Fatigue Strength Limit Research Articles

Study on the heating process, high temperature mechanical properties and fatigue properties of a low-carbon microalloyed steel

The dynamic continuous cooling transformation (CCT) experiments of a low-carbon microalloyed building structure steel were conducted on a Gleeble-3500 thermal simulation test machine, and the corresponding dynamic CCT curve was drawn. According to the dynamic CCT curves, different austenitization temperatures were designed to clarify the influence of austenitization temperature on the transformation and microstructure of the tested steel. The results showed that when the austenitization temperatures were set as 1050, 1150 and 1250 °C, respectively, the microstructure mainly consisted of ferrite and granular bainite. With the increase of austenitization temperature, the starting temperature of ferrite transformation gradually decreased, but the starting and ending temperatures of bainite transformation gradually increased, leading to the increase of the volume fraction of granular bainite. In addition, the tensile properties of the tested steel at different temperatures were determined. The tensile strength gradually decreased with the increase of the tensile temperature, and the highest tensile strength was 502 MPa for the room-temperature sample, while the elongation showed different trends. It was the largest elongation (57.8%) at the tensile temperature of 500 °C, while the smallest value of 19.2%–23.2% was obtained in the 200–300 °C tensile samples. Finally, the fatigue property of the experimental steel was detected by plotting the corresponding fatigue curves. The fatigue limit strength under 1 million cycles was about 376.2 MPa. Results provide a theoretical reference for the setting of heating process in the real industrial production and the application of the low-carbon microalloyed building structured steel.

Study on the fatigue life and toughness of recycled aggregate concrete based on basalt fiber

This paper studies the influence of basalt fibers on the mechanical properties, fatigue life, and toughness of Mechanically Recycled Aggregate Concrete (MRAC). Basalt fibers of varying volume fractions and lengths, along with quantified amounts of mineral powder and fly ash, are incorporated into MRAC to prepare Basalt Fiber Mechanically Recycled Aggregate Concrete (BFMRAC). The results of basic mechanical tests and fatigue tests showed that mineral powder and fly ash reduce cement consumption, achieve the effect of green construction, and basalt fibers improve the mechanical properties and toughness of concrete. The results of the response surface method (RSM) model indicate that the volume fraction of basalt fibers has a greater influence on the mechanical properties of BFMRAC compared to fiber length. The fatigue test results indicate that under different fiber volume fractions and lengths, the uniaxial compressive fatigue life (N) of specimens for each mix proportion is consistently improved. When the length of basalt fibers is 12 mm and the volume fraction is 0.3 %, the uniaxial compressive fatigue life of BFMRAC reaches its maximum (231638), which is twice that of MRAC. When the survival rate (P) is set to 0.5, with a basalt fibers volume content of 0.3 % and a length of 12 mm, the fatigue limit strength (Se) attains its maximum (0.8648 fc). When stress levels (S) reach 0.75 and the basalt fibers length is 12 mm, the relative CI Intensifying Coefficient achieves its maximum (1.133), resulting in optimal fatigue toughness. When the basalt fibers length is 6–12 mm, Se generally increases with the increase of fiber length, and the enhancement effect is best at 12 mm.

Finite Element Analysis and Fatigue Test of INTEGRA Dental Implant System.

The study involved numerical FEA (finite element analysis) of dental implants. Based on this, fatigue tests were conducted according to the PN-EN 14801 standard required for the certification of dental products. Thanks to the research methodology developed by the authors, it was possible to conduct a thorough analysis of the impact of external and internal factors such as material, geometry, loading, and assembly of the dental system on the achieved value of fatigue strength limit in the examined object. For this purpose, FEM studies were based on identifying potential sites of fatigue crack initiation in reference to the results of the test conducted on a real model. The actions described in the study helped in the final evaluation of the dental system design process named by the manufacturer as INTEGRA OPTIMA 3.35. The objective of the research was to identify potential sites for fatigue crack initiation in a selected dental system built on the INTEGRA OPTIMA 3.35 set. The material used in the research was titanium grade 4. A map of reduced von Mises stresses was used to search for potential fatigue crack areas. The research [loading] was conducted on two mutually perpendicular planes positioned in such a way that the edge intersecting the planes coincided with the axis of the system. The research indicated that the connecting screw showed the least sensitivity (stress change) to the change in the loading plane, while the value of preload has a significant impact on the achieved fatigue strength of the system. In contrast, the endosteal implant (root) and the prosthetic connector showed the greatest sensitivity to the change in the loading plane. The method of mounting [securing] the endosteal implant using a holder, despite meeting the standards, may contribute to generating excessive stress concentration in the threaded part. Observation of the prosthetic connector in the Optima 3.35 system, cyclically loaded with a force of F ≈ 300 N in the area of the upper hexagonal peg, revealed a fatigue fracture. The observed change in stress peak in the dental connector for two different force application surfaces shows that the positioning of the dental system (setting of the socket in relation to the force action plane) is significantly decisive in estimating the limited fatigue strength.

