High Cyclic Loading Research Articles

Application of an Equivalent Temperature Field for Emulating Thermal Autofrettage-Induced Residual Stresses in Thick-Walled Cylinder

Abstract The equivalent temperature field of residual stresses induced by autofrettage of thick-walled cylinders and spheres have been successfully implemented in a finite element method framework to study the crack growth in autofrettaged components. Thermal autofrettage is a potential alternative method for strengthening hollow cylinders against internal pressurization. The assessment of service life of thermally autofrettaged cylinders containing cracks is imperative when they are subjected to high pressure static or cyclic in-service loading. There the equivalent temperature field replicating the thermal autofrettage-induced residual stresses will serve as the input to the finite element method analysis to evaluate the important fracture parameters such as static fracture endurance and the rate of crack growth for predicting service life. This work presents evaluation of an equivalent temperature field by establishing an equivalence between the thermoelastic stress field and thermal autofrettage-induced residual stress field in a cylinder obtained from either an analytical or a numerical model. The evaluated equivalent temperature field is then used in a finite element method analysis to exemplify the replication of the original residual stresses generated by thermal autofrettage in SS304, aluminum cylinders and electroslag refined (ESR) steel gun barrel. It is found that the finite element stress solution due to the application of equivalent temperature field and the original analytical or numerical thermal autofrettage residual stress solution are in good agreement with less than 5% deviation in the case of SS304 and aluminum cylinders, and that in ESR steel barrel with less than 1% deviation.

Systematic Molecular Influenza A/B Screening Upon Hospital Admission in Belgium, January-April 2022: Positivity Ratios and Viral Loads According to Symptomatology, Age, and Vaccination Status.

Three hospitals implemented molecular point-of-care tests (POCTs) to screen patients for SARS-CoV-2 infection upon admission during the 2021/2022 influenza season, which in Belgium lasted from January to April 2022. The samples were simultaneously tested for influenza A/B. Influenza positivity at admission was examined in relation to patient characteristics and symptomatology. Influenza POCTs were performed on all patients requiring urgent hospitalization, regardless of the admission reason. A total of 9327 patients were included in the study, of which 411 (4.4%) tested positive for influenza A/B. Asymptomatic infection and mild illness accounted for respectively 11.2% (95% CI: 8.5%-14.6%), and 43.3% (95% CI: 38.6%-48.1%) of the cases. A total of 66% (95% CI: 60%-72%) of all patients in these symptom categories (asymptomatic and mild illness) showed a high viral load (cycle threshold [Ct] < 24). Only in 30 (7.3%, 95% CI: 5.2%-10.2%) of all cases and in two (4.4%, 95% CI: 1.2%-14.5%) of the asymptomatic cases, the symptomatology worsened during hospital stay. Coinfections with both influenza and SARS-CoV-2 occurred in 35 patients (8.5% of all influenza positive patients). There was no difference in symptomatology between patients with co-infections and those with an influenza mono-infection. Patients could not be reliably categorized into carriers with low versus high viral loads based on symptomatology, age, and vaccination status. More than half of the influenza-positive individuals were either asymptomatic or had mild symptoms upon admission, while often carrying high viral loads. Our results show that without screening of patients at hospital admission, a considerable number of patients with a high viral load may be incorrectly classified as being not infectious.

Prevention of the Fracture Problem Occurring in Automotive Alternator Heatsink Blocks Using Artificial Intelligence

In this study, prevention of fracture in vibration fatigue testing of automotive alternator heatsink blocks was investigated using an artificial neural network. Automotive components such as alternator heatsink blocks are subjected to high cyclic vibration fatigue loads throughout their lifespan, which can lead to the formation and propagation of fatigue cracks and ultimately component failure. The basic parameters affecting the resonant frequency of the heatsink blocks, including geometry and loading conditions, are determined. Data-driven decision making provides advanced predictive insights to analyze data for prediction and decisions using artificial intelligence approaches. An efficient artificial neural network model was defined to predict the resonance frequency in the vibration fatigue test. While the artificial neural network was trained to establish a functional relationship between the parameters and the resonance frequency, regression analysis was used to develop a predictive model to detect the resonance frequency of the heatsinks. The proposed approach aims to provide a comprehensive framework for preventing fracture problems in vibration fatigue tests of automotive alternator heatsinks and ultimately contribute to the reliable design and performance of these critical components. While the artificial neural network approach achieved high classification accuracy in predicting the new natural frequency, the regression model was also able to make accurate predictions. The results of this study showed that the time spent on design and simulation can be significantly reduced in preventing breakage problems that may occur before dynamic tests such as vibration tests of alternator components.

