Mean Fatigue Life Research Articles

A micro-crack initiation life simulation method by improving the Tanaka-Mura's model of slip behavior

A micro-crack initiation simulation model was proposed with varied slip irreversibility and slip hardening (VSISH), by improving the Tanaka-Mura's model. A power law to relate the slip irreversibility parameter to the load and the microstructure information was proposed. The shear strain range in Tanaka-Mura's model was re-derived for introducing slip hardening behavior. Several microstructure examples in three-dimensions were given and the evaluated mean fatigue life has a minimum error less than 3.3% compared with the experimental data. It was demonstrated that the constant-slip-irreversibility strategy and an existing irreversibility model were specific cases of our model.

Degradation analysis on high-cycle bending fatigue for woven SiC/SiC composites based on Wiener process model

A comprehensive investigation of degradation analysis under high-cycle bending fatigue (HCBF) loading for composite materials was conducted based on the Wiener process model. Degradation data are generated by conducting the probabilistic progressive damage analysis of composite materials considering the variability of material properties including mechanical properties and strength. Based on the degradation data, the Wiener process model is established with the power time transformation function and linear time-scale functions. The HCBF tests of composite cantilever beam specimen (CBS) and turbine guide vane (TGV) are conducted to evaluate the degradation process of composite materials. Compared with the experimental data and Monte Carlo simulation (MCS) method, the proposed methodology has the promising potentials to improve computational efficiency with acceptable computational accuracy for the CBSs. As for the TGV, the maximum relative errors for mean fatigue life are within 17.89%, while the degradation tendency from experiments is similar to the simulated degradation curves, verifying the rationality of the proposed method based on Wiener process model. Moreover, reliability analysis is conducted based on the stochastic degradation process, which can be used to determine whether the performance of the structure meets the design requirement.

Fatigue life prediction of self compacting concrete made with recycled concrete aggregates under flexural loading

This study primarily aims at the estimation of mean fatigue lives, design fatigue lives and theoretical fatigue lives of Self Compacting Concrete (SCC) made by 100% coarse fraction of Recycled Concrete Aggregates (RCA). For reference, SCC mix containing 100% Natural Aggregates (NA) was also tested. The Weibull distribution has been found to be suited for description of the fatigue life stats showing higher variance in fatigue life for SCC containing RCA. The mean values of the distribution parameters have been used for determining the mean, design and theoretical fatigue lives of SCC containing RCA and NA separately. Two million cycles endurance limit has also been determined for the SCC containing RCA and NA. It has been found that SCC containing RCA shows inferiority in terms of mean fatigue life, design fatigue life and theoretical fatigue life along with endurance limit and is mainly due to the substandard properties of RCA.

Reliability assessment of flexural fatigue failure of asphalt mixture: A new perspective

This study aims to evaluate the evolution of reliability with number of cycles for asphalt mixture under repeated fatigue loading, i.e. degradation reliability. A novel methodological framework was developed to analyze the reliability, which integrates four theories (reliability theory, probability distribution function transformation, fatigue damage and Weibull distribution). Based on the developed framework, a novel and simple method was established to calculate the degradation reliability through a probabilistic simulation technique. Flexural fatigue performance of asphalt mixture was then analyzed statistically by Weibull distribution function. The five numerical methods were adopted and compared to estimate Weibull parameters. Kolmogorov-Smirnov test was conducted for further confirming the validity of this distribution. The reliability of asphalt mixture under fatigue loading was assessed using the established method. Results show that the randomness evolution behaviors of asphalt mixture under fatigue loading can be described by the developed framework. The degradation reliability under non-fatigue damage behaviors may be able to be calculated by the established method. The two-parameters Weibull distribution allows to describe fatigue life data of asphalt mixture. The evolutions of reliability with number of cycles show a decrease trend with three-stage. The degradation reliability of asphalt mixture in practical project should be larger than the value corresponding to mean fatigue life as far as possible. Method of moments should be adopted to estimate distribution parameters for the evaluation of degradation reliability of asphalt mixture, the health state of asphalt mixture is thus early warned timely.

