Double‐Cantilever‐Beam Testing of a Transversely Isotropic Fibrous Silica Material

The double‐cantilever‐beam (DCB) geometry was used to study the fracture behavior of a transversely isotropic fibrous silica material that is used in the thermal protection system of the Space Shuttle. For this testing geometry, the evaluation of K c requires measurement of the elastic constants of the material. Determination of the compliance behavior of the material allowed the various analytical beam models that have been put forward to describe the DCB geometry, to be distinguished. The Timoshenko beam on a generalized foundation was found to be the best model to describe the experimental compliance behavior and the K c measurements. The measured K c values were found to be higher than for previous work that had used the double edge‐notched tensile geometry. Crack propagation in the material was found to be characterized by variations in the crack‐resistance force, probably reflecting microstructural variations. The subcritical crack‐growth behavior was studied using the constant‐load‐mode DCB technique, and the results were in agreement with the predictions of an earlier study.