Modeling and Analysis of Current Loading Effects on Electric Vehicle’s Lithium-Ion Batteries: A MATLAB-Based Model Approach

Beyond portable mobile devices, lithium-ion batteries play a crucial role in electric vehicle operations and stationary grid power generation. However, the aging of lithium-ion batteries, often accelerated by extreme temperatures and load current influences, requires thorough examination and solution. The high load current, cycling, temperature differential, and operational conditions are factors contributing to the reduction in capacity and shortened lifespan of lithium-ion batteries. In this study, a lithium-ion (LiNixMnyCozO2) battery was modeled by using the MATLAB/Simulink model technique. In order to investigate the effect of resistance build-up in the batteries, the capacity of the batteries (old and new batteries) was analyzed over different usage periods: 360 cycles, 1000 cycles, and 2000 cycles. A cooling system was introduced to explicitly carry out an inductive analysis of the effect of temperature on the performances of the batteries. The effect of load current on the capacity of the battery was examined between 30 A and 100 A. The results showed that the available capacity of a battery is proportional to its usage rate. Generally, when the load current on the batteries (old and new batteries) was 30 A, the battery was ideally in good health even after 1000 cycles for a 2 h discharge time. In addition, the old battery, however, showed a capacity decrease to about 74.15% and 74.94% for scenarios 1 and 2 after 1000 cycles for a 2 h discharge time when the batteries were subjected to a 100 A discharge current. Amongst other factors, scenarios 1 and 2 can be differentiated by whether the battery pack discharges uniformly or non-uniformly, whether the individual cells operate under the same or different discharge cycles, and whether the batteries are with cooling or without a cooling system. The voltage and temperature differences between the old and new batteries, after 2000 cycles for the 100 A load current, are 4.0 V and 5.3 °C (scenario 2), respectively. Moreover, after 360 cycles at a 100 A discharge current, the temperature difference between the old and new batteries was 4.5 °C in scenario 1 and 2.3 °C in scenario 2. Based on the results obtained in this study, useful equations for proper calibration, voltage, and cooling switching time characteristics were proposed. Additionally, the study results indicated that at higher load currents, battery degradation became less affected by temperature differentials. The results of this study will aid in the adequate load optimization and thermal management of lithium-ion batteries for electric vehicle applications.

A new control strategy of direct exergy balance for coal-fired power plants: Fundamentals and performance evaluation

In order to facilitate the increasing penetration of grid-connected renewable power, coal-fired power plants should operate more and more flexibly. Most of the-state-of-the-art control strategies, which are mainly based on the idea of direct energy balance, cannot perform well when coal-fired power plants change load with high load cycling ramp rate. To enhance the operational flexibility of coal-fired power plants, the control idea of the direct exergy balance is proposed in this study, which directly characterizes the work capacity balance between the boiler and the steam turbine. The new control strategy of direct exergy balance emphasizes the feedback of the deviation between the turbine exergy demand signal and the boiler exergy signal. Dynamic models of a reference power plant were developed and validated, and performances of control strategies based on direct energy balance and direct exergy balance were evaluated and compared. In the 50 %–75 % load cycling process of the reference power plant, the control strategy of direct exergy balance demonstrated markedly improvements in the load cycling ramp rate (29.2 % relatively), the load cycling comprehensive index Kp (39.4 %), and reduction in the maximum deviations (28.2 %), overshoots (59.8 %), and cumulative deviations (28.7 %) of the key thermal parameters. In conclusion, the control strategy of direct exergy balance significantly strengthens the control performance during rapid load cycling processes and attains a notable enhancement in operational flexibility and a slight improvement in energy efficiency of coal-fired power plant.

