Residual Fatigue Life Research Articles

Fatigue life prediction of gasoline storage tank considering varying current density and weld stress

In the field of corrosion fatigue crack research, how to couple corrosion and fatigue under various conditions is a problem worthy of discussion. According to the electrochemical corrosion principles and the superposition principles, studies have been made on the interaction between corrosion and fatigue, and the relationship model between the corrosion fatigue crack size and the corrosion fatigue remaining life in the Corrosion of Hydrogen evolution (COHE) fatigue long crack growth stage is established. The feasibility of the model is verified by using the experimental data. According to the specific structure of the dislocation butt weld of large storage tank, the stress at the crack is calculated. Based on the above model and the experimental data, the corrosion fatigue residual life of large storage tank is predicted. The feasibility of the model is verified, which provides a new method for corrosion fatigue life prediction of large storage tanks.

Corrosion characteristics of Q690qE high-strength bridge steel in simulated coastal–industrial environment and its influence on mechanical and corrosion fatigue behaviors

The corrosion behavior of Q690qE high-strength bridge steel in simulated coastal–industrial environment was investigated through accelerated corrosion, and the corrosion features under different corrosion times were characterized. The effect of pre-corrosion level on mechanical and corrosion fatigue behaviors was also studied by using pre-corroded fatigue samples. Results show that corrosion pits were more likely to form in this environment, with chloride ions concentrating at the bottom of the pits, resulting in significant loss of the mechanical property and corrosion fatigue life. The corrosion fatigue initiation mechanism was proposed, and a prediction model for the residual corrosion fatigue life of corroded Q690qE steel was developed.

Effect of the Progressive Failure of Shear Connectors on the Behavior of Steel-Reinforced Concrete Composite Girders

Pre-stressed steel-concrete composite beams are widely used in bridges around the world. Loads during the service life of bridges may cause failure in the form of fracture in the studs near the ends of the bridge girders. The effect of stud failure on the residual static capacity and residual fatigue life of composite girders is not well investigated. Therefore, this study presents numerical investigations into the effects of the progressive failure of stud shear connectors on the residual static performance and remaining fatigue life of post-tensioned steel-concrete composite beams. The Finite Element (FE) model was validated using existing experimental work. Moreover, the effects of the progressive failure of stud shear connectors on the steel-concrete interface slippage, shear stress range, and compressive and tensile strains were investigated. The behavior of the composite girders in terms of the estimated fatigue life and residual capacity was inversely affected by the number of fractured studs. The AASHTO theoretical equation conservatively estimated the remaining fatigue life until 15% of the rows were removed and then the FE model predicted fewer remaining fatigue cycles than the theoretical equation. Until 15% of the rows were removed, the strengthened sample had a better response in terms of the stress range, tensile and compressive strains, and residual capacity. After that, both the strengthened and non-strengthened samples exhibited similar responses to the failure of studs. Subsequently, the positive effects of the post-tensioning vanish as the end studs fail. Therefore, designers should pay special attention to the ends of post-tensioned composite beams where the local failure of studs is expected.

Stress Evaluation of Welded Joints with Metal Magnetic Memory Testing Based on Tension-Compression Fatigue Test.

Metal magnetic memory testing (MMMT) is an effective nondestructive technique for fatigue damage monitoring of weldments because of its capacity for stress evaluation. An experimental investigation of the effect of the applied fatigue stress on MMMT signals, including the tangential component Bx and the normal component Bz, during tension–compression fatigue tests in welded joints was carried out systematically. The Bx and Bz signals at different fatigue cycles and fatigue stresses were collected and analyzed, and the results showed that there was a peak of Bx and abnormal peaks of Bz that existed at the welded joint before loading. After loading, the peak of Bx and the abnormal peaks of Bz reversed, and the Bx signals moved upward and the Bz signals rotated anticlockwise dramatically in the first few fatigue cycles. After the fatigue cycle number was larger than 1000, Bx and Bz were stable, with very little fluctuation. In addition, the characteristics of Bx signals, the mean value, and the peak value of the average of Bx had an extremely significant linear relationship with the applied fatigue stress during the stable stage of the fatigue test, which indicates that MMMT is a feasible method for fatigue stress evaluation and even residual fatigue life estimation for weldments in service.

