Series Of Fatigue Tests Research Articles

Fatigue crack initiation and energy-based life analysis for Q345qD bridge steel at low temperatures

The lack of in-depth understanding on the low-temperature fatigue cracking performance has limited the extensive application of the Q345qD bridge steel in cold and severely cold regions. This study investigates the resistance to the fatigue crack initiation of the Q345qD steel through a series of strain-controlled fatigue tests of smooth coupons at room and low temperatures. Experimental results present the cyclic stress-strain relationship, non-Masing properties and Coffin-Manson-type fatigue crack initiation resistance. Thereafter, this study analyzes the effect of low temperatures on the stain-controlled fatigue life of the studied Q345qD steel using the different energy approaches. Results indicate that the low temperatures within -60 °C increase the resistance to the fatigue crack initiation and the cyclic strain-hardening coefficients. A comparison with other structural steels demonstrates the excellent fatigue performance of the Q345qD steel at room and low temperatures. Since the corresponding stress amplitudes of the Q345qD steel under each cyclic strain range exhibit some strain-range-dependent cyclic softening/hardening behavior, the plastic strain energy density and the concept of fatigue toughness are more suitable and effective to predict the fatigue life of the Q345qD steel at room and low temperatures. Finally, a simple and accurate method for calculating the plastic strain energy density has been proposed.

Fatigue Characteristic of Designed T-Type Specimen under Two-Step Repeating Variable Amplitude Load with Low-Amplitude Load below the Fatigue Limit

In order to investigate the non-linear fatigue cumulative damage of joints in ocean structural parts, one type of low carbon steel Q345D was employed to prepare designed T-type specimens, and a series of fatigue experiments were carried out on the specimens under two-step repeating variable amplitude loading condition. The chosen high cyclic loads were larger than the constant amplitude fatigue limit (CAFL) and the chosen low cyclic loads were below the CAFL. Firstly, the S-N curve of designed T-type specimen was obtained via different constant amplitude fatigue tests. Then, a series of two-step repeating variable load were carried out on designed T-type specimens with the aim of calculating the cumulative damage of specimen under the variable fatigue load. The discussions about non-linear fatigue cumulative damage of designed T-type specimens and the interaction effect between the high and low amplitude loadings on the fatigue life were carried out, and some meaningful conclusions were obtained according to the series of fatigue tests. The results show that fatigue cumulative damage of designed T-type specimens calculated based on Miner’s rule ranges from 0.513 to 1.756. Under the same cycle ratio, the cumulative damage increases with the increase of high cyclic stress, and at the same stress ratio, the cumulative damage increases linearly with the increase of cycle ratio. Based on the non-linear damage evaluation method, it is found that the load interaction effect between high and low stress loads exhibits different damage or strengthening effects with the change of stress ratio and cycle ratio.

Fatigue damage numerical simulation of cement-treated base materials by discrete element method

Fatigue failure of the cement-treated base (CTB) is always paid more attention by highway constructors. Meso-scale cracking evolution plays an essential role in the research of fatigue deterioration mechanism, which is hard to be characterized using experimental techniques alone. The objective of this paper is to investigate the fatigue behaviour of CTB materials under cyclic loading through the discrete element method (DEM). A parallel bond evolution model (PBEM) was developed to simulate the time-dependent fatigue damage. Integrated with the PBEM, a fatigue damage evolution model (FDEM) was established and implemented in the Particle Flow Code (PFC5.0) to describe the fatigue decay behaviour under cyclic loading. The fatigue modelling parameters were further calibrated by the notched semicircular bending (NSCB) strength and fatigue test. Then a series of virtual NSCB fatigue tests were conducted to study the decay law of CTB materials. The simulation results indicate that the fatigue damage accumulates in a nonlinear manner under cyclic loading and the steady crack growth is the main stage of fatigue failure. With the increase of stress ratio, the stable crack growth stage is shortened obviously. The established PBEM is capable of capturing the fatigue behaviour and cracking process of CTB materials. It provides a reliable numerical technique for modelling and investigating fatigue damage of cement-treated base materials.

