Stainless Steel Block Research Articles

Effect of NaOCl and EDTA irrigating solutions on the cyclic fatigue resistance of EdgeTaper Platinum instruments

BackgroundTo compare the solution on the cyclic fatigue resistance of EdgeTaper Platinum (ETP) instruments with that of ProTaper Gold (PTG) in the presence of ethylenediaminetetraacetic acid (EDTA) or sodium hypochlorite (NaOCl) irrigating solutions.MethodsSixty PTG and 60 ETP instruments with the same size (#25) and taper (8%) were tested under 17% EDTA, 5.25% NaOCl, or distilled water (n = 20 each). Cyclic fatigue was tested using artificial canals that were milled in stainless steel blocks using a laser micromachining technique. The canals had a curvature angle of 60 and a curvature radius of 5 mm. The center of maximum curvature was set at 5 mm from the instrument tip. The block of artificial canals was stabilized inside a container that was filled with one of the tested solutions. The temperature was fixed at 37 °C with a tolerance limit of 1 °C. The number of cycles to fracture (NCF) was calculated and the fractured surfaces were examined using a scanning electron microscope. All statistical analyses were performed using SPSS software Version 20 (IBM-SPSS Inc., Chicago, IL) at a confidence level of 95%.ResultsETP showed higher NCF than PTG in any of the tested solutions (P < 0.05). Within each group, NaOCl drastically decreased the NCF compared to water and EDTA (P < 0.05) and changing the solution from distilled water to EDTA did not affect the fatigue resistance (P > 0.05).ConclusionsETP showed improved cyclic fatigue performance compared to PTG in all tested irrigating solutions. EDTA can be used in combination with NiTi instruments during canal instrumentation without compromising the cyclic fatigue resistance of PTG and ETP instruments. However, NaOCl drastically decreased the NCF.

Lightweight and Amplitude-Free Ultrasonic Imaging Using Single-Bit Digitization and Instantaneous Phase Coherence.

In the field of ultrasonic nondestructive testing (NDT), the total focusing method (TFM) and its derivatives are now commercially available on portable devices and are getting more popular within the NDT community. However, its implementation requires the collection of a very large amount of data with the full matrix capture (FMC) as the worst case scenario. Analyzing all the data also requires significant processing power, and consequently, there is an interest in: 1) reducing the required storage capacity used by imaging algorithms, such as delay-and-sum (DAS) imaging and 2) allowing the transmission and postprocessing of inspection data remotely. In this study, a different implementation of the TFM algorithm is used based on the vector coherence factor (VCF) that is used as an image itself. This method, also generally known as phase coherence imaging, presents certain advantages, such as a better sensitivity to diffracting geometries, consistency of defect restitution among different views, and an amplitude-free behavior as only the instantaneous phase of the signal is considered. Some drawbacks of this method must also be mentioned, including the fact that it poorly reproduces planar reflectors and presents a lower signal-to-noise ratio (SNR) than amplitude-based methods. However, previous studies showed that it can be used as a reliable tool for crack-like defect sizing. Thus, a lightweight acquisition process is proposed through single-bit digitization of the signal, followed by a phase retrieval method based on the rising and falling edge locations, allowing to feed the phase coherence imaging algorithm. Simulated and experimental tests were first performed in this study on several side-drilled holes (SDHs) in a stainless steel block and then extended to an experimental study on angled notches in a 19.05-mm ( 3/4" )-thick steel sample plate through multiview imaging. Results obtained using the array performance indicator (API) and the contrast-to-noise ratio (CNR) as quantitative evaluation parameters showed that the proposed lightweight acquisition process, which relies on binary signals, allows a reduction of the data throughput of up to 47 times. This throughput reduction is achieved while still presenting very similar results to phase coherence imaging based on the instantaneous phase derived from the Hilbert transform of the full waveform. In an era of increasing wireless network speed and cloud computing, these results allow considering interesting perspectives for the reduction of inspection hardware costs and remote postprocessing.

