جستجوی مقالات مرتبط با کلیدواژه « shape recovery » در نشریات گروه « مکانیک »

4D printing is an emerging technology in which the printed parts can change their shapes when exposed to an external stimulus. In this research, a relationship between the pre-stress stored in the printed discs and the amount of shape recovery was obtained using FE simulations. Then, the effect of layer height, bed temperature, nozzle temperature, and printing speed on the amount of pre-stress applied in the printed discs based on polylactic acid material in the Fused deposition modeling 3D printing was investigated. In this paper, 27 experimental tests were performed using a central composite design, and modeling was done with the least cost and time and the most reliability and accuracy. Then a relationship between the mentioned parameters and the amount of pre-stress applied to the printed discs was obtained. R2 and Adj R2 of the model were obtained more than 99% which shows the high accuracy of the model. In order to validate the experimental model, simulation and experimental tests were carried out in the conditions of the highest amount of shape recovery. The results showed that the experimental model error is 5.9% and the error between the applied pre-stress and the amount of shape recovery is 2.95%.

Shape memory polymers are a type of smart materials that can recover their original shape when exposed to external stimuli including temperature, magnetic field, light, and electric field. One of the most widely used of these polymers is thermalresponsive shape memory polymers. These polymers have advantages such as a high percentage of shape recovery and low cost and using them results in reducing complex mechanisms that lead to reducing the weight and volume of the systems. Thermalresponsive shape memory polymers have been used in many fields, including medicine, robotics, mechanics, and aerospace and have led to great changes. This paper aims to study thermal-responsive shape memory polymers behavior and their different applications. In fact, by investigating the thermomechanical cycle, constitutive models, different kinds of shape memory effect, different applications, their future, and challenges of these polymers including low recovery force and its solution and preparation of various tables from recent researches, these materials have been comprehensively studied. Due to the unique properties of these polymers and the effort to overcome their limitations, they will become a candidate for many self-assembled mechanical actuators in the future.

Memory-shaped polymers are thermally induced subsets of intelligent materials that require thermomechanical behavior to accurately understand their function. In this study, polymeric memory scaffolds were fabricated using polylactic acid by molten labeling method in three reticular honeycomb, rhombic and elliptical form. Parameters such as longitudinal dimensions and wall thickness of printed scaffolds compared to the designed scaffolds and solutions were presented to enhance the printing accuracy. Built-in scaffolds can be a good option for stent use. Formal memory properties experiments with 30% axial strain were performed to study the shape memory behavior of polymer on scaffolds. The results showed that the percentage of shape recovery in scaffolds with symmetric angular grid networks was higher than elliptical reticular stents. The minimum percentage of longitudinal recovery belonged to the elliptical reticular stent and was 74.5%. The percentage of longitudinal recovery of honeycomb and rhododendron reticular stents is approximately equal to 80.3%. The results of this study can be used to optimize the stent grid geometry to increase the retrieval force to resolving vascular clogging.

Shape memory polymers (SMPs) have the ability to store the deformation and recover the original shape. Shape memory behavior is associated with two features: shape recovery and stress recovery. Full shape recovery and increase the stress recovery value are the challenges ahead of the SMPs. In this paper, the polyurethane and polycaprolactone (PCL) were blended. The thermal stimulated SMPs ware fabricated by melt mixing and solution mixing method and thermo-viscoelastic behavior of SMPs ware analyzed. Two types of polyurethanes with the same chemical structure were used as the hard phase and polycaprolactone was used as the soft phase in SMP blend. The results show that the solution mixing method has advantages such as proper appearance without defect, free from cracks and cavities, higher storage and loss modulus values without fluctuations over temperature. The blend of PCL with low hardness polyurethane one showed better shape memory behavior. In order to investigate the shape memory effect, shape recovery test was carried out with 25% pre-strain at 60°C. Also, the stress recovery was carried out by 25% pre-strain at different temperatures (60°C, 45°C and 37°C) on the samples made by solution method. The stress-recovery function was highly affected by the deformation temperature. The maximum stress and maximum recovery rate were observed in the sample with a deformation temperature of 45°C. A stent was made by the solution method and its shape recovery results showed that recovery was done completely in less than 0.5 seconds at 60°C.