High Fatigue Life Research Articles

Preparation of Waste-LDPE/SBS Composite High-Viscosity Modifier and Its Effect on the Rheological Properties and Microstructure of Asphalt.

To reduce the cost of high-viscosity modifier (HVM) and alleviate white pollution problems, we prepared the environment-friendly HVM (E-HVM) by using waste-low density polyethylene/styrene-butadiene-styrene (waste-LDPE/SBS) composite. The physical characteristics of the E-HVM modifier were first investigated. Additionally, the effects of E-HVM modifier dosage (8 wt% to 20 wt%) on the rheological properties and microstructure of asphalt were, respectively, researched by dynamic shear rheometer (DSR), bending beam rheometer (BBR), and fluorescence microscopy (FM). The results show that the E-HVM modifier has lower molecular weight, and its distribution is wider than that of the Tafpack-Super (TPS) modifier; thus, the E-HVM modifier had better compatibility with asphalt, which has also been proven by FM images. Due to these reasons, the E-HVM modifier improves the high-temperature performances of asphalt more effectively than the TPS modifier, which is shown by the higher dynamic viscosity (60 °C) and G* and the lower and Furthermore, compared to TPS modified asphalt, E-HVM modified asphalt also has a higher fatigue life at different strain levels (2.5% and 5.0%), but worse low-temperature performance. Following a comprehensive consideration of performances, the reasonable dosage range of E-HVM modifier is 12 wt% to 16 wt%.

Natural Rubber Latex–Modified Concrete Pavements: Evaluation and Design Approach

Repetitive loads result in increased irrecoverable strain and, consequently, fatigue cracking failure. Fatigue resistance is the prime factor controlling the service life of the concrete pavements. This research study utilized natural rubber latex (NRL) to enhance the mechanical strength and flexural fatigue resistance of normal concrete. The effect of influence factors, such as water to cement (w/c) and dry rubber to cement (r/c) ratios, on the compressive and flexural strengths and flexural fatigue behavior was studied. Normal and NRL concretes were subjected to compressive, flexural, and flexural fatigue tests. At all w/c ratios, a higher r/c ratio resulted in a lower compressive strength but higher flexural strength. The highest flexural strength was found at the optimum r/c ratios of 0.58, 1.16, and 1.73 for w/c=0.3, 0.4, and 0.5, respectively. Concrete modified by NRL at the r/c ≤ optimum ratio had lower plastic deformation than normal concrete at the same applied flexural stress, hence, higher fatigue life (Nf). As a result, the NRL-concrete pavement at the optimum r/c ratio was found to have a thinner thickness than the normal concrete pavement for the same traffic load conditions at the same service life, which can reduce the operational cost. A cost-effective mix design method of NRL-concrete pavement with the optimized construction (operation and material) cost was also recommended. The outcomes of this research will facilitate the utilization of the NRL additive alternative to synthetic polymer for sustainable NRL-concrete pavement in Thailand and other Southeast Asian and South American countries, which are major global producers of natural rubber.

Dynamic, fatigue and harmonic analysis of a beam to beam system with various cross-sections under impact load

Contact of materials is inevitable in machine environment where a number of elements interact with each other causing impact force and consequent stress and strain at point of contact. The study of this behaviour is essential for machine design applications as it helps to predict life of a particular element as per the amount of stress it can sustain. This study is based on dynamic, fatigue and harmonic analysis of two-beams in contact with a combination of cross-section geometries of the beams. ANSYS, which is a Finite Element Analysis software is used for numerical modelling of stresses and deformations developed within the two-beam system. Three different combination of beam cross-sections were simulated: square-square, circular-circular and square-circular. Under dynamic and fatigue analysis, the results show that the least deformation coupled with the highest fatigue life and safety factor occurs when one beam is square and the other is circular (Square-circular), a slightly higher deformation occurs when two square beams (square-square) interact with each other while the highest deformation occurs when two circular beams interact with each other. This shows that Square cross-section beams have higher bending resistance while circular cross-section beams have low bending resistance and thus higher deformation. Under vibration analyses, due to higher natural frequencies, both the square-square and square-circular section beams show excellent durability and better margin of safety to the same extent during vibration. The results of this work will be useful in enlightening design engineers on the combination of beam cross sections that will give optimum performance in a beam-to-beam system for structural and machine design applications.

