Increasing Fatigue Cycles Research Articles

Research on the transverse flexural static and fatigue performance of the joint between a corrugated steel web and a concrete roof

To study the static and fatigue performance of the joint between the corrugated steel web and concrete roof under the action of a transverse bending moment, bending tests are conducted on four groups of 8 1:1 full-scale joint specimens, and the effect of different connector types is investigated. Moreover, the effect of prestress on the transverse flexural properties of twin perfobond shear connector (abbreviated as T-PBL) joint specimens is analysed. One specimen in each group is subjected to a static failure test to determine the ultimate bearing capacity and load‒deflection curve, and one specimen is subjected to a fatigue loading test to analyse the variation law of mechanical properties such as the ultimate bearing capacity, residual deflection and flexural stiffness during fatigue cyclic loading. The experimental results show that under the action of a transverse bending moment, the failure modes of joint specimens under static load and after fatigue static load are basically the same, but the failure modes of joint specimens with different types of connectors are different. The transverse flexural fatigue performance of the T-PBL joint and embedded connector joint is better than that of the stud connector joint. Specifically, after fatigue cyclic damage, the bearing capacity and stiffness of the T-PBL joint and embedded connector joint are not significantly degraded, while the bearing capacity and stiffness of the stud connector joint are greatly degraded. Applying transverse prestress can improve the transverse flexural static and fatigue performance of the T-PBL joint to a certain extent. Under the action of the fatigue load, the residual deflection of the joint will increase with increasing fatigue cycles. The development law of the residual deflection with the fatigue cycles is that the residual deflection increases rapidly in the initial stage and slowly in the later stage.

Gradual Deterioration Behavior of the Load-Bearing Strength of Main Cable Wires in a Suspension Bridge

The main cable is the primary load-bearing component of a long-span multi-tower suspension bridge. The interaction between a dead load, vehicle load, wind load, and the corrosion environment leads the main cable wire to exhibit tribo-corrosion-fatigue behaviors. This behavior causes wire wear and deterioration, as well as a reduction in the effective cross-sectional area. This leads to the gradual deterioration of the wire’s load-bearing strength and seriously affects the load-bearing safety of the main cable. In order to ensure the safety of suspension bridges, it is critical to investigate the gradual deterioration behavior of the main cable wire’s load-bearing strength. A wire tribo-corrosion-fatigue test rig was established to test the wire under different friction pairs (saddle groove or parallel wires). The cross-sectional failure area of the wire with different pairs was obtained by super-depth electron microscopy and calculation. The damage degree evolution model and the deterioration model of the wire load-bearing strength were established by combining the theory of damage mechanics and the finite element method. The results show that, as contact and fatigue loads increase, so does the cross-sectional failure area of the fatigue steel wire. The fatigue wire’s damage degree has a good quadratic function relationship with fatigue cycles. The damage degree of the wire increases and the load-bearing strength decreases with increasing contact load and fatigue load. The load-bearing strength of the wire changes little at the beginning and decreases with increasing fatigue cycles. The results have fundamental significance for the life prediction of the main cable wires of suspension bridges.

Multiscale computational framework for predicting viscoelasticity of red blood cells in aging and mechanical fatigue

Red blood cells (RBCs) experience significant cyclic deformation through large elastic stretching and relaxation as they circulate in the bloodstream. Such hundreds of thousands times cell deformation causes cumulative fatigue damage to the circulating RBCs, leading to alterations in cell deformability and membrane viscoelasticity. Here, we employ a two-step multiscale computational framework based on coarse-grained molecular dynamics (CGMD) and dissipative particle dynamics (DPD) to probe the viscoelastic properties of the surface-altered RBCs in aging and mechanical fatigue, using experimental information on the molecular structures of both RBC membrane and cytosolic Hb as well as Hb concentration of RBC cytosol. We perform CGMD simulations to compute the shear modulus and membrane viscosity of a small RBC patch with altered horizontal connectivity within spectrin network; meanwhile, we compute the shear viscosity of RBC cytosol under different Hb concentrations. We then use these computed parameters as inputs for a more coarse-grained DPD-based RBC model at the whole-cell level to probe cell deformation, dynamic relaxation, viscoelastic performance of the altered RBC membrane. We find that the RBC membrane rigidity increases with the enhanced horizontal connectivity within spectrin network, but by a factor less than the effective membrane viscosity, resulting in an elevated characteristic relaxation time with increasing fatigue cycles. In addition, we quantify the two-dimensional storage and loss moduli of RBC membrane under time-dependent loading, revealing that the loss modulus is much larger than the storage modulus throughout the entire frequency range covered by the simulations, especially under enhanced connectivity in the cytoskeletal network, which is analogous to the performance of typical viscoelastic materials. These quantitative findings provide unique insights into the progressive damage of circulating RBCs, and demonstrate the capability of the two-step multiscale framework in effectively predicting the altered viscoelastic properties of RBCs influenced by in vivo aging and mechanical fatigue.

