Single-edge V-notched Beam Research Articles

Zirconia specimens printed by vat photopolymerization: Mechanical properties, fatigue properties, and fractography analysis.

The mechanical and fatigue properties of zirconia specimens printed by vat photopolymerization (VPP) were evaluated and compared with those of zirconia specimens milled by computer numerical control (CNC). Bar-shaped specimens were printed by stereolithography (SL) and digital light processing (DLP). CNC-milled specimens were used as control samples. The fracture toughness, hardness, and flexural strength properties of the zirconia specimens were evaluated via single edge V-notch beam tests, Vickers hardness tests, and 3-point bending tests. Dynamic fatigue tests were carried out in distilled water using a step-stress test. After static bending and dynamic step-stress testing, fractography analysis was performed. Statistical analysis was carried out to compare the fracture toughness, hardness, flexural strength, and fatigue cycle results of each group (α = 0.05). The fracture toughness values did not significantly differ among the groups (p>0.05). The flexural strength was 894.10MPa for SL, 831.46MPa for DLP, and 1140.39MPa for CNC. The flexural strength of CNC was greater than that of SL and DLP (p<0.01). The mean fatigue cycles were 23498.07 for SL, 19858.60 for DLP, and 31566.80 for CNC. The mean fatigue failure strength was 643.13MPa for SL, 530.63MPa for DLP, and 903.75MPa for CNC. The fatigue failure strength of CNC was greater than that of SL and DLP (p<0.05). Fractography analysis revealed material defects at the fracture origin for each group. A partially fused structure of the incompletely debonded resin could be observed in SL, and a porous region of incompletely sintered zirconia grains could be observed in CNC. The fracture toughness and hardness of zirconia printed by VPP are comparable to those of zirconia milled by CNC. However, zirconia milled by CNC has superior static flexural strength and dynamic fatigue resistance. Further studies are needed to explore the clinical applications of VPP-printed zirconia.

Effect of glazing and thermocycling on the fracture toughness and hardness of a New fully crystallized aluminosilicate CAD/CAM ceramic material

BackgroundThe mechanical properties of fully crystallized lithium aluminosilicate ceramics may be influenced by intraoral temperature variations and postmilling surface treatment. The purpose of this study is to explore the interplay among glazing, thermocycling, and the mechanical characteristics (namely, fracture toughness and hardness) of fully crystallized lithium aluminosilicate ceramics.MethodsBending bars (n = 40) cut from LisiCAD blocks (GC, Japan) were randomly assigned to glazed or unglazed groups (n = 20) and subjected to the single edge v-notch beam method to create notches. A glazing firing cycle was applied to the glazed group, while the unglazed group was not subjected to glazing. Half of the specimens (n = 10) from both groups underwent thermocycling before fracture toughness testing. The fracture toughness (KIC) was evaluated at 23 ± 1 °C using a universal testing machine configured for three-point bending, and the crack length was measured via light microscopy. Seven specimens per group were selected for the hardness test. Hardness was assessed using a Vickers microhardness tester with a 1 kg load for 20 s, and each specimen underwent five indentations following ISO 14705:2016. The Shapiro–Wilk and Kolmogorov-Smirnov tests were used to evaluate the normality of the data and a two-way ANOVA was utilized for statistical analysis. The significance level was set at (α = 0.05).ResultsRegardless of the thermocycling conditions, the glazed specimens exhibited significantly greater fracture toughness than did their unglazed counterparts (P < 0.001). Thermocycling had no significant impact on the fracture toughness of either the glazed or unglazed specimens. Furthermore, statistical analysis revealed no significant effects on hardness with thermocycling in either group, and glazing alone did not substantially affect hardness.ConclusionsThe impact of glazing on the fracture toughness of LiSiCAD restorations is noteworthy, but it has no significant influence on their hardness. Furthermore, within the parameters of this study, thermocycling was found to exert negligible effects on both fracture toughness and hardness.

