Fatigue Resistance Behavior Research Articles

Effect of immediate dentin sealing on load-bearing capacity under accelerated fatigue of thin occlusal veneers made of CAD-CAM glass-ceramic and resin composite material.

The objective of this study was to assess the influence of immediate dentin sealing (IDS) on the fatigue behavior of laminate occlusal veneers fabricated with CAD/CAM lithium disilicate ceramic and resin composite. Forty sound human molars were prepared and randomly divided into 4 groups (n=10): RC-IDS+(IDS and resin composite occlusal laminate veneer); RC-IDS- (resin composite occlusal laminate veneer without IDS); LD-IDS+(IDS and lithium disilicate laminate veneer); LD-IDS- (lithium disilicate occlusal laminate veneer without IDS). The restorations were obtained using a digital workflow. After surface conditioning and bonding, thermocycling and accelerated fatigue tests (20Hz, 5000 cycles with an initial load of 300N, step-size of 100N for 10,000 cycles, up to 1000N, and then a step-size of 50N until failure) were conducted. Fatigue data were recorded for both outcomes (crack or fracture) and statistically analyzed. Fractographic and adhesive interface analysis were conducted. The indirect resin composite groups showed better fatigue behavior compared to lithium disilicate. IDS only had a positive effect for the survival of resin composite restorations for the 'fracture' outcome. Evident presence of micro-gaps at the adhesive interface in the LD-IDS- group could be noted. Immediate dentin sealing improved fatigue resistance behavior of resin composite occlusal veneers. However, this effect was not observed in lithium disilicate veneers.

Enhanced energy storage performance of Bi0.5K0.5TiO3-based ceramics via composition modulation

To meet the booming demands for advanced pulse power systems, developing dielectric ceramics with excellent energy storage performance is extremely urgent. In this work, a composition modulation strategy was adopted for designing Bi0.5K0.5TiO3-based ceramics. That is, incorporating Bi(Mg0.5Hf0.5)O3 into 0.6Bi0.5K0.5TiO3-0.4Sr0.7Bi0.2TiO3 matrix (abbreviated as (1-x)(BKT-SBT)-xBMH, x = 0.00, 0.04 and 0.08). The energy storage performance of the (1-x)(BKT-SBT)-xBMH ceramics was enhanced by increasing the breakdown strength. Ultimately, a recoverable energy density (Wrec) of 4.25 J/cm3 together with an efficiency (η) of 87 % was achieved for the x = 0.04 ceramic at 360 kV/cm. Furthermore, excellent energy storage properties (Wrec ≥ 2.71 J/cm3, η ≥ 85 %) were obtained over a wide range of temperatures (20–200 ℃), frequencies (0.5–100 Hz) and cycle numbers (105) under 260 kV/cm, indicating good thermal stability, frequency-independent character and fatigue-resistance behavior. Our work would open up a new avenue for preparing BKT-based dielectric ceramics.

Processing, structure, and properties of additively manufactured titanium scaffolds with gyroid-sheet architecture

While the relationships between processing, structure, and properties of solid titanium alloys produced by additive manufacturing have been established, these relationships are less understood for porous materials, particularly those with rough surfaces inherent to L -PBF. For orthopedics applications, porous architecture and surface roughness are desirable for bone growth, and thus optimization of fatigue life despite these inherent fatigue drivers is critical. The present results establishes relationships between post-processing, microstructure, and resulting fatigue properties for gyroid-sheet scaffolds with as-fabricated surfaces. By comparison of known factors driving fatigue behavior, the relative effect of each on normalized fatigue strength was quantified. Normalized compressive fatigue strength of the gyroid-sheet scaffolds which underwent no surface treatments was observed to be > 50%. The result is higher than that seen for tension fatigue of analogous gyroid-sheet scaffolds, or compared to previously reported normalized compressive fatigue strength of strut based scaffolds. The high strength and fatigue resistant behavior of gyroid-sheet scaffolds despite the inherent surface roughness of L -PBF is desirable for biomedical applications.