In Vitro Analysis of the Fatigue Resistance of Four Single File Canal Preparation Instruments.

Instrument separation during root canal therapy is inevitable in endodontics with several unfavorable clinical consequences. Therefore, examining the cyclic flexural fatigue resistance of commonly used rotary endodontic files is crucial. This study aimed to determine the cyclic flexural fatigue resistance of four nickel–titanium (NiTi) rotary files used as a single canal preparation technique: WaveOne, Reciproc, Protaper F2, and Unicone medium instruments. According to the manufacturer’s instructions, each file was rotated freely within a 1.3 mm deep and 1.3 mm wide V-shaped groove in a stainless-steel block with a 40° and 5 mm radius of curvature. Cyclic fatigue resistance was compared between the NiTi files by verifying the time needed to crack. The data were analyzed using one-way analysis of variance (ANOVA) followed by Scheffé post hoc with a significant level set at p < 0.05. Our results demonstrated that the WaveOne instrument had the highest cyclic flexural fatigue resistance among the tested groups (p ≤ 0.05), while Unicone had the lowest cyclic flexural fatigue resistance. This study concluded that WaveOne size 25/0.08 could illustrate a superior cyclic flexural fatigue resistance when instrumenting root canals with the lowest possibility to cause instrument separation.

Comparative evaluation of cutting efficiency, cyclic fatigue, corrosion resistance, and autoclave cycle effects of three different file systems: An in-vitro micro-CT and metallurgy analysis

Aim: To compare the cutting efficiency, cyclic fatigue, corrosion resistance, and autoclave cycle effects of ProTaper Gold, TruNatomy, and WaveOne Gold file systems. Materials and Methods: Thirty mesiobuccal roots of extracted maxillary first molars were randomly divided into three groups (10 specimens each) for testing cutting efficiency: Groups A, B, and C: ProTaper Gold, TruNatomy-Prime, and WaveOne Gold-Primary, respectively. Root canal instrumentation was carried out in each root accordingly. Specimens’ weights were measured and micro-computed tomography was used to scan the samples before and after root canal preparation. For cyclic-fatigue, corrosion-resistance, and autoclave-cycle-effects testing, 30 files were allocated into three groups at random, Groups A, B, and C: ProTaper Gold-F2, TruNatomy-Prime, and WaveOne Gold-Primary (10 specimens each). For cyclic-fatigue testing, the instruments were firmly held in a stainless steel block with an artificial canal without pressure. The time (s) was calculated until fracture. For the corrosion-resistance test, SEM surface-topographical analysis was carried out in response to 5.25% NaOCl, 2% CHX, and 17% EDTA. For evaluation of autoclave cycle effects, SEM surface-topographical analysis was carried out for 1, 5, and 10 autoclave cycles. Data were analyzed statistically using one-way analysis of variance followed by multiple comparisons with Bonferroni’s test at P<0.05. Results: TruNatomy was the most resistant to cyclic fatigue and ProTaper Gold the least. WaveOne Gold removed significantly more dentin and had the least corrosion resistance and highest autoclave cycle effects. Conclusion: TruNatomy can be considered as a better file system compared with WaveOne Gold and has comparable efficiency with that of ProTaper Gold.

A Comparative Examination of Cyclic Fatigue and Fragment Length of Three Different Types of Endodontic Rotary Files: An In Vitro Study

Introduction: Although of great scientific advancement in the properties and form, fracture of nickel-titanium (NiTi) files could occur during their use. The goal of this study was to compare resistance to cyclic fatigue of various rotary systems used in endodontics. Materials and Methods: Three types of NiTi rotary systems were tested – group A: One Curve, group B: Edge File, and group C: lusterdent NiTi files. In these files, taper is 0.06, and their diameter is 25 mm. Stainless steel block was used. This block contains artificial canals with a 60o curvature, 5 mm radius of curvature, 21 mm length, and 1.5 mm width. A number of cycles before fracture were obtained and measurement of fragment length was achieved. Statistical evaluation of readings was accomplished with ANOVA and Tukey post hoc test. Results: There were statistically significant differences between the three types of NiTi rotary systems considering the number of cycles before file fracture (P < 0.001). The differences between fracture lengths were not statistically significant (P = 0.15). Conclusion: The Edge File revealed the highest cyclic fatigue resistance.