Thermal Fatigue Life Prediction of BGA Solder Joint Incorporating Microstructural Coarsening Effect due to Thermal Diffusion.

A creep constitutive equation incorporating the effect of microstructure coarsening was introduced into the Finite Element Method analysis using a user subroutine to predict thermal fatigue life of solder joint. Dispersed particles in the microstructure grew due to thermal diffusion with increasing fatigue cycles, which resulted in the inelastic strain range and the inelastic strain energy density range increased. This increase in the inelastic strain range reduced the fatigue life by approximately 77% compared to the case where no microstructure coarsening effect was incorporated. Thus, it is necessary to incorporate the microstructure coarsening effect in the fatigue analysis of solders. Thermal fatigue life was found to be significantly affected by the microstructure coarsening effect. Thus, it is necessary to incorporate the microstructure coarsening effect in the fatigue analysis of solders.

Detecting fatigue in aluminum alloys based on internal friction measurement using an electromechanical impedance method

Detecting mechanical fatigue of metallic components is always a challenge in industries. In this work, we proposed to monitor the low-cycle fatigue of a 6061 aluminum alloy based on internal friction (IF) measurement, which is realized by a quantitative electromechanical impedance (Q-EMI) method using a small piezoelectric wafer bonded on the specimen. Large stress amplitude (230 MPa) was employed in the testing; thus, the fatigue life can always be below 105 cycles. It was found that except for the initial testing stage, the IF always increases steadily with the increasing fatigue cycles. Before the fatigue failure, the IF can reach 2.5–3.4 times the initial value, which is thought to be caused by the micro-cracks forming and growing. In comparison, the resonance frequency of the specimen just drops by about 2% compared with the initial value. Finally, a fatigue criterion based on IF measurement is suggested for aluminum alloys and it can also be extended to other metals.

Correlation between microstructure evolution and mechanical response in a moderately low stacking-fault-energy austenitic Fe–Mn–Si–Al alloy during low-cycle fatigue deformation

Through in-depth microstructural and mechanical characterization, a mechanism for low-cycle fatigue (LCF) deformation of an Fe-30.7Mn-4.3Si-1.8Al (in wt%) austenitic transformation-induced-plasticity (TRIP) steel at a total strain range of 2% was investigated. The LCF deformation of the steel was performed through two main deformation modes which were planar slip of Shockley partials, and ε-martensitic transformation and its reverse transformation. The varying significance of each deformation mode as well as the relevance between the two modes determined the microstructures evolved during fatigue deformation and resulted in a four-stage cyclic hardening behavior. With increasing fatigue cycles, the LCF deformation was dominated sequentially by the multiplication of partial dislocations, development of slip bands, reversible ε-martensitic transformation, and formation of more thick and crossed ε-martensite along with enhancement of planar dislocation slip, thus generating the characteristic deformation stages of primary cyclic hardening, cyclic softening, cyclic saturation, and secondary cyclic hardening correspondingly. In general, the superior LCF resistance of the steel was attributed to appreciably high plasticity reversibility during the entire fatigue deformation which was caused by reversible planar dislocation slip and ε-martensitic transformation.

Nonlinear resonance ultrasonic spectroscopy (NRUS) for the quality control of additively manufactured samples

Additive manufacturing (AM) is becoming increasingly popular due to its ability to build parts with customer-designed complex geometries. However, the lack of established quality control/assurance practices for the built parts poses a challenge to a wider adoption of additive manufacturing by some industries. In this study, we investigate the utility of nonlinear resonance ultrasonic spectroscopy (NRUS) for predicting the fatigue life of cylindrical Ti–6Al–4V samples manufactured using powder bed fusion on the same build. We use NRUS to measure several linear and nonlinear parameters for the samples before and after hot isostatic pressing (HIPing). The samples are then fatigue tested. We report the correlation between NRUS parameters and fatigue life. Our findings suggest that resonance frequency, quality factor, and the hysteretic nonlinearity of the samples are correlated to their fatigue life. These correlations are promising because the measurements are obtained from distinct samples as opposed to collecting data on the same sample undergoing increasing fatigue cycles. This study suggests that NRUS has the potential to be used as a nondestructive evaluation (NDE) tool for AM part quality control.

