Correlation of Matrix Prop. to Fatigue Behavior of FRP

Continuous fiber reinforced materials are a class of materials with exceptionally good fatigue properties, due to the durability of the fibers under cyclic loading. However, the polymer and the fiber-matrix interface are basic prerequisites to utilize these properties in a composite. The initiation can be, for example, a small crack or an increased fiber misalignment under compressive loading, due to lacking support from the matrix. Even though these damage mechanisms are typically on a microscale, it is established that this initial damage grows and threatens the laminate’s integrity on a macroscale. The identification of matrix properties that drive the damage formation is a challenging task, because most changes on the polymer level lead to undesired changes in the laminate as well. High-energy radiation could remedy this situation because most undesired changes such as differing geometric arrangement of the fibers can be avoided, as this treatment is the final step in specimen prepa-ration. An initial screening of different polymers from both classes of thermosetting and thermoplastic polymers lead to epoxy resin and polycarbonate as modifiable polymers used also in composites. Designated lay-ups and specimen geometries are used to make the material prone to specific damage modes like fiber kinking in compression or transverse matrix cracking in tensile loading. Special testing set-ups enable the in-situ observation of damage during formation. It has been shown that in some circumstances damage already forms within the first loading cycle at relatively low global strain. A currently ongoing systematic testing campaign of transverse tensile-tensile loading, on-axis compression-compression loading and alternating shear loading will build the database to facilitate a better understanding. Complementary micromechanical models support this effort.