Cyclic Fatigue Resistance of Five Different Glidepath Files in a Double Curved Artificial Canal.

The aim of this study was to examine the cyclic fatigue resistances #16 ProGlider, #15.02 Scout RaCe, #15.03 NeoNiTi GPS, One G and Path-File NiTi glide path files in S-shaped artificial canals. Twenty files from each group were tested. An artificial groove simulating double (S-shaped) curved canal measuring 1.5 mm in width at the top level decreasing towards the apical reaching 0.3 mm at the tip having a 0.06 taper, 18 mm in length, and 1.5 in depth machined in a stainless steel block was used in this study. Resistance to cyclic fatigue was determined by counting the numbers of cycles to failure (NCF). Furthermore, the fragment length of the fractured tips and angle and radius of curvature formed by each file in each trajectory were evaluated. The data were analyzed using the one-way analysis of variance and Tukey's HSD test and the level of significance was set at 5%. NeoNiti GPS and Scout RaCe glide path files showed significantly higher NCF values compared to other evaluated glide path files (P<0.001) but no significant difference when compared with each other (P=0.67). Based on this in vitro study NeoNiti GPS and Scout RaCe glide path files had the highest cyclic fatigue resistance in simulated double (S-shaped) curved artificial canals among the evaluated path finding files. Therefore, it seems that they can be used with more confidence in endodontic treatment of S-shaped canals clinically.

A comparative study of cyclic fatigue of 6 endodontic systems. An in vitro study.

BackgroundMechanical preparation and the formation of space for adequate obturation are included in root canal shaping, but the complex root canal anatomy may be affect it. Manufacturers have created different alloys like M-Wire, Blue-Wire, Gold-Wire or R-phase. Objective: This investigation was performed to verify the null hypothesis that there were not significant differences between size 25 instruments ESP Files Thermoflex, Protaper Ultimate, Protaper Next, Blueshaper, One Curve and 2Shape about cyclic fatigue and length of broken fragments. Material and Methods180 new size 25 files of the systems investigated were selected (n=30). Files were used with Endo Mate DT endo motor with speed and torque recommended by manufacturers, holding the instruments with clamping mechanism, with passive adjustment, glycerine and without pressure in a stainless-steel block. The time was calculated in seconds until fracture. Number of fatigue cycles was determined as (Resistance (s) x Speed)/60. Separated fragment lengths were calculated with digital Vernier caliper. Statistical analysis was carried out with the SPSS 18 programme at a 95% confidence level, using Levene´s Test to compare variances, Welch’s Test to compare means, and Games-Howell´s Test to reveal differences between groups. ResultsLevene’s Test determined no equal variances (P<0.05). Welch’s Test and ANOVA (P<0.05) showed significant differences in cyclic fatigue and separated fragment lengths. Games-Howell’s and Bonferroni´s Test established significant differences in multiple comparisons (P<0.05). ConclusionsESP Files Thermoflex was superior in cyclic fatigue. About separated fragment lengths, ESP Files Thermoflex, Protaper Ultimate and Blueshaper obtained longer lengths. Key words:Cyclic fatigue, continuous movement, separated fragment lengths, rotary systems.

