Surface Roughness Of Specimens Research Articles

Surface roughness and optical characteristics evaluations after chairside adjustment of different zirconia types.

Limited evidence is available for the effect of chairside adjustment using rotary cutting instruments on the surface roughness and optical properties of different zirconia types. To evaluate the effect of simulated adjustments on surface roughness and optical properties of different zirconia types. Three Partially Stabilized Zirconia (PSZ) types based on mole percent yttria (Y) concentration from the same manufacturer (Katana; Kuraray) were used: 3Y-PSZ, 4Y-PSZ, and 5Y-PSZ. Thirty disk-shaped specimens (Ø14 × 1.2 mm) from different zirconia types (N = 90) were prepared. Specimens were either left without adjustment (NA), adjusted with Dialite ZR finishing and polishing system (Brasseler) (APol), or adjusted with course diamond instruments only (ADia). The specimens were distributed into 9 groups (n = 10): Group 3Y-PSZ/NA, Group 3Y-PSZ/APol, Group 3Y-PSZ/ADia, Group 4Y-PSZ/NA, Group 4Y-PSZ/APol, Group 4Y-PSZ/ADia, Group 5Y-PSZ/NA, Group 5Y-PSZ/APol, and Group 5Y-PSZ/ADia. The surface roughness of specimen was analyzed using an Atomic Force Microscope (AFM) (Bruker's Dimension Icon, Bruker) and Root Means Square (RMS) were recorded (nm). Surface Gloss (SG), Translucency Parameter (TP), and Contrast Ratio (CR) values of all groups were recorded using an integrating sphere spectrophotometer. Statistical analysis was performed using analysis of variance (ANOVA) and Tukey's multiple comparison tests for pairwise comparisons at p < 0.05 and 95% confidence interval. APol had no effect on the surface roughness (p = 0.88) while ADia had a significant negative effect (p < 0.05) despite the type of zirconia. Out of the three testes optical properties, only SG was negatively affected by ADia for all types of zirconia (p < 0.05). The two adjustment types did not affect the TP of all the tested zirconia (p = 0.91). The CR was not affected by the tested adjustments for all zirconia types (p = 0.726). Proper zirconia adjustment following a sequence of burs and polishers can maintain acceptable roughness and optical properties. Adjustment of zirconia with rough diamond can lead to deleterious effects and should be avoided. Chairside adjustment of zirconia could lead to rougher surface and unpredictable changes of surface gloss. Therefore, zirconia adjustment should be minimized to the greatest extent possible and a proper protocol should be followed if had to be done.

Improvement of fatigue life of Ti-6Al-4V alloy treated by double-sided symmetric oblique laser shock peening

To improve the anti-foreign object damage (FOD) ability of Ti-6Al-4V alloy blisk blades, a blade simulation specimen was designed and subjected to double-sided symmetrical oblique laser shock peening (DSOLSP) treatment. Surface roughness, residual stress distribution, and microstructural evolution of simulated specimens of Ti-6Al-4V alloy without and with DSOLSP were investigated, and the strengthening effect was evaluated by flexural fatigue test. The results showed that after DSOLSP treatment, surface roughness of simulated specimens was reduced from Ra0.97 µm to Ra0.6 µm. DSOLSP treatment generated a compressive residual stress (CRS) field along the entire thickness direction of the simulated specimen. Nanostructures with a depth of ∼500 nm was observed at topmost surface layer, and the average size of the nanograins was about 35.2 nm. Compared with the base material, the flexural average fatigue life of the simulated specimen was increased by 8.45 times. Moreover, mathematical statistical analysis confirms that DSOLSP has a significant effect on the fatigue life of simulated samples. The development of CRS fields throughout the entire thickness direction, the grain refinement on the surface, and the reduction of surface roughness are primarily responsible for the enhancement of the flexural fatigue life of the DSOLSP simulated specimen.

