Set Of Fatigue Tests Research Articles

High-Cycle Fatigue Life Behaviour of Fabricated Glass Fibre-Reinforced Polymer

This study focuses on the fatigue behaviour analysis of glass fibre-reinforced polymer (GFRP) composite specimens under high-cycle fatigue loading conditions. Therefore, property validation is recommended in the material development process upon further investigation of the fabricated GRFP. This study aims to evaluate the behaviour of the fabricated GFRP fatigue specimen when subjected to high-cycle fatigue loads and compare it to existing studies. A GFRP fatigue test sample was fabricated using the hand layup process into a flat rectangular panel, which was then cut into a small dimension of 28×2×0.2 cm fatigue specimen. Fatigue tests were performed on five flat specimens at different constant amplitude loads or stress levels between 40% and 80% of ultimate tensile strength to obtain the stress–life curve for the fabricated GFRP. Results showed that the high-stress levels of 80% contributed to the most reduced fatigue life cycle of GFRP. This result is consistent with previous studies and lies within the published life cycle range, validating the fabricated GRFP. A new parameter called the failure modulus, or Mf, may be used to quantify a particular set of fatigue tests.

Nonlinear Analysis Method of High-Strength Steel Based on Local Buckling Fiber Hinge

Based on the analysis and summary of the research and application status of domestic and foreign high-strength steel local buckling fiber hinged rod stability and ordinary steel local buckling fiber hinged rod stability control, this paper proposes a fiber hinged rod suitable for spatial structures subject to local buckling. The new type is high-strength steel composite local buckling fiber hinged pressure rod. The influence of related parameters in the dislocation string model and the dislocation couple model on the ultrasonic nonlinear parameters is deeply analyzed. And, from the perspective of contact nonlinear acoustics, the mechanism of the ultrasonic nonlinear response of the crack is analyzed, and the finite element software ABAQUS is used to simulate it. The relationship between the nonlinear parameter and the internal crack shape of the material is simulated and analyzed, which proves the nonlinearity. A series of nonlinear ultrasonic testing was performed on three groups of FV520B high-strength steel fatigue specimens using a nonlinear testing system. Analyzing the results, it is found that the material has a good ultrasonic nonlinear cumulative effect, and the microcracks have a greater impact on the ultrasonic nonlinear response. The β-N curves under three sets of fatigue tests are obtained. The results show that the nonlinear parameters are very sensitive to the fatigue damage of FV520B high-strength steel, and the ultrasonic nonlinear parameters generally increase with the increase in the number of fatigue cycles.

Total life approach analysis of ductile cast iron smooth specimens

Ductile cast irons (DCIs) offer an interesting combination of good castability and high mechanical properties, with acceptable costs. DCI structural components are widely used in important applications like automotive components (e.g. crankshafts and truck axles), wind turbines components and pipelines components (e.g., valves, fit-tings and pipes). In this paper, several sets of fatigue tests, available in the literature, are simulated by using a total life approach, and the fatigue lifetime is computed. The examined ductile cast iron EN-GJS-400-18 specimens were alternatively subjected to tensile and torsional loading, and to in-phase and out-of-phase combined bending and torsion. The obtained results are compared with experimental ones, and a quite good accuracy of the criterion used is observed for the simulated tests.

Microstructure and Fatigue Behavior of a Ni-Cu-Sn Alloy

In this paper, the static and fatigue properties of a Cu-Ni-Sn alloy are investigated. Tensile tests, hardness tests and microstructural analyses using optical and scanning electron microscopy (SEM) were performed and two sets of fatigue tests, with load ratio (R) R = − 1 and R = 0 , respectively, were carried out. The results showed the capability of the alloy to bear high static stress, thanks to its good strength properties. However, the fatigue tests showed a strong sensitivity of the alloy fatigue properties depending on the raw material batch. The comparison between microstructural analyses and fatigue test results showed a strong correlation; in particular, the specimens having a more inhomogeneous microstructure showed lower durability. In addition, the different microstructure also affected the fracture surface morphology as highlighted by SEM analyses.

