Experimental and numerical investigations on the ratcheting characteristics of cylindrical shell under cyclic axial loading

M. Shariati,H. Hatami,H. Torabi,H.R. Epakchi 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.44 No.6

The ratcheting characteristics of cylindrical shell under cyclic axial loading are investigated. The specimens are subjected to stress-controlled cycling with non-zero mean stress, which causes the accumulation of plastic strain or ratcheting behavior in continuous cycles. Also, cylindrical shell shows softening behavior under symmetric axial strain-controlled loading and due to the localized buckling, which occurs in the compressive stress-strain curve of the shell; it has more residual plastic strain in comparison to the tensile stress-strain hysteresis curve. The numerical analysis was carried out by ABAQUS software using hardening models. The nonlinear isotropic/kinematic hardening model accurately simulates the ratcheting behavior of shell. Although hardening models are incapable of simulating the softening behavior of the shell, this model analyzes the softening behavior well. Moreover, the model calculates the residual plastic strain close to the experimental data. Experimental tests were performed using an INSTRON 8802 servo-hydraulic machine. Simulations show good agreement between numerical and experimental results. The results reveal that the rate of plastic strain accumulation increases for the first few cycles and then reduces in the subsequent cycles. This reduction is more rapid for numerical results in comparison to experiments.

Experimental and numerical investigation of expanded metal tube absorber under axial impact loading

M. Damghani Nouri,H. Hatami,A. Ghodsbin Jahromi 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.6

In this research, the cylindrical absorber made of expanded metal sheets under impact loading has been examined. Expanded metal sheets due to their low weight, effective collapse mechanism has a high energy absorption capacity. Two types of absorbers with different cells angle were examined. First, the absorber with cell angle α=0 and then the absorber with angle cell α=90. Experimental Study is done by drop Hammer device and numerical investigation is done by finite element of ABAQUS software. The output of device is acceleration- time Diagram which is shown by Accelerometer that is located on the picky mass. Also the output of ABAQUS software is shown by force-displacement diagram. In this research, the numerical and experimental study of the collapse type, force-displacement diagrams and effective parameters has been investigated. Similarly, the comparison between numerical and experimental results has been observed that these results are matched well with each other. From the obtained results it was observed that the absorber with cell angle α=0, have symmetric collapse and had high energy absorption capacity but the absorber with cell angle α=90, had global buckling and the energy absorption value was not suitable.

Experimental and numerical investigations on the ratcheting characteristics of cylindrical shell under cyclic axial loading

Shariati, M.,Hatami, H.,Torabi, H.,Epakchi, H.R. Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.44 No.6

The ratcheting characteristics of cylindrical shell under cyclic axial loading are investigated. The specimens are subjected to stress-controlled cycling with non-zero mean stress, which causes the accumulation of plastic strain or ratcheting behavior in continuous cycles. Also, cylindrical shell shows softening behavior under symmetric axial strain-controlled loading and due to the localized buckling, which occurs in the compressive stress-strain curve of the shell; it has more residual plastic strain in comparison to the tensile stress-strain hysteresis curve. The numerical analysis was carried out by ABAQUS software using hardening models. The nonlinear isotropic/kinematic hardening model accurately simulates the ratcheting behavior of shell. Although hardening models are incapable of simulating the softening behavior of the shell, this model analyzes the softening behavior well. Moreover, the model calculates the residual plastic strain close to the experimental data. Experimental tests were performed using an INSTRON 8802 servo-hydraulic machine. Simulations show good agreement between numerical and experimental results. The results reveal that the rate of plastic strain accumulation increases for the first few cycles and then reduces in the subsequent cycles. This reduction is more rapid for numerical results in comparison to experiments.

Performance-based evaluation of strap-braced cold-formed steel frames using incremental dynamic analysis

S. Hatami,M.R. Davani,A. Zare 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.21 No.6

This study is an effort to clearly recognize the seismic damages occurred in strap-braced cold formed steel frames. In order to serve this purpose, a detailed investigation was conducted on 9 full scale strap-braced CFS walls and the required data were derived from the results of the experiments. As a consequence, quantitative and qualitative damage indices have been proposed in three seismic performance levels. Moreover, in order to assess seismic performance of the strap- braced CFS frames, a total of 8 models categorized into three types are utilized. Based on the experimental results, structural characteristics are calculated and all frames have been modeled as single degree of freedom systems. Incremental dynamic analysis using OPENSEES software is utilized to calculate seismic demand of the strap-braced CFS walls. Finally, fragility curves are calculated based on three damage limit states proposed by this paper. The results showed that the use of cladding and other elements, which contribute positively to the lateral stiffness and strength, increase the efficiency of strap-braced CFS walls in seismic events.

