Staff

Abstract:
Composite materials, particularly honeycomb composites, are widely utilized in various industries, including aerospace, due to their high energy absorption against the impact and exceptional strength-to-weight ratio. This study aims to leverage the plastic and elastic properties of these materials to develop a simplified numerical model that incorporates orthotropic properties for core modeling. By doing so, the need for detailed honeycomb structure modeling is eliminated, resulting in reduced computational costs and time. A comprehensive three-dimensional finite element model, accounting for structural intricacies, is presented based on experimental data from a reputable source (isotropic model) and its equivalent finite element model (orthotropic model). The model is validated by the experimental results, demonstrating good agreement. The study also investigates parameters such as energy absorption, the internal energy of the core and faces, maximum displacement, and maximum contact force under low-velocity impact scenarios with spherical and cylindrical projectiles. These findings highlight the effectiveness of the orthotropic model, particularly in showcasing greater energy absorption in the core of the sandwich panel when subjected to a cylindrical impactor.

Keywords:
honeycomb, sandwich panel, homogenization, finite element analysis, impact

Abstract:
This study consists of a statistical study to identify spatial distribution parameters of non-metallic inclusions (NMIs) at hydrogen-induced cracking (HIC) nucleation sites in both low-strength and high-strength steel pipes. The electrochemical cathodic charging method was used to induce HIC in pipeline steel plates, and the nucleation of the HIC was monitored using straight beam ultrasonic testing. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to evaluate the shape, size, area fraction, and separation distance of NMIs. The hydrogen microprint technique (HMT), electron backscattered diffraction (EBSD) analysis, and finite element (FE) stress analysis were performed to characterize HIC nucleation sites. The findings showed that cubical and spinal NMIs, characterized by strong hydrogen trapping capacity due to high misfit strain and von Mises stress, are favored sites for HIC nucleation. The main finding of this study is that the shape and sharpness of NMIs are the factors that determine when NMIs will be a HIC nucleation site, rather than size, as generally accepted.

Keywords:
Hydrogen-induced cracking, Statistical study, Non-metallic inclusions, Hydrogen microprint technique, Finite element stress analysis