Active hybrid composites consisting of fiber reinforced polymers (FRP) and shape memory alloys (SMA) can be used for actuation purposes. With this they can provide substantial savings concerning weight, space and cost or also enable new functions. A critical point for the use of the complete actuation performance of active SMA wires for a large number of cycles is the load transfer between these wires and the FRP structure. Also the loosening of the wire from the FRP structure has to be prevented. In this paper we will have a close look to the load transfer. There solutions for the testing of this load transfer as well as its improvement still do not satisfy. We show an improved experimental set up for a pull-out test, which are used most commonly, with optical stress measurement via photo elasticity for an exact measurement of the transferred load leading to primary failure of the interface. This enables a better forecast of the transferred load of the specimen. We also compare our results with those of typical pull-out tests. From these results we estimate the shear stress at first failure and compare these to theoretical values. Furthermore, we present new experimental data and compare different possibilities to improve the load transfer.

Specimens of carbon or glass fiber reinforced polymer can be imaged using both conventional laboratory X-ray micro-computed tomography equipment and synchrotron light sources. The image quality when using intense (partially) coherent synchrotron light is still superior, especially when applying phase-retrieval algorithms. In the resulting volume images, the fiber direction distribution and other mechanically relevant parameters such as volume fractions or layer thickness can be determined. In this contribution, we will demonstrate how fiber direction results can be used to detect regions with locally different fiber orientations in carbon or glass fiber reinforced polymer which arise in the molding process of such samples. To this end, we evaluate the three-dimensional fiber orientation tensor locally across the thickness of different specimens. For each resulting individual layer, we can automatically detect the layer thickness and the preferred fiber direction. These methods have been successfully applied to various commercial specimens. We will demonstrate results on volume images of samples from both synchrotron and laboratory micro-computed tomography and discuss the specific advantages and disadvantages in this application.

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Today in most cases crash absorber elements are made of metals. Those materials absorb the energy during a crash event by ductile plastification, as e.g. by buckling. Fiber reinforced polymers (FRP) offer due to their heterogenic structure several failure mechanisms for energy absorption under compressive load, such as fiber-break, matrix-break, delamination, fiber pull-out, fiber-matrix-interphase failure and friction processes. This in combination with the low density leads to significantly better specific energy absorption of FRP absorbers (50 J/g to 200 J/g FRP, 20 J/g steel, 40 J/g aluminum). But in case of tensile load fiber reinforced polymers break brittle and the energy absorption level is low. Today as a consequence of rising energy costs FRP with their good specific mechanic properties are used more and more also for crash relevant structures as in automobiles and aircrafts. For this applications a good crash behavior in both cases, compressive and tensile loading, is important. The integration of metal elements in FRP-structures offers the possibility to improve the tensile crash behavior of fiber reinforced polymers as the metal elements can prevent a catastrophic failure of the structure in case of FRP-break and distributes the load during tensile deformation on a larger FRP volume. The integration of shape memory alloys (SMA) with their pseudoplastic martensitic detwinning plateau allows for manufacturing of an “endless” crash absorber in case of tensile load. Required is a well dimensioned structure of shape memory alloys, e.g. a wire mesh, the FRP component and their interface. Doing so, it is possible to get huge number of breaks in the SMA reinforced FRP. The pseudoplastic detwinning plateau and the huge strain hardening of the SMA material ensure that after a FRP-break and the drop of the force level associated therewith the force level in the whole structure raises again so that another FRP-break is initiated. Also the reinforcement prevents a complete failure of the structure. In this contribution we present a theoretical extrapolation of the behavior of these new hybrid structures under tensile loading, give an estimation of their potential and demonstrate a first experimental validation of this new concept.