High Fatigue Cycle Research Articles

Influence of load frequency and corrosive environments on fatigue behavior of as-extruded Mg–Zn–Zr–Nd alloy

Fatigue resistance is a key criterion for new material that would be applied as an implant. As a “smart” implant material with good biodegradability and high strength, Mg–2Zn–0.5Zr–0.5Nd alloy has been recognized as a promising candidate for bone implant. A series of tests on fatigue properties of extruded Mg–2Zn–0.5Zr–0.5Nd alloy are carried out in this study. Alternating cyclic dynamic loads at frequencies of 5 Hz and 10 Hz both in air and in 0.9 wt% NaCl solution were loaded on extruded Mg–2Zn–0.5Zr–0.5Nd alloy respectively. In air condition, the fatigue life variational trends of Mg–2Zn–0.5Zr–0.5Nd alloy at different frequencies are similar according to the stress-life (S–N) curves. However, under high fatigue cycles, the lower loading frequency prolongs the loading time of repetitive stresses and reduces the fatigue life of the samples. In 0.9 wt% NaCl solution, the S–N curves under different frequencies show different changing trends due to the synergistic effect of corrosion environment and loading frequency. It is also found that the fatigue resistance of the alloy in 0.9 wt% NaCl solution is poorer than that in air due to the significant promotion of the formation and growth of corrosion pits by the NaCl environment. In addition, according to the fatigue fracture morphology analysis, it can be found that the failed samples show different fracture patterns in air and 0.9 wt% NaCl solution.

Development of a fatigue strength testing machine

A profound engineering design and modeling of fatigue strength machine for testing the failure which occurs when a metallic material is subjected to cyclic stresses is presented. The main goal is developing a locally made fatigue strength machine that can be used in material science laboratory. A major direction in this development of the machine is the ability to thread on the path of technology transfer and dominance by concentrating on the building of indigenous capacity. In carrying out the machine development, engineering design formulae were applied and Computer Aided Design modeling was developed. The developed fatigue strength testing machine had a designed machine capacity of 18875Nmm that sustained a motor power of 5.93kw.The machine shaft diameter determined to be 9.88mm developed an equivalent torque and bending moment of 45799.8Nmm and 40890Nmm respectively. The machine designed critical speed of 23.52rad/s had belt tensions on the tight and slack sides to be 139.02N and 44.65N respectively. The fabricated machine has the ability to record low and high fatigue cycles.

Analysis of Planetary Gear of Toyota Rush AT 2012

Gear is one of the most important part of power transmission system in a vehicle, and as the time goes by there possibly some failure happened on the gears. However, there is no information provided by car manufacturer regarding the life and the material of the gears. This report presents the analysis of the planetary gear used in Toyota Rush AT year made of 2012. The objectives of the research are: to study the planetary gear mechanism and how it works; to analyze the force and stress acting on the gears; and to select a suitable gear material that can withstand against the loads that happen on the gear. The research methodology is started with finding the gear dimension and gear ratio. The force acting on gear is calculated based on the torque and rotation speed provided in car specification. Then the selection material is carried out based on the amount of stress applied on the gear teeth that were calculated using AGMA standard formulation. Finally, the fatigue life prediction of the gears is calculated based on the previous stress acting on the gears. The calculation result suggested AISI 1050 steel as the selected gear material that can carry the bending stress of 476 MPa and categorized as low to high fatigue cycle.

Enhancing functionalities in carbon fiber composites by titanium dioxide nanoparticles

Carbon fiber composite's high specific strength makes it incredibly useful for structural applications. However, their low strain-to-failure can be problematic in structural applications that can potentially see high strain conditions or high fatigue cycles resulting in sudden, catastrophic failure. This is further complicated by damage manifesting within the composite thus not showing damage indicators on the surface. Therefore, monitoring the structural integrity and strain history of the composite in application by itself―while maintaining positive composite performance―is vital to ensure safe operation. Here, a homogeneous dispersion of TiO2 nanoparticles on carbon fiber is demonstrated to generate a piezoresistive carbon fiber polymer matrix composite with enhanced self-sensing capabilities. The nanoparticle-embedded composites also exhibited superior strength and damping potential compared to the nanoparticle-free composites. The apparent interlaminar shear strength increased by up to 15% and the damping loss factor increased by an average of 150% while the piezoresistive sensitivity increased by up to 180% with the addition of a small weight fraction of nanoparticles to the fiber surface. These results demonstrate an approach to simultaneously improve the sensing capabilities, damping behavior and mechanical strength of carbon fiber composites by simply adding nanoparticles in the fiber sizing using a commercially scalable deposition method.

