Fracture Kinematics
In-plane sliding fracture mechanics characterize how bonded layers slide past each other along an interface under parallel shear loading. The stress state known as mode II shear drives crack propagation along adhesive interfaces or internal paperboard laminas where forces act parallel to the crack plane and perpendicular to the crack front. Testing protocols apply opposing longitudinal loads to measure critical energy release rates during sliding separation.
This fracture mode governs adhesive debonding in packaging seams subjected to torsion or offset tensile strain.
Loading Geometry
End-notched flexure test specimens isolate forward shear stresses along pre-cracked laminates. Three-point bending fixtures induce internal shear along the mid-plane of paperboard assemblies. Specimen geometry prevents out-of-plane opening displacement while maximizing sliding offset across the crack tip.
Crack Resistance
Interlaminar strength controls resistance to sliding failure in multi-ply paperboard structures. Short starch-bonded fibers at core plies yield lower mode II shear resistance than long virgin kraft fibers used in outer linerboard layers. High shear loads cause micro-void formation along the bond line prior to catastrophic crack propagation.
Test results demonstrate that high moisture content reduces shear modulus and accelerates sliding failure under dynamic stress. Fiber orientation affects shear propagation, with cross-direction fibers resisting lateral shear motion better than machine-direction alignment. Temperature fluctuations alter synthetic adhesive ductility, causing brittle shear fracture under cold storage conditions.
Evaluation of sliding resistance guides adhesive selection for heavy-duty corrugated containers and folded paperboard constructs.
