Fatigue Fracture Surface Analysis Research Articles

Novel integration of PSO-enhanced damage mechanics and finite element method for predicting medium–low-cycle fatigue life in perforated structures

In this research, we introduce an innovative approach that combines the Continuum Damage Mechanics-Finite Element Method (CDM-FEM) with the Particle Swarm Optimization (PSO)-based technique, to predict the Medium-Low-Cycle Fatigue (MLCF) life of perforated structures. First, fatigue tests are carried out on three center-perforated structures, aiming to assess their fatigue life under various strengthening conditions. These tests reveal significant variations in fatigue life, accompanied by an examination of crack initiation through the analysis of fatigue fracture surfaces. Second, an innovative fatigue life prediction methodology is applied to perforated structures, which not only forecasts the initiation of fatigue cracks but also traces the progression of damage within these structures. It leverages an elastoplastic constitutive model integrated with damage and a damage evolution model under cyclic loads. The accuracy of this approach is validated by comparison with test results, falling within the three times error band. Finally, we explore the impact of various strengthening techniques, including cross-sectional reinforcement and cold expansion, on the fatigue life and damage evolution of these structures. This is achieved through an in-depth comparative analysis of both experimental data and computational predictions, which provides valuable insights into the behavior of perforated structures under fatigue conditions in practical applications.

The effect of κ-carbides on high cycle fatigue behavior of a Fe-Mn-Al-C lightweight steel

Numerous studies have demonstrated the viability of lightweight Fe-Mn-Al-C steels for exhibiting an improved balance of high strength and high ductility in automotive applications. However, their high-cycle fatigue behaviour has been scarcely studied. This work examines the effect of κ-carbides formed during the aging treatment on the high-cycle fatigue performance of an austenitic Fe-29Mn-8.7Al-1C (wt. %) steel. The material is studied in solution-treated, under-aged, and peak-aged conditions. High-cycle fatigue tests and analysis of fatigue fracture surfaces were performed using SEM and EBSD techniques. The results indicate satisfactory high-cycle fatigue performance in the aged material, somewhat better than for high Mn steels. Fatigue crack formation and growth occur predominantly via a quasi-cleavage mechanism along the [1 1 1] crystallographic planes, which is also a plane for planar glide and the formation of persistent slip bands during plastic deformation. The nanoscale intragranular κ-carbides in the aged samples interact with the gliding dislocations, resulting in the shearing of nanoscale κ-carbides in a weakly coupled regime. The resistance of particles to shearing is determined by their size, volume fraction, and antiphase boundary energy (γAPB), which vary during the aging process. The aged Fe-29Mn-8.7Al-1C steel significantly improves the fatigue strength as the formation of persistent slip bands is delayed due to an additional energy barrier related to the shearing of the κ-carbides. This improvement peaks in the under-aged condition and decreases with further aging time.

Mixed mode fatigue crack growth and fatigue threshold analysis in polyurethane adhesives at elevated temperatures

The paper investigates mixed-mode fatigue crack growth in ductile polyurethane adhesives, emphasizing mode decoupling to distinguish the impact of each loading mode component on crack propagation. It also explores the temperature sensitivity of fatigue crack growth rates for each loading mode. Individual scrutiny of the role of each loading mode in tests is accompanied by an analysis of fatigue fracture surfaces to clarify failure mechanisms. The findings indicate differential sensitivity to ambient temperature between the mode I and mode II components in a mixed mode fatigue test. Notably, the fatigue response of the mode I component exhibited higher sensitivity to temperature than the mode II component in mixed mode fatigue fracture of the tested polyurethanes. The polyurethane adhesives' composition, particularly the hard segment ratio, emerged as a pivotal factor influencing their sensitivity to fatigue loading at elevated temperatures. Temperature effects led to a significant reduction (63%) in the mode I component of mixed mode fatigue for one of the tested adhesives, while the other exhibited a noteworthy increase (154%). This trend which was attributed to the hard segment ratio of the adhesives was also persisted in the shear mode of the mixed mode fatigue results.

