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This study aimed to clarify the fracture resistance of resin abutments built on endodontically treated roots with the remaining coronal teeth via static and cyclic loading tests. Endodontically treated bovine roots, which had a remaining coronal tooth covered with an occupied area for a quarter and half of the circumference at the tensile side or covered the circumference at both the tensile and compressive sides, were fabricated to build up to the resin abutment. Fracture resistance was evaluated via static and cyclic loading tests by applying a load of 30° to the tooth axis. Half of the circumference of the remaining coronal tooth showed a significantly higher static fracture load and survival rate. The remaining coronal tooth on the compressive side improved the dynamic fracture resistance associated with severe fractures. The occupied area and location of the remaining coronal tooth affected the static and dynamic fracture resistances. [ABSTRACT FROM AUTHOR]

We developed an error-propagation-analysis-based multi-scale reliability model in three steps to estimate the minimum time-to-failure of a full-size brittle component with environment-assisted crack growth. First, we use a time-to-failure formula according to Fuller et al. (1994), which was based on laboratory experiments on brittle materials for measuring time-to-failure of specimens that undergo moisture-enhanced crack growth under constant stressing. The formula predicted the mean time-to-failure of a specimen-size component in a power-law relationship with the applied stress involving two strength test parameters, S and Sv, and two constant stressing test parameters from regression analysis, and N′. Second, we use the classical laws of error propagation to derive a formula for the standard deviation of the time-to-failure of a specimen-size component and apply it to computing the standard deviation of the time-to-failure of a specimen-size component for a specific applied stress. Third, we apply the statistical theory of tolerance intervals and develop a conservative method of estimating the failure probability of the full-size components by introducing the concept of a failure probability upper bound (FPUB). This allows us to derive a relationship for the minimum time-to-failure, min-tf, of a full-size brittle component at a specific applied stress as a function f of the FPUB. By equating (1 – FPUB) as the Reliability Lower Bound, RELLB, we arrive at a relation, min-tf = f (RELLB), which expresses the min. time-to-failure as a function of the reliability lower bound, or conservatively as a function of reliability. [ABSTRACT FROM AUTHOR]

This study aimed to assess the effect of mechanical loading and heating on the cyclic fatigue and torsional fracture resistances of heat-treated nickel–titanium files after usage and autoclaving. Sixty files (One Curve) were tested for cyclic fatigue and torsional fracture resistances using customized devices. The files were divided into three groups according to the test conditions (n = 10); new (group-N), used for simulated canal shaping (group-U), and sterilized after use (group-S). For cyclic fatigue resistances, the files were freely rotated in a curved metal canal under body temperature; the time elapsed to fracture was recorded and the numbers of cycles to fracture (NCF) were calculated. For the torsional resistances, the file tip was fixed and rotated until the file fractured. The maximum torsional load and distortion angle were recorded. The toughness was calculated. Fracture fragments were examined with a scanning electron microscope. Data were analyzed using a one-way analysis of variance and Tukey's post hoc test at the significance level of 95%. Group-U showed significantly higher NCF than group-S (p < 0.05). However, there was no significant differences between groups-N and -S in the NCF (p > 0.05). Group-N showed a significantly bigger distortional angle and higher torsional toughness than groups-U and -S, but the ultimate torsional strength did not have significant difference between the groups. Under the limitation of this study, autoclave sterilization after single-usage did not improve the fracture resistance of heat-treated One Curve nickel–titanium files. [ABSTRACT FROM AUTHOR]

• Microstructural recovery dominates the degradation in mechanical properties of Al wires at elevated temperatures. • Cracking at the grains with 〈0 0 1〉 orientation on the surface is the major crack initiation mode. • Fatigue crack propagation of Al wires exhibits three distinctive stages. • The proportion of plane crack propagation regions decreases with increasing temperature. • A dynamic fatigue strength prediction model of Al wires is proposed. With the increase in transmission demand, overhead conductors are always in hot service. In this work, the commonly used commercially pure Al wires and Al-Mg-Si wires were selected to carry out dynamic fatigue tests at elevated temperatures, to investigate the dynamic influences of temperature on their fatigue properties and damage mechanisms during cyclic deformation. The results show that the dynamic mechanical properties become degradated with increasing temperature due to the microstructural recovery, and such mechanical degradation is more severe for Al-Mg-Si wires. Besides, the fatigue crack initiation and propagation mechanisms were revealed using electron backscattering diffraction. Cracking at the grains with 〈0 0 1〉 orientation on surface is the major crack initiation mode. While, the crack propagation mechanism is divided into three stages, i.e., the propagation in the direction of a single slip system (Stage I), the propagation in the direction of multiple slip systems (Stage II), and the instability propagation in the direction of the maximum shear stress (Stage III). The dynamic evolution mechanism of the plane crack propagation regions with temperature was also studied, which is related to the critical stress and force for the crack instability propagation. Finally, a dynamic fatigue strength prediction model of Al wires was proposed. [ABSTRACT FROM AUTHOR]

Soda lime/aluminosilicate glass is widely used in commercial and national defense industries due to its excellent physical properties such as high strength and high hardness. Fatigue fracture is one of the main failure modes of glass. Investigating the fatigue behavior is of great importance to its processing, life prediction and failure prevention. In this paper,the fundamental and experimental methods of static fatigue and dynamic fatigue of soda lime/aluminosilicate glass were reviewed.The conclusions obtained by comparing the fatigue behavior of soda lime silicate and aluminosilicate glass demonstrate that the threshold load for radial crack initiation of raw soda lime silicate glass is much lower than raw aluminosilicate glass, the threshold load for radial crack initiation of chemically strengthened soda lime/aluminosilicate glass is increased with the surface compressive stress; the crack growth rate of raw soda lime/aluminosilicate glass increase with fictive temperature and this phenomena is more evident in aluminosilicate glass; the raw soda lime/aluminosilicate glass shows a loading rate-dependent strength while the chemically strengthened aluminosilicate glass does not. Consequently, the effect of different stress state and environment atmosphere on the behavior of static fatigue and dynamic fatigue of static fatigue and dynamic fatigue is an important issue to be studied.

