Number Of Cycles For Failure Research Articles

Fatigue failure load of prefabricated fiber reinforced post: The influence of the post diameter and fatigue test method

The present study analyzed the fatigue performance of prefabricated fiber reinforced composite posts (FRC post) with different diameters by means of two different fatigue testing methods. A total of 69 FRC double-tapered posts, presenting 20 mm in length associated with different coronal diameters (1.4, 1.6, 2.0 mm) were embedded with acrylic resin in PVC cylinders, maintaining 6 mm free from the coronal part of the post. The posts of each diameter were submitted to step stress testing (inclination: 45°; initial load: 20 N; step-size: 10 N; cycles per step: 18,000; frequency: 5 Hz) (n = 5) or staircase testing (inclination: 45°; initial load: 60% of the monotonic load-to-fracture reported on existing literature; increment: 10% of the monotonic load-to-fracture reported on existing literature; cycles: 18,000; frequency: 5 Hz) (n = 18). The statistical differences were determined for Kaplan-Meier and Mantel-Cox (Log-Rank) tests for step stress testing and based on confidence interval overlapping for staircase testing. All the failures were analyzed in a stereomicroscope (10 × magnification) after the tests, and representative samples were analyzed by scanning electron microscope (500 × and 1000 × magnification). The FRC post with the wider diameter had greater fatigue failure load in step stress testing (DT1.4–56 N < DT1.6–60 N < DT2–100 N) however, a significant difference for the staircase testing was only found for DT1.4 and DT2 (DT1.4–57.4 N ≤ DT1.6–62.2 N ≤ DT2–74.5 N). Additionally, the step stress test revealed that the wider the FRC post diameter, the greater the number of cycles required for failure (DT1.4–73,319 < DT1.6–99,305 < DT2–154,743). A central longitudinal crack perpendicular to the applied load direction was the failure pattern observed for all conditions tested. Thus, the fatigue performance of FRC posts is influenced by its coronal diameter (wider diameter means higher failure loads and number of cycles for failure), but the fatigue test used (staircase or step stress) had no influence on the outcome, expressing similar results.

Experimental investigations on fatigue life enhancement of composite (e-glass/epoxy) single lap joint with graphene oxide modified adhesive

With the increased use of composites in various sectors as a lightweight material exhibits high strength to weight ratio with tailor made properties. It becomes necessary to focus on various joining methods and different types of composite joints and their strength. The present study aims to improve the mechanical strength of single lap joint of composite material comprises of E-glass fibers and nano modified adhesive. Epoxy adhesive has been modified by dispersing Graphene Oxide (GO) to investigate the possibility of enhancement in the fatigue strength and fracture resistance of the single lap joint. Modified Hummer’s method has been used for synthesis of Graphene Oxide. Experimental investigations have been carried out for comparison of tensile and fatigue strength which shows significant improvement in the number of failure cycles for 0.25 wt.% and 0.75 wt.% GO concentrations respectively as compared to neat adhesive. Tension test results showed a significant increase in the fracture toughness of the joint due to addition of GO nanoparticles. There has been 33% and 19% increase in fracture toughness in 0.25 wt.% and 0.75 wt.% GO samples respectively as compared to neat adhesive. Improvement in fracture toughness, among all other nano-reinforcements has been obtained using GO, mainly because of its better capability of deviating the crack growth path to the longer path causing the final failure to retard and consequently improving mechanical properties of the adhesive for the tensile and fatigue strength parameters.

Effect of Strain Range on High Temperature Creep-Fatigue Behaviour of Fe-25Ni-20Cr (wt.%) Austenitic Stainless Steel (Alloy 709)

ABSTRACT Since the preliminary data suggest that Fe-25Ni-20Cr austenitic stainless steel (Alloy 709) is an excellent candidate as a structural material for high-temperature applications such as Sodium-cooled Fast Reactor (SFR), the effect of strain range on creep-fatigue interaction of the Alloy 709 is investigated by conducting strain-controlled creep-fatigue tests with tensile hold times of 0, 600, 1,800 and 3,600 s at strain ranges varying from 0.6% to 1.2% at 750°C and 2 × 10−3 s−1 strain rate. Strain-controlled fatigue tests were performed at strain ranges from 0.3% to 2.5% at 750°C and 2 × 10−3 s−1 strain rate. The predicted fatigue life of Alloy 709 shows a better correlation with the characteristic slopes predictive method. With increasing strain range at a given hold time, the number of failure cycles decreases until saturation. The fractography of the deformed samples exhibited increased number of cracks with strain range along with M23C6 precipitates and high dislocation density.