Exploring the effect of complex hierarchic microstructure of quenched and partitioned martensitic stainless steels on their high cycle fatigue behaviour

Recent studies have demonstrated the viability of quenching and partitioning (Q&P) treatment for processing martensitic stainless steels showing an improved balance of high strength and sufficient ductility. However, to date, the fatigue behaviour of these materials has not been explored. This study examines the effect of their complex hierarchic microstructure on high cycle fatigue performance. Three steels with different alloying element contents underwent Q&P processing, resulting in multiphase microstructures rich in retained austenite. High cycle fatigue tests and analysis of fatigue fracture surfaces were performed using SEM and EBSD techniques. The results indicate satisfactory high cycle fatigue performance in Q&P treated martensitic stainless steels, surpassing traditional counterparts. Fatigue cracks predominantly form and propagate along martensite packet and block boundaries, while prior austenite grain boundaries and MnS inclusions have minimal influence on fatigue crack formation and growth. Microplastic deformation at the fatigue crack tip enhances local KAM values and triggers localized transformation of retained austenite grains. It is hypothesized that the developed Q&P treated martensitic stainless steels exhibit improved resistance to low cycle fatigue.

Solid-State Additive Deposition of AA7075 on AZ31B Substrate: Heat Treatment to Improve the Corrosion Fatigue Resistance

The influence of heat treatment on the coating microstructure, nanomechanical, and corrosion fatigue properties of solid-state deposition of AA7075 aluminum alloy on AZ31B cast Mg alloy is studied in detail. Transmission electron microscopy (TEM) microstructural analysis shows columnar grain at the interface of AA7075/AZ31B. Electron backscatter diffraction (EBSD) observation discovered elongated grains with a high fraction of deformed grain boundaries as-deposited and heat-treated at 200 °C conditions. In contrast, the annealed samples show recrystallized grains with increasing temperatures from 200 °C to 400 °C. The residual stress of the coating at the surface and subsurface measured by X-ray diffraction shows −55 MPa and −122 MPa, respectively, which transferred to tensile with increasing the annealing temperature up to 400 °C. Annealing treatment of the AA7075 coating considerably improved the nanomechanical properties and corrosion fatigue resistance. With increasing the annealing temperature from 200 °C to 400 °C, the hardness of the coating decreased, while the modulus increased significantly. The analysis of fatigue fracture surfaces revealed that corrosive solution entered through the cracks and accelerated the crack propagation, lowering the fatigue life. However, the presence of recrystallized grains improved the corrosion fatigue resistance.

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.

Fatigue Characteristics of Materials Used in Transport Industry Applications

Abstract Designers have a major interest about fatigue properties of materials used in transport industry. Each component in transport works under alternating stress. From this point of view the fatigue properties are important for single parts lifetime resulting into safety of whole components as cars and airplanes what leads to safety on the roads or air and have influence on human life as well. Therefore this paper deals with fatigue properties of wrought Inconel alloy IN 718 and aluminum cast alloy AlSi9Cu3. Both materials were put on fatigue push – pull test, but Ni – based IN 718 alloy at frequency of loading around 20 000 kHz (High Frequency High Cycles Fatigue) and aluminum alloy AlSi9Cu3 at frequency of loading around 80 Hz (Low Frequency High Cycles Fatigue). These parameters were chosen with respect of usage such materials for production of components used in transport industry applications. Results after fatigue tests are presented as Wohler curve. For prediction of source of fracture the SEM fractography analysis of fatigue fracture surfaces was made.