This study aimed to assess the effect of mechanical loading and heating on the cyclic fatigue and torsional fracture resistances of heat-treated nickel–titanium files after usage and autoclaving. Sixty files (One Curve) were tested for cyclic fatigue and torsional fracture resistances using customized devices. The files were divided into three groups according to the test conditions (n = 10); new (group-N), used for simulated canal shaping (group-U), and sterilized after use (group-S). For cyclic fatigue resistances, the files were freely rotated in a curved metal canal under body temperature; the time elapsed to fracture was recorded and the numbers of cycles to fracture (NCF) were calculated. For the torsional resistances, the file tip was fixed and rotated until the file fractured. The maximum torsional load and distortion angle were recorded. The toughness was calculated. Fracture fragments were examined with a scanning electron microscope. Data were analyzed using a one-way analysis of variance and Tukey’s post hoc test at the significance level of 95%. Group-U showed significantly higher NCF than group-S (p < 0.05). However, there was no significant differences between groups-N and -S in the NCF (p > 0.05). Group-N showed a significantly bigger distortional angle and higher torsional toughness than groups-U and -S, but the ultimate torsional strength did not have significant difference between the groups. Under the limitation of this study, autoclave sterilization after single-usage did not improve the fracture resistance of heat-treated One Curve nickel–titanium files.

The fatigue properties of lithium hydride (LiH) are crucial to its application as neutron shielding and moderating at elevated temperatures. The dynamic fatigue tests of LiH were investigated with the notched 3-point bend (3 PB) specimens over ranges of loading rates at RT up to 400 °C. At RT, the results showed that slow crack growth (SCG) occurred prior to failure as the minor deviation from linearity to nonlinearity in the load-deflection curves. In addition, the fracture strength of LiH decreased with decreasing stress rate and the SCG zone gradually became smaller with higher stress rates, indicating evident dynamic fatigue phenomenon. However, the trends were quite different at 200, 300 and 400 °C due to accumulative creep damage for low stress rates at elevated temperatures. With increasing temperature and decreasing stress rate, there existed a transition of the dominated failure mechanism, from SCG to creep rupture. Evidence of very small SCG zone could also be detected at the notch for the failure dominated by creep rupture. • Lithium hydride (LiH) shows obvious dynamic fatigue phenomenon and the slow crack growth parameter is determined to be 15.787 at room temperature. • A transition in the dominated failure mechanism, from slow crack growth (SCG) to creep rupture, is found with increasing temperature and decreasing stress rate in the dynamic fatigue tests. • Evidence of very small SCG zone could also be detected at the notch for the failure dominated by creep rupture. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the influence of height and thickness of the one wall remaining coronal tooth structure on the fracture resistance of an endodontically treated root with resin abutment build-up using resin composite and fiber-reinforced resin composite post. Static and dynamic fracture tests were performed by placing the remaining tooth wall on the tensile side and applying loads at an angle of 30° from the tooth axis. Superior static fracture resistance was observed when the wall remaining on the tooth had a height and thickness greater than 1.0 mm. The dynamic fatigue test showed high loading capacity or fracture resistance in specimens with large height and thickness. The dynamic fatigue test showed the influence of the remaining tooth structure on fracture resistance clearly. In conclusion, the static and dynamic fracture resistances increased with the height and thickness of the one wall remaining tooth structure. [ABSTRACT FROM AUTHOR]

This study aimed to clarify the fracture resistance of resin abutments built on endodontically treated roots with the remaining coronal teeth via static and cyclic loading tests. Endodontically treated bovine roots, which had a remaining coronal tooth covered with an occupied area for a quarter and half of the circumference at the tensile side or covered the circumference at both the tensile and compressive sides, were fabricated to build up to the resin abutment. Fracture resistance was evaluated via static and cyclic loading tests by applying a load of 30° to the tooth axis. Half of the circumference of the remaining coronal tooth showed a significantly higher static fracture load and survival rate. The remaining coronal tooth on the compressive side improved the dynamic fracture resistance associated with severe fractures. The occupied area and location of the remaining coronal tooth affected the static and dynamic fracture resistances.