Effect of Force and Heat Coupling on Machined Surface Integrity and Fatigue Performance of Superalloy GH4169 Specimens

GH4169 is one of the key materials used to manufacture high-temperature load-bearing parts for aero-engines, and the surface integrity of these parts in service conditions significantly affects their high-temperature fatigue performance. Under a coupling effect of high temperature and alternating load, the evolution process of the machined surface integrity index of superalloy GH4169 specimens was studied, and fatigue performance tests at 20 °C, 450 °C, and 650 °C were carried out to analyze the primary factors affecting the high-temperature fatigue performance of specimens. The results indicated that the surface roughness of specimens remained essentially unchanged. However, the value of surface residual stress decreased significantly, with a release of more than 60% at the highest temperature. At 650 °C, the surface microhardness increased, while the degree of surface plastic deformation decreased under alternating loads. Simultaneously, when the surface roughness was less than Ra 0.4 μm, surface microhardness was the main factor affecting the high-temperature fatigue performance of specimens. The influence of surface microhardness on low-cycle fatigue performance was not consistent with that on high-cycle fatigue performance. The latter increased monotonically, whereas the former initially increased and then decreased with increasing surface microhardness.

The effect of biomimetic laser surface treatment on the wear performance of high manganese steel

High manganese steel finds widespread applications in diverse friction and wear environments. The poor wear resistance of high manganese steel at low stress levels has prompted researchers globally to focus on studying its wear performance. Drawing inspiration from the protective features of pangolin scales, this study employed a pulsed radiation mode CO2 laser to conduct biomimetic laser surface treatment (BLST) on Mn13 high manganese steel. The BLST generated a biomimetic surface morphology consisting of tiny scales on the high manganese steel specimens. Subsequently, the biomimetic laser surface-treated (BLSTed) specimens underwent tests for surface morphology, microstructure, microhardness, and surface roughness. These tests employed metallographic microscopy, scanning electron microscopy, a microhardness tester, and a surface profilometer, respectively. A ring block friction and wear testing machine was utilized to evaluate the wear performance of the BLSTed specimens. Changes in laser power, laser frequency, and laser scanning velocity were found to alter the surface morphology of BLSTed specimens. The experimental results revealed that the microstructure of the BLSTed specimen surface comprised needle-like martensite. The increment in surface hardness and surface roughness of BLSTed specimens contributed to an elevation in their average friction coefficient. Furthermore, the surface hardness and wear performance of BLSTed specimens exhibited varying degrees of improvement with the increase in laser power, laser frequency, and laser scanning velocity. The tiny biomimetic scales, created through BLST, provided protection to high manganese steel akin to the protective scales on the body of pangolins. Finally, the study unveiled the wear resistance mechanism of BLSTed specimens.

Effect of propolis on the mechanophysical properties of addition silicon dental impression material

Background Dental impressions should be disinfected to stop the transmission of germs among dental workers since they provide a risk of diseases. The aim of this study was to examine the effects of two disinfectants (16 mg/ml propolis and 5.25% sodium hypochlorite) on the detail reproduction, linear dimensional change, compatibility with gypsum products, wettability, and surface roughness of addition silicon material. Methods Ninety specimens were created using Addition silicon impression material, and they were then divided into three groups at random. Ten specimens from each test group were used in each test. Utilizing apparatus made in accordance with ISO 4823:2015, detail reproduction, linear dimensional change, and compatibility with gypsum products are assessed. A digital Profilometer was uutilized to evaluate surface roughness, and a Goniometer was utilized to evaluate wettability by taking the contact angle. Before testing, the specimens were immersed for 10 minutes each in two disinfection solutions: 16 mg/ml propolis and 5.25% NaOCL. The control group received no disinfection. One-way ANOVA tests and the Kruskal-Wallis test, which was statistically significant at a level of p 0.05, were used to examine the data. Results Comparing the linear dimensional change, surface roughness, and wettability of Addition silicon specimens immersed in 16 mg/ml propolis, 5.25% NaOCL, or the control group demonstrated statistically significant differences (p&lt; 0.05), while details reproduction and compatibility with gypsum revealed statistically no significant differences (p &gt; 0.05). Conclusion Within the parameters of this study, the addition silicon can be immersed in 16 mg/ml propolis for 10 min. to disinfect it without compromising its dimensional accuracy, detail reproduction, compatibility with gypsum products, surface roughness, or wettability.

