Fatigue Fracture Analysis Research Articles

Study of the fatigue strength of steel 09G2S obtained by 3D printing based electric arc welding in a wide range of low temperatures

In this work, we consider the issues of obtaining workpieces from cold-resistant steel 09Mn2Si by a promising method of 3D-printing by electric arc surfacing (electric arc additive growing). The task of assessing the mechanical properties of the obtained material and understanding the process of its destruction is urgent. The assessment of the fatigue strength of the obtained material after deposition and after subsequent heat treatment (HT) (normalization) in a wide range of low temperatures is carried out. A fractographic analysis of fatigue fractures of 9Mn2Si steel using scanning electron microscopy was also carried out. Ultimately, this makes it possible to assess the reliability of parts manufactured by 3D-printing arc welding. In the course of the work, the mechanical properties were obtained and the analysis of the curves of low-cycle fatigue of the samples after 3D-printing and after further HT in the temperature range of -60 ... 20 °C was carried out. Metallographic studies have been carried out and structural changes have been established in the process of fatigue loading at different operating time of the sample. A relationship was established between the value of the maximum cycle stress and the operating time corresponding to the onset of the onset of the main crack and the moment of fracture of the sample for steel 9Mn2Si steel. The dependence of the average growth rate of the main crack on the applied stress during fatigue tests is obtained.

Analiza zmęczeniowa półosi napędowej samochodu osobowego

The subject of the research was the fatigue crack of the rear driveshafts in a BMW E36 car with a 2.5 L engine in sports driving conditions. The genesis of the work is the author's own experience, with the common type of damage to the driveshaft, consisting in fatigue-related twisting. The analysis was aimed at deter-mining the causes of fatigue failure. Additionally, the work proposes design changes that can improve fatigue properties. As part of the research, the analysis of steel composition with a spark spectrometer, analytical calculations identifying the stress state at the fracture site, fatigue calculations, FEM calculations and frac-tographic analysis of fatigue fractures were performed.

Study on the Effect of Deposited Graphene Oxide on the Fatigue Life of Austenitic Steel 1.4541 in Different Temperature Ranges

This paper presents the effect of deposited graphene oxide coating on fatigue life of austenitic steel 1.4541 at 20 °C, 100 °C, and 200 °C. The study showed a decrease in the fatigue life of samples with a deposited graphene oxide layer in comparison with reference samples at 20 °C and 100 °C. However, an increase in fatigue life of samples with a deposited graphene oxide layer in comparison with reference samples occurred at 200 °C. This relationship was observed for the nominal stress amplitude of 370 and 420 MPa. Measurements of temperature during the tensile failure of the sample and microfractographic analysis of fatigue fractures were performed. Tests have shown that graphene oxide deposited on the steel surface provides an insulating layer. A higher temperature of the samples with a deposited graphene oxide layer was observed during fracture compared to the reference samples.

Effect of plasma electrolytic oxidation on the hot salt corrosion fatigue behavior of the TC17 titanium alloy

AbstractIn this paper, the effect of plasma electrolytic oxidation (PEO) on the hot salt corrosion fatigue (HSCF) behavior of the TC17 titanium alloy at 420°C was investigated. Through microstructure characterization and fatigue fracture analysis, combined with a comparative study of its hot salt corrosion behavior, the mechanism of PEO on HSCF behavior was also investigated. The results showed that the high‐temperature fatigue resistance of the TC17 titanium alloy was significantly reduced by the deposition of 0.4 mg/cm2 of solid NaCl compared with that without a salt coating. This behavior was observed because the corrosion pits caused by hot salt corrosion promoted the initiation of fatigue cracks, and hydrogen penetration promoted the growth of fatigue cracks. However, the HSCF resistance of the TC17 alloy with the PEO ceramic coating could be effectively increased. This was because the PEO ceramic coating with high bonding strength and good compactness effectively inhibited hot salt corrosion damage and delayed the formation of the resident slip zone and hydrogen permeation, thereby inhibiting the initiation and propagation of fatigue cracks.