• MWZ can be prepared 6 times faster than CZ while preserving structural durability. • Degradation in flexural fatigue of as-sintered zirconia is due primarily to SCG. • MWZ possesses a slightly higher Weibull modulus than CZ. • MWZ and CZ exhibit similar resistance to SCG. • Accelerated fatigue testing protocols must cover a wide range of stress-rates. Continuous efforts have been made to hasten the zirconia densification process without compromising properties. This study evaluated the long-term structural durability of microwave speed-sintered zirconia (MWZ) relative to a conventionally sintered zirconia (CZ). As-machined dental 3Y-TZP discs (Ø12 × 1.2 mm) were speed sintered at 1450 °C for 15 min using an industrial microwave oven, while conventional sintering was conducted in a standard dental furnace at 1530 °C for 2 h. Both were followed by natural cooling. The total sintering time was 105 min for MWZ and 600 min for CZ. Groups were compared regarding density, grain size, phase composition, and fracture resistance. Structural durability was investigated employing two fatigue protocols, step-stress and dynamic fatigue. Compared to CZ, MWZ exhibited a slightly lower density (MWZ = 5.98 g/cm3, CZ = 6.03 g/cm3), but significantly smaller grain sizes (MWZ = 0.53 ± 0.09 μm, CZ = 0.89 ± 0.10 μm), lower cubic-zirconia contents (MWZ = 15.3%, CZ = 22.7%), and poorer translucency properties (TP) (MWZ = 13 ± 1, CZ = 29 ± 0.8). However, the two materials showed similar flexural strength (MWZ = 978 ± 112 MPa, CZ = 1044 ± 161 MPa). Additionally, step-stress testing failed to capture the fatigue effect in 3Y-TZP, whereas dynamic fatigue revealed structural degradation due to moisture-assisted slow-crack-growth (SCG). Finally, MWZ possessed a slightly higher Weibull modulus (MWZ = 7.9, CZ = 6.7) but similar resistance to SCG (MWZ = 27.5, CZ = 24.1) relative to CZ. Dental 3Y-TZP with similar structural durability can be fabricated six-times faster by microwave than conventional sintering. [ABSTRACT FROM AUTHOR]

With the development of rubber technology the requirements for rubber products are becoming more and more strict. Enhancing the interfacial bonding strength between vulcanized natural rubber (NR) and polyester fibers (PEF) has become our research goal. In the research described here the effect of rosin resin (RR) on the properties of NR/PEF was studied. Dynamic experiments were conducted within the strain range from 1 to 100% using a rubber process analyzer (RPA). The adhesive properties of the RR in the NR matrices with the PEF were further studied by the peel test, which indicated an enhancement of the bonding effect in the vulcanized NR-PEF composites. The failure modes of the mixtures following various aging conditions were studied by scanning electron microscopy (SEM). When 3phr of RR were added to the NR/PEF composite, the interfacial bonding strength between the rubber and fiber had the best value compare to samples with 0, 1, 2, 4 and 5phr. Our results indicated that RR used as a tackifier added to NR prior to vulcanization improved the bonding between vulcanized NR and the PEF. [ABSTRACT FROM AUTHOR]

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Dynamic fatigue behaviors of three microwave-sintered Si 3 N 4 -based ceramic tool materials in ambient and high-temperature (800 °C) environments were investigated. The flexural strength at different loading rate (0.05 MPa/s, 0.5 MPa/s, 5 MPa/s and 15 MPa/s) was conducted by three-point bending test. The results showed that the subcritical crack growth parameter N of monolithic Si 3 N 4 , Si 3 N 4 /(W,Ti)C and Si 3 N 4 /(W,Ti)C/Ni at ambient temperature was 57.5, 34.8 and 81, respectively. The fatigue resistance performance at ambient temperature was ranked as Si 3 N 4 /(W,Ti)C/Ni > monolithic Si 3 N 4 > Si 3 N 4 /(W,Ti)C. As the temperature increased to 800 °C, the flexural strength of all samples only decreased slightly, which indicated Si 3 N 4 -based ceramic tool materials had good thermal stability. The subcritical crack growth parameter N of monolithic Si 3 N 4 and Si 3 N 4 /(W,Ti)C ceramic tool materials did not change, while the value N of Si 3 N 4 /(W,Ti)C/Ni decreased by 76.5%. The addition of metal phase can increase the ambient temperature fatigue resistance, while it is detrimental to the high-temperature fatigue resistance due to its weak strength at high temperature. Additionally, defect source caused by the oxidative corrosion was also not conducive to fatigue resistance performance of Si 3 N 4 -based composite ceramic tool materials at high temperature. [ABSTRACT FROM AUTHOR]

Highlights • A new Ti(C 7 N 3) cermet micro-mill was successfully developed. • A stress distribution model on the cutting edge of micro-mill was proposed. • The cermet had superior fatigue resistance property at 500°C than at room temperature. • The cermet micro mill exhibited superiority over coated WC in machining TC4. • It was proved that Ti(C 7 N 3) cermet can be used as the material of micro-mill. Abstract The demands for 3D micro-products are increasing. However, few tool materials have been used to for micro-milling of difficult-to-cut-materials. A new type of the Ti(C 7 N 3)-based cermet micro-mill was designed. To verify that the cermet could satisfy the compressive strength of micro-mills, a contact stress distribution model on the round cutting edge of the cermet micro-mill was established. Dynamic fatigue tests of the Ti(C 7 N 3)-based cermet and micro-milling experiments using the cermet and the coated tungsten carbide (WC) micro-mill were carried out. The model indicted the maximum normal pressure on the cutting edge of the Ti(C 7 N 3)-based cermet micro-mill was less than the compressive strength of the Ti(C 7 N 3)-based cermet. Moreover, the cermet had superior fatigue resistance at 500°C than at room temperature. Also, the Ti(C 7 N 3)-based cermet micro-mill outperformed the coated WC micro-mill in consideration of tool wear, micro-milling force and machined surface quality. Therefore, the Ti(C 7 N 3)-based cermet could be used as the tool material of micro-mill. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

