Multifunctional polyurethane shape memory polymers (PU-SMPs) have been of increasing interest in various applications. Here we report structure characterization, detailed methodology, and obtained results on the identification of functional properties of a thermoset PU-SMP (MP4510) with glass transition temperature of 45 °C. The stable, chemically crosslinked network of this thermoset PU-SMP results in excellent shape memory behavior. Moreover, the proximity of the activation temperature range of this smart polymer to room and body temperature enables the PU-SMP to be used in more critical industrial applications, namely fast-response actuators. The thermomechanical behavior of a shape memory polymer determines the engineering applications of the material. Therefore, investigation of the shape memory behavior of this class of commercial PU-SMP is of particular importance. The conducted structural characterization confirms its shape memory properties. The shape fixity and shape recovery properties were determined by a modified experimental approach, considering the polymer’s sensitivity to external conditions, i.e., the temperature and humidity variations. Three thermomechanical cycles were considered and the methodology used is described in detail. The obtained shape fixity ratio of the PU-SMP was approximately 98% and did not change significantly in the subsequent cycles of the thermomechanical loading due to the stability of chemical crosslinks in the thermoset materials structure. The shape recovery was found to be approximately 90% in the first cycle and reached a value higher than 99% in the third cycle. The results confirm the effect of the thermomechanical training on the improvement of the PU-SMP shape recovery after the first thermomechanical cycle as well as the effect of thermoset material stability on the repeatability of the shape memory parameters quantities.

The purpose of this study was to assess the behavior of laminated thermoforming materials in an underwater environment to understand the durability of mouthpieces for scuba diving. Two thermoforming materials, polyolefin (PO) and ethylene-vinyl acetate copolymer (EV), were laminated and stored in air, 37°C water, and 37°C water under 0.2-MPa pressure for 1 and 4 weeks . The load/ bonding width (bonding strength: BS) and displacement at the start of delamination (SD) and fracture (FR) were analyzed with 3-way ANOVA. BS values at SD and FR in air were significantly greater than those under the other conditions, and the BS at SD of EV was significantly greater than that of PO, though the effects of materials, duration and their interactions were not significantly different. The displacements at SD and FR were significantly influenced by the material. These results suggest that both materials can be employed for making a diving custom mouthpiece.

The transformation-induced stress relaxation and stress recovery of TiNi shape memory alloy (SMA) in stress-controlled subloop loading were investigated based on the local variation in temperature and transformation band on the surface of the tape in the tension test. The results obtained are summarized as follows. (1) In the loading process, temperature increases due to the exothermic martensitic transformation (MT) until the holding strain and thereafter temperature decreases while holding the strain constant, resulting in stress relaxation due to the MT; (2) In the unloading process, temperature decreases due to the endothermic reverse transformation until the holding strain and thereafter temperature increases while holding the strain constant, resulting in stress recovery due to the reverse transformation; (3) Stress varies markedly in the initial stage followed by gradual change while holding the strain constant; (4) If the stress rate is high until the holding strain in the loading and unloading processes, both stress relaxation and stress recovery are large; (5) It is important to take into account this behavior in the design of SMA elements, since the force of SMA elements varies even if the atmospheric temperature is kept constant.

We demonstrated source gas depletion in our proposed method for internal diamond-like carbon (DLC) coating with microwaves by using high-speed camera imaging of the emission from Ar atoms and C₂dimers during DLC coating. Then, we investigated the effect of the plasma-on time on the axial distribution of the film thickness, hardness, and other properties. The axial variation in DLC coated inside a 1/4-in. stainless steel tube 50 mm in length was greatly reduced from 14% with a plasma-on timeT_on= 3.2 ms and a plasma-off timeT_off= 96.8 ms in our previous work to 2% withT_on= 1.6 ms andT_off= 98.4 ms in this work. The coating conditions except forT_onandT_offwere the same in both experiments. The decrease in the DLC film hardness with increasing plasma-on time was confirmed and is ascribed to a decrease in the film density and number of sp³carbons in the film.

Advanced subjects in mechanical properties of shape memory alloys and polymers are di- scussed. In the subloop loading under a stress-controlled condition of the shape memory alloy, the transformation-induced stress relaxation appears due to variation in temperature. The enhancement of corrosion and corrosion fatigue life of the shape memory alloy is discus- sed. The development of a functionally-graded shape memory alloy and polymer is expected to obtain better performance. Three-way motion appears in the shape memory composite with the shape memory alloy and polymer.