In brittle fracture, the tearing mode III of loading improves the conditions for non planar crack propagation (the direction of fracture propagation being perpendicular to the applied shear stress): this is because the average crack extension force (crack extension force averaged over the length of the oscillatory crack front) is much larger in mode III (vo + 3 v2) than in modes II (v0 + v2) and I (v0 - v2/3), v0 and v2 positive quantities, when the fractured surface is non-planar, with an oscillatory segmented crack-front in planes perpendicular to the direction of fracture propagation (the values of the average crack extension force above are for isotropic materials, see ours papers below). Presumably the experimental broken surfaces (in your experiments) are non-planar (rough) when viewed along the direction of fracture propagation. Please go through works dealing with calculation of the crack extension force when the fracture surface is non planar; see our contributions: A STUDY OF THE MIXED MODE I+III LOADING OF A NON- PLANAR CRACK USING INFINITESIMAL DISLOCATIONS ; An analysis of a non-planar crack under mixed mode I+III loading using infinitesimal dislocations with edge and screw average characters ; An analysis of a non-planar crack under general loading using continuously distributed sinusoidal edge and screw dislocations (ResearchGate).
Ductile materials are in general more difficult to break due to dislocations generation from the tip of the crack; this is because the crack extension force is lowered by the generated dislocations; please see our contribution: Significance of the deviations of the crack front into the plane perpendicular to the crack propagation direction- I. Crack-front dislocation generation
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Material Characterization