Numerical Investigation of Fluid – Structure Interaction (FSI) on Sodium Leakage Accident at Prototype Fast Breeder Reactor Monju

This study presents a numerical investigation of fluid-structure interaction about sodium leakage accident at prototype fast breeder reactor Monju. The dynamic forces of sodium liquid flow acting on the thermowell are the main cause of fatigue failure, which leads to the occurrence of thermowell cracking due to intense stresses and high fatigue-cycle. Since the location and magnitude of these stresses are unknown, an analysis of the vibrational characteristics and stresses caused by FSI was performed by using ANSYS to prevent similar accidents in the future. The most dangerous case was found for FSI analysis by comparisons between the natural frequency of thermowell and vortex shedding frequency at several operating conditions. The results showed that a stress concentration location is similar to the location of broken thermowell, and the amplitude of stress is large enough for fatigue damage.

The correlation between prior fatigue damage and remaining creep properties in a high chromium steel welded joint

Strain cycling prior to a constant load exposure is expected to influence the creep properties. The present work aimed to evaluate the effect of prior low cycle fatigue (LCF) damage on the remaining creep properties of P92 steel welded joints. Strain amplitudes of 0.25%, 0.4% and 0.6% and fatigue cycles ranging from 10% to 80% of the number of cycles to failure (Nf) were introduced in creep specimens to represent fatigue damage. A critical analysis of the creep test responses revealed that a high strain amplitude and high fatigue cycles induced a clear reduction in the remaining creep life; conversely, prior LCF also led to a significant increase in the creep rupture strain. It was found that prior LCF loading produced its saturated effect after fatigue cycles at 70% Nf or a strain amplitude of 0.4%. It is important to note that the degradation of the remaining creep life of a welded joint was more severe than that found in homogeneous base metal. It was also observed that the failure location and development of creep voids were dependent on both the number of fatigue cycles and strain amplitude. Additionally, the prior fatigue damage was evaluated using a defined damage parameter that revealed two nonlinear stages of fatigue damage.

ANALISIS PENGARUH GAYA TERHADAP FATIGUE LIFE BAJA STRUKTURAL PADA PEGAS DAUN MENGGUNAKAN ANALISIS ELEMEN HINGGA

Leaf spring is one of a component of the vehicle which are used to vibration damping caused by the force. Some cases that occur in the vehicle namely overload. This case can affect to fatigue life of steel leaf spring. One of a method that use to fatigue life prediction is high fatigue cycle where this method can be simulated using the finite element method. The number both element and node used in this research where 6961 element and 14726 nodes, respectively. Magnitude of the force used is 80 KN, 100 KN, and 200 KN where thus force are used to prediction of the fatigue life steel leaf spring. The result of this research revealed force 80 KN have the fatigue life longer than force 200 KN and 200 KN which is 10 6 cycle. In addition, the critical value of the fatigue life 80 KN is smaller than 100 KN, and 200 KN. As such as, the force 80 KN is recommendation as allowed force which use to vehicle. This value is validated by safety factor analysis where the force allowed as 80 KN with safety factor equal to 2.56.

Effect of fretting damage on characteristics of high strength bearing steel up to very high cycle fatigue

The fretting fatigue behaviour of SAE 52100 bearing steel has been investigated up to very high fatigue cycles. The fretting fatigue strength was found to be markedly lower than the plain fatigue strength of the alloy. The fatigue strength reduction is higher in very high cycle fatigue regime which varies with fretting contact load. The fretting fatigue life is restricted in high cycle fatigue regime when the contact load is higher than the critical one. The rate of fretting damage growth influences the fretting fatigue life in very high cycle fatigue regime. The specimens with lower surface wear rate acquire higher fretting fatigue life by impeding the increase of fretting damage size.

Research on a different method to reach the saturate limit of titanium aluminide alloy surface mechanical and fatigue properties by laser shock process

Laser shock peening is one of the best method to enhance the mechanical and fatigue properties of titanium aluminide alloys. Most research depends on the pressure model produced by Professor Fabrro, based on Von-Mise stress yield standard, when the pressure is 2 Hugoniot elastic limit (HEL), the plastic deformation reaches the maximum limit and when the pressure is 2.5HEL The stress release from the edge of laser shock area, This research discussed the titanium aluminide alloys surface mechanical and fatigue properties after reducing the pressure of laser shock and inducing the repetitions of laser shock properly. When the pressure reached HEL the material began plastic deformation, in the experiment environment there are several factors affect the results, so the pressure should be more than 1HEL and less than 2HEL-2.5HEL. As the same repetitive times the effective of 2HEL-2.5HEL pressure is better than the less pressure but with the repetitive times rise the 2HEL-2.5HEL pressure specimens would be cracked and the less pressure specimens mechanical and fatigue properties still increase. The results show that with inducing the repetitions and reducing the pressure the material surface hardness improved nearly 25% and the fatigue life increase nearly 40% in high fatigue cycle, the microstructure is similar but the less pressure more repetitive times specimens contains dislocation cells. It indicates that with 2HEL-2.5HEL pressure (the maximum plastic deformation) the mechanical and fatigue properties reached to its peak after 3 times LSP and with 1.5 HEL pressure 8 times repetitive laser shock can reach to the saturate limit of the material itself, that means with less pressure and more repetitive laser shock is more accurately to get close to the saturate limit of the material.

