IDENTIFICATION OF CRACK APPEARANCE BY SOUND EMISSION DURING STEEL QUENCHING
Heat treatment, especially quenching and tempering often represent almost the final stage of manufacturing process in the production of machine components. Only the most exacting piece of work like grinding, polishing etc. follows. Final mechanical properties, such as residual stresses and hardness layer, therefore depend on optimum parameters of a quenching process and monitoring of the process itself. Even then happens that some work-pieces failed also due to cracking of the material. Detecting such faults in the due time may reduce unnecessary costs due to final machining of the machine part or even due to damage of the machine occurred due to machine part breakdown. The paper treats an experimental setup comprising detection of sound emission in the course of quenching process. Due to heat transfer from a specimen’s surface to a quenching medium, film boiling and nucleate boiling occur round a heated specimen, which strongly affects quenching. An investigation of sound emission in the quenching process was carried out with cylindrical specimens made of chrome-molybdenum heat-treatable steel 42CrMo4 quenched in different quenching media. Sound-pressure signals demonstrated by different amplitudes depending on time at different frequencies are shown in 3D diagrams. It has turned out that an analysis of sound-emission signals can provide useful information that confirms differences occurring in quenching with different quenching media, different specimen’s shapes and under different quenching conditions. Analysis of sound emission signals and selection certain signals which differ from the regular sound emission can provide useful information regarding cracking with certain step of probability and confirm the differences occurring in quenching with different quenching conditions. The results lead to the applicability of the new approach to the control of the hardening processes of steels.
Investigation of sound phenomena during quenching process
The purpose of controlling the hardening process by selecting the most suitable quenching parameters is to ensure the required hardness and the residual stresses, particularly in the surface layer of a machine part. The article describes the system designed to capture acoustic emission in different quenching media, which includes the assessment of hardening efficiency during the quenching process itself. Analysis of these acoustic emission signals can give useful information and confirm the differences caused by different quenching conditions. The sound pressure signal, as the variation of time dependent amplitude at different frequencies, is presented by 3D diagrams. Analysis of the quenching results, i.e. cross-sectional hardness of the workpiece and the acoustic emission signals during the process itself, leads to a new approach in the monitoring of the hardening processes.
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.