https://scholarworks.bwise.kr/kumoh/handle/2020.sw.kumoh/20 2026-03-07T12:54:39Z https://scholarworks.bwise.kr/kumoh/handle/2020.sw.kumoh/28974 Title: Mechano-chemical degradation effects on slow crack growth in polyethylene pipes with multiple cracks Authors: Wee, Jung-Wook; Chudnovsky, Alexander; Deveci, Suleyman; Choi, Byoung-Ho Abstract: In a chemically aggressive environment, polyethylene pipes are affected by oxidation-induced brittle fracture as follows: (i) multiple crack initiation through a thin degradation layer, (ii) mechano-chemical discontinuous slow crack growth of a main crack, and (iii) eventual fast fracture. A new analytical model for the second stage is proposed based on a modified crack layer theory. The mechano-chemical degradation of the process-zone medium was modeled theoretically by diffusion-reaction equation. Interactions between cracks immediately follow multiple crack initiations based on Green's function. Also, the parametric study involved several model parameters to provide a physical explanation. Further, this study proposed a theoretical method to estimate the crack lifetime by simulating crack initiation and slow crack growth periods, providing a new framework for predicting the durability of polyethylene pipes under aggressive chemicals. 2024-11-01T00:00:00Z https://scholarworks.bwise.kr/kumoh/handle/2020.sw.kumoh/28952 Title: Unraveling the effects of asymmetric interfaces in three-dimensional solid oxide fuel cells Authors: Goh, Young Gyun; Kim, Jeong Hun; Kim, Hyoungchul; Shin, Sung Soo Abstract: The three-dimensional (3D) structuring of interfaces in solid oxide fuel cells (SOFCs) is a valuable morphological approach that maximizes the reaction area and ion transfer pathways, enabling operation at lower temperatures. To quantify the performance improvement attributable to these 3D interfaces, analyzing their effects on both the anode and cathode sides is necessary. In this study, we fabricated an SOFC with asymmetric, a microscale prism-shaped anode/electrolyte interface and a planar electrolyte/cathode interface. This was achieved using an integrated approach involving ceramic micropatterning and subsequent electrospray deposition. The fabricated 3D cell achieved a 42.8% increase in peak power density (1.115 W cm-2) at 650 degrees C relative to a reference cell with planar interfaces on both sides of the electrolyte layer. It also exhibited reductions of 38.4% and 23.9% in area-specific ohmic and area-specific polarization resistance (0.053 and 0.162 Omega cm2), respectively. Additionally, under controlled gas partial pressure conditions for the anode and cathode, the effects of the asymmetric interfaces on the electrochemical performance of the cell were evaluated via advanced electrochemical impedance analysis. The three-dimensional (3D) structuring of interfaces in solid oxide fuel cells (SOFCs) is a valuable morphological approach that maximizes the reaction area and ion transfer pathways, enabling operation at lower temperatures. 2024-09-01T00:00:00Z https://scholarworks.bwise.kr/kumoh/handle/2020.sw.kumoh/28955 Title: Plasticization-assisted slow crack growth modeling of high-density polyethylene Authors: Almomani, Abdulla; Wee, Jung-Wook; Deveci, Suleyman; Mourad, Abdel-Hamid I. Abstract: The existing crack layer model can theoretically predict the slow crack growth behavior of high- density polyethylene. However, it can only be applied to oxidative environments causing chemical degradation. Most oil and gas field components, such as pressurized pipes, are subjected to hydrocarbon exposures, leading to a plasticized material response, i.e., shear yielding instead of crazing. Therefore, the effect of such sorptive media diffusion on the slow crack growth behavior and lifespans tf f should be understood. In this work and for the first time, a novel crack layer model is developed that can simulate the diffusion-assisted slow crack growth behavior of plasticized high-density polyethylene. The proposed model was validated by comparing its prediction with experimental results and by conducting a sensitivity study on several input parameters. Using the proposed model, the reported plasticization results were reconstructed successfully including the SCG rate with R 2 = 0.95. This study expands the applicability of the crack layer model for the reliability assessment of polyethylene pipes under various environmental conditions, including plasticizers. 2024-09-01T00:00:00Z https://scholarworks.bwise.kr/kumoh/handle/2020.sw.kumoh/26476 Title: Brittle-Ductile Transitions of Rubber Toughened Polypropylene Blends: A Review Authors: Wee, Jung-Wook; Chudnovsky, Alexander; Choi, Byoung-Ho Abstract: Polypropylene (PP) blended with rubber particles has been recognized for significantly increasing impact resistance, which is increasingly demanded in industries such as electric vehicles and consumer electronics. However, a comprehensive understanding of the toughening mechanisms underlying these lightweight impact-resistant materials is imperative for future research. This article provides a detailed review of the ductile-to-brittle (DB) transition behavior and the improvements in impact resistance observed in rubber-toughened PP blends. Firstly, the fracture behavior of homogeneous PP is summarized across different strain rates and temperatures, including the DB transition and yielding and crazing criteria. Furthermore, the influence of notches and defects on the DB transition is discussed extensively. Subsequently, the article examines the theoretical and practical aspects of the toughening mechanisms facilitated by the rubber phase in PP-rubber blends. The percolation model is used to investigate the inter-distance criterion between neighboring rubber particles and the impact of particle size and content on toughening behavior. The primary objective of this article is to enhance the understanding of the toughening behavior exhibited by PP and rubber blends. Additionally, this study aims to provide valuable insights for developing advanced lightweight materials using PP-based blends for various industrial applications. 2024-07-01T00:00:00Z