Fatigue Life Prediction Research Articles

A Modified Multiaxial Fatigue Model and Its Application for the Fatigue Life Prediction of Aircraft Hydraulic Pipes

The fatigue failure of a structure may occur under a multiaxial vibration environment; it is necessary to establish a better multiaxial fatigue life prediction model to predict the fatigue life of the structure. This study proposes a new model (MWYT) by introducing the maximum absolute shear stress into the WYT model. The feasibility of the MWYT model is verified by using the multiaxial fatigue experimental data of 304 stainless steel, Q235B steel, 7075-T651 aluminum alloy and S355J0 steel. Further, finite element vibration simulations are performed on a typical parallel hydraulic pipe structure, and the vibration simulation results of the pipe structure are verified through the vibration experiment. Finally, the MWYT model is used to predict the fatigue lives of the pipe structure under random excitation and pulsation excitation, respectively, and the fatigue life of the pipe structure under the combined loading from random excitation and pulsation excitation is predicted based on Miner’s rule. By comparing with the design life of the aircraft, the predicted life of the pipe structure meets the service requirements for it.

Crack Propagation and Fatigue Life Analysis of Wind Turbine Blades

This dissertation investigates the fatigue and fracture behaviour of wind turbine blades exposed to varying wind speeds and load intensities, aiming to enhance their durability and operational lifespan in sustainable energy systems. The increasing reliance on wind energy underscores the need for durable blades that can withstand cyclic loads and extreme environmental conditions, as fatigue and fracture failures significantly impact maintenance costs and reliability. This research specifically examines fatigue life and fracture initiation at wind speeds of 15 m/s and 60 m/s, analysing the effects of increased load intensities (30 MPa and 62 MPa). Finite Element Analysis (FEA) through ANSYS is employed to model fatigue and fracture dynamics, incorporating fatigue life prediction using S-N curves, stress analysis with von Mises stress, and crack propagation simulation via fracture mechanics principles, such as Paris’ Law. Results reveal a notable reduction in fatigue life with increased loads, evidenced by a drop from 9e09 to 7.9e08 cycles at 15 m/s, with comparable fatigue cycle reductions at 60 m/s. Fracture analysis identifies critical crack initiation points in high-stress areas, and simulations indicate the progressive nature of crack propagation under cyclic loads. These findings underscore the importance of integrating fatigue and fracture assessments in the design and maintenance strategies of wind turbine blades to enhance resilience and support the sustainable advancement of wind energy systems.

On the prediction of fatigue life of WAAM-processed Ti-6Al-4V under consideration of manufacturing defects

PurposeThere is still a need for a comprehensive investigation into how wire and arc manufactured (WAAM) parts fail under cyclic loading. This study investigates the effect of process-induced defects on the high-cycle fatigue performance of WAAM-processed Ti-6Al-4V with dedicated thermal treatment. Furthermore, the study assesses the applicability of the fatigue life prediction model, which was originally developed and validated for laser beam-welded Ti-6Al-4V joints, to WAAM-fabricated structures.Design/methodology/approachThe fatigue life assessment model was adapted to WAAM-fabricated Ti-6Al-4V. This model is based on the NASGRO equation, which considers short crack growth from internal and surface defects, such as lack of fusion defects and pores. The model was used to create artificial Wöhler curves, and the results from stress intensity factor range-decreasing fatigue crack propagation rate tests are compared to the experimental data in the form of a Kitagawa–Takahashi (KT) diagram.FindingsThe results demonstrate that the model can accurately predict the minimum fatigue life of specimens extracted from WAAM structures. When considering that the crack from internal defects grows in a vacuum-like environment, accurate Wöhler curves are predicted. The experimental data does not follow the expected trends of the KT diagram. Nonetheless, the measured long crack threshold stress intensity factor range produces a suitable estimate of defect severity.Originality/valueThe study results in a model with which a probabilistic computation of the fatigue life of additively manufactured samples based on the defect size distribution is possible. Furthermore, the KT diagram as a criterion for the assessment of defect severity is evaluated.