Investigation of in-situ cryogenic assisted machining of 2205 duplex stainless steel in AWJM

An experimental investigation on Abrasive Water Jet Machining (AWJM) of duplex steel at cryogenic temperatures is discussed in this work. Material removal takes place in AWJM by abrasive induced fracture. The lowering of temperature during machining induces brittleness in metallic material. Hence, by reducing the temperature of the work piece, the occurrence of abrasive induced fracture can be promoted and the MRR will be increased. In this study, a 2205 duplex stainless steel block of thickness 20 mm and diameter 70 mm was selected as a work piece for the investigation due to its high toughness at normal temperature. Piercing experiments were conducted at three different pressures (254, 271, and 302 MPa) and three different stand-off distances (SOD) (2, 3, 4 mm). The work piece is machined at non-cryogenic temperatures between 28 °C and 35 °C. Subsequently, it is repeated at cryogenic conditions with the temperature ranges below −50 °C and their respective piercing times are noted. Comparison of machining at the normal and cryogenic temperatures, with a high pressure of 302 MPa and SOD of 4 mm, revealed 28.57% reduction in piercing time while machining under cryogenic temperature. Where-as, at low pressure of 254 MPa and SOD of 2 mm, the reduction in piercing time for machining at cryogenic temperature is about 5.84% only.

Measurement of Pool Boiling Heat Transfer Coefficient with an Insulated Stainless-Steel Block

We have designed an apparatus dedicated for measurement of heat transfer coeffcient during saturated nucleate pool boiling. After several performed measurements, we have applied three important modifications of the apparatus motivated by discrepancies between measured and correlated heat transfer coeffcients. Firstly, the cubic stainless-steel heated block of the apparatus no longer accommodates heating cartridges. It now stands on a copper carrier of the cartridges, which are vertically oriented. Secondly, we have insulated the heated block with plates made of cellular glass. Thirdly, thermocouples used for measurement of temperatures inside the block have been fixated with a special high-temperature adhesive. These modifications were applied in order to improve the temperature distribution inside the block and to eliminate the impact of surroundings on measured heat transfer coeffcients. This contribution presents and discusses experimental results obtained with these modifications.

Comparison of cyclic fatigue of a reciprocating file system at different angles of rotation

Aim: The purpose of this in vitro study is to compare the cyclic fatigue resistance of Reciproc Nickel-Titanium (Ni-Ti) rotary files while operating root canals using in three different reciprocal angles.&#x0D; Methodology: Forty-five pieces of Reciproc R25 canal files were tested using artificial canals with a 60° angle of curvature, 5 mm curvature radius, and 1.5 mm diameter carved into a stainless steel block. The Ni-Ti files were checked with a stereomicroscope and then randomly separated into 3 groups. Group 1 consisted of reciprocal angles CCW 150°–CW 30°, Group 2 consisted of CCW 180°–CW 60°, and Group 3 consisted of CCW 210°–CW 90°. The duration of the cyclic fatigue being measured, elapsed time until a file fractured was determined with a chronometer. The lengths of the fractured pieces were measured with a digital caliper. After the cyclic fatigue test, two samples from each group were examined with a Scanning Electron Microscope (SEM) to determine the signs of cyclic fatigue.&#x0D; Results: One-way analysis of variance (ANOVA) was applied to the normally distributed groups (p&lt;0,05). Since there was a significant statistical difference of file’s cyclic fatigue resistance (p=0,001) between the groups, Tukey’s honestly significant difference (HSD) post-hoc pairwise comparison test were used for determine to between which groups. While there were statistically significant differences between Group 1 and Group 2 (p=0,001), and between Group 1 and Group 3 (p=0,001), there was no significant difference between Group 2 and Group 3 (p=0,376). Group 1 displayed the highest resistance to cyclic fatigue. There were no statistically significant differences between the lengths of the fractured files within the three groups according to the one-way analysis of variance (p=0,847).&#x0D; Conclusion: In our study, it was observed that the reciprocal angles of CCW 150°–CW 30°, which were also suggested by the file manufacturer firms, had the highest fracture resistance against cyclic fatigue.&#x0D; &#x0D; How to cite this article: Akay A, Adıgüzel Ö, Erkan Akay S, Kaya S. Comparison of cyclic fatigue of a reciprocating file system at different angles of rotation. Int Dent Res 2021;11(Suppl.1):67-72. https://doi.org/10.5577/intdentres.2021.vol11.suppl1.11&#x0D; &#x0D; Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.&#x0D;

