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Advancements seeking structural components' strength and weight reduction necessarily pass through fatigue testing. Understanding failure phenomena and crack evolution is a way of methodologically achieving such a goal. An own‐designed resonant fatigue test rig was used to study the behavior of three distinctly manufactured crankshaft batches. A control system and a resonant frequency estimator were developed to follow the overall stiffness reduction with crack advancement. The control algorithm followed the frequency decay to compensate for the input load. The control strategies were validated by finding the system's natural frequency at the beginning of the test and maintaining a constant nominal load. Fractographies made with failed and non‐failed specimens revealed the connection between the expected physical results and the natural frequency shift evolution. The implemented logic enables crack advancement tracking and failure determination. The developments here can be overflown to different resonance fatigue systems to characterize their endurance performance. [ABSTRACT FROM AUTHOR]

Fatigue cracks initiated from holes in several zones and structural components of the RRJ‐95 aircraft frames were investigated. Using the method of quantitative fractography, the crack growth duration in the wing panels during full‐scale bench tests and in the brackets of the in‐service airframe was estimated by measuring the spacing of meso‐beach‐marks (MBM) and fatigue striations. The applied program of bench test consisted of blocks of variable loads that were equivalent to the wing loading in flight and reproducing schematized flight‐cycle. It was shown that the duration of fatigue crack propagation in several structural components of the RRJ‐95 aircraft frames was approximately the same as for the crack nucleation duration. The total lifetime is sufficiently long for cracks in the structural components to be detected and reliably monitored with a large operating time interval between adjacent inspections. [ABSTRACT FROM AUTHOR]

This article describes how a step‐stress accelerated life test (SSALT) can be designed for testing the fatigue life and reliability of structural components with a dominant failure mode. With simple numerical simulations of the crack's propagation in the notched area of the structural part for different loading levels, the slope of the S–N curve for a structural component is initially estimated. Then, a very few fatigue–life experiments are carried out in the high‐cycle domain to determine the intercept of the structure's S–N curve. By considering the scatter from the material's P–S–N curve, different SSALT designs for the structural component can be composed and checked for their expected acceleration factor. The procedure is experimentally validated for the case of a notched specimen and two different SSALT designs. From the results it can be concluded that the predicted durations of the SSALT experiments correlate well with the real experiments. [ABSTRACT FROM AUTHOR]

Fatigue damage, time‐dependent creep damage and their interaction are considered as the main failure mechanisms for many high temperature structural components. A generalized methodology for predicting both the high temperature low cycle fatigue (HTLCF) and creep‐fatigue lives by using the hysteresis energy density rate (HEDR) and fatigue damage stress concepts was proposed. Experimental data for HTLCF and creep‐fatigue in Alloy 617, Haynes 230 and P92 steel were respectively collected to validate the method. A better prediction capacity and most of the data points that fall within a 1.5 scatter band were obtained compared with the traditional energy‐based method, time fraction rule and ductility exhaustion model. Moreover, a creep‐fatigue damage diagram was also constructed by using the proposed approach. [ABSTRACT FROM AUTHOR]

In the present paper, a new analytical methodology to estimate both crack path and lifetime of metallic structural components under fretting fatigue elastic partial slip loading condition is proposed. Such a methodology consists in the joint application of (a) the criterion by Carpinteri et al for metallic structures under multiaxial constant amplitude fatigue loading in high‐cycle fatigue regime, (b) the critical direction method by Araújo et al, and (c) the critical distance method by Taylor, in the form of the line method. The accuracy of the above methodology is evaluated through experimental tests available in the literature, performed employing two cylindrical fretting pads pressed with a constant normal load against a dog‐bone type test specimen subjected to a cyclic axial load. All these components are made of Al 7075‐T651 aluminium alloy. [ABSTRACT FROM AUTHOR]

Abstract: The potentialities of the pressure stimulated currents technique to be used as a continuous structural health monitoring tool in applications related to stone monuments are assessed experimentally. The data gathered by this technique from experiments with notched marble plates submitted to direct tension are considered in juxtaposition to the respective ones provided by the acoustic emissions technique, a well‐founded and widely used sensing tool. The time evolution of the pressure stimulated currents produced provides clearly distinguishable fingerprints of upcoming fracture well before visible cracking is macroscopically observed. These fingerprints are in good qualitative agreement with similar ones provided by the acoustic emissions, and therefore, they can be considered as safe prefailure indicators designating entrance to a “critical stage.” Thus, the use of the pressure stimulated currents technique as an alternative structural health monitoring system appears quite promising, taking also into account the low cost and the small size of the respective sensors. [ABSTRACT FROM AUTHOR]

ABSTRACT Because of their simplicity, many isotropic damage models have been used to approximately predict the fatigue life of metallic engineering components. However, experimental observations confirm that the anisotropic damage evolves at probable failure sites even for isotropic materials. In this study, a model of microstructure of boom-panel is constructed to simulate a representative volume element (RVE), and the anisotropic damage of the RVE is described by the independent isotropic damage of boom and panel. Firstly, the constitutive equation of the RVE in terms of stiffness of boom-panel is deduced by the principle of deformation and static consistency. Then the expressions of damage-driving force for boom and panel based on the principle of thermodynamics are introduced, and the damage evolution equations are constructed. The parameters of boom and panel are identified from fatigue test data of uniaxial tension and pure torsion, respectively. Finally, the aforementioned method is applied to predict the fatigue life of two structures: one is Pitch-Change-Link, which is a kind of structure in helicopter, and the other is a specimen under tension-torsion. The prediction results all fit well with the experimental data. [ABSTRACT FROM AUTHOR]

ABSTRACT Fatigue and fracture assessment of structures weakened by multiple site damage, such as two or more interacting cracks, represents a very challenging problem. A proper analysis of this problem often requires advanced modelling approaches. The objective of this paper is to develop a general theoretical approach and investigate the fatigue behaviour of two interacting cracks. The developed approach is based on the classical strip yield model and plasticity induced crack closure concept. It also utilises the 3D fundamental solution for an edge dislocation. The crack advance scheme adopts the cycle-by-cycle calculations of the effective stress intensity factors and crack increments. The modelling results were validated against experimental data available in the literature. Further, the nonlinear effects of the crack interaction and plate thickness on the crack opening stresses and crack growth rates were studied with the new approach for the problem geometry. It was demonstrated that the both effects could have a significant influence on fatigue life and cannot be disregarded in life and integrity assessments of structural components with multiple site damage. [ABSTRACT FROM AUTHOR]

ABSTRACT Surface cracks are a common occurrence in structural components due to the frequently highest values of the stress at the outer boundary of the body and to the presence of defects. Such flaws can heavily reduce the service life of structural components leading to their premature failure, especially under repeated loading. During last decades, many research works based on theoretical, numerical and experimental techniques have been performed, mainly devoted to the determination of the stress-intensity factors for recurrent surface crack shapes, different loading types and boundary conditions. Further, fatigue behaviour of surface cracks has been examined through numerical analyses or by simplifying the expected crack growth process. In the present paper, a literature survey is carried out by discussing the main topics related to the safety assessment of structural components with surface cracks under static or fatigue loading. [ABSTRACT FROM AUTHOR]