Digital Prognosis of Fatigue Residual Life of Lightweight Metallic Materials

Digital Prognosis of Fatigue Residual Life of Lightweight Metallic Materials

Guided Wave Phase Velocity Dispersion Reconstruction Based on Enhanced Phased Spectrum Method.

Fibre-reinforced composite laminates are frequently used in various engineering structures, due to their increased weight-to-stiffness ratio, which allows to fulfil certain regulations of CO2 emissions. Limited inter-laminar strength makes composites prone to formation of various defects, which leads to progressive degradation of residual strength and fatigue life of the structure. Using ultrasonic guided waves is a common technique for assessing the structural integrity of composite laminates. Phase velocity is one of the fundamental characteristics of guided waves and can be used for defect detection, material property estimation, and evaluation of dispersion. In this paper, a phase velocity reconstruction approach, based on the phase-shift method, was proposed, which uses frequency sweep excitation to estimate velocity at specific frequency harmonics. In contrast to the conventional phase spectrum technique, the proposed approach is applicable to the narrowband piezoelectric transducers and suitable for the reconstruction of dispersion curves for direct, converted, and multiple co-existing modes with high accuracy. The proposed technique was validated with finite element simulations and experiments, both on isotropic and anisotropic structures, analysing the direct, converted, and overlapped modes. The results demonstrated that, using the proposed technique, the phase velocity dispersion can be reconstructed at −20 dB level bandwidth of the transducer, with a relative error of ±4%, compared to the theoretical velocity predictions.

Fatigue life enhancement of additive manufactured 316l stainless steel by LSP using a DPSS laser system

ABSTRACT Present work aims to study the fatigue life behaviour of additively manufactured (AM) stainless steel 316L in a laser shock peening (LSP) process. The fatigue behaviour of as-built samples and LSPeened sample were studied on the AM samples. A new diode-pumped laser system was utilized as an instrument to perform LSP operations. LSP operation was performed under two different sacrificial layers of different materials i.e. vinyl tape and aluminium tape. The other essential LSP parameters, namely energy, pulse width, spot size, overlap, and number of layers were kept constant based on the previous experimental findings. The characterization was done for analyzing the residual stresses using a hole drilling process, and a 4-point bending machine. A considerable improvement in compressive residual stress and fatigue life was observed in the LSPeened samples. Such improvements in residual stresses and fatigue life may pave a road to establishing diode-pumped lasers for LSP applications.

Strain-ageing effects on the residual low-cycle fatigue life of low-carbon steel reinforcement

Low-cycle fatigue (LCF) failures can be expected when rebars are subjected to a small number of cycles at large stress/strain amplitudes. Major seismic events are often preceded or followed by other events of smaller/larger magnitude. During each event, the residual fatigue life of the steel reinforcement may reduce, eventually leading to failure of the bars due to the cumulative damage. Strain ageing may reduce even more the residual fatigue life of steel. This paper presents the results of an experimental testing campaign conducted on samples fabricated from New Zealand Grade 300E steel. A benchmark LCF life was obtained for 12-mm steel reinforcing bars subjected to axial-strain-controlled completely reversed cyclic tests at amplitudes ranging between 0.78 and 2.75%. The reduction in fatigue life attributed to strain ageing was obtained by comparing the benchmark fatigue life with that of steel reinforcing bars precycled up to 33% and 66% of the benchmark life and artificially strain aged for an equivalent period of 1 year at 15 °C. The Coffin-Manson and Koh-Stephens models were employed to evaluate the experimental results. The study demonstrates that, depending on the strain amplitude, strain ageing can cause a reduction in total and residual fatigue life ranging from 20 to 70%. Strain ageing should not be ignored during the assessment of earthquake-damaged steel reinforcing bars.

