Stress intensity factor definition

The stress fields can be obtained by substituting the displacement fields into the Hooke s law, and then making use of the boundary conditions at both surfaces of the crack and the plate. Making use of the boundary condition for the 0-th order stress, = 0 at 0 = .ar, and the definition of the stress intensity factor in terms of the stress a ° we obtain the following equations. 

A minimum roughness of the support surface is also required to produce defect-free membrane layers. In the present context, surface roughness is defined as the average perpendicular (to the surface) distance between peaks and dips in the support surface. As discussed in Chapter 6, several other definitions of roughness can be given and used. The roughness of the support may limit the minimum achievable layer thickness. From a fracture mechanics point of view, surface roughness determines the maximum size and sharpness of flaws which can act as crack initiators (via the stress intensity factor). 

Stresses at a Crack Tip and Definition of Stress Intensity Factor... 

The scaling constant Ki for mode I crack opening, which occurs in these equations, is known as the stress intensity factor. It is proportional to the K of Eq. (9.7). The inclusion of the term is a result of the 1939 definition of Ki—logically it could be omitted. Both stress components given by Eq. (9.8) are zero along the crack surface, as required by the boundary... 

Another important quantity in interface fracture mechanics is mode mixity. The crack tip field of an interface crack is intrinsically mixed mode [8] due to the asymmetric elastic properties across the interface. Hence, mode mixity is required to fully characterize the loading conditions at the crack tip. Furthermore, the fracture toughness of an interface is known to depend on the mixed mode condition, typically observed to rise with increasing mixed mode. The degree of the mode mixity can be characterized using the definition of the complex interface stress intensity factor K = iK + after He and Hutchinson [5] ... 

Now the equation for the fracture stress Of estimation as a function of and sharp notch length a can be obtained. In Ref [4], the following definition of stress intensity factor A j as a fimction of was given ... 

The square root is required for consistency with the standard definition of the phase angle using applied stress-intensity factors [13]. A phase angle of 0° corresponds to a nominally pure mode-I configuration a phase angle of 90° corresponds to a nominally pure mode-II configuration. 

---