Damage models, particularly the Gurson-Tvergaard-Needleman (GTN) model, are widely used in numerical simulation of material deformations. Each damage model has some constants which must be identified for each material. The direct identification methods are costly and time consuming. In the current work, a combination of experimental, numerical simulation and optimization were used to determine the constants. Quasi-static and dynamic tests were carried out on notched specimens. The experimental profiles of the specimens were used to determine the constants. The constants of GTN damage model were identified through the proposed method and using the results of quasi-static tests. Numerical simulation of the dynamic test was performed utilizing the constants obtained from quasi-static experiments. The results showed a high precision in predicting the specimen's profile in the dynamic testing. The sensitivity analysis was performed on the constants of GTN model to validate the proposed method. Finally, the experiments were simulated using the Johnson-Cook (J-C) damage model and the results were compared to those obtained from GTN damage model.

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The present numerical research studies the effect of nano-materials in a lid-driven cylindrical cavity with rotation of circumferential top wall. The heat is transferred from two lateral walls to the domain by constant temperature conditions while other walls are kept isolated. The non-dimensional equations are solved by Finite Volume Method (FVM) and SIMPLEC method. The effect of Reynolds (Re = 100, 400, 1000), Ryleigh (Ra = 104, 105, 106) numbers are studied. In addition, the effect of concentration of nano materials (ϕ = 0%, 1%, 5%), the Height Ratio (HR = 1, 0.5, 2) on Nusselt number, isotherm lines and streamlines are studied. The results show that Reynolds number also can change the effect of nano particles on the heat transfer rate. It is observed that the height ratio increase can improve the Nusselt number since the number and the size of vortices inside the cavity changes. In addition, increase of Ra number can change the flow structure inside the cavity which can help in increasing of Nusselt number.

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A relatively complete procedure for high cycle fatigue life assessment of the engine components is outlined in the present paper. The piston is examined as a typical component of the engine. In this regard, combustion process and transient heat transfer simulations, determination of the instantaneous variations of the pressure and temperature in the combustion chamber, kinematic and dynamic analyses of the moving parts of the engine, thermoelastic stress analyses, and fatigue life analyses are accomplished. Results of the simulation are compared with the test data to verify the results. The heat transfer results are validated by the experimental results measured by the Templugs. The nonlinear multipoint contact constraints are modeled accurately. Results of the more accurate available fatigue criteria are compared with those of a fatigue criterion recently proposed by the first author. These results are also evaluated by comparing them with the experimental durability tests. The presented procedure may be used, e.g., to decide whether it is suitable to convert a gasoline-based engine to a bi-fuel one. Results of the various thermomechanical fatigue analyses performed reveal that the piston life decreases considerably when natural gas is used instead of gasoline.

This paper investigates the results of a frequency analysis performed on the blades of the last three compressor stages of two different gas turbines (Case A and B). The axial compressors in A and B have ten and eleven stages, respectively. The studied stages have identical number of blades in both compressors. However turbine B has higher number of upstream vanes before each rotating stage. Turbine B is actually a modified version of A with higher power output. The manufacturer provides acceptable ranges for several natural frequencies of blades of stage No.8 to 10 in case A. One of the purposes of this study is to figure out the logic behind the abovementioned ranges. FEM has been used in order to determine the natural frequencies of a single blade (for Campbell diagram) and bladed disk (for SAFE diagram). By surveying the results of the Campbell diagrams for blades of case A’s mentioned stages, it is concluded that the manufacturer has obtained the acceptable ranges by considering a 10% difference (at least) between single blade natural frequencies and excitation frequencies (upstream vane passage frequencies (VPF)). On the other hand, according to Campbell diagram, there is no resonance for these blades within the operational speed while SAFE diagrams show the existence of one resonance mode within the same range. The reason of this contradiction is found to be ignoring the disk stiffness effect on the blades frequencies. A same procedure was also followed to study the critical frequencies of the blades of the last three stages of turbine B’s compressor by SAFE diagrams. By checking the critical modes, it is concluded that these modes in case B are transferred to one or two modes higher in comparison to A which results in a much better vibrational behavior. This has been acquired by increasing the number of the upstream vanes. In addition, in case A’s compressor, the blades of the stage No.10 have been designed with far thicker airfoils (approximately 50%) when compared to stage No.8 and 9, even though their other dimensions are almost identical. But, this fault has been corrected in turbine B and the airfoils of all three stages almost have the same thickness. To sum up, although the design of mentioned blades in turbine B looks better and more logical than A, still a more precise look at its stages bladed disk SAFE diagrams reveals another issue. In some references there are some hints that low number of critical nodal diameter (veering region) might cause high level of blade vibration due to mistuning and this means that even in turbine B the design might not be optimal. A cure could be an increase or decrease in the number of upstream vanes in order to have a higher critical nodal diameter.

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