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W H I T E P A P E R
3.1 Griffith surface energy criterion
When a simulation begins, the joints connecting elements in a particle are undeformed. However,
when a particle interacts with other particles or boundaries, the relative movement between the
elements may produce linear and angular deformations on the joints. This is valid for fibers,
shells, and any other solid particle with multiple elements. For the Griffith surface energy
criterion, only the tensile stress at the joint is considered.
The normal force on a joint, depicted below in Figure 3, divided by the cross-sectional area
between the elements is defined as normal stress.
A joint will break when the normal stress is equal to or higher than the normal fracture stress:
where the normal fracture stress, σ
f
n
, is related to the normal stiffness, K
n
, the cross-sectional
area, A , and the surface energy user input, Γ :
3.2 Shear stress criterion
With this criterion, only the shear stress at the joints is considered. Similarly, the tangential
force on a joint, depicted below in Figure 4, divided by the cross-sectional area between the
elements results in the shear stress.
Figure 3: Example of normal forces acting on a joint between two elements of a particle.
Figure 4: Example of tangential forces acting on a joint between two elements of a particle.
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