Fatigue Life Of Structures Research Articles

Fatigue performance of bolted shear connectors

ABSTRACT A computer-aided engineering (CAE) fatigue life prediction technique is developed in this paper to determine the fatigue strength of bolted shear connectors in composite structures. A relatively new initiative in the composite construction industry is the use of the blind boltshear connector, which provides a sustainable and practical solution to the main limitation of using traditional welded stud regarding reuse of building components. Furthermore, fatigue is one of the major causes involved in fatal mechanical failures of composite structures. However, limited research has been currently undertaken to assess fatigue life of composite structure. Therefore, the fatigue performance of the blind bolt under constant amplitudes cyclic loading has been investigated using ABAQUS/explicit and FE-SAFE programs. First, the dynamic responses of steel-concrete composite structures under sinusoidal load cycles were simulated using ABAQUS/explicit. Then, the stress–strain time history based on the response law of the composite structure was introduced into the FE-SAFE software to obtain a good prediction on the fatigue life of the blind bolt shear connector. As a result, the logarithmic life distributions of the bolted shear connector were calculated using different constant amplitudes.

Numerical investigation on fatigue life of aluminum brazing structure with fin-plate-side bar under the low temperature thermal-structure cyclic stress

A stress analysis model was established to analyze the thermal and structural stress of aluminum brazing structure with fin-plate-side bar (ABS) in the LNG plate-fin heat exchanger. The fatigue life of ABS was evaluated based on the above stress analysis results by the different standard. The result shows that the thermal and structural stress concentration is generated at the brazed joint of ABS. Under the common action of thermal and structural stress, the equivalent stress is influenced mainly by the equivalent thermal stress. The equivalent alternating stress was calculated to be 153.5 MPa based on thermal and structural stress. The permissible cycle numbers at the brazed joint of ABS, which is calculated by the fatigue assessment procedure of ASME and JB4732, are 3311 and 2953, respectively. The fatigue assessment results based on the third strength theory is more conservative for the ABS. The influence of operation parameters is also analyzed for the fatigue life of ABS. The temperature difference between NG and MR, MR temperature and NG pressure will be the main factors to impact the fatigue life of that. And a method is proposed to predict the fatigue life of ABS according to the main factors. The error will be less than 10% between the prediction results and the simulation results.

High-cycle and very-high-cycle fatigue behavior of a stainless steel for air-conditioning compressor valve plates

PurposeThe investigations could guide the structural design and fatigue life prediction of air-conditioning compressor valve plates.Design/methodology/approachThe High-Cycle Fatigue (HCF) and Very-High-Cycle Fatigue (VHCF) behaviors of stainless steel used for air-conditioning compressor valve plates were investigated. Monotonic and cyclic loading conditions were designed to explore the fatigue responses according to the load characteristics of the structure.FindingsThe crack initiation can be observed as the arc-shaped cracks at both sides of specimens and Y-shaped crack bifurcation in the specimens. Moreover, the middle section and the cracks at both ends are not connected to the surface of the specimen. The stress-life results of the materials under two directions (vertical and horizontal) were provided to examine the difference in fatigue strength.Originality/valueMonotonic and cyclic loading conditions were designed to explore the fatigue responses according to the load characteristics of the structure. Based on the experimental data, the results indicate that specimens under cyclic loading conditions could demonstrate better mechanical performance than static loadings.

Research on rotor unbalance magnetic pull compensation method based on modular winding d‐axis current injection

Due to the dual air-gap topology of the direct-drive permanent magnet motor with inner enhance force (IEF-DDPMM), the radial EM exciting force generated in the inner and outer air gaps when the rotor is eccentric will act on the same rotor, and the unbalanced magnetic pull (UMP) on the rotor will reduce the fatigue life of the rotor structure and bring many problems such as vibration and noise. Therefore, the rotor UMP compensation method of IEF-DDPMM based on modular winding d-axis current injection is proposed to suppress the harm caused by eccentricity. The expression of electromagnetic (EM) exciting force considering the cogging effect and current time harmonic without rotor eccentricity faults is derived by the analytical method. Also, the EM exciting force newly introduced due to the rotor eccentricity is analysed. The effects of different eccentricity types on torque characteristics, the fatigue life of the rotor structure and stator vibration of IEF-DDPMM are compared and analysed by the FEM. Finally, the IEF-DDPMM rotor eccentricity models are optimised based on the method. The performance of the motor before and after rotor UMP compensation is evaluated by FEM. The results show that the proposed method is correct and effective.

