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Rapid methods for assessing the fatigue properties of materials have been developed, among which the self-heating method stands out as particularly promising. This approach analyzes the thermal signal of the specimen when subjected to cyclic loading. In this research, the self-heating method was utilized for the first time with laser powder bed fusion (LPBF) of NiTi alloys, examining two specific loading conditions: loading ratios of 0.1 and 10. A thorough examination of the material self-heating behavior was conducted. For comparative purposes, conventional fatigue tests were also conducted, alongside interrupted fatigue tests designed to highlight the underlying mechanisms involved in high cycle fatigue and potentially self-heating behavior. The investigation revealed several key mechanisms at play, including intra-grain misorientation, the emergence and growth of persistent slip bands, and the formation of stress-induced martensite. These findings not only deepen our understanding of the fatigue behavior of LPBF NiTi alloys but also highlight the self-heating method potential as a tool for studying material fatigue. [ABSTRACT FROM AUTHOR]

Over the past decade, relentless efforts have brought lightweight high-temperature γ-TiAl-based intermetallic alloys into real commercialisation. The materials have found their place in General Electric's (GE) high bypass turbofan aircraft engines for the Boeing 787 as well as in the PW1100GTF engines for low-pressure turbine (LPT) blades. In service, the alloys are required to withstand hostile environments dominated by cyclic stresses or strains. Therefore, to enhance the fatigue resistance of the alloys, a clear understanding of the alloys' response to fatigue loading is pivotal. In the present review, a detailed discussion about the low-cycle fatigue (LCF) behaviour of γ-TiAl-based alloys in terms of crack initiation, propagation and fracture mechanisms, and the influence of temperature and environment on cyclic deformation mechanisms and the resulting fatigue life has been presented. Furthermore, a comprehensive discussion about modelling and prediction of the fatigue property of these alloys with regard to the initiation and propagation lives as well as the total fatigue life has been provided. Moreover, effective methods of optimising the microstructures of γ-TiAl-based alloys to ensure improved LCF behaviour have been elucidated. [ABSTRACT FROM AUTHOR]

Rapid methods for assessing the fatigue properties of materials have been developed, among which the self-heating method stands out as particularly promising. This approach analyzes the thermal signal of the specimen when subjected to cyclic loading. In this research, the self-heating method was utilized for the first time with laser powder bed fusion (LPBF) of NiTi alloys, examining two specific loading conditions: loading ratios of 0.1 and 10. A thorough examination of the material self-heating behavior was conducted. For comparative purposes, conventional fatigue tests were also conducted, alongside interrupted fatigue tests designed to highlight the underlying mechanisms involved in high cycle fatigue and potentially self-heating behavior. The investigation revealed several key mechanisms at play, including intra-grain misorientation, the emergence and growth of persistent slip bands, and the formation of stress-induced martensite. These findings not only deepen our understanding of the fatigue behavior of LPBF NiTi alloys but also highlight the self-heating method potential as a tool for studying material fatigue.

Octet-truss lattice materials have excellent potential for use as lightweight structures due to their high strength and stiffness, but low relative density. Octet-truss lattice specimens fabricated by stereolithography technique with a photopolymer resin were studied in this research. The unit cell orientation effects on the compressive fatigue behaviors of octet-truss lattices were studied using experimental analysis and computer simulation. A detailed comparison was made between the failure modes of static and fatigue failures, and the deformation mechanisms of lattices in different orientations under compressive cyclic load were determined. Both the static mechanical properties and fatigue properties of octet-truss lattices are highly dependent on the lattice orientation. When normalized with respect to their orientation-dependent Young's moduli, the fatigue endurance of lattices in different orientations conforms very well (R2 = 0.88) to a single S-N curve described by a power law. Finally, the differences in fatigue performance between lattices in different orientations were explained and a simple compression–compression fatigue mechanism was determined. Compressive fatigue behaviors of octet-truss lattice structures in three different unit cell orientations were investigated and compared in this research. Orientation-Z structure has the best resistance to fatigue failure in comparison to other orientations. The absolute S–N curves of lattices in different orientations were normalized by their Young's moduli into a curve that can be expressed by one single power law. The mechanism of compressive fatigue failure of octet-truss lattice structures in different orientations was determined. Comparing with fatigue crack initiation and propagation in struts, cyclic ratchetting made dominant contribution to the compressive fatigue failure. The differences between the fatigue resistances of lattices in three orientations were explained by comparing the mechanical response in the finite element model. [ABSTRACT FROM AUTHOR]