Effect of microstructure on low-cycle fatigue property of Ti6321 alloy

The low-cycle-fatigue behavior of Ti6321 alloy with bimodal and lamellar microstructure have been investigated by analyzing of strain-cycles curve under different stress amplitudes. The results show that under the stress amplitude of 600 MPa, the fatigue life of lamellar microstructure is 6644 times, and the fatigue life of bimodal microstructure is 16252, which is more than twice that of the former. What’s more, two dislocation models of initiation and growth of cracks were demonstrated by analysis of fatigue fracture. The bimodal microstructure have the higher dislocation density and the shorter effective dislocation slip distance, which could hinder the initiation and propagation of fatigue cracks. The findings of low-cycle-fatigue property can provide data support and theoretical guidence for the safety assessment of titanium alloy pressure structures.

A new microstructure‐based multiaxial fatigue life prediction model for A319 casting alloys

AbstractThis paper describes a microstructure‐based multiaxial nonproportional fatigue life prediction model applied to A319 alloy. The materials made with different casting cooling rates and Sr modification are characterized and quantified in terms of secondary dendrite arm spacing, size, and aspect ratio of eutectic Si particles. Multiaxial nonproportional fatigue tests have been performed on six groups of A319 alloys to systematically analyze the effect of microstructure and loading path on the fatigue properties of Al–Si cast alloy. The first part of the paper is focused on microstructure quantitative characterization to determine the influence of different casting conditions, followed by stress response behavior and fatigue fracture analysis. Finally, a new multiaxial fatigue life prediction model for Al–Si alloy is proposed, for which 56% of the data points fall in the bound lines of factor of 2 and 83% of the data points fall in the bound lines of factor of 3.

Experimental investigation of ultra-low-cycle fatigue behaviors of plate bearings in spatial grid structures

Ultra-low-cycle fatigue failure of plate bearings in steel grid structures is likely to occur due to an earthquake, which leads to a failure or even complete grid collapse. In this study, the effects of different variables on the hysteretic behavior, skeleton curves, stiffness degradation, and angles of inclination of the bearings and the anchor bolts were investigated. These variables included the vertical force, diameter of anchor bolts and extra baffles. For these purposes, ultra-low-cycle fatigue tests on six groups of plate bearings were carried out under constant vertical loading and horizontal reciprocating variable loading. In addition, the morphological analysis of fatigue fractures was performed to investigate the failure mechanism of anchor bolts in the bearings. It was found that the anchor bolt is the weakest part of the plate bearings during strong earthquakes. Cracks originate at the root of the anchor bolt and expand as the stress concentration increases and a typical ultra-low-cycle fatigue fracture micro-morphology appears. Also, it was also found that adding a baffle in an appropriate position on the bearings can improve the resistance ability against falling from the base supports providing that the baffle capacity is designed properly. Furthermore, a formula for the relationship between horizontal stiffness degradation and cumulative damage of a plate bearing is established. This formula can provide a reference for the seismic capacity evaluation of plate bearings used in spatial grid structures.

SEM analysis of PA38-T6 aluminum alloy thin-walled tubular specimen fatigue fracture, and comparison to surface replication results

The paper presents results of SEM analysis of fatigue fracture surface of thin-walled tubular specimen manufactured from PA38-T6 aluminum alloy. In the previous research specimens were subjected to multiaxial loadings. They were axial, torsional, in-phase, 90º out-of-phase and asynchronous loadings. During the fatigue experiments, the process of initiation and development of cracks was tracked using the surface replication technique, using cellulose acetate thin foils. In the present work, SEM observations of fatigue fracture surface were conducted and compared to previously obtained data. It was confirmed, that the dominating mechanism of fatigue crack formation was the coalescence of small crack, regardless of loading type and level.

Retracted] Mechanical Strength and Fatigue Fracture Analysis on Al‐Zn‐Mg Alloy with the Influence of Creep Aging Process

The Al‐Zn‐Mg alloy comes under the aluminium alloy; it possesses good capability of age hardening and superior strength in contrast to other alloys. The numbers of creep aging experiments are conducted with the support of different temperature levels such as 180, 200, and 2000°C. The effects of tests are reflected on the tensile test and fatigue tests; the temperature and stress directly affects the creep characteristics, mechanical strength, and fatigue performance of the Al‐Zn‐Mg alloy. The time period of the creep test is maintained as 15 hrs with constant load of 200 MPa and 220 MPa. The increasing temperature increases the tensile strength and fatigue life of the Al‐Zn‐Mg alloy under initial condition; furthermore, continuous increment reduces the strength and fatigue existence. In the fatigue test, the fatigue span of the Al‐Zn‐Mg is extremely enhanced by the application of creep aging at a particular temperature. The 3D profilometry image visibly shows the influence of temperature in forming a fracture in fatigue analysis through microstructure analysis.