Experimental study on the water inlet and outlet position of a solar collector reservoir for maximum efficiency

S. Khodadadi,A. Ghanavati,M. R. Assari,M. Hatami,D. D. Ganji 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.5

An experimental study is conducted on the heat transfer in the reservoir of a solar water-heater flat-plate solar collector to obtain itstemperature distribution. A total of 29 temperature sensors are placed inside the reservoir, and 2 sensors in the water inlet and outlet passages. The effect of the inlet and outlet positions on the temperature distribution inside the reservoir is studied to obtain the best locationfor the maximum temperature range. When the inlet position is II and the outlet position is B (Fig. 3(c)), the reservoir exhibits the bestperformance because of the high temperature range and areas inside it.

Analytical thermal analysis of air-heating solar collectors

S. E. Ghasemi,M. Hatami,D. D. Ganji 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.11

In this paper, Optimal Homotopy Asymptotic Method (OHAM) and Homotopy perturbation method (HPM) are applied to investigate heat transfer in the air-heating flat-plate solar collectors. Results for different values of active parameters are compared with numerical method (fourth order Runge-Kutta method). The results confirm the notion that the HPM method is more accurate than OHAM and efficient technique for finding exact solutions for differential equations which have great significance in different fields of science and engineering. Effects of air flow rate, width and length of the collector on thermal efficiency are examined. As an important outcome, increasing in the collector’s dimensions (width and length) make a decreasing in thermal efficiency, but increasing in air mass flow rates improve it.

Slope variation effect on large deflection of compliant beam using analytical approach

Khavaji, A.,Ganji, D.D.,Roshan, N.,Moheimani, R.,Hatami, M.,Hasanpour, A. Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.44 No.3

In this study the investigation of large deflections subject in compliant mechanisms is presented using homotopy perturbation method (HPM). The main purpose is to propose a convenient method of solution for the large deflection problem in compliant mechanisms in order to overcome the difficulty and complexity of conventional methods, as well as for the purpose of mathematical modeling and optimization. For simplicity, a cantilever beam of linear elastic material under horizontal, vertical and bending moment end point load is considered. The results show that the applied method is very accurate and capable for cantilever beams and can be used for a large category of practical problems for the aim of optimization. Also the consequence of effective parameters on the large deflection is analyzed and presented.

Slope variation effect on large deflection of compliant beam using analytical approach

A. Khavaji,D.D. Ganji,N. Roshan,R. Moheimani,M. Hatami,A. Hasanpour 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.44 No.3

In this study the investigation of large deflections subject in compliant mechanisms is presented using homotopy perturbation method (HPM). The main purpose is to propose a convenient method of solution for the large deflection problem in compliant mechanisms in order to overcome the difficulty and complexity of conventional methods, as well as for the purpose of mathematical modeling and optimization. For simplicity, a cantilever beam of linear elastic material under horizontal, vertical and bending moment end point load is considered. The results show that the applied method is very accurate and capable for cantilever beams and can be used for a large category of practical problems for the aim of optimization. Also the consequence of effective parameters on the large deflection is analyzed and presented.

Accuracy of Endoscopic Ultrasonography for Determination of Tumor Invasion Depth in Gastric Cancer

Razavi, Seyed Mohsen,Khodadost, Mahmoud,Sohrabi, Masoudreza,Keshavarzi, Azam,Zamani, Farhad,Rakhshani, Naser,Ameli, Mitra,Sadeghi, Reza,Hatami, Khadijeh,Ajdarkosh, Hossein,Golmahi, Zeynab,Ranjbaran, M Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.8

Background: Gastric cancer (GC) is one the common lethal cancers in Iran. Detection of GC in the early stages would assesses to improve the survival of patients. In this study, we attempt to evaluate the accuracy of EUS in detection depth of invasion of GC among Iranian Patients. Materials and Methods: This study is a retrospective study of patients with pathologically confirmed GC. They underwent EUS before initiating the treatment. The accuracy of EUS and agreement between the two methods was evaluated by comparing pre treatment EUS finding with post operative histopathological results. Results: The overall accuracy of EUS for T and N staging was 67.9% and 75.47, respectively. Underestimation and overestimation was seen in 22 (14.2%) and 40 (25.6%) respectively. The EUS was more accurate in large tumors and the tumors located in the middle and lower parts of the stomach. The EUS was more sensitive in T3 staging. The values of weighted Kappa from the T and N staging were 0.53 and 0.66, respectively. Conclusions: EUS is a useful modality for evaluating the depth of invasion of GC. The accuracy of EUS was higher if the tumor was located in the lower parts of the stomach and the size of the tumor was more than 3 cm. Therefore, judgments made upon other criteria evaluated in this study need to be reconsidered.