Experimental and analytical study of random fatigue, in time and frequencies domain, on an industrial wheel

Industrial wheels are components subject to fatigue under a high number of stress cycles, depending on the type of vehicle they are installed to.The reliability of these components is strictly dependent on the accuracy of the fatigue validation method adopted.A common practice in the industry is to test loads under constant amplitude in laboratory through fatigue and test parameters according to the standards used in the industry.The object of this research is to compare the results in terms of damage and the number of failure cycles, adopting both the time domain and frequency domain approach on a real industrial component.Different theories were developed and applied to the real case of study of an industrial wheel, under specific load cases. Eventually, we applied different criteria to the numerical analysis.The added value of this study is the application of the fatigue criteria on a real industrial component, in order to check the reliability of the criteria.Eventually, we determined that the results show that, for these specific experimental load conditions, frequency-domain methods are a bit more conservative than time-domain methods.

Fatigue behavior and colorimetric differences of a porcelain-veneered zirconia: effect of quantity and position of specimens during firing

To evaluate the influence of quantity and positioning of veneered zirconia specimens during firing of porcelain on their fatigue performance and colorimetric differences. Bilayer discs (Ø=15 mm) were made, following ISO 6872 guidelines, using a Y-TZP core (yttria-stabilized tetragonal zirconia polycrystal ceramic; VITA In-Ceram YZ) and a feldspathic veneering material (VITA VM9), being both layers with 0.7 mm thickness. Y-TZP discs were sintered, the veneering material was applied over it, and the bilayer specimens were fired according to two factors (n=20): 'quantity' (1 or 5 samples per firing cycle; G1 and G5 groups respectively) and 'positioning' of the specimens inside the furnace (center or periphery of the refractory tray; G5C and G5P groups, respectively). The CIEL*a*b* parameters were recorded with a spectrophotometer and the color difference (ΔE 00 ) and translucency (TP 00 ) were calculated using CIEDE2000 equations. The step-stress fatigue test was performed with the veneer facing down (region of tensile stress concentration), 10 Hz frequency, initial tension of 20 MPa for 5,000 cycles, followed by steps of 10,000 cycles using a step size of 10 MPa, up to 100 MPa; data from strength and number of cycles for failure were recorded for statistical analysis. Unacceptable color differences (ΔE 00 >1.8) were observed comparing G5C vs. G1 (quantity) and G5C vs. G5P (positioning), meanwhile translucency parameters were not affected. Besides, only the 'quantity' factor influenced the fatigue performance (G1>G5C). None of the tested specimens survived beyond 90N and/or 75000 cycles. The quantity and position of the specimens during firing influence the final color of porcelain-veneered zirconia, and firing one specimen per cycle improved the fatigue performance of the bilayer system.

Using a variable value of the fictitious radius to estimate fatigue life of notched elements

AbstractThe article discusses the problem related to estimating fatigue life of elements containing stress concentrators. The algorithm for estimating fatigue life presented in this work uses a fictitious ray based on the Neuber method. The proposed algorithm takes into account the variability of microstructural length, which depends on the number of failure cycles. The function thus obtained can be used to select the appropriate value for this length, which simplifies the calculation procedure needed to estimate fatigue life. In addition, this work includes an analysis of the impact of variable cutout geometry on the value of the support coefficient. As a result, it was possible to extend the application of this concept to lower fatigue life values and to structural elements with different notch geometries. The method was verified by performing experiments using elements made of three steel grades. A good correlation between calculation and experimental results was obtained.

Modified Low-Cycle Fatigue Estimation Using Machine Learning for Radius-Cut Coke-Shaped Metallic Damper Subjected to Cyclic Loading

In this study, a coke-shaped steel damper that exhibits in-plane resistance is introduced as a passive damper. The double-coke damper presented in this study applies the concept of reduced beam sections to increase the ductility in the case of a prolonged earthquake. Multiplastic hinges are placed on each strip by setting the radius-cut section. The fatigue performance of the damper during earthquake loading is verified through a constant cyclic loading test. The results indicate that, as the number of plastic hinges inside the strip increases, the damper ductility increases, producing a stable hysteresis graph. In addition, a new equation that considers the damage index using parameters such as maximum strength and effective stiffness is proposed, and the experimental results are found to be in excellent agreement with the number of failure cycles obtained from the proposed model. By comparing the results of applying the proposed equation with the machine learning results, it is demonstrated that machine learning can be used for estimating the damper performance against the fatigue of the resistive cycle.