Fatigue performance of self-compacting concrete containing hybrid steel–polypropylene fibres

This study presents the flexural fatigue analysis of hybrid fibre-reinforced self-compacting concrete (HyFRSCC) in which design fatigue lives of HyFRSCC containing various combinations of steel fibres (SF) and polypropylene fibres (PPF) have been estimated. The proportions of SF and PPF were kept as 100PPF, 75PPF–25SF, 50PPF–50SF, 25PPF–75SF and 100SF. The total fibre volume fraction was taken as 1%. The calculated values of Weibull parameters were used to estimate the mean and design fatigue lives of HyFRSCC. The HyFRSCC mix 100PPF has lesser variability in the fatigue life data, whereas HyFRSCC mix having 25PPF–75SF has been found to exhibit higher fatigue lives as compared to other fibre mix proportions.

The effects of hot iso-static pressing on the porosity and fatigue properties of Galfenol steels

The fatigue behaviour of plain carbon (F) and stainless (C) steel Galfenol alloys grown by free standing zone melting was investigated. As-received samples of both alloys were laden with macroporosity and initial results were highly scattered. Hot iso-static pressing was pursued to reduce porosity, to potentially improve fatigue life and reduce scatter. For the C alloy, volume fraction porosity was reduced by 85%, scatter was reduced by 8% and the mean fatigue life improved by an order of magnitude. For the F alloy, porosity was reduced by 96% but fatigue results were not improved.

Effect of Quenching Media and Tempering Temperature on Fatigue Property and Fatigue Life Estimation Based on RBF Neural Network of 0.44 % Carbon Steel

Abstract. In this work, the effect of the quenching media (brine, water, and two types of naphthenic mineral oils) and the tempering temperature (200, 400, 600 ∘C) on the static mechanical properties and the fatigue life has been investigated using 300 fatigue and 36 static tension tests. S–N curves and standard deviations of fatigue life under each heat treatment condition were calculated and shown. The fracture surfaces of the selected 11 specimens were observed by the scanning electron microscope and the reasons of affecting the fatigue life were discussed. To estimate the mean fatigue life under the conditions of any given tempering temperature and cycle stress amplitude based on 300 fatigue tests, the mean fatigue life estimation method based on RBF neural network was presented and verified by 12 other fatigue tests. The test results have shown that (1) the mean fatigue life decreases with the increase of tempering temperature for the same quenching media, (2) the mean fatigue life using brine is more than water which is more than naphthenic mineral oils for the same tempering temperature, and (3) the proposed method based on RBF neural network could accurately estimate the mean fatigue life when the tempering temperature and cyclic stress amplitude are given for each quenching medium.

Fatigue properties of removable partial denture clasps fabricated by selective laser melting followed by heat treatment

The aim of the study was to investigate the effect of post-heat treatment on the microstructures and fatigue strengths of Co–Cr–Mo (CCM) clasps prepared by selective laser melting (SLM). Clasp specimens and rod-shaped specimens were fabricated by SLM using CCM powders with different angulations (0°, 45°, and 90°). Two heat treatment conditions were used: 1 and 6 h at 1150 °C in an argon atmosphere followed by cooling in a furnace. Subsequently, the fatigue strength and microstructure were investigated. The results revealed that for the control group, the mean fatigue life was different when building angulations were changed as manifested by the control-90 specimen, which exhibited the highest fatigue life, followed by control-45 and then control-0. One-hour heat treated samples showed higher fatigue strength in all axes than the 0°- and 45°-axes control samples and lower fatigue strength than the 90°-axes control samples. The survival rate after heat treatment for 1 h exhibited no significant difference in all the axes. In terms of microstructure, after heat treatment, the samples showed homogeneous equiaxed grain and randomized texture in all angulations. Therefore, using a post-heat treatment can reduce the anisotropy effect on the microstructure and fatigue strength due to homogenized microstructure.

A review on the fatigue behavior of Ti-6Al-4V fabricated by electron beam melting additive manufacturing

Electron beam melting (EBM) is a rapidly-developing metal additive manufacturing process that holds significant interest in the aerospace and biomedical industries for the high-strength titanium alloy, Ti-6Al-4V. These industries have fatigue-limited applications, but a lack of understanding of the EBM process-microstructure-fatigue relationships limit widespread use and presents challenges for certification. In this review, uniaxial fatigue data was collected and the effects of build orientation, surface roughness, and hot-isostatic pressing are linked to the fatigue properties highlighting microstructure, defects, and failure mechanisms. The observations and conclusions are supported by statistical analysis using the mean fatigue life obtained by the Statistical Fatigue-Limit Model. Both EBM-process and post-process structure relationships are discussed in order to identify the best-practice for fatigue-resistant design. The performance of the EBM material is compared to conventionally manufactured Ti-6Al-4V and possible methods to increase the fatigue resistance are discussed. Anisotropic fatigue behavior was observed in as-fabricated parts and no statistical distinction was found in the fatigue performance of HIPed and as-fabricated material provided the same as-fabricated rough surface condition. However, comparable fatigue life to traditionally manufactured lamellar Ti-6Al-4V is achieved when both post-process HIP and machining are applied to EBM-fabricated parts.

