Mechanical Microstructure Characterization of Discontinuous‐Fiber Reinforced Composites by means of Experimental‐Numerical Micro Tensile Tests

Abstract

The mechanical characteristics and especially the damage behavior of discontinuous-fiber reinforced composites greatly depend on its constituents and also on its microstructural properties, namely the extent and distribution of fiber agglomerations, the fiber orientation distribution, and the fiber-matrix interfaces. Several methods exist to individually analyze the different microstructural properties, such as µCT scanning to obtain the distribution of the fibers and their orientation and the Microbond test to obtain the interfacial characteristics. However, the interdependencies of the individual characteristics and the initiation of fracture with respect to the microstructure are still hard to analyze regarding a real composite structure. For this reason, the microscopic fracture behavior of a glass fiber reinforced sheet molding compound (SMC) shall be investigated by means of a micro tensile test. Therefore, a specimen with a gauge length of approx. 1 mm, 0.3 mm width and 0.1 mm thickness is extracted from a composite plaque and put to an in-situ observed tensile test. With a finite element model of each specimen, including the position and orientation of each fiber, the fiber-matrix-interface characteristics are extracted with a reverse-engineering approach. The tests show a microstructure-specific fracture behavior, which depends on the fiber dispersion, the fiber orientation, and the fiber-matrix interfaces. The numerical simulations well agree with the physical experiments, making the obtained parameters suitable for further simulations of the investigated structure on a larger scale.

Magnetically driven in-plane modulation of the 3D orientation of vertical ferromagnetic flakes

“…This feature is key to further develop a reverse-engineering approach to design complex in-plane orientations in composites according to geometrical, structural, or functional demands, using methods such as finite element analysis or machine learning. 51,52 Along with the modulation in-plane of the orientation of the flakes, a similar approach could be used to vary the local concentration in magnetic flakes. Indeed, gradients in magnetic field strengths can generate attractive forces on ferromagnetic flakes and concentrate them at the areas of strongest magnetic fields.…”