Retracted] Microstructure and Fatigue Properties of 6061 Aluminum Alloy Laser‐MIG Hybrid Welding Joint

Laser‐MIG hybrid welding of 6061‐T6 aluminum alloy was carried out with ER4043 welding wire, and the microstructure and fatigue properties of the joint were studied. The grain size of HAZ is larger than that of base metal (BM) due to the influence of welding heat cycle. Snowflake‐like equiaxed grains were found in the upper, middle, and lower parts of the welded joint (WJ). Based on the fatigue test with 1 × 106 cycles, the ultimate fatigue strength of BM and WJ is 101.9 MPa and 54.4 MPa, respectively. There are many pores with different sizes in WJ. The number of pores in the upper and middle parts of WJ is obviously larger than that in the lower part due to the influence of the cooling rate of the weld pool and the escape rate of pores. The porosity type is mainly metallurgical pores with regular morphology, which is mainly due to the bubbles formed by the evaporation of Mg elements and H2O in the oxide film on the BM surface. The fatigue fracture analysis shows that the main cause of fatigue crack is the near‐surface pores with 460 μm and 190 μm, respectively. The existence of pores near the surface is equivalent to the formation of a large‐scale prefabricated crack, resulting in serious stress concentration. The morphology of the grains around the pores has a great influence on the initiation and propagation of the fatigue microcracks.

Low-Cycle Fatigue Behavior of the Novel Steel and 30SiMn2MoV Steel at 700 °C.

As a newly developed gun barrel steel, the novel steel has shown excellent high-temperature strength, high resistance to wear and erosion, contributing to the superior ballistic life of gun barrels. As ballistic life increases, the fatigue life becomes essential for the safety and reliability of gun barrels. This paper presents a comparison of the low cycle fatigue (LCF) behaviors between a novel steel and 30SiMn2MoV steel at 700 °C. A strain-controlled fatigue test was carried out on the novel steel and 30SiMn2MoV steel in the strain range from 0.2 to 0.6%. The cyclic stress response behaviors of the novel steel and 30SiMn2MoV steel show cyclic softening behavior. In addition, the shape of the hysteresis rings of the novel steel and 30SiMn2MoV steel exhibit no-Masing model behavior. Energy–life relationships results show that the novel steel has higher fatigue resistance than the 30SiMn2MoV steel at 700 °C. The results of fatigue fracture analysis show that the failure mode of the 30SiMn2MoV steel is a mixed mode of intergranular fracture and transgranular fracture, while the failure mode of the novel steel is intergranular fracture. The cyclic softening of the two materials can be attributed to the lath structure with a high density of dislocations gradually transforms into low energy subcrystalline and cellular structures at 700 °C. The novel steel has a better fatigue life than the 30SiMn2MoV steel at 700 °C and different strain amplitudes, which is mainly related to the carbides and lath martensite in the materials.

Initiation and Propagation Characteristics of Multi-Source Fatigue Crack in Superalloy Disk

The multi-source fatigue crack growth characteristics of a turbine disk were studied via high-speed rotating low cycle fatigue test, fracture analysis and crack growth simulation analysis. The results show that the fatigue initiation life N0 of Superalloy disk and its simulation parts is less dispersive and similar, and the S-N0 curve of the material is not conservative to predict the N0 of the disk. The fracture of eccentric hole of disk is multi-source fatigue fracture, and the surface characteristic of the crack L/D decreases rapidly from 7.5 to 2, which is obviously different from the single source fatigue crack growth. Because of the long and thin stress distribution at the eccentric hole and the small dispersivity of GH698 crack initiation life, it's relatively easy to crack on the plane A of the eccentric hole, which is prone to multi-source fatigue. At the stage of a ≥ 1.23 mm, the reverse life of crack propagation fracture of 2# and 5# eccentric holes is consistent, and the error between the simulation value of single source fatigue crack propagation life and the reverse life is below 5%. In the stage of 0.61 mm ≤ a < 1.23 mm, the simulation crack growth rate of 5# eccentric hole of multi-source is close to that of fracture inversion. Accurate simulation analysis of multi-source crack growth needs to define the initial crack accurately, at the same time, consider the influence of existing fatigue damage on crack growth.