Implant Treatment in Atrophic Maxilla by Titanium Hybrid-Plates: A Finite Element Study to Evaluate the Biomechanical Behavior of Plates

A severely atrophied maxilla presents serious limitations for rehabilitation with osseointegrated implants. This study evaluated the biomechanical and long-term behavior of titanium hybrid-plates in atrophic maxilla rehabilitation with finite elements and probabilistic methodology. A three-dimensional finite element model based on a real clinical case was built to simulate an entirely edentulous maxilla with four plates. Each plate was deformed to become accustomed to the maxilla’s curvature. An axial force of 100 N was applied in the area where the prosthesis was adjusted in each plate. The von Mises stresses were obtained on the plates and principal stresses on maxilla. The difference in stress between the right and left HENGG-1 plates was 3%, while between the two HENGG-2 plates it was 2%, where HENGG means Highly Efficient No Graft Gear. A mean maximum value of 80 MPa in the plates’ region was obtained, which is a lower value than bone resorption stress. A probability cumulative function was computed. Mean fatigue life was 1,819,235 cycles. According to the results of this study, it was possible to conclude that this technique based on titanium hybrid-plates can be considered a viable alternative for atrophic maxilla rehabilitation, although more studies are necessary to corroborate the clinical results.

Flexural fatigue performance of concrete made with recycled concrete aggregates and ternary blended cements

Results of an investigation to evaluate the flexural fatigue performance of concretes made with fly ash, silica fume (SF) as partial replacement of Portland cement and 100% coarse recycled concrete aggregates (RCA) are reported. Flexural fatigue test data were obtained based on 168 static flexural tests and flexural fatigue tests conducted using Servo-controlled Actuator. The test data thus obtained were analysed and equations to estimate the flexural fatigue strength of concrete mixes were proposed. The probability distributions for the fatigue life of various concretes were also established. The flexural fatigue performance of various concrete mixes was assessed in terms of mean and design fatigue lives. The results obtained from the study show that flexural fatigue performance of concrete containing 100% RCA with 10% SF performed better than concrete containing 100% coarse natural aggregate.

Development of Domestic CT80S Sulfur Resistance Coiled Tubing

According to the demand of oil and gas field development with a small amount of hydrogen sulfide, CT80S sulfur resistance coiled tubing was developed through the raw materials and manufacturing technology. The microstructure, mechanical properties, fatigue life and corrosion resistance of the CT80S sulfur resistant coiled tubing were analyzed. The results showed that the microstructure of CT80S sulfur resistant coiled tubing was consisted of the ferrite and pearlite with the grain size of 12, banded structure of 1.0, and the inclusions was less than 1.0. The strength and hardness of the pipe meet the requirements of API Spec 5ST, and the hardness control was less than 18HRC. The pipe had excellent low cycle fatigue property, the mean fatigue life of Φ31.8 × 3.18mm tube was 1055 cycles when the internal pressure was 34.47MPa and the bending radius was 1219mm. According to NACE TM 0284 and NACE TM 0177 standard, the HIC and SCC performance tests were carried out in same solution. The results show that the developed tubing is insensitive to HIC and the resistance to sulfide stress corrosion is good, under 90%σs stress loading not break.

