The ability to design lightweight yet strong and durable components with composite materials has driven their continuous development. Nowadays, components from high-performance composite materials are used in a wide range of applications mostly aircraft, wind turbines, automotive and sports equipment. To ensure their safety, understanding the fatigue behaviour of composites is essential. Up to now, no universal fatigue-damage model exists for composite laminates despite continuous developments in this field over the past decades. This reflects the difficulty of developing such a model for composite laminates where effects on different length scales influence the development of fatigue damage. The anisotropic material behaviour, multiple damage modes and complex interactions have shown to be significant obstacles in the development of a universal fatigue-damage model. Many proposed models have critical limitations when it comes to their applicability to real-world components, which hinders them to become widespread engineering tools. Given the fact that fatigue modelling generally requires more experimental data than static analysis due to multiple added effects from fluctuating loads, the amount of tests needed for the calibration of models is particularly important. This thesis takes a rather engineering approach with regard to physical damage phenomena for the development of a ply-based fatigue damage model for matrix cracks. As of now, parts of the model are still under development, as this work marks the beginning of the development of a fatigue-damage model with the aim to provide an efficient and easy-to-use framework. A special focus is the applicability of the model and the ability to calibrate the model with standard experimental campaigns. The model builds upon the static ply-based damage model from Schuecker et al., which uses a multi-scale approach to compute the effects of matrix cracks on the stiffness of a laminate. The classical laminate theory is used for stress analysis of a given laminate. The effects of matrix damage are computed with a Mori-Tanaka model, which is an analytical micromechanical method. In order to develop such a model, information on the damage state during tests is essential. For this, a crack detection framework is presented which enables efficient quantification of the damage state for fatigue experiments. Also, the correlation with other measures and the effects of different stress states on the formation and evolution of matrix cracks is studied in detail.