Research on on-line monitoring technology of IGBT module junction temperature based on Kalman filter

IGBT is the core device of energy conversion and transmission, commonly known as the CPU of power electronic devices. However, with the continuous improvement of IGBT power density, its reliability is increasingly concerned by industry and academia. The failure of IGBT module is mainly related to the average junction temperature and the amplitude of junction temperature fluctuation, and with the increase of the amplitude of junction temperature fluctuation, the number of failure cycles of IGBT module will sharply decrease. It can be seen that the change of junction temperature in power module is the key to affect its fatigue life. In this paper, an on-line junction temperature monitoring method based on Kalman filter is proposed, which combines the actual temperature measured by IGBT module with the junction temperature obtained by RC thermal network, so it has the advantages of high reliability and real-time on-line monitoring. The simulation results show the effectiveness of the method.

Accelerated loading frequency does not influence the fatigue behavior of polymer infiltrated ceramic network or lithium disilicate glass-ceramic restorations

This study aimed to evaluate the influence of loading frequency on the fatigue mechanical behavior of adhesively cemented polymer-infiltrated ceramic-network (PICN) and lithium disilicate (LD) simplified monolithic restorations. Thirty (30) disc-shaped specimens (Ø = 10 mm; thickness = 1.0 mm) of each ceramic material (PICN – Enamic, Vita Zahnfabrik or LD – IPS e.max CAD, Ivoclar Vivadent) were produced and adhesively cemented onto dentin analogue discs made of fiber and epoxy resin material (Ø = 10 mm; thickness = 2.0 mm). PICN and LD cemented assemblies were randomly allocated into 2 groups (n = 15) according to the loading frequency used for the fatigue testing (20 Hz or 2 Hz), composing the PICN_20, PICN_2, LD_20 and LD_2 testing groups. Fatigue tests were run using the step-stress approach (initial load = 200 N; step-size = 100 N; 10,000 cycles per step) and the collected data (fatigue failure load – FFL and number of cycles for failure – CFF) were analyzed by survival tests (Kaplan Meier and Mantel-Cox) and Weibull analysis. Fractographic analysis of failed specimens were also performed. No statistically significant differences were detected in relation to FFL and CFF between the groups within the same ceramic material (PICN_20: 1127 N/102,667 cycles = PICN_2: 1120 N/102,000 cycles; LD_20: 980 N/88,000 cycles = LD_2: 900 N/80,000 cycles). All failures were radial cracks in the cementation surface. Therefore, the use of a 20 Hz loading frequency shows to be a viable alternative to accelerate cyclic fatigue tests without affecting the fatigue mechanical behavior and the failure pattern of simplified restorations made of lithium disilicate glass ceramic or polymer infiltrated ceramic network bonded to the dentin analogue.

Effect of resin cement space on the fatigue behavior of bonded CAD/CAM leucite ceramic crowns

This study evaluated the influence of occlusal resin cement space on the fatigue performance of bonded-leucite crowns to a dentin-analogue material. Leucite anatomical crowns were adhesively cemented to dentin-like preparations having distinct occlusal cement space (50, 100 and 300 μm) (n = 18), and subjected to step-stress fatigue testing (150 N – 350 N; step-size: 25 N; 20,000 cycles/step; 20 Hz). Fatigue data (load and number of cycles for failure) were analyzed using Kaplan–Meier and Mantel–Cox (log-rank) tests (p <0.05). Fractographic analysis and occlusal internal space measurements were also performed. There was no significant difference for the distinct occlusal cement layer (50 μm: 289 N, 136,111 cycles; 100 μm: 285 N, 132,778 cycles; 300 μm: 246 N, 101,667 cycles). Occlusal internal space analysis showed a mean thickness of 120.4 (50 μm), 174.9 (100 μm) and 337.2 (300 μm). All failures were radial cracks originating at the ceramic-cement interface. Distinct occlusal cement spaces had no effect on the fatigue behavior of anatomical leucite crowns.

