Increase In Fatigue Life Research Articles

A comparative study of fatigue behavior between S-shaped and involute POM gears

Abstract Applications of polymer gears have been gradually expanding from motion transmission to power transmission fields. Design of new gear teeth profiles plays a crucial role in meeting the requirement of replacing metallic gears with polymer ones. This work develops a computational framework consisting of tooth profile generation and fatigue life prediction of S-shaped and involute POM gears. The contact and bending fatigue performances of S-shaped and involute POM gears under oil lubrication are comparatively studied. It is found that the S-shaped profile reduces the tooth root stress by 25% and significantly improves the bending fatigue life by 10 times compared with the involute profile, especially under medium or high loading levels. Furthermore, the S-shaped gear with a single circular-filleted root curve benefits a 20% reduction of tooth root stress and a 30% increase in bending fatigue life compared to a double circular-filleted root curve S-shaped gear.

Prolonged fatigue life in aluminum clad steel by electropulsing treatment: Retardation of interface-microcrack formation

The prolonged fatigue life of aluminum clad steel (Al clad steel, ACS) using electropulsing treatment is systematically investigated by characterizing the microstructural change at different fatigue cycles. The microstructural changes associated with fatigue damage evolution show that cracks are prone to initiate at Al grains of the interface and propagate toward the Al side in the fatigue test due to a preferred accumulation of geometrically necessary dislocations (GNDs) in the soft Al grains near the interface. The electropulsing treatment with a subsecond duration is proved to be efficient in healing the fatigue damage and significantly prolonging the fatigue life of the ACS. The increased fatigue life by electropulsing treatment is attributed to the diminished density of piled GNDs and the retardation of microcrack formation at the interface. The present study elucidates the failure mechanism of ACS and proves that electropulsing treatment is an efficient method to prolong the fatigue life of laminated metal composites by healing the accumulated damage during the fatigue test.

Effect of Heat Treatment in Oxygen-Containing Medium on Fatigue Life of Zirconium Alloy

Abstract The effect of heat treatment in oxygen-containing medium on fatigue properties of zirconium alloy samples was shown. This gas treatment improved fatigue life in pure bending and cyclic tensile testing. An increase in fatigue life was explained by the formation of a hardened near-surface layer. According to the data of fractographic studies of destroyed samples, it was found that treatment in an oxygen-containing medium contributes to the formation of a structure with a higher energy intensity of destruction.

Fatigue performance of transverse welded attachment of high-strength structural steel series

This study presents an experimental investigation of the fatigue performance of non-load-carrying transverse fillet-welded attachments made of high-strength steel (HSS). Four typical HSSs were selected, with steel yield strength of 460 MPa, 550 MPa, 690 MPa, and 960 MPa. A total of 88 high-cycle fatigue tests were conducted. Based on the analysis of the morphological details of the fracture surfaces and the failure modes, three different methods for fatigue assessment, such as the nominal stress method, the effective notch stress method and the strain energy density method, were applied to directly compare the fatigue performance of HSS and conventional strength steel (CSS, with a yield strength of approximately 235–355 MPa). HSS transverse fillet-welded attachments have demonstrated excellent fatigue resistance compared with specifications (FAT 80) in the design codes by using the nominal stress method, the natural slope of the S–N curves is nearly 4.0, rather than 3.0 prescribed in the current design codes for fatigue assessment of welded structures. For the notch stress method, HSS transverse fillet-welded attachments show a greater increase in fatigue life for low notch stress ranges (approximately Δσk≤ 400 MPa). However, for high notch stress ranges (approximately Δσk > 400 MPa), the increase in fatigue life is limited. The results with the strain energy density method are similar to those with the notch stress method.

Fatigue behaviour and impact strength assessment of friction stir-welded carbon steel joints

The present study investigates the fatigue behaviour and impact strength of friction stir-welded (FSWed) carbon steel (AISI 1018) joints in comparison with the base metal (BM). The fatigue behaviour was tested using compact tension (CT) specimen of BM and FSWed joints under the constant amplitude load at different values of stress ratio (R) having a frequency of 10 Hz. A 20% increase in fatigue life along with a lower fatigue crack propagation rate was observed for FSWed specimens when compared to BM. The impact strength of BM and FSWed specimens was measured using the Charpy test. A higher value of impact strength was observed in FSWed specimens in comparison to BM. Additionally, regression analysis was carried out to model impact energy in terms of input parameters. Microstructural examination of a fractured surface of the FSWed specimen revealed the ductile fracture. A higher microhardness value was also observed in FSWed specimens when compared to BM.

