Intermediate fiber breakage

Intermediate fiber breaks: The breaks are caused by different stresses and directions of stress

At an intermediate fiber fraction ( English inter-fiber failure ; IFF) is defined as a failure ( breakage or cracking) between the fibers of a fiber-synthetic material composite . The intermediate fiber break runs through the matrix material ( cohesive break) and / or along the fiber / matrix interface ( adhesive break) of a unidirectional layer (UD layer) and usually cuts through the entire individual layer in its thickness; However, fibers per se are not severed, i.e. H. there is no fiber break .

An intermediate fiber break in the multilayer composite ( laminate ) can only be stopped at adjacent layers if these have a significantly different fiber orientation than the failing layer.

The occurrence of inter- fiber breaks is initiated by loads in which the forces run over the matrix material or the fiber / matrix interface:

• the transverse tensile stress , the most common reason for intermediate fiber breaks ${\displaystyle \sigma _{\perp }^{(+)}}$
• the transverse pressure stress ${\displaystyle \sigma _{\perp }^{(-)}}$
• the transverse longitudinal shear stress ${\displaystyle \tau _{\perp \parallel }}$
• the transverse-transverse shear stress ${\displaystyle \tau _{\perp \perp }}$

The crack formation is based on imperfections that run parallel to the fibers in the UD layer.

A transverse pressure load causes the multilayer composite to shear off and, if the pressure is further increased, it bursts open, which leads to a total failure of the laminate. This type of failure is known as wedge fracture and occurs primarily in thicker UD layers. In order to avoid this form of failure, the individual layers of a multi-layer composite must be made thin. ${\displaystyle \sigma _{\perp }^{(-)}}$

The proof of whether the load acting on a laminate leads to an inter-fiber break or not can be provided by the inter-fiber break criterion according to Puck .

Individual evidence

1. ↑ TU Berlin: Composite materials and their failure mechanisms ( Memento from January 2, 2014 in the Internet Archive ), accessed on January 2, 2014.
2. ↑ TU Berlin: Composite materials and their failure mechanisms, p. 25 ( Memento from January 2, 2014 in the Internet Archive ), accessed on January 2, 2014.
3. ^ M. Knops: Analysis of Failure in Fiber Polymer Laminates - The Theory of Alfred Puck . Springer, 2008. ISBN 978-3-540-75764-1 .