Prediction of fatigue life of a flexible foldable origami antenna with Kresling pattern

In this paper, we present a thorough mechanical analysis of a foldable origami helical antenna using the Kresling pattern. A precise simulation is required to explicitly capture the complex motion of an origami structure during the folding process. We perform this study by employing the Finite Element Method (FEM) available in ANSYS software. First, we analyze the folding behavior of the structure with three stories. The results indicate that after the second story is folded completely, the first and third stories begin to fold. Next, we predict the fatigue life of the structure using the mean stress with fully reversed loading. We investigate the effects of several design parameters such as length ratio (b/a), height of story, total height, thickness, length and thickness ratios of creases, and radius of the circumscribed circle of polygonal on the fatigue life. We find out that the origami structure with the length ratio (b/a) of 1.9 has the highest life cycles. The results indicate that the effects of the height of the story on the life cycle depend on the length ratio (b/a). We observe that the life cycle of the origami structure improves by decreasing the thickness or increasing the radius of the circumscribed circle of hexagonal. In addition, we discover that the creases design plays an important role in the fatigue life and folding behavior of the origami structure.

Инструменты и методы анализа усталостного многоциклового стохастического нагружения для оценки точности и надежности численных решений

The article presents methods of processing and the results of the analysis of the accuracy of solutions obtained when calculating the structure fatigue life in the case of random loading using domestic and foreign computer systems. Unlike foreign analogues, domestic software products for calculating the fatigue life of a product under random loading are based on the regulatory documents of the Russian Federation, which are proposed along with methods adopted abroad.

Fatigue life prediction of high-speed composite craft under slamming loads using progressive fatigue damage modeling technique

A reliable predictive method is developed based on the progressive fatigue damage modeling technique to estimate the fatigue life of high-speed composite craft. In this method, at each loading cycle, the occurrence of different failure types would be inspected and based on the failure type, either gradual or sudden degradation rules would be followed to update the material properties. This procedure continues until the final failure of the structure. To implement this method, a MATLAB code is developed based on material degradation rules which integrating with the Abaqus it can be used for complex geometries. This method enables us to predict the fatigue life of composite structures with different layup configurations under arbitrary loading conditions only by knowing the static and fatigue behavior of unidirectional laminates. To even more reduce the number of required tests, the energy-based unified fatigue life model is employed. Owing to the low number of required tests, this method can be very cost-effective in the design stage of composite structures that are intended to endure cyclic loads.

Numerical simulation and experimental verification of random pitting corrosion characteristics

Corrosion is the most common type of damage to the hull structures of ships, and pitting corrosion damage has garnered the attention of researchers owing to its complexity and randomness. This study investigated the effects of random pitting on the performance of ship hull plates by developing Python script and proposing a numerical simulation method for establishing the randomness of pitting (form and distribution). The applicability and reliability of the proposed method were then verified through a pitting test. Finally, under the same degree of pitting damage condition, the influences of different random pitting patterns on the tensile properties of unstiffened plates and the ultimate strength of stiffened plates were investigated. The method presented in this paper provides technical support and establishes a foundation for the investigation of the influence of pitting randomness on the fatigue life of steel plate structures and the development of methods for the intelligent identification of steel plate pitting damage.

Intelligent approach for accurately predicting fatigue damage in overhead highway sign structures

