Flexural Fatigue Research Articles

Optimum glide path motion is safer than continuous rotation of files in glide path preparation

This study evaluated the resistance to flexural fatigue and torsional strength of files for glide path preparation in continuous rotation or Optimum Glide Path motion (OGP). ScoutRace 15.02 and ProGlider 16.02 files were used in a dynamic testing device during preparation of simulating curved root canals (40-degree curvature and 5mm radius). For the torsional test, a machine was used to test torsion measured maximum torsional strength (N.cm). Two-way anova and Tukey's multiple comparisons test were used for statistical analysis. Files in OGP motion had a statistically better resistance to flexural fatigue (P<0.05). ProGlider files took longer time to failure than ScoutRace files only when OGP was used (P<0.05). The torsional test revealed that OGP produced significantly less torsional stress than rotary motions for both types of glide path files (P<0.05) In conclusion, OGP motion increased substantially the mechanical safety of endodontic glide path files.

Multilayered graphene/boron nitride/thermoplastic polyurethane composite films with high thermal conductivity, stretchability, and washability for adjustable-cooling smart clothes

Polymers having high filler loading levels are not able to meet the increasing requirements of thermal interface materials by themselves; therefore, fillers and structures with unique advantages have been developed. In this study, mechanical mixing was used to disperse graphene nanoplatelets (GNPs) and boron nitride (BN) fillers inside thermoplastic polyurethane (TPU)-based films, which were then compounded into a multilayered structure. The multilayered BN-GNP/TPU composite film created during this study exhibited a high thermal conductivity of 6.86 W m−1 K−1 at a low filler loading of 20 wt% BN with 20 wt% GNP, which was significantly higher (2844%) than that of the neat TPU film. The composite film also had good durability to flexural fatigue and laundering. This was exhibited by maintaining thermal conductivity values of 6.25 W m−1 K−1 after 5000 cycles of the flexural fatigue test, and 6.85 W m−1 K−1 after 10 cycles of laundering, respectively. Furthermore, enhanced thermal stability, cooling, and hydrophobic properties of the multilayered BN-GNP/TPU composite films were also observed with the resulting composite film. Overall, such a system provides a facile approach that is applicable for the fabrication of multifunctional materials as thermal interface materials within smart cooling garments.

Surface treatments and its effects on the fatigue behavior of a 5% mol yttria partially stabilized zirconia material

This study evaluated the effect of distinct surface treatments on the fatigue behavior (biaxial flexural fatigue testing) and surface characteristics (topography and roughness) of a 5% mol yttria partially stabilized zirconia ceramic (5Y-PSZ). Disc-shaped specimens of 5Y-PSZ (IPS e.max ZirCAD MT Multi) were manufactured (ISO 6872–2015) and allocated into six groups (n = 15) considering the following surface treatments: Ctrl – no-treatment; GLZ – low-fusing porcelain glaze application; SNF – 5 nm SiO2 nanofilm; AlOx – aluminum oxide particle air-abrasion; SiC – silica-coated aluminum oxide particles (silica-coating); and 7%Si – 7% silica-coated aluminum oxide particles (silica-coating). The biaxial flexural fatigue tests were performed by the step-stress method (20Hz for 10,000 cycles) with a step increment of 50N starting at 100N and proceeding until failure detection. The samples were tested with the treated surface facing down (tensile stress side). Topography, fractography, roughness, and phase content assessments of treated specimens were performed. GLZ group presented the highest fatigue behavior, while AlOx presented the lowest performance, and was only similar to SiC and 7%Si. Ctrl and SNF presented intermediary fatigue behavior, and were also similar to SiC and 7%Si. GLZ promoted a rougher surface, Ctrl and SNF had the lowest roughness, while the air-abrasion groups presented intermediary roughness. No m-phase content was detected (only t and c phases were detected). In conclusion, the application of a thin-layer of low-fusing porcelain glaze, the deposition of silica nanofilms and the air-abrasion with silica-coated alumina particles had no detrimental effect on the fatigue behavior of the 5Y-PSZ, while the air-abrasion with alumina particles damaged the fatigue outcomes.

