Excellent Fatigue Properties Research Articles

纤维金属层板的疲劳裂纹扩展行为及预测方法研究进展

纤维金属层板(Fiber Metal Laminates，简称FMLs)是一种由金属薄板和纤维增强复合材料组成的层间混杂复合材料，具有优良的疲劳和损伤容限性能，是飞机结构的理想材料。纤维金属层板的疲劳损伤模式较为复杂，既有金属层内的裂纹扩展，又有金属/纤维层间的分层扩展，两者相互作用，增加了层板裂纹扩展速率与寿命预测的难度。国内外学者对纤维金属层板的疲劳裂纹扩展行为开展了大量的研究并取得了一定的成果。本文介绍了纤维金属层板的疲劳损伤机制，总结了恒幅载荷下纤维金属层板的疲劳裂纹扩展行为预测模型，并对变幅载荷下纤维金属层板的疲劳裂纹扩展及分层行为研究进行了概述。 Fiber Metal Laminates (FMLs) are advanced hybrid materials combining the excellent fatigue and damage tolerant properties of metals and fiber reinforced composites, which are ideal materials for aerospace. The fatigue crack growth behavior of FMLs is complex, which includes both crack growth in the metal layers and delamination growth at the metal/fiber interfaces in wake of the metal crack. This interaction makes it harder for the prediction of crack growth rate and damage tolerance. The fatigue crack growth behavior of FMLs has been studied by many researches and valuable results were obtained. In this paper, the fatigue damage mechanism of FMLs is reviewed. The prediction models for fatigue crack growth rate and life of FMLs under constant amplitude (CA) loading are summarized. Furthermore, the researches on fatigue crack growth and delamination behaviors of FMLs under variable amplitude (VA) loading are also overviewed.

G0301601 AC4CH鋳造アルミニウム合金の超高サイクル疲労特性

In order to investigate very high cycle fatigue property of AC4CH-T6 casting aluminum alloy, axial loading fatigue tests were performed. Because it was known that the fatigue property of casting aluminum alloy was affected by the influence of casting defects inside the material, the defect inspection of the specimen was conducted by computed tomography with the industrial X-ray CT scanner after making them. As a result, it was expected that this material showed an excellent fatigue property, because there was no large defect in all of the specimens. However, this material had poor fatigue property contrary to expectation. And then, some large size facet of α-dendrite structure weres observed in the crack initiation site.

Effect of vanadium on the high-cycle fatigue fracture properties of medium-carbon microalloyed steel for fracture splitting connecting rod

Abstract The present investigation effort was made to study the effect of V up to 0.45% on the high-cycle fatigue properties of medium-carbon microalloyed (MA) steel 37MnSiVS, for the development of new crackable MA forging steel with excellent fatigue properties. The results show that the amount of V(C,N) precipitates increases with increasing V content and most of the precipitates are less than 5 nm. Owing to the significant precipitation strengthening effect of these nanosized particles, the hardness increase of ferrite with increasing V content is higher than that of pearlite and accordingly a decrease of pearlite/ferrite hardness ratio. Therefore, both fatigue strength and fatigue strength ratio increase with increasing V content and excellent fatigue properties could be obtained when V content is higher than about 0.28%. The fatigue crack growth (FCG) behavior is similar for all the three 37MnSiVS samples with an exponent m ≈ 3.5. It is concluded that V can improve the fatigue properties of ferrite–pearlite steel mainly through precipitation strengthening and therefore it is anticipated that MA steel’s fatigue property could be further improved as well as more fine V(C,N) particles be obtained.

Fatigue and Fracture Resistance of an Aircraft Landing Gear Steels V-ROL N and VIP P-ROL N Heat Treated to Lower Strength Limit

V-ROL N is an aircraft steel produced in Czech Republic at Poldi Kladno, used for many years for a manufacture of aircraft landing gears, particularly for a small passenger aircraft L 410. The V-ROL N steel, known by its very good or even excellent fatigue and fracture properties, has not been more available due to recent privatization of the company. Therefore, a substitution of materials previously used became an issue. The paper contains results of a comprehensive experimental programme aimed at comparison of the V-ROL N steel used in the past, still available for research purposes, with another steel of a similar type, VIP P-ROL N steel, manufactured in Czech Republic by another company. Fatigue resistance of both versions can be considered as good. Slightly higher scatter of fatigue results of VIP P-ROL N version can be attributed to an occurrence of impurities, although quite rare, responsible for fatigue crack initiation.

