Fatigue Resistance Of Materials Research Articles

Characterization of fatigue resistance in photochromic composite materials for 3D rewritable optical memory applications

Abstract Fatigue resistance of the photochromic diarylethene molecules 1,2-bis[2-methylbenzo[b]thyophen-3-yl]-3,3,4,4,5,5-hexafluoro-1-cyclopentene embedded in three different acrylic polymers is studied upon multiple coloration–decoloration cycles. The resistance to photofatigue is found to be different in the three polymeric materials when one-photon excitation was used for the reversible photoconversion experiment. In particular, the photochromic molecules lose their photoisomerization ability faster if they are embedded in poly(methyl methacrylate) (PMMA) with respect to poly(ethyl methacrylate- co -methyl acrylate) (PEMMA) and poly(ethyl methacrylate) (PEMA). We propose several explanations based on the physico-chemical properties of the matrix and of the photochromic molecules. In the case of two-photon excitation, which is necessary for 3D optical writing, the fatigue resistance is found to be poorer than in the one-photon case. The accelerated photodegradation can be assigned to the non-linear nature of interaction between the polymeric composite material and light.

High‐temperature low‐cycle fatigue behaviour of a cast Al–12Si–CuNiMg alloy

ABSTRACTThe low‐cycle fatigue behaviour of a cast Al–12Si–CuNiMg alloy, with a high content of Si, is investigated at 200, 350 and 400 °C. The fatigue test results show that the alloy exhibits symmetrical hysteresis loops, moderate cyclic softening and higher fatigue resistance at higher temperature. The fracture surface analysis reveals that more tear ridges are formed at higher temperature, which strongly affect the fatigue resistance. Furthermore, evaluation of the material fatigue resistance using an energy‐based Halford–Marrow model indicates that the material's ability to absorb and dissipate plastic strain energy is enhanced as temperature increases.

Effect of Basalt Fiber on the Asphalt Binder and Mastic at Low Temperature

The effect of basalt fiber on asphalt binder and mastic at low temperatures is investigated in this study. Basalt fibers are dispersed into the asphalt binder and mastic specimens to prepare the fiber-reinforced binding materials. The fiber-reinforced specimens are tested using the direct tension test and a newly developed fatigue test procedure, which is able to directly apply cyclic tensile loading to the asphalt binder and mastic specimens. The reinforcement effects of basalt fiber to the fatigue resistance of asphalt binding materials are evaluated. The direct tension test results show that with an appropriate content, the tensile strength of the asphalt binder is improved with the use of basalt fiber. The basalt fiber also restrains the axial strain and increases the stiffness of both the asphalt binder and mastic specimens. The fatigue test results indicate that the fatigue life of both asphalt binder and mastic specimens is significantly improved by the basalt fibers. The effect of basalt fibers is also analyzed using numerical simulations of direct tension and fatigue tests based on the finite-element method. The internal structure of the fiber-reinforced mastic is considered with the assistance of X-ray tomography technology. The fiber-reinforced mastic model is a heterogeneous composite in which the asphalt binder, fillers, and basalt fibers are treated as different materials. The axial stress and strain of the model are analyzed under unidirectional tensile loading and cyclic tensile loading. The results show that the fiber added between fillers releases the stress concentration of the critical area and diminishes the fatigue damage caused by cyclic loading.

Thermocracks®, a Specific Testing Machine for Evaluation of the Thermal Fatigue Resistance of Materials

Cracking by thermal fatigue is one of the major problems encountered during the operation of numerous parts such as exhaust manifolds or brake discs. One way to improve their lifespan is to develop new materials solutions. Estimating thermo-mechanical fatigue resistance of new materials can be performed with a specific test machine developed by CTIF, associating a multi-position wheel, an induction heating and a cooling by air blowing. Test consists in measuring the number of thermal cycles corresponding to the first crack appearance and to the complete failure of a specific versatile sample.Two examples of studies performed with this machine are shown hereafter.First tests were performed to compare the thermo-mechanical fatigue resistance of different grades of ferritic spheroidal graphite cast iron. These materials are an interesting alternative to alloyed steels or nickel-alloyed cast irons, for the constitution of exhaust manifolds and turbine housings working in the upper-middle temperatures (up to 950°C). The compared materials are SG irons alloyed with silicon (with or without molybdenum), and aluminium.Truck brakes dissipate several megajoules of energy every few seconds, which leads to high thermal stresses in the rubbing discs. Therefore, truck brake discs are mainly damaged by thermal fatigue cracking. One improvement way is to evolve disc material with the aim of increasing their thermal fatigue resistance while keeping the braking performance. For the thermal fatigue tests being as close as possible to real brake conditions, a specific geometry of sample and inductor was developed, to reproduce the thermal gradients observed during tests on real brake discs. The test parameters were then chosen after a coupled numerical-experimental study on full-scale braking. Behaviour of different materials under cycling loading (microstructural changes and cracking) is compared with regard to the results obtained during braking tests.