Biocompatibility and cyclic fatigue response of surface engineered Ti6Al4V femoral heads for hip-implant application

A major problem with femoral head (FH) for hip implant (HI) applications is that it often fails in service. As a result, revision surgery becomes a must. The related trauma is tremendous for the patient, especially the aged ones. This also implies additional expenses. Keeping these aspects of the problem in view, here we report the development of wear, corrosion and fatigue resistant Ti6Al4V alloy based FH; by a duplex surface engineering (DSE) technique. Thus, the DSE based FHs are developed by a novel combination of plasma nitriding (PN) and Ti/TiN multilayer coating (MLC). The MLCs are formed by magnetron sputtering technique. The Ti6Al4V based FHs are called Ti. The only plasma nitrided FHs are called TiPN. The DSE based FHs are called TiPNML. The corrosion resistances are studied in hank's solution. The sliding wear resistance is studied in simulated body fluid (SBF). The biocompatibilities are studied by the standard MTT assay technique. The cyclic fatigue resistance behaviour up to one million walking cycles is studied in SBF in a HIP simulator with the UHMWPE acetabular cups used as the counter bodies in articulation. The results of the corrosion, biocompatibility, wear, and cyclic fatigue resposnses clearly reveal that the performances of the TiPNML and TiPN FHs are much better than that of the Ti based FHs. The reasons behind such spectacular improvement in biocompatibility as well as corrosion, wear and fatigue resistance are explained in terms of the prevalent phases, microstructural factors, wear mechanisms and surface roughness. The implications of the current results in terms of futuristic FH developments for HI applications are discussed. Such futuristic FH development could provide better HI. These prospects would minimize HI failure and hence, revision surgeries. Thus, the related trauma for numerous patients; especially the aged ones; could be significantly reduced.

Polythiourethane Covalent Adaptable Networks for Strong and Reworkable Adhesives and Fully Recyclable Carbon Fiber-Reinforced Composites.

The development of adhesives with superior optical and mechanical performance, solvent resistance, and reworkability is gaining increasing attention in recent years. However, traditional materials do not possess reprocessability and healing characteristics for sustainable development. Here, a superior dynamic polythiourethane (PTU) adhesive with high reprocessability was developed by introducing covalent adaptable networks (CANs). Specifically, dynamic thiocarbamate bonds (TCB) were used to prepare PTU CANs, which showed dramatically enhanced malleability and recyclability. The Young's modulus of the material was 2.0 GPa and the tensile strength was 62.7 MPa. The reprocessing temperature of CANs was reduced to 80 °C while more than 90% of their mechanical properties were retained, even after being reprocessed several times. Moreover, the highly transparent and water-resistant PTU CANs featured an excellent bonding property and reworkability for various materials including glass, with a lap shear strength of 2.9 MPa, metal (5.1 MPa), and wood (6.3 MPa), compared with commercially available adhesives. Additionally, carbon fiber-reinforced composites constructed with PTU CANs were capable of being fully recycled and reused. Importantly, laminated glass with a toughened PTU-PU elastomer interface exhibited an outstanding impact fatigue-resistance behavior, sustaining thousands of impacts. These features demonstrate that PTU CANs show great potential as sustainable materials.

Hybrid Ultradeepwater-Riser Configuration Saves Costs, Pushes Depths

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 29389, “Single Independent Riser: A Cost-Efficient Ultradeepwater Riser,” by François Lirola, Eric Revault, and Jean-François Lunven, Saipem, prepared for the 2019 Offshore Technology Conference, Houston, 6–9 May. The paper has not been peer reviewed. Copyright 2019 Offshore Technology Conference. Reproduced by permission. The single independent riser (SIR) is a hybrid riser configuration optimized for ultradeepwater field development. The SIR is composed of a flexible jumper and a rigid part vertically tensioned by means of distributed or continuous buoyancy. This configuration features improved dynamic behavior under fatigue and extreme environmental conditions for the rigid riser section thanks to its compliant shape. The design is versatile and can be staggered easily to comply with design constraints or congested layouts. Introduction The SIR is adapted to both turret-moored and spread-moored vessels as well as most other types. The configuration is also suitable for a wide spectrum of environments, from the mild conditions of west Africa to those in the Gulf of Mexico or the North Sea. The configuration can be designed for production risers, whether single-pipe or pipe-in-pipe, and injection and export risers. The strength of this configuration lies in its compliant, fatigue-resistant behavior. Its steep-wave configuration facilitates the mitigation of potential interference; the relative position of the sag and hog of each neighboring riser can be adjusted while reducing the load at the hang-off location. Overview The SIR features a steep-wave shape. The upper part is a flexible jumper, and the lower part is a rigid, steel-pipe string maintained in a near-vertical position either by means of continuous buoyancy or distributed buoyancy modules. These methods are used instead of a conventional air can in order to provide the up-thrust necessary to keep the riser vertical. The use of continuous or distributed buoyancy implies that each section compensates for its own weight, meaning that the concept is applicable to any water depth for which buoyancy materials are qualified. The transition between the rigid and the flexible parts is achieved with a sub-sea connector. An overview of the SIR configuration is given in Fig. 1. The SIR features the following technical advantages: The design relies on field-proven technology such as rotolatches to connect the rigid section to its anchor or standard shallow-water flexible-jumper technology to perform the transition between the rigid section and the floater. Though the SIR can be deployed in any water depth, the cost of the flexible jumper limits the suitability of the SIR for water depths below 1000 m, which should be considered the minimum applicable water depth. The SIR is compatible with any installation method. The fabrication process of the SIR can be reversed fully, meaning the system can be retrieved for relocation or maintenance purposes. The SIR features a small dynamic response, thus leading to less-stringent fatigue and welding requirements.