Study on the fatigue performance of steel-composite grillage deck of large-span arch bridge

In this paper, based on the finite element numerical method, an arch bridge with a main span of 252m was selected as the engineering background, and three standard grillage segments of the bridge deck in the derrick area were selected to establish a refined finite element model, and the fatigue characteristics of the steel-composite grillage deck were studied. The fatigue calculation mode III in General Specification for Design of Highway Bridges and Culverts (JTG D60-2015) was loaded into the finite element model for calculation, and the fatigue key points were determined, the stress time course curves were extracted, and the fatigue damage calculation was carried out. The results indicate that the most unfavorable stress point of the steel-composite structure model is at the bottom plate (outside) of the intersection of the middle longitudinal beam and the secondary crossbeam under the longitudinal loading of vehicle load in the transverse position; the stress amplitude of the maximum critical point in the longitudinal bridge stress course under the standard fatigue vehicle model is less than the fatigue strength limit of the normal amplitude, which meets the design requirements.

Optimized bilateral ultrasonic surface rolling process assisting directed energy deposition of thin-walled medium-entropy alloy with high mechanical performance

Laser directed energy deposition (DED) offers significant advantages for the integral manufacturing of large-scaled thin-walled workpieces. Nevertheless, how to improve the yield strength (YS) and fatigue properties of thin-walled parts fabricated by DED is a crucial issue. As an advanced surface strengthening technology, ultrasonic surface rolling process (USRP) is aimed to improve the mechanical performances of additively manufactured workpieces. In this work, an optimized bilateral USRP parameter (including the load, repeated times, scanning speed, etc.) with high manufacturing efficiency and surface integrity was developed to fabricate thin-walled CoCrNi medium-entropy alloy (MEA) parts (~1.5mm thickness). Compared to the as-deposited sample, the sample treated by USRP shows a good strength-ductility balance (ultra-high YS and ductility with 1026.6MPa and 21.9%, respectively), as well as an impressive improvement in the high-cycle fatigue limit strength of 76.9%. The reasons for high mechanical performance are revealed through multi-scale characterization and calculation. Ultra-high strength is predominantly attributed to the high-density pre-existing dislocations and deformation twins (DTs); Good ductility is related with high hetero-deformation induced stress and the activation of multiple deformation substructures induced by high flow stress, such as dislocations, DTs and hexagonal close-packed phase. Further, the improvement in fatigue performance is ascribed to the closure of manufacturing defects in the surface or subsurface and inhibited surface roughening behavior from stable gradient nanotwinned layer. Finally, the work reveals the quantitative relationship among processing-properties-promotion mechanism (PPP), which provides a criterion to meet the specific mechanical performance of DEDed thin-walled components by precisely tuning the bilateral USRP parameters.

Achieving ultrahigh fatigue resistance in AlSi10Mg alloy by additive manufacturing.

Since the first discovery of the fatigue phenomenon in the late 1830s, efforts to fight against fatigue failure have continued. Here we report a fatigue resistance phenomenon in nano-TiB2-decorated AlSi10Mg enabled by additive manufacturing. This fatigue resistance mechanism benefits from the three-dimensional dual-phase cellular nanostructure, which acts as a strong volumetric nanocage to prevent localized damage accumulation, thus inhibiting fatigue crack initiation. The intrinsic fatigue strength limit of nano-TiB2-decorated AlSi10Mg was proven to be close to its tensile strength through the in situ fatigue tests of a defect-free microsample. To demonstrate the practical applicability of this mechanism, printed bulk nano-TiB2-decorated AlSi10Mg achieved fatigue resistance more than double those of other additive manufacturing Al alloys and surpassed those of high-strength wrought Al alloys. This strategy of additive-manufacturing-assisted nanostructure engineering can be extended to the development of other dual-phase fatigue-resistant metals.