Effect of mesoscale phase contrast on fatigue-delaying behavior of self-healing hydrogels.

We investigate the fatigue resistance of chemically cross-linked polyampholyte hydrogels with a hierarchical structure due to phase separation and find that the details of the structure, as characterized by SAXS, control the mechanisms of crack propagation. When gels exhibit a strong phase contrast and a low cross-linking level, the stress singularity around the crack tip is gradually eliminated with increasing fatigue cycles and this suppresses crack growth, beneficial for high fatigue resistance. On the contrary, the stress concentration persists in weakly phase-separated gels, resulting in low fatigue resistance. A material parameter, λtran, is identified, correlated to the onset of non-affine deformation of the mesophase structure in a hydrogel without crack, which governs the slow-to-fast transition in fatigue crack growth. The detailed role played by the mesoscale structure on fatigue resistance provides design principles for developing self-healing, tough, and fatigue-resistant soft materials.

Short-beam shear fatigue life assessment of thermally cycled carbon–aluminium laminates with protective glass interlayers

Fibre metal laminates (FMLs) are attractive construction materials, especially for use in aerospace and transport facilities. Throughout their service life, thin-walled structures made of FMLs are exposed to static and dynamic loads, as well as corrosion and the unfavourable influence of environmental conditions. The paper presents an experimental analysis of the combined mechanical and environmental long-term behaviour of carbon-based fibre metal laminates and their variants with protective glass layers. The Al alloy/CFRP and Al alloy/GFRP/CFRP laminates in a 3/2 configuration were used. The tested laminates were subjected to 1500 thermal cycles with a temperature range of 130 °C. The static and fatigue interlaminar shear strengths were tested before and after thermal conditioning. It was shown that the stable stiffness reduction in the tested laminates was observed with increasing fatigue cycles, due to the progressive fatigue damage accumulation. The thermally cycled laminates feature slightly smoother stiffness loss, while a more rapid decrease was observed in thermally untreated laminates. Moreover, the fatigue life of the tested laminates subjected to thermal cycling revealed nine times fewer fatigue cycles of laminates with glass protectors after thermal cycles in comparison to the laminates not subjected to thermal cycling.

Experimental Study of the Probabilistic Fatigue Residual Strength of a Carbon Fiber-Reinforced Polymer Matrix Composite

Degradation of the mechanical properties of fiber-reinforced polymer matrix composites (PMCs) subjected to cyclic loading is crucial to the long-term load-carrying capability of PMC structures in practice. This paper reports the experimental study of fatigue residual tensile strength and its probabilistic distribution in a carbon fiber-reinforced PMC laminate made of unidirectional (UD) carbon-fiber/epoxy prepregs (Hexcel T2G190/F263) with the ply layup [0/±45/90]S after certain cycles of cyclic loading. The residual tensile strengths of the PMC laminates after cyclic loading of 1 (quasistatic), 2000, and 10,000 cycles were determined. Statistical analysis of the experimental data shows that the fatigue residual tensile strength of the PMC laminate follows a two-parameter Weibull distribution model with the credibility ≥ 95%. With increasing fatigue cycles, the mean value of the fatigue residual strength of the PMC specimens decreased while its deviation increased. A free-edge stress model is further adopted to explain the fatigue failure initiation of the composite laminate. The present experimental study is valuable for understanding the fatigue durability of PMC laminates as well as reliable design and performance prediction of composite structures.

Damage evolution of 3D woven carbon/epoxy composites under tension-tension fatigue loading based on synchrotron radiation computed tomography (SRCT)

A method combining mechanical testing, infrared thermography (IRT) and synchrotron radiation computed tomography (SRCT) is proposed for the damage evolution of 3D woven carbon/epoxy composites under tension-tension (T-T) fatigue loading. To study the relationship between the damage evolution and the stiffness degradation, fatigue tests of six specimens are carried out to different stages before detection by SRCT and optical microscope. The detected results have revealed how cracks initiate, distribute and develop with increasing fatigue cycles. Particularly, the effects of fiber yarn undulation and twist caused during the manufacturing process are discussed.

