Superior Fatigue Research Articles

Fatigue Life Optimization of Steel by Thermomechanical Treatment with the Use of Physical Thermomechanical Simulator

The investigated 34CrNiMo steel is traditionally used for highly loaded components with very high hardenability, fatigue strength and toughness. There were obtained very good experiences with this material, therefore there is no demand for change of the material, but for the material full potential utilization. This goal could be attained by application of thermo-mechanical treatment to the material of interest. There are compared several materials states obtained by conventional thermal treatment with new thermo-mechanically processed states in the current study. Conventionally treated materials exhibit about half tensile strength of the material after the thermomechanical treatment. The material fatigue life is related to tensile strength of the material. Therefore for representative comparison it is useful to compare materials with similar tensile properties, if the advantage of thermomechanical over heat treatment is to be evaluated. Samples of material of similar tensile strength to thermomechanically treated state were prepared by heat treatment. Fatigue tests were performed for traditionally treated samples with thermomechanically treated state and heat treated state. Thermo-mechanically treated state exhibits superior strength and fatigue life in comparison to all other states investigated. There was also performed metallographical investigation of microstructures of compared states providing information on what sort of microstructures were obtained by which treatment, that could be related to mechanical properties. The study presented here shows potential of thermo-mechanical treatment of traditionally used steels.

Studies on synthesis and properties of novel polyurethane pavement joint sealant modified with polydimethysiloxane

The development of a general use pavement joint sealant is described in this paper. A novel two-component polyurethane (PU) modified with hydroxyl terminated polydimethysiloxane joint sealant was developed for the needs of inland Chinese cement concrete pavement joint sealant production and applications. The performances of these sealants after hot pressing and hard drawing were also investigated. The cohesional strength of this new joint sealant material maintained 93·20% after hot pressing and hard drawing and was much higher than conventional PU and tar based PU joint sealants. This new sealant has superior tensile strength, cohesional strength, fatigue and aging resistance compared with currently used sealants.

Thermal Fatigue Testing of Plasma Transfer Arc Stellite Coatings on Hot Work Tool Steels under Steel Thixoforming Conditions

The thermal fatigue performance of Stellite 12 coating deposited on X32CrMoV33 hot work tool steel via the plasma transfer arc (PTA) process was investigated under steel thixoforming conditions. Stellite 12 coating has made a favorable impact on the thermal fatigue performance of the X32CrMoV33 hot work tool steel. The latter survived steel thixoforming conditions lasting much longer, for a total of 5000 cycles, when coated with a PTA Stellite 12 layer. This marked improvement is attributed to the higher resistance to oxidation and to temper softening of the Stellite 12 alloy. The Cr-rich oxides, which form during thermal cycling, provide adequate protection to high-temperature oxidation. In contrast to hot work tool steel, Stellite 12 alloy enjoys hardening upon thermal exposure under steel thixoforming conditions. This increase in the strength of the coating is produced by the formation of carbides and contributes to the superior thermal fatigue resistance of the Stellite 12 alloy. When the crack finally initiates, it propagates via the fracture of hard interdendritic carbides. The transformation of M7C3 to M23C6, which is more voluminous than M7C3, promotes crack propagation.

PREMOMET ALLOY

Abstract PremoMet offers superior strength, toughness and fatigue resistance and may be considered as a lower-cost alternative to many cobalt containing steel alloys. Consider PremoMet alloy for high-demand power train components in heavy-duty diesel engines and other commercial ground transportation including locomotive. This datasheet provides information on composition, hardness, tensile properties, and shear strength as well as fracture toughness and fatigue. It also includes information on corrosion resistance as well as forming and heat treating. Filing Code: SA-617. Producer or source: Carpenter Specialty Alloys.

Ni-based superalloy as a potential tool material for thixoforming of steels

Semisolid processing, already a well established manufacturing route for the production of intricate, thin walled aluminium and magnesium parts with mechanical properties as good as forged grades, faces a major challenge in the case of steels. The tool materials must withstand complex load profiles and relatively higher forming temperatures for thousands of forming cycles for this near-net shape process to be attractive for steels on an industrial scale. The potential of a Ni-based superalloy, Inconel 617, reported to exhibit superior thermal fatigue resistance in demanding tooling applications, was investigated. The response to thermal cycling of this alloy at high temperatures was compared with that of X38CrMoV5 hot work tool steel widely used in the manufacture of conventional forging dies. The favourable thermophysical properties of the latter were completely negated by its limited temper resistance, while the Inconel 617 alloy responded to thermal cycling by the usual heat cracking mechanism.