On the robustness of the Single-Edge-Precracked-Beam (SEPB) method for fracture toughness testing of ceramic materials

The Single-Edge-Precracked-Beam (SEPB) method for the testing of fracture toughness (KIc) of ceramic materials is a variation of the Single-Edge-Cracked-Beam (SEPB) method for the test of metallic materials that creates a sharp precrack not by fatigue, but by a “bridge indentation” technique that induces a crack to pop-in under compression loading. This precrack is sharp and overcomes the issue of blunt notch-root radii resulting from the Single-Edge-V-Notched-Beam (SEVNB) method, which overestimates the KIc of ceramics with submicrometric microstructures. However, the difficulties in obtaining a valid precrack and measurement make of the SEPB a low-yield, time- and cost-intensive method. Here we evaluate the SEPB method using large datasets of two fine dental grade ceramics to assess the sensitivity of the validity criteria in ISO 15732 and ASTM C 1421 and the effect of their violations in the obtained KIc. We compile datasets including or excluding validity criteria and combine those of the two standards to establish their effect on the mean and scatter of the data. We discuss the appropriateness of the validity ranges and of some criteria as a whole, while arguing for tightening the criterion precrack frontline asymmetry and for the dropping of criteria regulating the extent of stable crack extension.

A modified single edge V-notched beam method for evaluating surface fracture toughness of thermal barrier coatings

The surface fracture toughness is an important mechanical parameter for studying the failure behavior of air plasma sprayed (APS) thermal barrier coatings (TBCs). As APS TBCs are typical multilayer porous ceramic materials, the direct applications of the traditional single edge notched beam (SENB) method that ignores those typical structural characters may cause errors. To measure the surface fracture toughness more accurately, the effects of multilayer and porous characters on the fracture toughness of APS TBCs should be considered. In this paper, a modified single edge V-notched beam (MSEVNB) method with typical structural characters is developed. According to the finite element analysis (FEA), the geometry factor of the multilayer structure is recalculated. Owing to the narrower V-notches, a more accurate critical fracture stress is obtained. Based on the Griffith energy balance, the reduction of the crack surface caused by micro-defects is corrected. The MSEVNB method can measure the surface fracture toughness more accurately than the SENB method.

Comparison between different fracture toughness techniques in zirconia dental ceramics.

Vickers indentation (IF) and single-edge-V-notched beam (SEVNB), to measure the fracture toughness (KIC ) of zirconia-based dental ceramics and mathematical models were proposed to establish a correlation between both. Zirconia (ZrO2 ) stabilized with 3mol. % of Y2 O3 (3Y-TZP) and 5mol% of Y2 O3 (5Y-PSZ) were compacted (n=42) and sintered for 2h at different temperatures (1475°C, 1500°C, 1550°C, or 1600°C). After sintering, they were characterized by relative density using the ASTM C373-88 standard, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average grain size was measured according to the ASTM E1382-97 standard. The fracture toughness (KIC ) was determined using two methods: Vickers indentation fracture toughness (KIC-IF ): method based on mathematical modeling that considers the parameters used for the Vickers hardness test and Fracture toughness by the single-edge-V-notch-beam (KIC-SEVNB ): method proposed by ISO 23146:08. The main phases of the 3Y-TZP and 5Y-PSZ ceramics were ZrO2 -tetragonal and ZrO2 -cubic, respectively. The 3Y-TZP specimens showed equiaxed grains with average grain sizes ranging from 0.55 to 0.79 μm. The grain sizes of 5Y-PSZ of specimens sintered at 1475°C and 1600°C were 0.62 and 2.32 μm, respectively. For all ceramics the crack size ratio was c/a < 2.5, suggesting a Palmqvist-type crack system. The fracture toughness measured by the Vickers indentation method (KIC-IF ) and by the SEVNB method (KIC-SEVNB ) was the same when the experimental data were fit to a mathematical model.

Fracture toughness of 3Y-TZP ceramic measured by the Chevron-Notch Beam method: A round-robin study