Enhancing cooling performance of NiTi elastocaloric tube refrigerant via internal grooving

• A grooved NiTi tube is designed and fabricated as the elastocaloric refrigerant. • A buckling-prevention frame is developed to ensure uniform compression of the tube. • Compared with ungrooved one, the grooved tube has 53% larger SCP (1.30 W g −1 ). • With the buckling-prevention frame, the grooved tube endures 2 million cycles. Developing novel heat transfer surface structure on NiTi shape memory alloy tubes has big potential to enhance the elastocaloric cooling performance. In this work, an internally grooved superelastic NiTi tube (outer diameter 5 mm, wall thickness 1 mm and length 50 mm) is designed and fabricated as the refrigerant in a compressive regenerative elastocaloric cooling prototype. The geometric parameters of the longitudinal grooves (groove width, groove depth, and groove spacing) are optimized by a numerical heat transfer simulation. A buckling-prevention frame is developed to ensure uniform compression of the NiTi tube in the cooling prototype. Compared with the ungrooved tube of the same size, the specific internal heat transfer area of the grooved NiTi tube (3.44 mm −1 ) is increased by 360%, producing 53% larger specific cooling power (1.30 W g −1 ) and 33% larger maximum system temperature lift (8 K). With the buckling-prevention frame, the grooved NiTi tube endures 2 million reversible phase transition cycles under the compressive stress of 800 MPa in the prototype. Such significantly enhanced cooling power of the grooved NiTi tube with high fatigue life demonstrates the critical roles of heat transfer surface structure and buckling prevention in enhancing the elastocaloric cooling performance under compression.

Effect of cross-sectional geometry on the compression fatigue behavior of NiTi refrigerants

Elastocaloric refrigeration requires refrigerants with a good heat transfer ability and a high fatigue life. A million-level fatigue life can be normally obtained for NiTi refrigerants via compressive loading. However, existing compression-based NiTi elastocaloric prototypes only focus on tube refrigerants, and no research has been reported on the cross-sectional geometry design and its influence on the compression fatigue behavior of NiTi refrigerants. Here, we propose tubular NiTi refrigerants of hole-type, fin-type, and layer-type cross sections and compare their compression fatigue behavior with NiTi tubes of the same cross-sectional area under cyclic loading of 20 Hz and 900 MPa. Results show that to achieve a larger specific heat transfer area (SA), the compression fatigue life of NiTi tubes monotonically decreases because of the decrease in the wall-thickness, while the layer-type NiTi refrigerant maintains a relatively high fatigue life of 1.7 × 106 cycles at a high SA level (3.83 cm2 g−1). This gives us insight into enhancing elastocaloric refrigerants’ heat transfer ability and fatigue life via geometry design.

Hot isostatic pressing of laser powder-bed-fused 304L stainless steel under different temperatures

Hot isostatic pressing (HIP) is becoming a key strategic technology for post-processing metallic materials fabricated with laser powder bed fusion (LPBF), acting to eliminate the processing-induced pores and improve the mechanical properties. This paper comprehensively investigated material characteristics (porosity, residual stress, microstructures, phase composition, and inclusion), mechanical properties (microhardness, tensile properties, and fatigue properties), and deformation behaviors of LPBF 304L austenitic stainless steel (ASS) subjected to HIP process with different temperatures (965°C, 1165°C, and 1365°C). Experimental results indicated that the grain size, inclusion size, recrystallization fraction, and dimple size increased with increasing HIP temperature, which resulted in homogenized microstructure, reduced yield strength and microhardness, and significantly improved ductility. The fatigue life of HIP-treated samples after surface post-treatment was mainly influenced by porosity, inclusion, residual stress, and dislocation density. The HIP-1165°C samples with low porosity and small-sized inclusions had a higher fatigue life than HIP-965°C and HIP-1365°C samples. In addition, the evolution of crystallographic texture and inclusion composition associated with the HIP temperature were systematically revealed with the aid of orientation distribution function (ODFs) and elemental mappings. This study provides a profound understanding of the rational design of the hybrid process of LPBF and HIP.