Tool wear mechanisms in the machining of Nickel based super-alloys: A review

Nickel based super-alloys are widely employed in aircraft engines and gas turbines due to their high temperature strength, corrosion resistance and, excellent thermal fatigue properties. Conversely, these alloys are very difficult to machine and cause rapid wear of the cutting tool, frequent tool changes are thus required resulting in low economy of the machining process. This study provides a detailed review of the tool wear mechanism in the machining of nickel based super-alloys. Typical tool wear mechanisms found by different researchers are analyzed in order to find out the most prevalent wear mechanism affecting the tool life. The review of existing works has revealed interesting findings about the tool wear mechanisms in the machining of these alloys. Adhesion wear is found to be the main phenomenon leading to the cutting tool wear in this study.

Investigation of Usability of Brucite Fiber in Asphalt Mixture

The objective of this study is to investigate the usability of brucite fiber in asphalt mixture. In order to compare the characteristics of brucite fiber with other fibers usually used in asphalt mixtures, the water absorption test, oven heating test, Mesh-basket draindown test, and scanning electron microscopy are conducted on brucite fiber, lignin fiber, basalt fiber, and polyester fiber. Also, the Marshall test, wheel tracking test, low temperature bending test, water sensitivity test, and fatigue test are used to evaluate the performance of different fiber-reinforced asphalt mixtures. These experimental results show that brucite fiber has a good state of preservation in the moist storage environment, and its thermo-stability is better than lignin fiber. Its absorption and adhesion of asphalt is better than basalt fiber and polyester fiber. The best performance of asphalt mixtures are obtained for 0.40% brucite fiber content. Asphalt mixture prepared with brucite fiber also has excellent high temperature stability, water sensitivity, and fatigue property, especially low temperature properties. Addition of brucite fiber is feasible to improve major performance properties of asphalt mixture.

Bipolar fatigue-resistant behavior in ternary Bi0.5Na0.5TiO3–BaTiO3–SrTiO3 solid solutions

A ternary solid solution (0.935–x)Bi0.5Na0.5TiO3–0.065BaTiO3–xSrTiO3 (BNBST, BNBSTx), reported in our previous work, that exhibits a large strain response at a critical composition, was investigated with the emphasis on its bipolar fatigue behavior. The results indicated that BNBST with a high SrTiO3 content owning an ergodic relaxor state exhibited fatigue-free behavior after 106 cycles. Furthermore, unexpected almost fatigue-free behavior was also observed in BNBST with a low SrTiO3 concentration which has a typical ferroelectric long-range order. The excellent fatigue properties are quite favorable for practical applications.

Mechanical strength and failure characteristics of cast Mg–9%Al–1%Zn alloys produced by a heated-mold continuous casting process: Fatigue properties

The fatigue properties and failure characteristics of a cast Mg alloy (AZ91: Mg–Al8.9–Zn0.6–Mn0.2) produced by heated-mold continuous casting (HMC) and conventional gravity casting (GC) are investigated. Excellent fatigue properties are obtained for the HMC alloy compared with the GC alloy. The high fatigue strength of the HMC alloy is a reflection of its improved microstructural characteristics, namely, tiny α-Mg grains and fine spherical eutectic structures (β-Mg17Al12). Fatigue cracks propagate mainly in the α-Mg grains and along high-hardness β-phases in both alloys. The direction of fatigue crack growth is altered as the crack reaches the eutectic phases. Because the tiny eutectic phases are distributed randomly in the HMC alloy, a meandering crack path is formed, which results in high crack growth resistance, leading to the high fatigue strength. For the HMC alloy, a striation-like failure mode can be seen in the crack growth stage, and dimple fracture is the dominant feature in the final failure stage. On the other hand, cleavage-like brittle failure with many microcracks can occur in the GC alloy. Severe lattice strain occurs during the final failure stage, especially for the HMC alloy, resulting in strong work hardening, although this is weak in the crack growth site. Severe strain is distributed uniformly around the entire cracks in the HMC alloy when the sample is fractured by monotonic loading. The lattice strains in the HMC alloy under monotonic and cyclic loading are overall higher than those in the GC alloy, owing to the high material ductility of the HMC alloy.