Over the past decade, relentless efforts have brought lightweight high-temperature γ-TiAl-based intermetallic alloys into real commercialisation. The materials have found their place in General Electric’s (GE) high bypass turbofan aircraft engines for the Boeing 787 as well as in the PW1100GTF engines for low-pressure turbine (LPT) blades. In service, the alloys are required to withstand hostile environments dominated by cyclic stresses or strains. Therefore, to enhance the fatigue resistance of the alloys, a clear understanding of the alloys’ response to fatigue loading is pivotal. In the present review, a detailed discussion about the low-cycle fatigue (LCF) behaviour of γ-TiAl-based alloys in terms of crack initiation, propagation and fracture mechanisms, and the influence of temperature and environment on cyclic deformation mechanisms and the resulting fatigue life has been presented. Furthermore, a comprehensive discussion about modelling and prediction of the fatigue property of these alloys with regard to the initiation and propagation lives as well as the total fatigue life has been provided. Moreover, effective methods of optimising the microstructures of γ-TiAl-based alloys to ensure improved LCF behaviour have been elucidated.

Fatigue resistance is a crucial requirement to the novel high-entropy alloys when they come to engineering applications, as many metal structures used in practice are failed by cyclic loading. Here, a thorough analysis of the information on the low-cycle fatigue, high-cycle fatigue, crack-growth rates, and fatigue mechanisms in the high-entropy alloy literature unveils a guideline through which the discovery and design of fatigue-resistant high-entropy alloys can be facilitated. Overall, multi-phase alloys, particularly the metastable ones, are favorable to fatigue resistance over single-phase alloys. Suggestions are proposed in the end to accelerate the discovery and design of candidates for fatigue-resistant applications. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an advanced method for the characterization of the fatigue failure and corresponding load process of fastening systems in concrete. The required hysteresis model is based on mathematical and physical principals with a secondary approximation of the hysteresis loops using measurement data in accordance with conformance criteria. Thus conventional characteristic values of the hysteresis loop, displacements, stiffness's and energies could be determined. The developed predictive model uses four adjustment parameters (determined through regression analysis) and was applied to experimental fatigue tests of anchor channels in concrete. Investigations of these adjustment parameters revealed the potential to identify an indicator for the early prediction of experimental tests, in relation to specific changes and processes in the shape and area of hysteresis loops. These geometric properties effect modifications of the hysteresis centroid – being a sensitive characteristic of the loop form, is determined through numerical methods and analysed in correlation with the four adjustment parameters. [ABSTRACT FROM AUTHOR]

This study reviewed the literature discussing repeated sprint ability (RSA) in Australian Football (AF) in order to create recommendations that coaches can apply in the field. The review was conducted at the University of Canberra Library using books, journals and online journals. Movement demands of AF were examined with results showing that the current RSA testing practice of 6x30m is not sport specific. A revised test of 10x20m is proposed, as this more accurately represents the movement demands of AF. Understanding the fatigue mechanisms that underpin RSA, and how best to train them is vital. Training should incorporate a wide variety of interval running, with work to rest ratio's varying from 1:10 with 30 seconds work, to 2:1 with 120 seconds work. Specific RSA drills such as 3 x ([2 x 10, 15, 20m sprint: 15 sec rest]: 4.5 min rest) should be included. Undulating resistance training programs should be implemented to improve strength, power and muscle endurance. The repetition range will vary depending on specific athlete's needs and training history. Plyometric training, including weighted sled sprints, are essential to improve the stretch shortening cycle and increase acceleration. A maximum of 140 landings per session during pre-season and a maximum of 100 landings in season are advised. Incorporating small sided games (SSG) into training sessions can improve RSA whilst concurrently training match awareness and skills. One proposed SSG session is a 4 vs. 4 game, duration 6 x 4 minutes performed at >90% maximum heart rate with 3 minutes active recovery at <60% maximum heart rate. Specific details are provided for each of these training modes and where possible have been adapted specifically for AF. [ABSTRACT FROM AUTHOR]

