Polymers and composites are important construction materials in mechanical engineering. Their mechanical response is more complex than that of traditional materials such as steel. It is often non-linear, which requires care and expertise from the analyst. The same holds true for composites, for example fiber-reinforced polymers. Aspects such as the correct assignment of fiber orientations in the pre-processing of complicated composite layups are as important as the proper application of failure criteria suitable for predicting damage and failure in composite structures.