Influence of corrosion fatigue on the fatigue strength of an AlSi10MgMn high‐pressure die‐casting alloy with regard to the surface condition

AbstractThis study investigates the influence of corrosion fatigue on the fatigue strength of an AlSi10MgMn high‐pressure die‐casting alloy with regard to the surface condition. Two different surface conditions are compared. First, an unmachined surface condition with a rough surface () and second a machined and polished surface condition with a smooth, polished surface () are tested. The specimens are loaded with a cyclic bending moment at a constant stress ratio of R = 0 till failure. A 5 wt% NaCl solution enables the corrosion fatigue tests. Corrosion fatigue leads to a significant reduction of the endurable stresses along the whole load spectrum independent from the surface condition. The applied corrosive solution prevents the formation of a pronounced long‐life fatigue strength limit within the tested load cycle range. Hence, the reduction of the endurable stresses increases with the increasing number of load cycles, reaching approximately 37% at load cycles. No significant influence of the surface condition, independent of the environment (air, 5 wt% NaCl), on the fatigue behaviour is found.

Effect of Nitrogen Content on the High Cycle Fatigue Properties of Titanium Microalloyed Steel

The high cycle fatigue properties of three industrial 0.12% Ti microalloyed steels with different nitrogen contents (56, 40, and 30 ppm in molten steel of tundish) are investigated. The results show that <20% of the fatigue crack initiation sites are oxide inclusions of size in 16.8 μm ≈ 55.9 μm, while the rest 80% are surface defects. No TiN inclusions cause fatigue failure and the fatigue limit strength slightly decreases with increasing N contents as the yield strength decreases with a coarser ferrite grain. Inclusions characterization in the section near the fracture shows that the average sizes of TiN inclusions in H56, M40, and L30 steels are 3.50, 3.22, and 2.89 μm, and the maximum sizes are 6.92, 6.67, and 6.23 μm, respectively. Calculating for a cooling rate of 0.2 K s−1 using ChemAppPy precipitation model, the size of TiN inclusions will increase from 6.1 to 7.1 μm, when increasing N content from 30 to 60 ppm. The relationships between nitrogen content, TiN inclusions, and fatigue failure quantified by experimental test and modeling show that the nitrogen content in steel can be relaxed up to 60 ppm when considering economical denitrogenization and fatigue safety.

Study of repair welding on microstructure, mechanical properties and corrosion resistance of dissimilar welded joints of SUS304 and Q345B steel

In this study, the influence of repair welding on microstructure evolution, mechanical properties, and corrosion resistance of SUS304-Q345B dissimilar metal active gas arc (MAG) welding plates was investigated via optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), hardness, tensile, fatigue, intergranular corrosion, and electrochemical tests, in which the zero (R0), primary (R1), and secondary repair welding (R2) were performed by MAG welding. The results showed that, after repair welding, the δ-ferrite morphology in the weld evolved from a continuous dendritic shape to a dispersed worm-like structure and the bar ferrite in the heat-affected zone of SUS304 (HAZSUS304) evolved into short bar ferrite. The grain size of the weld was reduced due to the remelting caused by repair welding. The hardness of the weld increased first and then decreased which was related to the decrease of δ-ferrite morphology and grain size of weld. In the tensile test, all specimens were fractured at Q345B base material (BMQ345B), which revealed that repair welding had little effect on the tensile properties. The fatigue limit strength of R1 didn't reduce significantly, while the fracture position of R2 transferred from the SUS304 base material (BMSUS304) to the fusion line of SUS304 (FLSUS304). The corrosion resistance of R1 weld possessed the best corrosion resistance owing to the finer grain size and better δ-ferrite morphology. The results indicated that repair welding was feasible for the repair and reuse of welded joints, and it was of great importance in engineering applications of welded plates.