Evaluating low cycle fatigue property of nanoscale ZrO2 particles strengthening molybdenum alloy

Dispersion strengthened molybdenum alloys with different nano-size ZrO2 content were prepared by liquid-liquid doping method. The effect of ZrO2 on the microstructure and low cycle fatigue properties of Mo alloys after vacuum annealing was studied, and the relationship between fracture mode, strain amplitude and life was analyzed. The results show that ZrO2 can dreamily refine grains size of Mo alloy. The grain size of Mo-1.2% ZrO2 alloy is reduced to about 3 μm compared with 114 μm of pure Mo. As a result, the yield strength of Mo–ZrO2 alloys was significantly improved. The yield strength of Mo-1.2% ZrO2 alloy is 29.9% higher than that of Mo alloy. The main reason is the dispersion strengthening and dislocation pinning effect of intra-granular ZrO2 on molybdenum alloy. ZrO2 has a remarkable influence on the fatigue properties of Mo alloy. When the content of ZrO2 is 1.2%, and molybdenum alloy has good plastic deformation ability, high fatigue strength coefficient and long fatigue life. The fatigue life of Mo-1.2% ZrO2 alloy is 37.6% higher than that of Mo-2.0% ZrO2 alloy when the strain amplifier is 0.5. The fracture mode of molybdenum alloy is related to the content of ZrO2. The content of ZrO2 increases from 1.2% to 2.0%, and the fatigue fracture mode changes from mixed fracture to inter-granular fracture.

Design and structural analysis of non-pneumatic tyres for different structures of polyurethane spokes

NPTs have vast applications because of no tyre puncture, no need for air pressure, low rolling resistance, and also have higher flexibility for design and recyclability. In this research work, different structures of polyurethane (PU) spokes have been designed and analyzed under radial loading conditions which include structures like honeycomb with varying cell angles, simple spoke, and trapezoid type by keeping in view that the cell wall thickness and somehow the mass of the structures remain the same. Based on the Mooney-Rivlin hyper-elastic material model and performing 2D non-linear static structural analysis on different types of NPTs using ANSYS, it has been observed that the simple spoke structure has the lowest spoke stress and deformation values of 2.01 MPa and 11.7 mm, while HC–A1 has the least value of strain energy of 2.58 mJ, at a load of 2500 N. The above results show that the straight spoke structures like simple spoke and trapezoid type have a high load-carrying ability than the honeycomb type NPTs under same boundary conditions. While honeycomb NPTs have higher fatigue life as compared to straight-spoke NPTs.

LOW-CYCLE FATIGUE OF COLD-DRAWN TYPE 304 AUSTENITIC STAINLESS STEEL IN ANNEALING CONDITIONS

Type 304 austenitic stainless steel, or better known as SS304, generally has alloying elements: C < 0.1%, Cr 18 – 20%, Fe 66 – 74%, Mn <2%, Ni 8 – 10.5%, P <0.045%, Si <1%, and S <0.030%. In general, this material has good ductility, high tensile strength, and excellent corrosion resistance. In application, type SS304 will be subjected to repeated loading, and eventually, the material will undergo plastic deformation, which leads to structural failure in a short life. The failure of SS304 is generally due to the inability of the material to repeat loading, which results in large amounts of plastic deformation so that the SS304 will experience fatigue and then fracture. Based on the description above, this study aims to evaluate the LCF properties of 304 CDS stainless steel with annealing heat treatment. The parameter used was the strain amplitude 0.003 – 0.013 mm/mm. The results of this study revealed that the highest fatigue life in the LCF test was experienced by steel with heat treatment at an amplitude of 0.003 mm/mm with 48367 cycles. In contrast, at the amplitude condition of 0.013 mm/mm, the fatigue life of the steel decreased drastically with the resulting plastic strain being larger, namely 0.0094 mm/mm and elastic strain of 0.0035 mm/mm, with an average modulus of elasticity of 194 GPa. Annealing treatment conditions experienced decreased mechanical strength but tended to be ductile. Using Basquin-Coffin-Manson Equation, empirical equations to predict LCF of 304 stainless steels can be determined.

