Meaning
Fracture test quantifies the Mode II fracture toughness of composite materials or adhesive bonds. The end notched flexure test utilizes a three point bending setup where a specimen contains a pre-existing crack at one end along the neutral axis. Bending the specimen induces sliding shear at the crack tip to measure the resistance to delamination.
Shear Resistance
Energy requirements to propagate a crack under sliding loads differ greatly from those under opening loads. A high value in the end notched flexure test indicates that the material can withstand substantial shear stress without the layers separating. This property is necessary for battery enclosures that face twisting loads.
Loading Mechanism
Force application occurs at the center of the beam while two supports hold the ends. The sliding motion at the crack tip results from the different bending radii of the upper and lower arms. Friction between the surfaces can influence the final calculation and must be accounted for in precise measurements.
A span length is chosen to ensure that the material remains within its elastic limit during the loading phase.
Delamination Behavior
Failure modes in composites often start with shear induced separation. Engineering teams use data from the end notched flexure test to select materials that prevent crack growth. Testing under various temperatures helps map the safety margins of the pack structure.
