Fatigue behaviour of composite tubes under multiaxial loading

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specimens under biaxial stress ratios.
Fifth International Conference on Fatigue of Composites
The current paper contains the experimental results of uniaxially and sequentially loaded tube
specimens. Thereby, the occurring damage mechanisms (matrix cracking, delamination and final failure)
measured with different non-destructive test methods and the fatigue behaviour for different load cases
are shown. Additionally, these phenomenological results can be used as input for future models
describing the fatigue behaviour of composites under sequence loading.
2. Material
Matter of the investigation is a nominally defect-free wound tube specimen made of E-Glass-fibre
rovings from Owens-Corning (OC 111A) and a resin/hardener-combination of RIM135/ RIMH137 from
Hexion. In order to produce these specimens at a high quality standard a self-designed winding machine,
which enables the manufacturing of arbitrary lay-ups is used. The winding process and one tube
specimen are shown in figure 1. As in a previous investigation of the fatigue behaviour under biaxial
loading [12] the specimens used in the current research consist of 8 layers with a symmetric lay-up of
[0 o /45 o /90 o /-45 o ]S. The applied mass per unit area and the relative mass fractions are shown in talbe 1.
Using resin transfer moulding (RTM) the wound tube specimens are manufactured in the way that the
plies orientated in 0 o -direction (identical to the axial direction of the specimens) are the inner and outer
plies.
Fig. 1. Winding process (left) and nominally defect-free wound tube specimen (right).
Table 1. Lay-up of the wound tube specimens
Orientation ( o ) Mass per unit area (g/m 2 ) Relative mass fraction (%)
0 638 49
45 301 23
90 63 5
-45 301 23
The testing specimens are tubes of 46 mm outer diameter, a length of 328 mm and a wall thickness of
approximately 2.0 mm. Due to the wall thickness the fibre volume fraction is about 50 %. After having
completed the RTM-process both ends of the tube specimens are strengthened by a GFRP-doubler of
70 mm length and bonded steel inserts which prevent failure due to the fixing pressure of the testing
machine. Such a configuration of wound tube specimens makes it possible to