Effect of high energy radiation on technical polymers

Fiber reinforced polymers (FRP) offer excellent fatigue resistance in combination with low specific weight. However, in contrast to metals, microscopic damage is usually present right from the beginning of cyclic loading and calls for insights on initiation and propagation. As with other properties, the overall performance of a composite is determined by its constituents namely fiber, matrix and fiber-matrix interface. Especially, the matrix polymer is supposedly responsible for damage initiation. To study this, different methods for altering the matrix properties can be used. The presented research makes use of Co-60 irradiation to modify the polymer on a molecular level. Six potential candidate materials for FRP are investigated, two thermoplastics and four thermosets. After irradiating the neat polymer samples with (30, 100, 200 and 500 kGy) the properties are investigated by quasi-static tensile tests and fatigue experiments. The resulting fractures are inspected visually. The results for thermoplastic materials show deteriorating tensile properties, whereas some of the thermosetting resins improve. Despite this, it could also be shown that deterioration in monotonic loading does not necessarily deteriorate the fatigue properties. The fracture surfaces indicate yielding as possible cause. Finally, it was shown that irradiation is a promising modification method for the investigation of composites and possible also a method to improve the fatigue performance.