An accelerated corrosion-fatigue testing method for marine high-strength steel based on equivalence principle of fatigue crack growth

The corrosion-fatigue test is widely used to assess marine equipment. However, due to the low-frequency and high-cycle loading of marine equipment in service, conventional test methods require long cycle times and high costs. This makes it challenging to meet the rapid evaluation demands associated with equipment development effectively. In this study, an accelerated corrosion test method was proposed for steel by adjusting the composition, temperature, pH and H2O2 concentration of environment. Fatigue crack growth tests were conducted under various corrosion environments and load frequencies. The matching relationships between corrosion fatigue acceleration multiplier, corrosion environment parameters and load parameters were established. Additionally, a corrosion fatigue acceleration test method was proposed based on the equivalent principle of fatigue crack growth. The results show that effective coupling between corrosion and fatigue can be achieved by gradually reducing the load frequency as the stress intensity factor amplitude increases throughout the crack growth process. It is consistent with the trend of fatigue crack growth rate in the seawater environment. The 4.85% fatigue life deviation and the 15.68 times corrosion fatigue acceleration can be achieved by our method. This work improves the accuracy and reliability of fatigue performance evaluation for offshore equipment.

Achieving superior aluminum-steel dissimilar joining via ultrasonic spot welding: Microstructure and fracture behavior

High-strength dissimilar welded joints of AA2024-T3 alloy with an AA1230 coating and galvanized high-strength low-alloy (HSLA) steel were attained through ultrasonic spot welding (USW) in this study. The tensile lap shear failure loads over a welding energy range between 2000 J and 3000 J were observed to meet or surpass the values specified in the AWS D17.2 standard. The highest average tensile lap shear strength was obtained to be ∼169 MPa due to the formation of a ∼30–70 μm thick Al-Zn diffusion layer without the presence of intermetallic compounds. The substrate failure from the softer AA1230 coating on the AA2024 side under tensile loading and cyclic loading at higher cyclic loads was observed, which reflected a robust sticking capability. The partial failure from AA1230 coating consisted of characteristic shear dimples, allowing high plasticity upon shear deformation. While the 1000 J welds failed mainly via substrate failure from AA1230 and transverse through-thickness (TTT) cracking in AA2024, the cohesive failure across the Al-Zn diffusion layer and adhesive failure from the Al-Fe-intermetallic/Al-Zn-diffusion layer interface were observed in the welds made at 3000 J, corresponding to the superior bonding strength and longer fatigue life.

AN AERODYNAMIC INVESTIGATION OF A HIGH-PRESSURE TURBINE USING ROTOR CASING STATIC PRESSURE MEASUREMENTS AT ENGINE REPRESENTATIVE CONDITIONS WITH DIFFERENT TIP DESIGNS, TIP GAPS AND INLET TEMPERATURE PROFILES

Abstract A rotating High-Pressure (HP) turbine, in modern aircraft engines, is subjected to high cyclic thermal and mechanical loads. Shroudless turbines experience high heat loads on the rotor tip and casing, which makes them one of the life-limiting components for an engine. If the rotor tip starts to erode, then the tip clearance increases which increases the over-tip leakage flow, resulting in reduced stage efficiency and ultimately, the engine lifetime. The Oxford Turbine Research Facility (OTRF) is a high- speed rotating transient test facility that allows unsteady aerodynamics and heat transfer measurements, at engine representative conditions. This paper presents an experimental investigation, of the HP turbine rotor casing aerodynamics, performed in the OTRF. Steady and unsteady casing static pressure measurements were acquired, using pneumatic lines and high-frequency response (∼ 100 kHz) Kulite pressure transducers respectively. The single-stage HP turbine consisted of cooled vanes (featuring film and trailing edge slot cooling), and uncooled rotor blades. Three different tip designs (two squealers and one flat) were tested, at two tip gaps, and with two inlet temperature profiles that included a spatially uniform total temperature profile and an engine representative HP turbine inlet total temperature profile. In parallel, a numerical investigation of the experimental test cases is presented using unsteady Computational Fluid Dynamics (CFD) predictions. The experimental results from this study provide a unique dataset to validate numerical models.

