This International Standard specifies the principles for determining the fracture toughness of plastics in the crack-opening mode (mode Ⅰ) under defined conditions. Two test methods with cracked specimens are defined, namely three-point-bending tests and compact-specimen tensile tests in order to suit different types of equipment available or different types of material.
The methods are suitable for use with the following range of materials:
— rigid and semi-rigid thermoplastic moulding, extrusion and casting materials;
— rigid and semi-rigid thermosetting moulding and casting materials.
Certain restrictions on the linearity of the load-displacement diagram, on the specimen width and on the thickness are imposed to ensure validity (see 6.4) since the scheme used assumes linear elastic behaviour of the cracked material and a state of plane strain at the crack tip. Finally, the crack must be sharp enough so that an even sharper crack will not result in significantly lower values of the measured properties.