The screen is thought to be based on manufactured sapphire, a material that has a toughness rating above glass, but a new patent reveals how Apple might be stacking the odds in its favor with a process to make it even stronger.
Landis, C., Pardoen, T., Hutchinson, J. W., " Crack velocity dependent toughness in rate dependent materials". Mechanics of Materials, 32, 663-678 (2000).
Cyclic toughness, the rates of energy-absorption under seismic loading, was proposed to characterize the HSLCF performance of rebars.
System failure was analyzed considering a range of coating parameters (elastic modulus, fracture toughness, energy release rate for cohesive propagation, thickness and residual stresses), coating/substrate interface properties (interface toughness and adhesive crack energy release rate) and the radius of the spherical indenter.
Consequently, no standard test has yet been defined for measuring the mode I fracture toughness under high rates of loading.
The results show that the dynamic compressive strength and impact toughness increase with strain rate, while the elastic modulus decrease with strain rate.
For samples in the same orientation group, the fracture toughness shows clear loading rate dependence, with the fracture toughness increasing with the loading rate.
The mechanical response of STF was studied at high strain rates in terms of the stress-strain behavior and variation of the impact toughness with the loading rate of the fluid specimen.
The experiments showed an apparent increase of fracture toughness with increasing loading rate.
Also, there is a clear tendency for a decrease in fracture toughness with increasing impact rate for all materials investigated.
