The effect of materials' rheology on process energy consumption and melt thermal quality in polymer extrusion

YesPolymer extrusion is an important but an energy intensive method of processing polymeric materials. The rapid increase in demand of polymeric products has forced manufactures to rethink their processing efficiencies to manufacture good quality products with low-unit-cost. Here, analyzing the operational conditions has become a key strategy to achieve both energy and thermal efficiencies simultaneously. This study aims to explore the effects of polymers' rheology on the energy consumption and melt thermal quality (ie, a thermally homogeneous melt flow in both radial and axil directions) of extruders. Six commodity grades of polymers (LDPE, LLDPE, PP, PET, PS, and PMMA) were processed at different conditions in two types of continuous screw extruders. Total power, motor power, and melt temperature profiles were analyzed in an industrial scale single-screw extruder. Moreover, the active power (AP), mass throughput, torque, and power factor were measured in a laboratory scale twin-screw extruder. The results confirmed that the specific energy consumption for both single and twin screw extruders tends to decrease with the processing speed. However, this action deteriorates the thermal stability of the melt regardless the nature of the polymer. Rheological characterization results showed that the viscosity of LDPE and PS exhibited a normal shear thinning behavior. However, PMMA presented a shear thickening behavior at moderate-to-high shear rates, indicating the possible formation of entanglements. Overall, the findings of this work confirm that the materials' rheology has an appreciable correlation with the energy consumption in polymer extrusion and also most of the findings are in agreement with the previously reported investigations. Therefore, further research should be useful for identifying possible correlations between key process parameters and hence to further understand the processing behavior for wide range of machines, polymers, and operating conditions

Validation of a fabric model for crash simulations of composite structures

The paper describes recent progress in DLR's research on the analysis of the crash behaviour of composite energy absorbing structures. Latest developments and verifications of a material model to simulate the crash behaviour of structures made of composite fabric plies with the explicit FE-code PAM-CRASH will be presented. Basic material properties of two different fabric materials are summarised which are used to generate the input data for the new fabric material model. With this material model verification analyses are performed starting on single element and specimen level which showed a good agreement to the corresponding test results. In a final step, simulations on hybrid trapezoidal beams which were crash tested under complex loading conditions are presented. In this study two of the beams were tested with a partial overlap of the specimen and impactors of different shapes, while a third one was tested on an inclined surface of 20° in the longitudinal direction. The forth test was performed on a specimen with two circular holes in the web area to investigate the evolution of damage and failure. In general, a very good correlation between the test results and the simulations with the improved fabric material model was found

Numerical Simulation of Composite Aircraft Structures under Crash Loading

The paper describes DLR's research on the crash behaviour of composite energy absorbing structures as used in sub-floor assemblies of modern helicopter and general aviation aircraft. Especially latest developments in the field of numerical simulation of the crash behaviour of these structures using an explicit Finite Element code are presented