There is a major interest in replacing cobalt binder in hardmetals (cemented carbides) aiming for materials with similar or even improved properties at a lower price. Nickel is one of the materials most commonly used as a binder alternative to cobalt in these metal-ceramic composites. However, knowledge on mechanical properties and particularly on fatigue behavior of Ni-base cemented carbides is relatively scarce. In this study, the fatigue mechanics and mechanisms of a fine grained WC–Ni grade is assessed. In doing so, fatigue crack growth (FCG) behavior and fatigue limit are determined, and the attained results are compared to corresponding fracture toughness and flexural strength. An analysis of the results within a fatigue mechanics framework permits to validate FCG threshold as the effective fracture toughness under cyclic loading. Experimentally determined data are then used to analyze the fatigue susceptibility of the studied material. It is found that the fatigue sensitivity of the WC–Ni hardmetal investigated is close to that previously reported for Co-base cemented carbides with alike binder mean free path. Additionally, fracture modes under stable and unstable crack growth conditions are inspected. It is evidenced that stable crack growth under cyclic loading within the nickel binder exhibit faceted, crystallographic features. This microscopic failure mode is rationalized on the basis of the comparable sizes of the cyclic plastic zone ahead of the crack tip and the characteristic microstructure length scale where fatigue degradation phenomena take place in hardmetals, i.e. the binder mean free path. [ABSTRACT FROM AUTHOR]

Abstract: The fatigue damage of a glass-reinforced PolyButylene Terephthalate and PolyEthylene Terephthalate with the fiber volume fraction of 30% (PBT+PET GF30) is investigated by means of various techniques. Fatigue tests at R =0.1 are carried out on dogbone specimens and tubular specimens with different fiber orientations. The macroscopic evolution of the material behavior is evaluated and fatigue damage mechanisms are observed with a replica technique, Infrared imaging and scanning electron microscopy. A fatigue damage scenario is finally proposed. It is shown that the propagation of a single macroscopic crack is not the major fatigue mechanism under fatigue loading. Damage is spatially distributed in the material and the classical circular crack at the end of the fiber is confirmed as the based fatigue mechanisms. It is also shown that the damage observed alongside the fibers is related to spatial distribution of fiber rather than stress distribution around one single fiber. [Copyright &y& Elsevier]

Abstract: A Laser Engineered Net Shaping (LENSTM) processed AISI 316L-grade stainless steel possesses unique microstructural features that affect its fatigue damage incubation mechanisms and fatigue life. As observed experimentally, fatigue damage was incubated almost exclusively at a relatively large pore located at or near the specimen surface, or at an incompletely melted powder particle on the surface in some rare cases. Micromechanical simulations were conducted on a series of representative volume elements to probe the micromechanism of fatigue damage incubation. A non-local plastic shear strain range-based fatigue manage parameter was introduced to represent the micronotch plasticity accumulation state under a large deformation gradient region. This microplasticity parameter was found to correlate to the fatigue endurance limit and transition between high cycle and low cycle fatigue regimes quite well. In the high strain amplitude regime , the spatial distribution extends no or little effect on fatigue damage incubation. The scatter in fatigue life is primarily dominated by small crack growth. In the low strain amplitude regime, the void on the edge of the specimen induced two times higher microplasticity compared to void inside the specimen. Due to the high population of the voids inside the alloy, the fatigue strength is limited by the voids on the surface. The microplasticity threshold is approximately 0.15% which corresponds to the fatigue endurance limit of 30.8 MPa. Micromechanical simulation demonstrated that the microplasticity induced by the unmelted powder particle is significantly lower than that generated by the void in the microplasticity threshold regime. Therefore, there must be an interactive effect between unmelted powder particles and the surround porosity in the alloy that incubated the fatigue damage. [Copyright &y& Elsevier]