RETRACTED: Fatigue fracture analysis of the semi-auto shotgun mechanism by using finite element analysis and experimental setup

This article has been retracted: please see Elsevier Policy on Article Withdrawal ( https://www.elsevier.com/about/our-business/policies/article-withdrawal ). This article has been retracted at the request of the Editor-in-Chief. The authors have plagiarized part of a paper that had already appeared in [Engineering Failure Analysis, Volume 16 (2009) 2235-2244. https://doi.org/10.1016/j.engfailanal.2009.03.014 ] One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not appeared in a publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

Effect of surface nanocrystallization on fatigue crack initiation and propagation behavior in pure Zr

Through an innovative fatigue test design, the initiation and propagation of fatigue cracks were observed with a microscope in real time, and the effects of surface nanocrystallization on the fatigue properties of pure Zr were systematically studied in the work. The results showed that the fatigue limit of pure Zr treated by ultrasonic shot peening (USSP) for 45 min was up to 11.2% higher than that of the original pure Zr. Both the initiation life and propagation life of fatigue cracks could be increased after USSP treatment. When the cyclic stress was set as 225 MPa, the initiation life and propagation life of fatigue cracks in the 45-min USSP-treated pure Zr were 3.1 times and 1.48 times those of the original samples, respectively. The lower the cyclic stress was, the more obvious the improvement in the initiation life of the fatigue cracks. This improvement in initiation life was the main reason for the promotion in the overall fatigue life of the USSP-treated samples. The results of the fatigue fracture analysis showed that a large number of secondary cracks and dimples appeared in both the original and the USSP-treated samples. However, the fatigue bands in the original pure Zr were disorderly, whereas those in the USSP-treated pure Zr were parallel to each other and perpendicular to the direction of crack propagation.

A review of failure modes and fracture analysis of aircraft composite materials

Composite material-based structures have become increasingly common for aircraft construction. While a large number of researches focused on the understanding of composite materials and structures’ behavior under a variety of scenarios to determine their performance when being exposed to flight loads, it is also critical to consider how these materials fail and fracture, especially in an aircraft accident. In this study, tension, compression, bend, impact, and fatigue fracture analysis of composite laminates and sandwich structures are reviewed, and the failure modes and characteristics of adhesively and mechanically fastened joints are analyzed. Furthermore, aircraft accidents in which composite materials failed are described to highlight the significance of the understanding of composite materials failure modes and fracture analysis on the overall aircraft accident investigation process. Thus, the presented study has a twofold purpose. To provide an all-encompassing review of current research in the area of composite material failure modes and fracture analysis, as well as presenting exemplary cases of aircraft accidents in which the composite material failure modes and fracture analysis body of knowledge has been practically applied. Three overarching themes were observed during the study. First, the complexity of composite material fracture analysis when compared to metallic material fracture analysis. Second, the relationship and dependency between fractographic features of composite materials and the composite structure itself and the failure mode. Lastly, the study and further investigation of composite material failures are found to be critical for aircraft accident investigations. The results from this review can be applied to identify areas of future development concerning composite material failure modes and fracture analysis, especially with applications to material analysis during aircraft accident investigations.

Fatigue fracture analysis of brake disc bolts under continuous braking condition

In this research, the bolts fracture problem of brake disc under a section downhill of the Lanzhou-Wulumuqi railway (LW) line has been studied via experimental and fatigue analysis. The physical and chemical properties of the bolts were examined to analyze the fracture causes. In addition, the LW line condition was investigated and fitted to obtain the altitude-velocity histories. The finite element model of the brake disc was established with the thermo-mechanical coupling method to obtain the temperature and stress variation. Results revealed that the material defect was inexistence at the thread root, and the bolt performances meet relevant standards. Due to special geographical conditions in LW line, the train have to brake continually. The bolt fracture of the brake disc is caused mainly by high temperature during the continuous braking.

