A new multilayer slip‐flow model has been developed to simplify and to overcome current numerical difficulties of two‐dimensional model in predicting the internal air temperature inside a mold during a rotational molding process. The proposed methodology considers a macroscopic “layer‐by‐layer” deposition of a heating polymer bed onto the inner mold surface. A semi‐implicit approach is introduced and applied to compute the complex thermal interactions between the internal air and its surroundings. In the model, the lumped‐parameter system and the coincident node technique are incorporated with the Galerkin finite element model to address the internal air and the deposition of molten polymer beds, respectively. The simple phase‐change algorithm has been proposed to improve the computational cost, numerical nonlinearity, and predicted results. The thermal aspects of the inherent warpage are explored to study its correlation to the weak apparent crystallization‐induced plateau in the temperature profile of the internal air, as in practice. The overall predicted results are in favor with the available experimental data for rotomolded parts of cross‐sectional thicknesses up to 12 mm. POLYM. ENG. SCI. 46:960–969, 2006. © 2006 Society of Plastics Engineers

In the rotational moulding process, the internal air temperature has been widely recognised as a tool to predict an optimum cycle time. This paper presents a new numerical approach to predict the internal air temperature in a two-dimensional (2-D) static model without requiring the consideration of the tumbling motion of polymer powder. The initial non-isothermal heating of the static model is actually formed by two changeable plastic beds (stagnant and mixing beds), which represent the actual stagnant and mixing pools inside a rotating mould respectively. In the numerical approach, the lumped-parameter system and coincident node technique are proposed to incorporate with the Galerkin Finite Element Method in order to account for the complex thermal interaction of the internal air. It helps to overcome the difficulty of multidimensional static models in predicting an accurate internal air temperature during the heating stage of rotationally powdery plastic. Importantly, the predicted temperature profiles of the internal air, oven times for different part thicknesses and process conditions accord with the available experimental results.PRC/2029

The analysis of heat transfer in the rotational moulding process is a non-linear multi-dimensional matter, which involves a number of process conditions and thermal parameters. The present study mostly involves dimensional analysis, the changing effects of the process parameters and conditions on the process times for different processing circumstances. They have been explored and compared by using the two-dimensional slip flow model from Lim and Ianakiev.1 The modelling helps to further identify and understand the dependence of the key thermal parameters due to external heating, external cooling, external-internal cooling and warpage on cycle times of the rotational moulding. In addition, the detail of the coincident node technique is discussed to present the key components of the conductivity matrix for an element 'abutting' a coincident node interface.

Combination of different materials used both in the projectile and the sandwich panel is getting more important in designing for maximization of energy absorption during impact. In the present study, we have simulated the bulging process during projectile impact for axisymmetric impact problems. We have discussed the bulging velocity tendency depending on some important geometrical and material parameters such as the yield strength, and tensile limit of the core for several different core thickness and different elapsed time after impact by using the AUTODYN commercial software. From our simulation, we have found that material properties have more dominant effects than the geometric properties on the bulging velocity.