Experimental study and reliability assessment of fatigue loaded reinforced concrete beams combined with chloride exposure

Fatigue life of reference RC beams (Nu) and residual fatigue life of RC beams after pre-fatigue loading (0.01–1.2 million cycles, ∼0.2% − 30%Nu) and chloride exposure (3, 6 months) in sequence, were tested. Fatigue behaviors significantly degrade at the pre-fatigue cycles of 1% to 30%Nu, where obvious degradations are shown as the pre-fatigue cycles increase to 10%Nu. Fatigue life of corroded and un-corroded beams can be modeled by the two-parameter Weibull distribution at a given load level, and hence a reliability assessment method is proposed to give the minimum safety fatigue life of RC structures with chloride exposure.

Estimation of residual fatigue life of polymer composites after preliminary low-velocity impact

Composites are replacing traditional metals and alloys in many industries, including aviation, space, building, automotive, petrochemical, due to their lower weight and physical and mechanical characteristics, which allows them to be introduced into critical high-loaded structures and parts. At the same time, in the process of operation, composite structures can be in conditions of complex thermomechanical action. Data on changes in the residual mechanical characteristics, available damages allow increasing the prediction life, survivability and safety of destruction of composite structures.The paper presents the results of studying the processes of accumulation of fatigue damage and destruction of CFRP specimens with layouts [0º/90º]n and concentrators of an operational nature. The study was carried out with the implementation of a preliminary transverse impact by a falling load according to the three-point bending and subsequent cyclic stretching. In accordance with the developed technique, the value of the ultimate strength (σB) of the carbon fiber under study was determined from quasi-static tensile tests. The nominal fatigue life (Nmax) is obtained from tests with the parameters with the maximum stress in the cycle σmax=0.75∙σB, the asymmetry coefficient R=0.1 and the frequency ν=20 Hz. During the cyclic tests, the frequency and amplitude of the loading were selected in such a way that the heating of the sample did not exceed 20°C relative to the temperature of the beginning of the test. From experiments on impact bending, the potential energy (Emax) was determined, at which the samples were destroyed. Further tests for preliminary impact according to the three-point bending were carried out in the range from 0.3 to 0.9 of the destruction energy (e’). Single blows were made across the entire width of the samples. After each impact, a visual inspection of the samples was carried out. Microstructural studies and analysis of fracture patterns of prototypes under complex shock impacts and cyclic loading were performed using a Carl Zeiss SteREO Discovery V12 stereomicroscope.As a result, experimental dependences of the influence of different intensity of impact bending on the residual fatigue life of carbon fiber specimens were obtained. Analysis of the diagram of the change in the residual fatigue life versus the impact bending intensity made it possible to reveal the presence of a shock sensitivity threshold. Impact actions with energies exceeding the threshold value led to a significant decrease in fatigue life, by more than 10% of the nominal value of Nmax, for the studied CFRP composites.

Evaluation of the fatigue properties for the long-term service asphalt pavement using the semi-circular bending tests and stereo digital image correlation technique

Reliable assessment of the fatigue resistance of asphalt pavement with a long-term service is critically crucial for the rational formulation of original pavement utilization strategies in reconstruction and expansion projects. Currently, the pavement performance evaluation indicators are mainly used to guide pavement preventive maintenance, and its applicability in reconstruction and expansion projects of the freeway is limited. This paper aims to propose an evaluation method of fatigue resistance of asphalt concrete utilizing semi-circular bending (SCB) tests and stereo digital image correlation (stereo-DIC) techniques. A total of 27 asphalt concrete cores were drilled from the three freeways (K84, K124, and K165) with a service life of more than 20 years, and the SCB specimens were produced to conduct the SCB fracture and fatigue tests. During the SCB test, the stereo-DIC technique was employed to monitor the evolution process of the strain distribution and crack length for the specimens. K-dimension tree neighbor-searching algorithm (K-d tree algorithm) was used to effectively measure the change of crack length corresponding to each fatigue load cycle. Meanwhile, the strain threshold of asphalt concrete crack initiation was determined by the bilinear softening cohesive zone model (CZM) to ensure the accuracy of the crack length calculated by the K-d tree algorithm. Furthermore, the relationship between crack growth rate and stress intensity, which was used to fit the Paris law parameters, was determined. The CZM and DIC results indicated that the strain threshold of asphalt concrete crack should be set as 2000 με when using the K-d tree algorithm to determine the crack length. With the stress ratio increase, the Paris law parameter A increased wavily, and the parameter n decreased steadily, while the threshold of the stress intensity factor increased steadily. The Paris law master curves could characterize the fatigue performance of various road sections at a wide load range. The residual fatigue life of K84, K124, K165 the road sections were 2.13E + 08, 3.57E + 08, and 1.02E + 07, respectively.