Impact of process parameters on improving the performance of 3D printed recycled polylactic acid (rPLA) components

The main goal of this research was to investigate the influence of additive manufacturing (AM) printing parameters on the mechanical properties and surface roughness of specimens fabricated using recycled polylactic acid (rPLA). In order to achieve this goal, significant printing parameters such as layer thickness, infill density, and nozzle temperature were selected based on prior research. A three-level L9 orthogonal array, based on the Taguchi method, was used in the experimental design. The mechanical properties of virgin PLA and recycled PLA printed specimens were examined and compared. To facilitate the analysis of variance (ANOVA) examination, the response data for mechanical and surface roughness parameters were transformed to signal-to-noise (S/N) ratios. The inspected responses under consideration were the surface roughness, shore D hardness, tensile strength, flexural strength, and impact strength. The main findings suggest that careful consideration of the layer height is crucial for achieving optimum mechanical properties in the recycled PLA specimens. Furthermore, the nozzle temperature also played an important factor that affected the mechanical and surface roughness properties of the 3D printed PLA specimens. Microscopic investigation demonstrated that the number and size of voids increased significantly when the layer thickness and temperature were low, namely, 0.1 mm and 195 ℃, respectively. Finally, the optimal combination of printing parameters for each performance characteristic was determined. Following this, a confirmation test was performed using the preferred combination of parameters, which indicated a strong correlation with the outcomes predicted statistically. The results obtained from this study revealed that recycled PLA exhibited mechanical properties comparable to that of virgin PLA under certain conditions. In summary, the results of this study will serve as a valuable dataset in the field of additive manufacturing, providing valuable insights for other researchers working with recycled PLA material.

Investigation on surface characteristics of wall structures out of stainless steel 316L manufactured by laser powder bed fusion

AbstractPressure equipment poses a high risk of harming people and the environment in case of failure. They are, therefore, highly regulated by the Pressure Equipment Directive. To enable laser powder bed fusion of metals (PBF-LB/M) for the manufacturing of such components, component appearance and quality need to be characterized and qualified for each specific system. In this study, the surface roughness of wall structures out of austenitic stainless steel (316L) is investigated. Wall structure specimens were produced by four manufacturing systems on different PBF-LB/M machines and with different powder materials. Surface roughness of specimens are compared in the upskin and downskin areas in relation to different slope angles and wall thicknesses. Although different process setups, parameters and powder feedstocks have been used, similarities in the dependency of the surface roughness related to the slope angle and wall thickness can be observed. This work furthermore presents a mechanism-based analytical approach to predict system-specific surface roughness. Particularly, the analytical approach on the influence of slope angle on the surface roughness of the downskin areas has not been covered in publications about PBF-LB/M before. The results of this work enable the prediction of system-specific surface roughness, which is especially important for parts with downskin areas and hidden surfaces without the possibility of additional surface treatment.

Effect of polishing versus glazing of CAD-CAM ceramics on wear and surface roughness of opposing composite resin

Background: This study aimed to assess the effect of polishing versus glazing of computer-aided design-computer-aided manufacturing (CAD-CAM) ceramics on depth of wear and surface roughness of opposing composite resin. Materials and Methods: This in vitro study was conducted on 40 Z250 composite and 40 CAD-CAM ceramic specimens including Celtra Duo, Vita Mark II, e.max CAD, and Vita Suprinity ceramics. All ceramic specimens were roughened by a fine-grit bur after primary glazing to simulate an adjusted surface in the clinical setting. They were then randomly assigned to two subgroups and underwent reglazing or polishing. All composite and ceramic specimens underwent profilometry after surface treatment and prior to the wear test, and the results were recorded quantitatively. Composite specimens were then subjected to 120,000 wear cycles against ceramic specimens in a chewing simulator, and the depth of wear was measured by a scanner. Data were statistically analyzed by repeated measures two-way analysis of variance (ANOVA) and one-way ANOVA (α = 0.05). Results: Comparison of the surface roughness of composite specimens before and after the wear test revealed significant differences in both glazed Suprinity (P = 0.048) and Vita Mark II (P = 0.026) ceramics groups. The change in surface roughness after the wear test (compared with baseline) was significant in glazed (P = 0.000) and polished (P = 0.013) Vita Mark II and polished Suprinity (P = 0.037) ceramics, but this change was not significant in other ceramics (P &gt; 0.05). The depth of wear after the wear test was not significantly different among the ceramic and composite subgroups (P &gt; 0.05). Conclusion: Assessment of depth of wear and surface roughness of composite specimens showed that the polishing kits of CAD-CAM ceramics can serve as a suitable alternative to reglazing.