A Highly Fatigue-Resistant Zr-Based Bulk Metallic Glass

The strength-normalized fatigue endurance strength of the bulk metallic glass (BMG) Zr52.5Cu17.9Ni14.6Al10Ti5 (Vitreloy 105) has been reported to be the highest for any BMG; however, to date, there has been no explanation of why this material is so much better than other Zr-based compositions. In this study, the fatigue-crack growth behavior of Zr52.5Cu17.9Ni14.6Al10Ti5 was compared in ambient air vs dry nitrogen environment. The excellent fatigue life behavior is attributed to a relatively high fatigue threshold (ΔKTH ≈ 2 MPa√m) and a lack of sensitivity to environmental effects on fatigue-crack growth in ambient air, as compared to other Zr-based BMGs. Fatigue life experiments conducted in ambient air confirmed the excellent fatigue life properties with a 107-cycle endurance strength of ~0.24 of the ultimate tensile strength; however, it was also found that casting porosity, even in limited amounts, could reduce this endurance strength by as much as ~60 pct. Overall, the BMG Zr52.5Cu17.9Ni14.6Al10Ti5 appears to have excellent strength and fatigue properties and should be considered as a prime candidate material for future applications where good mechanical fatigue resistance is required.

Effect of Annealing Temperature on the Properties of Sputtered Bi3.25La0.75Ti3O12Thin Films

<TEX>$Bi_{3.25}La_{0.75}Ti_3O_{12}$</TEX>(BLT) thin films were prepared on the Pt(150 nm)/Ti(50 nm)/<TEX>$SiO_2$</TEX>/Si substrate using the rf magnetron sputtering method. The BLT thin films were annealed at temperatures ranging from <TEX>$600^{\circ}C$</TEX> to <TEX>$750^{\circ}C$</TEX> using the rapid thermal annealing. The structure and surface morphology of the thin films were characterized by x-ray diffraction and field emission scanning electron microscopy. The hysteresis loop of the BLT thin films showed that the remanent polarization (2Pr) of the film annealed at <TEX>$700^{\circ}C$</TEX> was 10.92 <TEX>${\mu}C/cm^2$</TEX>. The fatigue characteristic of the BLT thin film annealed at <TEX>$700^{\circ}C$</TEX> was shown change polarization up to <TEX>$1.2{\times}10^9$</TEX> switching cycles. We confirmed the excellent remnant polarization (Pr) and fatigue properties compared with other fabrication methods and suggested a good method for BLT thin films fabrications.

†Microstructure and Biocompatibility of Porous Ti-Nb-Zr-CPP Composite Fabricated by Spark Plasma Sintering and Leaching Process

Metallic biomaterials such as titanium and its alloys have been widely used as permanent implant materials due to their excellent corrosion resistance, fatigue property, and strength. Calcium pyrophosphate (CPP) is an attractive bioceramic for human tissue implantation due to its good biocompatibility and similar composition to human bone. High energy mechanical milling and spark plasma sintering (SPS) can be used to fabricate a sound composite of the Ti-Nb-Zr-CPP. In a biomaterial such as the Ti-6Al-4V ELI alloy, the coating property between the bioceramic and Ti-based alloy is very important. By addition of CPP to the Ti-Nb-Zr alloy, the Ti-Nb-Zr alloy can improve the wetability between the Ti alloy and bioceramic as a coating material. Also the porous surface of the biomaterials can improve the symphyseal ability with osteoblast. In this study, a porous surface can be made by using several different leaching solutions such as aqueous diluted H3PO4. Ti-Nb-Zr-CPP composite was fabricated by spark plasma sintering (SPS) at 1000 ℃ under 70 MPa using high energy mechanical milled powder. A porous surface was successfully fabricated by using a 40 vol%H3PO4+ 60 vol.%H2O leaching solution at room temperature for 24 h.