Flexural Properties of Carbon/Glass Hybrid Thermoplastic Epoxy Composite Rods Under Static and Fatigue Loadings

Cables are primarily used in structures as tensile elements, but they are also subjected to compressive, flexural, and shear loadings. Therefore, in addition to the hybrid rods’ tensile properties, the other corresponding mechanical properties must also be characterized. This study is an investigation of the flexural behavior of carbon/glass hybrid thermoplastic epoxy composite rods. Test results indicated that an increase in the void content to a decrease in the flexural strength, and consequently the Weibull modulus as well. The flexural fatigue performance (in terms of maximum stress) increases with the static flexural strength. The intercept for power law model increased with increasing carbon fiber volume fraction, and decreasing matrix content and void content. The absolute values of slope for power law model decreased with increasing carbon fiber volume fraction, and increasing matrix content and void content. The fatigue strength at 1 × 107 cycles for the hybrid rods was less than 20–30% of the ultimate flexural strength. The static and fatigue flexural properties for the hybrid rods were strongly influenced by kinking, buckling, and delamination behaviors of unidirectional carbon fiber bundle composites.

Incidence of Different Types of Intracanal Fracture of Nickel–Titanium Rotary Instruments: A Systematic Review

The aim of this systemic review is to investigate these parameters by analyzing the characteristics of fractured instruments to determine which is the most relevant mechanical stress that induces intracanal separation in vivo. The fracture of nickel-titanium (Ni-Ti) instruments is a result of flexural fatigue and torsional fatigue. An electronic search was conducted in MEDLINE database, Web of Science, and Cochrane following preferred reporting items for systematic reviews and meta-analyses guidelines. Data were collected and the key features from the included studies were extracted. Overview quality assessment questionnaire scoring assessed the quality of the articles. A total of 12 articles were selected, where the lowest score was 13. Considering Ni-Ti rotary instruments, this overall evaluation comprehends 939 broken instruments with an incidence of fracture of 5%. Out of the 12 selected articles, 10 studies revealed that flexural failure was the predominant mode (range of 62-92%). It appears that motion plays an important role when it comes to mechanisms of fracture. The majority of defects found in hand-operated instruments were in the form of torsional failure. Although the major cause of separation of rotary instruments is flexural fatigue, smaller instruments show more torsional fracture than the larger instruments. The average fragment length was found to be 2.5 mm and 3.35 mm, respectively, for torsional failure and flexural failure. The risk of bias depends on fractographic analysis. Flexural fatigue is the predominant mode of fracture in rotary Ni-Ti instruments. The type of motion and size of the instrument seem to affect the mechanism of fracture. Fragment length may show a strong association with the type of fracture mechanism. This systemic review found that flexural fatigue is the most relevant mechanical stress that induces intracanal separation in vivo. Moreover, in clinical practice, the fragment length might be an excellent indicator of the type of fracture.

Mechanical evolutionary behavior of steam‐cured concrete under the coupling effect of flexural fatigue and minus temperature

AbstractSteam‐cured concrete products have been widely employed in building slab ballastless track for China High‐Speed Railway lines, such as track sleeper and track slab. These components are usually subjected to long‐term fatigue load due to the wheel‐rail interactions by high‐speed trains. Especially in Northeast China where the winter temperature keeps subzero for months, the concrete elements are exposed to the coupling effects of fatigue load and minus temperature environment. Therefore, this paper investigated the mechanical damage evolutionary behavior of steam‐cured concrete under coupling effects of flexural fatigue loading and minus temperature. Additionally, the mechanism behind it was discussed. The results showed that the mechanical damage of steam‐cured concrete subjected to fatigue loading under minus temperature was more significant than that under room temperature. The influences of ice content on the degradation in mechanical properties of steam‐cured concrete are illustrated by the phenomenological model. A two‐stage statistical damage variable can well reveal the impact of fatigue cycles and temperature on fatigue damage and total damage concrete. Steam‐cured concrete based on PC‐FA‐GGBS binder system exhibits better resistance to the flexural fatigue loading and minus temperature coupling effects due to its better pore structure and less ice content.

