Surface Properties Of Specimens Research Articles

Exploration of Key Process Parameters and Properties of 40Cr Steel in Ultrasonic Surface Rolling Process

Ultrasonic surface rolling (USRP) is an effective process to improve a workpiece’s fatigue property, in which ultrasonic vibration and static force are applied on the workpiece’s surface. In order to clarify the ultrasonic rolling strengthening mechanism of critical components and optimize the USRP parameters, a theoretical model of ultrasonic rolling was established. Based on the stress-strain curve of 40Cr steel, the USRP parameters were formulated. The compressive residual stress field of single point impact was analyzed by finite element simulation, and the simulation results were validated by conducting an experimental research. In addition, the changes in the surface properties of specimens under different USRP parameters were studied experimentally. The results show that with the increase in depth, the compressive residual stress on the external surface increases firstly and then decreases, and the maximum compressive residual stress is −338 MPa. As the amplitude is 12 μm and the frequency is 20 kHz, the static force of 600 N is optimal for the ultrasonic rolling of 40Cr steel. This study could provide a guide for the key parameters’ selection in USRP.

Evaluation of In Vitro Biofilm Formation on Titanium Nitride Specimens

Objective: The purpose is to characterize the surface properties of specimens coated with titanium nitride (TiN) and to investigate the in vitro biofilm formation on TiN coated specimens.Methods: Ti6Al4V specimens were coated with a <1 μm thick coating of TiN. Surface roughness, surface chemistry, and wettability were measured using 2D stylus profilometry, SEM/EDX, XPS, XRD, and contact angle analysis, respectively. The specimens were preconditioned with artificial saliva and thereafter incubated with a coculture of Streptococcus sanguinis, Actinomyces oris, and Porphyromonas gingivalis. Biofilm formation was evaluated with plate counts, qPCR, Live/dead, and Crystal Violet staining.Results: Except for surface chemistry no significant differences regarding surface characteristics were found. EDX analysis showed oxygen content of the outermost part of the TiN coating, which was confirmed with XPS. XRD also showed the presence of TiNxOy compounds. Viable counts of the bacterial load on TiN after 24 hours incubation showed a log 2 reduction (p<0.05), but no difference was seen with qPCR.Conclusion: TiN coatings are covered by a thin layer of TiNxOy. A biological effect could be shown based on bacterial viability. Its potential benefit for a dental application and the elucidation of the underlying mechanism require further investigation.

The effect of laser‐treated titanium surface on human gingival fibroblast behavior

Surface modification, as a means of enhancing soft tissue integration in titanium would have significant advantages including less marginal bone resorption, predictable esthetic outcome, improved soft tissue stability, and seal against bacterial leakage. The aim of this study was to evaluate the effects of laser-roughened titanium surfaces on human gingival fibroblast (HGF) viability, proliferation, and adhesion. Titanium discs were ablated with impulse laser in four different patterns. Polished and sand-blasted titanium discs were used as control groups. Specimen surface properties were determined using optical profilometry and scanning electron microscopy. HGF behavior on modified surfaces was analyzed using cell adhesion, viability, proliferation, and ELISA assays. Results suggested that modified Ti surfaces did not affect the viability of HGFs and improved adhesion was measured in laser treatment groups after 24 h. However, proliferation study showed that the adsorbance of fibroblast cells after 72 h cultured on polished titanium was higher and comparable with that of control cells. As for focal adhesion kinase (FAK), cells grown on laser modified surfaces had higher expression of FAK as compared with polished titanium. In conclusion, tested laser-treated surfaces seem to favor HGF adhesion. There were no significant differences between different laser treatment groups.

Probabilistic prediction of high cycle fatigue reliability of high strength steel butt‐welded joints

ABSTRACTThe aim of this paper is to develop a probabilistic approach of high cycle fatigue (HCF) behaviour prediction of welded joints taking into account the surface modifications induced by welding and the post‐welding shot peening treatment. In this work, the HCF Crossland criterion has been used and adopted to the case of welded and shot peened welded parts, by taking into account the surface modifications which are classified as follows: (i) the compressive residual stresses, (ii) the surface work‐hardening, (iii) the geometrical irregularities and (iv) the superficial defects. The random effects due to the dispersions of: (i) the HCF Crossland criterion material characteristics (ii) the applied loading and (iii) the surface modifications parameters are introduced in the proposed model. The HCF reliability has been computed by using the ‘strength load’ method with Monte Carlo simulation. The reliability computation results lead to obtain interesting and useful iso‐probabilistic Crossland diagrams (PCD) for different welding and shot peening surface conditions. To validate the proposed method, the approach has been applied to a butt‐welded joint made of S550MC high strength steel (HSS). Four types of specimens are investigated: (i) base metal (BM), (ii) machined and grooved (MG) condition, (iii) As welded (AW) condition and (iv) as welded and shot peened (AWSP) condition. The comparison between the computed reliabilities and the experimental investigations reveals good agreement leading to validate the proposed approach. The effects of the different welded and post‐weld shot peened specimen's surface properties are analysed and discussed using the design of experiments (DoE) techniques.

Strength Prediction of Ceramic Components Under Complex Stress States

The capability to perform accurate fast-fracture strength predictions for ceramic components under complex stress states must be available in order to transition the use of advanced, high-strength ceramic materials from the laboratory to the high-strength/high-temperature applications they are intended for. Multiaxial strength prediction theories have provided the prediction capabilities, but only limited testing of these theories under complex states of stress and stress gradient conditions has been performed previously. Presented here are comprehensive test results and strength predictions for ceramic components subjected to complex states of stress and stress gradient conditions. The results show excellent agreement of the predictions from the multiaxial theories with test results for volumetrically distributed flaws. An important finding of this work is the problem that arises in performing component surface strength predictions from database-type specimens. Database-type specimens and component surface properties are not necessary correlated, and in many cases it may be completely inaccurate to use database-type specimen surface properties for component surface strength predictions.