Effect of Heat Treatment Duration and Cooling Conditions on Flexural Strength and Surface Roughness of Cobalt-Chromium Alloys produced by Selective-Laser-Melting

Post-heat treatment may enhance mechanical properties of selective laser melting (SLM) Cobalt chromium (Co-Cr) alloys, however it is unknown what duration the heat treatment needs to last and how the rate of cooling impacts the alloy's flexural strength and surface roughness. In this study, SLM Co-Cr alloy specimens were heated at 1150 C for 1 or 6 hours and subsequently cooled by air cooling (AC), furnace cooling (FC), or water quenching (WC). Flexural strength and surface roughness were then tested. Aim of this study: Investigate the effect of heat treatment and different cooling conditions on the flexural strength and surface roughness of SLM Co-Cr alloy specimens. The heat treatment will be conducted at 1150 C for two different durations (1-hour and 6-hours) and under three cooling conditions (AC, FC, and WC). Materials and methods: A total of forty-two rectangular specimens, measuring (34×13×1.5 mm) were manufactured through SLM and divided into seven groups, six specimens for each group as follows: The first group denoted as control with no heat treatment and no cooling applied, second and third groups heated for 1 or 6 hours then cooled in the air (AH-1 and AH-6), fourth and fifth groups heated for 1 or 6 hours and left inside the furnace until they cooled (FH-1 and FH-6), sixth and seventh groups heated for 1 or 6 hours and cooled by water quenching (WH-1 and WH-6). Flexural strength and surface roughness tests were performed on the specimens. A flexural strength value of (2147.33 MPa) was indicated that the control group exhibited the highest flexural strength, whereas the FH-6 group exhibited the lowest flexural strength value (1282.66 MPa). The control group showed the worst surface roughness (1.63 μm) while all other groups demonstrated no significant differences in surface roughness ranging from (0.32 to 0.49 μm) with a slight increase in the 6-hours heated groups. Conclusions: Slow cooling rate inside the furnace affects flexural strength negatively. Therefore, a high cooling rate is recommended to get a better flexural strength. On the other hand, surface roughness results suggests that 1-hour is better than 6-hours in terms of heat treatment duration and time saving

The Effect of Se ect of Several Electric Cigar al Electric Cigarette Puffs on Nanohybrid ette Puffs on Nanohybrid Composite Resin Surface Roughness

Nanohybrid composite resin is a dental restorative material comprising micro and nano-sized fillers. When accompanied by smoking habits, it can alter the surface roughness of composite resin. Objective: This study aimed to determine the effect of several electric cigarette (e-cigarette) puffs on the surface roughness of nanohybrid composite resin. Methods: This study was conducted in the experimental laboratory with a pretest-posttest control group design using 48 nanohybrid composite resin specimens divided into six groups. Subsequently, the experimental groups were exposed to 75, 150, 225, 300, and 450 puffs of e-cigarette, and the control group was given artificial saliva immersion without exposure for 21 days. The surface roughness of specimens was measured with a surface roughness tester and evaluated through statistical analysis, including One-Way ANOVA and Post-Hoc LSD. Results: The average pre-test and post-test differences between groups I, II, III, IV, V, and VI were 0.013, 0.022, 0.033, 0.044, 0.065, and 0.005 μm. These results showed a significant difference in the surface roughness of nanohybrid composite resin (p &lt; 0.05), with variations between all groups. Conclusion: This study showed that the number of e-cigarette puffs had a significant effect on the surface roughness of nanohybrid composite resin. Specifically, an increase in the number of e-cigarette puffs led to a rise in the surface roughness value of nanohybrid composite resin.

Experimental investigation of surface roughness of CT3 steel on adhesion strength of ARC spray Al -Mg alloy coating

Thermal spray-applied AlMg alloy coatings are frequently utilized in a variety of technical applications because of great corrosion resistance, and environmental friendliness. In this work, the effect of abrasive spraying parameters on the surface roughness of CT3 steel specimens as well as the effect of the surface roughness on the adhesion strength of Al-Mg alloy spray coating were experimentally investigated. The surface roughness was assessed using a portable roughness gauge. The adhesion strength of the coating was evaluated by the pull-off test, according to the JIS H8664-1977 standard. The experimental findings indicate that air pressure and spraying distance have great impacts on the surface roughness of CT3 steel. The adhesion strength of the Al-Mg coating applied on CT3 steel is found to be almost linearly proportional to the surface roughness. The maximum adhesion strength of 14 MPa was achieved at the highest Rz of about 61 µm.