Design Optimization of a Marine Propeller Shaft for Enhanced Fatigue Life: An Integrated Computational Approach

This study investigates the design and potential failure modes of a marine propeller shaft using computational and analytical methods. The aim is to assess the structural integrity of the existing design and propose modifications for improved reliability and service life. Analytical calculations based on classification society rules determined acceptable shaft diameter ranges, considering torsional shear stress limits for SAE 1030 steel. A Campbell diagram analysis identified potential resonance issues at propeller blade excitation frequencies, leading to a recommended operating speed reduction for a safety margin. Support spacing was determined using both the Ship Vibration Design Guide and an empirical method, with the former yielding more conservative results. Finite element analysis, focusing on the keyway area, revealed stress concentrations approaching the material’s ultimate strength. A mesh sensitivity analysis ensured accurate stress predictions. A round-ended rectangular key geometry modification showed a significant stress reduction. Fatigue life analysis using the Goodman equation, incorporating various factors, predicted infinite life under different loading conditions, but varying safety factors highlighted the impact of these conditions. The FEA revealed that the original keyway design led to stress concentrations exceeding allowable limits, correlating with potential shaft failure. The proposed round-ended rectangular key geometry significantly reduced stress, mitigating the risk of fatigue crack initiation. This research contributes to the development of more reliable marine propulsion systems by demonstrating the efficacy of integrating analytical methods, finite element simulations, and fatigue life predictions in the design process.

Study on the dynamic characteristics of double row self-aligning roller bearings with surface faults

Purpose The aim of this study is to establish the nonlinear dynamics equations of roller bearings with surface faults on outer raceway, inner raceway and rolling elements to analyze the dynamic characteristics of the double row self-aligning roller bearings, and provided theoretical basis for bearing fault diagnosis and life prediction. Design/methodology/approach First, based on the momentum theorem, the formulas for quantitative calculation of impact load were established, when roller was in contact with the fault of the inner or outer raceway. Then, the fault position piecewise functions and the load-carrying zone piecewise functions were established. Based on these, the nonlinear dynamic equations of double row self-aligning roller bearings are established, and Matlab is used to simulate the faulty bearings at different positions, sizes and rotational speeds. Finally, the vibration test of the fault bearings are completed, and the correctness of the nonlinear dynamic equations of the rolling bearing are verified. Findings The simulation and test results show that: the impact load increased with the increasing rotate speed and fault size, and the larger the fault size, the longer the impact load existed and the shorter vice versa. Originality/value The nonlinear dynamic equation of double row self-aligning roller bearings is established, which provides a theoretical basis for bearing faults diagnosis and fatigue life prediction.

Improving Fatigue Life Prediction of Natural Rubber Using a Physics‐Informed Neural Network Model

ABSTRACTTraditional physical models and purely data‐driven approaches often struggle with small sample sizes and the complex effects of strain ratios. To overcome these challenges, this study integrates physical principles with machine learning techniques to improve fatigue life predictions for natural rubber (NR). A uniaxial fatigue test on NR was performed, generating data to construct a physical model. A physics‐informed neural network (PINN) model was subsequently developed, utilizing the fatigue life predicted by the physical model, along with engineering strain amplitude and strain ratio as input variables, whereas the experimentally observed fatigue life served as the output variable. The accuracy of the physical model, a data‐driven model, and the proposed PINN model was evaluated by comparing their predictions against measured fatigue life data. The findings demonstrate that the PINN model significantly enhances prediction accuracy, with its fatigue life estimates consistently falling within 1.5 times the measured values.

Low cycle fatigue properties and life prediction based on plastic work of back stress in a Zr-2.5Nb alloy

Pressure tubes of Zr-2.5Nb alloy in Pressurized Heavy Water Reactors experience low cycle fatigue (LCF) due to cooling water flow and power fluctuations, which could be a factor destroying their structural integrity. Therefore, it is essential to systematically investigate their LCF properties and develop accurate life prediction models. Existing research primarily focuses on single-phase Zr alloys, leaving a gap in understanding the fatigue behavior and microstructural evolution of the dual-phase Zr-2.5Nb alloy. This study addressed these gaps by conducting LCF tests on the Zr-2.5Nb alloy under strain amplitudes ranging from ± 0.50 % to ± 1.5 % at room temperature. The results indicated that the cyclic response can be divided into three stages (Ⅰ, Ⅱ, Ⅲ) based on the relative number of cycles. Cyclic softening/hardening originated from microstructural changes such as dislocation sub-structure, grain rotation, and texture evolution. A novel fatigue life prediction model was proposed based on the plastic work of back stress. For non-Masing materials, this model overcame the limitations of traditional plastic strain energy models and demonstrated higher prediction accuracy. This work contributes to a more accurate prediction of fatigue life in Zr alloys and provides new insights into their fatigue behavior and microstructure evolution under LCF conditions.