Experimental and finite element analysis on determining the fatigue life of pb-free solder joint (Sn-0.5Cu-3Bi-1Ag) used in electronic packages under harmonic loads

Electronic packages that are used these days are exposed to different types of vibration loadings in their usage environment. This vibration exposure can be categorized as harmonic and random vibrations. When reliability assessment of modern electronic systems is considered, vibration loading has an important role to play. One of the biggest challenges facing today is the accurate and rapid assessment of fatigue life under the vibration loading. Conventional solder joints were made of lead-tin alloy. According to many environment legislations and rules, lead is prohibited as an ingredient in the solder alloy. The reason for the prohibition of the usage of the lead is that it poisons the environment. In this study, Sn-0.5Cu-3Bi-1Ag is used as the lead-free solder alloy. Fatigue life prediction of electronic package containing SAC405 is conducted with the aid of vibration testing and Finite element analysis under harmonic vibration loading. A specially designed Plastic Ball Grid Array Package (PBGA) component is mounted on Printed Circuit Board (PCB). It is taken as a test vehicle for the vibration test. The test vehicle is excited by a sinusoidal vibration. The frequency of this excitation equals the fundamental frequency of the test vehicle and it is continued till the component fails. Since the solder balls are very small for direct measurement, Finite Element analysis (FEA) is used for noting down the stresses. The stress versus failures cycles (S-N) curve is made by relating both the stresses on the solder balls obtained and the number of failure cycles from vibration analysis. The fatigue life of the component can be estimated from the generated S-N curve. It is analyzed that the methodology is effective in predicting the component’s life. Hence, the reliability of electronic package can be improved.

Grinding, polishing and glazing of the occlusal surface do not affect the load-bearing capacity under fatigue and survival rates of bonded monolithic fully-stabilized zirconia simplified restorations

This study aims to evaluate the effect of distinct surface treatments (grinding, polishing and glaze) of the occlusal surface of fully-stabilized zirconia (FSZ) simplified restorations bonded onto epoxy resin on the fatigue behavior of the restorations. Disc shaped specimens of FSZ (IPS e.max Zircad MT Multi) were produced (Ø = 10 mm and 0.8 mm in thickness) and randomly allocated into 5 groups, considering the factor ‘surface treatment’ of the occlusal surface: Ctrl – as-sintered; Gr – ground with coarse diamond bur; Gr + Pol– grinding + polishing with two-step polishing system; Gr + Gl – grinding + glaze application; Gr + Pol + Gl – grinding + polishing + glaze application. Next, the FSZ intaglio surface was air-abraded with 45 μm aluminum oxide powder for 10 s at 15 mm of distance under 2 bar pressure and the discs were adhesively cemented (Multilink Automix) onto its dentin analogue pair (Ø = 10 mm; thickness = 2.7 mm). Finally, the step-stress fatigue test was executed (load ranging from 200 to 1300 N; step-size of 100N; 10,000 cycles per step, 20 Hz). In addition, surface topography, roughness, phase transformation and fractography analyses were performed. Grinding altered the topographical pattern introducing defects into the material surface and increasing roughness. Polishing and glaze application led to a smoothening effect, reducing surface defects and statistically decreasing roughness. However, the effect on roughness of polishing and glaze was statistically similar. No phase transformation was observed, thus only cubic and tetragonal phases were detected. No surface treatment had a deleterious effect regarding the fatigue failure load, number of cycles for failure and survival rates. All failures (cracks) started on the bonding surface. Thus, polishing and glaze are indicated to reduce surface roughness, despite not leading to differences in terms of fatigue performance.

Experimental and numerical study on behaviour of HSFRC overlay strip strengthened flexural deficient RC beams

