NBN ISO 13586:2021

This document 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, including their compounds
containing short fibres of the length = 7,5 mm:
— rigid and semi-rigid thermoplastic moulding, extrusion and casting materials;
— rigid and semi-rigid thermosetting moulding and casting materials.
In general, short fibre lengths of 0,1 mm to 7,5 mm are known to cause heterogeneity and anisotropy
in the crack tip fracture process zone. Therefore, where relevant, Annex B offers some guidelines to
extend the application of the same testing procedure, with some reservations, to rigid and semi-rigid
thermoplastic or thermosetting plastics containing such short fibres.
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 needs
to be sharp enough so that an even sharper crack does not result in significantly lower values of the
measured properties.