• DIC technology is used to study the quasi-static and dynamic fracture mechanisms. • Strain concentration is the main reason for quasi-static and dynamic fracture of aluminum/steel joints. • FEM results explained the different fatigue fracture behaviors of aluminum/steel joints with reinforcement. • The weld reinforcement has an important effect on the performance and fracture behavior. • It is important to retain proper weld reinforcement of aluminum/steel joints in practical applications. The primary focus of this study was the fracture mechanism of aluminum/steel laser-arc welded-brazed joints under quasi-static tensile and dynamic fatigue conditions. Digital image correlation (DIC) was applied to record the tensile and fatigue fracture process, while finite element method (FEM) was employed to analyze stress distributions during fatigue tests. The tensile results indicated that the weld reinforcement changed the strain evolution and significantly improved mechanical properties of aluminum/steel joints. During fatigue tests, the weld reinforcement enhanced fatigue properties and changed the joint geometry of aluminum/steel joints, leading to the emergence of distinct failure behaviors. At larger stress loads, the maximum cyclic stress on the interface surpassed the interfacial bonding strength, which resulted in a gradual shift of strain concentration from the weld toe to the interface. At smaller stress loads, the interfacial region exhibited tremendous crack resistance, and strain gradually accumulated in the weld toe, which led to fatigue damage. Interestingly, the strain in the interfacial region became more significant during the fatigue process after removing the weld reinforcement. Overall, this study shed light on the fracture mechanism of aluminum/steel joints under different loading conditions. Knowledge of this mechanism is essential for developing reliable aluminum/steel structures. [ABSTRACT FROM AUTHOR]

Dynamic fatigue of a low dielectric loss steatite was investigated. To this end, the values of n and B, the so-called subcritical crack growth (SCG) parameters were experimentally determined. The steatite exhibited the expected dynamic fatigue behaviour, so that the stress corrosion susceptibility parameter, n, of 24 was obtained. In addition, the material/environment parameter B, which is a constant for a given test environment, was also attained. These parameters are instrumental in predicting the lifetime of components under stress. When the applied load is such that the resulting strength equals half of the inert strength (σi), defined as the strength of a sample tested in an inert environment or at a fast stress rate, i.e. where no subcritical crack growth occurs, the time to failure (tf) of the material was found to be ∼140 h. Measurement of the fracture toughness of steatite is also of upmost importance and so it was determined using three test methods. A value of KIc = 1.91 ± 0.29 MPa m1/2 was attained by the indentation fracture method through measurement of the cracks emanating from the Vickers indentation. This value is in good agreement with those determined using the KIsc (surface crack in flexure) test method (2.21 ± 0.07 MPa m1/2) and fractography analysis test method (2.00 ± 0.44 MPa m1/2). Differences in test procedure and analysis causing the values from each test method to be different are discussed. [ABSTRACT FROM AUTHOR]

The slow crack growth behavior of Si 3 N 4 ceramics in ambient and cryogenic environment had been investigated by dynamic fatigue testing. The fracture strength was principally dependent on stress rate at 293 K while the fracture strength was comparatively independent of stress rate at 77 K. The morphologies of the fracture surface and the crack tip region were examined to correlate with the slow crack growth behavior. The experimental results revealed that the Si 3 N 4 ceramics exhibits a very high resistance to slow crack growth (SCG) in cryogenic environment. The reasons for such high resistance are likely related to the local residual stress associated with either the thermal anisotropies arising from the presence of the grain boundary glass phase, or from the crack tip shielding mechanism. [ABSTRACT FROM AUTHOR]

Objectives The aim of this study was to determine the Weibull and slow crack growth (SCG) parameters of bulk-fill resin based composites. The strength degradation over time of the materials was also assessed by strength-probability-time (SPT) analysis. Methods Three bulk-fill [Tetric EvoCeram Bulk Fill (TBF); X-tra fil (XTR); Filtek Bulk-fill flowable (BFL)] and a conventional one [Filtek Z250 (Z250)] were studied. Seventy five disk-shaped specimens (12 mm in diameter and 1 mm thick) were prepared by inserting the uncured composites in a stainless steel split mold followed by photoactivation (1200 mW/cm 2 /20 s) and storage in distilled water (37 °C/24 h). Degree of conversion was evaluated in five specimens by analysis of FT-IR spectra obtained in the mid-IR region. The SCG parameters n (stress corrosion susceptibility coefficient) and σ f0 (scaling parameter) were obtained by testing ten specimens in each of the five stress rates: 10 −2 , 10 −1 , 10 0 , 10 1 and 10 2 MPa/s using a piston-on-three-balls device. Weibull parameter m (Weibull modulus) and σ f0 (characteristic strength) were obtained by testing additional 20 specimens at 1 MPa/s. Strength–probability–time (SPT) diagrams were constructed by merging SCG and Weibull parameters. Results BFL and TBF presented higher n values, respectively (40.1 and 25.5). Z250 showed the highest (157.02 MPa) and TBF the lowest (110.90 MPa) σ f0 value. Weibull analysis showed m (Weibull modulus) of 9.7, 8.6, 9.7 and 8.9 for TBF, BFL, XTR and Z250, respectively. SPT diagram for 5% probability of failure showed strength decrease of 18% for BFL, 25% for TBF, 32% for XTR and 36% for Z250, respectively, after 5 years as compared to 1 year. Significance The reliability and decadence of strength over time for bulk-fill resin composites studied are, at least, comparable to conventional composites. BFL shows the highest fatigue resistance under all simulations followed by TBF, while XTR was at par with Z250. [ABSTRACT FROM AUTHOR]