Reinforcing the concrete matrix using the steel fibres is an efficient technique for improving the mechanical characteristics of the concrete matrix. In the present study, at first, hybrid steel fibre reinforced concrete (HSFRC) consisting of micro- and macro- steel fibres in the fixed ratio of 1:3 in the concrete mixture is developed for repair applications of deficient/damaged reinforced concrete (RC) structures. HSFRC with 1.5% volume fraction of hybrid fibres is used for pre-casting of overlay strips for retrofitting of flexural deficient (FD-30% deficient) beams. Analytical formulations are presented to arrive at thickness and reinforcements of HSFRC overlay strip for the flexural deficient RC beams to reach the required level of load carrying capacity. HSFRC overlay strips are affixed to the bottom surface of flexural deficient RC beams. Experimental studies are carried out on control, flexural deficient and HSFRC overlay strengthened flexural deficient (HSFRC-SFD) RC beams under static and fatigue loading. It is noted that HSFRC overlay strip of 20 mm thickness has improved the ultimate load and fatigue life of flexural deficient RC beam surpassing that of the control beam (without flexural deficiency). Expression relating stress in reinforcement steel and number of fatigue cycles for failure of RC beams is proposed based on experimental data. This study has demonstrated the efficacy of application of HSFRC overlay strip for retrofitting of flexural deficient beams in easier, cost-effective and effective manner.

Vibration lifetime estimation of PBGA solder joints using Steinberg model

The work studies the vibration lifetime modeling of Sn37Pb soldered plastic ball grid array (PBGA) assemblies on the basis of vibration tests, finite element analysis (FEA) and Steinberg's empirical formulation. The test vehicles for the vibration tests consist of twelve PBGA components with built-in daisy-chained circuits, which are assembled on a printed circuit board (PCB) symmetrically. First, the natural frequencies of the test vehicle were determined by modal tests. The first three natural frequencies were obtained using FEA, which were compared with those from the modal test. Then, narrow-band sinusoid vibration tests were conducted at the first natural frequency of the test vehicle using constant-amplitude excitation, and the number of failure cycles was recorded by monitoring the overall electrical resistance. FEA was performed to obtain the stress of the critical solder joints under various levels of sinusoidal vibration loadings. To construct the stress versus failure cycles (SN) curve of the solder joints, the stresses of solder joints were used in conjunction with the lifetime obtained from the sinusoidal vibration tests. The random vibration test was conducted on the test vehicle to assess the lifetime of the solder joints subjected to broad-band excitation. Random vibration analyses were performed numerically to obtain the displacement responses of the PBGA assembly. Finally, a fatigue life prediction based on Steinberg's model was deduced from all these procedures. A comparison of the lifetime between the experimental results and the prediction suggests that the methodology is valid and practicable in predicting the vibration lifetime of PBGA solder joints.

Newer vs. older CAD/CAM burs: Influence of bur experience on the fatigue behavior of adhesively cemented simplified lithium-disilicate glass-ceramic restorations

This study evaluated the effect of the CAD/CAM burs experience (newer vs older as consequence of the milling sequence) on fatigue failure load (FFL), number of cycles for failure (CFF), and survival rates of lithium disilicate glass-ceramic simplified restorations adhesively cemented to a dentin analogue substrate. Three sets of CAD/CAM burs were used to mill disc-shaped ceramic specimens (1 bur set – 18 milled discs with 10 mm diameter and 1.5 mm thickness), considering the bur experience as a result of the milling sequence to compose the study groups: G1-6 – discs obtained from the 1st to 6th milling of each bur set; G7-12 – specimens from the 7th to 12th milling; G13-18 – discs from the 13th to 18th. Discs of dentin analogue (G10, 10 mm diameter and 2.0 mm thickness) were made to serve as substrate (base material) and randomly assigned into pairs with the respective ceramic discs. Then, the ceramic discs were adhesively cemented onto the dentin analogue substrate, composing a three-layer specimen that mimics a monolithic restoration of a posterior tooth. Specimens were tested under stepwise fatigue approach: frequency = 20 Hz, 5000 cycles at maximum load of 400 N to accommodate the testing assembly, followed by incremental steps of 200 N with initial load ranging from 10 to 1000 N, to a maximum of 20,000 cycles/each step, until the occurrence of failure (radial crack). FFL and CFF were recorded at the end of the testing and subjected to statistical analysis. Supplementary roughness analysis of the milled surface was performed (n = 18) using a contact profilometer. Residual stress after milling and acid etching were accessed via X-ray Diffractometry analysis. FFL and CFF were not affected by increase on bur experience (no statistical differences among groups), despite that, it affected both Ra and Rz parameters (G1-6 had the smoothest surface). The residual stress concentration was negligible (milling did not induce residual stress concentration). It is concluded that the fatigue behavior of adhesively cemented lithium-disilicate glass-ceramic restorations was not influenced by CAD/CAM bur experience (newer vs older as consequence of the milling sequence), and so the residual stress concentration induced by milling was negligible.