Assessment of the effect of stress concentration on the fatigue resistance of structural materials under asymmetrical loading

A computational and experimental assessment of the sensitivity of structural materials to stress concentration under high-cycle asymmetrical loading by tension–compression, bending, and torsion has been performed. A proposed limiting state model is used in the solution. A satisfactory agreement of the calculation results with the experimental data has been obtained.

Fatigue Properties of Asphalt Materials at Low In-Service Temperatures

Fatigue damage is one of the most common distresses observed in the asphalt-concrete pavements. Both the initiation and propagation of fatigue cracking are complicated and very difficult to detect because they develop generally within pavement structure. To understand the fatigue performance of asphalt concrete thoroughly, the behaviors of the major components of asphalt concrete under cyclic loading were investigated in this study. A new experimental method was developed to evaluate the performance of asphalt binder, mastic, and fine-aggregates mixture under cyclic tensile loading. The test results showed that fatigue performance of asphalt binder is closely related to the loading magnitude, temperature, and loading frequency. Mastic specimens with varied filler contents were tested. It was found that the mastic specimen with 30% filler content had better fatigue resistance and higher permanent strain. The differences between the test results of mastic and mixture were then compared and analyzed using X-ray tomography imaging. It was indicated that the fatigue resistance is closely related to the air-void content of the specimens. Three-dimensional digital specimens of asphalt binder, mastic, and mixture were developed and tested in the numerical simulation of fatigue tests based on the finite-element method. Both mastic and mixture were modeled as heterogeneous composite materials in which the asphalt binder, filler, and aggregate were described by different mechanical models. Fatigue damage of asphalt concrete was simplified by a damage model, which characterizes the degradation of the elastic modulus of the asphalt binder. It was found that with proper selection of damage parameters, the simulation results agree well with laboratory test results and can be used as a basis for future fatigue research. Finally, the reinforcement effect of basalt fiber was evaluated as an additive to improve the fatigue resistance of asphalt-binding materials. It was found that with proper content, the fatigue resistances of asphalt binder and mastic were significantly improved. The numerical simulation analysis also showed that fibers release the stress concentration in the interface area of two fillers and mitigate the fatigue damage caused by cyclic loading.

Comparative evaluation of fatigue resistance of material for semi-treated axles produced by advanced technologies

In the article the analysis of results of comparative tests on determination of endurance limit of the material in semi-treated axles produced by different technologies is carried out and the conclusions on prospects and stability of new manufacturing technologies for the semi-treated axles are drawn.

Reliability‐Based Design Optimization Considering Probabilistic Degradation Behavior

This article proposes a reliability‐based design optimization methodology by incorporating probabilistic degradation in the fatigue resistance of material. The probabilistic damage accumulation is treated as a measure of degradation in the fatigue resistance of material and modeled as nonstationary probabilistic process to capture the time‐dependent distribution parameters of damage accumulation. The proposed probabilistic damage accumulation model is then incorporated into reliability‐based design optimization model by building a dynamic reliability model inferred from the stress–strength interference model. The proposed approach facilitates to capture the dynamic degradation behavior while optimizing design variables at an early design stage to improve the overall reliability of product. The applicability of the proposed approach is demonstrated using suitable examples. Copyright © 2012 John Wiley & Sons, Ltd.

Effects of strength level and loading frequency on very-high-cycle fatigue behavior for a bearing steel

Rotating bending (52.5 Hz) and ultrasonic (20 kHz) fatigue tests were performed on the specimens of a bearing steel, which were quenched and tempered at 150 °C, 300 °C, 450 °C and 600 °C, respectively, to investigate the influence of strength level and loading frequency on the fatigue behavior in very-high-cycle regime. Influences on fatigue resistance of materials, characteristics of S– N curves and transition of crack initiation site were discussed. The specimens with higher strength showed interior fracture mode in very-high-cycle regime and with slight frequency effect, otherwise cracks all initiate from the surface and the fatigue strength was much higher under ultrasonic cycling.