The cutting performance and failure modes of an Al 2 O 3 /TiC micro–nano-composite ceramic tool in the machining of austenitic stainless steel were investigated. Orthogonal test and range analysis were employed to determine the optimal cutting parameters. The largest metal removal amount was got at the speed of 80 m/min, the feed rate of 0.15 mm/r and the depth of cut of 0.1 mm. The wear resistance of Al 2 O 3 /TiC micro–nano-composite ceramic tool were better than that of the alumina-based ceramic tool only reinforced by micro-scale TiC particles. Failure modes of the present tool were cutting edge fracture and tool material peeling off, which mainly resulted from the subcritical crack growth in the tool. The ceramic tool life was predicted based on the dynamic fatigue behavior of the tool material. Due to the inherent fatigue behavior of ceramics, the tensile stress distributing in ceramic tool would cause cracks initiation and promote the cracks extension. The life of ceramic tool for the failure mode of breakage was closely related to the fatigue behavior of the tool material. So, the ceramic tool life could be predicted by calculating the fatigue life of tool material. The stochastic tool life well scattered in the tool life prediction interval. [ABSTRACT FROM AUTHOR]

The dynamic fatigue of 3 mol% Y 2 O 3 stabilized tetragonal zirconia ceramic (3Y-TZP) was assessed at 293 K and 77 K by testing the same batch of specimens in four-point flexure at various stress rates. The crack propagation velocities were also measured using Vickers indentation specimens under dynamic-loading conditions in ambient and cryogenic environment. The slow crack growth (SCG) parameter n at 77 K was larger than that at 293 K. Also, the crack propagation velocity under cryogenic circumstance is much slower than that under ambient circumstance. The experimental results suggest that the 3Y-TZP exhibits a lesser degree of SCG behavior in cryogenic environment. It should be ascribed to two reasons. The negligible effect of stress corrosion and crack tip shielding mechanism induced by temperature. The high SCG resistance in cryogenic environment makes the 3Y-TZP a promising candidate material for long-term service in cryogenic structural applications. [ABSTRACT FROM AUTHOR]

An extensive experimental work for Pyroceram™ 9606 glass-ceramic was conducted to determine static fatigue at ambient temperature in distilled water. This work was an extension and companion of the previous work conducted in dynamic fatigue. Four different applied stresses ranging from 120 to 170 MPa was incorporated with a total of 20-23 test specimens used at each of four applied stresses. The slow crack growth (SCG) parameters n and D were found to be n = 19 and D=45 with a coefficient of correlation of rcoef =0.9653. The Weibull modulus of time to failure was in a range of msf = 1.6-1.9 with an average of msf= 1.7 ±0.2. A life prediction using the previously determined dynamic fatigue data was in excellent agreement with the static fatigue data. The life prediction approach was also applied to advanced monolithic ceramics and ceramic matrix composites (CMCs) based on their dynamic and static fatigue data determined at elevated temperatures. All of these results indicated that a SCG mechanism governed by a power-law crack growth formulation was operative, a commonality of SCG in these materials systems. [ABSTRACT FROM AUTHOR]

Dynamic fatigue behavior of Al2O3/TiC micro–nano-composite ceramic tool materials with/without metallic phase was investigated using three-point bending technique at different loading rates at ambient and high temperatures in air. When the loading rate was low, the flexural strength of two kinds of materials increased with the increase of loading rate at 23°C and 900°C, but they were more susceptible to slow crack growth at 900°C. The composite with cobalt exhibited better slow crack growth resistance than that of the composite without cobalt at ambient and high temperatures. The slow crack growth zone of specimens all originated from the tensile surface. Slow crack growth was generally a result of a stress corrosion process involving the stable growth of pre-existing defects (machining cracks on the tensile surface and residual pores in the bulk material). Crack initiation zone became larger at higher temperature, which should be attributed to the oxidation-assisted defects and the low dynamic viscosity of Co-based grain boundary phases. At 1200°C, the composite with cobalt exhibited larger plastic deformation at the loading rates of 0.08 and 0.8MPa/s, and the plastic deformation was carried out by dislocation slip and twinning. The dominated failure mechanism at the lower loading rate was ascribed to creep rather than stress-corrosion cracking. [ABSTRACT FROM AUTHOR]

Abstract: Recent reports on bilayer ceramic crown prostheses suggest that fractures of the veneering ceramic represent the most common reason for prosthesis failure. Objective: The aims of this study were to test the hypotheses that: (1) an increase in core ceramic/veneer ceramic thickness ratio for a crown thickness of 1.6mm reduces the time-dependent fracture probability (P f) of bilayer crowns with a lithium-disilicate-based glass–ceramic core, and (2) oblique loading, within the central fossa, increases P f for 1.6-mm-thick crowns compared with vertical loading. Materials and methods: Time-dependent fracture probabilities were calculated for 1.6-mm-thick, veneered lithium-disilicate-based glass–ceramic molar crowns as a function of core/veneer thickness ratio and load orientation in the central fossa area. Time-dependent fracture probability analyses were computed by CARES/Life software and finite element analysis, using dynamic fatigue strength data for monolithic discs of a lithium-disilicate glass–ceramic core (Empress 2), and ceramic veneer (Empress 2 Veneer Ceramic). Results: Predicted fracture probabilities (P f) for centrally loaded 1.6-mm-thick bilayer crowns over periods of 1, 5, and 10 years are 1.2%, 2.7%, and 3.5%, respectively, for a core/veneer thickness ratio of 1.0 (0.8mm/0.8mm), and 2.5%, 5.1%, and 7.0%, respectively, for a core/veneer thickness ratio of 0.33 (0.4mm/1.2mm). Conclusion: CARES/Life results support the proposed crown design and load orientation hypotheses. Significance: The application of dynamic fatigue data, finite element stress analysis, and CARES/Life analysis represent an optimal approach to optimize fixed dental prosthesis designs produced from dental ceramics and to predict time-dependent fracture probabilities of ceramic-based fixed dental prostheses that can minimize the risk for clinical failures. [Copyright &y& Elsevier]

