By using a simple model, a method was proposed to calculate size of crack side ligaments formed during brittle crack propagation. The crack side ligaments cause difference between K1a and Kca.
The present method can explain the following items which are well known empirically.
(1) Kca can be said to be a material constant when measured by means of the standard ESSO test.
(2) Kca can not be a material constant when measured by means of the ultra wide plate ESSO test.
It was concluded that the current fracture control method based on Kca of the standard ESSO test is always on conservative side.