Fatigue Resistance of 2 Different CAD/CAM Glass-Ceramic Materials Used for Single-Tooth Implant Crowns

To evaluate the fatigue resistance of 2 different CAD/CAM in-office monoceramic materials with single-tooth implant-supported crowns in functional area. A metal experimental model with a dental implant was designed to receive in-office CAD/CAM-generated monoceramic crowns. Laterally positioned axial dynamic loading of 300 N at 2 Hz was applied to implant-supported crowns machined from 2 different glass materials for 100,000 cycle. Failures in terms of fracture, crack formation, and chipping were macroscopically recorded and microscopically evaluated. Four of 10 aluminasilicate glass-ceramic crowns fractured at early loading cycles, the rest completed loading with a visible crack formation. Crack formation was recorded for 2 of 10 leucite glass-ceramic crowns. Others completed test without visible damage but fractured upon removal. Lack in chemical adhesion between titanium abutment and dental cement likely reduces the fatigue resistance of machinable glass-ceramic materials. However, relatively better fractural strength of leucite glass-ceramics could be taken into consideration. Accordingly, progress on developmental changes in filler composition of glass-ceramics may be promising. Machinable glass-ceramics do not possess sufficient fatigue resistance for single-tooth implant crowns in functional area.

Fatigue resistance of acrylic resin denture base material reinforced with E‐glass fibres

The purpose of the study was to determine the effect of different forms and concentrations (2.5, 3, 4, 5% by volume) of glass fibres (chopped strand mat, continuous and woven) on fatigue resistance of acrylic denture base resin. The fatigue resistance was measured by applying repeated three-point bending deflection to the specimens, the cycle frequency of 1.05 g and magnitude of deflection of 2.0 mm. The number of loading cycles needed to cause a fracture in the test specimen was considered the fatigue resistance of the specimen. The results of this study revealed that the addition of three different glass fibre forms at all concentrations to acrylic resin did not produce a statistically significant increase in the fatigue resistance (p ≥ 0.05). This study also revealed that there were significant differences (p < 0.05) between glass fibres forms used concerning the effects on the fatigue resistance. This study showed that the woven glass fibres had a definite superiority over the chopped fibres and the continuous fibres in regard to the fatigue resistance of the acrylic denture base resin.

Influence of Precorrosion on Fatigue Properties of Shot-Peened Aluminium 7075-T651

Abstract Pitting corrosion has a major influence on aging of structural elements made of high-strength aluminium alloys as corrosion pits lead to much earlier fatigue crack initiation under tensile dynamic loading. In order to improve material resistance to corrosion fatigue, it is necessary to reduce pit-tip stresses in the corroded pits areas. Shot peening (SP) is an important and well-known cold working process, having been used in industrial applications for a long time. Shot peening as intense plastic deformation in the thin surface layer affects cold surface hardening by primary inducing favorable residual compressive stresses. It is used in order to increase fatigue strength in operation and to improve fatigue resistance of precorroded material. The paper deals with the surface integrity of shot-peened high-strength 7075-T651 aluminium alloy. The paper describes the effects of SP treatment by presenting analyses of surface roughness measurement, residual stresses, material bending fatigue resistance, fractographic analysis of fatigued specimens, and electrochemical potentiodynamic testing.

Physicomechanical aspects of fretting and fretting fatigue of metallic stiff joints

The models of fretting corrosion and fretting fatigue mechanisms and the processes in the contact zone of parts subjected to fretting fatigue are discussed. Experimental data on the fretting and fretting fatigue mechanisms and on the effect of fretting on the fatigue resistance of structural materials are presented.

Effects of striated laser tracks on thermal fatigue resistance of cast iron samples with biomimetic non-smooth surface

In order to enhance the thermal fatigue resistance of cast iron materials, the samples with biomimetic non-smooth surface were processed by Neodymium:Yttrium Aluminum Garnet (Nd:YAG) laser. With self-controlled thermal fatigue test method, the thermal fatigue resistance of smooth and non-smooth samples was investigated. The effects of striated laser tracks on thermal fatigue resistance were also studied. The results indicated that biomimetic non-smooth surface was benefit for improving thermal fatigue resistance of cast iron sample. The striated non-smooth units formed by laser tracks which were vertical with thermal cracks had the best propagation resistance. The mechanisms behind these influences were discussed, and some schematic drawings were introduced to describe them.

Assessment of improvement techniques effect on fatigue behaviour of friction stir welded aerospace aluminium alloys

This research work is based on analysis of the improvement of friction stir welded joints of the aerospace aluminium alloy AA2024-T351. Therefore, initially, the Taguchi method was used to obtain the optimal FSW parameters for improvement its mechanical behaviour. Then the fatigue resistance of base material, joints in as-welded condition and sound and defective FSW welded joints improved by grinding were detailed investigated. The influence of process parameters was addressed via statistical analysis of weld bead appearance parameters, mechanical tensile and bending resistance, metallurgical features and hardness field characterization. Validation tests demonstrate the Taguchi design’s feasibility in the optimization of the FSW parameters and fatigue results show the resistance of improved welded joints overcoming base material.