On the effects of heat and surface treatment on the fatigue performance of high-strength leaf springs

Leaf springs constitute the most effective suspension way of commercial vehicle axles from the cost and maintainability point of view. Especially in case of front axles, they overtake both the guidance and suspension functions, which consequently designates them as safety components, whose pre-mature failure is explicitly prohibited. The present paper deals with the fatigue performance of downsized parabolic leaf specimens made of the high-strength spring steel 51CrV4 under serial manufacturing conditions. It focuses on the influence of the major manufacturing steps, i.e. the heat treatment and the subsequently applied stress shot peening. The effectiveness of the applied heat treatment on the microstructure transformation and the extent of surface decarburization is determined by means of optical microscopy and corresponding microstructural analyses. Comprehensive series of constant amplitude fatigue tests are executed before and after the applied stress shot peening to quantify its effectiveness on the fatigue performance. The tests cover two characteristic stress ratios of operational significance with the complete range of interest being experimentally investigated. Additionally, surface residual stresses measurements together with micro- and macro-hardness and roughness values before and after stress shot peening are executed to expose the influence of each individual technological effect on the overall fatigue performance.

Experimental and numerical analysis of fatigue cracks emanating from internal defects in Ti6Al4V SLM

In the present work a series of fatigue tests on Ti6Al4V SLM parts are analyzed via both SEM and confocal microscopy. On the one hand, fracture surfaces are studied, and a common pattern is found, formed by a series of different textures which show the complex crack front evolution from crack initiation in a particular internal defect to complete failure. On the other hand, fatigue strength is observed to highly depend on the defect where initiation takes place, so experimental observation of that critical entity is carried out. Both defect location within the specimen and shape are studied, considering the crack-like or blunt feature of every defect. Once experimental analysis is complete, numerical simulation is attempted. By making use of critical defect and residual stress measurements obtained experimentally, both fatigue strength and crack front evolution are estimated.

Tape winding angle influence on subsea cable sheathing fatigue performance

A fundamental component of subsea power cables is the thin galvanized steel tape winded around the dielectric and sheathing layer in order to prevent permanent thermal cycling induced deformation. The pressure state induced by the resistance offered by such tapes against radial reformation reduces the triaxiality ratio of the stress state of the lead sheathing layer. It is known that a reduced triaxiality has a beneficial effect on ductility and fatigue life of metals. In the present work a series of finite element simulations are performed in presence of galvanized steel tapes at three different winding angles and without such reinforcement at all, obtaining a qualitative indication of its effect on the stress state induced in the sheathing layer. Loading conditions as internal pressure related to thermal dielectric expansion and cable bending are modelled. The numerical qualitative results are discussed in connection to a series of full-scale fatigue tests performed on subsea power cables with and without the support of steel tapes.

Fatigue strength characterization of high and ultra-high-strength steel cut edges

This paper investigates the fatigue strength characteristics of CO2 laser, fiber laser and plasma cut edges of S690 and S1100 steel grades. The effect on fatigue performance of surface quality, which was examined by contact measurements and 3D scanning, residual stresses and microhardness profile, is studied and edge surface characteristics are compared for different cutting methods and 8 mm and 12 mm plate thicknesses. Four main experimental fatigue test series were performed and analyzed to estimate fatigue performance (defined as FAT classes) of the cut surface. Additional tests were conducted to study critical defects and residual stresses influence on fatigue properties. Scanning electron microscopy (SEM) revealed multiple critical locations in the specimens. Fatigue properties were characterized based on critical defects and crack initiation and propagation origins. Geometrical discontinuity points in the cut edges were found to have a significant influence on fatigue performance. It is concluded that classification of thermally cut edges by cut edge characteristics could be used in fatigue strength assessment as an alternative to standard FAT classes.

Experimental study on the bond degradation of basalt fiber reinforced polymer grid-concrete interface under fatigue loading

In this study, a series of shear fatigue tests on the basalt fiber reinforced polymer (BFRP) grid-concrete interface at different loading levels were conducted to analyze the interfacial fatigue failure modes. According to the different failure modes, the stiffness degradation characteristics of the load-relative slippage curves under fatigue loading were investigated in groups and an interfacial fatigue damage model based on the degradation of the stiffness coefficient was proposed. Furthermore, on the basis of the test results and the Popovics model, fatigue damage variables were introduced to further establish a theoretical model, which reflected the bond-slip fatigue degradation characteristics of the BFRP grid-concrete interface under fatigue loading. The model fitted well to the test data. This provides a certain reference for the durability and fatigue reinforcement design of fiber reinforced polymer (FRP) grid strengthened concrete structures.