Fatigue life of a pressure vessel based on residual strength and crack size

The study of fracture failure is very important for analyzing the fatigue life of pressure vessels. According to the Paris Law, the relationship between fatigue-crack size and residual fatigue life is established by considering the circumferential stress and the relationship between crack length and the crack depth. Based on the specific structure of the pressure vessel, the relationship between fatigue-crack size and the residual strength was established according to the permissible residual strength. The curve for stress vs. number of cycles (S–N) of a pressure vessel was obtained. The fatigue life of the pressure vessel was predicted and compared with actual test data. The accuracy of the model was verified by comparing the actual service life with the model predictions, which confirmed that this model provides a new method for predicting the residual life of pressure vessels.

Determination method for metal bridge superstructure replacement priority using strength, economic and operational criteria

The article describes the problem arising from the setting trains with increased axleloads into operation on bridges with superstructures, engineered according to the old design standards. On the railways used riveted metal bridge superstructures, which require replacement due to significant corrosion, mechanical and fatigue damage, due to insufficient carrying load and residual fatigue life to pass the prospective load. Superstructures, designed in the 30s-40s, are more than 80-90 years used in conditions of a relatively difficult operation. During long-term operation, processes occur in elements and joints that lead to the formation and development of various hazard degrees damages, and failures. It is necessary to resolve the further exploitation issue of old bridge superstructures and their replacement. The author has applied the analyzing method of the criteria system, with the account of economic and technical capabilities for replacement priority determination of bridge superstructures. A set of criteria were proposed for solving this problem in digital form. Compiled matrices of pair-wise comparison, the comparison was performed using a relative importance scale with the test significance determination. By the linear algebra methods the eigenvector of matrix components values — local priorities — are calculated for each pair-wise comparisons matrix. As a result of calculations by the proposed criteria, were obtained global priorities for replacing options for riveted metal superstructures made by old design standards. The mathematical apparatus of the criteria hierarchy method is easy to use and allows you to get a solution in digital form, you can use other criteria.

Effects and optimization of biomimetic laser shock peening on residual fatigue life improvement of aluminum alloy used in aircraft skin

This paper aims to study the effects of biomimetic laser shock peening (BLSP) on crack resistance ability of aluminum alloy aircraft skin. The extracted feature parameters obtained from cherry leaves obey normal distribution. Based on the extracted biomimetic parameters, a 3D finite element model (FEM) is developed to study the effects of BLSP treatment on the residual stress distribution, stress intensity factors and residual fatigue life of specimens. Results show that BLSP treatment contributes to form leaf-shaped residual stress distribution. In-depth residual stress field is divided into three layers of compressive residual stress at both surfaces and tensile stress in the middle. Since the compressive residual stress generated by BLSP balances the load applied on specimens, stress intensity factors of treated specimens are reduced effectively, greatly increasing residual fatigue life. The asymmetry of residual stress distribution facilitates crack turning to prolong the crack path. An artificial neural network (ANN) with three layers is established to predict the optimal structure by linking with Monte-Carlo method (MCM). The relative error of the ANN-MCM prediction, merely 3.26%, indicates that the proposed method is able to employed to save design time and computation resource.

Quantitative thermography for fatigue damage assessment and life prediction of welded components

The objective of this paper is to use quantitative thermography for fatigue damage assessment and life prediction of welded components. The energy dissipation during fatigue process is taken as an effective index of fatigue damage to develop a nonlinear damage accumulation model, and the model is extended to evaluate the fatigue damage and residual life of the specimen subjected to variable loading. Experiments are performed to validate its applicability, and the relationships between the fatigue damage variable to the cycle number and the accumulated energy dissipation are presented and discussed. The results show that the energy dissipation has the same trend as the temperature increment evolution, and a power law relationship between the stress range and the energy dissipation is experimentally determined. The linear relationship between the accumulated energy dissipation and the cycle number is confirmed at different constant stress levels, and the total energy dissipation to failure is shown to be a constant value. The developed nonlinear damage accumulation model is used to predict the residual fatigue life, and a good agreement is achieved. It is concluded that the developed approach is applicable for fatigue damage accumulation and residual life evaluation of materials.