The slow crack growth rate and inert strength of multispectral zinc sulfide were measured for use in aircraft window lifetime analysis. Dynamic fatigue data for uncoated multispectral zinc sulfide were fit to a power law by linear regression and to an exponential law by computer-aided numerical integration to obtain best-fit slow crack growth rate parameters. For the power law slow crack growth equation, crack velocity (v) = A * (KI/KIc)n, we find A * = 0.00769 m / s and n = 14.65, where KI is the stress intensity factor, KIc = 0.72 MPam is the critical stress intensity factor, and we assign the value of the geometric factor to be Y = 2 / π. Parameters for the exponential law slow crack growth equation, crack velocity (v) = vo exp (βKI) are vo = 3.02 × 10 − 14 m / s and β = 43.64 (MPam) − 1. There were only small differences in the crack growth rate between uncoated and antireflection-coated material. The crack growth rate that we observe is 10 to 200 times faster than previously reported for a stress intensity factor KI = 0.25 MPam, which is a representative value of KI for an aircraft window in service. The faster crack growth rate predicts a correspondingly shorter window lifetime. The inert strength of uncoated biaxial flexure disks (38.1 mm diameter with 15.88 mm load diameter and 31.75 mm support diameter) measured in dry nitrogen exhibited a 50% Weibull failure probability at 115 MPa with an unbiased ASTM C1239 Weibull modulus of 4.68. Antireflection-coated material had a 50% Weibull failure probability at 100 MPa with a Weibull modulus of 5.25. [ABSTRACT FROM AUTHOR]

Abstract: The effects of dynamic fatigue frequency, temperature and number of cycles on the adhesion of rubber to steel cord in a carcass recipe were examined. A new test method with special rubber/steel cord specimens was developed for the dynamic fatigue measurements which were carried out on a De Mattia Rubber Flexometer. It was found that the dynamic “pull-out forces” decreased with increase of fatigue frequency, but first increased and then decreased with increasing temperature and the number of fatigue cycles. The adhesion failure mainly occurred in the rubber phase rather than at the rubber/steel cord interface. The covered rubber on the “pulled-out” cord after fatigue appeared to form a screw thread and the greater pull-out force corresponded to more uniform and clearer screw threads in the rubber remaining on the cord. Steel cord with an outer wrapping wire had greater static adhesion force and better adhesion after fatigue; the adhesion failure mainly occurred in the rubber phase but some occurred at the contact point of the outer wrapping wire and the wrapped main steel wires. The screw threads of rubber coverage appeared along the twist direction of the outer wrapping wire. SEM indicated that un-dispersed filler agglomerates may initiate adhesion failure. [Copyright &y& Elsevier]

Abstract: The dynamic fatigue of a chemical vapor infiltration 2D-C/C composite was investigated in three-point flexure using different stress rates from 0.07 to 70MPas−1. Flexure strength of the specimens increased in proportion to the increase of stress rate. From the ln σ–ln diagram, stress corrosion factor n was obtained. The n value of 58 in the present work indicated that slow crack growth controlled the fracture process. The fracture under different stress rates shows characteristics of the slow crack growth, which agree with the result of dynamic fatigue. [Copyright &y& Elsevier]

The fatigue parameters of dental resin composites Ceram-X Mono, Clearfil Majesty and Saremco Els were studied. The dynamic fatigue method was used to obtain the crack growth exponent n and a material constant dependent on the test environment and initial material strength, σfo, through linear regression analysis. Clearfil Majesty showed a lower n than Ceram-X Mono and Saremco Els, but the highest σfo. Fractographic analysis revealed that the fracture origin was located on or near the surface opposite to loading. Fatigue parameters obtained from dynamic testing provide significant information about the mechanical degradation rate of the materials. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: Verify the influence of different filler distributions on the subcritical crack growth (SCG) susceptibility, Weibull parameters (m and σ 0) and longevity estimated by the strength–probability–time (SPT) diagram of experimental resin composites. Methods: Four composites were prepared, each one containing 59vol% of glass powder with different filler sizes (d 50 =0.5; 0.9; 1.2 and 1.9μm) and distributions. Granulometric analyses of glass powders were done by a laser diffraction particle size analyzer (Sald-7001, Shimadzu, USA). SCG parameters (n and σ f0) were determined by dynamic fatigue (10−2 to 102 MPa/s) using a biaxial flexural device (12×1.2mm; n =10). Twenty extra specimens of each composite were tested at 100 MPa/s to determine m and σ 0. Specimens were stored in water at 37°C for 24h. Fracture surfaces were analyzed under SEM. Results: In general, the composites with broader filler distribution (C0.5 and C1.9) presented better results in terms of SCG susceptibility and longevity. C0.5 and C1.9 presented higher n values (respectively, 31.2±6.2a and 34.7±7.4a). C1.2 (166.42±0.01a) showed the highest and C0.5 (158.40±0.02d) the lowest σ f0 value (in MPa). Weibull parameters did not vary significantly (m: 6.6 to 10.6 and σ 0:170.6 to 176.4MPa). Predicted reductions in failure stress (P f =5%) for a lifetime of 10 years were approximately 45% for C0.5 and C1.9 and 65% for C0.9 and C1.2. Crack propagation occurred through the polymeric matrix around the fillers and all the fracture surfaces showed brittle fracture features. Significance: Composites with broader granulometric distribution showed higher resistance to SCG and, consequently, higher longevity in vitro. [Copyright &y& Elsevier]

