Marcelling

As undulation (derived from Latin unda 'wave' or French onde 'wave' ), the artificial introduction of curls or waves is called the head or beard hair. This curling irons are used, for example. The curling iron is heated, the hair is then pressed with the curling iron in the form. The procedure was developed in 1872 by Marcel Grateau and is also used in the Perückenmacherei. Later, the curling iron has been replaced by electrically operated Ondulierstäbe. 1906 Karl Ludwig Nessler invented the first Dauerondulation (hot wave ) by chemical and thermal treatment. Such methods are now referred to as a perm. The different types of undulation may cause damage to the hair.

But the term also refers to the deflection of fibers within tissues, for example in fiber composite materials. Are interwoven fiber bundle and held together by a warp thread, then there may be a deviation of the fiber bundle, which is caused by the warp yarns. The undulation results in a decrease of the fiber strength of the fabric parallel.