Badania eksperymentalne zestawu cienkościennych konstrukcji lotniczych

Contemporary aircraft structures, and especially their load-bearing structures, are made almost exclusively as thin-walled structures, which perfectly meet the postulate of minimizing the weight of the structure. While local loss of roofing stability is acceptable under operational load conditions, exceeding the critical load limits of structural elements (frames, stringers) is practically tantamount to the destruction of the structure. The effectiveness of these ideas is influenced by the development of science about materials, processing, and machining processes, as well as the continuous improvement of technological processes. These disciplines allow for the construction of complex, geometrically integral structures that create opportunities not only for a more rational use of material characteristics, but also by their appropriate shaping, significantly increasing the mechanical properties of the supporting structure. The most important advantage in favor of the use of integral systems is economic efficiency, gained by eliminating or limiting assembly operations. Densely ribbed roofing elements belong to the category of load-bearing structure elements which, by reducing the weight which they must support, increase the strength parameters of the load-bearing structure. By reducing the thickness of the coating and, at the same time, introducing sufficiently dense stiffening longitudinal elements, it is possible to obtain a structure with significantly higher critical load values, and consequently a more favorable distribution of gradients and stress levels, which translates directly to an increase in fatigue life. The use of new technologies requires research for evidence purposes, showing that structures manufactured in this way are as safe as those manufactured using conventional methods. For this purpose, the authors conducted tests of the selected structure and performed FEM and experimental verification on the test stand. The results of the tests showed positive results, which confirmed that the method of manufacturing integral structures meets even the stringent requirements set by aviation.

Study on the Surface Layer Properties and Fatigue Life of a Workpiece Machined by Centrifugal Shot Peening and Burnishing

This paper presents the results of research on the impact of finishing method on surface topography, surface roughness (parameters Ra, Rt, Rpk, Rk, Rvk), surface layer microhardness, residual stresses and fatigue life. Ring samples made of C45 steel were used to conduct the experiments. The following finishing machining methods were selected: slide burnishing, ball burnishing, centrifugal shot peening, centrifugal shot peening + slide burnishing and centrifugal shot peening + ball burnishing. In the first stage, the use of combined shot peening + burnishing enables microhardness to be increased on the surface layer, the values of residual stresses to be increased and the creation of characteristic machining traces on the surface, the so-called “dimples” (effect of centrifugal shot peening). On the other hand, burnishing (slide burnishing or ball burnishing) is aimed at smoothing the surface and providing favorable stereometric properties to the surface layer. It was noted that, after finishing, the surface roughness parameters decreased from 59% to 83% in relation to the reference surface. The exception is the centrifugal shot peening technology. The use of burnishing (slide or ball burnishing) after centrifugal shot peening reduces the surface roughness parameters by a maximum of 82% compared to the value after centrifugal shot peening. The highest increase in microhardness was obtained after centrifugal shot peening + slide burnishing (ΔHV = 105 HV 0.05), while the highest thickness gh (gh = 120 μm) was obtained after centrifugal shot peening + ball burnishing. The combination of centrifugal shot peening and ball burnishing results in the highest absolute value of compressive residual stresses σmax = 602 MPa and depth gσ = 0.41 mm). Application of an additional operation after centrifugal shot peening increases fatigue life from 27% to 49%. ANOVA analysis of variance confirms the significance of the processing effect of centrifugal shot peening combined with slide burnishing (CSP + SB) and centrifugal shot peening + ball burnishing (CSP + BB) on the analyzed dependent surface.

Improvement of the Fatigue Resistance of Super Duplex Stainless-Steel (SDSS) Components Fabricated by Wire Arc Additive Manufacturing (WAAM)

This study aimed to improve the overall fatigue properties of WAAM-produced SDSS by changing the interpass temperatures. Micro-computed tomography was used to quantitatively characterise the internal defects, such as porosity, in large-volume WAAM-fabricated SDSS materials. An increase in the interpass temperature led to a reduction in the ferrite phase balance by up to 20%. The fatigue anisotropy was still evident, but the fatigue limit in the weakest (transverse) direction was increased to 250 MPa or by approximately 40%. Meanwhile, the increased interpass temperature had no significant effect on fatigue resistance in the longitudinal direction. This study suggests that the interpass temperature can be critical for both achieving isotropic mechanical properties and increasing fatigue life of structural components fabricated with the WAAM method.