Additive Manufacturing of 316L Stainless Steel by a Printing-Debinding-Sintering Method: Effects of Microstructure on Fatigue Property

Abstract Additive manufacturing (AM) technology has been broadly applied to the fabrication of metallic materials. However, current approaches consume either high energy or large investment that considerably elevates their entry threshold. An economic extrusion-based AM method followed by debinding and sintering could efficiently produce the metal parts with relatively low cost and high material utilization. However, an in-depth analysis of the fatigue performance of the component built by such a technology has been little documented so far. Herein, the 316L stainless steel was fabricated throughout the printing-debinding-sintering (PDS) pathway and its fatigue properties were comprehensively assessed. Tensile and flexural fatigue tests were conducted to reveal the fatigue strength and fractural behaviors under different loading conditions, while the fatigue crack growth (FCG) test was performed to quantify the crack propagation. The results indicated the number of 105 cycles can be reached for the tensile specimens under the fatigue loading of 120 MPa, whereas 1.37 × 105 cycles were endured by the flexural specimens under 150 MPa. The fractural morphology indicated an adverse impact of the pore-induced voids on the tensile fatigue crack propagation, but such a drawback could be alleviated in the flexural loading condition. The FCG test unveiled the crack growth rate with the number of cycles and determined the material-related coefficients in the fatigue crack growth model. The research findings provided valuable insights into the effects of the PDS process and microstructures on the resultant fatigue properties of the metal component.

Correlation of fatigue behavior and dynamic mechanical properties of hybrid composites of polypropylene/short glass fibers/hollow glass beads

Ternary hybrid composites of Polypropylene (PP)/Short Glass Fibers (GF)/Hollow Glass Beads (HGB) were prepared using untreated and aminosilane-treated HGB, compatibilized with maleated-PP, and with varying total and relative GF/HGB contents. Static/short-term flexural strength properties data revealed, through lower flexural strength values, that the presence of untreated HGB particles induces to fiber-polymer interfacial decoupling at much higher extent than in the presence of aminosilane-treated HGB particles. This phenomenon is also evident when evaluating the data from displacement-controlled three-point bending fatigue tests. Monitored up to 106 cycles, the analyzed hybrid composites presented distinct performance relative to their fatigue stress relaxation rate: the lower the matrix-reinforcements’ interfacial adhesion, more pronounced the stress relaxation rate as a function of the number of fatigue cycles. Dynamic Mechanical Thermal Analysis (DMTA) results could successfully reveal the hybrid composites behavior at the microstructural level when they were submitted to both static flexural test and fatigue, depending on the degree of interfacial interactions between the polymer matrix of PP and the hybrid reinforcements of GF and HGB (with and without aminosilane surface treatment).

Preparation and flexural fatigue resistance of self-compacting road concrete incorporating nano-silica particles

In this study, the mix proportion of self-compacting road concrete with ternary cementitious materials was optimized by incorporating nano-silica particles to improve its flexural fatigue performance. The filling property and compressive strength were selected as evaluating indicators to design L9(33) orthogonal test, and then four kinds of mix proportions were selected to prepare the nano-modified self-compacting concrete (SCC) according to the results of grey relational analysis and comprehensive weighting method. The four-point flexural fatigue tests were conducted to establish the probabilistic fatigue equations of nano-modified SCC based on the two-parameter Weibull distribution with survival rates of 50% and 95%, respectively. The modification mechanism was revealed with the help of scanning electron microscopy and X-ray diffraction phase analysis. The results indicate that the optimal mix proportion of self-compacting road concrete could be obtained when nano-silica accounts for 1% of the mass of cementitious materials. The specimens with 1% nano-silica particles showed the best flexural fatigue performance, with the reduction factor of flexural strength increased by 1.5%–5.0% and the sensitivity of fatigue life to the stress levels decreased by 2.1%–9.7% at survival rate of 50%. The nanoparticles provided a physical filling effect and facilitated the formation of low-density calcium silicate hydrate gel, filling the internal micro-pores to make the structure more compact. Nano-silica improved the flexural fatigue performance of self-compacting road concrete to a certain extent.

