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Session 9

Finite element analysis of localised impact loading on short glass fibre- reinforced polyamide engine oil pan subjected to low velocity impact from flying projectiles
This paper investigates low velocity impact involving a glass fibre-reinforced polyamide engine oil pan as part of a complete new development of thermoplastic components. The assessment of the impact resistance has driven the need to employ LS DYNA for finite element modelling in order to virtually benchmark and predict the strength and fracture behaviour of stressed plastic parts. In order to develop a reliable predictive capability and to validate simulations, complete components were manufactured by injection moulding techniques for the experimental samples. Low velocity impact investigations were carried out using a gas gun and a falling weight tester in order to simulate impact events to which the oil pan is subjected whilst in operational service. This was intended to point out damage tolerance and failure mechanisms likely to occur in the structure. The study results show the significant contribution of the design in terms of shock absorption. Specific oil pan design with protective ribbing combined with a superior material considerably improves the impact resistance. The paper provides results and discussions on experimental and finite element analysis investigations before concluding with some remarks.
Analysis of Fibre Orientation using μCT Data
Integrative simulations are based on a calculated bre orientation from which the local material properties can be derived in several ways. For instance the micro-mechanical model proposed by Tandon and Weng may be used coupled with an orientation averaging approach to include the bre orientation. This approach then gives the elastic properties of the bre matrix compound with a strong dependency, of e.g. the elastic modulus, on the bre orientation. Modeling failure for nite element simulations, e.g. crash, also requires knowledge of the bre orientation, because the failure strains and energy dissipation also depend on the orientation of the bres [1, 2]. The accuracy of the calculated bre orientation depends on several simulation input parameters, which are not necessarily physical properties. The most important example is the bre interaction coecient (c). This parameter allows the user to modify the calculated bre orientation from isotropic to transversely isotropic [3]. In this paper a new experimental method to determine the bre interaction coecient is presented. The classical approach to validate the calculated bre orientation would be the usage of optical microscope images of cut surfaces of the specimen and the calculation of the bre orientation by measuring the cut ellipsis dimensions. This method is very time consuming and with respective to the necessary magnication not very accurate, because not all bres can be accounted for. The new method is using a model based algorithm to analyze three-dimensional micro computer tomography measurements. This enables the identication of up to 90% of the bres within the specimen and calculate a second order orientation tensor and the bre length distribution in any arbitrary space. Due to the fact that a model based algorithm is used, the bre detection can also be performed, if the density of the matrix polymer is near to the density of the bre material. This is a novelty to existing bre orientation measurements with computer tomography. To obtain reliable data which can be directly compared with injection moulding simulations, several steps had to be taken. First of all a representative volume must be dened, in which the bre orientation will be evaluated. This representative volume must be the same in the injection moulding simulation and the μCT measurement. As the injection moulding model is already discretized, the representative volume is set as a stack of nite elements over the part thickness. To calculate the second order orientation tensor in exactly the same geometrical space and the same coordinate system as in the injection moulding simulation, it was necessary to develop a method which allows a reconstruction of the original part from which the μCT specimen was taken. A special painting and evaluation procedure were implemented into the existing method to recalculate the original position and orientation of the specimen, enabling us to achieve the desired measurements. At the moment the determination of the bre interaction coecient requires still many injection moulding simulations, which then are compared to the measured values. This allows for a more realistic bre coecient in comparison to the default parameter. The next steps are to automate the described procedure and to correlate the measured bre orientations directly with the bre interaction coecient to avoid unnecessary simulations.
Improving the Prediction of LS-DYNA Calculations with Rhodia Data and Digimat
Material Data Determination and Crash Simulation of Fiber Reinforced Plastic Components
The quality of the mechanical simulation of reinforced thermoplastics depends on very com­ plex input parameters regarding the complex material behaviour. At the beginning of the sim­ ulation chain the material data has to be determined in different mechanical tests (tension, compression and shear, different fibre orientation to load direction, etc.). After the injection moulding simulation the calculated fibre orientation has to be mapped to the structural FE mesh. For the structural simulation a combination of the material model MAT108 and MAT54 was used to simulate the orthotropic, load case sensitive material behaviour.
Prediction of structural response of FRP composites for conceptual design of vehicles under impact loading
For the predictability of composite material behaviour under highly dynamic loads like crash, there is a need for better models reproducing the exact physics of failure mechanisms (matrix cracking, delamination, heat dissipation etc.). This belongs to the state-of-the-art research topics in numerical modelling. The conceptual design of vehicle structures however requires a qualitative understanding of the load-displacement characteristics, absorbed energy and the load distribution in other structural components and therefore may not necessarily demand a precise modelling of the physical behaviour. From the results of material testing of a variety of composite specimens, the necessary parameters for different LS-DYNA specific constitutive material laws are identified. After that, the modelling and simulation of simplified part samples have been carried out with dynamic loading conditions. The results are then compared with experimental testing of these part samples; hence the suitable parameters for composite design are identified. The scope, drawback and opportunities for numerical prediction using the considered constitutive laws and modelling schemes are then discussed based on the verification of the results.