Effect of heat treatment on tensile and fatigue deformation behavior of extruded Al-12 wt%Si alloy

This study investigated the effect of heat treatment on tensile and high-cycle fatigue deformation behavior of extruded Al-12 wt%Si alloy. The material used in this study was extruded at a ratio of 17.7: 1 through extrusion process. To identify the effects of heat treatment, T6 heat treatment (515 °C/1 h, water quenching, and then 175 °C/10 h) was performed. Microstructural observation identified Si phases aligned in the extrusion direction in both extruded alloy (F) and heat treated alloy (T6). The average grain size of F alloy was 8.15 °C, and that of T6 alloy was 8.22 °C. Both alloys were composed of Al matrix, Si, Al2Cu, Al3Ni and AlFeSi phases. As T6 heat treatment was applied, Al2Cu phases became more finely and evenly distributed. Tensile results confirmed that yield strength increased from 119.0 MPa to 329.0 MPa, ultimate tensile strength increased from 226.8 MPa to 391.4 MPa, and the elongation decreased from 16.1% to 5.0% as T6 heat treatment was applied. High-cycle fatigue results represented F alloy’s fatigue limit as 185 MPa and T6 alloy’s fatigue limit as 275 MPa, indicating that high-cycle fatigue properties increased significantly as heat treatment was conducted. Through tensile and fatigue fracture surface analysis, this study considered the deformation behaviors of extruded and heat treated Al-Si alloys in relation to their microstructures.

Fatigue Fracture Surface Analysis by Local Lattice Rotation Measurement at FIB-milled Areas

Fatigue Fracture Surface Analysis by Local Lattice Rotation Measurement at FIB-milled Areas

Effects of ultrasonic impact treatment combined with the electric discharge surface alloying by molybdenum on the surface related properties of low-carbon steel G21Mn5

Abstract To enhance the fatigue, corrosion and wear behaviors of low-carbon casting steel 20GL (G21Mn5 in EN classification) it was subjected to the effects of severe plastic deformation induced by ultrasonic impact treatment (UIT) and the electric discharge surface alloying (EDSA) with molybdenum. The structural formations in the sub-surface layers were characterized by means of light microscopy, X-ray diffraction analysis and transmission electron microscopy (TEM). Several intermetallic phases were observed in the EDSA-induced layer. TEM studies of transition area between the EDSA layer and steel substrate (at a depth of 15–30 μm) demonstrate that the combined EDSA + UIT process induces the formation of a dislocation-cell structure in the alloyed ferrite grains. Both the cell boundaries and separate dislocations are often blocked by fine intermetallic and/or carbide particles. SEM analysis of fatigue fracture surfaces reveals the subsurface crack nucleation in the UIT-processed specimens instead of superficial crack initiation observed in the pristine and EDSA-processed ones. This provides enhanced fatigue strength and prolonged lifetime of the steel specimens after UIT and EDSA + UIT processes. High molybdenum content supports the improved corrosion resistance and fine intermetallic precipitates in the Fe-Mo protective layer provide the increased hardness and wear resistance of the EDSA + UIT-treated specimens. Thus, the specimens underwent combined EDSA + UIT treatment were shown to exhibit simultaneously increased fatigue strength (by ~ 5%) in low cycle fatigue regime, anti-corrosion properties (by ~ 85%) and wear resistance (by ~ 43%) in comparison with those of the pristine steel G21Mn5.

Fatigue Cracking of AA2519-Ti6Al4V Laminate Bonded by Explosion Welding

This paper presents test results of AA2519/TI6AL4V composite laminate structure and mechanical properties. The composite laminate was merged by explosive welding using a transition AA1050 alloy layer. The tested composite after formation was annealed, quenched in water and then aged to strengthen it. The heat treatment process was carried out in order to improve the physical and strength properties of the laminate. Weld endurance properties were determined through fatigue testing performed in constant total deformation amplitude (εac) conditions.The paper also describes the influence of test conditions on hysteresis loop shape, process of cyclic material strengthening and weakening, and fatigue life. Low cycle test results were approximated using a straight line with the following formula: σa = K'(εap)n which enables the K'fatigue strength coefficient, and the n' cyclic strengthening index to be determined. Test results also include fatigue fracture surface analysis. Distinctive fatigue fissure characteristics were investigated through studying fatigue fracture surface microstructure using a scanning electron microscope.