Timber for small wind turbine blades

This paper addresses material properties of Douglas fir and Sitka spruce and the development of an accurate and low-cost method to manufacture small wind turbine blades. Fatigue tests performed on Douglas fir and Sitka spruce show that these timbers have excellent fatigue properties for use in small wind turbine blades. A copying router was developed and tested to manufacture timber wind turbine blades of less than about 1.5m in length by reproducing the shape of a master turbine blade. A co-ordinate measuring machine was used to establish that the copying router has an accuracy of ±0.5mm when copying cylindrical bars. It reproduced the general shape and twist of a master wind turbine blade. Future versions of the copying router can be improved by reproducing the trailing edge of turbine blades with higher accuracy.

G030015 高清浄度鋼のギガサイクル疲労における寸法効果

Ultrasonic fatigue tests up to gigacycle regimes were conducted for double-melted SCM440 low-alloy steel using enlarged and conventional specimens, comparing the results with those of single-melted steel in the previous study. Although both types of specimens of the double-melted steel showed internal fracture, the difference between the enlarged and conventional specimens was very small in spite of large difference in case of the single-melted steel. The inclusion sizes of an internal fracture origin also showed negligible difference between the two types of the specimens. Namely, size effects were small in case of the double-melted steel, unlike the case of the single-melted steel. These results meant that the double-melted steel showed excellent gigacycle fatigue properties when the enlarged specimens were used in the fatigue tests, while the difference was small between the double-melted and single-melted steels when conventional specimens were used. Hence, using the enlarged specimens was highly advisable in evaluating the gigacycle fatigue properties, particularly in case of high-cleanliness steels.

Corrosion fatigue behavior of a biocompatible ultrafine-grained niobium alloy in simulated body fluid

The present study reports on the corrosion fatigue behavior of ultrafine-grained (UFG) Niobium 2 wt-% Zirconium (NbZr) alloy in simulated body fluid (SBF). The alloy was processed using multipass equal channel angular processing at room temperature, resulting in a favorable combination of high strength and ductility along with superior biocompatibility and excellent corrosion resistance. Electrochemical measurements revealed stable passive behavior in SBF saline solutions, similar to conventional Ti–6Al–4V alloy. High-cycle fatigue tests showed no alteration in the crack initiation behavior due to the SBF environment, and an absence of pitting and corrosion products. More severe test conditions were obtained in the fatigue crack growth experiments in saline environments. Crack growth rates in UFG NbZr were marginally increased in SBF as compared to laboratory air at a constant test frequency of 20 Hz. Upon a 100 fold decrease in the test frequency, slightly higher crack growth rates were observed only in the near-threshold region. Such excellent corrosion and corrosion fatigue properties of UFG NbZr recommend it as an attractive new material for biomedical implants.

Influence of direction of notch on thermal fatigue property of a directionally solidified nickel base superalloy

Thermal fatigue property of a directionally solidified nickel base superalloy at the condition of different notched orientation and upper temperatures was investigated. The results show that cycle numbers of crack initiation decrease, propagation rate of crack increases and resistance of thermal fatigue reduces with the rise of upper temperature. Thermal fatigue property of the specimen with the notched direction vertical to orientation of dendrite growth (DZ319T) is superior to that of the specimen with the notched direction parallel to orientation of dendrite growth (DZ319L). DZ319L alloy initiates thermal fatigue crack by carbide and propagates along the direction of carbide distribution, which resultes in big propagation rate and poor thermal fatigue property. Crack initiation of DZ319T alloy is mainly by oxidized cavity. The join of oxidized cavity makes crack propagate. There are two cracks in DZ319T alloy, which greatly drops the stress concentration near the notch and decreases the propagation rate of crack. DZ319T alloy has excellent thermal fatigue property.

Fabrication, dielectric and ferroelectric properties of Ba0.6Sr0.4TiO3 film with preferred orientation

Ba0.6Sr0.4TiO3 films were fabricated by RF magnetron sputtering method. The X-ray diffraction (XRD) showed that the preferred orientation of films growing on platinum Si substrates can be tailored by sputtering pressure. The processing parameters such as sputtering pressure and substrate temperature were optimized to obtain a developed perovskite film with (110) preferred orientation. The polarization hysteresis loops and permittivity–voltage curves of the (110)-oriented film have been investigated,which demonstrated that the film is in ferroelectric phase at room temperature. Besides, it had excellent fatigue properties without polarization reduction after about 1010 switch cycles, and showed low leakage current (10−9–10−7 A/cm2) within an applied voltage of 5 V. Finally, the leakage current mechanism was studied.