Thermal Fatigue Testing of Tool Materials for Thixoforging of Steels

Semisolid processing, already a well established manufacturing route for the production of intricate, thin-walled aluminium and magnesium parts with mechanical properties as good as forged grades, faces a major challenge in the case of steels. The tool materials must withstand complex load profiles and relatively higher forming temperatures for thousands of forming cycles for industrial application to be attractive. Since the forming pressures are much lower than those encountered in conventional forging, the principle die failure mechanism in steel thixoforging is expected to be thermal fatigue. Hence, suitable materials able to withstand the steel thixoforming environment for an economically acceptable life, can be best identified with a thermal fatigue test. Such a test is described in the present work. A novel CrNiCo and a nickel-base superalloy, reported to exhibit superior thermal fatigue resistance in demanding tooling applications, was tested under thermal fatigue conditions encountered in the thixoforming of steels.

基板表面へのマイクロディンプル形成によるＤＬＣ膜被覆材料の摩擦係数制御

DLC (Diamond Like Carbon) coatings possess many attractive properties, including high hardness, a low friction coefficient, and extreme wear resistance. Due to these properties, DLC coatings have elicited considerable interest within high technological industries, such as those for magnetic hard disks, ball and rolling bearings, high-precision gears, cutting tools, etc.But in some cases, sliding components including car clutches, and laptop hinges require frictional controlled DLC surfaces. They are expected to have appropriate torque, and superior fatigue and wear resistance, but lower friction coefficients are less important.In this study, experiments were conducted on the controlling of frictional forces by topographically structuring contact surfaces. Fine Particle Bombardment (FPB) has been employed to create micro-dimples that act to control surface roughness. The friction coefficient at the DLC surface changes according to the surface roughness.Therefore, the method presented in this study provides a simple and effective way of controlling the friction between DLC coated surfaces in contact.

Enhancing Fatigue Properties of Nanostructured Metals and Alloys

Recent research on the fatigue properties of nanostructured metals and alloys has shown that they generally possess superior high cycle fatigue performance due largely to improved resistance to crack initiation. However, this advantage is not consistent for all nanostructured metals, nor does it extend to low cycle fatigue. Since nanostructures are designed and controlled at the approximately the same size scale as the defects that influence crack initiation attention to preexisting nanoscale defects is critical for enhancing fatigue life. This paper builds on the state of knowledge of fatigue in nanostructured metals and proposes an approach to understand and improve fatigue life using existing experimental and computational methods for nanostructure design.

Composite army bridges under fatigue cyclic loading

Military composite bridges offer many unique advantages to the army—for example their high strength-to-weight ratio and superior corrosion and fatigue resistance properties—compared to current steel and aluminum bridges. This paper presents the results of part of a comprehensive, on-going research program sponsored by the US Army to develop innovative field repair techniques for military composite bridges. The virtual tests were performed on the composite treadway under four different loading cases: (i) maximum shear static loading case, (ii) maximum bending static loading case, (iii) fatigue progressive failure analysis for the moving load case, and (iv) fatigue progressive failure analysis for the maximum flexural loading case. Results of virtual testing and progressive failure analysis (PFA) simulation conducted on a composite army bridge (CAB) prototype demonstrated a good match with the full-scale laboratory test results conducted in an earlier study. For instance, the variation between the maximum deflections predicted by the GENOA simulation for the maximum shear and those obtained from the full-scale tests was only 3.2%. In addition, the location and type of damages at the ultimate load were very close to those obtained from the full-scale laboratory tests.