The Effect Of Machining Cooling Strategies On The Corrosion Fatigue Performances Of the AZ31 Magnesium Alloy

Magnesium alloys are very attractive biomaterials thanks to their biocompatibility, nontoxicity, and biodegradability. However, they have not been used extensively until nowadays because of their susceptibility to corrosion especially when in synergy to mechanical loads. In this framework, the present work deals with the analysis of the influence that different machining strategies may have on the corrosion fatigue performances of the AZ31 magnesium alloy. To this aim, cryogenic and dry machining operations were carried out, and the machined samples were then subjected to corrosion fatigue tests in a physiological environment at different imposed stresses, namely 100 MPa, 110 MPa and 120 MPa. The obtained results show that the samples processed with the liquid nitrogen adduction had a higher fatigue life than the corresponding dry samples, regardless of the imposed level of stress. After corrosion fatigue testing, both the types of samples showed similar failure characteristics. However, the microstructures of the cryogenic machined samples were characterized by a lower amount of deformation twins thanks to the grain refinement induced by cryogenic cooling close to the machined surface. Both the grain refinement and the reduced amount of deformation twins were used to explain the enhance corrosion fatigue characteristics of the cryogenic machined samples. These results indicate that cryogenic machining can represent a promising approach to enhance the poor corrosion fatigue behavior of the AZ31 magnesium alloy.

Effect of Dopant ratio of CNF on Fatigue Life and Noise for Injection Molded Polyacetal Gear filled with Cellulosenanofibril

Almost plastic gears are produced by injection molding, recently, their demands are expanding instead of metal gears. Since the mechanical properties of plastic resin have temperature dependency, problems arise depending on the driving conditions and the environment. For this reason, many composite resin materials used for plastic gears are considered. On the other hand, cellulose nanofibril (referred to as CNF) is focused on the perspective of sustainability, and CNF-enhanced thermoplastic resin has been developed. The present authors investigated the fatigue life of injection molded plastic gears made from polyacetal (referred to as POM) and CNF composite resin (referred to as POM/CNF) and confirmed the high strength and long fatigue life at high load. Therefore, the availability of CNF was reported as a reinforcing material for POM gears. However, there are many unknown points about the details. Under such circumstances, In the present study, test gears are prepared for the injection molded POM/CNF gear with two different dopant ratios of CNF. the effects of the CNF dopant ratio on the gear temperature, noise, and fatigue life were studied experimentally.

Combined Measurement Based Wing-Fuselage Assembly Coordination via Multiconstraint Optimization

In the field of aircraft manufacturing, the demand for high aerodynamic performance and long fatigue life is growing. This makes high-precision assembly of large components and assembly coordination increasingly important. This is particularly prominent for wing-fuselage joining due to the large size, measurement difficulty, and multi-constraint coordination. In this paper, we propose a novel optimization method for the wing-fuselage assembly coordination problem, as well as an assembly gap measurement approach. First, a gap measurement framework combining laser tracker, 3D scanner and photogrammetry is adopted to solve the occlusion problem that makes measurement difficult in traditional methods. A compatible tooling is utilized to transform the scanned point cloud data in the local coordinate system to the global aircraft assembly coordinate system. Based on this, a comprehensive wing-fuselage pose coordination model is then established, which takes engineering constraints into account to realize assembly gap redistribution for wing-fuselage joining. The transformation parameters of pose adjustment are solved by the proposed multi-constraint optimization algorithm based on the Gauss-Newton method. Finally, experiments on synthetic data and actual data have verified the effectiveness of the coordination method. Results show that our method significantly optimizes the gap distribution within the given tolerance and outperforms traditional methods in both accuracy and efficiency. With advantages of high efficiency and accuracy, our method can be well applied to the wing-fuselage joining and satisfy the requirement of the large component assembly.