Piezo-impedance based fatigue damage monitoring of restrengthened concrete frames

The present study proposes a novel application of wavelet transform energy of piezo-impedance signatures in monitoring the premature fatigue damage of restrengthened reinforced concrete (RC) frames. The steel plates on one column of the damaged RC frame and carbon fibre reinforced polymer (CFRP) wrap on the other are utilized as the local strengthening elements. The lead zirconate titanate (PZT) patches bonded externally to the retrofitted elements were used to acquire the global and local vibration response of the test frame under high-cycle and low-strain fatigue loading environment. The electro-mechanical impedance (EMI) technique combined with discrete wavelet transform (DWT) is employed on frequency domain PZT-admittance signatures to identify, localize, and quantify the severity of premature fatigue damages. The EMI-identified structural damping and DWT energy based damage dependent models shows extraordinary ability in estimating residual fatigue life of the structure. The results of combined local and global dynamics technique indicate the higher performance of the PZT-identified equivalent stiffness parameters (ESP) in detecting and quantifying plate debonding failures. Further, for the first time, the miniature AD5933 chipset displays a higher correlation of ESP in estimating premature fatigue damages, ultimately proving its efficacy for using it as a low-cost impedance-based health monitoring solution for retrofitted RC structures.

Novel Fatigue-Damage Sensor for Prediction of Remaining Fatigue Lifetime of Mechanical Components and Structures

In this paper, a novel Internet of Things (IoT) fatigue damage sensor is presented to predict the fatigue damage accumulation level and residual fatigue life of critical mechanical and structural components. The intelligent radio-frequency identification (RFID)-integrated fatigue sensor system has special designed breakable mini beams with multiple parallel oriented geometry and symmetric U-type stress concentrated notches. The fatigue sensing beams with different stress and fatigue lifetime levels are designed to estimate the fatigue damage accumulation and remaining fatigue life of unidirectional and multidirectional structural or mechanical elements, including composite structures. The fatigue damage sensor attached on a real structure goes through the same fatigue life experience of critical structural elements or mechanical components from the beginning of service life or any point in the service life to the end of service life. A fatigue sensor with five parallel symmetric U notched mini beams with different fatigue lifetimes (10% N, 25% N, 50% N, 70% N, 85%–90% N) normalized to the total life (N) of a structure are considered to predict the remaining fatigue lifetime of a real structure using the cumulative damage Miner’s rule. The mini fatigue sensor beams attached to the surface of a structure are designed to fail, depending on their fatigue life, earlier than the total fatigue lifetime of the structure, like a fatigue fuse system. The fatigue damage sensing beams fail gradually while passing through the same fatigue cycles as a structural member. When the service lifetime of a real monitored structure is very close to the total fatigue life, the critical maximum lifetime (80%–90% N) notched mini sensor beam breaks and issues an alarm that the service life of the real structural part is approaching its fatigue strength limit and the end of its service life. The smart fatigue damage sensor is wireless-enabled, which makes it possible to check the health status of the sensor over a sensor network as often as one likes. Since the wireless distributed fatigue sensor network system monitors the fatigue health conditions of structures periodically or on demand, the data collected on the sensor network system can be used not only for condition-based fatigue life prediction but also for sensor-based predictive fatigue maintenance and the development of new fatigue design tools for fatigue-sensitive complex and large engineering structures or mechanical systems.