Irradiation, thermal and mechanical properties of ethylene-tetrafluoroethylene copolymer for use in wings of unmanned aerial vehicle

To study the properties of ethylene-tetrafluoroethylene (ETFE) copolymer materials in wings of unmanned aerial vehicles, electron beam irradiation was performed to prepare the corresponding irradiated ETFE for air atmosphere. All these irradiated samples were characterized by SEM, FTIR, TGA, DSC, flexural fatigue measurement and tensile test. The results revealed that the logarithm of the flexural fatigue of ETFE decreased with the irradiation dose increased, which could be explained by the growing effect of chain scission. The elongation-at-break decreased with the dose increase, while the tensile strength was kept constant. As shown in FTIR results, the scission of the macromolecular chains induced by irradiation resulted in the relative oxidation of groups, such as carbonyl groups. TGA analysis showed that the initial and maximum decomposition temperatures increased with dose increase due to the inherent cross-linking structures. Besides, the number of the crystalline regions with regular formation (such as crystallization temperature, crystallization degree and crystallization enthalpy) decreased with the dose increase as a result of the formation of unsaturated structures after the elimination of HF from the broken chains, which was confirmed by FTIR. It is expected that our findings can provide important information to promote the development of aircraft materials.

Flexural fatigue behaviour of a heated ultra-high-performance fibre-reinforced concrete

A comprehensive experimental campaign was carried out to assess the flexural fatigue behaviour of an ultra-high-performance fibre-reinforced concrete. Several concrete mixes were submitted to room temperature, 100 °C, 200 °C, and 300 °C. Two types of reinforcement were explored: steel fibres and a combination of steel and polypropylene fibres. The influence of the addition of fibres and the temperatures in the microstructure were analysed through X-ray CT scans. In addition, the mechanical and fracture properties of the concrete were determined with monotonic tests and a connection between macroscopic and microscopic results was established to explain the fatigue behaviour. The beneficial effect of the fibres was observed essentially at a low cyclic fatigue regime. In heated concretes, the reduction of matrix porosity due to the presence of steel fibres led to significant damage after being exposed to 300 °C by spalling failure. By contrast, the concrete reinforced with polypropylene fibres maintained remarkably similar fatigue behaviour at room temperature and 300 °C.

Static and Flexural Fatigue Behavior of GFRP Pultruded Rebars.

This paper presents the experimental results of composite rebars based on GFRP manufactured by a pultrusion system. The bending and radial compression strength of rods was determined. The elastic modulus of GFRP rebars is significantly lower than for steel rebars, while the static flexural properties are higher. The microstructure of the selected rebars was studied and discussed in light of the obtained results—failure processes such as the delamination and fibers fracture can be observed. The bending fatigue test was performed under a constant load amplitude sinusoidal waveform. All rebars were subjected to fatigue tests under the R = 0.1 condition. As a result, the S-N curve was obtained, and basic fatigue characteristics were determined. The fatigue mechanism of bar failure under bending was further analyzed using SEM microscopy. It is worth noting that the failure and fracture mechanism plays a crucial role as a material quality indicator in the manufacturing process. The main mechanism of failure under static and cyclic loading during the bending test is widely discussed in this paper. The results obtained from fatigue tests encourage further analysis. The diametral compression test reflects the weakest nature of the composite materials based on the interlaminar compressive strength. The proposed methodology allows us to invariantly describe the experimental transversal strength of the composite materials. Considering the expected durability of the structure, the failure mechanism is likely to significantly improve their fatigue behavior under the influence of cyclic bending. The reasonable direction of searching for reinforcements of composite structures should be the improvement of the bearing capacity of the outer layers. In comparison with steel rebars (fatigue tensile test), the obtained results for GFRP are comparable in the HCF regime. It is worth noting that in the near fatigue endurance regime (2–5 × 106 cycles) both rebars exhibit similar behavior.

