Bending Fatigue Loading Research Articles

Novel method for improving fatigue behaviour of laminated glass

AbstractFatigue‐prone structures made of the laminated glass (LG) are yet not given the due consideration by the scientific community. In this work, a novel method that increases the fatigue life and improves the post breakage performance of the LG structure (by modifying the fracture pattern) is reported in the present work. The fatigue life of LG samples (having PVB interlayer of 0.76‐mm thickness) is evaluated using the standard method. Further, a theoretical explanation is presented for improved fatigue behaviour of LG. The effect of treatment of LG and cyclic bending fatigue load on cyclic fatigue strength is reported. The cyclic fatigue strength of LG increases 19.1% to 30.5% for treated LG samples when compared to untreated samples. The finite element model is developed (for treated and untreated LG) using the transient analysis in ANSYS 14.5 (Explicit Dynamics Module) to obtain the maximum deformation at failure load for the corresponding number of cycles. The strain‐life relations are established. The previously established fracture models and underdeveloped nanofracture mechanics concepts are used to explain the fracture patterns of the LG samples. Analysis of variance is conducted to ensure the validity of the experimental results.

Effects of simultaneous fatigue loading and corrosion on the behavior of reinforced beams

This paper investigated experimentally the behavior of reinforced concrete (RC) beams under simultaneous fatigue loading and steel corrosion. Fourteen specimens were manufactured and tested under four-point bending fatigue loading, during which reinforcement corrosion was induced by an accelerated method using a 5% NaCl solution combined with a constant impressed current. Four different levels of maximum fatigue loads, namely 50%, 55%, 65% and 75% of ultimate loading capacity with fatigue loading frequencies of 1.5 Hz and 4.5 Hz and corrosion impressed currents of 0.5 A, 1.0 A, 1.5 A and 2.5 A were applied to the beams. Crack patterns, failure modes, fatigue life, reinforcement corrosion, and flexural stiffness were investigated. Test results indicated that the inclusion of corrosion significantly decreased the ductility, fatigue life and flexural stiffness of the RC beams. Greater levels of maximum fatigue loads and impressed current tended to shorten fatigue life. General and local corrosion occurred simultaneously under the joint effects of fatigue loading and corrosion. It was also found that the flexural stiffness of RC beams under coupled fatigue loading and corrosion increased in early loading cycles and then remained approximately stable, followed by a rapid decrease just prior to failure.

Modeling of material bend-twist coupling on wind turbine blades

Material bend-twist coupling (BTC) as a mean to passively alleviate wind turbine blade loads is assessed. It is accomplished by introducing an offset angle on the plies of the uni-directional material over the spar caps of the blade. At first, the ability of the multibody, FEM, aeroelastic tool hGAST to consistently predict deflections of BTC beam structures is proved through comparisons against existing measured data and numerical predictions. Next, the effect of the plies offset angle and the spanwise position wherefrom offset of the plies starts on maximum attainable tip torsion deflection is assessed. Bend-twist coupling coefficient distributions along the blade span are generated and associated with the corresponding ply offset angles. Finally, the potential of the material BTC method to alleviate blade loads is demonstrated through aeroelastic analyses based on IEC design load cases. Blade root flapwise bending fatigue (7–10%) and ultimate (6–8%) load reduction is possible by means of moderate ply offset angles of 9–12.5°.

Experimental investigation on fatigue failure characteristics of QP-16 type ball-eye under bending load

Abstract In order to ensure the safety and reliability of power delivery systems, the fatigue characteristics and mechanical properties of ball-eyes (BE) are studied by proprietary equipment: bending fatigue test equipment (BFTE), scanning electron microscope (SEM), stereomicroscope, energy dispersive spectrometer (EDS), hardness display equipment. It was found that, compared with the BEs of the annealing process and quenching and tempering process (QTP), the mechanical properties of BE treated by normalizing process are the best under the three different bending fatigue loads, which are 200, 300, 400 MPa. The three kinds of BE with different processes have their own characteristics, in which, the fatigue fracture of BE treated by normalizing process has obvious cowrie pattern and multi fatigue origins. The fatigue extension region is relatively smaller, but the appearance are more smooth and delicate, whose color are black and dark. In final fracture region, there is obvious rust, coarse, a granular surface. The microstructure is fine uniform ferrite and pearlite. The fracture morphology are characterised by transgranular and quasi-cleavage fracture with a few intergranular cracks and the fracture surface contains more impurities. Fatigue fractures of BE from the other two processes of the characteristics of inhomogeneous microstructure, large difference of micromorphology, rough fracture surface and different impurity elements. Under the same stress amplitude, the life of the BE under bending load is lower than that of the BE under tensile load.