ObjectiveThis interlaboratory round robin test investigated the robustness of the Chevron-Notch Beam (CNB) test method and the effect of the processing and testing variations on the fracture toughness of a dental 3Y-TZP ceramic. MethodsThe round robin test was performed precisely following the procedures recommended in ISO 24370:2005 and applied on a commercial 3Y-TZP ceramic (product information). A total of 335 test specimens with dimensions 3×4 x 45 mm³ was equally distributed among 10 participating laboratories of varying experience in fracture toughness testing. A standard operating procedure was defined with either narrow processing tolerances or alternative (wider) processing tolerances (as proposed in ISO 24370). Fracture toughness data (series 2) was analyzed using one way ANOVA followed by post hoc Tukey HSD test and 95% Confidence Intervals (CI) were computed (p < 0.05). A further, preceding round-robin (series 1) test was conducted with - more possible variations of test conditions regarding CNB notch processing and storage conditions. Those results are summarized in the supplement and discussed with the actual ISO 24370 test. ResultsFracture toughness of the 3Y-TZP ceramic material, summarized over all laboratories was measured to KIc = 4.48 ± 0.11 MPam0.5 for the standard processing tolerance and KIc = 4.55 ± 0.31 MPam0.5 for the alternative tolerance. The results revealed a significant influence of cutting offset and notch geometry on KIc when using CNB method. The test medium also has a significant influence on KIc in terms of reduced fracture toughness under the influence of water. With defined testing conditions the number of valid tests and reduced standard deviation increased. In case of strictly following such standard operation procedures, KIc can be determined with high reliability. There is no difference between the involved laboratories, but significant influence of cutting offset on KIC was observed. SignificanceThe CNB method is suitable method for determination of KIc on fine-grained ceramics such as 3Y-TZP ceramic. By using tighter tolerances for processing and testing, i.e. closely following the ISO 24370 procedure, a highly-precise evaluation of fracture toughness with low data variation is achievable. The information of the storage medium should always be reported along with the data. CNB fracture toughness testing is an alternative method compared to Single-edge V-notch beam (SEVNB), especially for fine-grained ceramics.

Towards the development of self-healing and antibacterial dental nanocomposites via incorporation of novel acrylic microcapsules

ObjectiveThe main aim of the current work was to develop the novel self-healing dental composites contained poly(methyl methacrylate) (PMMA) microcapsules. The effects of PMMA microcapsule content in self-healing performance and mechanical properties of dental composites including flexural strength, flexural modulus, and fracture toughness were discussed. The antibacterial activity and non-toxicity properties of optimum self-healing dental composites were also investigated. MethodsNovel acrylic microcapsules were prepared using triethylene glycol dimethacrylate (TEGDMA) as healing agent and PMMA as microcapsule shell via solvent evaporation method. The silica nanoparticles with the mean size of 15–20 nm were treated by 3-methacryloxypropyltrimethoxysilane (MPS) to enhance their adhesion and dispersion within the acrylic matrix of composite. Acrylic microcapsules with mass fractions of 0%, 5%, 10%, and 15% were added into a mixture of acrylic resins and MPS-grafted SiO2 nanoparticles. The strength and elastic modulus of dental composites were measured by the flexural test. The single edge V-notched beam (SEVNB) method was applied to investigate fracture toughness (KIC) and healing efficiency. The results were then statistically analyzed using one-way analysis of variance (ANOVA) at the confidence level of 0.95. ResultsAcrylic microcapsules were synthesized with the mean size around 30 µm and the core content of about 15 wt%. The grafting percentage of MPS surface modifier onto SiO2 nanoparticles was measured 3.2%. The incorporation of PMMA microcapsules into the dental composites had no significant effect on flexural properties. The self-healing dental composites also indicated the high efficient healing performance in the range of 78–121%. The self-healing dental composites also exhibited impressive antibacterial activity against Streptococcus mutans (S. mutans). The MTT assay also revealed that the incorporation of acrylic microcapsules in dental composites has no cytotoxicity effects. SignificanceIn the current study, for the first time, the self-healing dental nanocomposites contained acrylic microcapsules were prepared with excellent healing performance and antibacterial properties.

Microstructural evolution and mechanical properties of nano-ATZ ceramics by solid solution precipitation

Alumina toughened zirconia (ATZ) nanoceramics accompanied with high-strength, high-toughness and high-hardness were prepared by in-situ nanoprecipitation from using solid solution micro-powders. The submicron-sized Al2O3 (∼445 nm) and ZrO2 (∼361 nm) grains contained low-density precipitated nano-ZrO2 (∼35 nm) and nano-Y4Al2O9 (YAM, ∼87 nm) particles, respectively, making high-performance nano-ATZ ceramics with ultrafine intracrystalline nanostructure yet achieved. There was a parallel or eutectic lattice orientation relationship between the submicrocrystals and its internal nanoparticles of their crystal planes, which is very conducive to the improvement of the mechanical properties of nano-ATZ ceramics. The fracture toughness and hardness of 30wt%Al2O3/70wt%ZrO2(3 mol%Y2O3) can reach up to 5.68 ± 0.17 MPa m1/2 (single-edge V-notched beam method, SEVNB) and 16.32 ± 0.45 GPa, respectively, which are improved by ∼25% and ∼20% compared with those of 3Y-TZP ceramics. Therefore, this method can be used to prepare nano-ATZ ceramics contained ultrafine nanoparticles and uniform distribution of Al2O3 phases.

