The reduction of friction and wear in systems presenting metal-to-metal contacts, as in several mechanical components, represents a traditional challenge in tribology. In this context, this work ...presents a computational study based on the linear Archard's wear law and finite element modeling (FEM), in order to analyze unlubricated sliding wear observed in typical pin on disc tests. Such modeling was developed using finite element software Abaqus® with 3-D deformable geometries and elastic–plastic material behavior for the contact surfaces. Archard's wear model was implemented into a FORTRAN user subroutine (UMESHMOTION) in order to describe sliding wear. Modeling of debris and oxide formation mechanisms was taken into account by the use of a global wear coefficient obtained from experimental measurements. Such implementation considers an incremental computation for surface wear based on the nodal displacements by means of adaptive mesh tools that rearrange local nodal positions. In this way, the worn track was obtained and new surface profile is integrated for mass loss assessments. This work also presents experimental pin on disc tests with AISI 4140 pins on rotating AISI H13 discs with normal loads of 10, 35, 70 and 140N, which represent, respectively, mild, transition and severe wear regimes, at sliding speed of 0.1m/s. Numerical and experimental results were compared in terms of wear rate and friction coefficient. Furthermore, in the numerical simulation the stress field distribution and changes in the surface profile across the worn track of the disc were analyzed. The applied numerical formulation has shown to be more appropriate to predict mild wear regime than severe regime, especially due to the shorter running-in period observed in lower loads that characterizes this kind of regime.
Compacted graphite iron is an interesting material class for automotive applications. CGI-450 grade cast iron was subjected to various surface treatments: plasma nitriding (PN), laser hardening (LH), ...and PN followed by LH (PN+LH). The resulting tribological behaviors were evaluated by means of linear scratch testing under progressive loading (40–70 and 70–95 N). The PN+LH treatment yielded the lowest friction coefficient and shallowest scratching. In this case, the outermost layer was composed of oxide phases (Fe2O3 and Fe3O4), underlain by a compound layer (oxides + nitrides + martensite) and a high-resistance martensitic layer with accompanying nitrides and carbides. These underlying layers provided high load capacity for the external layers, allowing them to function as solid lubricants.
•Different surface treatments were applied on the CGI-450 compacted graphite iron.•Scratch tests revealed best performance of duplex treatment (PN + LH).•Hematite phase could act as a solid lubricant.•Critical load for nitrided layer was higher, above 80 N.
The life history of Dules auriga, a small hermaphrodite serranid species inhabiting deep waters and a frequent component of the discarded catch of bottom trawling in southern Brazil, was studied to ...assess the fishery effects on the stock through the estimation of the remaining spawning‐potential ratio. Sampling was conducted throughout a year and included specimens to determine sex, maturity and age. Age was validated by the edge type and marginal‐increment analysis. The oldest and the largest individuals were 9 years and 195 mm total length. Growth parameters fitted to the von Bertalanffy equation were L∞ = 178·34 mm, k = 0·641 year−1 and t0 = −0·341 years. Length and age at first maturity were 140·72 mm and 2 years, respectively. The reproductive season was throughout the austral spring and summer. The assessment of the effects of fishing showed that it may have resulted in a loss of 50% of the spawning potential. This loss may be higher when taking into account the uncertainty in the life‐history parameters and could be considered of concern for the population. Fast growth, moderate longevity, long spawning season, small size and age at maturity make D. auriga relatively resilient to the removal of biomass by fishing. When considering the uncertainty, however, the losses of the spawning potential have been severely reducing the population resilience in the face of ecosystem changes.
هدفت الدراسة إلى تقييم فعالية مغلي أوراق الشجرة المعروفة بالمورينجا في إزالة الطبقة السميكة مقارنة بمادتين أخريين وكذلك الأنشطة المضادة للميكروبات.
تم استخراج أوراق الشجرة باستخدام مغلي الماء الساخن ...بتركيزين مختلفين. تم تحضير ما مجموعه ثلاثين سنا بشريا مستخرجا ذو جذر واحد لتقييم فعالية إزالة الطبقة السميكة. تم حساب وجود الطبقة السميكة في الثلث الأوسط من قناة الجذر باستخدام الميكروسكوب الليزري الماسح الضوئي الحويصلي. ثم تم إجراء النشاط المضاد للبكتيريا على نوعين من البكتيريا باستخدام طريقة تشتت الأغار.
وجدنا أن التراكيز 2,5% و 5% من المغلي أكثر فعالية بشكل ملحوظ في إزالة الطبقة السميكة، ومع ذلك، لم يتم ملاحظة فرق ملحوظ عند المقارنة مع المادتين الأخريين. أظهرت نتائج اختبار المضادات الحيوية المختبرية أن خمسة بالمائة من المغلي يظهر نشاطا مضادا للميكروبات أعلى ضد كلا المسارين التجريبيين.
تشير هذه النتائج إلى أن مغلي أوراق الشجرة يمكن اعتباره محلولا فعالا في علاج الجذور.
This study evaluated the effectiveness of moringa (Moringa oleifera) leaves decoction for removing a smear layer compared to sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA), as well as its antimicrobial activities.
The moringa leaves were extracted using hot water decoction at two different concentrations (2.5% and 5.0% w/v). A total of 30 extracted human single-rooted teeth were prepared to assess the smear layer removal efficacy. The presence of a smear layer in the middle third of the root canal was detected by confocal microscopy. Then the antibacterial effects were assessed against Enterococcus faecalis and Streptococcus mutans bacteria using the agar diffusion method.