Fatigue resistant lead-free multilayer ceramic capacitors with ultrahigh energy density

Electrical homogeneity is vital in optimising energy storage performance in BiFeO3–BaTiO3–xBi(Li0.5Nb0.5)O3 ceramic multilayer capacitors, giving rise to high recoverable energy density ∼13.8 J cm−3 under electric field ∼950 kV cm−1 and fatigue resistance behaviour.

Calcium phosphate bioceramics with polyvinyl alcohol hydrogels for biomedical applications

Polyvinyl alcohol (PVA) hydrogels show desirable characteristics to use as a biomaterial especially for soft tissue replacement. However, their bio inertness restricts their application in vivo. In this study, polyvinyl alcohol was blended with bi-phasic calcium phosphate and to develop a composite hydrogel by a physical freeze-thawing method, followed by annealing treatment. The synthesized bi-phasic calcium phosphate (BCP) and composite hydrogels were characterized by SEM, XRD and FTIR. The concentration of BCP was optimized and it was found that BCP modifies the hydrogel network by developing the secondary electrostatic bonding between matrix and reinforcement. The highest tensile and compressive strength could reach 5.2 ± 0.6 MPa and 14.9 ± 0.3 MPa respectively for PVA/2.5BCP and they exhibit time-dependent, rapid self-recoverable and fatigue resistant behavior based on the cyclic loading-unloading compression test. Similar observations were found for viscoelastic properties which are relevant for the tissue engineering application. Friction study showed the composite hydrogel had a cartilage-like frictional response, dominated by the interstitial fluid support. Besides composite hydrogel showed excellent antimicrobial activity against bacterial species, Escherichia coli, Staphylococcus aureus and Candida albicans fungi, and the cytocompatibility towards L929 fibroblast cells provides a potential pathway to develop a hydrogel as a promising substitute for tissue engineering scaffold material.

Nanohydroxyapatite Reinforced Chitosan Composite Hydrogel with Tunable Mechanical and Biological Properties for Cartilage Regeneration

With the continuous quest of developing hydrogel for cartilage regeneration with superior mechanobiological properties are still becoming a challenge. Chitosan (CS) hydrogels are the promising implant materials due to an analogous character of the soft tissue; however, their low mechanical strength and durability together with its lack of integrity with surrounding tissues hinder the load-bearing application. This can be solved by developing a composite chitosan hydrogel reinforced with Hydroxyapatite Nanorods (HANr). The objective of this work is to develop and characterize (physically, chemically, mechanically and biologically) the composite hydrogels loaded with different concentration of hydroxyapatite nanorod. The concentration of hydroxyapatite in the composite hydrogel was optimized and it was found that, reinforcement modifies the hydrogel network by promoting the secondary crosslinking. The compression strength could reach 1.62 ± 0.02 MPa with a significant deformation of 32% and exhibits time-dependent, rapid self-recoverable and fatigue resistant behavior based on the cyclic loading-unloading compression test. The storage modulus value can reach nearly 10 kPa which is needed for the proposed application. Besides, composite hydrogels show an excellent antimicrobial activity against Escherichia coli, Staphylococcus aureus bacteria’s and Candida albicans fungi and their cytocompatibility towards L929 mouse fibroblasts provide a potential pathway to developing a composite hydrogel for cartilage regeneration.