Full-span overhead sign support structures can be found along any major highway across the US. Such structures experience different wind loading scenarios varying with time. As a result, these structures start to build up fatigue cracks within their members near the end of their fatigue life. Due to economic realities, the needed routine fatigue inspections on such highway structures can not be performed regularly. This paper is intended to present a comprehensive tool to accurately predict the remaining fatigue life of full-span overhead highway sign support structures subjected to a long and sustained wind fluctuation. Synthetic wind time histories were developed by superimposing cosine waves over a range of frequencies of 3–300 Hz and randomly generated phase angles. Kaimal spectrum was utilized to build a database of wind time histories for each daily mean wind speed along a period of 45 years in the State of Kansas. Moreover, each wind time history was modified to capture both the mean speed and high speed in each given day. After that, the wind speed vs. the number of cycle relationship, for a given time span, was extracted from the synthetic wind time history using the Rain Flow counting technique. Fatigue evaluations were conducted using axial truss member stresses extracted from a finite element solution corresponding to each wind speed in any given time range. Potential fatigue failure was assessed for each structural member after amplifying the stress range using an average dynamic amplification factor generated by integrating the frequency-response curve of harmonic excitations. These assessments evaluate the ratio of consumed fatigue cycles to ultimate fatigue cycles using Miner’s rule to estimate the fatigue life. A computationally affordable simulation package was developed to carry out the generation of wind time histories, cycle counting, structural modeling, and fatigue life calculations. This package was used to evaluate the fatigue life of a non-cantilever sign structure in Wichita, Kansas. The software predicted the end-of fatigue life of two members in this structure. Accordingly, inspections of these two members revealed the existence of unnoticed severe fatigue cracks while other members did not show any sign of distress.

In situ and experimental analysis of longitudinal load on carbody fatigue life using nonlinear damage accumulation

In this paper, a multi-disciplinary analysis method is proposed for evaluating the fatigue life of railway vehicle car body structure under random dynamic loads. Firstly, the hybrid fatigue analysis method was used with Multi-Body System simulation and finite element method for evaluating the carbody structure dynamic stress histories. The dynamics stress is calculated from the longitudinal load using longitudinal train dynamics. Secondly, the nonlinear damage accumulation model was used in fatigue analysis, and carbody structure fatigue life and fatigue damage were predicted. The mathematical model simulations are compared with results produced experimentally, showing good agreement. Finally, the mode is determined after the finite element model is established. To achieve the dynamic stress at each node, the modal response is used as excitation. The carbody damage was obtained by combining dynamics stress with the NMCCMF damage accumulation model. As a result, the effect of longitudinal load on carbody fatigue damage is investigated. The longitudinal load contributes significantly to the fatigue damage of the carbody.

Ensemble learning for remaining fatigue life prediction of structures with stochastic parameters: A data-driven approach

An effective approach is proposed to predict the remaining fatigue life (RFL) of structures with stochastic parameters. The extended finite element method (XFEM) was firstly used to produce a large amount of datasets associated with structural responses and RFL. Then, a RFL prediction model was developed using the ensemble learning algorithm, which employed multiple machine-learning algorithms to learn useful degradation patterns of the structures from the XFEM datasets. Several numerical examples were investigated to evaluate the performance of proposed RFL prediction approach. The analysis results demonstrate that the ensemble learning is able to effectively predict the RFL of the structures with stochastic parameters.

Research on the transmission law of kurtosis of SDOF system under nonstationary and non-Gaussian random excitations

Vibration fatigue failure of structures under complex random excitations is a common problem in the field of engineering, and it seriously endangers the reliability and safety of major equipments and structures. It is particularly important to accurately predict the vibration fatigue life of structures under random excitations. Generally, it is assumed that the vibration excitation of engineering structures follows a stationary Gaussian distribution, but the actual excitation usually follows a nonstationary and non-Gaussian distribution, especially under harsh or variable working conditions. The vibration fatigue life of structures is closely related to the structural dynamic response characteristics, and the kurtosis of the structural response has a particularly obvious influence on the vibration fatigue life. In this paper, taking the single-degree-of-freedom system as an example and by decomposing complex random excitations in frequency segments, the dynamic response law of the system under nonstationary and non-Gaussian random excitations is studied in depth, and a mathematical model describing the transmission law of the kurtosis between the decomposed signal of excitation and response signal is established. The results show that there is a close linear relationship between the kurtosis of the structural dynamic response and the kurtosis of the decomposed signal obtained by frequency decomposition of the excitation signal by 3.2 times the half power bandwidth at the damped natural frequency of the structure. It is possible to quantitatively estimate the kurtosis of the structural response according to this relationship, which lays the foundation for accurately predicting the vibration fatigue life of structures under nonstationary and non-Gaussian random excitations.