Effect of hammer peening with tungsten coating on fatigue properties of carbon steel under rotating bending

Abstract In the present study, we investigated the influence of hammer peening (HP) with tungsten carbide surface coating (WCSC) on high cycle bending fatigue performance of the carbon steel (CS) manufactured as specified in Bureau of Indian Standards BIS 2062 steel. Totally there are twenty-four numbers of specimens cast and tested to investigate fatigue performance. Constantly high cycle bending fatigue load (HBFL) were applied for all specimen, different range of bending stress applied to the specimen and the stress ratio maintained as R = 1. Investigation results show there is up to 40 percent of the fatigue life improvement possible by the surface treatments to the CS material. From the research to date the corrosion and pitting corrosion can be treated by modifying the surface layer of the metal by treating different peening methods and coating.

Stringer effect on fatigue crack propagation in A2024-T351 aluminum alloy welded joint

This paper describes fatigue crack growth in a friction stir welded T joints made of aluminum alloy A2024-T351 under three point bending loads. For this purpose, three dimensional homogeneous isotropic model is used to study the mechanical properties of the welded structure. Extended Finite Element Method (xFEM) including ABAQUS and Morfeo software are used to demonstrate the results of the growth of cracks in FSW 2024-T351 welded joints. Three point bending fatigue load stress is applied in the center of the plate opposite to the initial crack. The material properties in all welded regions of the joint are adopted from available experiments, as well as the fatigue crack growth. Although limited to relatively small crack growth, good agreement between experimental and numerical results, indicate significant potential of the xFEM, enabling also reliable prediction of stringer effect on fatigue crack growth.

Study on bending fretting fatigue damage in 17CrNiMo6 steel

Bending fretting fatigue behavior of 17CrNiMo6 alloy structural steel at room temperature was investigated under different bending and contact loads; and the [Formula: see text]–[Formula: see text] curve also was built up. The results showed that the [Formula: see text]–[Formula: see text] curve had a “C” shape. The bending fretting fatigue life was mainly dependent on the bending fatigue stress and fretting displacement. The limit of the specimens and the fretting fatigue life were dramatically decreased by fretting actions. The bending fretting fatigue damage changed under varied bending fatigue stress levels. When the wear first occurred, there is a lower bending fatigue stress; and with a higher bending fatigue load, microcracks were generated. However, some serious wear and surface delamination were observed under the highest fatigue load.

Numerical prediction of fretting fatigue crack trajectory in a railway axle using XFEM

In this paper, we present for the first time the application of a fretting fatigue crack propagation predictive technique to a railway axle subjected to bending fatigue loading condition. We also present the first numerical study on predicting fatigue crack trajectory in an axle and wheel model of a railway axle. The technique is based on combining the eXtended Finite Element Method (XFEM) with two fatigue crack growth criteria, namely Maximum Tangential Stress (MTS) and minimum shear stress range. In the implementation of XFEM, enrichment functions, shifted formulation and overlay elements are adopted. The element crack closure is taken into account using the punctual restriction criterion. To calculate MTS criterion, the stress intensity factors are extracted using interaction integral method, in which mode I and mode II can be separated. The implementation is validated using a complete contact problem and experimental data from literature. It is found the minimum shear stress range criterion provides crack paths closer to the experimental results than those obtained using MTS criterion. The technique is further applied to a Chinese railway axle and the results are compared to the available experimental data. Good agreement between the numerically predicted and experimentally measured crack trajectory in the railway axle is found.

時効硬化Al合金のき裂伝ぱ形態に及ぼす大気環境の影響（回転曲げ疲労と超音波疲労）

時効硬化Al合金のき裂伝ぱ形態に及ぼす大気環境の影響（回転曲げ疲労と超音波疲労）

Fatigue Resistance of Self-hardening Aluminium Cast Alloy

Cast aluminium alloys are widely used in fatigue critical structural applications, such as engine blocks, cylinder heads, chassis and suspension components, to improve automotive fuel economy. However, it may be difficult to use these alloys for parts that require a high fatigue strength and high reliability because of a large number of casting defects as porosity and microshrinkages exist in them. Fatigue properties of cast aluminium components are controlled by maximum defect size in the material. The larger maximum defect size, the lower the fatigue strength and life.Self-hardening Al-alloys (Al-Zn-Si-Mg alloys) introduce an innovative class of light Al-alloys. Fatigue properties of AlZn10Si8Mg cast alloy in the high cycle region were tested by rotating bending fatigue loading in a high cycle region with the used of parameters - frequency f = 40 Hz, temperature T = 20 ± 5 °C and stress ratio R = -1. Because of that large pores are near or at specimeńs surface and its dominant reason of fatigue crack initiation and propagation.