Evaluation of fatigue performance of cement-treated composites based on residual strength through discrete element method

Fatigue damage is the process of material fatigue failure caused by cyclic loading, and the development of damage degrades the material properties. This paper aims to investigate the fatigue degradation law of cement-treated base (CTB) materials using a discrete element method (DEM) simulation technique. A fatigue evolution model was adopted to characterize the time-dependent fatigue damage under cyclic loading. Virtual semi-circular bending (SCB) fatigue and residual strength tests at different fatigue stages were performed on mesoscale DEM model to evaluate the fatigue damage of CTB material. With residual strength variable, the fatigue damage model was established to reveal the accumulation of damage. The results show that the residual strength evolution nearly appears an exponential correlation with the fatigue stages. In the first stage, the strength degradation is stable and appears as approximately linear. At about 80% of the fatigue life, the degradation rate is significantly accelerated. The residual strength degradation rate is related to the initial stress level and decreases with the increase of stress ratio. At the same fatigue life stage, the greater residual strength attenuation will be generated with a lower load level. The fatigue damage evolution model indicates the fatigue damage accumulation approximately linearly in the early stage and rapidly in the late stage. The late fatigue stage has the main contribution to fatigue failure. The degradation law demonstrates the lower the load level is, the more the damage accumulation at the same fatigue life stage will be, and the corresponding critical damage is greater. Moreover, based on the strength degradation law, a prediction model is established to evaluate the residual fatigue life of pavement base material.

Effect of Hostile Solutions on the Residual Fatigue Life of Kevlar/Epoxy Composites after Impact Loading.

Due to the enormous benefits inherent to composite materials, they have been widely used in the most diverse fields of engineering. Therefore, it is not surprising that in many of these applications they can be exposed to hostile environments, which can affect the mechanical performance of such materials. Therefore, the main goal of this work was to study the effect of immersion into different hostile solutions on the impact strength and, subsequently, to evaluate the residual fatigue life. For this purpose, the specimens were initially immersed into solutions of hydrochloric acid (HCl), sodium hydroxide (NaOH), sulphuric acid (H2SO4), diesel, distilled water, and seawater. Subsequently, the specimens were subjected to impact loads with an energy of 12 J and, finally, subjected to fatigue loads to assess the residual fatigue life. Seawater and NaOH solution provided the lowest impact strength. This was confirmed by the lower energy restored and impact bending stiffness (IBS), a parameter that allows evaluating the damage resistance of a composite. In terms of restored energy, for example, the seawater promoted a decrease around 30.4% in relation to the value obtained with non-immersed samples, while this value was 27.6% for the alkaline solution (NaOH). In terms of IBS, the lowest values were also obtained with these solutions (437.4 and 444.9 N/mm, respectively). Finally, the lowest residual fatigue life was also observed for these two solutions, and it was noticed that there was a direct relationship between the IBS and the residual fatigue life.

Compressive fatigue response and reliability analysis of thermoplastic composite with low‐velocity impact damage

AbstractThermoplastic composite has attracted more and more attentions for its higher fracture toughness and better damage tolerance than thermosetting composites. AS4/PEEK laminate is a representative thermoplastic composite, which has been widely used in the fabrication of fuselages and aircraft wings. In this paper, low‐velocity impact tests had been carried out on AS4/PEEK laminates. Different impact energy levels were selected for forming impact dent with depth of 1 mm for the three stacking sequences: [0/0/‐45/90/45/0/0/45/90/‐45/0]S, [0/0/45/90/‐45/0/45/90/‐45/0]S, and [45/‐45/0/45/90/‐45/0/45/‐45/0]S, which were 25.5, 21.0, and 20.0 J successively. Then, compression–compression fatigue tests with stress ratio of 10 and frequency of 10 Hz were used to obtain the residual fatigue life and damage propagation. It was found that significant local buckling appeared around the impact dent, which extended perpendicular to the loading direction during the compressive fatigue loading. The increase of the transverse dimension of local buckling could be divided into three stages. The experimental results indicated that a joint Weibull distribution could be used to describe the residual compressive fatigue life of the impacted laminates. This paper assumed an equal rank relationship between the residual strength and fatigue life, and the B‐basis value of fatigue stress was calculated to ensure the reliability of the impacted AS4/PEEK laminates, which were 0.53, 0.50, and 0.53 (normalized by residual compressive stress) at 106 cycles for the three kinds of laminates mentioned earlier.