CFK-Versuchsaufbau vom Bearbeiter Stettner

Experimental testing of stresses and stability properties of CFRP sample components and comparison with numerical calculation processes

Shortcomings and aims of the project

While in operation, components are subject to stresses, among other things, due to the forces and torques that in turn give rise to
component tension. An engineer’s task is now to calculate this component tension based on the external stresses, and to compare them against the maximum permissible tension of the components. The aim of this
is to ensure that the existing tension is always smaller than the permissible tension.
As a result of the geometric design of components (recesses, notches, drill holes, etc.) that must be derived from the construction requirements,
the existing component tension may be influenced, for example, when the component profile is the same. The reason for this is the concentration of force lines at the notched site.
 
To make this easier for the design engineer and the calculation engineer to ascertain, an elaborate series of tests and calculation methods for homogeneous materials in mechanical engineering were used to determine the notch factor αK for
static stresses (αK = Smax/Sn) and the fatigue notch factor βK for dynamic stresses (βK = SWmax/SWn). The notch factors according to notch geometry are available to the engineer
in the form of diagrams. 
 
These notch factors are still not available for fibre-reinforced structures, and cannot be transferred from the existing tests for metallic materials and the various
notch shapes that have already been tested, because fibre-reinforced composites (FRC) 
1. have no homogeneous material structure and therefore exhibit anisotropic
     behaviour,
2. are produced using different manufacturing processes (coiling and laminating) to the machining
     production process in conventional mechanical engineering (turning, cutting,
     etc.)
3. therefore always have different design shapes. Components are not only
     weakened by notches but also by structural irregularities such as
     inserts (sockets, discs, or adapter parts integrated into FRCs to allow for connection
     to other components). For this reason, we refer below to non-disrupted and
     disrupted components.
 
In addition, FRCs demonstrate fatigue under dynamic stresses, which is distinct from fatigue in metallic materials. This is primarily due to the multi-component structure of FRCs. 
In the simplest case, an FRC consists of glass, aramid, or carbon fibres that are encased in a plastic matrix.
 
The aim of this project is to determine the influence of specifically fibre-reinforced shapes in disrupted and non-disrupted samples of carbon fibre-reinforced polymers (CFRPs). The priority here is to investigate the fatigue behaviour of the component samples.