Analysis of Fatigue Fracture and Strength Improvement of Backup Rolls

As an important part of the cold rolling mill, the backup rolls are always in service under complicated stress conditions. Once the roll fails, it will bring huge economic losses. In this paper, the problem of fracture failure of the backup roll neck position in an 1150mm six-roll reversible cold rolling mill of a company is analyzed. The stress distribution of the barrels under working condition is calculated by the finite element software ABAQUS, and the stress value at the dangerous section of the backup roll is obtained. The fatigue strength safety factor of the backup roll is obtained by analytical calculation. Combined with the actual production situation, from the perspective of structure and size design, improved schemes can be proposed to improve the fatigue strength of the backup roll. This analysis can provide reference for related enterprises.

Applying Digital Image Correlation Technique for Studying the Growth of a Fatigue Crack in VT23 Titanium Alloy Welded Joints

We present results of applying a combined approach to studying fatigue fracture processes in VT23 titanium alloy with a laser-welded joint. The approach involves fractographic examination using scanning electron microscopy and analysis of strain fields at the sample surface (using digital image correlation technique). Samples with permanent connections are presented in two forms: in the initial state and subjected to post-welding treatment by ultrasonic forging and pulsed high-energy impact. It is shown that applying the proposed integrated approach to the analysis of fatigue fracture has allowed identifying features in the development of processes of nucleation and propagation of cracks and locating them in the bulk of the material, as well as determining running times after which transition from one stage to another takes place: crack initiation, stable growth, and rupture. The results have made it possible to explain the mechanisms of how post-welding treatment of permanent joints affects their fatigue properties.

Variable amplitude fatigue test of M30 high-strength bolt in bolt-sphere joint grid structures

Fatigue failure of a grid structure using bolt-sphere joints is liable to occur in a high-strength bolt due to the alternating and reciprocal actions of a suspension crane. In this study, variable amplitude fatigue tests were carried out on 20 40 Cr steel alloy M30 high-strength bolts using an MTS fatigue testing machine, and four cyclic stress amplitude loading patterns, Low-High, High- Low, Low-High-Low, and High-Low-High, were tested. The scanning electron microscope images of bolt fatigue failure due to variable amplitude stress were obtained, and the fractographic analysis of fatigue fractures was performed to investigate the fatigue failure mechanisms. Based on the available data from the constant amplitude fatigue tests, the variable amplitude fatigue life of an M30 high-strength bolt in a bolt-sphere joint was estimated using both Miner's rule and the Corten-Dolan model. Since both cumulative damage models gave similar predictions, Miner's rule is suggested for estimating the variable-amplitude fatigue life of M30 high-strength bolts in a grid structure with bolt-sphere joints; the S-N fatigue curve of the M30 high-strength bolts under variable amplitude loading was derived using equivalent stress amplitude as a design parameter.

Corrosion and corrosion fatigue performances of micro‐arc oxidation coating on AZ31B cast magnesium alloy

In this work, the corrosion performances of micro‐arc oxidation (MAO) coating on AZ31B cast alloy were examined. MAO coating synthesized at a low current density of 34 mA/cm2 has a uniform and compact microstructure with very fine micro‐pores and few structural defects; thus, robust protection is provided for the AZ31B substrate in corrosive solutions. The long‐term corrosion and corrosion fatigue behaviors of the MAO coatings formed at the optimal current density for 5 and 10 min were characterized. The results show that the MAO coating formed for 10 min provides greater protection in a salt fog environment than the coating formed for 5 min does because it is thicker. The fatigue life and fracture analysis of bare, MAO‐coated and E‐paint MAO‐coated AZ31B indicate that the MAO coating reduces corrosion fatigue life by 55% due to the micro‐pores and micro‐cracks on its surface providing initiation sites under stress conditions and accelerating crack propagation. However, E‐paint MAO‐coated specimens show improved corrosion fatigue strength in 107 cycles at ∼60 and ∼50 MPa under the same conditions due to the sealing of the micro‐pores and micro‐cracks in the MAO coatings.