CAD-CAM milled versus pressed lithium-disilicate monolithic crowns adhesively cemented after distinct surface treatments: Fatigue performance and ceramic surface characteristics

To evaluate the fatigue failure load (FFL), number of cycles for failure (CFF) and survival probabilities of lithium-disilicate (LD) monolithic crowns manufactured by two processing techniques (pressing vs. CAD/CAM) adhesively cemented to a dentin-analogue material, considering two surface treatments (conventional vs. simplified). Surface characteristics (topography, roughness and fractal dimensions) were also assessed. Forty (40) monolithic crowns were manufactured considering two specific processing techniques for each ceramic system: LDCAD – CAD/CAM lithium-disilicate (IPS e.max CAD, Ivoclar Vivadent); LDPRESS – pressed lithium-disilicate (IPS e.max Press, Ivoclar Vivadent). The crowns were adhesively cemented (Multilink Automix System, Ivoclar Vivadent) onto dentin analogue preparations considering two distinct protocols of surface treatments (conventional – hydrofluoric acid etching + silane application [HF+Sil] or simplified – etching with one-step primer (Monobond Etch&Prime, Ivoclar Vivadent) [EP]). The cemented assembly was stored in distilled water at 37 °C for 3 days and fatigue tests were run (step-stress approach: load ranging from 400 to 2000 N, step-size of 100 N, 15,000 cycles/step, 20 Hz). Fractography, surface topography, roughness, and fractal dimension analyses were performed. LDPRESS[EP] group depicted higher FFL, CFF and survival probabilities in comparison to LDCAD groups, regardless of the conditioning method. A tendency of higher Weibull modulus (mechanical reliability) was observed when using [EP] for both LDPRESS and LDCAD. SEM and AFM analysis showed very distinct initial surface patterns for the distinct processing techniques considered (LDCAD with higher fractal dimension and lower roughness than LDPRESS), and both surface treatments distinctly affected these surface characteristics. All failures were radial cracks originating at the ceramic-cement interface. Pressed lithium-disilicate monolithic crowns showed better fatigue performance in comparison to CAD/CAM milled crowns, especially when they were treated with self-etching ceramic primer. The surface treatment with self-etching primer led to similar fatigue performance when compared to hydrofluoric acid plus silane application for the same processing technique, but it tended to provide higher mechanical reliability.

Study on frost resistance of magnesium cement composite sheets

In order to study the frost resistance of magnesium cement composite sheets, the effects of freeze-thaw cycles on the bending properties of glass fiber reinforced basic magnesium sulfate cements blended with mineral admixtures and glass fiber reinforced chlorine were studied by freeze-thaw test method. Magnesium silicate cement is compared. The composition and microstructure of the hydration products of the board before and after freezing and thawing were analyzed by XRD and SEM. The results show that before the 128 freeze-thaw cycles, the flexural strength of the undoped composite sheet is 8.2%, 7.3% and 9.1% higher than the initial strength of the slag, fly ash and silica fume board, respectively. When the number of freeze-thaw cycles reaches 160, the strength retention rate of composite sheets with various ratios has been reduced to less than 75%, and the test pieces fail; the number of freeze-thaw cycles for failure of the magnesium oxychloride cement-based board is about 150 times, The number of basic magnesium sulfate cements is almost the same This indicates that in the freeze-thaw test, the failure of the specimen may be caused only by physical damage, and the number of times depends on the strength of the previous period.

Lithium disilicate glass-ceramic vs translucent zirconia polycrystals bonded to distinct substrates: Fatigue failure load, number of cycles for failure, survival rates, and stress distribution

