1,721,013 research outputs found
Mesoscale simulation of the solidification process in injection moulded parts
No full textDue to their wide range of applications and their complex material properties, it is desirable to be able to predict the behaviour of injection moulded parts with the help of simulation tools. For semi-crystalline materi- als, this can only take place with considerable accuracy if the inhomogeneous material properties are taken into account. Because of this, it is necessary to calculate the microstructure of the solidified melt and to incorporate these findings in the simulation. We present an integra- tive, multiscale simulation approach in which the manu- facturing process is calculated on a macroscale and the solidification process on a mesoscale. A multiphase filling and cooling simulation is done to calculate temperature and velocity fields, which are used as boundary condi- tions for the calculation of the spherulite distribution in the part. We present the used nucleation and growth model and shortly describe the parallelisation approach of the mesoscale simulation
Multiscale Modeling of Polymer Crystallization
No full textThe crystallization process during
filling and cooling in an injection molding
process is investigated. The numerical methods,
crystallization models and their implementation
into a simulation chain with COMSOL and
SphäroSim software are describe
Multi-scale thermal simulation of polymer crystallization.
No full textCrystallization from polymer melt is one of the most fundamental phenomena of material phase transformations. The possibility of controlling crystallization kinetics is essential to achieve the proper polymer microstructure and consequently obtain the desired material properties. The main objective of the presented work is to compute crystallization kinetics of semicrystalline thermoplastics in an injection molding process with multi-scale modeling. This is done by identifying the analytical parameters needed to connect crystallization kinetics with molecular material properties and applying the analytical scheme to the numerical simulation during cooling. The numerical method, crystallization kinetics and their implementation into numerical software are described as well as the experimental data
Analysis of polymer crystallization and residual stresses in injection molded parts
No full textThe main objective of the presented work is to develop an integrated computational environment that predicts final part properties made of semicrystalline thermoplastics. This objective is fulfilled by adopting the following two-step approach: 1) identification of an analytical scheme to correlate crystallization parameters with engineer properties; 2) apply the analytical scheme to the numerical simulation to study the polymer and final properties of the part. In this work the crystallization evolution in cooling phase, mainly influenced by thermal gradients, and its effect on the final part properties are investigated. The numerical method, crystallization models and their implementation into numerical software are described as well as the experimental dat
A new method for the calculation of the spherulite growth in solidifying semi-crystalline polymer melts
No full textThis paper presents a new algorithm named "Continuous Cellular Growth" (CCG) method for the calculation of the crystal growth process of spherulites in solidifying semi-crystalline polymer melts. The concept is developed in one dimension, then transferred to three dimensions and finally implemented as an executable algorithm in the in-house code Sph„roSim. The CCG method is compared to an inaccurate but fast Monte-Carlo based and an accurate but slow integration based growth algorithm which uses a Raytracing method. It turns out that the results of the CCG method are very close to those of the integration method with differences of only a few percent. However, the computation time was reduced by two orders of magnitude compared to the Raytracing method, and thus is only slightly above the computation time of the Monte Carlo algorithm
Two-Level Homogenization of 3D Polypropylene Microstructures of an Injection Moulded Component
No full textMultiscale simulation of semi-crystalline thermoplastics in the injection moulding process
No full textSemi-crystalline materials are one of the most important material groups in polymer processing. In contrast to the amorphous materials the macromolecules of the semi-crystalline polymers can arrange in periodic patterns and form crystalline superstructures. Because of several limiting factors such as entanglements or variations in the molecular weight crystals are usually not perfect but consist of amorphous and crystalline domains with different physical properties. The mechanical properties depend on the morphology, the degree of crystallinity and the molecular orientation of the formed microstructure.
To take locally variable thermo-elastic properties of injection moulded plastic components into account, an original integrative and multi-scale simulation model is proposed here. This approach starts with a 3D injection moulding simulation, involving mould filling, heat transfer between melt and mould, and melt cooling. This simulation is performed by using the CFD and heat transfer (HT) modules of COMSOL Multiphysics [1] to compute the filling and cooling process at the macro-scale for an isotactic polypropylene (PP). From this analysis, result fields, written in the VTK format, are transferred to the 3-D SphaeroSim program, developed at IKV, for the simulation of the solidification process. Based on the concept of cellular automata, this program calculates the free energy function and converts it to a nucleation probability. This probability is used to determine the distribution of spherulite germs. By integrating the line integral from the germ to the crystal growth front the expansion of the spherulites is specified and the resulting microstructure calculated [2]. We take temperature and flow fields from the injection moulding simulation into account to consider cooling and flow induced effects on the microstructure.
The predicted crystalline microstructures, at different locations in the thickness of a PP plate, are transferred to the homogenisation tool HOMAT. HOMAT uses the method of asymptotic homogenization [3] to evaluate the effective thermo-elastic properties of each semi-crystalline microstructure. A special two level homogenization scheme [3] has been developed to take into account the radial
distribution of amorphous and crystalline lamellas. The predicted effective local
mechanical properties are finally used in a structural analysis of the PP plate at the
macro-scale. The presented multi-scale simulation model takes account of the
inhomogeneous material properties during injection moulding processes and offers a
wide range of new simulation possibilities, such as the prediction of residual stresses,
shrinkage and warpage of semi-crystalline plastics part
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