Physical cracking

Even for the large particle of 10mm, the maximum internal relative pressure inside the particle is only a little more than 70Pa. Under such a low pressure, the physically cracking process caused by internal pressure can not be the case for biomass particles as it is for coal particles. 

In Eqn. (4.7), 2a is the effective crack diameter. Formally 2a represents the diameter of the physical crack and the associated plastic zone correction factor, namely. 

In essence, the physical crack size 2ao is being considered in relation to the crack-tip plastic zone size through the following three cases ... 

The question now is how much nonlinearity is considered to be not excessive. Formally, the nonlinearity should not exceed that which would correspond to an increase in the initial (or physical) crack diameter (2ao) by the plane strain plastic zone correction factor i.e., by Iriy (see Eqn. (3.49)). Physically, it is acceptance of the fact that a plastically deformed zone would develop at the crack tip, and its presence is equivalent to a change in the effective crack length at the onset of fracture from Itto to Itto -I- 2riy i.e.,... 

By combining Eqns. (5.1) and (5.2) and solving for a, the physical crack size (a) at the onset of leakage/fracture becomes ... 

BS mm physical crack length augmented to account for crack tip plastic deformation (fracture mirror length)... 

Ji N mm physical crack initiation value determined from intersection of stretch zone width and /-R curve... 

With the geometrical details of the specimens, including the initial crack length a, the physical crack length augmented to account for crack tip plastic deformation (the fracture mirror length) aBs> the dynamic yield stress o-y and the dynamic flexural modulus E, the fracture mechanics parameters Ki, Ju and can be calculated [OlGre]. 

---