Comparison of fatigue life assessment by analytical, experimental and damage accumulation modelling approach for steel SAE 1045

AbstractFatigue life assessment for two‐phase steel SAE 1045 has been carried out by experimental and simulation techniques. Analytical approach, termed as fatigue lifetime calculation, was employed making use of a load increase testing procedure and constant amplitude tests equipped with measurement techniques – plastic strain amplitude, change in temperature and change in electrical potential difference. The predicted fatigue life has been validated by constant amplitude tests and compared with fatigue life estimation by microstructure‐based simulation. Simulation has been carried out over the complete cross section of the specimen. The simulation uses damage accumulation in the gage section of the specimen culminating in the macro‐crack propagation, taking into account the inhomogeneous fatigue resistance of the material element. The results show that at the initial intervals of high cycle fatigue range at relatively higher stress amplitudes, the experimental and simulation results are in agreement; whereas in the (high cycle fatigue) region at relatively low stress amplitudes, the simulation results were found more optimistic and the corresponding fatigue scatter is also increased. Each scatter is attributed to the relatively small number of analysed models of the material structure. Scanning electron microscope was used to determine volume fraction of the microstructure for simulation. Fatigue fracture surface analysis shows that crack initiated from internal defect of material and crack propagation is driven by silicon oxide inclusion.

A failure analysis study of a prestressed steel cable of a suspension bridge

This paper presents results of a failure analysis study to characterize the damage phenomenon that occurred in prestressed steel cables of a suspension bridge. This study includes: material characterization using chemical, microstructural and hardness analysis; fractographic analysis by scanning electron microscopy (SEM); mechanical tests of the material in static tension; fatigue tests (S–N curves) and fractographic analysis of fatigue fracture surfaces. The fatigue tests were carried out in laboratory air only and in the laboratory air also but after previous exposure in tap water to simulate the working environment of the cables. Fractured surfaces of the rods were of brittle failure type and also of cup and cone type. Due to the characteristics of the work environment (close to a river) stress corrosion was also observed and it is likely oxygen embrittlement was obtained.Results from fatigue tests and fractographic study allow to the conclusion that the main cause of cable failure, which led to a collapse of the bridge, was stress corrosion cracking (SCC).

Low Cycle Fatigue Properties Laminate AA2519-TI6AL4V

This paper presents test results of AA2519/TI6AL4V composite laminate structure and mechanical properties. The composite laminate was merged by explosive welding using a transition AA1050 alloy layer. Weld endurance properties were determined through fatigue testing performed in constant total deformation amplitude (ɛac) conditions. The paper also describes the influence of test conditions on hysteresis loop shape, process of cyclic material strengthening and weakening, and fatigue life. Low cycle test results were approximated using a straight line with the following formula: σa = K′(ɛap)n which enables the K′ fatigue strength coefficient, and the n′ cyclic strengthening index to be determined. Test results also include fatigue fracture surface analysis. Distinctive fatigue fissure characteristics were investigated through studying fatigue fracture surface microstructure using a scanning electron microscope.

In-situ investigation on the fatigue crack propagation behavior in ferrite-pearlite and dual-phase ferrite-bainite low carbon steels

The purpose of this study was to describe the roles of microstructure types and grain boundary characteristics in fatigue crack propagation behavior in ferrite-pearlite steel and ferrite-bainite steel. The ferrite-bainite dual-phase steel was obtained by intermediate heat treatment conducted on ferrite-pearlite low carbon steel. This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy (SEM), electron backscattering diffraction (EBSD) and fatigue fractography analysis. Microscopic images arrested by in-situ SEM showed that the second hard bainite phase distributed in the soft ferrite matrix had a significant effect on preventing the cracks opening compared with pearlite, and that the cracks in ferrite-bainite steel were “locked” in the second hard bainite phase while the crack propagation path in ferrite-pearlite steel was more tortuous. Moreover, the fatigue fracture surface analysis and the coincidence site lattice (CSL) obtained by EBSD indicated that low-Σ CSL grain boundaries in ferrite-bainite steel distributed more uniformly, which has a more significant effect on the resistance of crack propagation. It was revealed that ferrite-bainite dual-phase microstructures could inhibit the fatigue crack propagation more effectively than ferrite-pearlite microstructures.

