This paper presents an experimental investigation on the effect of structural (geometrical) design on the thermomechanical behavior of shape memory polymers. Three beams with identical dimensions (length, width, and thickness), material, and mass, but with different geometrical cells (honeycomb, diamond, and rounded rectangle) are designed by solving a set of nonlinear equations and produced using additive manufacturing method. Then, thermomechanical tests under bending and tensile loading at different temperatures are conducted. As a result, shape recovery and force recovery of the beams, due to the shape memory behavior of the material, are measured. In bending and tensile tests, shape and force recovery results of each beam are compared with their own pre-force and other beams. According to the results, the beam with rounded rectangle cells has the most shape recovery and force recovery ratios (compared to its applied pre-force). Shape recovery for this beam type in bending and tensile tests is 93.03% and 87.86%, respectively. The beam with honeycomb cells requires more pre-force in bending and tensile modes for programming, which leads to a higher maximum force recovery, due to its higher strength.

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An exact frequency analysis of a rotating beam with an attached tip mass is addressed in this paper while the beam undergoes coupled torsional-bending vibrations. The governing coupled equations of motion and the corresponding boundary condition are derived in detail using the extended Hamilton principle. It has been shown that the source of coupling in the equations of motion is the rotation and that the equations are linked through the angular velocity of the base. Since the beam-tip-mass system at hand serves as the building block of many vibrating gyroscopic systems, which require high precision, a closed-form frequency equation of the system should be derived to determine its natural frequencies. The frequency analysis is the basis of the time domain analysis, and hence, the exact frequency derivation would lead to accurate time domain results, too. Control strategies of the aforementioned gyroscopic systems are mostly based on their resonant condition, and hence, acquiring knowledge about their exact natural frequencies could lead to a better control of the system. The parameter sensitivity analysis has been carried out to determine the effects of various system parameters on the natural frequencies. It has been shown that even the undamped systems undergoing base rotation will have complex eigenvalues, which demonstrate a damping-type behavior.

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Mechanical properties and manufacturing processes of Glass Fiber/Polypropylene (GF/PP) composites for application of flexible internal long bone fracture fixation plates have been investigated. PP/Short Chopped Glass Fiber (PPSCGF), PP/Long Glass Fiber (PPLGF) and PP/Long Glass Fiber Yarn (PPLGFY) were used in fabrication of the fixation plates. The PPSCGF and PPLGF plates were made by the heat-compressing process and Three-dimensional (3D) printing method was used to make the PPLGFY ones. The values of Young’s modulus, tensile strength, flexural modulus and strength, and impact strength of the PPSCGF in the fiber longitudinal direction were found to be [Formula: see text]GPa, [Formula: see text]MPa, [Formula: see text]GPa, [Formula: see text]MPa and [Formula: see text]kJ/m2, respectively. Where, these values for the PPLGF were to [Formula: see text]GPa, [Formula: see text]MPa, [Formula: see text]GPa, [Formula: see text]MPa, and [Formula: see text]kJ/m2 and for the PPLGFY were to [Formula: see text]GPa, [Formula: see text]MPa, [Formula: see text]GPa, [Formula: see text]MPa and [Formula: see text]kJ/m2. These have been found to be in close agreement with the human bone properties. Furthermore, the strength and modulus values of the plates were reasonable to be used as a bone implant applicable for bone fracture reconstructions. Hence, the study concluded that the GF/PP composites are useful for load-bearing during daily activities and would be recommended as a choice in orthopedic fixation plate applications. It will help the researchers for development of new fixation designs and the clinicians for better patient’s therapy in future.

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Due to their functional and biological benefits, shape memory polymer (SMP) stents have attracted the attention of researchers in the biomedical science area. The highlights of this article are the evaluation of stent performance including radial force recovery and recovery start temperature (RST) in a constrained state. The effects of polyurethane (PU) mechanical properties and fabrication method are investigated on thermo-viscoelastic properties, sample defect and shape recovery of PU and polycaprolactone (PCL) blend. Thereafter, three tubular stents fabricated with the different diameter to thickness (d/t) ratio and their mechanical behavior are examined in loading, relaxation, and unloading. Finally, the radial force recovery of the stents is measured after stimulation in temperatures up to 45 °C. Emerging more peaks in the delta tangent graph implies that samples fabricated with solution-mixing has a better viscoelastic behavior and shows fewer defects compared to the melt-mixing ones. The fabrication method was much more effective on enhancement of the storage and loss modulus compared to double increasing of Young's modulus of applied PU from 4.3 to 9 MPa. Moreover, an increase in the stent's d/t from 15 to 10 causes not only an increase in the radial stiffness and force recovery but also leads to the reduction of irreversible deformation and RST. The results of this research reveals the importance of the dimensional and geometric design of SMP stents in controlling the force recovery and RST.

Shape memory polymer composites have attracted significant attention due to novel properties and great applications. In this article, we focus on the fabrication and simulation of polyurethane/polycaprolactone nanocomposites. The polyurethane/polycaprolactone blends containing ZnO nanoparticles (5 to 30 wt%) are fabricated using a solution mixing and casting method. It is found that significant improvement of polyurethane/polycaprolactone composites in Young’s modulus is achieved by incorporating 20 wt% of ZnO nanoparticles; also, the results of the shape recovery ratio reveal that adding an optimum amount of ZnO (the reinforcement) can increase the shape recovery ratio (for 20 wt% of ZnO). These results could most likely be explained by the fact that some particles restrict the hard segment–soft segment interactions and provide more mobility to polycaprolactone components, while the other nanoparticles can act as the nucleating agent for polycaprolactone chains. A generalized Maxwell model is then used to examine the shape memory behavior of shape memory polymer composites. The dynamic mechanical thermal analysis results are utilized to define the model coefficients and the simulation is carried out to determine the shape recovery ratio. Simulation of this shape recovery ratio for shape memory polymer composites reveals that the numerical results are in good agreement with those of the experimental data.