Stiffness Degradation under Cyclic Loading Using Three-Point Bending of Hybridised Carbon/Glass Fibres with a Polyamide 6,6 Nanofibre Interlayer

The stiffness degradation of hybrid carbon/glass fibre composites are investigated under cyclic loading in three-point bending. The composites are compared to toughened composites interlayered with PA 6,6 nanofibre (veil) and a matrix toughened with 5% rubber particulate. With the incorporation of veil into the hybridised composite, the hybrid interface experienced extensive localised delamination, due to crack deflection, causing longitudinal cracking between the fibre and veil interface. It is observed that delamination was redirected and reduced by veil interlayering, due to crack bridging as the cracks propagated. The carbon fibre composites toughened by rubber particulate showed similar stiffness retention to carbon fibre after 1,000,000 cycles. The veil interlayering within carbon fibre improved the stiffness retention by 66.87% for the flexural modulus, compared to carbon fibre and rubber toughened carbon fibre laminates. In both glass and carbon fibre samples, the stiffness retention with veil showed a 10-fold increase in fatigue life, compared with untoughened controls. It is observed from the failure mechanics that veil acted as a randomly orientated fibre layer, rather than a matrix toughener.

Comparative assessment of strain-controlled fatigue performance of SS 316L at room and low temperatures

In the present study, strain-controlled low cycle fatigue (LCF) behaviour of SS 316L at room temperature (RT) and −80 ℃ were investigated. RT LCF specimens show cyclic softening, whereas −80 ℃ specimens show initial cyclic softening followed by hardening due to strain-induced martensitic transformation (SIMT). Fatigue damage evolution mechanism is proposed for specimens tested at −80 °C, where compressive stresses develop due to SIMT and retards the crack growth. This leads to an increase in fatigue life for −80 °C specimens. An increase in back stress component at the initiation of secondary hardening is noticed for −80 °C specimens.

Mechanical Properties Enhancement of Dissimilar AA6061-T6 and AA7075-T651 Friction Stir Welds Coupled with Deep Rolling Process.

The main purpose of this research was to enhance the mechanical properties of friction stir welds (FSW) in the dissimilar aluminum alloys 6061-T6 and 7075-T651. The welded workpiece has tensile residual stress due to the influence of the thermal conductivity of dissimilar materials, resulting in crack initiation and less fatigue strength. The experiment started from the FSW process using the 2k full factorial with the response surface methodology (RSM) and central composite design (CCD) to investigate three factors. The experiment found that the optimal rotation speed and feed rate values were 979 and 65 mm/min, respectively. Then, the post-weld heat treatment process (PWHT) was applied. Following this, the 2k full factorial was used to investigate four factors involved in the deep rolling process (DR). The experiment found that the optimal deep rolling pressure and deep rolling offset values were 300 bar and 0.2 mm, respectively. Moreover, mechanical property testing was performed with a sequence of four design types of workpieces: FSW, FSW-PWHT, FSW-DR, and FSW-PWHT-DR. It was found that the FSW-PWHT-DR workpiece had an increase in tensile strength of up to 26.29% and increase in fatigue life of up to 129.47% when compared with the FSW workpieces, as well as a maximum compressive residual stress of −414 MPa.

Effect of fiber orientation on the fatigue crack initiation and propagation of glass fiber reinforced plastics

AbstractIn recent years, glass‐fiber‐reinforced plastic (GFRP) applications have expanded. This study elucidates the fatigue fracture mechanism of GFRP with different fiber orientations and experimentally clarifies the relationship between fiber orientation and fracture mechanism by using specimens with unidirectional simple fiber orientations. First, Static tensile and fatigue tests are performed on two types of specimens with fibers oriented in a single direction (parallel to the load axis and orthogonal to the load axis), and it is found that specimens with a single fiber orientation parallel to the load axis shows higher strength in both tests. Next, In the case of GFRP with fibers oriented parallel to the load axis, it is found that fatigue loading causes fatigue crack initiation at the fiber ends, followed by fiber localized debonding due to crack propagation at the fiber‐matrix interface and that the crack propagation rate gradually decreases and stops. Therefore, this suggests that the increase in fiber length of fibers oriented parallel to the load axis in GFRP leads to an increase in the crack propagation life at the fiber‐matrix interface, which leads to an increase in fatigue life.