Fatigue improvements of cracked rectangular hollow section steel beams strengthened with CFRP plates

Concerns over means to improve fatigue behavior of cracked rectangular hollow section (RHS) steel beams exist. This paper presents the details of strengthening schemes that was carried out using prestressed or high modulus carbon fiber reinforced polymer (CFRP) plates. A set of fatigue tests were conducted and results indicated that prestressed CFRP technique could increase fatigue crack propagation life 35.57 times longer than that of unrepaired one. The results also indicated that high modulus CFRP is effective at increasing fatigue life. Following crack propagation lives were calculated based on finite element models and close agreement with test results were observed. Thereafter, a parametric study was conducted considering the influence of various parameters such as the CFRP prestressing level, plate width and modulus on the fatigue life of the strengthened specimens. The findings of this paper can be employed to formulate design guidance for RHS beams under fatigue loading.

Mode I fatigue crack arrest in tensile steel members using prestressed CFRP plates

Numerous studies in the literature have shown that the strengthening of steel members using carbon fiber reinforced polymer (CFRP) composites can significantly extend the fatigue life of these structures. However, not enough attention has been focused on the potential of prestressed CFRP reinforcements for fatigue crack arrest in such members. In the current study, a simple analytical model is proposed to calculate the required prestressing level in the CFRP reinforcements in order to arrest the propagation of an existing fatigue crack in tensile steel members. Furthermore, a novel mechanical unbonded system is developed to anchor the high prestressing forces in CFRP reinforcements to the steel substrate using friction. A set of fatigue tests are performed on unstrengthened and strengthened precracked steel plates to verify the proposed model. The experimental results of the current study showed that the application of nonprestressed ultra-high modulus CFRP plates as externally bonded reinforcements can increase the fatigue life of precracked steel plates by a factor of 4.3. However, fatigue crack arrest is only possible when prestressed CFRPs of a certain prestressing level are used. Based on the analytical, numerical, and experimental results of the current study, it can be concluded that existing fatigue cracks in tensile steel members can be arrested using the proposed prestressed unbonded reinforcement system with the initial prestressing level calculated using the proposed model. In addition, some design recommendations are provided for fatigue crack arrest in practical cases.

Practical Method to Determine Strain Level for Cyclic Direct Tension Fatigue Testing in the Asphalt Mixture Performance Tester

This paper presents a practical procedure for estimating strain levels in the asphalt mixture performance tester cyclic direct tension fatigue test and provides practitioners with guidance for selecting a strain value for testing materials with unknown fatigue characteristics. A large variety of plant-produced and laboratory-prepared mixtures were analyzed. These included hot- and warm-mix asphalt, reclaimed asphalt pavement, and recycled asphalt shingles and various gradations and air void contents; all were tested following the AASHTO TP 107 procedure. The experimental results from a segregated material illustrate that AASHTO TP 107 could produce repeatable results and was sensitive to field variations in binder content. Data for satisfactorily performing and poorly performing mixtures were clustered on the plot of cycles to peak phase angle versus actuator strain level and a Black Space diagram evaluated at the AASHTO TP 107 test temperature. Curves of cycles to peak phase angle versus actuator strain level were built from the experimental database, with each curve representing one ideal mixture that followed a particular power function. The dynamic modulus data are used to determine a recommended actuator strain level to start the set of fatigue tests for each cluster.

Interaction of Creep and High Cycle Fatigue of IN 713LC Superalloy

The study deals with the interaction of creep and high cycle fatigue of cast polycrystalline nickel-based superalloy IN 713LC at high temperatures. Previous works indicated that creep lifetime of superalloy structures was un-affected or even slightly increased in the cases with superimposed vibrations. The reason for this behaviour was not well described up to now. Therefore, set of fatigue tests was conducted at high mean stresses level to observe this phenomenon. The mean stress was kept constant while the stress amplitudes were selected in order to measure wide range of conditions from pure creep to pure fatigue. Fractographic analysis by scanning electron microscopy (SEM) was done with the aim to identify governing damage mechanisms for particular test conditions as a preliminary evaluation of conducted tests.