Crack initiation induced by twin-martensite and inclusion in rotatory bending fatigue of a high nitrogen martensite bearing steel

Rotating bending fatigue tests, together with microstructural characterization, have been performed on the high nitrogen martensite bearing steel Cronidur30. The results show that the fatigue stress amplitude gradually decreases with the increasing number of fatigue cycles, with a fatigue strength limit of 867 MPa after 1.0 × 107fatigue cycles. Crack sources due to both inclusions and twin-martensite volumes are found from inspection of fracture surfaces, with nearly 40% of the fatigue failures identified as originating from twin-martensite volumes. Based on a detailed microstructural examination, it is concluded that twin-martensite volumes first fracture locally along the maximum shear stress direction, and these locations then act as the sources for crack propagation and finally resulting in fatigue failure. The stress intensity factors calculation of two types of crack sources initiated by the subsurface shows that the two types of crack sources play basically the same role in fatigue crack initiation. Granular bright facet (GBF) will be formed around the crack source to meet the threshold value of crack propagation. When the initial size of these two crack sources is large enough, the crack can directly propagate without forming GBF. The novel observation of twin-martensite induced crack nucleation highlights the fact that fatigue failures of the investigated bearing steel do not only originate from inclusions, and help to provide an in-depth understanding on the fatigue mechanisms of bearing steels.

Comparison between Fractal and Statistical Approaches to Model Size Effects in VHCF

Size effects concern the anomalous scaling of relevant mechanical properties of materials and structures over a sufficiently wide dimensional range. In the last few years, thanks to technological advances, such effects have been experimentally detected also in the very high cycle fatigue (VHCF) tests. Research groups at Politecnico di Torino are very active in this field, observing size effects on fatigue strength, fatigue life and fatigue limit up to the VHCF regime for different metal alloys. In addition, different theoretical models have been put forward to explain these effects. In the present paper, two of them are introduced, respectively based on fractal geometry and statistical concepts. Furthermore, a comparison between the models and experimental results is provided. Both models are able to predict the decrement in the fatigue life and in the conventional fatigue limit.

Study of Microstructure and Fatigue in Aluminum/Steel Butt Joints Made by CMT Fusion-Brazing Technology.

Cold metal transfer (CMT) fusion brazing technology was used to weld 6061 aluminum alloy and Q235 galvanized steel with ER4043 welding wire. The microstructure, hardness, tensile performance, and fatigue performance of the welded joint were observed and analyzed. The results show that the tensile strength of the welded joint is 110.83 MPa and the fatigue strength limit is 170 MPa. In the fatigue process, the coupon first undergoes cyclic hardening and then cyclic softening and a ratchet effect occurs. The coupon was broken at the interface layer or weld zone where the fatigue strength limit is the lowest. The fatigue crack initiation is mainly caused by: (1) inclusions and second-phase particles; and (2) porosity and incomplete fusion. When cracks encounter holes during expansion, the expansion direction will change. The fatigued coupon displays a toughness fracture in the instantaneous fracture zone.

Four-Point Bending Fatigue Behavior of Al2O3-ZrO2 Ceramic Biocomposites Using CeO2 as Dopant

This work investigated the effect of adding ceria-stabilized tetragonal zirconia (Ce-TZP) on the fatigue behavior of alumina-based ceramic composites. Alumina powder (control group) and mixtures containing 5 wt.% (group A) and 20 wt.% (group B) of a commercial m-ZrO2/Al2O3/CeO2 powder mixture were milled/homogenized, compacted, sintered at 1600°C-2h, and submitted to hydrothermal degradation. The samples were characterized by relative density, microstructure, crystalline phases, and static mechanical properties. The cyclic fatigue strength was determined using the modified staircase method in 4-point bending tests. The results indicate that adding the m-ZrO2/Al2O3/CeO2 powder mixture to the Al2O3-matrix increases the tetragonal-ZrO2 grains (Ce-TZP) content, presenting 2.9 wt.% of Ce-TZP and 11.9 wt.% of Ce-TZP for group A and group B, respectively. Furthermore, the addition of Ce-TZP improves densification (98.5% → 99.1%) with a slight reduction in hardness and modulus of elasticity and a significant KIC increase of the composite (KIC = 6.7 MPa.m1/2, group B) when compared to monolithic alumina (KIC=2.4 MPa.m1/2). The fatigue strength limit of the control group was around 100 MPa, while the composites (groups A and B) presented the values ​​of 279 MPa and 239 MPa, respectively. The results indicated that the incorporation of Ce-TZP significantly improves the fracture toughness of alumina-based ceramics. On the other hand, regarding the fatigue behavior, there was an increase in fatigue resistance in group A, resulting from the benefits of the t→m Ce-TZP grains transformation, which occurs during cyclic loading, producing a zone shielding that involves the tip of the crack, slowing its growth. The increase in the amount of Ce-TZP (group B) leads to an increase in the internal residual stresses between the phases due to anisotropy and difference in the thermal expansion coefficients, which accelerates the phase transformation and formation of microcracks at grain boundaries, reducing the fatigue strength of composites of group B.