The 2.5% and 5.0% decoction were significantly more effective than 0.25% NaOCl in removing the smear layer (p < 0.05); however, no significant difference was observed compared to EDTA (p > 0.05). The in vitro antimicrobial assay showed that 5.0% decoction had higher antimicrobial activity against both of the test pathogens.
The findings of this study suggest that moringa leaves decoction can be considered an effective irrigant in endodontics.
AISI H13 tool steel discs were pulsed plasma nitrided during different times at a constant temperature of 400
°C. Wear tests were performed in order to study the acting wear mechanisms. The samples ...were characterized by X-ray diffraction, scanning electron microscopy and hardness measurements. The results showed that longer nitriding times reduce the wear volumes. The friction coefficient was 0.20
±
0.05 for all tested conditions and depends strongly on the presence of debris. After wear tests, the wear tracks were characterized by optical and scanning electron microscopy and the wear mechanisms were observed to change from low cycle fatigue or plastic shakedown to long cycle fatigue. These mechanisms were correlated to the microstructure and hardness of the nitrided layer.
The mechanisms of plasma post-oxidation of plasma nitrided AISI 1045 plain steel were investigated. The influence of plasma post-oxidation temperature and time on the oxide layer thickness, ...morphology, and composition were addressed. The oxide thickness grows exponentially with temperature, with activation energy of 68±5kJmol −1. The time dependence of the oxide layer thickness, on the other hand, is governed by a diffusion-reaction process. It was verified that temperature plays an important role on the morphology of the oxide. Indeed, at the highest temperature, 550°C, the oxide layer is not homogeneous and has a lower hardness than oxide layers obtained at 480 to 500°C. The latter seem to be more favorable temperatures to grow compact, homogeneous, and harder oxide layers. The oxide–nitride bi-layer produced here contains a mixture of γ′-Fe4N and ε-Fe2-3N and only one iron oxide, Fe3O4 (magnetite). The proportions between these phases vary with the plasma processing temperature and time.
►Oxygen and nitrogen profiles were determined by alpha-particle resonant scattering. ►The oxide thickness as a function of time does not follow a pure parabolic law. ►The oxidation process is governed by a diffusion-reaction mechanism.
The ATLAS Pixel detector is designed to sustain high dose integrated over several years of operation. Nevertheless, the radiation hardness should also favour the survival of the detector in case of ...accidental beam losses. An experiment performed in 2006 showed that ATLAS Pixel detector modules (silicon planar coupled with FE-I3 electronics) could survive to beam losses up to 1.5ċ1010 protons/cm2 in a single bunch with minimal or no deterioration of performance. The upgrade of LHC to even higher luminosity (HL-LHC) calls for a new test of these properties. Two test beam campaigns have been conducted in 2017 and 2018 at the High-Radiation to Materials (HiRadMat) facility of the CERN Super Proton Synchrotron in order to establish for the first time the survival threshold of different types of ATLAS IBL pixel modules under very intense proton beam irradiation.
The effect of hydrogen on plasma post-oxidation following plasma nitriding of a ferrous alloy was investigated. The increase in the hydrogen concentration in the plasma progressively reduces the ...hematite/magnetite concentration ratio in the outermost oxide layer down to zero at 25% H
2 concentration. Atomic hydrogen originating from scission of hydrogen molecules in the plasma leads to reduction of Fe(III) in hematite into Fe(II) in magnetite by controlling the gas mixture reduction potential.
We investigated the low load friction behavior of plasma post-oxidized, plasma- nitrided AISI 1045 plain steel, using unidirectional sliding tests. The hydrogen content in the post-oxidation plasma ...was varied between 0 and 25%. The nitrided or oxidized layer thicknesses ranged from approximately 340–380 μm or 0.7–1.1 μm, respectively. The outermost iron oxide layer decreases the friction, whereas the underneath iron nitride layer increases the mechanical strength. The incorporation of hydrogen in the oxidative plasma mixture allows to control the type of iron oxide phase. It is observed that the presence of a superficial magnetite layer leads to a decrease of the friction coefficient with respect to the non-oxidized nitrided steel. The results are interpreted on the lights of crystal chemistry and with a model to explain the in-depth effects of hydrogen in the oxidative plasma.
► Hydrogen improves the oxidation performance in terms of oxide layer thickness. ► Magnetite reduces both friction and roughness. ► The hydrogen effect takes place in-depth at the whole layer.
Received date: 10 October 2018 Accept date: 19 November 2018 Introduction According to the World Health Organization (WHO), dental caries are a major health problem worldwide with 60-90% prevalence ...in school-aged children and adults.1,2 Caries are a common oral disease and result in loss of tooth structure and requires restoration to restore the function, form and aesthetic of the tooth.3-5 Composite resins are the most widely used restorative materials today. ...the tooth undergoes finishing and polishing (Figure 5). ...the natural anatomy of the existing tooth is lost.17,18 Restoration of the composite resin in the posterior tooth is a challenge for the dentist because it requires recontouring of anatomical tooth surfaces. Gaps occur when the composite polymerization pressure is greater than the composite bond strength with the tooth structure.10,19,20 Several methods for reducing polymerization shrinkage have been reported in posterior restorations, such as the use of liner materials with a low elastic modulus, techniques of curing, and application technique of composite resin material.19,20 Incremental technique has been reported to reduce microleakage with resin composite restoration.
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