Workpiece vibration in feed direction assisted electrochemical cutting using tube electrode with inclined holes

Electrochemical cutting using tube electrode with inclined holes is a machining method that directly and obliquely injects electrolyte into the machining gap through inclined jet-flow holes on the sidewall of a tube electrode, allowing the electrochemical cutting of a workpiece. To improve the machining efficiency and accuracy of this cutting technique, a method of workpiece vibration in feed direction–assisted electrochemical cutting is proposed in which workpiece vibration rapidly and periodically changes the machining gap. The near-instantaneous increases in the machining gap promote the renewal of electrolyte and the removal of electrolytic products. At the same time, the electrochemical reaction time under the nonuniform flow field caused by the inclined downward injection of electrolyte is reduced. The flow field simulation of electrolyte in machining gap indicates that the near-instantaneous increases in the machining gap can improve the flow velocity of electrolyte. The effect of the vibrational amplitude and frequency on the machining result is investigated by cutting slit experiments. Compared with that of electrochemical cutting without workpiece vibration in feed direction, the average feed rate of electrochemical cutting assisted by workpiece vibration with amplitude of 0.1 mm and frequency of 1.5 Hz can be increased by 50%, and the width difference between the upper and lower end of the slit is reduced from 115.56 to 49.6 μm. The machining efficiency and machining accuracy of electrochemical cutting using tube electrode with inclined holes are improved. Finally, an array slice structure is fabricated on a stainless steel block with a cross-section of 10 mm × 10 mm at average feed rate of 6 μm/s using a vibrational amplitude and frequency of 0.1 mm and 1.5 Hz, respectively.

Design development and testing of mutual inductance type level sensor for molten lead-lithium alloy

Continuous level measurement of molten Pb-Li in various Pb-Li containing tanks is a challenge owing to the high operating temperature of molten Pb-Li and its corrosive nature. A mutual inductance type level sensor has been designed and developed for molten Pb-Li applications, based on knowledge and experience gained form the development of similar level sensor for liquid sodium system. Appropriate temperature compensation technique has been implemented to compensate for the temperature effects on Pb-Li electrical conductivity for the operating temperature range. The testing of level sensor has been performed in solid Aluminium as well as Stainless Steel blocks, followed by molten Pb-Li at 300 °C. In all the cases, the temperature compensated output of MI probe has been found to exhibit adequate sensitivity and vary linearly with the change in level of the conducting medium. In the case of molten Pb-Li at 300 °C, the testing was carried out in reference to a conductivity level switch, and the accuracy was found to be within 2% of full scale.

Stationary Fatigue Resistance of Various Rotary Instruments with Different Alloys after Preparing Three Root Canals.

Objective:This study aimed to evaluate the stationary fatigue resistance of three endodontic instrument systems after preparing three root canals with different curvatures and comparing them with unused instruments.Methods:A total of 60 endodontic files from 3 instrument systems, TruNatomy (TRN), HyFlex CM (HFC) and Revo-S (RS), were selected for this study. These systems were divided into 2 groups: Group I (Used files) and Group II (Unused files). Each group was further divided into 3 subgroups, each containing 10 TRN (#26/v.04), 10 HFC (#25.04) and 10 RS (#25/.04) rotary files. The group I instruments were used for shaping the root canals of extracted third molars, while the group II instruments were not used for canal shaping procedures. Both Group I and Group II instruments were subjected to stationary cyclic fatigue testing at simulated body temperature (37±0.5°C) using a stainless-steel block with an artificial canal. The number of cycles to failure (NCF), the length of fractured instruments and the preparation time were recorded. The statistical analysis was performed using two-way ANOVA and Tukey post-hoc tests with a 95% confidence interval (P=0.05).Results:NCF was significantly affected by the instrument type and whether the instrument was unused or used (P<0.001). The Group II instruments were more resistant to stationary cyclic fatigue than Group I (P<0.05). HFC instruments were most resistant to stationary fatigue among all tested conditions, followed by TRN and RS instruments. Canal preparation with TRN was significantly faster than with HFC and RS. During preparation, no file was fractured. A statistically significant difference (P<0.05) was observed in the mean length of the fractured instruments among used instrument groups.Conclusion:The stationary cyclic fatigue resistance of HFC instruments were significantly greater than that of the TRN and RS instruments (P<0.05). TRN was faster in shaping the root canals than other instruments tested in the study.