Fracture properties of a fiber-metal laminates based on magnesium alloy

Fiber-metal laminates (FMLs) are high performance laminated structures based on stacked arrangements of composite material and aluminum alloy. Currently, a glass fiber reinforced epoxy/aluminum alloy FML (GLARE) is being considered for use in the manufacture of the upper fuselage of the A380 Airbus aircraft [1]. Previous work on FMLs has shown that they combine the excellent durability and machinability common to many metals with the superior fatigue and fracture properties offered by many fiber-reinforced composites [2–4]. Krishnakumar [2] tested a Kevlar fiber FML (ARALL) and showed that its ultimate tensile strength is considerably greater than that of a conventional aluminum alloy. Vogelsang [3] conducted tension-tension fatigue tests on a number of FML systems as well as a plain aluminum alloy and showed that crack growth rates in the former were significantly less than those in the plain aluminum alloy. Several workers have investigated the impact response of aerospace-grade fiber-metal laminates [5, 6]. Vlot et al. [5] conducted low and high velocity impact tests on a GLARE system, a plain aluminum alloy and a carbon fiber reinforced thermoplastic. Their results showed that the FML offered the highest damage threshold energy of all the systems considered. The aim of the present work is to investigate the fracture properties of a novel fiber-metal laminate based on a lightweight magnesium alloy and a carbon fiber reinforced plastic. Magnesium alloys offer a number of advantages over many metals including their low density (thirty percent lower than an aluminum alloy), their superior corrosion resistance and their excellent electromagnetic shielding ability. Currently, magnesium alloys are being used in the automotive industry in the manufacture of transmission casings and in the aerospace industry for the manufacture of gearboxes and other lightweight components. The fiber-metal laminates examined in this study were based on 0.5 mm thick magnesium alloy sheets (AZ31 alloy from Advance Metals International Ltd.) and a woven carbon fiber reinforced toughened epoxy (Stesapreg EP121-C15-53 from Stesalit Ltd, Switzerland). The composite and metal plies were placed in a picture frame mold with dimensions 240 × 200 mm and cured for 4 h at 125 ◦C. All of the laminates tested in this research project were based on a 2/1 configuration (two magnesium alloy skins either side of a carbon fiber reinforced epoxy core). Table I summarizes the stacking configurations investigated in this study. The composite volume fraction within the FMLs was varied by increasing the number of composite plies between the two outermost magnesium alloy skins from two to eight. The tensile properties of the FMLs and the magnesium alloy were evaluated using 20 mm wide rectangular samples at a crosshead displacement rate of 2 mm/min. The initial strain history in each sample was recorded using a clip-on extensometer fixed to the specimen edge. The extensometer was incapable of measuring large strains. In such cases, the crosshead displacement was normalized by the length of the working section to yield a nominal strain (this was only undertaken when a complete stress-strain curve was required). The energy-absorbing properties of the fiber-metal laminates were evaluated through a series of single edge notch bend (SENB) tests on specimens with dimensions 100 × 18 mm × thickness. Prior to testing, a 9 mm long pre-crack was introduced at the mid-span. The precrack was sharpened by swiping a sharp razor blade along the tip of the stress concentration. The SENB specimens were positioned on two simple supports positioned 72 mm apart and loaded at a crosshead displacement rate of 5 mm/min. The work of fracture was then determined by dividing the area (energy) under the load-displacement curve by the cross-sectional area of the fractured ligament. Fig. 1 shows typical stress-strain (nominal) curves for the three FMLs and the plain magnesium alloy. The stress-strain curve for the plain magnesium alloy indicates that although its tensile strength is below that of the FMLs, it does exhibit quite a high degree of ductilty beyond the elastic limit. The stress-strain curves for all of the FMLs exhibited an almost linear response up to maximum stress at which point the composite layers fractured in a brittle manner. An examination

Phase transformation and fatigue properties of austempered ductile irons

A series of studies were carried out regarding ausferrite transformation, the growth of ferrite from austenite, during isothermal holding. The mechanical properties associated with microstructures of alloyed and unalloyed austempered ductile irons (ADIs) were also investigated. Heat released from ausferrite transformation has been quantitatively measured in a previous study. The effect of alloying elements on the heat evolution rate and on the morphology of ausferrite has also been discussed. Mechanical property testing was carried out on specimens of ductile iron austempered at 593 K and 633 K for 2 hrs. Tensile properties and high-cycle fatigue life tests were also made. In addition, phase transformation of ADIs during ultrasonic vibration treatment was also investigated. SEM micrographs of deformed samples indicate and confirm the occurrence of stress-induced transformation of ADIs. The alloyed ADIs isothermally-held at 633 K develop an optimum tensile strength, elongation and superior impact toughness and good high-cycle fatigue strength. These properties are attributed mostly to a large amount of dispersed blocky austenite. This retained austenite may become work hardened during deformation.

