Kinkband formation in wood and fiber composites––morphology and analysis

Kinkband formation in wood and in fiber composites display several similarities as well as several dissimilarities. In comparison with wood the morphology of fiber composites is relatively simple and yet, on an overall scale, kinkbands in both kinds of materials look very much like each other. There are, however, important differences between the two, both on a local morphological scale and in terms of the load-displacement characteristics. While carbon fibers break wood fibers buckle, which to some extent explains why the steady state load in wood is closer to the peak load than in fiber composites. Another circumstance which plays an important role in this connection is that wood contains many more and more severe geometric imperfections in the alignment of the fibers, which lowers the peak load and thus brings it closer down to the steady state load, which is known to be independent of the imperfection level. Two methods of analysis are presented here. The first one is a (semi)analytic approach, while the second is a simplified finite element analysis utilizing Bernoulli–Euler beam finite elements to model the fibers in combination with the simplest possible Timoshenko beam elements which model the matrix material