furthermore, the experimental FLD of the specimen steel was considerably predicted using the obtained GTN model parameters.

Production of Ultrafine-Grained Titanium with Suitable Properties for Dental Implant Applications by RS-ECAP Process

Mehdi Abbasi,Farshid Ahmadi,Mahmoud Farzin 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.4

The only problem of pure titanium for dental implant applications is its low strength and failure under different loadings. Various studies have shown that the utilization of severe plastic deformation processes such as Equal Channel AngularPressing (ECAP), through reducing the grain size of titanium, can improve not only its mechanical properties but also itscorrosion resistance and biocompatibility. In this study, a reduced-scale ECAP process on pure titanium was performed toinvestigate the effects of scale reduction. An ECAP die was made with an internal diameter of d = 3 mm, and the tests wereperformed at 250 °C for several number of passes. It was found out that after 10 passes of reduced-scale ECAP, the grainsize of CP Ti had strongly been reduced from 25 to 122 nm. This sharp reduction in grain size resulted in an increase inmicro-hardness from 205.5 to 321.3 Hv. Moreover, Nano-hardness test results showed that after 10 passes, the hardness oftitanium increased from 2461 to 3812 MPa, and simultaneously elastic modulus decreased from 108.1 to 94.8 GPa. Suchreduction of elastic modulus of titanium for dental implant applications decreased stress-shielding and jaw bone damages. According to the results of this research, after RS-ECAP process the strength of titanium is greatly increased and its elasticmodulus is reduced, which are desirable features for dental implant applications. Since dental implants are small in size, thereduced ECAP process (d = 3–5 mm) can produce titanium implants with improved properties.

Different Attempt to Improve Friction Stir Brazing: Effect of Mechanical Vibration and Rotational Speed

Behrouz Bagheri,Mahmoud Abbasi,Farzaneh Sharif,Amin Abdollahzadeh 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.9

A developed version of friction stir brazing (FSB) entitled friction stir vibration brazing (FSVB) was presented to fabricatelow carbon steel joint using %67wt Sn-%33wt Pb alloy as a braze metal. This attempt aims to analyze the role of mechanicalvibration and rotational speed on microstructure and mechanical behaviors of the brazed samples. Furthermore, the thermalanalysis, the thickness of intermetallic compounds (IMCs) layers, and void volume percentage at the joint interface werestudied. It was concluded that the temperature during the joining process increased and the coherency of the joint interfaceenhanced while FSVB was applied instead of FSB. In addition, the grains in the joint zone under the FSVB process weresmaller than those produced under the conventional FSB process. The results also showed that the mechanical performance,namely hardness, and shear strength increased and the thickness of the IMCs layer along with the void volume percentagein the brazed sample decreased as rotational speed increased from 850 to 1150 rpm. The results indicated that rotationalspeeds over 1150 rpm had detrimental effects on mechanical properties. This is related to the effect of high heat input andinduced temperature on brazing flow and filler-base metal interaction.

Advanced Approach to Modify Friction Stir Spot Welding Process

Behrouz Bagheri,Mahmoud Abbasi,Amin Abdollahzadeh,Hamid Omidvar 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.10

Nowadays, friction stir spot welding (FSSW) is used in automotive, rail vehicle construction, the aerospace industry, andelectrical industry. In the current research, a modified version of the FSSW process entitled friction stir spot vibration weldingwas introduced to join Al5083 specimens. The joining specimens were vibrated normal to the tool movement direction,while the joint position cooled by passing coolant through the fixture. Different characteristics of developed joint namelymicrostructure, mechanical properties, corrosion behavior were studied. The results showed that stir zone grain size decreasedsignificantly as the vibration was employed and the joint position was cooled. It was found that vibration enhanced thedynamic recrystallization and coolant decreased the grain growth. Both led to enhanced grain refinement in the stir zone. The results also indicated that shear strength and hardness of the weld region increased as the modified version of FSSWwas applied. Corrosion tests revealed that corrosion resistance increased as the modified method was applied.

Effects of Vibration on Microstructure and Thermal Properties of Friction Stir Spot Welded (FSSW) Aluminum Alloy (Al5083)

Behrouz Bagheri,Mahmoud Abbasi,Mohammad Givi 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.7

Friction stir spot welding (FSSW) is a solid state joining technique with a simple concept. A non-consumable rotating tool with a specially designed pin and shoulder are inserted into the sheets or plates to be joined. In this study, the effect of vibration on microstructure and thermal properties of Al5083 weldment made by FSSW using rotation speed of 1500 rpm and different dwelling times, namely 5 and 10 s, was investigated. This new method was entitled FSSVW (friction-stir-spot-vibration welding). The experimental and numerical results, obtained using Abaqus software, were compared. In this work, the Johnson–Cook hardening condition was used for modeling of deformable metals. The results showed good comparability between experimental and FEM data. Also, metallography analyses indicated that the grain size decreased and the temperature increased as FSSVW method was applied. The results showed that vibration during FSSW leads to grain size decrease of about 30–50% in the weld region.