Abstract: The present study provides a survey on in situ fatigue devices suitable for loading specimens in a scanning electron microscope (SEM). Particular emphasis is placed on the experimental methods employed to operate a small-scale load frame in an environmental SEM (ESEM). Specimen design and surface preparation, various modes of conducting the fatigue tests, specimen heating and imaging at elevated temperatures are considered. In addition, recent data from in situ fatigue studies conducted in an ESEM between room temperature and 600°C are summarized. Fatigue tests conducted on AM60B cast magnesium demonstrate a substantial environmental effect on cyclic deformation and fatigue damage evolution even at room temperature. Fatigue behaviour of high-temperature titanium alloy IMI 834 at 400°C illustrates a completely different effect of environment on slip band formation and crack nucleation as compared to AM60B. Investigations performed on IMI 834 at 600°C reveal current limitations of the in situ fatigue technique applied. An approach to overcome these limitations is discussed. Ambient conditions can be simulated in an ESEM using pure water vapour atmosphere at a pressure similar to the partial pressure of the ambient environment. This is demonstrated for AM60B at room temperature and IMI 834 at 400°C. However, this approach cannot necessarily be applied to all other material/environment combinations as is exemplarily shown for in situ fatigue loading of IMI 834 at 600°C. Data obtained from in situ fatigue testing are compared to those from post-mortem SEM studies of failed specimens, which portray a wrong impression in certain cases. Experimental issues specific to environmental in situ testing at elevated temperatures are addressed as are the ramifications of such tests with respect to modelling of fatigue life. [Copyright &y& Elsevier]

Purpose. To provide an overview of select existing fatigue models and propose a neuroendocrine-based regulatory fatigue model that can serve as a foundation for interventions to manage fatigue. Conceptual Framework. Biobehavioral systems based on a neuroendocrine regulatory framework. Methods. Empirical data and literature review to develop a fatigue model to serve as a foundation for interventions to manage fatigue. Conclusions. The proposed model will facilitate testing of interventions based on the premise that common neuroendocrine transmitters provide the mechanisms of fatigue in patients diagnosed with chronic illnesses, such as with cancer treatment-related fatigue. The model may also be used to identify predictors of fatigue in specific patient populations, provide guidance for clinicians in their selection of precise interventions to be implemented, and identify the effects of treatments captured in these populations. By clearly identifying the mechanisms of fatigue, we can discover which interventions are effective for particular types of fatigue. [ABSTRACT FROM AUTHOR]

Fatigue crack growth is represented using the Unified Approach in terms of two crack-tip driving forces, ΔK and Kmax. In this approach, crack growth is related solely to fracture mechanics parameters. Using this approach, crack-growth trajectory path can be defined in terms of ΔK&ast;–Kmax&ast;, which are two limiting values (they are the same as the thresholds when da/dN=0), for a given crack-growth rate. Pure fatigue is represented by a line ΔK&ast;=Kmax&ast; (a 45° line in the ΔK&ast;–Kmax plot). Normally, fatigue crack growth occurs along with superimposed environmental effects at low crack-growth rates (or low ΔK values) and/or with monotonic fracture modes at high crack-growth rates (or high ΔK values). Both of these superimposed effects are functions of the applied Kmax. They cause shifts in the ΔK&ast;–Kmax&ast; crack-growth trajectory maps. In the Unified Approach, the ΔK&ast;=Kmax&ast; line provides a reference that can be used to quantify the superimposed effects of environment and overload fracture. This paper presents a detailed analysis of these effects, taking as an example an idealized superimposition model. The model predictions are compared with the actual materials behavior of several aluminum alloys and their composites. In SiC particulate-reinforced Al composites, the coarse particulates ahead of the crack-tip fracture readily, causing rapid growth of fatigue crack. The fracture process is Kmax-dependent and hence this superimposed monotonic fracture process get reflected in the crack-growth trajectory map represented in terms of ΔK&ast;–Kmax&ast;. The analysis also shows that the relative ratio of monotonic to fatigue modes varies with load ratio, R. At low load ratios, due to low Kmax value, the crack-growth process is predominantly fatigue-dominated, while at high R-ratios due to high Kmax value crack growth is fracture-dominated. These regimes are reflected differently in the trajectory map. It is shown that crack-growth trajectory maps provide a powerful tool to investigate the changing fatigue mechanisms as a function of load ratio, crack-growth rate and environment. Without proper understanding and quantification of these mechanisms as function of crack-tip driving forces, any life-prediction methodology can only be empirical at best. [Copyright &y& Elsevier]

