M. Endo

Thermomechanical Properties of Polyurethane-Shape Memory Polymer Foam

The thermomechanical properties of polyurethane-shape memory polymer foam were investigated by the compressive tests. The results are summarized as follows. (1) The material contracts uniformly in the axial direction with the ratio of lateral strain to axial strain 0.4 in the early stage, but about 0.15 thereafter. (2) The deformation resistance is large at low temperature and at high strain rate. (3) In the case of thermomechanical loading, strain is recovered at temperatures in the vicinity of Tg. The rate of strain recovery is 99%. The rate of strain fixity is 100%.

Shape fixity and shape recovery of polyurethane shape-memory polymer foams

Abstract The thermomechanical properties of polyurethane shape memory polymer (SMP) foams were investigated experimentally. The results obtained can be summarized as follows. (1) By cooling the foam after compressive deformation at high temperature, stress decreases and the deformed shape is fixed. Stress decreases markedly in the region of temperature below the glass transition temperature Ts during the cooling process. (2) By heating the shape-fixed foam under no load, the original shape is recovered. Strain is recovered markedly at the temperature region in the vicinity of Tg. (3) The ratio of shape fixity is 100 per cent and that of shape recovery 98 per cent. Neither ratio depends on the number of cycles. (4) Recovery stress increases by heating under constraint of the fixed shape. Recovery stress is about 80 per cent of the applied maximum stress. Relaxed stress at high temperature is not recovered. (5) The shape deformed at high temperature is maintained for six months under no load at Tg’60 K without depending on maximum strain, and the original shape is recovered by heating thereafter. (6) If the deformed shape is kept at high temperature, the original shape is not recovered. The factors influencing the shape irrecovery are the holding conditions of strain, temperature, and time.

Thermomechanical Properties of Polyurethane-Shape Memory Polymer

The development of applications of shape memory polymers (SMPs) is currently of great interest [1–4]. Because SMPs are light, high in shape recovery, easy to manipulate and economical compared with shape memory alloy, their development is being actively promoted. In many SMPs, the phase transition temperature is around room temperature. Characteristics such as shape recovery and shape fixity exist due to the difference in mechanical properties of materials above and below the phase transition temperature. SMPs possessing these characteristics are being used as temperature sensors and actuators.

Deformation behavior of TiNi shape memory alloy under strain- or stress-controlled conditions

The deformation properties of TiNi shape memory alloy subjected to strain control and stress control were investigated experimentally. The result obtained are summarized as follows. In the case of full loop, the stress- strain curves under stress-controlled condition are similar to those under strain-controlled condition with high strain rate. The overshoot and undershoot do not appear at the start points of the stress-induced martensitic transformation in these curves. In the case of subloop under stress-controlled condition, temperature decreases and therefore strain increases owing to the martensitic transformation at the early stage in the unloading process. At the early stage in the reloading process, temperature increase and therefore strain decease owing to the reverse transformation. In the case of subloop under stress- controlled condition, the starting stresses of the martensitic transformation and the reverse transformation in the loading and unloading processes coincide with the transformation stresses under strain-controlled condition with low strain rate, respectively. The deformation behaviors for subloop under stress-controlled condition are prescribed by the condition for progress of the martensitic transformation based on the transformation kinetics. The deformation behaviors subjected to cyclic loading under stress-controlled condition at constant temperature are also prescribed by the condition for progress of the martensitic transformation.