Application of a NiTi alloy two-way shape memory helical coil for a versatile insulating jacket

As an application of two-way shape memory effect (TWSME), NiTi shape memory alloy (SMA) helical coils were incorporated into a cold weather jacket for intelligent insulation that senses and reacts to environmental conditions. The coils were annealed and thermo-mechanically trained such that the pitch of the coil is 10 mm or 15 mm under cold conditions and the coil is flat in warm conditions. The effects of the TWSMA coils on insulation and temperature buffering properties of the clothing system were evaluated under transient temperatures (30 °C, 55% relative humidity to 0 and −5 °C, 19% relative humidity) using a human-clothing-environment simulator. The flat coils at 30 °C were expanded at both 0 and −5 °C spontaneously, creating an adequate air layer between the adjacent layers of the clothing system. Consequently, the microclimate temperatures were raised and buffering effects upon a sudden drop of environmental temperature as well as thermal insulation were improved. The insulation effects increased as the pitch of the coil increased. The wearers reported a warmer feeling with the TWSME coil attached clothing system. However, the reported thermal feeling ratings did not show statistically significant differences except at the moment of the transition point. The results point toward the possible application of TWSME using SMAs in the development of intelligent garments and provide useful insights into the further studies for practical use.