Direct Bundle Simulation approach for the compression molding process of Sheet Molding Compound

The manufacturing process of Sheet Molding Compounds (SMC) induces a reorientation of fibers during the flow, which influences local properties and is of interest for structural computations. Typically, the reorientation is described with an evolution equation for the second order fiber orientation tensor, which requires a closure approximation and multiple empirical parameters to describe long fibers. However, CT scans of SMC microstructures show that fiber bundles stay mostly intact during molding. Treating hundreds of fibers in such a bundle as one instance enables direct simulation on component scale. This work proposes a direct simulation approach, in which bundle segments experience Stokes’ drag forces and opposing forces are applied to the fluid field. The method is applied to specimens with a double-curved geometry and compared to CT scans. The Direct Bundle Simulation provides increased accuracy of fiber orientations and enables prediction of fiber-matrix separation with affordable computational effort at component scale

Study of material homogeneity in the long fiber thermoset injection molding process by image texture analysis

To quantify the homogeneity of fiber dispersion in short fiber-reinforced polymer composites, a method for image texture analysis of 3-dimensional X-ray micro computed tomography (µCT) images is presented in this work. The adaption of the method to the specific requirements of the composite material is accomplished using a statistical region merging approach. Subsequently, the method is applied for evaluating the homogeneity of specimens from an intermediate step of the long fiber thermoset injection molding process as well as molded parts. This new injection molding process enables the manufacturing of parts with a flexible combination of short and long glass fibers. By using a newly developed screw element based on the Maddock mixing element design, the material homogeneity of parts molded in the long fiber injection molding process is improved

Techno-economic heliostat field optimization: Comparative analysis of different layouts

This paper presents an analysis of the effect of the land cost on the size and shape of the solar field. A parametric study has been performed, where the effect of the land cost is considered through the introduction of a parameter k, representing the ratio between the land and heliostats surface cost. Three different field layouts and two different geographical sites have been taken into consideration. The selected field layouts have been studied for several k-values within a relevant range. Results show that introducing a cost ratio k different from 0 has a strong influence on the shape of the resulting fields, significantly compressing the heliostats fields also for low land costs. For example, for k=0.02, the area is reduced, with respect to k=0, from 28% to 49%, following the considered cases; on the same time, the yearly collection efficiency is reduced by only about 1% in all cases

Optical performance comparison between heliostat field generation algorithms

This paper summarizes the collaborative work done by CENER, Fraunhofer ISE and CRS4 within the scope of the STAGE-STE project related to heliostat field generation algorithms and their application to small heliostats (<10 m2). Radially staggered heliostat field layouts have been commonly applied to real solar fields with known results. However, their use in conjunction with small heliostats or the use of brand new ways for heliostat allocation, such natural pattern based algorithms, is still unknown. Herein, the most promising heliostat field generation algorithms are studied and compared, in annual optical efficiency terms, for different scenarios. These efficiencies correspond to the best heliostat layouts found by the optimization process that each generation algorithm can create, for three scenarios. Results show that the fields from the selected algorithms lead to similar optical efficiencies. The slight differences are not enough evidence to nominate one of the algorithms as the best choice, taking into account the inherent error of the simulation tools, the optimization process and further requirements needed in commercial applications (e.g. access paths) not coped in this study

Solar Field Heliostat Selection Based on Polygon Optimization and Boundaries

A novel methodology for the design of heliostat fields is presented, based on the selection of heliostats from an oversized field by means of a polygon. To obtain the ideal field shape, the polygon vertices are optimized with an evolutionary algorithm. The objective function calculates a weighted tradeoff between annual optical efficiency and ground usage and is applied to the entire field instead of individual heliostats. Various other figures of merit could be readily integrated. To be able to deal with complex shaped land available for the Solar Tower plant, area boundaries are taken into account during the optimization phase. The application of the methodology is demonstrated by means of a reference scenario and multiple variations of parameters and area boundaries. The polygon selection creates smooth, coherent heliostat fields with high performance regarding the objectives, while solving several practical issues in the heliostat field design phase at the same time

Virtual process chain of sheet molding compound: Development, validation and perspectives

A virtual process chain for sheet molding compound (SMC) composites is established and validated by means of experimental investigations on a demonstrator structure. The flow in the compression molding step is simulated via a Coupled-Eulerian-Lagrangian approach using an anisotropic non-Newtonian fluid flow model. Evolution of the fiber orientation distribution (FOD) is described by Jeffery's equation. The predicted FOD is mapped to structural simulations employing a neutral data format. A mean-field anisotropic damage model is used to predict the damage evolution in the demonstrator. Simulated FOD at the end of the compression molding is validated by computer tomography. Structural simulations are validated by means of a cyclic four-point bending test on the demonstrator. The predicted results show increased accuracy with the experiments by transferring FOD data within the virtual process chain. Critical points of high damage concentrations leading to failure agree with the experimental observations