Research on CO2 capture performance and reaction mechanism using a novel low energy consumption and high cyclic performance absorbent for onboard application

High desorption energy consumption and low cyclic loading are critical issues limiting the application of onboard carbon capture (OCC) systems. In this study, a tetraethylenepentamine (TEPA) and 2–amino–2–methyl–1–propanol (AMP) mixed amine solvent with low desorption energy consumption and high CO2 cyclic loading, suitable for the operational environment of OCC systems, has been proposed. Detailed research was conducted on the capture performance and mechanism of the TEPA + AMP mixed amine solvent. The 0.25M TEPA+0.75M AMP mixed amine solvent exhibited the best performance, with an 86.5% increase in CO2 loading, a 214% increase in single–cycle CO2 loading, a 236% increase in CO2 loading after four cycles compared to monoethanolamine (MEA), and a 20.76% reduction in desorption energy consumption. In addition, to address the challenge of applying polyamine mixed solutions in the simulation studies of OCC systems, the capture mechanism was analyzed using density functional theory (DFT) calculations and nuclear magnetic resonance (NMR) characterization. The results indicated that increasing AMP promoted HCO3− formation in the TEPA + AMP mixed amine solvent. Since HCO3− decomposed more easily than carbamate, it reduced desorption energy consumption. However, an excess of AMP inhibited the absorption rate of TEPA, affecting the absorption capacity. Increasing the concentration of TEPA enhanced the amine concentration in the absorbent and improved the absorption performance. Nevertheless, excessive TEPA caused AMP to participate only in deprotonation reactions, which was not conducive to reducing desorption energy consumption.

Assessment of Power Equipment Operational Safety in the Sustainable Management of Residual Lifespan

Introduction. Ensuring the safe operation of energy facilities is a critical issue at all life cycle stages. It is associated with the adoption of management decisions when rescheduling and assessing the remaining resources, which are made based on a comprehensive assessment of the technical condition of the equipment, taking into account the economic efficiency and environmental requirements for further operation, which is the basis for technical and economic assessments. Aim and tasks. This study aims to develop a technical and economic assessment of the safe operation of power equipment to ensure sustainable management of the remaining service lifespan. Results. An algorithm for assessing pipeline system elements by the coolant environment is proposed, which allows for the pipeline load and changes in erosion and corrosion caused by coolant movement. It was proposed that the equipment be systematised by safety class and coolant. When conducting a technical and economic assessment, these parameters and the costs of extending the service life and upgrading the existing equipment were considered in the standard calculations of a certain type of equipment. For this purpose, mathematical models for calculating the residual life for each type, obtained and confirmed based on empirical studies, are proposed. Research findings into ensuring the reliability and safety of operation with various heat carriers have shown that it is necessary to consider low-cycle and high-cycle loads and erosion processes. It was found that the erosive wear rate is 0.3-0.4 mm/year for bending sections of the main circulation pipeline, where maximum loads occur relative to low-cycle and vibration loads, and the stress is 212.5 MPa when assessing the residual life of 7 years. Conclusions. The cost-effectiveness of reassigning the service life is reasonable, as it does not require additional investment in upgrading or replacing equipment subject to annual technical diagnostics. The systematisation of pipelines, improved codifiers, lifespan assessment models, and algorithms for evaluating the remaining life under various loadings enhance the regulatory framework for safe nuclear power plant operations and support technical and economic evaluations for extending their lifespan.

Structural design and experimental verification of a thin-walled plastic chairs based on the finite element method

This study focuses on the design and preparation of a thin-walled plastic chair, and its mechanical properties were investigated by high load, cyclic load and drop impact. The finite element method (FEM) was employed to accurately evaluate the chair’s safety under these forces. Additionally, the effects of important structural parameters on the loading process in different states were investigated. Furthermore, a solid plastic chair prototype was created for experimental analysis. The findings revealed that increasing the thickness of the key structural parameters enhanced the safety properties of the chair under various load conditions. Optimal results were obtained when both dimensions were set to 5 mm. The deformation errors in FEM, experimental strength analysis, fatigue analysis, and drop impact analysis were measured at 3.7%, 3.6%, and 11.7%, respectively. Similarly, the stress errors were determined to be 5.9%, 5.2%, and 6.5%. These results suggest that the structural design of the chair demonstrates excellent reliability. Studying the crucial structural parameters of a plastic chair can provide valuable insights for the scientific design and safety evaluation of thin-walled furniture.

