  We study the crossover scaling behavior of the height-height correlation
function in interface depinning in random media. We analyze experimental data
from a fracture experiment and simulate an elastic line model with non-linear
couplings and disorder. Both exhibit a crossover between two different
universality classes. For the experiment, we fit a functional form to the
universal crossover scaling function. For the model, we vary the system size
and the strength of the non-linear term, and describe the crossover between the
two universality classes with a multiparameter scaling function. Our method
provides a general strategy to extract scaling properties in depinning systems
exhibiting crossover phenomena.
