Physically motivated FEM material law based on the material and processing induced morphology during injection molding by unreinforced as well as reinforced thermoplastic materials

• Applicants: Professor Dr.-Ing. Michael Gehde (†); Professor Dr.-Ing. Jörn Ihlemann
• Subject Area: Plastics Engineering ; Mechanics
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 284349961

There is a deficit in the repatriation of existing constitutive laws for semi-crystalline thermoplastics on basic physical coherences and processes, such as their crystallization. This impedes their applicability in FE-simulations. Furthermore, the basic mechanisms and determining factors for the crystallization and their effects on macroscopic material behavior are only partially understood. Accordingly, it is not possible to reliably control the crystallization process in relation to a predefined crystallinity degree. This opposes a reliable and precise simulation of semi-crystalline thermoplastics, which is the basis for computer-assisted development and optimization of hybrid plastic-metal-composites.The overall objective of the project is to understand the reasons and effects of the crystallization in hybrid-structures. These studies should be done on unreinforced and reinforced (second period of founding) thermoplastics. The results are required to control the crystallization during the manufacturing process and to create a physically based constitutive law.The aim of the proposed research project is the controlled crystallization of the unreinforced thermoplastics PA6 and PBT. One step to reach this aim is the experimental characterization of the crystallization peculiarity with different, precisely defined process parameters and material properties, like melt and mold temperature, tool topography and rheological properties, by using partially new inspection methods. Another aim is to create a computer simulation, based on a "multi-particle system" with self-organized structure formation to reproduce the solidification of semi-crystalline thermoplastics as well as to perform an array of systematical simulations. It should be possible to identify experimentally graspable characteristics and correlations. Therefore, the simulation allows to access experimentally inaccessible information about the crystallization process and enables its manipulation.Based on the state of the art, existing constitutive laws and models are transferred into the continuum mechanic representation together with experimental results of the macroscopic polymer characterization, the optical structure analyzes, the calorimetric crystallization analyzes and the simulation of crystallization by using the forecast model. The arising representation can be integrated into a new material model. To implement the experimental results into a FEM simulation for the development and optimization of the hybrid-thermoplastic-metall composites is the final objective.

• DFG Programme: Research Grants
• Major Instrumentation: Fast Scanning Calorimetry (Flash DSC)
• Instrumentation Group: 8660 Thermoanalysegeräte (DTA, DTG), Dilatometer