Fractography Evaluation of Fracture Surfaces of Aluminium Alloy After Fatigue Tests

Secondary cast alloy AlZn10Si8Mg (UNIFONT-90) is generally used for engine and automotive constructions, hydraulic unit and mold making without any additional heat treatment. It has good properties such as castability, very good mechanical strength, light weight, good wear resistance and very good machining. At present, one of the main limits to a wide use of aluminium alloys for engine or automotive applications is a lack of complete understanding of their fatigue behaviour and of the relationships to microstructural features, particularly as far as casting alloys are concerned.Fatigue properties of AlZn10Si8Mg cast alloy in the high-cycle cycle region were tested by rotating bending fatigue loading with the used of parameters - frequency f = 40 Hz, temperature T = 20 ± 5 ℃ and stress ratio R = -1. Numerous studies shown those cast aluminium alloys are very sensitive to casting defects as porosity and microshrinkages and whenever large pore is present at or near the specimen's surface, it will be the dominant cause of fatigue crack initiation.

Fatigue failure analysis of rotor compressor blades concerning the effect of rotating stall and surge

Abstract Detailed investigation was performed on the effect of the rotating stall and surge on the fatigue failure mechanisms of the axial compressor first stage rotor blades. The static stress distribution of the blades was analysed using three dimensional (3D) finite element method (FEM). The critical fracture stress was calculated using the linear elastic fracture mechanics. Fractographic observation revealed different fatigue fracture modes corresponding to the different fatigue loads. Results demonstrated that during operation two kinds of fatigue loads can occur which are tension-torsion fatigue and bending fatigue. The tension-torsion fatigue stems from the periodic tension-torsion stress induced by the surge, while the bending fatigue load is caused by the rotating stall.

Fatigue Behavior and Prediction of NSM CFRP-Strengthened Reinforced Concrete Beams

AbstractIn this study, a total of 16 reinforced concrete beams (dimensions of 203×305×3,861 mm) strengthened with near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) rods and strips were tested under four-point bending fatigue loading. Monotonic loading was applied to their corresponding control specimens to obtain the static monotonic flexural strength. Fatigue loading with a range of 10% of the corresponding static strength to various upper limits was applied to determine the empirical relationship for each type of specimen. It was found that the dominating failure mode under fatigue was rebar rupture. Mixed failure modes of rebar rupture and unstable cracks in concrete were also observed in specimens with longer fatigue life. As the specimens underwent more fatigue cycles, an increase was observed in their tensile strains of CFRP and deflections due to accumulated damages and the losses of stiffness. A fatigue bond model was developed, which simulated the process of fatigue loading as fa...

Fatigue and durability behavior of RC beams strengthened with CFRP under hot-wet environment

Real service environment has a significant influence on fatigue and durability behavior of the members since the main reinforced concrete (RC) structural members of bridges are served under vehicle loads and environment coupling action. However, environment and loads were considered separately (uncoupling) in traditional durability experiments. This was different from the real service conditions of the main structural members of bridge. In this paper, three groups of RC beams strengthened with carbon fiber laminate (CFL) were tested under three point bending fatigue loads with uncoupled hot-wet environment (Group A: 50°C, 95% R.H) and coupled environments (Group B: 50°C, 95% R.H; Group C: 50°C, 85% R.H) to discover the effect mechanism on fatigue and durability behavior of RC members strengthened with carbon fiber reinforced polymer (CFRP) under environment and fatigue load coupling and uncoupling action. Moreover, the fatigue test results in atmospheric condition at room temperature (23°C, 78% R.H) in earlier stage were compared and analyzed. The research results have shown that the hot-wet environmental fatigue equation of strengthened beams that being proposed was effective and feasible. Comparing with traditional environment fatigue experiment (uncoupled), fatigue limit of strengthened beams under coupling action was relatively lower (decreased 20%) in high temperature and humidity environment (50°C, 95% R.H). The higher load level was, the greater the fatigue life decreased.

Effect of Shot Peening on the Fatigue Properties of 40NiCrMo7 steel

Fatigue properties of 40NiCrMo7 low alloy steel in the high cycle region were tested by rotating bending fatigue loading (f = 40 Hz, T = 20 5 , R = -1) on notched specimens after application of shot peening surface treatment (cast steel balls with diameter of 0.43 mm, Almen intensity 12A, coverage 100 % and consequently the surface was re-peened with glass beads to decrease the final roughness). The compressive residual stresses created by shot peening increased the time necessary for fatigue crack initiation what in the final case increased fatigue properties. The fatigue limit σc was higher for almost 28 % in the case of notched shot peened specimens.

