Effect of Curvature on the Impact Damage Characteristics and Residual Strength of Composite Plates
The results of a study of the response and failure characteristics of thin, cylindrically cusrved, composite plates subjected to low-speed impact damage are presented. The results indicate that the plate radius and the plate thickness are important structural parameters that influence the nonlinear response of a plate for a given amount of impact energy. Analytical and experimental contact-force results are compared for several plates and the results correlate well. The impact-energy levels required to cause damage initiation and barely visible impact damage are a function of the plate radius for a given plate thickness. The impact-energy levels required to initiate impact damage for plates with a certain range of radii are greater than plates with other radii. The contact-force results corresponding to these impact-energy levels follow a similar trend. Residual strength results for plates with barely visible impact damage suggest that the compression-after-impact residual strength is also a function of plate radiu. The residual strength of impact-damaged flat plates appears to be lower than the residual strength of the corresponding cylindrically curved plates.
NONLINEAR RESPONSE AND DAMAGE-INITIATION CHARACTERISTIC S OF CURVED COMPOSITE PLATES SUBJECTED TO LOW-SPEED IMPACT
The results of an analytical and experimental study of the impact response of thin curved plates is presented. The geometrically nonlinear analysis method used in the study is described. The analysis is based on the Lagrangian equations of motion which are solved using the Rayleigh-Ritz method and assumed mode shapes. Generalized beam functions are used to represent different boundary conditions. The nonlinear terms in the analysis that contribute to the softening of the response are identified. The analytical results correlate well with the experimental results. The experimental results indicate that the radius of curvature and thickness of the curved plates are the primary parameters that influence the nonlinear response of an impacted curved plate. The magnitude of the maximum contact force associated with impact decreases and then increases as the plate radius of curvature increases for a given thickness and given impactor parameters. The impact-energy level required to initiate damage for a given thickness is a function of panel radius of curvature, and this impact-energy level generally increases as the panel radius of curvature decreases. The magnitude of the impact contact force is not always the primary cause of damage initiation. The combination of plate radius of curvature and thickness strongly influence the magnitude of the impact contact force, the damage modes, and the impact energy required for damage initiation.
Cross talk between redox signalling and metabolic activity of osteoblasts and fibroblasts in the presence of hydroxyapatite-based biomaterials influences bone regeneration
Regeneration of bone tissue defects that result from metabolic disorders, including periodontal diseases, can be supported by biomaterials based on hydroxyapatite. Despite of good biocompatibility of biomaterials they can cause oxidative stress and inflammatory processes as a result of mechanical interaction with surrounding tissues. Because osteoblasts are responsible for bone regeneration process in which gingival fibroblasts may also participate, the aim of the work was to investigate the influence of hydroxyapatite-based biomaterials (allogeneic and xenogeneic) and biomaterials combined with enamel matrix derivative (Emdogain) on osteoblast and fibroblast redox balance in the context of osteoblast proliferation and differentiation.
The results showed that examined substitutes were not cytotoxic in vitro, but affected redox balance of osteoblasts and fibroblasts (ROS level increase and GSH level decrease) which led to oxidative stress (MDA and protein carbonyl groups level increase) resulting in an increase of the Nrf2 and NFκB expression. The consequence of these changes was partial inhibition of proliferation and osteoblast differentiation. Emdogain alone and combined with biomaterials decreased ROS generation and increased GSH level in both osteoblasts and fibroblasts leading to reduction of transcription factors expression especially proinflammatory NFκB, which promoted osteoblast differentiation and mineralization process.