Konvansiyonel, Eksiltmeli ve Eklemeli İmalat Tekniklerinde Kullanılan Geçici Kron Materyallerinin Yüzey Pürüzlülüğüne Diş Fırçalama ve Yüzey İşlemlerinin Etkisi: İn Vitro Çalışma

Background: This study aimed to compare the effect of the surface treatment and toothbrushing abrasion on the surface roughness of interim crown material specimens manufactured using conventional, subtractive, and additive processing techniques.&#x0D; Material and methods: 80 disk-shaped specimens were prepared from 4 different interim crown materials; one auto-polymerized polymethyl methacrylate resin (PMMA);(IM) and one bis-acryl composite resin;(AC) for conventional technique, one computer-aided design/computer-aided manufacturing (CAD-CAM) PMMA block;(TC) for subtractive process, one 3-dimensionally (3D) printed resin;(CB) for additive process. Specimens of each interim crown material were divided into two subgroups according to applied surface treatments; conventional polishing or surface sealant agent coupling (n=10). The surface roughness values of specimens before (Ra0) and after 10,000 cycles of toothbrushing (Ra1) were measured with a profilometer. Data were statistically analyzed.&#x0D; Results: The polished groups of all interim crown materials showed significantly higher Ra0 values compared to the sealant groups before toothbrushing (p˂0.05). While the polished IM groups exhibited the highest Ra0 value (0.44±0.08), the sealed TC groups exhibited the lowest Ra0 value (0.23±0.06). The Ra values of all material groups increased after simulated 1-year toothbrushing. While the polished IM group exhibited the highest Ra1 value (0.45±0.14), the sealed CB group had the lowest Ra1 value (0.31±0.09).&#x0D; Conclusion: It was observed that toothbrushing caused an increase in the surface roughness of all interim materials. The application of a surface sealant agent to these materials is more effective than polishing to reduce surface roughness. Sealed 3D printed resin for additive process exhibited the lowest mean roughness value after toothbrushing.&#x0D; Keywords: Additive Manufactured, Interim Crown Material, Roughness, Subtractive Manufactured, Toothbrushing Abrasion

Comparative study of anodizing and chromate conversion coatings in enhancing the wear and corrosion properties of 6063 Al alloy

ABSTRACT The present study compares the corrosion and tribological performance of anodic oxide (AO) and chromate conversion (CC) coatings deposited on 6063-T6 aluminum alloy. The goal is to determine how these treatments benefit the performance of the underneath substrate. The corrosion protection properties of the coatings were evaluated by potentiodynamic polarization measurement in 3.5 wt. % NaCl solution. The friction and sliding wear behavior of coatings were studied by pin-on-disk test and their erosion behavior was examined by air jet solid particle erosion test. The surface structure, chemical composition, roughness, wettability, and hardness of specimens were also characterized. The results showed that the AO coating with porous surface morphology was found to be thicker, rougher, and harder along with greater wettability, when compared to CC coating. Furthermore, the AO coating with polarization resistance of 6.64 × 103 Ω.cm2 enhanced the corrosion resistance of the substrate more than 8 times. In addition, the AO coating under dry and wet sliding conditions reduced the aluminum alloy substrate wear rate by about 80% and 52%, respectively. However, due to being more brittle, the AO coating lost more weight than the CC coating during the solid particle erosion test.

Electropolishing with Circulated Electrolyte for Improving Surface Finish of Brass

Electropolishing has been widely used for surface finishing of metallic products in the industry, owing to its excellent capability of producing metallic components with a homogeneously smooth surfaces. However, this treatment is often constrained by the long duration required for the processing. Therefore, an improvement in this process is needed. The aim of this research is to introduce the use of electropolishing with circulated electrolytes for improving the surface finish of brass. In this work, electropolishing was carried out by using circulated H2SO4 electrolyte for 10 to 30 min in a customized electropolishing chamber. The effect of this treatment on surface morphology, surface roughness, and thickness reduction of the brass specimen was determined. The results showed a better capability of electropolishing with circulated electrolyte in decreasing the brass roughness, i.e., by 84%, than that without electrolyte circulation which only reached 45% during 30 min of the treatment.