Evaluation of electrical fatigue limits in REBCO coated conductor tapes through static fatigue testing at 77 K

Significant development has been made toward guaranteeing the performance of high-temperature superconducting (RE)Ba2Cu3O7−x coated conductor (CC) tapes in superconducting devices such as high-field magnets and coils. To understand the superconducting behaviors of CC tapes used in such devices under various mechanical- and thermal-induced loads, their mechanical and electromechanical properties should be evaluated in consideration of their application environments. Under static or cyclic fatigue loads, critical current (I c) can degrade as a result of damage to the superconducting layer, even under loads that do not exceed the irreversible stress limits for I c degradation (σ irr). Therefore, prediction of the stress level that can degrade I c under various conditions, such as the endurance limit (stress), is significant for actual coil or magnet applications of CC tapes. A static fatigue tester for CC tapes at 77 K was used in this study to apply a static fatigue load to a 12 mm wide GdBa2Cu3O7−x CC tape specimen under simultaneous axial tension and bending stresses in a U-shaped configuration. Bending mandrels were used to superimpose various bending strains onto the applied static axial tensile strain, and I c across various voltage tap separations was measured over time, up to 100 h. The electrical static fatigue strength and endurance limit for I c degradation were determined based on the 95% I c retention criterion and 100 h of elapsed time, respectively. Results show that bending strain, dependent on mandrel diameter, can greatly influence I c degradation behaviors and that I c can drop considerably in the bent sections compared to the straight sections over time. Analyses of the combined strains in the bent sections allowed the prediction of diameter-dependent electrical static endurance limits under subcritical crack growth. The CC tape’s electrical static endurance limit was greatly affected at smaller bending diameters. When CC coils with diameters smaller than or equal to 50 mm are made using 12 mm wide CC tapes, the electrical static endurance limit is low, roughly ⩽0.63σ irr.

Novel Fatigue-Damage Sensor for Prediction of Remaining Fatigue Lifetime of Mechanical Components and Structures

In this paper, a novel Internet of Things (IoT) fatigue damage sensor is presented to predict the fatigue damage accumulation level and residual fatigue life of critical mechanical and structural components. The intelligent radio-frequency identification (RFID)-integrated fatigue sensor system has special designed breakable mini beams with multiple parallel oriented geometry and symmetric U-type stress concentrated notches. The fatigue sensing beams with different stress and fatigue lifetime levels are designed to estimate the fatigue damage accumulation and remaining fatigue life of unidirectional and multidirectional structural or mechanical elements, including composite structures. The fatigue damage sensor attached on a real structure goes through the same fatigue life experience of critical structural elements or mechanical components from the beginning of service life or any point in the service life to the end of service life. A fatigue sensor with five parallel symmetric U notched mini beams with different fatigue lifetimes (10% N, 25% N, 50% N, 70% N, 85%–90% N) normalized to the total life (N) of a structure are considered to predict the remaining fatigue lifetime of a real structure using the cumulative damage Miner’s rule. The mini fatigue sensor beams attached to the surface of a structure are designed to fail, depending on their fatigue life, earlier than the total fatigue lifetime of the structure, like a fatigue fuse system. The fatigue damage sensing beams fail gradually while passing through the same fatigue cycles as a structural member. When the service lifetime of a real monitored structure is very close to the total fatigue life, the critical maximum lifetime (80%–90% N) notched mini sensor beam breaks and issues an alarm that the service life of the real structural part is approaching its fatigue strength limit and the end of its service life. The smart fatigue damage sensor is wireless-enabled, which makes it possible to check the health status of the sensor over a sensor network as often as one likes. Since the wireless distributed fatigue sensor network system monitors the fatigue health conditions of structures periodically or on demand, the data collected on the sensor network system can be used not only for condition-based fatigue life prediction but also for sensor-based predictive fatigue maintenance and the development of new fatigue design tools for fatigue-sensitive complex and large engineering structures or mechanical systems.