The present study evaluated the fatigue behavior of monolithic translucent zirconia polycrystals (TZ) and lithium disilicate glass-ceramic (LD) bonded to different substrates. Disc-shaped specimens of ceramic materials TZ and LD were bonded to three substrates with different elastic modulus (E) (fiber-reinforced composite (FRC) – softest material, E = 14.9 GPa; titanium alloy (Ti) – intermediary properties, E = 115 GPa; and zirconia (Yz) – stiffest material, E = 210 GPa). The surfaces were treated and bonded with resin cement (disc-disc set-up). Fatigue testing followed a step-stress approach (initial maximum load = 200 N for 5000 cycles, incremental step load = 200 N for 10,000 cycles/step). The fatigue failure load and number of cycles until failure were recorded and statistically analyzed. Fractographic and finite element (FEA) analyzes were conducted as well. TZ ceramic depicted higher fatigue failure load, number of cycles until failure, and survival probabilities than LD, irrespective of the substrate. Moreover, TZ and LD presented better fatigue behaviors when bonded to substrates Ti and Yz in comparison to FRC. FEA revealed lower tensile stresses at restorative material when bonded to stiffer substrates. Fractography showed that the fracture origin started at bottom surface of restorative material (except for TZ bonded to Yz, in which crack initiated at load contact point). Translucent zirconia polycrystals present superior mechanical behavior than lithium disilicate glass-ceramic. The substrate type influences the mechanical performance of monolithic dental ceramics (stiffer substrates lead to better fatigue behavior).

Load-bearing capacity under fatigue and survival rates of adhesively cemented yttrium-stabilized zirconia polycrystal monolithic simplified restorations

This study evaluated the fatigue failure load, number of cycles for failure and survival probability of 2nd and 3rd generation yttrium-stabilized zirconia (YSZ) adhesively cemented to a dentin analogue substrate. Disc-shaped specimens (n = 10; Ø = 10 mm; thickness = 1.0 mm) were produced from four 2nd generation YSZs (Lava Plus, 3M ESPE; Vita In-Ceram YZ-HT, VITA Zahnfabrik; Zirlux FC, Ivoclar Vivadent; Katana ML-HT, Kuraray) and two 3rd generation YSZs (Katana UTML and Katana STML, Kuraray). Each YSZ disc was adhesively cemented (Multilink Automix System) onto its dentin analogue pair (epoxy resin, Ø = 10 mm; thickness = 2.5 mm). Fatigue tests were conducted through step-stress approach (load ranging from 400 to 2600 N; step-size of 200 N; 20,000 cycles per step, 20 Hz) and the obtained data were analyzed using Kaplan Meier and Mantel-Cox tests. Surface topography and phase transformation (m-, t-, and c-phases) inspections after particle air-abrasion of the YSZs were performed, as well as fractographic analysis of the failed specimens. Second-generation zirconia materials presented higher fatigue failure load, number of cycles for failure, and survival probability than 3rd generation. Similar topographical characteristics of the YSZs could be noted. Phase transformation (t- to m-phase) after YSZ air-abrasion was only observed for 2nd generation materials. All failures started from the surface/sub-surface defects located at the cementation interface. 2nd generation zirconia presented higher load-bearing capacity under cyclic loading than 3rd generation materials.

Fatigue Failure Load of Lithium Disilicate Restorations Cemented on a Chairside Titanium-Base.

To evaluate the fatigue failure load of distinct lithium disilicate restoration designs cemented on a chairside titanium base for maxillary anterior implant-supported restorations. A left-maxillary incisor restoration was virtually designed and sorted into 3 groups: (n = 10/group; CTD: lithium disilicate crowns cemented on custom-milled titanium abutments; VMLD: monolithic full-contour lithium disilicate crowns cemented on a chairside titanium-base; VCLD: lithium disilicate crowns bonded to lithium disilicate customized anatomic structures and then cemented onto a chairside titanium base). The chairside titanium base was air-abraded with aluminum oxide particles. Subsequently, the titanium base was steam-cleaned and air-dried. Then a thin coat of a silane agent was applied. The intaglio surface of the ceramic components was treated with 5% hydrofluoric acid (HF) etching gel, followed by silanization, and bonded with a resin cement. The specimens were fatigued at 20 Hz, starting with a 100 N load (5000× load pulses), followed by stepwise loading from 400 N up to 1400 N (200 N increments) at a maximum of 30,000 cycles each. The failure loads, number of cycles, and fracture analysis were recorded. The data were statistically analyzed using one-way ANOVA, followed by pairwise comparisons (p < 0.05). Kaplan-Meier survival plots and Weibull survival analyses were reported. For catastrophic fatigue failure load and the total number of cycles for failure, VMLD (1260 N, 175,231 cycles) was significantly higher than VCLD (1080 N, 139,965 cycles) and CDT (1000 N, 133,185 cycles). VMLD had a higher Weibull modulus demonstrating greater structural reliability. VMLD had the best fatigue failure resistance when compared with the other two groups.