Impact of laser scanning strategies on microstructure in laser powder bed fusion (LPBF) of nanoparticle-infused pre-alloyed water-atomized iron powder

This study investigates how two scan strategies impact the microstructural and tensile properties of nanoparticle-infused pre-alloyed water-atomized low-alloy iron powder (Fe-1.50Cu-1.75Ni-0.50Mo) during Laser Powder Bed Fusion (LPBF) under uniform volumetric energy density laser conditions. The two strategies were the rotation method (ROT), in which the laser scan vector was rotated by 67° for each layer (10°, 77°, 144°, 211°, …), and the zig-zag method (ZZ), in which the vector was rotated by 90° for each layer (45°, −45°, …). As a result, the relative density of the ROT specimens was measured to be 95.61 ± 1.01 %, while that of ZZ specimens was 99.76 ± 0.17 %. Furthermore, the surface roughness of ROT specimens was higher than that of ZZ specimens (24.05 μm vs. 10.30 μm). It was found that the scan strategy influences not only the bulk characteristics but also the microstructural changes of the specimens, due to variations in intrinsic heat treatment (IHT). In the ZZ specimens, the regular laser scanning direction resulted in a uniform microstructure across different heights. However, in the ROT specimens, the laser scanning direction varied from layer to layer, with fluctuating heat dissipation influencing the melt pool structure, recrystallized grain distribution, sub-grain cellular structure, and precipitation behavior to obtain lower density and higher surface roughness than those of ZZ samples. Therefore, the samples printed using the ZZ method are found to be advantageous for printing pre-alloyed WA iron powders with uniform microstructure and reliable tensile properties.

Surface Quality of AZ91D Magnesium Alloy After Precision Milling with Coated Tools

This study investigates the surface quality of AZ91D magnesium alloy specimens after precision milling. The milling was conducted with the use of TiB2- and TiAlN-coated carbide end mills. The following variables were used in the milling process: cutting speed vc, feed per tooth fz and axial depth of cut ap. The surface quality was analysed based on surface roughness parameters and Abbott-Firestone curves. The results showed that the surface quality after machining depended on the tool coating type and applied machining parameters; the only exception was the axial depth of cut because changes in its value did not have any significant effect on the obtained surface quality. After precision milling, AZ91D specimens were characterized by very low surface roughness parameters. The impact of machining conditions was also evaluated with ANOVA analysis, which confirmed the significant effect of cutting speed and feed per tooth. It also indicated the dependence of the roughness parameters on the tool coating type. The tool coating type and machining conditions did not have any significant effect on the Abbott-Firestone curves. Despite the changes applied, the shape of the curves remained similar. The obtained results provide both theoretical and practical knowledge about the achievable surface roughness of AZ91D magnesium alloy specimens after precision milling.

Surface characteristics of 3D printed PEEK polymer using atomic force microscopy

High-performance polymer three-dimensional printing is becoming more popular for producing unique parts suitable for different applications. It has been utilized extensively in biomedical applications such as dental prosthetics, surgical equipment, and implants. However, the performance of the material is significantly influenced by its surface qualities, particularly in aspects of its adhesion and biocompatibility. This study involves the fabrication of PEEK specimens S1, S2, S3, and S4 with different printing parameters such as layer height of 0.10 and 0.15 mm and printing speed of 20 and 25 mm/s using a fused deposition modeling process. The surface roughness of the fabricated specimens is measured using atomic force microscopy. The results showed that the printing parameters significantly impact the surface roughness of the PEEK specimens. The surface roughness of specimen S3, printed at a layer height of 0.15 mm and a speed of 20 mm/s, has a low roughness value of 0.017 μm, which is considerable in comparison to the other specimens. In addition to the measurement of surface roughness from roughness profile, the force curve separation graph was plotted and the adhesion force values were calculated for all the specimens to determine the interlayer bonding strength.

