Fatigue tests under multiaxial loading were conducted on Ni-based superalloy GH4169 tubular specimens. The microstructures of fracture surfaces under different loading paths were compared. Several multiaxial fatigue criteria were reviewed and evaluated with multiaxial fatigue test data. The criteria of equivalent strain, maximum shear strain and Kandil–Brown–Miller provided unsatisfactory results for GH4169. Fatemi–Socie and Wu–Hu–Song parameters showed better life prediction abilities for this material. Minor modification has been introduced in Wu–Hu–Song parameter. The material constants of modified Wu–Hu–Song criterion are only dependent on torsional fatigue tests. The satisfactory prediction results based on modified Wu–Hu–Song model were obtained for GH4169.

Multistage fatigue tests were conducted on the single-edge-notch tension specimens of Ni-based superalloy GH4169. Fatigue crack growth data at different stages were recorded with the surface replica technique. Continuum damage mechanics incorporating critical distance theory was used to evaluate fatigue crack initiation life. Then, small and long fatigue crack grow rates were modeled using Shyam's model and modified Paris law, respectively. Finally, the multistage fatigue model deriving from the above theories was proposed to predict total fatigue life of GH4169. Fatigue life prediction results show that the proposed multistage fatigue model has high accuracy for GH4169.

Compared to traditional temperature control methods, the electrocaloric (EC) effect offers several advantages such as small size, rapid response, and environmental friendliness. However, current EC effects are generally used for the cooling area rather than heating. Here, poly(vinylidenefluorideter-trifluoroethylene-ter-chlorofluoroethylene) [P-(VDF-TrFE-CFE)] film is combined with an electrothermal actuator (ETA) composed of polyethylene (PE) film and carbon nanotube (CNT) film. The heating and cooling process of the EC effect is used to help drive the ETA. The P(VDF-TrFE-CFE) film can produce a temperature change (ΔT) of 3.7 °C at 90 MV/m, and this process occurs within 0.1 s. With this ΔT, the composite film actuator can produce a deflection of 10°. In addition, due to the electrostrictive effect of P(VDF-TrFE-CFE), the composite film can also be used as an actuator. At 90 MV/m, the composite film actuator can produce a deflection over 240°w ithin 0.05 s. Apart from other current driving modes for thermally responsive actuators, in this paper, a new type of soft actuating composite film by the temperature change of the EC effect is proposed. Except from ETAs, the EC effect can also have a wide application prospect in other thermally responsive actuators, including shape memory polymer actuators, shape memory alloy actuators, and so on.