Mesoporous silica aerogel reinforced dental composite: Effects of microstructure and surface modification

A mesoporous silica aerogel (SiA) with a high specific surface area was synthesized through the sol-gel process and subsequently modified with two different silane-based modifiers to reveals the effect of microstructure and surface modification on the fracture mechanics of a dental composite. The synthesized and modified aerogel were characterized using field-emission scanning electron microscopy (FESEM), nitrogen adsorption-desorption, and Fourier-transform infrared spectroscopy (FTIR). The prepared aerogels were then incorporated within methacrylate-based dental composites with the filler content of 0–35 wt%. Flexural modulus (FM) and Flexural strength (FS) were evaluated by the three-point bending test. The fracture toughness (FT) of the composites was evaluated by single edge V-notched beam (SEVNB) flexure test, while FESEM was employed to investigate the fracture surface morphology of the composites. Furthermore, the wettability of the composites was assessed according to the sessile drop method. The characterization of synthesized aerogels revealed the formation of SiA with a surface area of 550–560 m2/g and porosity of 77%, while FTIR results confirmed the successful modification. Statistical analysis (ANOVA, p≤0.05, and n = 5) revealed that FM significantly enhanced (from 1.43 GPa to 2.66 GPa) as filler content increased over 0–30 wt%, and FS improved (from 80 to 95 MPa) as filler content increased over 0–15 wt%. Furthermore, the modification of aerogels improved both fracture characteristics and the wettability of the composites. The FT evaluations and fractography analysis revealed that the mesoporous structure of the fillers mainly dominated the filler-matrix adhesion strength at the same filler content.

An investigation of the microstructure and mechanical properties of dental zirconia manufactured by digital light processing 3D printing.

This study was performed to investigate the microstructure and mechanical properties of dental zirconia manufactured by digital light processing (DLP) 3D printing and the clinical application prospects of this material. The experiment (DLP) group was zirconia manufactured by DLP 3D printing, and the control (MILL) group was milled zirconia. The density, grain size, and phase composition were measured to study the microstructure. Flexural strength was measured by using three-point bending tests, while Vickers hardness was determined through a Vickers hardness tester. Fracture toughness was tested using the single-edge V-notched beam method. Zirconia density of the DLP group was (6.019 8±0.021 3) g·cm-3, and the average grain size was (0.603 0±0.032 6) μm, but without statistical difference with the corresponding values of the MILL group (P>0.05). Tetragonal phase was found in the X-ray diffraction patterns of the DLP and MILL groups. The flexural strength of the DLP group was (1 012.7±125.5) MPa, and Vickers hardness was (1 238.5±10.8) HV1, which was slightly lower than that of the MILL group (P<0.05). The fracture toughness of the DLP group was (7.22±0.81) MPa·m1/2, which was not statistically different from that of the MILL group (P>0.05). Zirconia manufactured by DLP 3D printing had microstructure and mechanical properties similar to those of the milled zirconia. Only the flexural strength and the Vickers hardness of the experimental zirconia were slightly lower than those of the milled zirconia. Therefore, DLP-manufactured zirconia has a promising future for clinical use.

Fracture Behavior of Single-Crystal Sapphire in Different Crystal Orientations

In order to study the anisotropy of fracture toughness and fracture mechanism of single-crystal sapphire, the three-point bending tests and the single-edge V-notch beam (SEVNB) were used to test the fracture toughness of A-plane, C-plane, and M-plane sapphire, which are widely used in the semiconductor, aerospace, and other high-tech fields. Fracture morphology was investigated by a scanning electron microscope and three-dimensional video microscopy. The fracture toughness and fracture morphology of different crystal planes of sapphire showed obvious anisotropy and were related to the loading surfaces. C-plane sapphire showed the maximal fracture toughness of 4.24 MPa·m1/2, and fracture toughness decreases in the order of C-plane, M-plane, and A-plane. The surface roughness is related to the dissipation of fracture energy. The surface roughness of the fracture surface is in the same order as C-plane &gt; M-plane &gt; A-plane. The fracture behavior and morphology of experiments were consistent with the theoretical analysis. C-plane sapphire cleavages along the R-plane with an angle of 57.6 degrees and the rhombohedral twin were activated. M-plane and A-plane sapphire cleavages along their cross-section.

