Impulsive sheet metal forming based on standoff charge for conical geometry

Recently, explosive forming has gained much attention from researchers to overcome problems of conventional methods in manufacturing complex geometries such as cone. Despite these developments, analytical studies especially on cone with sharp apex angle are rarely reported. Past analytical studies in explosive forming on cone ignored the effects of friction between the blank and the die, redundant work in the work sheet blank and strain rate on blank material behaviour. Likewise, in finite element (FE) method, Arbitrary Lagrangian Eulerian (ALE) approach, most frequently method in the past is very time consuming and costly especially for large number of simulation tests. An alternative to ALE, Coupled Acoustic-Structural Analysis (CASA) approach has been seen gradually applied to model damage on the marine structure subjected to under water explosion but reports on its applications in modelling of explosive forming is somehow very limited. Moreover, in the past reported works, estimation of explosive mass, deformation history and damage accumulation models were analysed independently which creates difficulties to predict all aspects of the blank behaviour simultaneously. An integrated model that addresses these three issues concurrently is however, not available. The main aim of this research is to establish a satisfactory explosive mass estimation equation for modelling cone forming behaviours under integrated conditions with reasonable number of trials, i.e. simulation and experimental. Analytical model based on the impulse method was adopted to estimate the explosive mass by considering the effects of deformation efficiency and strain rate during cone forming process. This was done prior to establishment of FE model. ABAQUS software was used to develop a FE model based on CASA approach. Both models were validated via a series of experimental tests. Three different circular blank materials were tested, i.e. AISI 1006, Cu-ETP and Al 6061-O subjected to C-4 explosive forming under water. Four geometrical parameters were varied in the experiments. They were blank diameter (100 and 110mm), blank thickness (0.8, 1 and 1.2 mm), standoff distance (130, 150 and 170 mm) and half apex angle of cone (45 and 60 degree). Height of deformed cone was measured after each test and these results was used an indicator for the right explosive mass determination. An analytical equation was established by taking into consideration the effects of strain rate, friction and redundant work during forming process. Verification via experimental tests showed that the error of explosive mass required for forming all blank materials into a complete cone is about 20% ± 2.91. The developed FE model was also able to predict concurrently the deformation history, thickness distribution and damage accumulation in a good agreement with experiments. In conclusion, this study provides very encouraging evidences that both impulse method and CASA approach can be used together for predicting material behaviours during explosive forming process

On the Performance of Small-Scale Horizontal Axis Tidal Current Turbines. Part 1: One Single Turbine

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

Using Finite Element Approach for Crashworthiness Assessment of a Polymeric Auxetic Structure Subjected to the Axial Loading

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

Physically-based modelling for sheet metal cone parts forming under blast loading

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

Creep behaviour characterisation of a ferritic steel alloy based on the modified theta-projection data at an elevated temperature

This paper establishes and examines the constitutive model of the modified theta-projection concept for predicting the creep-rupture behaviour of a 2.25 Cr-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

Hole quality assessment in drilling process of basalt/epoxy composite laminate subjected to the magnetic field

Drilling is one of the most important machining processes which are currently carried out on fiber-reinforced composites. These composites possess a layered structure and different properties through their thickness. When drilling such structures, internal defects like delamination occur, caused by the drilling forces and their uneven distribution among the plies. The current study investigates the effect of magnetic field on drilling process of basalt/epoxy composite laminate in order to reduce delamination and the thrust force and improve some hole quality parameters i.e. roughness and cylindricity. A comparison is made between the responses for both normal drilling and drilling with applying a magnetic field. For this purpose, after finding the best combinations of normal drilling parameters, magnetic field is applied to the different configurations of solenoids on the setup of the drilling process. The results highlighted that using different magnet solenoids on the top and the bottom of drilling zone reduces the delamination and can obtain better roughness and cylindricity with lower damage

Comparative Modelling and Artificial Neural Network Inspired Prediction of Waste Generation Rates of Hospitality Industry: The Case of North Cyprus

This study was undertaken to forecast the waste generation rates of the accommodation sector in North Cyprus. Three predictor models, multiple linear regression (MLR), artificial neural networks (ANNs) and central composite design (CCD), were applied to predict the waste generation rate during the lean and peak seasons. ANN showed highest prediction performance, specifically, lowest values of the standard error of prediction (SEP = 2.153), mean absolute error (MAE = 1.378) and highest R2 value (0.998) confirmed the accuracy of the model. The analysed waste was categorised into recyclable, general waste and food residue. The authors estimated the total waste generated during the lean season at 2010.5 kg/day, in which large hotels accounted for the largest fraction (66.7%), followed by medium-sized hotels (19.4%) and guesthouses (2.6%). During the peak season, about 49.6% increases in waste generation rates were obtained. Interestingly, 45% of the waste was generated by British tourists, while the least waste was generated by African tourists (7.5%). The ANN predicted that small and large hotels would produce 5.45 and 22.24 tons of waste by the year 2020, respectively. The findings herein are promising and useful in establishing a sustainable waste management system

Experimental investigation on energy absorption of auxetic foamfilled thin-walled square tubes under quasi-static loading

Auxetic materials are modern class of materials that have recently been gaining popularity within the research community due to their enhanced mechanical properties. Unlike conventional materials, they exhibit a negative Poisson's ratio when subjected to a uniaxial loading. This present research experimentally investigates the crush response and energy absorption performances of auxetic foam-filled square tubes under axial loading. For comparison, the crush response and energy absorption of empty and conventional foam-filled squares tubes have also been examined with respect to deformation modes and force displacement curve. Standard compression tests were conducted on a series number of thin-walled tube samples. An additional compression test on conventional and auxetic foam has also been conducted to observe the behavior of foam itself. It is evident that the auxetic foam-filled square tubes are superior to empty and conventional foam-filled square tubes in terms of energy absorption capacity. It shows that such tube is preferable as an impact energy absorber due to their ability to withstand axial loads effectively. Furthermore, it is found that the load capacity increases as the crush length increases. The primary outcome of this study is design information for the use of auxetic foam-filled square tubes as energy absorbers where impact loading is expected particularly in crashworthiness applications