Effects of tension fatigue on the structure and properties of carbon black filled-SBR and SBR/TPI blends

Abstract The aim of this study was to explore the impact of tension fatigue on the structure and properties of filled SBR and SBR/TPI blends. The effect of tension fatigue on the dynamic properties of carbon black-filled styrene-butadiene rubber (SBR) and SBR/trans-1,4-polyisoprene (SBR/TPI) blend vulcanizates were investigated by dynamic mechanical analysis (DMA). The Mooney-Rivlin analysis of tensile stress-strain data is used for the determination of a rubber network crosslink density. The fatigue fracture surface of SBR/TPI vulcanizates was observed with a scanning electron microscopy (SEM). The crystallinity of TPI in carbon black-filled SBR/TPI (80/20) was characterized by X-ray diffraction (XRD). The results showed that the incorporation of TPI into SBR vulcanizates influences the fatigue properties of the blend vulcanizates. The blend vulcanizates showed optimum fatigue properties with 20 phr TPI. With increasing fatigue cycles, the tensile properties and crosslink density of SBR vulcanizates were decreased substantially. Compared with that of SBR vulcanizates, the tensile properties and crosslink density of SBR/TPI (80/20) blend vulcanizates changed little with the increase in fatigue cycles, and tan δ and E′ decreased gradually with the fatigue cycles. There was a sharp decrease in the E′ and tan δ curve in the temperature range of 40 ~ 60°C. The XRD diffraction peak corresponding to 3.9 Å broadened when the fatigue cycles were increased to 1 million times, and a new peak with inter-planar spacing at 7.6 and 4.7 Å appeared.

Mechanical fatigue of human red blood cells

Fatigue arising from cyclic straining is a key factor in the degradation of properties of engineered materials and structures. Fatigue can also induce damage and fracture in natural biomaterials, such as bone, and in synthetic biomaterials used in implant devices. However, the mechanisms by which mechanical fatigue leads to deterioration of physical properties and contributes to the onset and progression of pathological states in biological cells have hitherto not been systematically explored. Here we present a general method that employs amplitude-modulated electrodeformation and microfluidics for characterizing mechanical fatigue in single biological cells. This method is capable of subjecting cells to static loads for prolonged periods of time or to large numbers of controlled mechanical fatigue cycles. We apply the method to measure the systematic changes in morphological and biomechanical characteristics of healthy human red blood cells (RBCs) and their membrane mechanical properties. Under constant amplitude cyclic tensile deformation, RBCs progressively lose their ability to stretch with increasing fatigue cycles. Our results further indicate that loss of deformability of RBCs during cyclic deformation is much faster than that under static deformation at the same maximum load over the same accumulated loading time. Such fatigue-induced deformability loss is more pronounced at higher amplitudes of cyclic deformation. These results uniquely establish the important role of mechanical fatigue in influencing physical properties of biological cells. They further provide insights into the accumulated membrane damage during blood circulation, paving the way for further investigations of the eventual failure of RBCs causing hemolysis in various hemolytic pathologies.

Calculation Method for Flexural Damage of RC Beams Subjected to Cyclic Loads and Corrosive Actions

Fatigue constitutive laws of concrete and S-N curves of steel bars have been investigated widely. This study aims to explore the failure problems of reinforced concrete (RC) beams subjected to cyclic loads and corrosive actions. The live loads obtained from Chinese technical standards and practical surveys were adopted in experiments and numerical calculations. A series of tests were conducted to study the fatigue performance of normal and corroded RC beams. A numerical method was proposed to calculate the fatigue damage of RC beams under corrosive actions and cyclic loads. The performance of RC beams with increasing fatigue cycles were analyzed with using MATLAB software in which the global stiffness degradation was introduced to represent the properties evolutions of corroded steel bars and concrete.

Effects of flexural fatigue cycles on the internal friction behavior of SiCnws-C/C composites

After loaded for different cycles at stress level of fatigue limit, the internal friction behavior of SiC nanowires reinforced carbon/carbon (SiCnws-C/C) composites was investigated. Experimental results indicate that the fatigue limit of SiCnws-C/C composites is 70% of the static flexural strength. Influence of temperature on internal friction is correlated with the synergistic effect of SiC nanowires, pyrolytic carbon, as well as defects induced by fatigue load. For SiCnws-C/C composites, internal friction increases with the increasing fatigue cycles. The reason is attributed to the increasing interfacial sliding and friction induced by the formation of matrix cracks, interfacial debonding and interlayer delamination. Despite the matrix internal friction decreases a bit due to the increasing Van der Waals force between carbon layers, this partial reduction is smaller compared with the increased internal friction caused by interfacial sliding. Thus, the post-fatigued SiCnws-C/C composites still exhibit increased internal friction.