Mechanical properties of ceria-calcia stabilized zirconia ceramics with alumina additions

Ceria-stabilized zirconia-based composites have been developed aiming to obtain ceramic materials with enhanced hardness, strength, fracture toughness, and resistance to low temperature degradation. These composites are based on ceria-calcia stabilized zirconia (10 mol% CeO2-1 mol% CaO TZP) and α-alumina (0−15 wt%) as a second phase. Raw materials in the form of powders were dispersed through ball milling, dried by slip casting, and subsequently grounded before being pressed and conventionally sintered at 1450 °C. Compared to the strength and hardness of 10Ce-TZP ceramics (typically 500 MPa and 6 GPa), an increase was observed for all compositions, especially for 10Ce-1CaO-5Al2O3 (739 MPa and 10.2 GPa). Single Edge V-Notched Beam fracture toughness values ranged from 5.1 to 6.6 MPa∙√m, indicating a loss of transformability for all compositions. As in 10Ce-1CaO-TZP co-doped ceramics, the aging resistance of all alumina-containing composites was also excellent.

A systematic study on the quality improving of fracture toughness measurement in structural ceramics by laser notching method

The single-edge V-notched beam (SEVNB) method based on the laser notching approach can effectively overcome the shortcoming of time-consuming and avoid large errors in traditional fracture toughness measurement ways, yet there is still a lack of systematic research on the normativity of V-notches as well as the applicability of ceramics with various compositions and microstructures. Taking oxide (ZrO2 and Al2O3), carbide (SiC), nitride (Si3N4) and boride (ZrB2-based) ceramics as the research objects, this paper systematically discussed the effects of notch tip sharpness, relative notch depth (a/W) and equivalent notch angle on the measured value of fracture toughness, thereby clearly defining the range of these parameters that is required for measuring the fracture toughness accurately. Furthermore, in order to give full play to the advantages of the laser notching method, the feasibility of sample miniaturization was also discussed. This study could provide important data reference and theoretical basis for the standardization of laser method in the future.

Influence of microcapsule parameters and initiator concentration on the self-healing capacity of resin-based dental composites

ObjectiveFracture is one of the main causes for failure of resin-based composite restorations. To overcome this drawback, self-healing resin-based composites have been designed by incorporation of microcapsules. However, the relationship between their self-healing capacity and microcapsule and resin parameters is still poorly understood. Therefore, the objective of this study was to systematically investigate the effect of initiator concentration (in the resin) and microcapsule size and concentration on the self-healing performance of commercially available flowable resin-based composites. MethodsPoly(urea-formaldehyde) (PUF) microcapsules containing acrylic healing liquid were synthesized in small (33±8μm), medium (68±21μm) and large sizes (198±43μm) and characterized. Subsequently, these microcapsules were incorporated into a conventional flowable resin-based composite (Majesty Flow ES2, Kuraray) at different contents (5–15wt%) and benzoyl peroxide (BPO) initiator concentrations (0.5–2.0wt%). Fracture toughness (KIC) of test specimens was tested using a single edge V-notched beam method. Immediately after complete fracture (KIC-initial), the two fractured parts were held together for 72h to allow for healing. Subsequently, fracture toughness of the healed resin-based composites (KIC-healed) was tested as well. ResultsThe fracture toughness of healed dental composites significantly increased with increasing microcapsule size and concentration (2wt% BPO, p<0.05). The highest self-healing efficiencies (up to 76%) were obtained with microcapsules sized 198±43 um. Significancecommercially available resin-based composites can be rendered self-healing most efficiently by incorporation of large microcapsules (198±43μm). However, long-term tests on fatigue and wear behavior are needed to confirm the clinical efficacy.