An Ultra-High Frequency Vibration-Based Fatigue Test and Its Comparative Study of a Titanium Alloy in the VHCF Regime

This paper proposes an ultra-high frequency (UHF) fatigue test of a titanium alloy TA11 based on electrodynamic shaker in order to develop a feasible testing method in the VHCF regime. Firstly, a type of UHF fatigue specimen is designed to make its actual testing frequency reach as high as 1756 Hz. Then the influences of the loading frequency and loading types on the testing results are considered separately, and a series of comparative fatigue tests are hence conducted. The results show the testing data from the present UHF fatigue specimen agree well with those from the conventional vibration fatigue specimen with the loading frequency of 240 Hz. Furthermore, the present UHF testing data show good consistency with those from the axial-loading fatigue and rotating bending fatigue tests. But the obtained fatigue life from ultrasonic fatigue test with the loading frequency of 20 kHz is significantly higher than all other fatigue test results. Thus the proposed ultra-high frequency vibration-based fatigue test shows a balance of high efficiency and similarity with the conventional testing results.

Probabilistic fatigue life of welded plate joints under uncertainty in Arctic areas

This paper develops a new practical framework of high-cycle fatigue (HCF) probability analysis of local welded plate joints considering the uncertainty in Arctic areas. The framework includes 1) a meta-model of the local energy concentration factor relying on the genetic algorithm and neural network (GA-NN) approach, 2) the identification of uncertainties in the fatigue assessment procedure, and 3) the probability analysis relying on the Monte Carlo simulation with Latin hypercube sampling method. The GA-NN determines the interactive relationship among the geometrical properties for a good estimation of the energy-based indicator concentration factor. The probability analysis considers the uncertainty caused by the meat-model, the local welding geometry, the Young modulus under different temperatures, and the combination of the ice and wave loadings. To determine the uncertainties involved in probability analysis, this study conducts a series of experimental measurements and high-cycle fatigue tests of cruciform welded plate joints. Furthermore, this study discusses the effect of the ice loading, maximum wave stress, and main plate thickness of welded plate joints on the expected fatigue life. The additional ice loading on the welded plate joints can almost cut the expected fatigue life in 33% in comparison with that only under wave loadings, implying the necessity of considering ice loading in Arctic areas. This study also proposes a probability S-N curve with the cumulative probability of 50% based on the maximum local energy-based indicator to estimate the expected fatigue life.

Experimental investigations on mechanical performance of rocks under fatigue loads and biaxial confinements

In this research, a series of biaxial compression and biaxial fatigue tests were conducted to investigate the mechanical behaviors of marble and sandstone under biaxial confinements. Experimental results demonstrate that the biaxial compressive strength of rocks under biaxial compression increases firstly, and subsequently decreases with increase of the intermediate principal stress. The fatigue failure characteristics of the rocks in biaxial fatigue tests are functions of the peak value of fatigue loads, the intermediate principal stress and the rock lithology. With the increase of the peak values of fatigue loads, the fatigue lives of rocks decrease. The intermediate principal stress strengthens the resistance ability of rocks to fatigue loads except considering the strength increasing under biaxial confinements. The fatigue lives of rocks increase with the increase of the intermediate principal stress under the same ratio of the fatigue load and their biaxial compressive strength. The acoustic emission (AE) and fragments studies showed that the sandstone has higher ability to resist the fatigue loads compared to the marble, and the marble generated a greater number of smaller fragments after fatigue failure compared to the sandstone. So, it can be inferred that the rock breaking efficiency and rock burst is higher or severer induced by fatigue loading than that induced by monotonous quasi-static loading, especially for hard rocks.

Design, analysis and experimental validation of Inconel-625 bellows for critical applications

This paper presents the methodology for design, analysis and experimental validation of Inconel-625 bellows for critical applications. By conducting a series of fatigue tests on Inconel-625 bellows, a curve representing the variation of fatigue life with equivalent stress range was generated. For critical applications such as in nuclear systems, the design of bellows needs to comply with the standard nuclear design codes such as ASME section-III. A design curve was generated by incorporating a factor of safety (FOS) on the experimental data. The experimental stress analysis approach given in ASME section-III/appendix-II was used to obtain the FOS. Design of the Inconel-625 bellows as per the generated fatigue design curve in the present work is simple and can be adopted by bellows suppliers. Also, the proposed method has required compliance with design codes such as ASME section-III. This paper also presents the design by analysis approach for design of nuclear bellows as per ASME section-III/NB).