Efficient and accurate determination of crack propagation rate without unloading-induced crack closure

The accurate delineation of the fatigue crack growth rate (da/dN) model, encompassing the short crack stage, assumes paramount importance in the operation and maintenance of transportation vehicles such as aircraft. Nonetheless, the determination of the da/dN encounters challenges, notably crack closure engendered by unloading observations on the specimen and the attendant issue of exorbitant test expenditures due to low load amplitude (ΔP), thereby impeding the precise establishment of the da/dN model, particularly in the short crack stage. Hence, this study initially posits a novel crack observation methodology employing a self-engineered stress transfer apparatus to sustain the stress (σ) on the specimen at its closure stress (σcl) level post-unloading, thus mitigating the impact of crack closure on crack observation and augmenting the accuracy of da/dN curve determination. Subsequently, building upon this innovation, a fatigue crack propagation (FCP) test protocol tailored for the short crack stage is advanced, principally by substantially augmenting ΔP to surmount the cost constraints of the test, thereby broadening the scope of da/dN curve determination to 10−8 mm/cycle. Lastly, premised on the acquisition of high precision and comprehensive da/dN curves, a da/dN model is posited by integrating with the extant da/dN model, which can comprehensively and precisely delineate the FCP behavior across the entire crack growth spectrum, particularly in the short crack stage. Illustratively demonstrated through a case study on 42CrMo steel crankshaft, a fatigue life (Nf) prediction investigation conducted based on this da/dN model substantiates its efficacy in accurately assessing the FCP behavior of crankshaft materials vis-à-vis existing models, thereby reducing the Nf prediction error by 14.64 %.

Fatigue fracture mechanism and life prediction of two Al-Si-Mg alloys used in catenary cantilever system

Fatigue fracture mechanism and life prediction of two Al-Si-Mg alloys used in catenary cantilever system

Study on stress concentration and fatigue life of tubing with slip indentation

The indentation caused by slip on the outer wall of tubing is a significant contributor to stress concentration and, consequently, fatigue failure in the tubing string. Through an analysis of the interaction between slips and tubing, a mathematical model to predict slip-tubing interaction and slip crushing load is formulated, accounting for external pressure, internal pressure, and axial forces. On this basis, the influence factors and influence rules of slip crushing load are studied, and three-dimensional yield surface and tri-axial stress ellipse of tubing are investigated, considering different transverse load factors and design factors. To accurately forecast the fatigue life of tubing subjected to slip indentation, two models are established: one for fatigue life prediction and the other for tubing string vibration. In order to quantitatively assess the stress concentration arising from slip indentation, a finite element model of tubing featuring slip indentation is established. Finite element analysis reveals that stress concentration and non-uniformity are evident in the vicinity of slip indentation, with their severity intensifying as the indentation depth grows. The initial step in assessing fatigue life involves fatigue life tests on tubing material subjected to varying stress levels. Subsequently, a case study is conducted and the variations of wellhead pressure and axial stress are evaluated. Fatigue life analysis reveals that the fatigue life is notably sensitive to variations in stress amplitude and slip indentation depth. An increase in the magnitude of alternating stress and the depth of slip indentation will result in a significant reduction in the fatigue lifespan. The methodologies employed in this research, along with the resulting findings, offer a robust theoretical framework and a solid practical basis for forecasting and managing stress concentration and fatigue durability in tubing affected by slip indentation.

