Notch effect in highly deformable material sheets

• Stress/Strain Concentration Factor (SCF) in highly deformable sheets is considered.
• Experimental and theoretical SCF analyses are performed on notched sheets.
• Notch SCF mitigation induced by large deformation is studied.
• Notch geometry change and sheet buckling effects on SCF are quantified.
• Damage tolerance safety assessment in soft materials is proposed.

Defect tolerance is usually understood as the ability of a material to withstand an external load in the presence of a geometrical flaw. The case of a defect represented by a notch (i.e. a geometric discontinuity with finite curvature radius) can be described by the so-called stress (strain) concentration factor at the notch root and by the stress (strain) gradient in the vicinity of the notch root which is a preferential site for crack nucleation and propagation. Under static loads and within the elastic regime, notch effect in traditional structural materials is simply governed by the initial notch geometry. On the other hand, in highly deformable materials, such as soft matters (biological tissues, colloids, polymers, gels, foams, etc.), notch effect must be evaluated by considering large strain values arising around the notch, responsible for its blunting. In addition, when notches are contained in non-confined plate-like components, a sort of augmented notch blunting might occur as a consequence of local flexural instability of the material plate in the compressed zones. In the present paper, an experimental and theoretical study is discussed for a silicon sheet with different levels of notch severity. It is shown as the safety against notch concentration effect (that can reduce up to about 40–70%) can be greater than that in low deformable materials, and so notch blunting and plate's localized instability are beneficial contributions, leading to an increase of the element’s tensile strength.