Influence of hydrothermal aging on the shear bond strength of 3D printed denture-base resin to different relining materials

ObjectivesThis study evaluated the repairability of three-dimensional printed (3DP) denture bases based on different conventional relining materials and aging. Material and methodsThe groups for surface characterization (surface-roughness and contact-angle measurements) were divided based on the denture base and surface treatment. Shear bond strength test and failure-mode analysis were conducted by a combination of three variables: denture base, relining materials, and hydrothermal aging (HA). The initial characterization involved quantifying the surface roughness (n = 10) and contact angle (n = 10) of denture base specimens with and without sandblasting (SB) treatment. Four relining materials (Kooliner [K], Vertex Self-Curing [V], Tokuyama Rebase II (Normal) [T], and Ufi Gel Hard [U]) were applied to 3DP, heat-cured (HC), and self-cured (SC) denture-base resin specimens. Shear bond strength (n = 15) and failure-mode analyses (n = 15) were performed before and after HA, along with evaluations of the fractured surfaces (n = 4). Statistical analyses were performed using a two-way analysis of variance (ANOVA) for surface characterization, and a three-way ANOVA was conducted for shear bond strength. ResultsThe surface roughness peaked in HC groups and increased after SB. The 3DP group displayed significantly lower contact angles, which increased after treatment, similar to the surface roughness. The shear bond strength was significantly lower for 3DP and HC denture bases than for SC denture bases, and peaked for U at 10.65 ± 1.88 MPa (mean ± SD). HA decreased the shear bond strength relative to untreated samples. Furthermore, 3DP, HC, and SC mainly showed mixed or cohesive failures with V, T, and U. K, on the other hand, trended toward adhesive failures when bonded with HC and SC. ConclusionThis study has validated the repairability of 3DP dentures through relining them with common materials used in clinical practice. The repairability of the 3DP denture base was on par with that of conventional materials, but it decreased after aging. Notably, U, which had a postadhesive application, proved to be the most effective material for repairing 3DP dentures.

Rolling contact fatigue failure mechanism of bearing steel on different surface roughness levels under heavy load

It is inherent knowledge that rolling contact fatigue (RCF) failure of subsurface-initiated spalls usually occur under optimum surface under heavy load. However, our previous work has revealed surface-initiated RCF failure mechanism under heavy load and initial high roughness surface. The formation of surface crack caused by RCF is a complicated phenomenon that is accompanied by surface morphology and lubrication condition, as well as stress distribution and microstructure evolution. To clarify the main failure mechanism, this study carried out systematic RCF tests with different surface roughness specimens and conducted characterization of superficial microstructure for specimens of pre-service and post-service by Focused Ion Beam (FIB). The results clearly suggest precursor of collapsed morphology and nanocrystalline layer are the main factor that causes the RCF life with high roughness is lower than that with low roughness. While the spalling failure initiating from low roughness surface under heavy load are strongly relied on surface plastic deformation. Two main plastic deformation mechanisms are conductive to formation of surface cracks: the micro-plastic deformation and the local severe plastic flow. A newly failure mechanism that spalling failure initiates from surface has been proposed to link surface roughness and microstructure evolution.

Ductile-to-brittle transition of ferritic steels: A historical sketch and some recent trends

The phenomenon of ductile-to-brittle transition in ferritic steels has been a ubiquitous research challenge for the last 50 years. The characterization of this problem using the fracture mechanics concept, from the earliest studies based on the linear-elastic fracture mechanics to the application of the elastic–plastic fracture mechanics, has become inevitable over time. The fracture toughness is not an intrinsic material property but depends on geometrical factors (such as the specimen shape, thickness, and surface roughness), defect type and distribution, loading mode, and environmental conditions. The pronounced scatter of experimental data on fracture toughness, characteristic of all ferritic steels in the ductile-to-brittle transition temperature region, necessitated the use of statistical methods for data processing. That approach, which emerged in the 1970 s, can still be found today as the basis for interpreting fracture toughness data in ductile-to-brittle transition problems. This paper presents a brief historical overview of such studies along with the problems that have arisen as a consequence of using fracture mechanics concepts, such as constraint effects, as an example. In the time-honored research tradition, all the proposed methods and models, as well as their criticisms, provided the basis for the development of new approaches to the ductile-to-brittle characterization of ferritic steels. Specifically, these include size effects and scaling of geometrically similar samples, with the aim of predicting material behavior beyond experimental limits. Brief outlines of two new approaches are provided in this succinct review. The criticisms of all presented methods are oriented mostly on the application domain, as well as their capability to predict fracture toughness, with short overview of their most conspicuous advantages and disadvantages.