The Effects of Coenzyme Q10 on Contrast-Induced Acute Kidney Injury in Type 2 Diabetes: A Randomized Clinical Trial

Ashkan Karbasi,Ali Abbasi,Abbas Mohagheghi,Jalal Poorolajal,Farzad Emami,Shirin Moradkhani,Iraj Khodadadi,Mahmoud Gholyaf,Heidar Tavilani 전남대학교 의과학연구소 2024 전남의대학술지 Vol.60 No.1

Contrast-induced acute kidney injury (CI-AKI) is a frequent challenge following the injection of contrast media and its subsequent oxidative stress. The aim of the present study was to evaluate the preventive effects of coenzyme Q10 (Q10), as a mitochondrial-targeted antioxidant in CI-AKI in diabetic patients, who account for a large proportion of angiographic cases. A total of 118 diabetic patients were randomly assigned to receive 120 mg of oral coenzyme Q10 (Q10 group) or placebo (Placebo group) for four days, starting 24 hours before contrast media injection. Blood urea nitrogen (BUN), serum and urinary creatinine, estimated glomerular filtration rate (eGFR), urinary malondialdehyde (UMDA), urinary total antioxidant capacity (UTAC), and urinary mitochondrial to nuclearDNA ratios (mtDNA/nDNA ratio) were evaluated before and after the treatment period. Urine sediments were also evaluated to report the urine microscopy score (UMS).The levels of BUN, serum and urine creatinine, and UMS were similar in the Q10 and placebo groups. EGFR was lower in the Q10 group before the treatment (p=0.013) but not after. The urinary mtDNA/nDNA ratio was 3.05±1.68 and 3.69±2.58 in placebo and Q10 groups, but UTAC was found to be lower in Q10 both before (p=0.006) and after the treatment (p<0.001). The incidence of CI-AKI was 14.40% and the mtDNA/nNDA ratio was similar between CI-AKI and non-CI-AKI patients. In conclusion, Q10 treatment shows no favorable effect on prevention of CI-AKI or a urinary mtDNA/nDNA ratio among diabetic patients.

Chitosan Scaffold Containing Periostin Enhances Sternum Bone Healing and Decreases Serum Level of TNF-α and IL-6 after Sternotomy in Rat

Salehiamin Mehdi,Toolee Heidar,Azami Mahmoud,Tafti Seyed Hossein Ahmadi,Mojaverrostami Sina,Halimi Shahnaz,Barakzai Shogoofa,Sobhani Aligholi,Abbasi Yasaman 한국조직공학과 재생의학회 2022 조직공학과 재생의학 Vol.19 No.4

BACKGROUND: In the aftermath of bone injuries, such as cranium and sternum, bone wax (BW) is used to control bleeding from the bone surfaces during surgery. Made up of artificial substances, however, it is associated with many complications such as inflammation, increased risk for infection, and bone repair delay. We, therefore, in this study set out to design and evaluate a novel BW without the above-mentioned side-effects reported for other therapies. METHODS: The pastes (new BW(s)) were prepared in the laboratory and examined by MTT, MIC, MBC, and degradability tests. Then, 60 adult male Wistar rats, divided into six equal groups including chitosan (CT), CT-octacalcium phosphate (OCP), CT-periostin (Post), CT-OCP-Post, Control (Ctrl), and BW, underwent sternotomy surgery. Once the surgeries were completed, the bone repair was assessed radiologically and thereafter clinically in vivo and in vitro using CT-scan, H&E, ELISA, and qRT-PCR. RESULTS: All pastes displayed antibacterial properties and the CT-Post group had the highest cell viability compared to the control group. In contrast to the BW, CT-Post group demonstrated weight changes in the degradability test. In the CT-Post group, more number of osteocyte cells, high trabeculae percentage, and the least fibrous connective tissue were observed compared to other groups. Additionally, in comparison to the CT and Ctrl groups, higher alkaline phosphatase activity, as well as decreased level of serumtumor necrosis factor-a, interleukin-6, andOCNin the CT-Post group was evident. Finally, Runx2, OPG, and RANKL genes’ expression was significantly higher in the CT-Post group than in other groups. CONCLUSION: Our results provide insights into the desirability of pastes in terms of cellular viability, degradability, antibacterial properties, and surgical site restoration compared to the BW group. Besides, Periostin could enhance the osteogenic properties of bone tissue defect site.