Micro-Scale Permeability Characterization of Carbon Fiber Composites Using Micrograph Volume Elements

To manufacture a high-performance structure made of continuous fiber reinforced plastics, Liquid Composite Molding processes are used, where a liquid resin infiltrates the dry fibers. For a good infiltration quality without dry spots, it is important to predict the resin flow correctly. Knowledge of the local permeability is an essential precondition for mold-filling simulations. In our approach, the intra-bundle permeability parallel and transverse to the fibers is characterized via periodic fluid dynamic simulations of micro-scale volume elements (VE). We evaluate and compare two approaches: First, an approach to generate VEs based on a statistical distribution of the fibers and fiber diameters. Second, an approach based on micrograph images of samples manufactured with Tailored Fiber Placement (TFP) using the measured fiber distribution. The micrograph images show a higher heterogeneity of the distribution than the statistically generated VEs, which is characterized by large resin areas. This heterogeneity leads to a significantly different permeability compared to the stochastic approach. In conclusion, a pure stochastic approach needs to contain the large heterogeneity of the fiber distribution to predict correct permeability values.

EFFECT OF MICROSTRUCTURE ON INITIATION OF DELAMINATION IN CROSS PLY LAMINATES FROM A TRANSVERSE CRACK

Transverse crack propagating towards a cross-ply interface is investigated in this study. The non-uniform fiber distribution near ply interface is modelled explicitly in order to study the effect of microstructure on crack path and initiation of delamination. The growth of fiber/matrix interfacial debond and debond kinking out of interface are analyzed based on a combination of energy and stress-based approach, which is convenient in predicting matrix crack path. Kinking of transverse crack tip when it approaches ply interface is investigated using an energy-based approach. It is found that predicted matrix crack path and crack tip kinking behavior near interface is strongly influenced by the local microstructure. The obtained results indicate that an induced symmetrical delamination, i.e., interface cracks of equal length on either side of the transverse ply crack, as often assumed in modeling studies, is not always a favorable damage mode.

Stochastic aeroelastic analysis of laminated composite plate with variable fiber spacing

In this paper, the dynamic and aeroelastic analysis of variable fiber spacing composite (VFSC) laminated plates are carried out. The effects and benefits of changing the fiber distribution pattern on natural frequency and mode shape are explored taking various boundary conditions. Taking cantilever boundary condition flutter characteristics of VFSC plate with different fiber distribution patterns are compared. Further stochasticity of flutter velocity due to randomness in material properties that could arise due to complex manufacturing and fabrication process of VFSC laminates is investigated. The perturbation technique is implemented to perform the stochastic as well as reliability analysis. Various parametric studies are conducted to check the accuracy and efficiency of perturbation technique, by comparing the results with that of Monte Carlo simulation and the first-order reliability method.

Characterization of Internal Defects and Fiber Distribution of BFRC Based on the Digital Image Processing Technology

Adding basalt fiber into concrete can significantly improve its mechanical properties. In order to explore the influence of basalt fiber content on the uniaxial compressive strength and splitting tensile strength of concrete and the mechanism of fiber action, this paper conducts compressive and splitting tensile tests on three kinds of basalt fiber concrete specimens with different fiber content and obtains the relationship between the macro mechanical properties and the fiber content. At the same time, with the help of CT scanning equipment and digital image processing technology, the microstructure of basalt fiber concrete with three groups of fiber content is reconstructed, and the pore, crack, and fiber distribution are quantitatively described using the calculation and processing function of the Avizo reconstruction software. The results show that when the optimal fiber content is 3 kg/m3, the improvement rates of uniaxial compressive strength and splitting tensile strength are 31.9% and 23.7%, respectively. The network structure formed by fiber in concrete has the best compactness and the least number of pores, with an average sphericity of 0.89 and an average pore volume of 20.26 μm3. Through analysis, it was found that the initial defects of basalt fiber concrete exist in the form of pores, and the addition of basalt fiber will destroy the large pore size of concrete, change the pore size distribution, and increase the average sphericity; The distribution of the fiber in the concrete is a three-dimensional network, and the distribution of the fiber in the initial defect distribution area is parallel to the direction of pore arrangement.