Three-point bending fatigue life prediction of TC4 titanium weld joints based on tungsten inclusion defects

Three-point bending fatigue life prediction of TC4 titanium weld joints based on tungsten inclusion defects

Investigation of indoor and field tests on asphalt pavement with inverted asphalt layers based on the vertical vibration compaction method

An inverted asphalt pavement is created by reversing the sequence of the lower and middle layers in a conventional asphalt pavement. The lower layer is composed of material with larger particle size and lower asphalt content, which improves its ability to withstand deformation caused by rutting. On the other hand, the middle surface has a higher asphalt content, specifically designed to resist fatigue cracking. This paper examines the mechanical response of two pavement structures and investigates the potential of two measures, inverted asphalt pavement and asphalt mixture design by vertical vibration compaction method (VVCM), in reducing stresses and stress levels in asphalt pavements. Additionally, a large thickness rutting and fatigue test method was developed to study the rutting resistance and fatigue life of the pavement structures, and to construct rutting deformation and fatigue life prediction models. Finally, test sections were paved to verify the feasibility of the inverted pavement and VVCM materials. The findings show that inverted pavement and VVCM materials have a minimal impact on pavement stress, but can reduce pavement shear and tensile stress levels by up to 18% to 25%. Furthermore, inverted pavement and VVCM materials have positive effects on improving the rutting resistance and fatigue life of asphalt pavements.

Vibration fatigue of film cooling hole structure of Ni-based single crystal turbine blade: Failure behavior and life prediction

The vibration fatigue failure behavior and fatigue life of the film cooling hole (FCH) structure of Ni-based single crystal superalloy were investigated at high temperature. The vibration fatigue test of the FCH specimens were carried out based on the paired staircase method. The cracks are mostly initiated in the stress concentration area at the edge of the FCH, and may also be initiated in non-stress concentrated areas with large defects. At high temperature, the crack initiation mechanism of the FCH specimens of Ni-based single crystal superalloy is oxidative cracking nucleation in stress concentration area, and the crack propagation mechanism is the competition mechanism of dislocation slip and dislocation climbing. Based on the Fatigue Indicator Parameter (FIP) of the critical plane method, a vibration fatigue life prediction model for FCH structures considering stress concentration and high temperature oxidation damage is proposed. The life prediction model proposed in this paper is applied to the vibration fatigue life prediction of FCH specimens. The deviation between the predicted results and the experimental results is within 2.5 times at 850℃, and the deviation is within 2 times at 980℃. Besides, the life prediction method proposed is compared with other two FIP life prediction methods, and the high accuracy and effectiveness of the proposed life prediction method are verified.

A unified strain energy-based fatigue life prediction methodology for composite and metal adhesive joints: Effects of adhesive, geometry and, environment

Ensuring the efficiency and safety of bonded structures across diverse engineering sectors requires a robust fatigue model for adhesive joints in both composite and metal substrates. This study presents a unified fatigue life prediction methodology for similar and dissimilar composite and metal adhesive joints. The proposed model integrates hydrostatic and deviatoric strain energy density components with the theory of critical distances. The model has been validated against diverse experimental data from different joint geometries, loading conditions, and different environments. The linear-elastic assumption is sufficient for toughened epoxies, whereas an elastoplastic model is necessary for ductile methacrylate adhesives. Calibration based on a single fatigue test yields the highest accuracy, while quasi-static test calibration is also satisfactory. The methodology addresses diverse loading conditions and environmental factors, showing a strong correlation with experimental results. It advances the performance, design, and reliability of similar and dissimilar composite to metal adhesive joints.

Improving safety by fatigue life assessment of pressure hull considering corrosion factors: a review

Abstract Research on determining fatigue endurance of submarine pressure-resistant hulls is crucial for determining their remaining operational lifespan. These studies typically focus on the effects of hydrostatic pressure on fatigue under ideal conditions without taking into account other significant factors. However, the actual condition of pressure hulls is influenced by multiple elements, one of which is operational environmental factors such as corrosion. While current research has examined these factors individually, there is a notable absence of a comprehensive analysis that integrates all of them. Corrosion can reduce structural strength due to the resulting plate thinning effect caused by hydrostatic pressure and low cyclic fatigue. This oversight hampers the development of accurate models for predicting fatigue life and compromises the safety and reliability of underwater structures. This paper addresses the research gap by emphasizing corrosion factors in fatigue life assessments using the low-cyclic fatigue method. By incorporating these elements into the assessment methodology, a more comprehensive understanding of pressure hull fatigue can be achieved, leading to more accurate predictions of pressure hull remaining lifespan.