Abstract: Objectives: The aim of this study was to evaluate the mechanical properties and the subcritical crack growth behavior of a presintered dental Y-TZP (Kavo Everest ZS) and a hot isostatic pressed Y-TZP (Kavo Everest ZH) and to perform life data analysis. Methods: For each material 150 bending bars were produced. The initial fracture strength was determined in a four-point bending test. The subcritical crack growth parameters n and A were determined in a dynamic fatigue method at four decreasing loading rates from 110MPa/s to 0.11MPa/s in distilled water at 38°C. For each loading rate Weibull statistics were performed and the Weibull moduli m and characteristic strengths σ 0 were calculated. Using these data, strength–fracture probability–life time (SPT) predictions were derived for 1 day, 1 year, 5 years and 10 years, based on a static crack growth mechanism. Results: The “hipped” Y-TZP ceramic exhibited a higher initial strength (σ c =1618.18), characteristic strength (σ 0 =837.15) and fracture toughness (K IC =4.52MPa/m1/2) than the pre-sintered ceramic (σ c =1431, σ 0 =745.46 and K IC =3.17MPa/m1/2, respectively). Fatigue parameters, n and A, were 28.5 and 7.97×10−24 for Everest ZH and 30.15 and 5.47×10−20 for Everest ZS. The predicted fracture stress at 5% failure probability for a lifetime of 10 years was 259.34MPa for Everest ZH and 263.2MPa for Everest ZS. Conclusions: Although the “hipped” Y-TZP showed favorable initial mechanical properties, no significant difference could be found in the susceptibility of both ceramics to subcritical crack growth and their long-term strength. [Copyright &y& Elsevier]

Abstract: Objectives: To more efficiently determine the subcritical crack growth (SCG) parameters of dental ceramics, the effects of stressing rate and choice of statistical regression model on estimates of SCG parameters were assessed. Methods: Two dental ceramic materials, a veneering material having a single critical flaw population (S) and a framework material having partially concurrent flaw populations (PC), were analyzed using constant stress-rate testing, or “dynamic fatigue”, with a variety of testing protocols. For each material, 150 rectangular beam specimens were prepared and tested in four-point flexure according to ISO6872 and ASTM1368. A full-factorial study was conducted on the following factors: material, stress rate assumed vs. calculated, number of stress rates, and statistical regression method. Results: The proportion of specimens for which the statistical models over-estimated reliability was not significantly different based on regression method for Material S (P =0.96, power=94%) and was significantly different based on regression method for Material PC (P <0.001). The standard method resulted in SCG parameters, n and ln B, of 35.9 and −11.1MPa2 s for Material S and 12.4 and 9.61MPa2 s for Material PC, respectively. Significance: The method of calculation that uses only the median strength value at each stress rate provided the most robust SCG parameter estimates. Using only two stress rates resulted in fatigue parameters comparable to those estimated using four stress rates having the same range. The stress rate of each specimen can be assumed to be the target stress rate with negligible difference in SCG parameter estimates. [Copyright &y& Elsevier]

Abstract: The mechanical strength of carbon hermetically coated fibres, compared to standard single mode silica optical fibre, has been investigated through chemical exposure to fluorinated vapour reagents, known as the harshest reagents for silica. Two reagents were used: ammonium hydrogenofluoride and hydrofluoric acid. Dynamic fatigue tests for different stress rates were implemented using a two-point bending testing device in order to determine n-stress corrosion parameter from Weibull statistics. As-received and chemically etched fibres were compared. Hermetically coated fibres appeared extremely durable in harsh chemical conditions. No significant change in the Weibull distribution and the mean fibre strength was observed after 6 days of chemical exposure to hydrofluoric vapours. In the same conditions, the mechanical strength of the epoxy-acrylate polymer coated standard fibres has decreased to nearly 50% of the initial strength value. SEM observations revealed crystal deposition on the chemical exposed fibres. Chemical analysis provides partial information on the complex mechanisms of fibre corrosion. [Copyright &y& Elsevier]

Abstract: Objectives: To measure subcritical crack growth parameters in vitro and to correlate those with clinical observations from the 12 years recall of a prospective clinical study. Methods: Bending bars were manufactured and the inert fracture strength was determined in four-point bending and silicon oil. Weibull statistics were applied and the parameters m and σ 0 were calculated. Dynamic fatigue experiments were performed in water at four decreasing loading rates from 1.3 to 0.0013MPa/s. The parameters of subcritical crack growth n and A were calculated. Strength-fracture probability-life time (SPT) predictions were derived for 1, 4, 8 and 12 years, based on a static crack growth mechanism. The 12 years clinical recall of a prospective clinical study on the same material was performed. Bulk, chipping and marginal fractures or detoriations were focused here. Failure rates were calculated according to Kaplan–Meier survival analysis and merged into the SPT diagram. Results: Inert fracture strength of the glassceramic was measured to σ 0 =134MPa and the Weibull modulus to m =8.1. The subcritical crack growth parameter n was calculated to n =19.2 and the extrapolated crack velocity to A =0.0014m/s. Based on a clinical relevant failure probability of P F =5%, material strength was predicted to decrease from initial σ 0.05 =93MPa down to σ 0.05 =33MPa after 12 years (−64%). The clinical survival rate dropped from 100% (1 year) to 93% (4 years), 92% (8 years) and 86% after 12 years. The incidence of inlay defects like chipping and marginal fractures increased from 1% at baseline, 7% after 4 years, 26% after 8 years to 57% after 12 years. Significance: Clinical data match the slow crack growth measurements in terms of dramatically increased clinical bulk fractures and detoriations from marginal and chipping fractures after 12 years. Clinical survival rate seems to converge towards the in vitro lifetime predictions with increasing time. A failure level of P F =5% is clinically exceeded after 4 years of clinical service, which corresponds to an experimental prediction of fracture releasing static loading of 35.5MPa. Since average chewing pressure over time is less deleterious compared to static loading, this regression analysis provides a conservative threshold value. [Copyright &y& Elsevier]