Defect chemistry of SrBi2Ta2O9 and ferroelectric fatigue endurance

The defect chemistry and charge transport properties of doped and undoped SrBi2Ta2O9 (SBT) were studied by making 4-point dc equilibrium electrical conductivity, thermopower, ionic transport number, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) measurements. Results of high temperature equilibrium dc conductivity, thermoelectric power, and transport number measurements as a function of oxygen activity in the temperature range 650–725°C revealed that undoped SBT displays a broad centrally located plateau of ionic conductivity with an activation energy of mobility of 0.94 eV and a prominent upturn at high oxygen activity, caused by p-type conductivity. The effects of acceptor and donor dopants are consistent with a 1–2% net acceptor excess in the undoped compound. It has been observed that there is substantial (several percent) cation place exchange between the Sr2+ and Bi3+ in SBT. It is proposed that the net acceptor excess in undoped SBT consists of disordered Sr2+ substituting for Bi3+ in the fluorite-like bismuth oxide layers which are locally compensated by oxygen vacancies. The formation of the net donor excess by disordered Bi3+ substituting for Sr2+ in the perovskite-like layers does not manifest itself as n-type conductivity behavior, because the band gap is large and the mobility is highly thermally activated. The superior intrinsic ferroelectric fatigue endurance of SBT is attributed to the lack of mobile charged defects in the perovkite-like layers which create the ferroelectric response of the compound. The metallic bismuth presence on the surface of undoped SBT, as revealed by qualitative XPS measurements, is believed to result from long exposure to the highly reducing conditions in the XPS system.

The thermoelastic behaviour of semicrystalline and of glassy poly(ether-ether-ketone)

A thermoelastic evaluation, based on simultaneous measurements of the mechanical work and of the concomitant heat of deformation by a stretching micro calorimeter, was performed on semicrystalline and glassy PEEK. The objective of this study was to utilize the sensitive technique to detect differences that would account for observed effects of micro structure on mechanical performance. A clear difference was detected beyond a 0.6% strain, where the behaviour of glassy PEEK began to exhibit inelastic features such as yielding and plastic deformation. This difference between the glassy and the semicrystalline polymers was considered the reason for the superior mechanical fatigue and fracture properties produced by the latter micro structure.

In situ fatigue of Al-Li-X alloys

The introduction of Al-Li based alloys into commercial applications has not occurred without some major difficulties in alloy development. Poor ductility and low fracture toughness in these alloys has hindered their use in structures where they must serve as integral load-carrying members. On the other hand, superior fatigue and stiffness properties of these alloys has provided great incentive to pursue further development. The reason for the low ductility and poor fracture toughness has been attributed to several possible mechanisms including: i) shear band formation due to planar slip., and ii) strain localization resulting from large grain boundary precipitates. The rather good fatigue crack propagation characteristics have been attributed to significant macroscopic out-of-plane crack growth. However, little work has aimed at understanding the micromechanisms of this out-of-plane crack growth during cyclic loading. In addition, the role of the numerous precipitates that can exist in these complex Al-Li-X alloys to the fatigue crack growth resistance has not been examined closely.In this research we have examined the microscopic evolution of fatigue deformation in two Al-Li-X alloys using in-situ fatigue experiments conducted within an intermediate voltage transmission electron microscope.

New ARALL Development Offers Promising Potential for Aircraft Design

Initial work on aramid aluminium laminates (ARALL) was done by Professor L. B. Vogelesang and his co‐workers at the Delft University of Technology, The Netherlands. ARALL is now being commercialized by Alcoa and 3M. This was stimulated by Vogelesang's early work which showed the adhesively bonded laminate of high strength isotropic aluminium sheet and fatigue and fracture resistant aramid fibres provides superior specific strengths and fatigue resistance. The fatigue crack growth characteristics are such that cracks will not propagate in ARALL under normal loading conditions.

