The stress needed to fracture bulk glass is around 100 MPa.
* The theoretical stress needed for breaking atomic bonds of glass is approximately 10000 MPa.

A theory was needed to reconcile these conflicting observations. Also, experiments on glass fibers that Griffith himself conducted suggested that the fracture stress increases as the fiber diameter decreases. Hence the uniaxial tensile strength, which had been used extensively to predict material failure before Griffith, could not be a specimen-independent