Polyurethane foams are one of the most common auxetic structures regarding energy absorption enhancement. This present study evaluates the result reliability of two different numerical approaches, the H-method and the P-method, to obtain the best convergence solution. A polymeric re-entrant cell is created with a beam element and the results of the two different methods are compared. Additionally, the numerical results compare well with the analytical solution. The results show that there is a good agreement between converged FE models and the analytical solution. Regarding the computational cost, the P-method is more efficient for simulating the re-entrant structure subjected to axial loading. During the second part of this study, the re-entrant cell is used for generating a polymeric auxetic cellular tube. The mesh convergence study is performed on the cellular structures using the H- and P- methods. The cellular tube is subjected to tensional and compressive loading, the module of elasticity and Poisson’s ration to calculate different aspect ratios. A nonlinear analysis is performed to compare the dynamic response of a cellular tube versus a solid tube. The crashworthiness indicators are addressed and the results are compared with equivalent solid tubes. The results show that the auxetic cellular tubes have better responses against compressive loading. The primary outcome of this research is to assess a reliable FE approach for re-entrant structures under axial loading.

This paper treats the influence of auxetic foam on the crush response and energy absorption response of square-section tubes when subjected to uniaxial quasi-static loading. The study aims at quantifying the energy absorption capability of auxetic foam-filled square tubes for variations in wall thickness, initial height, aspect ratio and slenderness ratio of the tube. The capability of simulating the crush response of auxetic foam-filled tubes using the validated numerical models is also presented. Based on the experimental results, the influence of the auxetic foam in the thin-walled square tubes was quantified in terms of energy absorption capacity, specific energy absorption and crush force efficiency. It is evident that a thicker tube filled with auxetic foam is preferable if the energy absorption level is the primary goal, yet this compromises the crush force efficiency. The outcome of this present study is the establishment of empirical models for estimating the quasi-static crushing response of auxetic foam-filled tubes with varying slenderness ratio and aspect ratio.

The blade number of a current tidal turbine is one of the essential parameters to increase the stability, performance and efficiency for converting tidal current energy into rotational energy to generate electricity. This research attempts to investigate the effect of blade number on the performance of a small-scale horizontal tidal current turbine in the case of torque, thrust coefficient and power coefficient. Towards this end and according to the blade element momentum theory, three different turbines, i.e., two, three and four-bladed, were modeled using Solidworks software based on S-814 airfoil and then exported to the ANSYS-FLUENT for computational flow dynamics (CFD) analysis. SST-K-ω turbulence model was used to predict the turbulence behavior and several simulations were conducted at 2 ≤ tip speed ratio ≤ 7. Pressure contours, turbulence kinetic energy contours, cut-in-speed-curves, and streamlines around the blades and rotors were extracted and compared to provide an ability for a deep discussion on the turbine performance. The results show that in the case of obtainable power, the optimal value of tip speed ratio is around 5, so that the maximum power was achieved for the four-bladed turbine. Out of optimal condition, higher blade number and lower blade number turbines should be used at less than and greater than the optimal values of tip speed ratio, respectively. The results of simulations for the three-bladed turbine were validated against the experimental data with good agreement.

This paper establishes and examines the constitutive model of the modified theta-projection concept for predicting the creep-rupture behaviour of a 2.25Cr-1Mo ferritic steel alloy foil at the loading conditions of practical interest. For this purpose, a series of creep-rupture tests are conducted on 0.15 mm thick foil specimens at an elevated temperature of 1 027 K and applied stresses in the range of 90 – 210 MPa. The creep-rupture behaviour of the foil is well represented using the model of the modified three-parameter theta-projection concept. Each model parameter is well represented as a function of the applied stress. Moreover, the creep failure mechanism was analysed by means of field emission scanning electron microscopy. The results showed that chromium atoms diffuse to the grain boundary and form carbide precipitates at the elevated temperature, leading to inter-granular fracture in the material.

Forming sheet metals under blast loading or the explosive forming technique has many advantages for productions, but it is restricted due to its accuracy. This paper introduces a novel theoretical-empirical study for explosive sheet metal forming based on the simple plasticity principles. It provides a method of producing the sheet metal cone parts forming under blast loading, including an analytical model and experimental validation. Firstly, a theoretical-empirical model for cone forming based on underwater explosion employing the impulse method is developed. The model on the whole revealed the relationships among the geometrical parameters of forming a process that is very useful to predict the certain explosive mass for complete forming a cone part. Afterward, a series of experiments are conducted to validate the developed model and also for the required modification in the solution. Comparing the theoretical-empirical solution and experimental results, the ability of the presented model for estimation of the explosive mass is demonstrated. Experimental results show that the theoretical model matched the experiments well.