Analysis of virtual fatigue life of welding structure of tracked vehicle based on load spectrum

Welding has become the main processing method of the supporting structures on tracked vehicles. The accurate evaluation of fatigue life of welding structures is of great significance significant to the reliability of tracked vehicle. The whole analysis process, based on strengthened load spectrum and structural stress method, is proposed in the study to predict the fatigue life of welding structures. Initially, the road-load spectrum of different conditions was obtained by vehicle tests. Then, the data which had been preprocessed were compressed based on pseudo-damage editing. Furthermore, the load spectrums were extrapolated and equivalent to program-loaded spectra according to the non-parametric rain-flow extrapolation method. On the other hand, the finite element model of the welding structure of the tracked vehicle was established to calculate the structural stress at the welding seam

Shape memory alloy strands as cross-ties: Fatigue behavior and model-cable net tests

NiTi Shape Memory Alloy (SMA) has the potential for use as cross-ties to mitigate cable vibration due to its superelasticity and high damping capacity. However, recent studies revealed that the fatigue problem of the NiTi SMA should be addressed. This paper investigates the fatigue characteristic of SMA strands. The superelastic and structural fatigue characteristics of SMA strands were tested under uniaxial cyclic tensile loading at different strain amplitudes. The maximum stress, residual strain, and dissipated energy were derived from a superplastic fatigue test with 2000 cycles. The test results showed that the parameter values related to the superelastic behavior of the SMA strand decreased in the early stage and then stabilized. A structural fatigue test conducted at strain amplitudes of 0.3% to 2.5% indicated that the structural fatigue life of the SMA strand decreased with increasing strain amplitude; the fatigue life reached two million cycles at the strain amplitude of 0.3%. The free vibration test result indicated that the SMA cross-tie significantly increased the frequency and moderately increased the damping ratio of the cable net. An optimal cross-tie location existed in each vibration mode with the maximum damping ratio.

Uncertainty Quantification for Fatigue Life of Offshore Wind Turbine Structure

Abstract This study aims to address the question: can the structural reliability of an offshore wind turbine (OWT) under fatigue loading conditions be predicted more consistently? To respond to that question this study addresses the following specific aims: (1) to obtain a systematic approach that takes into consideration the amount of information available for the uncertainty modeling of the model input parameters and (2) to determine the impact of the most sensitive input parameters on the structural reliability of the OWT through a surrogate model. First, a coupled model to determine the fatigue life of the support structure considering the soil-structure interaction under 15 different loading conditions was developed. Second, a sensitivity scheme using two global analyses was developed to consistently establish the most and least important input parameters of the model. Third, systematic uncertainty quantification (UQ) scheme was employed to model the uncertainties of model input parameters based on their available—data-driven and physics-informed—information. Finally, the impact of the proposed UQ framework on the OWT structural reliability was evaluated through the estimation of the probability of failure of the structure based on the fatigue limit state design criterion. The results show high sensitivity for the wind speed and moderate sensitivity for parameters usually considered as deterministic values in design standards. Additionally, it is shown that applying systematic UQ not only produces a more efficient and better approximation of the fatigue life under uncertainty, but also a more accurate estimation of the structural reliability of offshore wind turbine's structure during conceptual design. Consequently, more reliable, and robust estimations of the structural designs for large offshore wind turbines with limited information may be achieved during the early stages of design.

Conjoint influence of environment and load on fatigue life of a bolted aluminum alloy structure

In this paper, an attempt is made to describe the decline in fatigue life of an aluminum alloy structure containing bolted joints under the conjoint influence of an aggressive aqueous environment and loading that is essentially cyclic in nature. In an attempt to project the real situation experienced by an aluminum alloy structure containing bolted joints while in service, an alternate cycle test method was used to essentially include the damage caused by the environment and cyclic loading. A chloride-containing solution was used to simulate the damage caused to the bolted structure upon exposure of the aluminum alloy structure containing a joint to the environment. The nature of fatigue loading was essentially cyclic tension. It was found that following an observable amount of environment-induced damage caused by exposure to a wet–dry environment followed by cyclic loading, the fracture position revealed a noticeable shift from the centerline of the bolt hole to the loading end. This can be attributed to the occurrence of fretting-related damage at the fine microscopic level. Based on an assumption of an average fracture line, a life prediction model was established. Compared with experimental results, the prediction method considering the fracture position to shift from the centerline of the bolt hole does provide results with a reasonably high degree of accuracy. The method proposed in this study does provide a convincing approach for reliable estimation of life, or endurance, of an aluminum alloy structure containing joints.

