Constitutive Equation for Stainless Steel Used in Structural Engineering
Stainless steel is characterized by nonlinear stress-strain behavior, material anisotropy and different mechanical properties in tension and compression. As a result, it is necessary to define stress-strain relations of stainless steel precisely for the researches of mechanical behavior and stability of stainless steel member. This paper reviews the researches in constitutive relations models home and abroad, after introducing, analyzing, comparing the exist models, presents the three-stage stress-strain model proposed by Quach, which is defined using the three basic Ramberg-Osgood parameters and could be used in structural design by the current codes, considering the Quach equation as the most accurate constitutive equation for stainless steel material.
Mechanical Properties of Stainless Steel Lipped Channels
SUMMARY This paper describes and discusses the results obtained from a series of tensile tests performed on cold formed stainless steel Type 304 members of lipped channel cross-section. Standard tensile tests on coupons cut from the webs of the sections were carried out, as were full section tensile tests. Ramberg-Osgood type curves based on the procedure suggested in the ASCE design code were fitted to the stress-strain results and these are compared with the experimental results and Ramberg-Osgood type curves derived on an alternative basis.
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.