After a fire, the assessment of concrete residual strength can be a challenge. Since the strength reduction depends on the distance from the heated surface examination based on destructive test, i.e., core samples, is not precise enough. Therefore, more detailed methods can establish the influence of the high temperature in the zone, which no longer has visible cracks. That method can be used to assess layer thickness to remove due to the fire damage. The Ultrasound Pulse Velocity (UPV) method with point heads was used in the paper to examine samples taken from a structure after the real fire. Moreover, to make the analysis more precise, an effect associated with the porosity in concrete was also considered to separate pure fire effect.
The mathematical model of the polymer plasticization in the reciprocating screw injection moulding machine is presented in this paper. Methods of calculation of the most important flow characteristics, such as the solid bed profile, the pressure and temperature profiles, the mass flow rate, the power demand, the screw torque and the energy consumption were analysed. According to the mathematical model, a computer program was developed. Based on the computer program, simulation studies of the injection moulding process were conducted. Thereafter, the experimental studies, evaluating the theoretical model from the accuracy and usefulness point of view, were carried out. Important output quantities, such as the temperature and pressure profiles, the power demand by the screw, the torque on the screw and the screw rotation time were measured. The studies were performed on a specially made research office. The simulation results were compared with the experimental data measured for the most popular polymers and different operating parameters of the injection machine. The experimental studies have indicated the need to introduce some corrections to the mathematical model. Several modifications have been made to the model, mainly related to the methods of stress determining in the polymer layer. Finally, the output characteristics of the plasticization process in the injection moulding are now correctly determined by the model with an average error less than 10%.
This paper is a continuation of the work on a comprehensive model of the plastication process in injection molding. The aim of this research is the analysis of the results generated by the proposed model by comparing these results with the wide experimental characteristics of real plasticating system of injection molding machine for two polymers-PE-LD and PE-HD, differing in rheological and thermal properties due to the different physical structure of both polymers. It was found that the model correctly determines the dynamics of changes of characteristics of the plastication process by changing the input parameters of the process. The average quantitative differences between the experimental and theoretical characteristics do not exceed 20 %. Computer model still requires minor changes to improve compliance of model results with characteristics of real unit of injection molding machine, primarily for determining more accurate values of melt pressure and torque.
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