Development and Experiment Research on Multi-function Wire Rope for Manned Rescue Lifting Equipment

Starting from the introduction of the method of manned rescue lifting for deep hole with large diameter, a multi-function requirement was proposed for loading and communication transmission to develop a special wire rope for ZMK5200QJY40 rescue and lifting vehicle, and a built-in four-strand 4V × 39S non-rotating wire rope structure was established with the coal mines safety requirements. Through the combination of numerical calculation and experimental research, the specific parameters of the wire rope were calculated, the wire and the central cable material, the workshop production process were optimized, and a multi-function wire rope was trial-produced. Based on the failure tensile test, the wedge-shaped ring combination was preferred as the connection method between the wire rope and the lifting cabin, after a series of fatigue and insulation tests, actual working condition simulation tests, etc., a kind of wire rope with functions of manned lifting and communication has been successfully developed, the structure was reliable enough to ensure the safety of the manned rescue process, and it has a reference significance for the series of multi-functional wire ropes development.

Ratcheting Fatigue Behavior of Modified 9Cr–1Mo Steel at Room Temperature

Fusion reactor components undergo asymmetric cyclic loading,that leads to a progressive increase in plastic strain and causes deterioration in life of engineering components. This investigation deals with fatigue behavior of modified 9Cr–1Mo steel at room temperature and presents the effect of mean stress (σm), stress amplitude (σa) and stress rate ( $$\dot{\sigma }$$ ) on fatigue life, deformation and fracture behavior under asymmetric cyclic loading. A series of fatigue tests were conducted under asymmetric stress-controlled loading with different combinations of σm (190–210 MPa), σa (400–420 MPa) and $$\dot{\sigma }$$ (50–450 MPa/s). The plastic strain increased with increase in σm and σa and the fatigue life was reduced, whereas increase in $$\dot{\sigma }$$ reduced the accumulated plastic strain and the cyclic life was increased. The deformation behavior and microstructural changes under the influence of the three parameters (σm, σa and $$\dot{\sigma }$$ ) were examined by tranmission electron microscope (TEM). With increase in the three parameters (σm, σa, $$\dot{\sigma }$$ ), the lath martensitic structure changed to subgrain structure along with dislocation cells and forest dislocations. Scanning electron microscopy revealed unique features of fractured specimens, with progressive reduction in diameter towards the fracture-end, fatigue striations on the tapered circumferential surface and dimples on the fracture surface.

Application of polymeric materials for obtaining gears with involute and sinusoidal profile

In the article research related to the increasing in the scope of application of additive technologies in the construction of machines for the production of gears with involute and sinusoidal profile from polymeric materials was presented. The designed original research stand and with its use carried out a series of preliminary fatigue tests of the obtained polymer gears with an involute and sinusoidal profile was show. The tested gears were obtained in the technology of rapid prototyping by the FFF (Fused Filament Fabrication) method from polymer composites obtained in the form of an ABS (acrylonitrile/butadiene/styrene) – based filament. Based on the results obtained, it was noticed that the temperature in the meshing zone of the gears with involute profiles is higher than for sinusoidal profiles, regardless of the type of composite from which the gears were made. It should also be noted that in the range of nominal load, the sound intensity level of the meshing zone is also lower for gears with a sinusoidal profile than for gears with an involute profile. Based on the tests carried out, an increase in sound intensity was noticed in the case of gears obtained from selected composites (Table 2) compared to the gear obtained from unfilled ABS. However, in the case of gears obtained from the tested composite materials, we observe a decrease in the gear operating temperature (Table 2). The most favorable results of these tests were obtained for gears with a sinusoidal profile obtained from ABS + P2 composite, which show the lowest operating temperature of the gear. It should also be mentioned that slightly worse results were obtained for involute gears.

A semi-quantitative explanation of the cold dwell effect in titanium alloys

Cold dwell fatigue has become one critical issue in titanium industry over the past decades. Though some reports have emphasized the importance of time-dependent plastic strain on cold dwell effect in titanium alloys, the mathematical relationship between plastic strain and fatigue life has never been discussed because plastic strain changes continuously no matter in normal cyclic fatigue or dwell fatigue. In this paper, a series of fatigue tests under constant plastic strain is designed to investigate the mathematical relationship between plastic strain and fatigue life in titanium alloys at room temperature in air. Results show that plastic strain has a definitely detrimental effect on fatigue life in titanium alloys. Different from the traditional qualitative mechanisms, one semi-quantitative explanation for cold dwell effect in titanium alloys is proposed by introducing hysteresis energy density.

