Microstructural Adjustment of the Degenerated Graphite Layer in Ductile Iron for Targeted Evaluation on the Fatigue Properties

Graphite degeneration is the most prominent microstructural defect in the casting skin of ductile iron. Induced by either sulfur or oxygen contained in the molding material, its occurrence can be observed in a large range of iron castings, having substantial negative influences on the mechanical properties, especially fatigue resistance. Previous investigations predominately focused on the influence of the degenerated graphite layer, while accompanying changes of the iron matrix were neglected. The superposition of these effects hinders the evaluation of casting skin defects in state-of-the-art design of ductile iron components. The presented solution utilizes an experimental procedure, which enables the production of specimens with specific, individual microstructural configurations in the casting skin. This approach is based on the application of a modified sand core coating. By adding sulfurizing additives to the coating and adjusting its binder content and viscosity, a predominately homogeneous degenerated layer of 0.5 mm thickness was obtained. Using specific heat treatment steps assured a fully ferritic or pearlitic iron matrix, isolating the degenerated layer as the main microstructural defect. Fatigue testing of these specimens will further enable the numerical evaluation of the fatigue resistance in dependence of the casting skin microstructure.

Simvastatin Improves the Jaw Bone Microstructural Defect Induced by High Cholesterol Diet in Rats by Regulating Autophagic Flux

Objective. The objective of this study is to evaluate the effect of simvastatin on the jaw bone microstructural defect and autophagy in rats with high cholesterol diet (HCD). Methods. Male Sprague-Dawley rats were fed a standard rodent chow (NC group) or a high cholesterol diet for 32 weeks and the HCD-fed rats were treated with vehicle (HC group) or simvastatin (5 mg/kg orally daily for 8 weeks, HC + SIM group, and n=10/group). The static histomorphometric changes in the jaw bone tissues in individual rats were evaluated. The relative levels of OPG, RANKL, NF-κB, LC3, and p62 in the jaw bone tissues were determined by quantitative RT-PCR and/or immunohistochemistry. Results. Compared with the NC group, the HC groups had lower trabecular bone volume, trabecular thickness and trabecular number, and increased ratios of RANKL/OPG in the jaw bone, accompanied by enhanced NF-κB activation and autophagy. Simvastatin treatment inhabited these changes, including the decreased levels of serum proinflammatory cytokines and increased autophagy. Conclusion. Simvastatin treatment could inhibit the hyperlipidemia-induced jaw bone microstructural defect in rats by increasing autophagic flux.