Evaluation of translucency, Marten’s hardness, biaxial flexural strength and fracture toughness of 3Y-TZP, 4Y-TZP and 5Y-TZP materials

ObjectivesTesting and comparing of different non-shaded zirconia materials (3Y-TZP, 4Y-TZP and 5Y-TZP) on optical and mechanical properties. Materials and methodsZirconia materials (N = 320, Opaque O, Translucent T, Extra Translucent ET, High Translucent HT) were investigated on translucency, Martens parameter, biaxial flexural strength, Chevron-Notch-Beam (CNB) fracture toughness (KIC) and grain size. The grain size was analyzed using a scanning electron microcopy (SEM). Univariate ANOVA, post-hoc Scheffé, partial eta-squared, Kolmogorov-Smirnov-, Kruskal-Wallis- and Mann-Whitney-U-tests (p < 0.05) were performed. The reliability of flexural strength was calculated with two-parametric Weibull analysis and 95 % confidence level. ResultsThe translucency of ET and HT increased with the thermo-mechanical aging (p < 0.001). The zirconia material and aging had no impact on the Martens hardness and the indentation modulus. ET showed the highest flexural strength values after initial and thermo-mechanical aging (p < 0.001 – 0.683). All four materials showed the highest flexural strength after thermo-mechanical aging after 1.2 Mio cycles. Thermo-mechanically (1.2 Mio cycles) aged HT presented the highest Weibull modulus (m = 15.0) regardless of aging. Within initial groups, T (p ≤ 0.001) showed the highest fracture toughness, followed by O (p ≤ 0.001), ET (p < 0.003) and HT (p ≤ 0.001). SignificanceTranslucency of ET and HT increases with thermo-mechanical aging. Chevron-Notch-Beam (CNB) is a valid alternative to the single-edge-V-notched beam (SEVNB) method for testing fracture toughness.

Structure and mechanical properties of ceramic materials based on alumina and zirconia with strontium hexaaluminate additives

In this study, the effect of a small amount of strontium hexaaluminate (3 wt %) additives on the properties of alumina- and zirconia-based ceramics is discussed. α-Al2O3, 3Y-ZrO2 and SrO submicron powders are used as the starting materials. Specimens are prepared by water suspension dispersion in a bead mill, spray drying granulation, isostatic pressing and pressureless sintering. Structural studies are conducted using a scanning electron microscope. The Archimedes approach is employed to determine the density and porosity of the specimens. Microhardness, flexural strength at three-point bending and fracture toughness are determined by the single-edge V-notch beam (SEVNB) method and indentation. A material containing 50-wt. % Al2O3 and 50-wt. % ZrO2 exhibited the most rational combination of characteristics such as strength (950 ± 50 MPa), microhardness (1800 HV) and fracture toughness (6.5 MPa m1/2). The SEVNB fracture toughness tests showed that the highest recorded value of a critical stress intensity factor was 9 MPa m1/2 for specimens containing 47-wt. % Al2O3, 3-wt. % SrAl12O19 and 50-wt. % ZrO2. The length of strontium hexaaluminate platelets decreased with an increase in the zirconia content in the materials and reached 0.8–2.6 μm. A pronounced fragmentary structure is characteristic of the strontium hexaaluminate platelets. The platelets under study comprised one or two boundary-separated blocks with a thickness of ~150–200 nm. Each block is divided into smaller fragments. The structure of strontium hexaaluminate platelets affects the crack propagation trajectory. The identified mechanisms of crack propagation are as follows: transcrystalline and intercrystalline fractures of alumina grains, crack deflection from the propagation trajectory, crack branching and failure of SrAl12O19 platelets.

Fiber reinforcement of a resin modified glass ionomer cement

ObjectivesUnderstand how discontinuous short glass fibers and braided long fibers can be effectively used to reinforce a resin modified glass ionomer cement (RMGIC) for carious lesion restorations. MethodsTwo control groups (powder/liquid kit and capsule) were prepared from a light cured RMGIC. Either discontinuous short glass fibers or braided polyethylene fiber ribbons were used as a reinforcement both with and without pre-impregnation with resin. For the former case, the matrix was the powder/liquid kit RMGIC, and for the latter case the matrix was the capsule form. Flexural strength was evaluated by three-point beam bending and fracture toughness was evaluated by the single-edge V-notch beam method. Compressive strength tests were performed on cylindrical samples. Results were compared by analysis of variances and Tukey’s post-hoc test. Flexural strength data were analyzed using Weibull statistical analysis. ResultsThe short fiber reinforced RMGIC both with and without pre-impregnation showed a significant increase of ∼50% in the mean flexural strength and 160–220% higher fracture toughness compared with the powder/liquid RMGIC control. Reinforcement with continuous braided fibers gave more than a 150% increase in flexural strength, and pre-impregnation of the braided fibers with resin resulted in a significant flexural strength increase of more than 300% relative to the capsule control. However, for the short fiber reinforced RMGIC there was no significant benefit of resin pre-impregnation of the fibers. The Weibull modulus for the flexural strength approximately doubled for the fiber reinforced groups compared to the control groups. Finally, compressive strength was similar for all the groups tested. SignificanceBy using a RMGIC as a matrix, higher flexural strength was achieved compared to reported values for short fiber reinforced GICs. Additionally, the short fibers provided effective toughening of the RMGIC matrix by a fiber bridging mechanism. Finally, continuous braided polyethylene fibers gave much higher flexural strength than discontinuous glass fibers, and their effectiveness was enhanced by pre-impregnation of the fibers with resin.