Investigating flexural performance of waste tires steel fibers-reinforced cement-treated mixtures for sustainable composite pavements

In many parts of the world, the cement-treated base course material has been extensively used within composite pavements for enhancing the load-carrying capacity of pavements. However, its vulnerability to cracking under repetitive traffic loading, due to its brittle nature, significantly cuts off its lifespan and hence reducing the sustainability of composite pavements. To provide a solution to this problem, this study is aimed to investigate the flexural performance of cement-treated base (CTB) mixtures reinforced with the Waste Steel Fibers (WSF) extracted as a residual product from the scrap tires. The flexural performance is evaluated in terms of flexural fatigue and flexural strength. Moreover, the effect of steel fiber reinforcement on the dynamic modulus of the cement-treated base mixtures was also studied. The specimens for dynamic modulus were prepared by using a gyratory compactor to better simulate the traffic loading. Furthermore, the basic split tensile strength and unconfined compressive strength of WSF reinforced CTB mixtures were also studied. Lastly, important correlations were derived based on the results obtained in this study, to predict the flexural performance of CTB mixtures in terms of dynamic modulus and fatigue life by conducting basic split tensile strength tests and flexural strength tests. Based on the results, WSF reinforcement has noticeably enhanced tensile strength, dynamic modulus, flexural strength, and fatigue life of CTB mixtures. On the other hand, the variations in the compressive strength due to WSF reinforcement were trivial. Based on the results, the steel fibers content of 0.3% by volume of the wet compacted blend has shown more promising results than lower and higher WSF contents.

Flexural Fatigue Life Reliability of Alkali‐Activated Slag Concrete Freeze‐Thaw Damage in Cold Areas

Studying the application of alkali‐activated slag concrete for roads in cold areas is of great significance for promoting and developing green building materials. In this study, the effect of freeze‐thaw damage on the flexural fatigue properties of alkali‐activated slag concrete was studied and the fatigue life of alkali‐activated slag concrete with various degrees of damage after freeze‐thaw cycles was studied through a three‐point flexural test. The results show that the flexural fatigue life decreases with freeze‐thaw cycles from 0 to 150 times. Through a distribution fitting test and K‐S test results, the flexural fatigue life followed both the two‐parameter and three‐parameter Weibull distributions. Between them, the three‐parameter Weibull distribution fitting had a higher accuracy and better test results. The results of the reliability analysis show that the curves of alkali‐activated slag concrete samples with various degrees of freeze‐thaw damage for various failure probabilities have good correlation under different stresses, and the correlation correlations were greater than 0.81. The flexural fatigue life of alkali‐activated slag concrete samples with various degrees of freeze‐thaw damage was more sensitive to freeze‐thaw damage under high stresses. It is suggested that the fatigue design of alkali‐activated slag concrete should consider the adverse effects of cold areas, and the reliability should be improved accordingly.

Resin matrix ceramics – mechanical, aesthetic and biological properties

ABSTRACT Resin matrix ceramics consist in a polymeric matrix with predominantly inorganic refractory compounds which may include porcelain, glass, ceramics, and glass ceramics, and are divided into three subgroups: Nanoceramics, Vitroceramics, and Zirconia-silica. The aim of this study was to compare, through a literature review, the mechanical and biological properties of resin matrix ceramics, with glass matrix ceramics and polycrystalline ceramics. After reviewing 44 articles found in the US National Library of Medicine (PubMed) database (studies published in English, human clinical studies, in vitro or in vivo studies) that evaluated some properties of this material, such as elasticity modulus, wear resistance, adhesiveness, stain resistance and hardness, this article concluded that, although they belong to the same group, resin matrix ceramics are different from each other due to their microstructures. Moreover, when compared to other ceramic groups, it showed some superior properties, such as flexural strength, fatigue strength and internal adaptation.

Investigate road performance using polymer modified concrete

Abstract Polymer-modified cement concrete pavement can not only improve the problem of insufficient durability of asphalt pavement, but also improve the joint damage and cracks of cement concrete pavement. It has become the current research focus of new road materials. Through indoor test methods, the compressive, flexural tensile strength and impact resistance, flexural fatigue resistance, impermeability, frost resistance, shrinkage characteristics and wear resistance of polymer modified cement concrete with different polymer content are studied. The research results show that the polymer has improved these properties, and the improvement effect gradually increases with the increase of the polymer content.