Modeling of Shakedown Accumulation of Secondary Deformation of Granular Soils Subjected to Low-Amplitude High-Cycle Loading

Modeling of Shakedown Accumulation of Secondary Deformation of Granular Soils Subjected to Low-Amplitude High-Cycle Loading

Fatigue prediction and optimization of laser peened turbine blade using artificial neural networks and ANFIS

AbstractThis paper investigates the fatigue behavior prediction of Ti‐6Al‐4V thin‐leading‐edge turbine blade specimens treated with laser shock peening (LSP) using two advanced artificial intelligence (AI) methods: artificial neural networks (ANNs) and adaptive network‐based fuzzy inference system (ANFIS). The study aims to estimate the endurance under high cycle loading conditions. First, using ABAQUS and MATLAB software, the modified Crossland criterion for uniaxial loading is applied to recalibrate endurance limit values based on modifications induced by the LSP process. Then, these techniques are employed to predict the modified Crossland criterion profile and endurance limit values influenced by the LSP treatment. Specifically, numerical values are used as training and testing data for these AI models. As a result, these AI methods provide highly accurate prediction and optimization of the modified Crossland criterion and endurance limits, demonstrating their reliability and effectiveness.

Conceptual design of coolant circuits and thermal stress analysis for JA-DEMO divertor

Engineering design of the JA-DEMO divertor concept, i.e. double-coolant circuits of 200°C coolant (5MPa) for high heat load targets (CuCrZr-pipe) and 290°C coolant (15MPa) for high neutron load Plasma Facing Units (F82H-pipe) and cassette body (CB), has been developed. Computational fluid dynamics (CFD) calculation of the coolant distributions to targets, baffles, reflectors, dome and to CB was performed in order to determine the feasibility of the key concepts. (i) All PFU support designs for the coolant distribution to PFUs were optimized to reduce variation of the flow velocity (Vcool) at the inlet of PFUs less than 5 – 6 %. Parallel coolant circuit design for the dome and reflectors was also developed, and mass flows were adjusted by orifices and the main mass flow rate. (ii) A new cooling concept with two layers of puddles and fins at the side routes was proposed for CB. The design provided Vcool = 0.55 – 1.27 m⋅s−1 and average Vcool = 1.04 m⋅s−1 with the fin transparent ratio of 0.1. It was enough to exhaust the nuclear heat, and the design issues were identified under the coolant condition. (iii) Heat exhaust on fish-scale surface target and stress-strain of the CuCrZr pipe were investigated under assuming a DEMO divertor condition. Steady-state heat load at wet region by plasma (qtwet) was restricted below 13.5 MWm−2 to avoid W-recrystallization. In the stress-strain cycle of higher qtwet ∼15.3 MWm−2, maximum tensile σ (120 – 200 MPa) and total change in strain during the heat load cycle (Δε ∼0.25 %) were relatively small. These evaluations suggested that such high heat load cycle may not be a critical lifetime issue, but reduction in Tcool is preferable to handle ITER-like slow transients such as 15 – 20 MWm−2.

Analysis of the destruction of a die insert used in the industrial process of hot die forging to produce a yoke forging

The article performs an analysis of the destruction of forging dies (with two impressions for a double system) used in the industrial process of forging on a hydraulic hammer to produce a yoke forging with a complex geometry. A detailed analysis was performer on one of the lower dies made of non-standard hot chromium-molybdenum-vanadium tool steel, selected for the tests due to its premature damage (a crack) and relatively low durability equalling only 1200 forgings, that is 600 forged elements. Based on the performed complex studies (surface scanning, microhardness tests, microscopic tests, numerical modelling, impact strength trials) it was demonstrated that the most dangerous destruction mechanism for the analyzed process is mechanical cracking and thermo-mechanical fatigue. As a result of the tool working under extreme conditions (high cyclic mechanical impact loads as well as thermal loads), the most intensive damage of the roughing pass, caused by thermal fatigue and abrasive wear, takes place in the areas of complex geometry as well as intensive flow of the forging material on the radii of the roundings. In turn, in the case of the finishing pass, we observe mechanical fatigue cracking of the tool in the areas of stress and high pressure concentration. The results of FEM modelling combined with the results of a microstructural analysis made it possible to determine the causes of the formation of cracks in the working area of the die, which included cyclic high thermal and mechanical loads as well as abrasive wear as a result of intensive flow of the forging material. Within the conducted studies, directions of further investigations were also proposed in order to improve the durability of the examined tool. Additionally, the observed high tendency of the tool material to crack, based on thermal expansion and impact tests and the determination of the crack resistance coefficient K1C, led to the proposal of an alternative material with higher impact strength.