Large strain response and fatigue-resistant behavior of lead-free (1-x)(Bi0.5Na0.5)TiO3-xSrTiO3 ceramics at a relatively low driving field

Lead-free (1-x)(Bi0.5Na0.5)TiO3-xSrTiO3 (abbreviated as BNT-100xST, x = 0.19–0.27) piezoceramics were synthesized via the traditional solid-state process. The micromorphology, phase structure, strain response and fatigue behavior were studied in detail. For all the composition range, the ceramics are pure perovskite structures. And the tetragonal phase gradually changes into pseudocubic phase. The ferroelectric order was destroyed with the increase of ST concentration. Strains up to 0.289% for BNT-23ST can be achieved at the driving fields (45 kV cm−1) with a high corresponding normalized strain d33* (Smax/Emax) of 642 pm V−1. Furthermore, the BNT-23ST ceramics exhibit an excellent fatigue resistance, and the unipolar strain value decreased by only 8.24% after 107 cycles.

Significantly Enhanced Energy-Harvesting Performance and Superior Fatigue-Resistant Behavior in [001]c-Textured BaTiO3-Based Lead-Free Piezoceramics

Energy-harvesting utilizing piezoelectric materials has recently attracted extensive attention due to the strong demand of self-powered electronics. Unfortunately, low power density and poor long-term stability seriously hinder the implementation of lead-free piezoelectrics as high-efficiency energy harvesters. For the first time, we demonstrate that tailoring grain orientations of lead-free ceramics via templated grain growth can effectively produce ultrahigh power generation performance and excellent endurance against electrical/mechanical fatigues. Significantly improved fatigue resistance was observed in (Ba0.94Ca0.06)(Ti0.95Zr0.05)O3 grain-oriented piezoceramics (with ∼99% [001]c texture) up to 106 bipolar cycles, attributed to the enhanced domain mobility, less defect accumulation, and thus suppressed crack generation/propagation. Interestingly, the novel energy harvesters, which were developed based on the textured ceramics with high electromechanical properties, possessed ∼9.8 times enhancement in output power density compared to the nontextured counterpart while maintaining stable output features up to 106 vibration cycles. The power densities, which increased from 6.4 to 93.6 μW/mm3 with increasing acceleration excitation from 10 to 50 m/s2, are much higher than those reported previously on lead-free energy harvesters. This work represents a significant advancement in piezoelectric energy-harvesting field and can provide guidelines for future efforts in this direction.

Effect of deposition material and heat treatment on wear and rolling contact fatigue of laser cladded rails

To develop a laser cladding technique for repairing rail surface damages due to rolling contact, wear and rolling contact fatigue characteristics of a set of laser cladded rails were investigated using a roller-on-disc test machine. Three deposition materials 410L, SS420 and Stellite 6, were chosen to clad a premium hypereutectoid steel rail under two different heat treatment processes. In the first heat treatment, only preheating at 350 °C was conducted and in the second heat treatment, preheating at 350 °C, post-heating at 350 °C (1 h) then slow-cooling to room temperature was conducted. Preheating the substrate was insufficient to prevent martensite formation resulting from the rapid cooling rate, whereas post heat treatment was beneficial for refining the lamellar spacing and eliminating martensite formation in the clad layer and heat affected zone. Following the roller-on-disc tests, wear loss was calculated from wear track profiles using a laser optical profilometer. The level of surface degradation, surface cracking and spalling was investigated using an optical microscope. Experimental results revealed that SS420 cladding had the highest wear resistant behaviour but severe surface cracks and spalling were found in the worn area. Stellite 6 cladding showed similar wear resistance as the parent substrate rail and the best fatigue resistance behaviour among the three cladded rail samples. Based on this research, Stellite 6 is the most promising deposition material for repairing rails by laser cladding.