Microstructure evolution and fatigue crack initiation life prediction of actual failed bearings under GRCF conditions

During the operation of bearings under alternating stress, contact fatigue failure often occurs, primarily due to non-metallic inclusions in bearing steel (GCr15). Based on actual fatigue-failed bearings, this study used Aspex scanning electron microscopy to analyze the inclusion distribution in bearing steels produced by two processes: electroslag remelting and vacuum refining. FIB-TEM technology was employed to characterize the microstructural evolution characteristics at the fatigue failure source area. Finally, considering the depth, area, and matrix hardness of the inclusions, a fatigue life prediction model based on gigacycle rolling contact fatigue (GRCF) was proposed. The prediction results closely matched the fatigue data of actual failed bearings.

Research Progress on Fatigue of Carbon Fiber Composite Materials and Their Bolted Connection Structures

This paper primarily investigates the fatigue performance of carbon fiber composites and their bolted joint structures. Carbon fiber composites have gained increasing attention due to their high strength, lightweight properties, and corrosion resistance. However, technical challenges remain regarding the fatigue characteristics of carbon fiber composites and the durability of their joint structures in practical applications. This paper reviews the research progress on fatigue performance testing of carbon fiber composites at home and abroad, focusing on failure mechanisms under cyclic loading, fatigue life prediction methods, and key influencing factors. Additionally, the paper discusses the current research status of bolted joint structures in carbon fiber composites, analyzing the impact of different joint methods on structural fatigue performance, as well as existing experimental and simulation research methods.

Fatigue life prediction of selective laser melted titanium alloy based on a machine learning approach

A machine learning (ML) approach is introduced to predict the high-cycle fatigue (HCF) life of selective laser melted (SLM) TA15 titanium alloy, addressing life prediction variability caused by defect characteristics and spatial distribution. Using HCF data, tensile properties, and defect characteristics across different building directions (BD), a training dataset was established. Comparative analysis shows that incorporating defect parameters significantly enhances the prediction accuracy of the ML model. Correlation analysis identified Adefect/h as highly relevant to fatigue life, enabling a refined training dataset. Incorporating this defect parameter significantly improved the ML model’s prediction accuracy. The S-N curve generated from predictions using defect values at 50 % reliability appeared relatively conservative compared to the experimental S-N median curve. The S-N curve at ± 3σ reliability closely aligned with experimental results, encompassing nearly all data points. This highlights the potential of the ML approach in predicting fatigue life for SLM titanium alloys.

Fatigue life prediction of hybrid carbon-flax-epoxy laminates using progressive failure analysis and cohesive zone model

A 3D progressive fatigue damage model was incorporated into ABAQUS software to predict the fatigue life of hybrid carbon-flax-epoxy composites. A cohesive zone method was employed to simulate delamination damage at carbon/flax interface. To evaluate the accuracy of the finite element model, two different layups, namely, unidirectional [0–90C2/0 F6]S (UD) and angle-ply [0–90C2/(±45) F6]S (AP), consisting of 12 flax fibers layers (F) sandwiched between four woven carbon fibers layers (C) were created using hand lay-up technique and then placed in compression molding. There is a good agreement between experimental and predicted fatigue life. It was observed that the predicted fatigue life is reduced by about 14% by changing the void content from 0.38% to 3.83%. The finite element analysis revealed that the matrix in the flax region of the AP layup failed at 12% of fatigue life, followed by delamination at the carbon/flax interface, consistent with SEM results.

Study on Structure Optimization and Vibration Fatigue Analysis of Aluminum and Composite Brake Control Boxes

ABSTRACTThe brake control box beneath an EMU is exposed to dynamic and fluctuating load cases, increasing its susceptibility to vibration fatigue failure. A novel lightweight design approach was implemented to integrate structural and material optimizations. Static and fatigue tests of the T700/5429 CFRP were carried out to augment the stress analysis and predictions of the vibration fatigue life. The local stresses perpendicular and parallel to the welds were obtained to calculate the stress ratio, stress range, and allowable stress value corresponding to the stress component. The fatigue strength of the aluminum box was estimated on the basis of multiaxial criteria, and the fatigue life of the two boxes was predicted with Dirlik's theory. These computational findings unequivocally indicated a noteworthy reduction in damage to the composite box subsequent to lightweight modification, thereby successfully satisfying both the stiffness and strength criteria essential for the safety and reliability of the EMU.