Fatigue damage initiation mechanisms in bearing steel

This work deals with an experimental investigation of fatigue damage initiation mechanisms in high-grade, low-alloyed 100Cr6 bearing steel. The fatigue tests were carried out at rotative bending loading with parameters, frequency f = 50 Hz, stress ratio (coefficient of cycle asymmetry) R = −1, temperature T = 20 ± 2 °C, in the region ranged from Nf ≈ 1.5 × 103 to Nf ≈ 1.0 × 108 cycles. The surface fatigue failure mechanism was observed in the area of low number of cycles Nf ≈ 1.5 × 103–Nf ≈ 4.3 × 104 cycles (persistent slip bands from surface roughness), while subsurface fatigue failure mechanism was observed in the area of very high number of cycles, Nf ≈ 1.0 × 107–Nf ≈ 1.0 × 108 cycles (from non-metallic inclusions, mostly TiN inclusions but also from Al2O3 inclusion). The paradox is that on one hand the high fatigue life is required for bearing steels, while on the other hand, the content especially titanium is not prescribed in standard for the chemical composition of this 100Cr6 bearing steel.

Relative contact width evaluation of end hemispherical cavities rollers as an indication of Hertzian contact pressure

In a recent investigation, the end hemispherical cavities (EHC) rollers exhibited better strength against fracture than hollow rollers. Furthermore, EHC rollers looked promising from a higher fatigue life aspect than conventional solid rollers in a simulation study. Therefore, it necessitated further exploration of the EHC roller concept and to this end, in the present investigation, the contact widths of EHC rollers were relatively evaluated to judge its contact stresses' behavior with respect to the solid roller because the contact stresses are responsible for the fatigue life of rolling bearings. In the experiments, the contact footprints were obtained by forcing specimens of rollers against chemically etched surfaces and were examined by a microscope for measurement of contact widths. The experimental trials were performed with individual roller-on-plate tests and also with full-bearing samples. The etch correction factor was used to correct anomalies of real and observed contact widths due to etching film thickness. The parabolic relationships were established for roller variants which yielded constants signifying their relative ranks. The contact semi-widths, thus derived from corrected experimental results of individual roller-on-plate tests, demonstrated good agreement (<5%) with those derived from simulation results. The results of full-bearing sample tests for roller variants also ranked same as individual roller-on-plate tests. The encouraging results of contact semi-width assuredly favor the prospects of relatively higher fatigue life in case of EHC rollers.

Numerical Investigation of Fatigue Behavior of Non-patched and Patched Aluminum/Composite Plates

In this study, the fatigue behavior of composite patched and non-patched Al 5083 aluminum plates was numerically investigated. Al 5083 Aluminum plates with semi-circular notched (2, 3 and 4 mm long cracked) and "V" notched (30°, 45° and 60° angled) were used in the analyzes. Mechanical properties of Al 5083 Aluminum plate, DP460 type adhesive of produced by 3M and [0°]8 glass fiber reinforced composite patch material was used for the study. The Finite Element Method was applied for numerical study. Numerical analyzes were performed with the Ansys version 15.0 Workbench Package program. As a result of the numerical study, the highest fatigue life (1593.2 N) is seen on the 30° angled "V" notched and patched specimen. However, the fatigue life in non-patched specimen (30° angled "V" notched) was found to be 277.69 N. Thus, the study revealed that the composite patch's contribution is very important.

A Tough Reversible Biomimetic Transparent Adhesive Tape with Pressure-Sensitive and Wet-Cleaning Properties.

Dry adhesives that combine strong adhesion, high transparency, and reusability are needed to support developments in emerging fields such as medical electrodes and the bonding of electronic optical devices. However, achieving all of these features in a single material remains challenging. Herein, we propose a pressure-responsive polyurethane (PU) adhesive inspired by the octopus sucker. This adhesive not only showcases reversible adhesion to both solid materials and biological tissues but also exhibits robust stability and high transparency (>90%). As the adhesive strength of the PU adhesive corresponds to the application force, adhesion could be adjusted by the preloading force and/or pressure. The adhesive exhibits high static adhesion (∼120 kPa) and 180° peeling force (∼500 N/m), which is far stronger than those of most existing artificial dry adhesives. Moreover, the adhesion strength is effectively maintained even after 100 bonding-peeling cycles. Because the adhesive tape relies on the combination of negative pressure and intermolecular forces, it overcomes the underlying problems caused by glue residue like that left by traditional glue tapes after removal. In addition, the PU adhesive also shows wet-cleaning performance; the contaminated tape can recover 90-95% of the lost adhesion strength after being cleaned with water. The results show that an adhesive with a microstructure designed to increase the contribution of negative pressure can combine high reversible adhesion and long fatigue life.