Effect of the fiber surface treatment on the mechanical performance of bamboo fiber modified asphalt binder

• The properties of silane-treated bamboo asphalt, alkali-treated bamboo asphalt, and heat-treated bamboo asphalt were evaluated and compared. • Silane-treated bamboo fibers exhibit the best interfacial properties with asphalt. • The rheological properties of treated fiber asphalt are improved compared to untreated fiber asphalt. • Silane-treated fiber asphalt has the longest fatigue life of the three treated fiber asphalts. Bamboo fibers exhibit better interfacial properties with asphalt after surface treatment. Therefore, it is essential to evaluate the effect of bamboo fiber surface treatment on asphalt properties. In this paper, the adhesion of bamboo fibers to asphalt after silane coupling agent, alkali treatment, and heat treatment was investigated. And the rheological properties and fatigue performance of the fiber asphalt binder were evaluated. The adhesion and stripping work of the fibers and asphalt were characterized by measuring the contact angle. The microstructure of treated fibers was analyzed using a scanning electron microscope (SEM). The thermal stability of the fibers was then evaluated by thermogravimetric analysis (TG). Finally, the rheological properties and fatigue performance of fiber asphalt were studied by Dynamic Shear Rheological test (DSR), Multiple Stress Creep Recovery Test (MSCR), and Linear Amplitude Sweep tests (LAS). In the SEM images, it can be observed that the silane-treated fibers have a rough surface and multiple independently existing fibers, which can provide support for the fact that the silane-treated fiber asphalt has favorable adhesion. In addition, the silane-treated fibers showed the most significant improvements in wettability and rheology. The adhesion work of silane-treated fibers was 66.7% greater than that of untreated fibers. All treated fiber asphalt showed better rheological properties than untreated fiber asphalt. The addition of treated fibers resulted in lower δ values, higher G*/sin δ, and increased fatigue life of the asphalt. Silane-treated fiber asphalt has the largest G*/sin δ and fatigue life of tested asphalt. Based on the results, several fiber treatment methods are evaluated, improving the reference for choosing a suitable fiber surface treatment for bamboo asphalt.

Investigation of titanium nanoparticles-reinforced Asphalt Composites Using Rheological Tests

Asphalt binder modification techniques are beneficial for the performance improvement of roads because they can be durable, present less permanent deformation, and provide longer fatigue life. The main modification agents involved in this process are polymers, fillers, fibers, and, more recently, nanomaterials, which have presented technical and economic feasibility. The nanoparticles were added to the base asphalt binder at a concentration of 3% of weight in pure and surface-modified states. This study aims to analyze the effect of surface modification of titanium dioxide nanoparticles using three different agents: oleic acid, benzyl alcohol, and oleylamine. The results have indicated that surface modification of the nanoparticles with oleylamine improved the interaction between the particles and the binder, contributing to increasing fatigue life and resistance to permanent deformation and delaying the aging process. Furthermore, the results of rheological tests have indicated that incorporating nanoparticles surface-modified with oleylamine into modified asphalt binder 55/75-E and asphalt binder 50/70 has produced higher resistance to the aging process less susceptibility to permanent deformation and cracks.

Single and periodic overloading effects on the mode I fatigue crack growth of a ductile adhesive

Variable amplitude fatigue loading, where overloading is included, is commonly experienced by bonded structures. Thus, this work aims the assessment of the influence of overloads on the total fatigue life and fatigue crack growth (FCG) of a ductile adhesive. Double cantilever beam (DCB) specimens were subjected to different fatigue loading spectra including constant amplitude, single and periodic overloads. Stiffness degradation and its rate variation were also evaluated. Results showed that overloads can have a fatigue retarding effect leading to an increase in fatigue life up to 4 times. However, for periodic overloads, this increase in fatigue life was less pronounced.

A Review of Laser Peening Methods for Single Crystal Ni-Based Superalloys

Single crystal Ni-based superalloys are often used to create gas turbine engine blades for their high strength under intense thermo-mechanical loading. Though they are remarkably capable under these conditions, a particular class of premature failure mechanisms known as surface-initiated damage mechanisms can lead to the early fracture of an otherwise healthy blade. This review paper discusses the current progress of post-processing techniques that can greatly mitigate the potency of surface-initiated damage mechanisms. In particular, laser peening (LP) is of significant interest due to the relatively low amount of cold work it induces, greater depth of compressive residual stresses than other cold working methods, ability to accommodate complex part geometries, and the minuscule effect it has on surface roughness. The residual stresses imparted by LP can greatly hinder crack growth and consequently allow for enhanced fatigue life. Given that turbine blades (constructed with single crystal Ni-based superalloys) are prone to fail by these mechanisms, LP could be a worthy choice for increasing their service lives. For this reason, initiative has been taken to better understand the mechanical and microstructural modifications imparted by LP on single crystal Ni-based superalloys and a summary of these investigations are presented in this review. Results from several works show that this class of alloy responds well to LP treatment with improvements such as ~30–50% increase in microhardness, 72% increase in low cycle fatigue life, and elevated resistance to hot corrosion. The primary objective of this review is to provide insight into current state-of-the-art LP techniques and summarize the findings of numerous works which have utilized LP for increasing the service lives of single crystal Ni-based superalloy components.

