چكيده لاتين
Four-dimensional (4D) printing is a new technology that adds the dimension of time to three-dimensional (3D) printing. In this method, the printed structure changes shape over time in response to stimuli such as heat, light, and humidity. Among these stimuli, heat is considered one of the most common activation factors for these structures. One of the challenges in 4D printing is controlling these structures. This study aimed to control these structures by adjusting the printing parameters. In this study, a comprehensive investigation was conducted on the influence of process parameters in a fused deposition modeling printer on bending deformation, as well as the time and temperature required for heat activation of strip-shaped samples made of polylactic acid. Each parameter was examined as changes of one factor at a time. The results of the study indicated that layup, layer thickness, printing speed, and nozzle temperature had the most significant impact on the amount of bending deformation at the selected levels. To optimize the bending deformation, the Taguchi design of experiment was used, selecting the four most influential parameters. An L18 Taguchi orthogonal array was employed with three parameters having three levels and one parameter having two levels. The results indicated that the most effective printing parameters among the selected surfaces are layer thickness, layering, nozzle temperature and printing speed, respectively. Also, the prediction of the optimal state of Taguchi design with the experimental value showed a difference of less than two percent. The optimal sample was selected for the numerical study, and tests were conducted on the optimal specimen, including differential scanning calorimetry, dynamic mechanical thermal analysis, and uniaxial tensile testing. These tests were performed to obtain specific heat values, changes in elastic modulus, and Poissonʹs coefficients. In this study, an innovative method utilizing digital image correlation was employed to determine thermal expansion coefficients. It was also proven that 3D-printed polylactic acid can exhibit transverse isotropic behavior. Using the transformation relationship from Poisson’s ratio ν12 to ν21 for transversely isotropic materials, an error of 3.45% was obtained. The data obtained from these different experiments were then inputted into the ABAQUS to model both the shell and solid behaviors in bending mood and the shell behavior for torsional deformation of a transversely isotropic material. To reduce the computational load in the numerical study, the expansion coefficients of the intermediate layers were first determined using the trial-and-error method in the shell modeling approach. The results obtained from the shell modeling for bending deformation demonstrated an error of 0.79% in the longitudinal direction and 6.03% in the transverse direction when compared to the values obtained from the experimental study. For the solid modeling, the maximum errors were 3.08% and 4.85% in the longitudinal and transverse directions, respectively. Also, the simulation result for torsional deformation showed an error of less than 10% compared to the experimental test. Ultimately, it can be stated that the modeling approach in this study has the potential to be extended to various types of deformations. These deformations, due to their common occurrence, can be utilized in applications such as clamps, hinges, and medical stents
