Design, manufacturing, and verification of laminates with embedded SMA actuators

Fiber reinforced thermoplastics offer some substantial advantages over fiber reinforced thermosetts. Besides high specific stiffness and strength and excellent resistance to impact damage, especially with respect to the manufacturing process, considerable cost reductions can be realized due to the reduction of the processing times. However high process temperatures (250 degrees Celsius to 400 degrees Celsius) can be problematic with respect to the embedding of shape memory wires as actuators. Moreover the adhesion between the sma wires and the matrix must be carefully taken into consideration. Therefore different thermoplastic matrix systems such as polyetherimid and polyamid were chosen. To get some comparative results a classical duroplastic matrix was included into the investigations. Before embedding the sma- wires were characterized with respect to their thermo-mechanical properties. Among other things differential scanning calorimetric tests were performed to determine the phase transition temperatures. Moreover the necessary current for the phase transition as a function of time was measured. To manufacture specimens by different manufacturing processes such as autoclave forming, power press, or diaphragm forming, a universal mold was designed which allows a variable pre-straining of the sma-wires. Moreover the number of embedded wires can be adapted to control the fiber volume fraction of active wires. With the manufactured specimen numerous verification tests were performed as static and dynamic deflection measurements as function of time and current. The adhesion of the embedded wires was measured by pull-out tests. As a global result it turns out that the polyamid matrix is the best host material among the compared matrix systems.