A Multiscale Overview of Modelling Rolling Cyclic Fatigue in Bearing Elements.

During service, bearing components experience rolling cyclic fatigue (RCF), resulting in subsurface plasticity and decay of the parent microstructure. The accumulation of micro strains spans billions of rolling cycles, resulting in the continuous evolution of the bearing steel microstructure. The bearing steel composition, non-metallic inclusions, continuously evolving residual stresses, and substantial work hardening, followed by subsurface softening, create further complications in modelling bearing steel at different length scales. The current study presents a multiscale overview of modelling RCF in terms of plastic deformation and the corresponding microstructural alterations. This article investigates previous models to predict microstructural alterations and material hardening approaches widely adopted to mimic the cyclic hardening response of the evolved bearing steel microstructure. This review presents state-of-the-art, relevant reviews in terms of this subject and provides a robust academic critique to enhance the understanding of the elastoplastic response of bearing steel under non-proportional loadings, damage evolution, and the formation mechanics of microstructural alterations, leading to the increased fatigue life of bearing components. It is suggested that a multidisciplinary approach at various length scales is required to fully understand the micromechanical and metallurgical response of bearing steels widely used in industry. This review will make significant contributions to novel design methodologies and improved product design specifications to deliver the durability and reliability of bearing elements.

Performance and increased fatigue life for a Ti workpiece produced by the EDM process

Performance and increased fatigue life for a Ti workpiece produced by the EDM process

Viscoelastic Behavior and Phase Structure of High-Content SBS-Modified Asphalt.

To investigate the effect of styrene-butadiene-styrene (SBS) modifier content on the viscoelastic behavior of SBS-modified asphalt (SBSMA) at different temperatures and phase structures, the star SBS modifier was chosen to fabricate seven types of SBSMA with different contents. Multiple stress creep recovery (MSCR), linear amplitude sweep (LAS), and low-temperature frequency sweep tests were adopted to study the influence of SBS modifier content on the viscoelastic performance of SBSMA at high to low temperatures. The SBSMA’s microstructure with different contents was investigated using a fluorescence microscope. The results indicated that the change in non-recoverable creep compliance and creep recovery rate was bounded by 4.5% content at high temperatures, with an apparent turning point. The changing slope of content at less than 4.5% was much higher than that of the content greater than 4.5%. At medium temperatures, the fatigue life of SBSMA increased exponentially with the rising modifier content. The rate of increase in fatigue life was the largest as the content increased from 4.5% to 6.0%. At low temperatures, the low-temperature viscoelastic property index G (60 s) of SBSMA decreased logarithmically as the modifier content increased. In terms of the microscopic phase structure, the SBS modifier gradually changed from the dispersed to the continuous phase state with the increasing SBS modifier content.

Superior low cycle fatigue property from cell structures in additively manufactured 316L stainless steel

We have investigated the low cycle fatigue (LCF) properties and the extent of strengthening in a dense additively manufactured stainless steel containing different volume fractions of cell structures but having all other microstructure characteristics the same. The samples were produced by laser powder bed fusion (L-PBF), and the concentration of cell structures was varied systematically by varying the annealing treatments. Load-controlled fatigue experiments performed on samples with a high fraction of cell structures reveal an up to 23 times increase in fatigue life compared to an essentially cell-free sample of the same grain configuration. Multiscale electron microscopy characterizations reveal that the cell structures serve as the soft barriers to the dislocation propagation and the partials are the main carrier for cyclic loading. The cell structures, stabilized by the segregated atoms and misorientation between the adjacent cells, are retained during the entire plastic deformation, hence, can continuously interact with dislocations, promote the formation of nanotwins, and provide massive 3D network obstacles to the dislocation motion. The compositional micro-segregation caused by the cellular solidification features serves as another non-negligible strengthening mechanism to dislocation motion. Specifically, the cell structures with a high density of dislocation debris also appear to act as dislocation nucleation sites, very much like coherent twin boundaries. This work indicates the potential of additive manufacturing to design energy absorbent alloys with high performance by tailoring the microstructure through the printing process.