Dynamic wear evolution of steel wires during multi-axial fretting-fatigue

In order to study the dynamic wear evolution of steel wires during multi-axial fretting-fatigue, experiments were carried out on a self-made multi-axial fretting fatigue test rig. The results show that the maximum length, maximum width, area and depth of wear scar will increase with the fatigue cycles, and the cross angle decreases from 11° to 4° with increasing fatigue cycles. The wear coefficient increases quickly at first and then tends to be stabilized when fatigue cycles increases from 5000 to 20000.

Resistance Analysis and Fatigue Life of COG Assemblies Under Thermal Cycle Aging

This paper reports the resistance change and fatigue behavior of chip-on-glass (COG) modules undergoing various aging time of cyclic temperature, electric current, and stress by shear fatigue tests. It is noted that as the COG assemblies are exposed in the environment of cyclic temperature, the relative resistance of COG assemblies decreases initially and then increases with the thermal cycling aging time. Moreover, the fatigue life of COG assemblies decreases with an increase of thermal cycling aging time during the shear fatigue tests. The change of relative resistance shows different trends under the different aging time. The relative resistance of COG assemblies having not more than 96 h thermal cycling aging time increases sharply in the initial stage, and then remains at a stable value, and toward the final stage of aging, the relative resistance has a radical change that rises first and then drops. However, when the aging time is not less than 192 h, the relative resistance increases rapidly with increasing fatigue cycles. In contrast, the relative resistance of COG assemblies without aging treatment increases dramatically in the initial stage and is then kept stable, and ultimately surges rapidly. Finally, Miner’s damage rules were applied to analyze the damage resulting from the temperature cycling tests, and to obtain empirical correlation between the damage factor and thermal cycling aging time.

Fatigue life and resistance analysis of COG assemblies under hygrothermal aging

The present work deals with studying fatigue life and electrical properties of chip-on-glass (COG) assemblies undergoing the coupling loads of temperature, electrical current and hygrothermal stress by shear fatigue tests. Firstly, as the COG assemblies are exposed in hygrothermal environment, an increased hygrothermal aging time leads to an increased relative resistance of COG assemblies. Secondly, during the fatigue experiments, the fatigue life of COG assemblies decreases with an increase of hygrothermal aging time. The change of relative resistance displays different trends under different aging degrees. When the hygrothermal aging time is less than 96h, the relative resistance increases rapidly in the initial stage, then the rate of rise decreases subsequently, and finally the relative resistance falls to a stable value suddenly. By contrast, the relative resistance of COG assemblies having more than 168h hygrothermal aging increases rapidly with increasing fatigue cycles. Owing to the effects of hygrothermal aging and fatigue on the change of assemblies’ resistance, the total of relative resistance increases with increasing hygrothermal aging time. Finally, the hygrothermal aging damage defined as life reduction after degradation aggravates exponentially with aging time on the basis of the Miner’s linear damage rule. The fatigue life prediction model based on the Miner’s linear damage rule and the Basquin’s equation is proposed and yielded to good prediction for the COG assemblies undergoing hygrothermal aging.

Fatigue Behavior of Reinforced Concrete T-Beam

AbstractEqui-amplitude fatigue loading experiments on five reinforced concrete T-beams were conducted to observe the fatigue damage development. Three stages of fatigue damage were seen in the experiments. The damage rapidly developed early and late periods of the experiment but was relatively stable in between. The beam failed because of the brittle failure of the steel bars. The number of cracks, and the width and height also follow three stages: rapid development, stable development, and failure. The growth of almost all of the cracks stopped at the time of beam failure, except one or two main cracks that continued to grow. The deflection of the test beam and strain of the steel bars and concrete increased rapidly early in the fatigue cycles, with increasing fatigue cycles, whereas they were relatively stable in the middle stage but increased rapidly near the failure point. Finally, the S–N curve of the reinforced concrete T-beam was obtained.

Characterization of early fatigue microstructure in AISI 321 steel using eddy current non-destructive methodology

Accumulative damage during early stage of fatigue in AISI 321 steel was investigated by eddy current test, atomic force microscopy, X-ray diffraction and transmission electron microscopy. Surface slip, dislocation, and strain-induced martensite were determined as the main damage types. Moreover, damage during the fatigue was found to be increased with the increasing fatigue cycles and load amplitude. The contribution of strain-induced martensite to the total eddy current amplitude (Vmax) was enhanced with the increase in its volume fraction. Finally, a linear relationship between Vslip and the height of surface slip was established.