Deep Cryogenic Treatment: Effects on Mechanical Properties of AISI 302 Stainless Steel and 18NiCrMo5 Carburized Steel

In this paper, the influence of deep cryogenic treatment (DCT) on mechanical properties of two commercial steels is analysed. Hardened AISI 302 stainless steel and 18NiCrMo5 carburized steel specimens were subjected to DCT after standard treatments. For both materials, the fatigue behaviour is a key property considering their usual applications requirements. Surface hardness, tensile properties and axial fatigue resistance of both materials were measured and compared with and without DCT. From the analysis of the experimental results and from their interpretation in the light of the previous literature, some useful indications are obtained about the DCT potential fallout on design and construction of structural components.

Properties of 3Cr2W8V Die Steel With Striations Processed by Laser

The striations on the surface of 3Cr2W8V die steel were processed by laser. The microstructure, hardness, wear resistance and thermal fatigue behavior of the specimens processed by laser were measured. The appearance and mechanism of thermal fatigue crack propagation in the zone processed by laser were observed and discussed. The results show that the wear resistance and thermal fatigue resistance of materials processed by laser are all better than those of the unprocessed material. The processed zone by laser plays a role in baffling wearing process and crack propagation. The pile-nail effect of processed zone is the main factor for improving the wear resistance and thermal fatigue resistance of material.

Numerical simulation of plasma dynamics in laser shock processing experiments

Laser shock processing (LSP) is based on the application of a high intensity pulsed laser beam ( I > 1 GW/cm 2; τ < 50 ns) at the interface between the metallic target and the surrounding medium (a transparent confining material, normally water) forcing a sudden vaporization of the metallic surface into a high temperature and density plasma that immediately develops inducing a shock wave propagating into the material. The shock wave induces plastic deformation and a residual stress distribution in the target material. Laser shock processing is being considered as a competitive alternative technology to classical treatments for improving fatigue, corrosion cracking and wear resistance of metallic materials. The description of the relevant laser absorption phenomena becomes hardly complicated because of the non-linear effects appearing along the interaction process and which significantly alter the shocking dynamics. A simulation model (SHOCKLAS), dealing with the main aspects of LSP modelling in a coupled way, has been developed by the authors. In this paper the study will be centred on the simulation of the hydrodynamic phenomenology arising from plasma expansion between the confinement layer and the base material using HELIOS (1-D radiation-hydrodynamics lagrangean fluiddynamic code). This code is used to study plasma dynamics under laser shock processing conditions. The influence of the confining layer (medium and thickness) on plasma pressure is also studied.

Static and Fatigue Resistance of GRP Materials and Flywheel Disc of a Storage Unit for Environmentally Friendly Urban Vehicles

The paper presents results of a partial experimental programme carried out within the project EUREKA E! 2462 TRUS, which aim is to demonstrate a novel form of hybrid electric drive line without the need for overhead lines. The zero emissions public transport vehicle is based on a hybrid electric drive line with novel, strongly innovative features. The concept includes the use of a small on-board energy storage unit (flywheel) to store the energy that would otherwise be lost on braking. Results of an experimental complex programme of an evaluation of static mechanical and fatigue properties of long glass-fibre reinforced polyester composite material with biaxial or multiaxial structures, respectively, to be used for a manufacture of the flywheel hub disc are presented in the paper. It was shown that results of interlaminar shear fatigue strength of the disc mostly almost correspond to those obtained on basic material – biaxial GRP plates and are close to results obtained on a similar uniaxial GRP used for railways springs. Some ascertained differences are discussed.

Frictional Wear and Thermal Fatigue Behaviours of Biomimetic Coupling Materials for Brake Drums

In order to enhance frictional wear resistance and thermal fatigue resistance of brake drums, two kinds of biomimetic coupling materials are prepared by laser surface melting and laser coating technology respectively. These materials are all compounded by base metal and biomimetic coupling units, and have different coupling characteristics, such as the variation of the unit shape, different microstructures and hardness, different chemical compositions of units. The frictional wear resistance and thermal fatigue resistance of biomimetic coupling materials and gray cast iron used for brake drum are compared. The results indicate that frictional wear resistance and thermal fatigue resistance of biomimetic coupling sample is better than that of untreated sample, and among the biomimetic samples, laser coating treated sample has superior resistance to wear and thermal fatigue comparing with laser melting treated sample.