Failure Analysis on the GCr15 Bearing Steel and the 20CrMo Carburized Steel Nuts of the Ball Screw Pair

Failure analysis on the GCr15 bearing steel and the 20CrMo carburized steel nuts was performed after two sets of fatigue tests of GD8020×1100 ball screw pair. By means of scanning electron microscopy observation, energy dispersive analysis and microhardness testing, it is found that there is an obvious indentation, slight pitting and microcracks on the raceway of the GCr15 bearing steel nut and shows the characteristics of contact fatigue failure. The nonuniformity of microstructure and the lower carbon and chromium content in the indentation, leading to local lower hardness, account for the nut failure. While the raceway of the 20CrMo carburized steel nut is more rough with scratches caused by the damaged steel balls so as to show the characteristics of wear failure. Therefore there are different failure ways for the different nuts made by different steels and heat treatments under the same fatigue testing condition.

Experimental evaluation of crack shielding during fatigue crack growth using digital image correlation

AbstractIn the current paper, a methodology for the evaluation of fatigue crack shielding using 2D digital image correlation (DIC) is proposed. The crack tip shielding has been evaluated from the analysis of the displacements field observed at the vicinity of a growing fatigue crack. The proposed methodology is based on the evaluation of the stress intensity factors calculated from displacement fields measured around the crack tip using DIC. A comparative study employing four different mathematical models describing the crack tip displacements field (namely Westergaard, Williams and Muskhelishvili equations and Christopher, James and Patterson model) has been performed. For this purpose, a set of fatigue tests on aluminium 2024‐T3 compact tension specimens have been conducted at different R‐ratios. Results obtained from DIC technique have been compared with those obtained using compliance‐based methods. Results show a very good level of agreement illustrating the potential of the DIC technique for the analysis of crack shielding during fatigue crack growth.

Study on the Evaluation of Fatigue Life of RC Beams Strengthened with FRP Laminates

Extensive tests have shown that externally bonded fiber reinforced polymer (FRP) laminates are particularly suited for improving the short-term and long-term behavior of deficient reinforced concrete (RC) beam. Fatigue tests conducted to date indicate that fatigue life of RC beam bonded with FRP laminates lies in the response of steel rebar. Study on the method of nominal elastic stress (strain) for evaluating life-span of FRP strengthened beam is carried out in this paper. By analyzing fatigue tests, the acceptable stress concentration factors and S-N curves are suggested to be used to account for the fatigue behavior of RC beams strengthened with FRP laminates. Analytical results are compared with experimental data from two sets of fatigue tests on stresses and life-span, which shows agreeable trend. Based on the findings, the approach of nominal elastic stress (strain) can be extended to evaluate the fatigue life of RC beam bonded with FRP laminates.

On the Tensile and Compressive Fatigue Behaviour of Notched CFRP Laminates

This paper describes the experimental results of a set of fatigue tests performed on T300 carbon fiber / epoxy resin laminates cured in autoclave. The effects of anisotropy in laminates lay up have been investigated, as well as the influence of circular hole notches, for both the case of tensile and compressive loading conditions. Due to the high slenderness of specimens, that have the ASTM D3039 standard suggested geometry, a special gripping device has been designed in order to avoid the axial buckling. Fatigue failure probability of the material has been assessed by means of Maximum Likelihood Estimates (MLE) of the experimental data, as a function of the lay-up and load conditions. Eventually, the micrographic analysis of fractured surfaces outlined the combined effects of both the geometry and notches towards the damage behaviour of this kind of material.

A Reliability-Based Approach to Assess Fatigue Behaviour Based on Small Incomplete Data Sets

This paper outlines a new technique to address the paucity of data in determining fatigue life and performance based on reliability concepts. Two new randomized models are presented for estimating the safe life and pS-N curve, by using the standard procedure for statistical analysis and dealing with small sample numbers of incomplete data. The confidence level formulations for the safe and p-S-N curve are also given. The concepts are then applied for the determination of the safe life and p-S-N curve. Two sets of fatigue tests for the safe life and p-S-N curve are conducted to validate the presented method, demonstrating the practical use of the proposed technique.

