Optimization of the interface between shape memory alloys and epoxy matrix systems to enhance active composite structures

Abstract The presented research provides an investigation into the interface between shape memory alloys (SMA) and epoxy resin based matrix system representative as used in adaptive composite structures. The wire, made of a Nickel-Titanium alloy, is treated with mechanical, chemical and physical methods with the goal to adjust the adhesion between actuator and matrix. Two different experimental plans are designed. One aims at increasing the adhesion for a better force transmission. The second one investigates methods to lower the interfacial shear strength to reduce movement resistance while the SMA contracts. The different treatments are not only tested individually, but also in combination to determine possible synergies. The quality of the interface is tested using pull-out tests, where a single wire is pulled-out of a pure epoxy resin block. The results are then compared in terms of the maximum pull-out force. It shows that the adhesion can be increased through the use of mechanical sanding, plasma treatments and application of a bonding agent. The maximum effect results in an increase of 130% in pull-out force from a combination of sanding and bonding agent. On the opposite, the processes for the adhesion reduction show less effective. Only the usage of a release agent with or without a previous plasma treatment resulted in a slight decrease in interfacial shear strength. The interfacial shear strength appears already low for the origin state of the SMA. In the result, the present research provides successful routines to increase the adhesion for epoxy-based composites with integrated SMA wire actuators but does not recommend any procedures for the reduction of adhesion as the investigated approaches only showed marginal effects.