Cyclic loadings and crystallization of natural rubber: An explanation of fatigue crack propagation reinforcement under a positive loading ratio

Natural rubber is known to have excellent fatigue properties. Fatigue crack propagation studies show that, under uniaxial tension loading, fatigue crack growth resistance increases with the loading ratio, even if the peak stress increases. Studies dealing with crack initiation confirm this trend. If strain induced crystallization is believed to play a major role in this reinforcement process, it is not clear yet by which mechanism this reinforcement takes place. Using SEM investigation, it is shown here that the reinforcement process is associated with strong crack branching in the crack tip region. From experimental results it is shown that under particular reinforcing loading condition a cyclic strain hardening process can be observed on the natural rubber which is able to overcome classically observed softening effects. A cumulative strain induced crystallization process is proposed to explain the stress ratio effect on fatigue crack initiation and propagation properties of natural rubber.

Experimental and Numerical Investigation on Impact Performance of Carbon Reinforced Aluminum Laminates

It is known that fiber metal laminates (FML) as one of hybrid materials with thin metal sheets and fiber/epoxy layers have the characteristics of the excellent damage tolerance, fatigue and impact properties with a relatively low density. Therefore, the mechanical components using FML can contribute the enhanced safety level of the sound construction toward the whole body. In this study, the impact performance of carbon reinforced aluminum laminates (CARAL) is investigated by experiments and numerical simulations. Drop weight tests are carried out with the weight of 4.7 kg at the speed of 1 and 2 m/s, respectively. Dynamic non-linear transient analyses are also accomplished using a finite element analysis software, ABAQUS. The experiment results and numerical results are compared with impact load-time histories. Also, energy-time histories are applied to investigate the impact performance of CARAL.

The High Temperature Property of Ni/WC Infiltrated Composite Layer on Cast Iron Substrate

The surface composite layer Ni/WC on the cast iron substrate was fabricated through vacuum infiltration casting technique using Ni-based powder and WC particles with different content as raw materials. The micro-structure of infiltrated layer was compact for all infiltrated layer with different WC content, and WC particles distributed uniformly. The surface infiltrated layer was mainly composed of WC particle, intermetallic compound and solid solution. The thermal cycles were beyond 108 times when the infiltrated layer peeled off, which indicated that the specimen with infiltrated layer offered excellent thermal fatigue property. The oxidation rate of substrate was nearly three times as large as that of the infiltrated layer with 20% WC content. The oxidation resistance of the infiltrated layer improved obviously comparing with the substrate because the oxide layer for infiltrated layer was compact.

The preparation and ferroelectric properties of defect-free ultrathin films of vinylidene fluoride oligomer

The ultrathin, defect-free ferroelectric films of vinylidene fluoride oligomer were fabricated by vapor deposition. A narrow substrate temperature window was found to get high quality ferroelectric films. Ferroelectric phase was obtained when the substrate temperature was −90 °C. The ferroelectric phase is stable at room temperature, even after annealing at 120 °C for 30 min. A full memory stack based on the ferroelectric VDF oligomer may work as nonvolatile random access memory with superhigh density due to the smaller crystal grain comparing with that of poly(vinylidene fluoride-trifluoethylene) [P(VDF-TrFE)] copolymers. The cell shows prominent ferroelectric properties even as the thickness of VDF oligomer film is down to 60 nm with a coercive field of 95 MV/m and a remnant polarization of 125 mC/m2. After 1×105 cycles of switching, no ferroelectric degradation was observed, the ratio of polarization before and after fatigue is close to 1, which is in contrast to P(VDF-TrFE) thin film where the ferroelectric degradation starts after 1×104 times of switching. The pulse polarization test shows that switching takes place as fast as a few microseconds to reach 90% of the saturated polarization. At 60 °C and 8 V operating voltage, the cell still shows excellent fatigue property.