Microstructure Characterization of Al-TiC Surface Composite Fabricated by Friction Stir Processing

Titanium carbide (TiC) is an exceedingly hard and wear refractory ceramic material. The surface properties of the material are very important and the corrosion, wear and fatigue resistance behaviour determines its ability and applications. It is necessary to modify the surface properties of the materials to enhance their performance. The present work aims on developing a new surface composite using commercially pure aluminum and TiC reinforcement powder with a significant fabrication technique called friction stir processing (FSP). The metal matrix composite of Al/TiC has been developed without any defects formation to investigate the particles distribution in the composite, microstructural changes and mechanical properties of the material. The microstructural observations exhibited that the grain refinement in the nugget compared to the base metal and FSP without TiC particles. The developed composite properties showed substantial improvement in micro-hardness, friction factor, wear resistance and microstructural characteristics in comparison to parent metal. On the other side, the ductility of the composite specimens was diminished over the substrate. The FSPed specimens were characterised using X-ray diffraction technique and revealed that the formation of AlTi compounds and the presence of Ti phases in the matrix. The microstructures of the samples illustrated the uniform distribution of particles in the newly developed metal matrix composite.

Large strain response in Li/Nb co-doped Bi0.5(Na0.8K0.2)0.5TiO3 lead-free piezoceramics

A series of (Bi0.5Na0.4K0.1)Ti0.98Nb0.02O3-xLi lead-free ceramics were fabricated using the solid-state reaction technique. The effects of Li/Nb cations on the structural and electrical properties of the ceramics were investigated. All the sintered ceramics exhibited pure perovskite structure and the average grain size increased slightly with increasing the Li content. Shape of the P-E loops illustrated the relaxor characteristic of all the samples. A giant strain of 0.4% was obtained at 60kV/cm at x = 0.01 and the corresponding normalized strain was up to 683pm/V, moreover, the strain exhibits excellent fatigue-resistance behavior. The giant strain can be attributed to the ferroelectric-relaxor phase transition under external driving electric field. These results indicate the sintered Li/Nb co-doped lead-free ceramics can be promising candidate for actuator applications.

Recrystallization and thermal shock fatigue resistance of nanoscale ZrC dispersion strengthened W alloys as plasma-facing components in fusion devices

Recrystallization and thermal shock fatigue resistance behavior of nanoscale ZrC dispersion strengthened bulk tungsten alloys (W-0.5 wt% ZrC, WZrC) as potential candidates for plasma-facing components were investigated. By employing heat treatments with isochronal experiments, the evolution of the tungsten grain size/orientation, second phase particle distribution, thermal conductivity and mechanical properties were systematically studied. The effects of edge-localized mode like transient heat events on the as-rolled and recrystallized WZrC were investigated carefully. Pulses from an electron beam with durations of 1 ms were used to simulate the transient heat loading in fusion devices. The cracking thresholds, cracking mechanisms and recrystallization under repetitive (100 shots) transient heat loads were investigated. Results indicate that the cracking threshold of all the WZrC samples is 220–330 MW/m2 (corresponding to a heat load parameter F = 7.0–10.4 MJ/m2s1/2) at room temperature and the heat bombardment induced recrystallization occurs at a heat parameter of 10.4 MJ/m2s1/2.

Rapidly self-recoverable and fatigue-resistant hydrogels toughened by chemical crosslinking and hydrophobic association

Designing load-bearing hydrogels with superior toughness and stiffness are crucially important for cartilage replacement and tissue engineering. In this investigation, we report that hybrid hydrogels can simultaneously achieve high stiffness and toughness by introducing covalent and physical interactions. The chemical crosslinking can sustain hydrogel networks as a rigid component and the hydrophobic association is introduced as a dynamic crosslinking center for efficient energy dissipation. The storage modulus G′ can reach nearly 40kPa and the compression stress was nearly 8MPa at 95% compression strain. Moreover, the hybrid hydrogel exhibited time-dependent, rapid self-recoverable and fatigue resistant behavior based on the cyclic loading-unloading compression test. The hybrid hydrogels with excellent self-recovery and fatigue resistance would provide a large number of potential applications, such as artificial cartilages and muscles and scaffolds for tissue engineering.