Abstract: Optical fibers are key components in telecommunication technologies. Apart from optical specifications, optical fibers are expected to keep most of their physical properties for 10–20 years in current operating conditions. The reliability and the expected lifetime of optical links are closely related to action of the chemical environment on the silica network. However, the coating also contributes largely to the mechanical properties of the fibers. The aim of this work was to study the strength and the mechanical behavior of the silica optical fibers in an acid environment and with a permanent deformation. A container with ammonium bifluoride acid salt was plunged into hot water at different temperatures (55 and 75°C). This emitted acid vapors which attacked the optical fibers for a period of 1–18 days. An aging study was performed on silica optical fibers with standard polyacrylate coating and with hermetic carbon coating. A dynamic two-point bending bench at different faceplate velocities (100, 200, 400 and 800μm/s) was used. For comparison, the same dynamic measurements were also carried out on non-aged fibers. After acid vapor condensation, salt crystal deposits on the fibers were displayed using an electron scanning microscope. These crystals became visible to the naked eye from the seventh day. [Copyright &y& Elsevier]

The reliability and the expected lifetime of optical links are closely related to the chemical action of the water molecules on silica network. However, polymeric coating also contributes largely to the mechanical properties of the fiber. Dynamic fatigue measurements were performed on silica optical fibers, either bare or coated, using two-point bending bench. Water concentration in test atmosphere was 50% relative humidity or very dry atmosphere. When water content is a few ppm, the dynamic fatigue curve, which expresses the breaking strength as a function of stress rate deviates from linearity at high stress rate. The same behaviour is observed in ambient atmosphere for very high testing speeds. The comparison between bare and coated fibers shows that the fatigue behaviour at high stressing rate is influenced by the polymer coating. [Copyright &y& Elsevier]

Objectives. This study examined the influence of displacement-rate and relative layer heights (RLH) on the slow crack growth exponent and Weibull two-parameter estimates of bilayered ceramic composite disks composed of In-Ceram Alumina and Vitadur Alpha porcelain.Methods. Equibiaxial disks were fabricated with RLH of 1:2, 1:1 and 2:1, for In-Ceram Alumina and Vitadur Alpha porcelain, respectively. Ninety specimens each (30 1:2, 30 1:1, and 30 2:1) were tested in an equibiaxial ring-on-ring testing apparatus at displacement-rates of 0.127, 1.27 and 12.7 mm min−1.Results. Weibull parameters were statistically significantly affected by changes in RLH at a constant displacement-rate and the slow crack growth parameters were significantly affected by RLH. Many specimens exhibited nonbrittle failure modes. Nonbrittle failures usually exhibited a fall, followed by a rise in load prior to catastrophic failure, and most occurred in specimens with thicker cores at low displacement-rates.Significance. Geometries of layered materials may affect their reliability and longevity. [Copyright &y& Elsevier]

The objective of this study was to determine the influence of height and thickness of the one wall remaining coronal tooth structure on the fracture resistance of an endodontically treated root with resin abutment build-up using resin composite and fiber-reinforced resin composite post. Static and dynamic fracture tests were performed by placing the remaining tooth wall on the tensile side and applying loads at an angle of 30° from the tooth axis. Superior static fracture resistance was observed when the wall remaining on the tooth had a height and thickness greater than 1.0 mm. The dynamic fatigue test showed high loading capacity or fracture resistance in specimens with large height and thickness. The dynamic fatigue test showed the influence of the remaining tooth structure on fracture resistance clearly. In conclusion, the static and dynamic fracture resistances increased with the height and thickness of the one wall remaining tooth structure.

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The influence of matrix extensibility on the properties of a composite was studied using two glassy polymers of almost identical chemical structure but differing crosslink densities. The lower crosslink density gave a 73 % increase in tensile elongation at break and a 56% increase in specific fracture energy. Unidirectional laminates of glass, carbon, and Kevlar fibres were prepared with these two polymers and tested for shear strength, transverse tension, and dynamic fatigue. The shear strengths of the polymers were found to be almost independent of crosslink densities (about 100 MPa). The interlaminar shear strengths of the carbon fibre laminates corresponded to those of the matrix polymers (Kevlar fibre laminates failed at 60 %). In accordance with Griffith's equation the more extensible polymer and its laminates performed better in tensile tests transverse to the fibres due to improved fracture energy. Failure criteria based on strain magnification were useful in the case of glass fibre laminates, but proved inadequate for laminates based on anisotropic fibres such as carbon and Kevlar. The dynamic fatigue strengths of the two matrix polymers were unaffected by the difference in crosslink densities. Almost the same fatigue strengths were obtained for the matrix polymers as for the laminates (carbon, glass) transverse to the fibres. A lack of processability of the polymer with high functionality was identified as a source of deteriorating effects. [ABSTRACT FROM AUTHOR]