Fast Non-Stationary Deconvolution of Ultrasonic Beamformed Images for Nondestructive Testing

This paper addresses high-resolution ultrasonic image reconstruction from Full Matrix Capture (FMC) data in the context of nondestructive testing (NDT). In order to reduce the numerical complexity, the time-domain data and ultrasonic model are projected into the image domain through a linear beamforming procedure. The resulting model is interpreted as a shift-variant convolution process, affected by non-stationary and colored noise. An interpolation procedure is built in order to account for the spatial variations of the resulting point spread function. Under the same methodological framework, an approximate whitening filter is proposed and incorporated in the forward model. Both constructions then allow fast computations and limited memory storage. Deconvolution is performed by minimizing the least-squares data misfit error, with a penalization term favoring sparsity and spatial continuity of the output images. Results with synthetic data show that the proposed approach gives performances close to the inversion of raw FMC data, while being computationally much more efficient. The method is finally applied to laboratory data for the inspection of a stainless steel block containing closely spaced and small side-drilled holes. Successful detection and separation is achieved for flaws with diameters six times smaller than the wavelength, and distant from each other by three times less than the resolution limit given by the Rayleigh criterion.

Crosslinked Single-Ion-Conductor Polymer Electrolytes

Liquid based electrolytes used in conventional Li-ion batteries are made of a mixture of Li salt and flammable alkyl carbonate solvents. In addition, their transference number (t +) is low, typically 0.3, which limits the battery power performance because of the formation of strong gradient of concentration during operation.[1] To increase both safety of energy density a solution is to develop a Li metal based battery comprising a single-ion-conductor solid polymer electrolyte.[2]Poly(ethylene oxide) (PEO) doped with a Li salt is the fundamental solid polymer electrolyte due to its high ionic conductivity (> 10-4 S/cm) above its melting temperature (> 60°C), and, chemical and electrochemical stability towards Li metal. However, its t + is low, about 0.15.[3] A strategy is then to develop a single-ion-conductor polymer electrolyte comprising PEO to ensure Li metal stability and battery operation at room temperature.[4]In this study, we report on the facile synthesis and the physico-chemical and electrochemical characterizations of series of crosslinked single-ion electrolytes based on a PEO matrix. These materials are shown to be single-ion-conductors with interesting Li dendrite resistance. In addition, for these electrolytes a thorough study by impedance spectroscopy using symmetrical cells with either Li reversible electrodes or stainless steel blocking electrodes reveals a complex electrolyte resistance response composed of two contributions as encountered in materials with bulk and grains boundaries (Figure 1). We thus proposed a methodology to extract the grain and grain boundary contributions, which is essential to correctly determine in turn the electrolyte transport properties (transference number, diffusion coefficient). Furthermore, a discussion on the origin of this phenomena is proposed.

Underwater laser cutting of thick stainless steel blocks using single and dual nozzles

Laser cutting was performed using a 6-kW fiber laser with two different nozzle configurations to extend the permissible cutting thickness of steel blocks in a water environment. The first nozzle configuration involved a single minimum length nozzle (MLN) operating at an upstream gas gauge pressure of 15 bar; the second configuration consisted of a truncated aerospike nozzle coupled with an MLN. These configurations were designed to form a core air-filled cavity with the submerged jet to have denser and more lengthened characteristics for extending the possible transmission distance of the high-power laser beam, which is vulnerable to water absorption. Before underwater cutting, we performed a Schlieren visualization measurement of the gas jet’s flow behavior as it was discharged from the single and dual nozzles in the ambient air, after which, the stainless steel blocks were laser-cut underwater using both nozzle configurations. The thickness of the selected steel blocks varied from 60 to 80 mm according to the capabilities of the nozzles used to form the air cavity.