Effect of Nano clay on the fatigue of epoxy and glass fiber composites

This study describes the experimental results of the fatigue behavior manifested by fatigue strength, fatigue life, and fatigue limit composites for epoxy resin and its E-glass fiber (2,4,6) laminates, nano clay prepared in laboratory reinforced in with (2%, 4%, 6%) weight fraction. The evaluation of (S-N) curves of the tested specimens was depending according to the type of E-glass fibers, laminates number, and addition nano clays small granular volume which prepared in laboratory to a polymer. The fatigue tests showed high resistance to all samples after being immersed in water. Adding the nano clay reduced the brittle nature of the Epoxy resin as it is improved drastically.

Effect of Heat Treatment on Fatigue Characteristics of En8 Steel

Fatigue failure is an important factor in most of the engineering applications, especially in steel materials, and among the steel materials, it is an important phenomena in medium carbon steels like EN8, which is very commonly used in components like shaft, gears etc., since it is prone to fatigue failure. Hence, without changing the composition, an attempt is made to enhance the fatigue strength by different heat treatment techniques. In this study, the investigation is carried out on heat treatment of EN8 steel material. Various kinds of heat treatment techniques like quench and temper, normalizing and annealing are performed on EN8 steel. After exposure to the heat treatment, the EN 8 steel material specimens are machined as per the ASTM standards and are subjected to RR MOORE test and SN-curves are plotted from the obtained results; the obtained results from the fatigue tests are further analyzed with the help of ANSYS software. Fatigue life and Factor of Safety (FOS) comparisons for EN 8 steel material is made with the structural steel material and it is found from the comparisons, that the heat treatment process enhances the fatigue strength and endurance limit.

Uniaxial compressive fatigue behavior of ultra-high performance concrete reinforced with super-fine stainless wires

Super-fine stainless wires (SSWs) with micron diameter and large specific surface area can simultaneously strengthen and toughen reactive powder concrete (RPC) at low volume fraction, so SSW reinforced RPC composites have potential for developing infrastructures bearing fatigue load or with aseismic requirements. In this paper, the uniaxial compressive fatigue characteristics of such composites under high stress levels were investigated, and the modification mechanisms of SSWs to RPC were revealed through failure state and microstructure analyses. The results showed that incorporating only 0.5 vol% SSWs into RPC enables the fatigue life and energy dissipation capacity to increase by 252.0% and 262.3%, meanwhile, the fatigue limit strength of composites at the failure probability of 50% reaches up to 76.6% of static uniaxial compressive strength, due to the improvement effect on microstructure compactness, inhibiting effect on flaw initiation, and the ability to convert single main crack into radial multiple micro cracks centered on SSWs. Furthermore, the average maximum fatigue strain and residual strain of composites are improved by 73.7% and 87.2%, respectively, which can be ascribed to the bridging, debonding and being pulled-off effect of SSWs. It can be therefore concluded that the incorporation of SSWs endows RPC with excellent fatigue performance, thus further enlarging the application of composites.

Investigation of the fatigue strength limit of the material

Investigation of the fatigue strength limit of the material

Characteristics and life expression of fatigue fracture of G105 and S135 drill pipe steels for API grade

Characteristics and life expression of fatigue fracture of drill pipe steels for API G105 and S135 grade were investigated experimentally. S135 steel with higher tensile strength has higher fatigue strength and fatigue limit than that of G105 steel with lower tensile strength. A modified model for the S-N data, revealing the correlation between the fatigue life and fatigue limit, equivalent stress amplitude reflecting the effect of stress ratio, is suggested for predicting the fatigue damage. The fatigue limit and the fatigue strength coefficient are correlated to the tensile properties. The mechanism of the fatigue fracture was examined by scanning electron microscopy.