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In automated fiber placement (AFP), knowledge about the interaction between material properties and process parameters is essential to achieve cost-efficient manufacturing. Both, lay-up rate and defects are dependent on the properties of the uncured prepreg tapes which are out-time dependent. However, information thereof is not given in data sheets and there are no standardized test methods. To quantify the changes of the material properties, we conducted experiments on mechanical properties and tack with IM7/8552 up to 15 days out-time using previously evaluated test methods. Furthermore, we carried out AFP lay-up trials to quantify the effects on steering defects. The results for the mechanical properties reveal a non-linear increase of the shear modulus and the transverse tensile modulus and a strong correlation to the test temperature. Results from the probe tack tests show a strong dependence on out-time at 20°C and a weak dependence at 40°C. Results from a novel peel tack test method and the lay-up trials revealed a monotonous change as a function of out-time. In both cases, we identified the lay-up rate and the infrared (IR) emitter power as the process parameters with the largest influence. The obtained results present an overall view of the material behavior depending on different test and process parameters as a function of out-time. By this, they help optimize the AFP process parameters and serve as input for material models and AFP defect models.

To achieve cost-efficient manufacturing and a high part quality in Thermoset Automated Fiber Placement (TS-AFP), knowledge about the interaction between material and process parameters is of special interest. Material properties of prepregs are well known at the cured state of the resin. However, there are no standardized test procedures for the mechanical behavior of the uncured prepreg tapes. To investigate the intra-ply shear deformation behavior of uncured unidirectional prepreg tapes, we compared several measurement procedures and conducted experiments for rheometer based tests using 8552/AS4 material. We identified a rotational parallel platens rheometer test method and a torsion bar rheometer test method to be suitable. Experiments using both methods revealed that the Torsion Bar Test has a higher repeatability and the analysis is less complex. Furthermore, first results show that changes in material properties caused by aging can be analyzed using this method. In the future,we will use the Torsion Bar Test to characterize changes in deformation behavior due to material aging as well as material modifications. By this, we will be able to provide data for the material modeling thus enabling the prediction of lay-up defects such as buckling due to steering.

A numerical description of dry non-crimp fabrics is proposed at the scale of the filaments using a commercially available finite element software package. Deviations in the filament orientation of the fibrous layer is a dominant factor in the occurrence of local defects, which influences the mechanical response of the textile. Therefore, the introduction of variability in the orientation distribution is proposed in this paper. This approach enables to capture the entanglement of the filaments and models all interaction mechanisms. A stepwise generation of the numerical non-crimp fabric is proposed considering the main manufacturing steps to reproduce the local defects in the fibrous mat appropriately. Averaged periodic boundary conditions are developed ensuring an overall periodicity of the model while allowing reorientation at the scale of the filaments. Two various non-crimp fabrics are investigated and modelled. The distribution of the filaments in the simulation results correlate well with measurements of the filament orientation performed on the textiles. Moreover, a detailed comparison of the local defects shows a good agreement with measurements on the specimens. The presented approach can be used to generate geometries for subsequent virtual characterization.