Comparison of fracture toughness testing by the single edge v-notch beam and the surface crack in flexure method on silicon nitride

This work is intended to compare the SEVNB and the SCF methods for fracture toughness testing. Both of the test methods are applied to a silicon nitride. Both methods are standardized and both have some minor shortcomings with respect to practicability and match of the theoretical description of the test situation with the actual test situation. SEVNB is easy to perform, but uses a notch of known depth (+ small micro-cracks of unknown size in front of a notch) instead of a crack, SCF uses a presumably residual stress-free indentation crack which is sometimes difficult to measure, not always semi-elliptical, as assumed to apply the evaluation formula, and may be accompanied by lateral cracks. Both methods will be analysed with respect to possible experimental errors. Variations of the SCF method are applied in order to examine how pre-cracks can be introduced which can be detected on the fracture surface. The geometry of the SCF-pre-crack is varied by applying different loads and by removing different amounts of material. The geometry of the Knoop pre-cracks system is investigated. The results help to identify conditions under which the SCF method can be used successfully to measure the fracture toughness of silicon nitride ceramics.

On Preparation of Advance Ceramic for Single-edge V-Notch Beam Fracture Toughness Test of ISO/FDIS 23146:2008(E) Standards

With establishment of fracture toughness test for advance ceramic according ISO/FDIS 23146:2008(E) with the sample test of Single-edge V-Notch Beam/SEVNB, then the researcher related this activity should understand and able to realize how to prepare the sample of advance ceramic in order the requirements of the standard are fulfilled. In contrary with metals and polymers that usually easy to cut as the standard size for testing, the advance ceramics are found much more difficult to prepare since it is very hard and brittles. More even, specifically for fracture toughness test, the level of difficulty is added since the sharp initial crack should be introduced in the edge of the sample. This article introduce method on preparation of advance ceramic for the purpose of fracture toughness test completed with method to introduce the initial sharp V-notch crack which is valid and possible to be measured its length and diameter of the tip that yield valid result of fracture toughness test.

Development of novel self-adhesive resin cement with antibacterial and self-healing properties

This study aimed to develop novel self-adhesive resin cement with antibacterial and self-healing properties. Furthermore, the dentin bonding strength, mechanical properties, self-healing efficiency, and antibacterial property of the developed cement were measured. Novel nano-antibacterial inorganic fillers that contain quaternary ammonium salts with long-chain alkyls were synthesized. These fillers were added into self-adhesive resin cement containing self-healing microcapsules at mass fractions of 0, 2.5%, 5.0%, 7.5%, or 10.0%. The dentin shear bonding test was used to test the bonding strength, whereas the flexural test was used to measure the flexural strength and elastic modulus of the cement. The single-edge V-notched beam method was used to measure self-healing efficiency, and human dental plaque microcosm biofilms were chosen to calculate the antibacterial property. The dentin shear bond strength significantly decreased when the mass fraction of the nano-antibacterial inorganic fillers in the novel cement reached 7.5% (P<0.05). The incorporation of 0, 2.5%, 5.0%, 7.5%, or 10.0% mass fraction of nano-antibacterial inorganic fillers did not adversely affect the flexural strength, elastic modulus, fracture toughness, and self-healing efficiency of the cement (P>0.1). Resin cement containing 2.5% mass fraction or more nano-antibacterial inorganic fillers significantly inhibited the metabolic activity of dental plaque microcosm biofilms, indicating strong antibacterial potency (P<0.05). The novel self-adhesive resin cement exhibited promising antibacterial and self-healing properties, which enable the cement to be used for dental applications.