Fatigue Strain and Damage Analysis of Concrete in Reinforced Concrete Beams under Constant Amplitude Fatigue Loading

Concrete fatigue strain evolution plays a very important role in the evaluation of the material properties of concrete. To study fatigue strain and fatigue damage of concrete in reinforced concrete beams under constant amplitude bending fatigue loading, constant amplitude bending fatigue experiments with reinforced concrete beams with rectangular sections were first carried out in the laboratory. Then, by analyzing the shortcomings and limitations of existing fatigue strain evolution equations, the level-S nonlinear evolution model of fatigue strain was constructed, and the physical meaning of the parameters was discussed. Finally, the evolution of fatigue strain and fatigue damage of concrete in the compression zone of the experimental beam was analyzed based on the level-S nonlinear evolution model. The results show that, initially, fatigue strain grows rapidly. In the middle stages, fatigue strain is nearly a linear change. Because the experimental data for the third stage are relatively scarce, the evolution of the strain therefore degenerated into two phases. The model has strong adaptability and high accuracy and can reflect the evolution of fatigue strain. The fatigue damage evolution expression based on fatigue strain shows that fatigue strain and fatigue damage have similar variations, and, with the same load cycles, the greater the load level, the larger the damage, in line with the general rules of damage.

Surface crack growth subject to bending and biaxial tension-compression

Fatigue surface crack growth and the in-plane and out-of-plane constraint effects are studied through experiments and computations for aluminium alloy D16T. Subjects for studies are cruciform specimens under different biaxial loading and bending central notched specimens with external semi-elliptical surface crack. Both the optical microscope measurements and the crack opening displacement (COD) method are used to monitor and calculate both crack depth and crack length during the tests. The variation of crack growth rate and surface crack paths behaviour is studied under cyclic pure bending and biaxial tension-compression fatigue loading. This work is centered on the relations between crack size on the free surface of specimen considered configurations, COD and aspect ratio under different fatigue loading conditions. For the experimental surface crack paths in tested specimens the T-stress, the local triaxiality parameter h, the out-of-plane TZ factor and the governing parameter for the 3D-fields of the stresses and strains at the crack tip in the form of In-integral were calculated as a function of aspect ratio by finite element analysis to characterization of the constraint effects along semi-elliptical crack front. The plastic stress intensity factor approach is applied to the fatigue crack growth on the free surface of the tested bending and cruciform specimens as well as the deepest point of the semi-elliptical surface crack front. As result fatigue surface crack paths or crack front positions as a function of accumulated number of cycle of loading are obtained.

Chloride ion diffusion of structural concrete under the coupled effect of bending fatigue load and chloride

Through the bending fatigue load test and static load test on concrete specimens in a chloride environment, we, in this research, studied the law of chloride ion diffusion in concretes under the coupled effect of bending fatigue load and chloride. The results showed that the concrete chloride ion diffusion coefficient was higher under bending fatigue load than that under static load at the same load level. When the load level was greater than 47%, the amplification was very obvious. Under the coupled effect of bending fatigue load and chloride, the service life of the concrete structure would be greatly shortened.

Crack Arrest of 35CrMo Component with Fatigue Crack by Electromagnetic Heating

A specimen of 35CrMo with fatigue crack is used to perform electromagnetic heating crack arrest experiment using a self-made ZL-2 super pulse current generation equipment. The crack tip melted after discharging, and the crack tip melt into a tiny ellipse, reducing the stress concentration. Comparing chemical ingredient in the oval region near crack tip with the base material after crack arresting, the content of Mn, Si, Mo raises, and the grains are refine, increasing the hardness and strength of materials around the crack tip. Specimens before and after discharging are tested by multi axial load fatigue testing machine under three-point bending fatigue load, and the results show that the average fatigue life of specimens after discharge are increased by 13%. Based on the coupled thermal-electrical theory, a numerical simulation method is proposed to study the temperature field. The strain energy density factor in the small region around crack tip is theoretically calculated. Because of the electrothermal stress intensity factor, the strain energy density factor is reduced that prevent the cracks expanding, and lays the foundation for the application of electromagnetic thermal arrest techniques.

Bending fatigue failure mechanisms of twill fabric E-Glass/Epoxy composite

Composite materials exhibit very complex failure mechanisms because of their heterogeneous property leads the formation of different stress levels within the material and results various combinations of damage. The objective of this research is a contribution to physical understanding of composite failure mechanism under bending fatigue loading, as a physical understanding of composite failure mechanism is crucial step for developing both theoretical and numerical models. To investigate the fatigue damaging mechanism and the resulting material strength deterioration of a particular composite material, four-point flexural quasi-static and displacement-controlled fatigue tests have been performed. The analysis methodology relies on interrupted flexural fatigue tests. The damage formation and propagation was continuously monitored through the decrement of bending moment during cycling. This leads to a characteristic history curve that can be subdivided into three stage, namely initial, intermediate and final. Each of them has specific trend in stiffness degradation. Through microscope and SEM image analysis of the pre-cycled specimens, four different subsequent failure modes and mechanisms of the targeted material are identified at different stages of component life. A correlation between the trend of the bending moment time history and the sequence of the different failure modes is established.