Statistical Analysis and Fatigue Life Estimations for Quenched and Tempered Steel at Different Tempering Temperatures

In this paper, the statistical properties and fatigue life estimations of 0.44% carbon steel at different tempering temperatures are presented. The specimens were austenized at 900 °C for 10 min, quenched in water, tempered at different temperatures, and then machined to the design geometry and average surface roughness of Ra = 0.4 μm. The effect of tempering temperature on the fatigue life of 0.44% carbon steel was investigated using 75 fatigue tests, divided into three groups at temperatures 500 °C, 600 °C, and 700 °C. S–N and P–S–N curves were established. Two methods of estimating the mean fatigue life are presented. One is based on dislocation dipole accumulation and Paris’ law; another is based on the kriging model. Six more fatigue tests were carried out to validate the presented methods. Test results showed that the first method is superior to the second in terms of estimating accuracy from the validation datum. However, the second method could estimate the mean fatigue life of quenched and tempered 0.44% carbon steel with an average surface roughness of Ra = 0.4 μm when the tempering temperature was set to a value other than 500 °C, 600 °C, or 700 °C, with no additional fatigue test needed.

An experimental investigation on fatigue behaviors of HMPE ropes

With offshore oil and gas exploration moving into deeper waters, HMPE (high modulus polyethylene) ropes have been widely investigated. However, the tension-tension fatigue behavior of HMPE ropes, especially the effect of mean load on the fatigue life of HMPE ropes, is still lack of sufficient and quantitative understanding. Therefore, to capture the fatigue behavior of HMPE ropes, fatigue tests of HMPE ropes are systematically performed in the present work utilizing a specially designed experimental system. An experimental procedure is proposed and test results show the whole fatigue process of HMPE ropes including tension-time, strain-time and tension-strain curves. The dynamic stiffness of HMPE ropes is also investigated, which shows that it increases with increasing mean load, while decreases with increasing loading amplitude. An empirical expression that accounts for the relationship of the mean load, loading amplitude and fatigue life is proposed to describe the damage evolution of HMPE ropes under long-term cyclic loading. The present work is beneficial to understanding the fatigue resistance ability of HMPE ropes and to application of HMPE ropes in deepwater moorings.

Fatigue Life Estimation of Medium-Carbon Steel with Different Surface Roughness

Medium-carbon steel is commonly used for the rail, wire ropes, tire cord, cold heading, forging steels, cold finished steel bars, machinable steel and so on. Its fatigue behavior analysis and fatigue life estimation play an important role in the machinery industry. In this paper, the estimation of fatigue life of medium-carbon steel with different surface roughness using established S-N and P-S-N curves is presented. To estimate the fatigue life, the effect of the average surface roughness on the fatigue life of medium-carbon steel has been investigated using 75 fatigue tests in three groups with average surface roughness (Ra): 0.4 μm, 0.8 μm, and 1.6 μm, respectively. S-N curves and P-S-N curves have been established based on the fatigue tests. The fatigue life of medium-carbon steel is then estimated based on Tanaka-Mura crack initiation life model, the crack propagation life model using Paris law, and material constants of the S-N curves. Six more fatigue tests have been conducted to validate the presented fatigue life estimation formulation. The experimental results have shown that the presented model could estimate well the mean fatigue life of medium-carbon steel with different surface roughness.

Experimental Study of Static and Fatigue Behavior of CFRP-Balsa Sandwiches under Three-point Flexural Loading

Balsa wood is a natural cellular material with an excellent resistance-to-weight ratio that is ideal for manufacturing the core of sandwich structures. In this study, sandwich specimens with a carbon-fiber-reinforced polymer (CFRP) skin and a balsa wood core were tested with static and dynamic loading. Three-point flexural tests in static regime determined the mechanical characteristics of the CFRP-balsa specimens that were needed for subsequent fatigue strength tests. Also, experimental research was performed on the Charpy impact response of the CFRP-balsa sandwich specimens. This study implemented an accelerated fatigue testing method to identify and predict the mean fatigue life of the CFRP-balsa sandwich specimens subjected to cyclic fatigue via three-point flexural tests. Using the accelerated fatigue and the three-point flexural testing methodology on the CFRP-balsa sandwich specimens, the testing period was reduced by 11.9 times, and thus the material costs necessary for the tests were also reduced. Also, the breaking surfaces were analysed to reveal the failure modes of CFRP-balsa specimens subjected to static and fatigue tests at three-point flexural and at impact tests.

