A nonlinear coupled finite element model is developed to predict the behavior of large diameter tubes subjected to mechanical and thermal loadings during hot radial forging process. The model is formulated in a three-dimensional (3D) framework to account for both axial and circumferential effects. This model considers both material and geometric nonlinearities. A rate-dependent material model is used to describe the viscoplastic behavior of the workpiece subjected to high temperature and large strain. A tubular workpiece with the mandrel inside and four forging dies outside is modeled in commercial finite element code. A subroutine is developed and implemented to simplify the modeling process for radial forging simulation. Numerical results presented include residual stress, plastic strain, and temperature distribution along the axial and hoop directions in the deformed workpiece. Results are also presented for contact force to evaluate the performance of the die in the forging process. Finite element model predictions are compared with experimental and two-dimensional (2D) axisymmetric simulation results available in literature. A variety of case studies are conducted for hot radial forging process using the developed 3D model.

Sandwich composite structures are comprised of a low-density core (commonly honeycomb) and facesheets. They are typically used in applications that require lightweight for efficient design, such as in the marine and aerospace industries. This work investigates the feasibility of adopting triply periodic minimal surface (TPMS) cellular structures as the core for sandwich composites. Sandwich structures were manufactured using a carbon fiber-reinforced polymer (CFRP) facesheet and three different 304 L stainless steel core structures (honeycomb, gyroid TPMS, and diamond TPMS). Three mechanical tests, namely edgewise compression, three-point bend, and impact test, were carried out to evaluate the performance of each sandwich configuration. The experimental results of the non-traditional sandwich configurations were compared against those of a honeycomb core sandwich composite. The edgewise compression test showed that the ultimate edgewise compressive strength increased by 7% when the honeycomb core was replaced by the gyroid core and reduced by 2% when the diamond core replaced the honeycomb core. The three-point bend test showed that the traditional honeycomb core sandwich configuration had a higher shear yield stress when compared to the non-traditional sandwich structures. The shear yield stress was reduced by 54% when non-traditional sandwich cores were used. The shear ultimate stress was reduced by 41% and 37% when the honeycomb core was replaced by the gyroid and diamond structure, respectively. Impact test results, on the other hand, showed that the peak force recorded during the impact event was reduced, while the absorbed energy was increased when non-traditional cores were used. Peak force was reduced by 28% and 39%, while the absorbed energy was increased by 9% and 16% when the honeycomb core was replaced by the gyroid and diamond cores, respectively.

A sandwich structure consists of a two thin and strong facesheets, bonded to a thick lightweight core material. The mechanical response of a sandwich structure depends on the properties of its constituents. A numerical model and experimental validation of the three-point bending test of sandwich composites are presented in this study. The core material is aluminum honeycomb. The facesheets are made of IM7/Cycom5320-1, which is a carbon fiber/epoxy prepreg system. A comprehensive model of the failure under flexural loading was developed. Facesheet failure was modeled using Hashin’s failure criteria. A detailed meso-scale model of the honeycomb core was included in the model. The experiments indicated that failure initiation was due to local buckling in the honeycomb core. Failure propagation was in the form of core failure, facesheet compressive failure, and interlaminar failure. The developed meso-scale model was able to accurately simulate failure initiation and propagation in the composite sandwich structure. The effect of elevated temperature on the three-point bending behavior was studied numerically as well as experimentally. An increase in test temperature to 100°C resulted in a drop of 9.2% in flexural strength, which was also predicted by the numerical model.