Investigating the Effects of Lithium Phosphorous Oxynitride Lamination on PEO/PPC Blended Hybrid Electrolytes

Solid-state electrolytes play an important role in the development of new generations of technology including lithium metal batteries. Lithium conducting solid materials offer a solution to the safety issues that are present in lithium-ion batteries (LIBs). Conventional LIBs typically use highly flammable organic solvents as a transport medium for lithium ions, potential risks that arise due to these solvents include fire, volatilization, and explosions. Solid polymer electrolytes (SPEs) are great as electrolyte material because fabrication of the electrolyte films is cheap, and processing is simple. However, SPEs can have stability issues when in contact with lithium metal for extended periods which is a problem for cells required to offer long lifetimes. Poly (ethylene oxide) (PEO) has been extensively studied since the conception of SPEs, due to its ability to solvate ions due to its polar ether groups. However, PEO, being a semi-crystalline polymer, exhibits thermal history effects due to recrystallization behavior. Amorphous SPEs are highly desirable because there are no recrystallization kinetics at play, and the properties are consistent regardless of the thermal history. Poly(propylene carbonate) (PPC), an amorphous, biodegradable polymer, can offer high ionic conductivities. Blending PEO and PPC offers a solution to resolve the thermal history effects of PEO by interfering with the crystalline structures in blended electrolyte systems with the salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Inorganic solid electrolytes (ISEs) can offer better chemical stability and excellent mechanical properties compared to SPEs; however, brittleness may decrease the structural stability over time. Thin films ISE’s also tend to cost much more than SPEs due to the fabrication methods required such as electron beam evaporation, and chemical vapor deposition. Lithium phosphorous oxynitride (LiPON), produced through RF magnetron sputtering, was developed in the 1990s at Oakridge National Laboratories and offers great electrochemical stability against lithium and relatively high ionic conductivities on the order of 10-6 S/cm at room temperature. A new bilayer lithium-ion conducting hybrid solid electrolyte (HSE) consisting of a blended polymer electrolyte (BPE) coated with a thin layer of the ISE LiPON, has been prepared. PEO and PPC are blended in a 1:1 mass ratio, then the salt LiTFSI is incorporated. BPE films are then produced through a facile solution casting method using acetonitrile as the solvent. Structure-property relationships are then systematically evaluated to understand the effects of molecular weight and mass loading of LiTFSI on the BPE systems. Influences of molecular weight and salt loading on crystallinity is observed though X-ray diffraction and optical microscopy of the BPE films. Ionic conductivity is evaluated through impedance spectroscopy between two stainless steel blocking electrodes, thermal history measurements were taken by heating and cooling the SPE while recording EIS at specified temperatures. The best BPE based on ionic conductivity, consists of 100k molecular weight PEO, 50k molecular weight PPC, and 25(w/w)% LiTFSI, (denoted as PEO100PPC50LiTFSI25) and exhibits an ionic conductivity of ~2x10-5S/cm. Temperature dependent EIS shows that the lowest molecular weight polymers offer lower activation energies as a result of the higher degree of free volume and molecular motion of the polymer chain. The optimized BPE system is then coated with various thicknesses of LiPON. The effects of LiPON coating are evaluated and show promise for the development of lithium stable solid electrolytes. Linear sweep voltammetry (LSV) is used to assess the anodic voltage stability against lithium metal. Incorporating very thin layers of LiPON down to 20nm on the BPE shows an increase in the voltage window of the electrolyte system from 5.2 to 5.5V (vs Li/Li+). However, the incorporation of LiPON decreases the ionic conductivity of the BPE. Thinner layers of LiPON show the ionic conductivity approaches that of the BPE, with thicker LiPON layers offering lower ionic conductivies. To assess the stability against lithium metal over time, impedance spectroscopy is used. Cells consisting of the solid electrolyte against lithium metal are prepared, and impedance measurements are taken over a 20-day period to assess the changes in charge transfer resistance. From these measurements, it has been shown that only a 30nm thin layer of LiPON is required to improve the stability of the resulting HSE. Therefore, coating BPEs with a thin layer of LiPON is shown to be an effective strategy to improve the long-term stability of solid-state lithium ion conductors.