Fatigue life prediction of metal materials under random loads based on load spectrum extrapolation

The impact of random loading on the fatigue life of mechanical components contains numerous uncertainties. This study aims to enhance the precision of life prediction by developing mean and amplitude distribution models based on the road load spectrum and extrapolating the operational load beyond the threshold value in the time domain. Additionally, it considers the influence of high cycle fatigue (HCF) and low cycle fatigue (LCF) loads on the initiation life of metal cracks. To address this, a load correction factor is introduced, and critical stresses for high and low cycle loads are proposed. Furthermore, a two-dimensional programmed load spectrum is prepared, taking into account the mean and amplitude. The accuracy and rationality of the fatigue life model are validated through examples using 45# steel and 316L, while experiments on engine support are conducted to confirm the effectiveness and accuracy of the over-threshold extrapolation life prediction method under random loading.

Acoustic emission and fracture characteristics of red sandstone after high-temperature treatment

This paper investigated red sandstone’s acoustic emission (AE) and fracture characteristics under high temperature and cyclic load. The specimen’s behavior throughout the process from stabilization to failure was systematically analyzed in terms of the distribution of AE activities, rupture scale, crack type, crack evolution, and failure mode. A crack classification model based on K-medoids and support vector machine (SVM) algorithms was proposed, and the optimal dividing line for tensile-shear cracks at different temperatures was determined as AF=0.335×RA+76.890. The specimen’s failure precursor information was recognized based on the critical slowing down theory.

Failure analysis of stainless steel metal hose used for welding

While using ammonia (NH3) gas at 10 bar/500℃, a stainless steel 304 metal hose used as a bellow expansion joint was fractured. It was observed that the fracture of the metal hose started near the weld between the hose and the flange, and progressed to approximately 1/4 of the circumference of the weld.No metallurgical defects were found in the weld where the crack occurred. However, the folded part of the metal hose is welded to the flange, which can cause cracks. In other words, when the metal hose is forcibly compressed or stretched in order to weld it to the flange, the stress concentration due to cold work, including residual stress cause the metal hose to become brittle or crack. It is determined that when a high strain cyclic load or torsional deformation is applied to a high-hardness metal component, the metal hose will reach fatigue failure in a short period of time.

Challenges and Solutions to Meet the Euro 7 NOx Emission Requirements for Diesel Light-Duty Commercial Vehicles

The improvement of air quality requires a further reduction of pollutant emissions, especially in urban areas. The Euro 7 regulations aim at the development of a new generation of internal combustion engine vehicles capable of achieving ultra-low pollutant emissions under demanding, real-world operating conditions. They introduce new technical challenges in the holistic design of a vehicle’s powertrain and emission control system. To identify these, four real-world Euro 7 driving scenarios are investigated, covering demanding urban, highway and mountain driving situations. Technical solutions are then presented to address these challenges and ensure compliance with the Euro 7 emission requirements as set out in the latest regulation proposal of the European Commission. The study focuses on the NOx emissions of an N1 Class III light commercial vehicle with 3.5 t mass and a P2 diesel mild-hybrid powertrain. To ensure emission compliance, a Euro 6e exhaust gas aftertreatment system with enlarged catalysts is combined with NOx raw emission improvements. For low-load cold starts, a 4-kW electric heater in the exhaust system is considered in addition to a 2-l DOC and a 6-l DPF with SCR coating. For high-load cycles with high raw emissions, a 10-l underfloor SCR is considered to ensure the necessary deNOx performance.

Strain Virtual Sensing Applied to Industrial Presses for Fatigue Monitoring.

The techniques that allow one to estimate measurements at the unsensed points of a system are known as virtual sensing. These techniques are useful for the implementation of condition monitoring systems in industrial equipment subjected to high cyclic loads that can cause fatigue damage, such as industrial presses. In this article, three different virtual sensing algorithms for strain estimation are tested using real measurement data obtained from a scaled bed press prototype: two deterministic algorithms (Direct Strain Observer and Least-Squares Strain Estimation) and one stochastic algorithm (Static Strain Kalman Filter). The prototype is subjected to cyclic loads using a hydraulic fatigue testing machine and is sensorized with strain gauges. Results show that sufficiently accurate strain estimations can be obtained using virtual sensing algorithms and a reduced number of strain gauges as input sensors when the monitored structure is subjected to static and quasi-static loads. Results also show that is possible to estimate the initiation of fatigue cracks at critical points of a structural component using virtual strain sensors.