Crack propagation in flexural fatigue of concrete using rheological-dynamical theory

The concrete fatigue analysis can be performed with the use of fracture mechanics. The fracture mechanics defines the fatigue crack propagation as the relationship of crack growth rate and stress intensity factor. In contrast to metal, the application of fracture mechanics to concrete is more complicated and therefore many authors have introduced empirical expressions using Paris law. The topic of this paper is development of a new prediction of fatigue crack propagation for concrete using rheological-dynamical analogy (RDA) and finite element method (FEM) in the frame of linear elastic fracture mechanics (LEFM). The static and cyclic fatigue three-point bending tests on notched beams are considered. Verification of the proposed approach was performed on the test results taken from the literature. The comparison between the theoretical model and experimental results indicates that the model proposed in this paper is valid to predict the crack propagation in flexural fatigue of concrete.

Implementation of a cooling system to develop experimental fatigue tests below zero grades Celsius

Temperature is one of the matter properties with the greatest influence on the materials behavior existing in nature and those man designed. This physical magnitude allows to demonstrate and define behaviors and materials characteristics in the industry in general. Its influence is present in all the places where the materials fulfill functions, however, in some applications its influence is very little, which allows to disregard its effects. In the steels case (one of the most used materials at the industrial level today), the temperature variation produces dilation or contraction, depending on the temperature magnitude and its variation that affects them. Temperature increases generate an expansion phenomenon in the materials, which under load will reach a point where they present thermal fatigue failure. The opposite is that of temperature drops, where the phenomenon that occurs is contraction, often leading to the loss of adjustments and interference that compromise the equipment functionality and integrity. The fatigue failure mentioned is presented as a result of the stresses and deformations present in both cases. It is desired to condition a rotational flex fatigue test equipment with a cooling system to bring the sample material to temperatures below zero degrees Celsius, in order to check how low temperatures, affect the resistance of steel to fatigue. For this, a cooling system was designed and the fatigue equipment was adapted to reduce heat transfer. After carrying out this implementation and determining that the sizes of the devices were suitable for the proposed purposes, the initial temperature tests were carried out and, once this part was achieved, three repetitions of a rotary fatigue test were performed that demonstrated that the equipment can operate normally.

Cyclic flexural resistance of newly introduced NiTi rotary file system: An in-vitro study

This study aimed to compare the cyclic fatigue fracture resistance of different rotary NiTi file systems. Hero shaper rotary file, one shape rotary file and a new rotary file system profile vortex were tested. The cyclic fatigue testing was conducted using a simulated root canal apparatus with an angle of curvature 60⁰and radius of curvature of 5mm.Total sample size of 30 rotary files (10 files in each experimental group) were selected for the study. The files were rotated at 400 rpm using the triauto mini endomotor set at 2.5N/cm torque, until fracture occurred. The time until fracture was recorded in seconds by using a digital stopwatch, and the number of rotations till fracture was then calculated using a mathematical formula. The results were then statistically analysed. Profile vortex (Group 3) was found superior as compared to one shape (Group 2) and hero shaper (Group 1) endodontic rotary NiTi file system in cyclic fatigue testing. Keywords: Cyclic fatigue, Flexural fatigue resistance, Static flexural fracture resistance.

Flexural fatigue behavior of bamboo-based products

AbstractBamboo-based products are increasingly used in structural engineering fields. Specifically, their application requires consideration of factors that affect their service life, such as the fatigue behavior. Bamboo-based materials, such as bamboo scrimber, have a high density and uneven stress distribution. These structural properties seriously affect the quality of the bamboo-based materials, and lead to increased fatigue. To solve this problem, the fatigue behavior of bamboo laminated veneer lumber (BLVL) was studied. BLVL was manufactured by arranging rolled and broomed bamboo bundles and hot-pressing. This study describes the flexural fatigue behavior of BLVL at different stress levels. The fatigue was characterized by the fatigue failure, the fatigue hysteresis loops, the energy loss, and stiffness degradation. The results demonstrated that the BLVL material had good fatigue-resisting performances. The fatigue life of BLVL under 80% stress level was estimated to be about 1,700,000 cycles. The main failure modes of the BLVL included fiber tearing, fiber pullout, fiber breakage, and fiber-matrix debonding. The total energy loss at higher stress levels was less than that at low stress levels. Higher stress levels corresponded to a larger drop in stiffness.