Fatigue properties and microstructure of quasicrystalline AlFeCrTi alloy

Aluminium based material having chemical composition of Al93Fe3Ti2Cr2 (at.%) was prepared by hot extrusion of gas atomised powder. Microstructure consisting of aluminium matrix and icosahedral quasicrystalline particles was investigated by scanning and transmission electron microscopy a X-ray spectroscopy. Size, distribution and inner structure of quasicrystalline particles were determined. When quasicrystalline particles having submicron size were present in the microstructure together with fine-grained aluminium matrix, it resulted in enhancement of mechanical properties. Fatigue experiments were performed in load controlled regime with positive mean stress and fatigue life data for this quasicrystalline material were compared with similar results for commercially available aluminium alloys. Longer fatigue life together with higher fatigue strength reaching value of 350MPa was observed. It is approx. 100MPa higher than for commercially produced coarse-grained aluminium alloys. Fractographic observations revealed presence of fish eye fracture patterns and validity of weakest link fracture mechanism acting in this type of material under investigation.

Mean and design fatigue lives of SFRC containing cement-based materials

This paper examines the flexural fatigue performance of steel-fibre-reinforced concrete (SFRC) containing different cement-based materials in terms of mean and design fatigue lives. An experimental programme was designed to determine the fatigue lives of beam specimens of seven SFRC composites containing fly ash, silica fume, limestone powder and metakaolin as partial cement replacements in varying amounts. The fatigue life distributions of all mix combinations at different stress levels were statistically analysed using a two-parameter Weibull distribution. The Weibull modelling used to describe the distribution of cycles to failure is summarised. The Weibull distribution parameters as determined from fatigue/S–N equations were employed to determine the mean fatigue lives. The design fatigue lives were calculated corresponding to selected acceptable probabilities of failure (i.e. 0·01, 0·05, 0·10, 0·15 and 0·25). SFRC containing fly ash and silica fume in proportions of 20% and 10% by weight of binder respectively showed the best fatigue performance in terms of mean and design fatigue lives as compared with the other mix combinations.

Weibull statistical analysis of Krouse type bending fatigue of nuclear materials

A bending fatigue mini-specimen (Krouse-type) was used to study the fatigue properties of nuclear materials. The objective of this paper is to study fatigue for Grade 91 ferritic-martensitic steel using a mini-specimen (Krouse-type) suitable for reactor irradiation studies. These mini-specimens are similar in design (but smaller) to those described in the ASTM B593 standard. The mini specimen was machined by waterjet and tested as-received. The bending fatigue machine was modified to test the mini-specimen with a specially designed adapter. The cycle bending fatigue behavior of Grade 91 was studied under constant deflection. The S–N curve was created and mean fatigue life was analyzed using mean fatigue life. In this study, the Weibull function was predicted probably for high stress to low stress at 563, 310 and 265 MPa. The commercial software Minitab 17 was used to calculate the distribution of fatigue life under different stress levels. We have used 2 and 3- parameters Weibull analysis to introduce the probability of failure. The plots indicated that the 3- parameter Weibull distribution fits the data well.

Effects of TiN, CrN and TiAlN coatings using reactive sputtering on the fatigue behaviour of AA2024 and medium carbon steel specimens

ABSTRACTThe effects of ceramic coatings (TiN, CrN and TiAlN films) on the fatigue behaviour of 2024 aluminium alloy (AA2024) and medium carbon steel (MCS) specimens under cyclic loading have been investigated in this study. These ceramic thin films of about 2 μm thickness were deposited on the substrates using radio frequency reactive magnetron sputtering, with metallic Ti, Cr and Al targets in an Ar/N2 gas environment. The (111), (200) and (220) and (311) peaks of a face centre cubic (fcc) structure in CrN films, and the (111), (200) and (220) peaks in TiN/TiAlN films were observed using X-ray diffraction method, respectively. Fatigue tests were performed using rotational bending conditions at a speed of 3000 rpm with five stress levels (115, 173, 231, 288 and 346 MPa for AA2024; 288, 346, 404, 462 and 519 MPa for MCS) in air. Scanning electron microscopy was used for the analysis of surface morphologies and initial failure stage. The results show that the fatigue life of coated specimens is significantly increased under lower cyclic loading, for example, from 42% at 288 MPa, to 98% at 230 MPa and up to 434% at 173 MPa, for AA2024 with TiN coatings. The improvements of mean fatigue life for MCS coated with TiN films are 88% at 519 MPa, 197% at 462 MPa and up to 597% at 404 MPa, respectively. The experimental results also depict that the coated specimens with higher surface hardness (TiAlN) tended to increase in fatigue strength and fatigue life over uncoated and TiN/CrN specimens.