Electric‐field induced phase transition and fatigue behaviors of (Bi0.5+x/2Na0.5‐x/2)0.94Ba0.06Ti1‐xFexO3 ferroelectrics

AbstractThe dielectric, piezoelectric properties, and fatigue behaviors of stoichiometric (Bi0.5+x/2Na0.5‐x/2)0.94Ba0.06Ti1‐xFexO3 (BNBT‐xFe) ferroelectrics are investigated. Fe substitution leads to the downward shift of the ferroelectric‐relaxor transition temperature (TF‐R) and increase in strain. Meanwhile, fatigue behaviors of the modified ceramics are significantly enhanced. Ex situ X‐ray diffraction and transmission electron microscopy reveal microscopic mechanism for polarization fatigue on different compositions. The fatigue‐free behavior of ferroelectric BNBT‐0.03Fe is not only attributed to a mechanism involving the formation of defect dipoles, which reduces the pinning effect of migratory oxygen vacancies on domain walls, but is also connected to the decrease in easily suppressed field‐induced ferroelectric tetragonal phase. While for ergodic relaxor BNBT‐0.09Fe, the absence of domain wall contributes to the good fatigue resistance behavior. Interestingly, electric cycling results in an increased fraction of relaxor phase, accompanying by the increase in the total strain and decrease in remnant polarizations.

Effect of initial twins on the stress-controlled fatigue behavior of rolled magnesium alloy

The effect of initial twins on the fatigue behavior of rolled AZ31 alloy was investigated by introducing {10–12} twins into the alloy through pre-deformation and then conducting fully reversed stress-controlled fatigue tests along the rolling direction (RD) and the direction normal to the rolling plane (ND). It was found that the fatigue life of the alloy is higher under RD loading than under ND loading, but when initial twins exist, the fatigue resistance along the RD decreases, whereas the ND fatigue resistance increases, eventually reversing the fatigue resistance behavior under the ND and RD loading conditions. The tensile mean strain generated under ND loading is also changed to compressive strain by initial twins, whereas the reverse is true under RD loading. The fatigue strength of samples with and without twins is inversely proportional to the logarithm of their plastic strain energy density, which corresponds to the inner area of the hysteresis loop at half-life, irrespective of the loading direction.

Enhanced temperature stability and fatigue-resistant behavior in MgTiO3-doped 0.948(K0.5Na0.5)NbO3–0.052LiSbO3 lead-free ceramics

0.948(K0.5Na0.5)NbO3–0.052LiSbO3–xMgTiO3 (x=0, 0.005 and 0.010) (abbreviated as KNLNS–xMT) lead-free piezoelectric ceramics were prepared by normal sintering. The effect of MT addition on KNLNS ceramics was investigated through dielectric, ferroelectric and electric field-induced strain characterizations. The grain size decreased slightly after the addition of MT, and more uniform grains were obtained. Impedance measurements made over a wide range of temperatures (425–525°C) showed the presence of both bulk and grain boundary effects in the materials. The activation energies Ea were 0.483 and 0.507eV for KNLNS and KNLNS–0.005MT ceramics respectively, indicating that the conduction process was due to oxygen vacancies in the higher temperature region. The Pr and unipolar strain of the MT modified ceramics exhibited lower temperature sensibility than KNLNS ceramics in the temperature range 30–120°C. Meanwhile, the MT doped samples showed less degradation in both switchable polarization and unipolar strain after 106 switching cycles than those of KNLNS. It is expected that the KNLNS–xMT ceramics is promising candidate for lead-free piezoceramics and could be used in practical applications.

Large electric-field-induced strain in SrZrO3 modified Bi0.5(Na0.80K0.20)0.5TiO3 lead-free electromechanical ceramics with fatigue-resistant behavior

The effect of SrZrO3 (SZ) addition on the ferroelectric behavior and piezoelectric properties of Bi0.5(Na0.80K0.20)0.5TiO3 (BNKT20) lead-free piezoceramics were investigated. Results showed that BNKT20–xSZ samples underwent a phase transition from ferroelectric rhombohedral and tetragonal phases to relaxor pseudocubic phase with increasing SZ content, and such transition are accompanied with the significant disruption of ferroelectric order and the shift of the ferroelectric–relaxor transition temperature TF−R down to room temperature. Accordingly, it induced an enhancement of the field-induced strain with a peak at a value of ∼0.39% (at 80 kV/cm, corresponding to a large signal d33∗ of ∼488 pm/V) obtained in 1.5 mol%SZ-modified samples. Temperature dependent measurements of both polarization and strain suggest that the origin of the large strain is due to a reversible field-induced ergodic relaxor to ferroelectric phase transformation. Moreover, an attractive property for application as actuators was obtained in this system, as BNKT20 modified with 1.5 mol%SZ exhibits fatigue-free behavior up to 106 cycles. This exceptionally good fatigue resistance is identified due to the presence of an ergodic relaxor state.