Impact fatigue response of ultra-high molecular weight linear polyethylene

The impact fatigue response of ultra-high molecular weight linear polyethylene (UHMW LPE), in a special test, has been examined and the results are presented in this paper. In an attempt to understand the influence of high molecular weight on impact strength, identical measurements were made on a normal molecular weight linear polyethylene (NMW LPE). UHMW LPE is found to have a superior impact and impact fatigue behaviour to the NMW LPE. Almost all of the UHMW LPE materials perform equally well in the present impact fatigue test. However, one of the high bulk density UHMW LPE materials, resin G, performs quite poorly. Photomicrographs of the free surface of this material show that this may result from poor interparticle fusion during compression moulding.

A comparison of the physical properties of radiation and sulfur-cured poly(butadiene–co–styrene)

The physical properties of radiation- and sulfur-cured poly(butadiene-co-styrene)-based stocks were compared. It was found that the measured lower ultimate strength of radiation-cured stocks is in part attributable to the difference in the glass transition temperatures of the stocks cured by the two methods (an increase in T/sub g/ is caused by sulfur curing). Another factor contributing to the difference in performance is the apparent nonuniform crosslink density distribution in radiation-cured stocks containing carbon black filler. A higher crosslink density in the immediate vacinity of carbon black particles was postulated based on a to-be-expected distribution of secondary electron energy at interfaces with an appreciable change in density between neighboring phases. The invoked difference in network topology, supported by solvent swelling measurements on sulfur- and radiation-crosslinked vulcanizates can explain not only the slightly lower ultimate strength of radiation-cured stocks but also the superior fatigue and crack propagation performance measured for these vulcanizates. Finally, theoretical arguments were presented to explain the inferred large strength deficiency of radiation-cured rubbers reported by other investigators on the basis of chain scissions encountered during radiation crosslinking.

Some tensile and fatigue properties of Zn-ZnO powder composites at various temperatures

The tensile and fatigue properties of rods which were extruded from Zn-ZnO powder composites were determined at temperatures between 150°C and −196°C. Different particle sizes were used in the powders and the amount of 02 was varied from 0.12 to 1.71 weight per cent (w/o): The effect of ball-milling the powder prior to compaction was also studied.In general, the specimens of powder origin were stronger than fine-grained pure zinc and those made from powder containing very small particles (∼3 μm) displayed good ductility, particularly at room temperature. However, they possessed poor work-hardening properties so that the UTS was never more than 4000 psi above the 0.2% proof stress. Specimens of ball-milled powder origin were stronger and more brittle than other specimens. The superior tensile strengths of the powder composites over pure zinc were reflected by superior fatigue (push-pull) properties. The improvement at higher temperatures is surprising, in view of the very fine grain size of the composite specimens, so the results are rationalized in terms of oxide pinning of the grain boundaries. Résumé Des propriétés mécaniques en traction et en fatigue dans la gamme de temperature de 150°C à −196°C ont été déterminées pour des tiges du matériau composite Zn-ZnO, extrudées à partir de poudres. Des particules de différents diaméters ont été employees lors de la préparation des poudres, ainsi que diverses proportions d'O2 variant de 0.12 à 1.71% en poids. L'effet d'un broyage à boulets de la poudre avant compactage a également été étudié.D'une façon générale, les échantillons préparés à partir de poudres ont montré une plus grande résistance que ceux préparés à partir de zinc pur à grain fin; ceux contenant des particules trés fines ont montré une bonne ductilité, surtout à la température ambiante. Cependant, Ie taux de consolidation des composites demeure faible, ce qui explique que l' écart entre la résistance à la traction et la limite élastique à 0.2% d'allongement ne dépasse pas 4,000 psi Les échantillons dont la poudre a subi un broyage à boulets étaient plus résistants et plus fragiles que les autres échantil1ons. Le fait que la résistance à la traction des composites soit supérieure à celle du zinc pur s'est manifesté par de meilleures propriétés en fatigue (tension-compression). L'amélioration des propriétés mécaniques aux températures plus élevées est étonnante, compte tenu de la grosseur du grain tres faible des échantillons composites. Cette amélioration est expliquee en termes d'un piégeage des joints de grains par des oxydes.

MUELLER ALLOY 1820

Abstract MUELLER ALLOY 1820 (formerly MBCo 902) is a chromium-copper alloy with high electrical conductivity, high mechanical strength, and superior creep, fatigue and wear properties. It is used for resistance welding electrodes, switchgear, and electrical and electronic parts. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and compressive and shear strength as well as fracture toughness. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Cu-257. Producer or source: Mueller Brass Company.