Comparative study of adhesive fatigue in aeronautical bonded joints: A numerical approach in the frequency domain

The use of adhesively bonded structures has increased over the years, together with the development of composite materials. This work investigates a procedure for fatigue life prediction of an aeronautical bonded joint under random loads, in particular, the cohesive failure of the adhesive layer in a skin-to-stiffener bonded joint. The use of two different adhesives is investigated, and Dirlik’s method is employed to predict the stress response in the adhesive layer, from which the fatigue life is obtained. The effect of damping is also investigated, and it is shown that increases in damping result in higher fatigue life estimations.

Strain ratio effect on microstructural evolution during low cycle fatigue exploitation of nickel base superalloy IN 740H

Strain ratio (Rε) is varied during isothermal strain-controlled fatigue tests of nickel-base superalloy IN740H at 760 °C; Rε = −1, 0, 0.5. Unlike most alloys, highest fatigue life is observed under Rε = 0 test condition compare to Rε = 0.5 and −1. From extensive electron microscopy, i.e. energy-filtered TEM (EF-TEM), WDS and EDS studies, it is confirmed that the creep effect due to tensile mean stress under Rε = 0 condition was offset due to segregation of Nb at dislocation and formation of Nb(CN) at grain boundaries, which proved to be fatigue strengthening. Debonding of Nb(CN) and γ matrix provided preferential fatigue crack initiation sites and resulted in lowering the fatigue life for Rε = 0.5 test condition.

Crack initiation anisotropy of Ni-based SX superalloys in the very high cycle fatigue regime

The anisotropic fatigue properties of three Ni-based SX superalloys (AM1, CMSX-4 and MC-NG) were investigated in the very high cycle fatigue regime at 20 kHz, R = −1 and 750 °C. The fatigue testing shows that the [111] orientation has higher fatigue lives at high stresses and lower fatigue lives at very low stresses compared to the standard [001] orientation. At high stresses, the resolved shear stress on the octahedral slip systems explains the anisotropy effect. At low stresses, pseudo-cube slip in the matrix becomes the prominent deformation mechanism over γ′-shearing in the [111] orientation, resulting in comparatively lower fatigue properties.

Effect of microstructures restoration on high temperature fatigue behavior of DZ125 superalloy

Combination of hot isostatic pressing (HIP) and rejuvenation heat treatment (RHT) technology was used to restore creep-damaged DZ125 directional solidified superalloy, and the influence of microstructure restoration on high temperature fatigue behavior of the samples was explored. The results show that the HIP+RHT process could effectively heal internal cavities and recover the degraded γ′ phase in creep-damaged DZ125 superalloy to cubic particles similar as in as-received sample. After restoration treatment, the stress concentration areas inside the sample eradicated with the healing of the internal cavities, and the fatigue source areas were limited only to near surface than initiating from inside as in the as-received and creep-damaged samples. As a result, the restored sample had higher crack initiation life and lower crack propagation rate compared to as-received and creep damaged samples. The TEM microstructure characterization near fatigue fracture showed that the restoration of the degraded γ′ phase eliminated tangled dislocation in creep damaged sample and produced evenly distributed dislocations in the γ channel with short curved line-like morphology, like the as-received sample, which effectively hindered the dislocations movement during subsequent deformation, and strengthen the fatigue resistant of alloy. Therefore, it can be concluded that the HIP-RHT process, through the combined effect of internal cavities healing and the restoration of the degraded microstructures, renders higher high temperature fatigue life than creep-damaged and even higher than as-received DZ125 superalloy.