The Strength and Fatigue Life analysis of Sedan Car Ramp of The Ferry Ro-Ro 5000 GT Using Finite Element Method

The Ferry Ro-Ro 5000GT has three levels of car deck that are connected by internal ramps. Two issues that have to be paid attention during the operation of the internal ramp there are the strength capacity and the design fatigue life of the internal ramp structure. The purpose of the research is to determine the strength and fatigue life of the internal ramp construction. The method used the Finite Element Method using a static load by load case of point load at top girder and between girders. Results of the research detected the maximum stress value is in the load case of the point load (three sedan car) at between of the girder is 52.143 MPa with the fatigue life is 44.47 years with the load cycle is 7300000 cycle while the minimum stress value detected at the load case of the point load (two sedan cars) at top girder is 34.199 MPa with the fatigue life is 195.92 years with the load cycle is 50000000 cycle. For the safety factor, ramp construction 6.08 ~ 10.38. The safety factor value above is still in safe condition because the value is SF > 1.

One damping estimation approach of the parked offshore wind turbine supported by wide-shallow bucket foundation

The damping characteristic has an important influence on reliably predicting the dynamic response and fatigue life of the support structure of an offshore wind turbine (OWT). Generally, the damping sources of an OWT in parked conditions always include hydrodynamic damping, structural damping, and soil damping, ignoring aerodynamic damping. However, the difficulties in identifying the total damping of the OWT have created uncertainty and variation in the value of damping recommended in the design. In this research, an estimation approach for total damping was proposed for an OWT supported by a wide-shallow bucket foundation (WSBF), which is considered a novel bucket foundation, and its damping characteristics are still unclear. The hydrodynamic damping calculated based on Morison's equation of 0.0128% for the OWT supported by WSBF is smaller than the value of the monopile foundation. The soil damping is approximately 0.120%, obtained using the proposed theoretical method. Finally, the computational damping of the OWT in parked conditions was verified by the measured total damping of two parked OWTs at two different offshore wind farms (OWFs) of China. The results show that the damping obtained by these two methods was in good agreement with the average deviation of 11.20%.

Finite element parametric study of the split sleeve cold expansion on residual stresses and pulling force

Split sleeve cold expansion (SSCE) is a crucial cost-effective process to improve the fatigue life of metallic structures with holes in the aerospace industry. In this study, the effects of the workpiece material’s yield strength (290.9 MPa to 377.8 MPa) and the applied SSCE expansion percentage (3.330% to 4.377%) on mandrel pulling force and residual stresses were investigated numerically for aluminum 2024-T351. A three-dimensional finite element (FE) model was developed to simulate the SSCE process using a commercial FE software, ABAQUS. The model geometries, material non-linearities, and contact conditions were adopted according to aerospace industrial applications’ standards. After the numerical model was validated with the published data, a parametric study with variable material properties and expansion percentage was conducted using the FE model. Our parametric study shows that an increase in both the Al workpiece’s yield strength and SSCE expansion percentage can improve the induced residual stresses in the hoop direction around the cold expanded hole; however, the workpiece’s yield strength has a higher impact on the residual stress field. The in-process pulling force during the SSCE process increases with increasing workpiece yield strength and expansion percentage.

Debonding development in cracked steel plates strengthened by CFRP laminates under fatigue loading: Experimental and boundary element method analysis

Carbon fiber reinforced polymer (CFRP) laminates can effectively enhance the fatigue life of steel structures. However, few studies have investigated the influence of crack-induced debonding in the CFRP-steel interface on the CFRP strengthening efficiency and the relationship of crack propagation and debonding development. This study experimentally and numerically – with the boundary element method (BEM) – investigated crack propagation and debonding development in CFRP-strengthened cracked steel (Q345, Q460, and Q690) plates. The fatigue test specimens were subjected to a maximum stress of 50% steel yield stress and a stress ratio of 0.1, during which real-time changes in CFRP strain distribution were recorded by digital image correlation (DIC). The CFRP strain gradient calculations showed that crack-induced debonding was crack length-dependent. The numerical fatigue life results were in good agreement with the experimental data when considering debonding and overestimated the experimental data without considering debonding, demonstrating the necessity of considering crack-induced debonding in calculation and design. Furthermore, a relationship was obtained between crack propagation and debonding development.