Fatigue Properties for Micro-Sized Ni-P Amorphous Alloy Specimens

AbstractFatigue crack propagation tests at different stress ratios of 0.1 and 0.5 have been performed on microsized Ni-P amorphous alloy specimens to investigate the influence of stress ratio in the crack growth properties of microsized materials. The specimens tested were cantileverbeam-type with dimensions of 10 × 12 × 50 νm3 prepared by focused ion beam machining. Notches with a depth of 3 [m were introduced in all specimens. The entire set of fatigue tests as performed using a newly developed fatigue testing machine in air at room temperature. Fine stripes deduced to be striations were observed on the fatigue fracture surface. Careful measurements of the striation spacings were made. Fatigue crack propagation rate, that is striation spacing, is plotted as a function stress intensity factor range. Fatigue crack propagation rate at stress-ratios of 0.1 and 0.5 in microsized Ni-P amorphous alloy specimens are given by da/dN ∼ 1.3 × 10−8 ΔK;1.16 and da/dN ∼ 3.7 × 10−8 ΔK0.5, respectively. At a given ΔK, crack propagation rate at a stress ratio of 0.5 was higher than that at 0.1. It is considered that a decrease in crack propagation rate at stress ratio of 0.1 is due to adecrease in effective stress intensity factor range ΔKeff, by the effect of crack closure.

Thermomechanical Fatigue Behavior of a Quasi-lsotropic SCS-6/Ti-15-3 Metal Matrix Composite

The response of a quasi-isotropic laminate of metal matrix composite, SCS-6/Ti-15-3 in a thermomechanical fatigue (TMF) environment was investigated. To achieve this, three sets of fatigue tests were conducted: 1) in-phase TMF (IP-TMF), 2) out-of-phase TMF (OP-TMF), and 3) isothermal fatigue (IF). The fatigue response was dependent on the test condition and the maximum stress level during cycling. The IF, IP-TMF, and OP-TMF conditions yielded shortest fatigue life at higher, intermediate and lower stress levels, respectively. Examination of the failure mode through the variation of strain or modulus during cycling, and post-mortem microscopic evaluation revealed that it was dependent on the fatigue condition and applied stress level. Higher stresses, mostly with IP-TMF and IF conditions, produced a primarily fiber dominated failure. Lower stresses, mostly with the OP-TMF condition, produced a matrix dominated failure. Also, an empirical model based on the observed damage mechanisms was developed to represent the fatigue lives for the three conditions examined here.

異材境界到達までの疲労き裂成長特性のシミュレーション的研究

As a basic model of fatigue cracks in composite materials, the fatigue crack growth behavior was studied for the case that a crack grows perpendicularly to the bonded boundary of two dissimilar materials from the material of lower Young's modulus (E1) to that of higher one (E2). A set of fatigue tests were conduced on plate specimens of epoxy-epoxy or epoxy-metal composite. These specimens were selected and prepared for this study to produce a wide range of E2/E1 and to have a fully bonded boundary. The fatigue crack growth rate (da/dn) in the material E1 for the specimens with various E2/E1 ratios was measured and compared with that in the homogeneous material (E1). The stress intensity factor range ΔKre was calculated experimentally from this comparison of da/dn. The data of fatigue crack growth rate were corrected with ΔKre/E1, and the ΔKre/E1-da/dn relation was represented by one straight line for various dissimilar materials including dissimilar metals. From these results, it is confirmed that the fatigue crack growth rate in dissimilar materials depends on K and the present testing method is useful as the simulation test of fatigue crack growth in general dissimilar materials.

The effect of molecular weight on the fatigue behavior of polystyrene

AbstractSignificant improvements in the fatigue life of polystyrene can be realized by increase in molecular weight. In this investigation, samples of polystyrene of varying molecular weight were subject to alternating cycles of axial tension and compression at a test speed of 1600 rpm. One set of fatigue tests was made on samples machined from commercial whole polymer rod. A second set of samples was prepared from a PS standard having an average molecular weight of 160,000 and a narrow molecular weight distribution. A third set of samples had a high average molecular weight of 860,000. For a whole polymer, the S–log N curves tended to have the same general shape as for metals, and the endurance limit appeared to be about 1400 psi. The test results show that the average fatigue life, at any given stress amplitude, is significantly increased by increase in molecular weight. For example, the average life of the high molecular weight standard at any given stress level was found to be more than tenfold that of the low molecular weight standard.