Experimental study on the coefficient of restitution of grain against block interfaces for natural and engineered materials

The coefficient of restitution (COR) is an important input parameter in the numerical simulation of granular flows, as it governs the travel distance, the lateral spreading, and the design of barriers. In this study, a new custom-built micromechanical impact loading apparatus is presented along with impact experiments on engineered and natural materials. The COR and energy loss of various grains and base block combinations are studied, including fairly regular-shaped Leighton Buzzard sand (LBS) grains as a natural soil and granite or rubber as base blocks, apart from the use of engineered materials for the grains (chrome steel balls, glass balls) and blocks (stainless steel, brass). The repeatability of the new micromechanical impact loading apparatus was checked by impacting chrome steel balls on stainless steel block. In all the test combinations, the higher and lower values of the COR are found for granite block (ranging between 0.75 and 0.95) and rubber block (ranging between 0.37 and 0.44) combinations, respectively. For the tested grain–block combinations, lower values of COR were observed for impacts between materials of low values of composite Young’s modulus. However, within the narrow range of composite surface roughness of the tested grain–block interfaces no particular trend was observed in the COR values. Compared to glass balls and chrome steel balls, greater scatter in the COR values is observed for natural sand grains. This is due to the variation of the elastic and morphological characteristics among individual LBS grains.

Removability of 316L stainless steel cone and block support structures fabricated by Selective Laser Melting (SLM)

Support structures are needed due to the complexities of induced structural, thermal and process factors in Selective Laser Melting (SLM). To date, little systematic study is found to unveil the support removability by a post-machining process. This paper presents an experimental study of removing 316L stainless steel cone and block supports by milling. The effect of different supports is identified by the variation in the microhardness distribution and microstructure of the workpieces. The milling performance of cone and block supports at different cutting depths is studied on the surface finish, surface roughness, milling force, and tool wear and chip formation. The cone supports are subjected to severe collapse, whilst the block supports are mainly removed by localized shearing. The milling force and specific cutting energy of cutting block supports are lower than that of cone supports, and so is the tool wear. A finite element method (FEM) model is developed to explain the removal mechanisms. The results of this study provide an essential reference and unique insight into removal of metal support structures. Moreover, the removability of supports, which is derived from the post-processing stage, should be considered as a new factor in the support design for additive manufacturing.

Evaluation of reverse torque values and failure loads of three different abutment designs with internal connections

High percentage of biomechanical complications such as screw loosening in dental implants can be related to implant-abutment (I/A) connection properties which affect the behavior of implant assembly against functional loads in the oral cavity. The aims of the present study were to compare the reverse torque values (RTVs) and failure loads of three abutment types with internal Morse taper connection. In this experimental in vitro study, eighteen implants (4.5 mm × 10 mm bone level implants, Implantium, Dentium Co, Seoul, South Korea) were divided into three groups with different abutments: two-piece (TP) abutment, one-piece (OP) abutment, and screw abutment (SA), mounted in stainless-steel blocks according to ISO 14801. After completion the torque/detorque protocol, a compressive load (1 mm/min) was applied at 30° off-axis until failure. Mean reverse torque/tightening torque (RT/TT) values and failure loads were analyzed with one-way ANOVA test and Tukey's honest significant difference (α = 0.05). Failure modes were evaluated by radiography and stereomicroscopy. RT/TT values in the TP group were lower than those in other groups (P < 0.001). Highest failure loads were observed in SA group (P = 0.002). In radiographic evaluation, all specimens showed deformation in I/A interface. I/A connections with larger surface areas may lead to higher RTVs (e.g., OP and SA groups). Use of an additional screw and indexed area in TP group did not reduce the bending resistance under static loading.