Effect of intermetallic compound thickness on mechanical fatigue properties of copper pillar micro-bumps

As the continuous miniaturization of integrated circuits (ICs), 3D integration technology becomes one of mainstream methods, in which copper pillar micro-bumps play significant role in the interconnection. In this paper, the effect of intermetallic compound (IMC) thickness on mechanical fatigue properties and fatigue life of Cu pillar micro-bumps was systematically investigated. Specifically, different IMC thicknesses between interconnected micro-bumps were obtained along with the treatment of isothermal aging at 150 °C under different time duration. Additionally, a series of mechanical shear fatigue tests were carried out on micro-bumps with variation in shear type and shear load, which indicated that the fracture toughness degraded with the growth of IMC thicknesses. Furthermore, the initiation and propagation of micro-cracks in the interconnection interfaces was characterized using SEM. It was found that different fracture modes were presented with respect to different IMC thicknesses of micro-bumps. Finally, the fatigue life of micro-bumps was calculated based on shear fatigue experiments as well as predicted by Coffin-Manson fatigue model, which implicated that experiments and simulations were in agreement with the trend of fatigue life of micro-bumps against different IMC thicknesses. These results in this work could provide useful insights to improve the quality and reliability of interconnection using copper pillar micro-bumps in 3D integration.

Comparison of the fatigue performance of ferrite–pearlite and ferrite–bainite dual-phase steels

Recent demands for large vessels and deep water exploration have increased the requirements for thicker plates to ensure the sufficient strength of such structures. The use of thicker plates, however, has an adverse influence on the fatigue performance. To enhance the fatigue life, post-weld treatments, such as weld-toe grinding, TIG (tungsten inert gas) dressing, hammer peening, and high-frequency mechanical impact (HFMI) treatments are commonly employed. On the other hand, these techniques require additional fabrication time and production cost. Therefore, there is keen interest with respect to thick steel plates with improved fatigue strength. This study examined the fatigue characteristics of conventional steel (Ferrite–Pearlite, F–P steel) and Ferrite–Bainite dual-phase steel (F–B steel). The fatigue behavior of both steels was investigated by a series of fatigue tests with three different types of welded joints. In case of gusset and cruciform-welded joints, fatigue strength of F–B steel is higher than that of F–P steel. F–B steel is known to exhibit improved fatigue performance associated with the existence of bainite microstructure. In addition, the fatigue data in this study are validated against the existing literatures. Based on the fatigue test results, a modified fatigue design curve is suggested from this study. In order to discuss the effects of fatigue crack path, the fatigue crack growth rate (FCGR) of both steels was investigated in terms of Paris’ law. Finally, microstructural analysis was conducted to discuss the fatigue performance.

Study on fatigue failure of glass fibre-reinforced thermoplastic pipe

The long-term fatigue performance of a glass fibre-reinforced thermoplastic pipe (RTP) is mainly determined by that of its glass fibre reinforcement layer. Glass fibre has an irregular network structure consisting of SiO4 tetrahedrons. In this network structure, there exists numerous defects. Under cyclic loading, cracks are initiated at these defects and grow steadily and perhaps even disruptively, ultimately leading to the fracture of the glass fibre. The mean stress corresponding to the occurrence of disruptive crack propagation is referred to as the critical fatigue stress. When the mean cyclic load is smaller than the critical value, the growing cracks stop propagating when in contact with high-energy chemical bonds. When the mean cyclic load is larger than the critical value, the glass fibre is doomed to fracture. In the present study, a series of fatigue tests was performed on a RTP subjected to cyclic loadings of different mean stresses. The numbers of cycles to failure at different mean stresses obtained from the tests were then used to estimate the critical fatigue stress of the RTP. The mechanism underlying the fatigue failure was analysed using fatigue mechanics and chemical bond theories.

Ratcheting Fatigue Behaviour of Zircaloy-2 at 300 °C

In laboratory, materials designed for engineering applications, specifically for fatigue, are generally tested under symmetrical cyclic loading (stress ratio, R = −1), but many structural components exhibit less fatigue life than predicted from symmetric loading due to asymmetric cyclic loading during service. This study deals with fatigue behaviour of Zircaloy-2 and presents the effect of mean stress (σm), stress amplitude (σa), stress rate ($$\dot{\sigma }$$) on fatigue life, deformation and fracture behaviour at 300 °C under asymmetric cyclic loading. A series of fatigue tests are performed at 300 °C under asymmetric stress-controlled loading with different combinations of σm (60–80 MPa), σa (115–135 MPa) and $$\dot{\sigma }$$ (30–750 MPa/s). Deformation behaviour and microstructural changes under the influence of above parameters (σm, σa and $$\dot{\sigma }$$) are examined by transmission electron microscope. It is observed that plastic strain increases with rise in σm as well as σa and cyclic life is reduced; on the other hand, with increase in $$\dot{\sigma }$$ accumulation of plastic strain decreases and fatigue life is enhanced. The results are correlated with microstructural changes and fracture behaviour of the material under different test conditions.