Cyclic deformation fields interactions between pores in cast high manganese steel

Cast pores are known to cause stress/strain concentrations, facilitating the initiation of fatigue cracks and shortening the fatigue lifetime of cast materials; however, it is an open question regarding how the deformation fields generated by different pores interact each other and evolve with fatigue loading. The present study addresses the local deformation behavior in cast-pore containing high manganese steel during fatigue loading investigated using single- and multi-pore finite-element models. These models take into account the actual size, shape and distribution of pores based on X-ray computed tomography images and consider the actual material properties of the steel, i.e. the high strain-hardening rate, cyclic hardening law and Bauschinger effect using a viscoplastic constitutive model within the framework of Chaboche model. The results demonstrate that the local stress, strain and hysteresis loop energy around an actual pore evolve progressively with fatigue loading, and reach as large as 2 to 4, 2.5 to 8.5 and 6 to 30 times their corresponding far-field values at high fatigue cycles. More importantly, two different effects, i.e. "umbrella-like stress shielding" and "overlapping stress amplifying", are identified in the presence of multiple pores, due to the deformation fields interactions between pores. And, which of the two effects takes place or predominates depends on the specific location of concern and the spatial distribution of pores. These findings may be extended to provide some new insight into the fatigue damage micromechanisms in various cast-pore containing materials and to help understand the scatters of their fatigue lifetime in terms of the local deformation fields around pores and their interactions.

Thermal, High and Low Cycle Fatigue Life of 80 Micron Thick Graded Alumina PVD Coatings for Oxidation Resistance Application

In this study, to accommodate higher interfacial shear stress between alumina coating system and metallic substrate, coating modulus and compressive stresses are graded from interface to 80 µm thickness. . The modulus gradient is achieved by varying Al to O ratio by tuning the oxygen flow and compressive stresses are varied from 0.1GPa to 2.5GPa by changing bias voltage during the reactive sputtering process. Static thermal fatigue life of coated samples were evaluated using simple heating and cooling cycles, significant change in microstructures and mechanical properties were observed. Room temperature high fatigue cycle (HCF) was evaluated using vibration testing and the coating fatigue life was evaluated as 2.0X106 cycles. Low cycle fatigue was evaluated using axial compressive and tensile mode and the coatings were cracked beyond 10,000 cycles. The Micro tensile testing revelled that modulus and compressive stress graded coatings are failed at 1.1% tensile strain and which is higher tensile load bearing capacity than the monolithic stoichiometric alumina coating. Hardness and modulus of the 80 µm thickness is 34GPa and 240 GPa. At higher strain coating started cracking and post-microscopy analysis shows variation of crack width at different zones of the tensile specimen. .

Influence of the WEDM process on the fatigue behavior of Inconel® 718

The use of alternative processes for the manufacturing of aeronautical components is essential in order to fulfill the requirements that have been set by the aircraft sector. One particular solution that has been used for certain applications is that of Electrical Discharge Machining (EDM). The EDM process can machine any electrically conductive material, irrespective of its hardness or mechanical properties, and is thus a useful solution for difficult-to-machine aerospace alloys. However, due to its thermal nature, the EDM process induces metallurgical changes in the machined material, which in turn may reduce its fatigue service life. For this reason, the aerospace industry has restricted the use of EDM to the manufacturing of selected components. Nevertheless, there have recently been significant advances in the development of EDM generators that minimize thermal input toward the machined component. As a consequence, it is critical to know the extent to which these new EDM processes affect fatigue service life in aerospace alloys, in order to adequately evaluate the feasibility of using this process. Given the limited information in the literature regarding this topic, the present paper describes a study of the fatigue life of WEDM produced nickel-based Inconel® 718. In order to examine the capabilities of WEDM, fatigue specimens were manufactured using both this procedure and the grinding process (used as a reference for comparison). Surface analysis, metallographic studies, residual stresses, fractography and axial fatigue tests are described and discussed. The results showed that conducting the WEDM process with the new generation of machines has a detrimental effect at high fatigue cycles, reducing fatigue strength by approximately 10% in comparison with ground specimens. However, at low fatigue cycles, no significant differences were observed between ground and WEDM samples. These findings have implications for the potential use of the WEDM process in the manufacturing of disk turbine fir-trees.