Fatigue crack growth behaviors in hot-rolled low carbon steels: A comparison between ferrite–pearlite and ferrite–bainite microstructures

The roles of microstructure types in fatigue crack growth behaviors in ferrite–pearlite steel and ferrite–bainite steel were investigated. The ferrite–bainite dual-phase microstructure was obtained by intermediate heat treatment, conducted on ferrite–pearlite hot-rolled low carbon steel. This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy (SEM), fatigue crack growth (FCG) rate tests, and fatigue fractography analysis. Microscopy images arrested by in-situ SEM showed that the fatigue crack propagation in F–P steel could become unstable more ealier compared with that in F–B steel. The fatigue cracks in ferrite–pearlite were more tortuous and could propagate more freely than that in ferrite–bainite microstructures. However, frequent crack branching were observed in ferrite–bainite steel and it indicated that the second hard bainite phase effectively retarded the crack propagation. The variation of FCG rate (da/dN) with stress intensity factor range (ΔK) for F–P and F–B steels was discussed within the Paris region. It was shown that FCG rate of F–P steel was higher than that of F–B steel. Moreover, the fatigue fracture surface analysis proved that grain boundaries could also play a role in the resistance of crack propagation.

Fractographic analysis of fatigue damage in 7000aluminium alloys

In this paper, an attempt is made to correlate the fatigue damage in 7000 aluminium alloys with different impurity contents to the microstructural features and to explain their interdependence through fractographic observations. The Paris constants of these alloys in the form of hot-forged plates subjected to the overaged T73 temper are evaluated and differences in the fatigue crack growth rate described by striation spacing measurements. Scanning electron microscopy analysis of fatigue fracture surfaces revealed that the type and morphological parameters of coarse intermetallic particles play a critical role in fatigue crack growth behaviour. The elemental distribution determined by means of energy-dispersive spectroscopy analysis showed that the fractured particles accelerating the crack advances are larger particles of Fe-rich phases. The fatigue crack growth rate increases considerably with increasing amounts of these particles. The smaller eta, S and Mg(2)Si particles contribute beneficially to fatigue life.

レール鋼の疲労き裂進展特性に及ぼす累積通過トン数の影響

Influence of accumulative passing tonnage on fatigue crack growth in rail steels was investigated. The fatigue crack growth was measured using compact tension specimens cut from three kinds of rails with accumulative passing tonnage of 100MGT, 200MGT, 600MGT respectively. The fatigue crack growth rate was estimated by the effective stress intensity range ΔKeff obtained by an unloading elastic compliance method. In addition, the measurements of crack opening displacement and the analysis of fatigue fracture surfaces were carried out to clarify the mechanism of crack closure behavior by a scanning electron microscope. It was concluded that the roughness of fatigue crack surface dependent on the grain size of each rail steel influences the crack growth behavior, and that the influence of accumulative passing tonnage on fatigue crack growth behavior can be estimated by the threshold effective stress intensity range ΔKeff, th.

342 破面接触を伴う疲労損傷破面の解析(GS-7 疲労(2))

342 破面接触を伴う疲労損傷破面の解析(GS-7 疲労(2))

Some studies on the influence of stress ratio and test temperature on X-ray fractography observations in C45 steel specimens

This paper deals with additional “X-ray fractography” observations made on C45 steel, subsequent to the earlier work [K. Rajanna, B. Pathiraj and B. H. Kolster, Fatigue fracture surface analysis in C45 steel specimens using X-ray fractography. Engng Fracture Mech. 39, 147–157 (1991)]. Fatigue crack: growth tests were carried out at 20°C on CT samples prepared from this steel using different stress ratios (0.1 R, 0.5 R and 0.7 R). Tests were also carried out at different temperatures (−20°C, 20°C and 115°C) using a stress ratio of 0.1. The fractured surfaces were analysed for their residual stress state. The influence of the test conditions on the residual stresses developed is discussed.