• Effects of thin cladding layer and annealing on mechanical properties of AISI4340 steel were investigated. • Fatigue crack initiation and propagation processes were in-situ characterized. • The fatigue life decrease obviously after cladding but rise again after annealing. • Fatigue cracking is induced by residual stress and microdefects. In this study, a NiCrFeBSi alloy layer with a thickness of about 140 μm was cladded on the AISI4340 steel and then annealed at 700 °C, and the influences of cladding and annealing on tensile and fatigue damage mechanisms of the AISI4340 steel were investigated. The fatigue stress ranges were set from 0 to 0.30–0.75 of the yield strength, and the fatigue deformation and cracking morphologies after different cycles were in-situ compared to reveal the dynamic damage mechanisms. The results reveal that the yield strength of the substrate shows little change after cladding, while the tensile fracture strain and fatigue life decrease significantly due to the high cracking susceptibility of the cladding layer. After the annealing treatment, the yield strength decreases obviously, while the fracture strain and fatigue life recover somewhat. For the original AISI4340 steel specimen, a few fatigue cracks initiate around the stress concentration region at relative high stress level, and the crack initiation cycles are high. After cladding, more fatigue cracks initiate along the cladding track boundaries at a stress far lower than the yield strength, resulted by the residual stress and microdefects, and some of the microcracks propagate into the substrate, makes the crack initiation cycle decreases sharply. For the annealed specimen, fewer fatigue cracks appear and the main crack initiates at the edge of the cladding layer, and the crack initiation and propagation cycles recover. All the fatigue fracture surfaces are composed of a flat area, a radial area and a fibrous area, and the fracture mode transforms from quasi-cleavage to microporous polymerization with crack propagation. [ABSTRACT FROM AUTHOR]

An overview of our research performed during the last 15 years is presented to improve the understanding of fatigue crack propagation mechanisms. The focus is devoted to ductile metals and the material separation process at low and intermedial crack propagation rates. The effect of environment, short cracks, small-scale yielding as well as large-scale yielding are considered. It will be shown that the dominant intrinsic propagation mechanism in ductile metallic materials is the formation of new surface due to blunting and the re-sharpening during unloading. This process is affected by the environment, however, not by the length of the crack and it is independent of large- or small-scale yielding. [ABSTRACT FROM AUTHOR]

ABSTRACT Several specific features of high-cycle fatigue (HCF) and ultra-high-cycle fatigue (UHCF) are discussed both on the basis of direct experimental results and on the basis of speculations extrapolating HCF data to the UHCF regions. The following points are dealt with: (i) Extent and distribution of cyclic plastic deformation. (ii) Sensitivity of the fatigue behaviour in the HCF and UHCF regions to the start-up procedure of the test and to the preceding stress–strain history. (iii) Role of persistent slip bands (PSBs) and the microcrack initiation in the HCF and UHCF regions. (iv) Dependence of the notch sensitivity on the amplitude of cycling. (v) Effect of high number of very small amplitude cycles on creep behaviour of superalloy single crystals. [ABSTRACT FROM AUTHOR]