Study on Crack Propagation Life under Low Cycle Fatigue and High Cycle Fatigue of Nuclear Steam Turbine Rotors

The calculation and assessment methods for the crack propagation life under low cycle fatigue and high cycle fatigue of nuclear steam turbine rotors is presented. The low high fatigue cycle stress amplitude and stress range as well as the crack propagation life calculation methods for low cycle fatigue and high cycle fatigue of nuclear steam turbine rotors are introduced. The calculation and assessment methods for the crack propagation calendar life under low cycle fatigue and high cycle fatigue of nuclear steam turbine rotors are given together with an application example for calculation and improvement of the fatigue crack propagation calendar life of a low pressure welded rotor for 1 000 MW nuclear steam turbines. The example results indicate that effect of the high cycle fatigue on the fatigue crack propagation calendar life of nuclear steam turbine rotors is bigger, it is necessary that assessment for the crack propagation life under low cycle fatigue and high cycle fatigue of rotors in the rotor structure design of new development for nuclear steam turbine and the rotor safety assessment for operation steam turbine for nuclear power plants.

Studying the Effects of Internal and External Microstructure on Fatigue Strength of Materials by Electromagnetic Excitation Technique

A fatigue testing setup based on electromagnetic excitation was built to apply cyclic stresses to the specimens near their resonance frequency. A test near the resonance frequency has the advantage that higher stresses can be applied to test specimens at a reduced input power. Stress amplitude up to 1000 MPa can be applied to the test specimens and up to four specimens can be tested simultaneously. The setup can test specimens at high fatigue cycle regime i.e. 100 million stress cycles can be achieved in 48 hours.The setup has been used to study the effects of internal and external microstructure on the fatigue strength of materials. Specimens especially stainless steel-304 was prepared by different techniques i.e. electric discharge machining EDM, etching and laser cutting. Specimens prepared by these techniques were tested and their fatigue strengths were compared. To probe the material endurance limit, tests were also performed on the above mentioned steel specimens in very high stress cycle regime i.e. > 109 cycles. In order to investigate the effect of internal microstructure on fatigue strength of material, CuZn37 fabricated by etching was tested and the effect of different grain size on fatigue strength was compared. SN curves have been plotted for materials with no prior fatigue strength data. Stainless steel-1.4404 specimens prepared by Rapid Prototyping (RP) has been tested for fatigue analysis. The test results showed higher degree of scattering when compared to the traditionally manufactured steel. Fractography revealed the existence of inherent material flaws which was the main reason of higher degree of test point scattering. In addition to these data, the SN curve was plotted for Innolot which is an important soldering alloy and prompts to fatigue failure in electronic assemblies.

Fatigue properties and failure characterisation of self-piercing riveted 6111 aluminium sheet joints

Aluminium has been long considered as an alternative material for steel in the automobile industry. However, welding of aluminium is more difficult and prone to defects compared with steel. Therefore other methods of joining aluminium sheets are being investigated. In the present investigation, the fatigue properties of self-piercing riveted joints in 6111 aluminium alloy sheets has been studied using tensile shear and coach peel type specimens. Different thickness combinations of aluminium sheet joints and different load ratio R were also investigated in the fatigue tests. Fatigue crack initiation and growth were observed and analysed. It has been found that the maximum fatigue load increases with increasing sheet thickness in both tensile shear and coach peel specimens, but this increase is smaller for high fatigue cycles. With the same maximum fatigue load, specimens under load ratio of R=0·3 have a longer fatigue life than that of specimens under R = 0·1. In most of the cases (>90%), specimens failed in the upper sheet (with the rivet head) during fatigue loading in the case of equal thickness combination and thick upper sheet combination, for both tensile shear and coach peel specimens. As for different thickness combination rivet joints, the thinner sheets are usually the places where failure occurs whichever it is the upper sheet or lower sheet in the combination.

Polarization recovery of fatigued Pb(Zr,Ti)O3 thin films: Switching current studies

In the process of fatiguing Ir/Pb(Zr0.35Ti0.65)O3/Pt capacitors we have observed the splitting and separation of both the positive and negative switching currents into two distinct peaks. By measuring the current response to a post-fatigue, triangular, voltage waveform, we have observed a shift of the majority of the switching current to higher voltages and, eventually, beyond the voltage testing range. At high fatigue cycle numbers, this current peak shift is large enough to reveal a smaller switching current peak whose position remains invariant. Subsequent higher amplitude switching pulses access the high coercive voltage switching peaks, returning the remanent polarization values, though not the overall switching profile, to unfatigued levels. Pulse polarization measurements reveal that the switchable polarization that appears lost at lower testing voltages is highly recoverable when higher voltages are applied. Thus, the fatigue cycling appears to primarily increase the polarization switching resistance while inducing very little irrecoverable switching loss. Finally, we measured increased resistance to switching with fatigue cycling even when the majority of the capacitor volume was no longer switching during the fatigue pulses, suggesting that only voltage cycling, and not the concomitant polarization switching, are necessary to induce fatigue.