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•A structural strain method is proposed to evaluate fatigue data of weldments.•A master E-N curve is presented in conjunction with the structural strain method.•Both low- and ...high-cycle fatigue regimes are covered by the master E-N curve.•The method can deal with fatigue data of different base metals in a unified manner.
This paper further investigates into the effectiveness of the structural strain method recently proposed by Dong et al. (2014) to model low-cycle fatigue behavior of welded structures. More precisely, an equivalent structural strain range parameter is introduced and implemented here in order to evaluate fatigue behaviors of welded components spanning both low-cycle and high-cycle fatigue regimes. A large number of well-documented fatigue data of weldments with various joint types, loading modes and base materials have been investigated in detail by using the structural strain approach. These components include gusset-to-plate, plate-to-plate and pipe-to-pipe joint. The fatigue loading varys from load-controlled to displacement-controlled conditions, and the base metals ranges from structural steel of different grades and aluminum alloys as well as titanium alloys. The obtained results show that the equivalent structural strain range parameter enables a unified presentation of the fatigue behaviors of all the test data investigated in this paper.
In order to provide a sufficient theoretical basis for the fatigue‐resistant design of the aircraft wheels, strain‐controlled low‐cycle fatigue (LCF) tests were carried out on specimens machined in ...the extrusion direction (ED) and transverse direction (TD) of die‐forged 2014 aluminum alloy wheels. Although the TD specimens have lower tensile strength and yield strength, the fatigue test results show that the TD specimens have superior fatigue life compared with the ED specimens at total strain amplitudes of 0.5–0.8%. This is predominantly caused by the coarse Al12(MnSi)2(FeCu) intermetallic particles close to the surface layer, which results in a relatively short crack initiation stage for the ED specimens. In contrast, TD specimens with finer and more uniform recrystallized grains exhibit more excellent resistance to fatigue crack initiation (FCI) and propagation (FCP). Moreover, the fatigue life of alloys could be accurately predicted via a Manson–Coffin–Basquin (MCB) model based on total strain.
Highlights
A new die forging method was used to fabricate the aircraft wheel.
Fatigue characteristics and fracture behavior of aircraft wheels were explored.
The accuracy of different fatigue life prediction models was evaluated.
Coarse Al12(MnSi)2(FeCu) intermetallic particles affected fatigue crack initiation.
This work investigates the fatigue response of a class of ductile closed‐cell aluminium alloy foams, known by their commercial name Alulight M8. In order to determine the yield stress of the used ...foams, preliminary experimental tests were performed, at room temperature, in monotonic compression on cylindrical specimens of 25 mm diameter and 25 mm height, with a loading speed of 10 mm/min. Fatigue tests were performed in uniaxial compression on cylindrical specimens (25 mm × 25 mm) with a stress ratio of R = 0.1, at a frequency of 10 Hz. The peak stress was varied from 110 to 135% of the yield stress in compression. Tested specimens were cut from the same cylindrical bar, and the density of the investigated material was 500 kg/m3 ± 10%, or a total of 18 specimens being investigated. With the gathered experimental data, S–N curve was generated, and the effect of cellular structure (e.g. structure irregularity–the number and the size of cells) being investigated and discussed.
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•Welds are created with laser beam or plasma arc techniques, but often constitute the weak point in steel structural entities.•Weld performance often depends on the orientation of the ...weld, and transverse and diagonal welds are commonly used.•With high-strength low-alloy steels, transverse welds exhibit higher fatigue life than diagonal welds.•With high-strength low-alloy steels, laser welded seams exhibit higher fatigue lives than plasma-arc welded seams.
Welded steel structures can be exposed to high dynamic forces and failure typically occurring at the weakest zone within a few (less than 102) cycles. In order to investigate low-cycle fatigue fracture in weld joints of high-strength low-alloy (HSLA) steels, we have studied the fatigue properties in different weld seam orientations and welding processes. The fatigue performance showed that with transverse welding, fatigue lives at high strains (2%) were approximately seven times higher than with diagonal welding, and, for laser welded seams, fatigue lives were approximately two times higher than those for the plasma arc welded seams.
•Uniaxial and multiaxial cyclic deformation behavior of materials is studied.•Cross-Entropy loss function is proved to be useful for regression prediction.•Three Transformer models describe the ...cyclic deformation behavior of materials well.•Attention mechanism of the three models each plays a different role.
In this study, the experimental study of cyclic deformation behavior of Z2CN18.10 austenitic stainless steel under uniaxial, cross, rhombus and circular paths is investigated. Based on Transformer deep learning method, three models are built to predict the cyclic deformation behavior of the material. One is the single input–single output model, which is used to predict the uniaxial cyclic deformation behavior. The second is the double input–single output model, which is used to predict the biaxial cyclic deformation behavior. The third is the time series multi-step model, which is used to predict the stress evolution under all paths. The Cross-Entropy loss function is adopted to train the models and the rationality of its application in the regression model is deduced from the theoretical point of view. Transformer deep learning method is based on attention mechanism, which can focus on the historical effect of Z2CN18.10 stainless steel cyclic deformation and accurately describe the uniaxial and multiaxial cyclic deformation behavior of the material.
Film cooling holes (FCHs) geometric structure significantly affects low‐cycle fatigue (LCF) of the single crystal turbine blade. This study investigates the LCF behavior of Ni‐based single crystal ...plate specimens with two different structure FCHs, including elliptical and fan‐shaped FCHs, by high temperature fatigue tests and crystal plasticity simulation. The results show that the LCF life of the fan‐shaped FCHs is shorter than those of the elliptical FCHs. The fracture characteristics and microstructure evolution of different structure FCHs are dissimilar. Oxidation affects the fatigue crack nucleation process at the FCH edge. The resolved shear stress (RSS) around fan‐shaped FCHs is greater than elliptical FCHs under one cyclic stress, and the area with larger RSS is consistent with fatigue crack nucleation position. The early LCF failure is mainly attributed to the high temperature oxidation of the local slip deformation induced by RSS concentration around the FCHs.
Highlights
Based on real‐shaped structure, the elliptical and fan‐shaped FCHs were designed.
Impact of FCH shape on low‐cycle fatigue behavior was investigated.
Failure mechanism of shaped FCHs was studied by fatigue test and simulation.
Coupling effect of stress oxidation on fatigue crack initiation is discussed.
•Cyclic loading reduces reinforced UHPC flexural strength and deformation capacity.•Cyclic loading reduces UHPC fiber-bridging capacity.•Fiber distribution impacts structural performance under ...different loading directions.•Reducing fiber volume increases UHPC structural ductility under monotonic and cyclic loading.
Ultra-high performance concrete (UHPC) is a promising material for many structural applications given its high compressive strength, its tensile ductility, and its potential durability through low permeability. Most research on steel reinforced UHPC (R/UHPC) flexural components has focused on monotonic performance and less is known about R/UHPC cyclic performance. Additionally, the steel fibers, which typically comprise 2% of the volume of a UHPC mix and account for 30% of the material cost, could potentially be reduced to improve both cost efficiency and performance of R/UHPC components. This study explores the impact of high-amplitude cyclic loading on R/UHPC beams with different fiber volumes (1% and 2%) and reinforcing ratios (0.96% and 2.10%). A total of eight simply-supported beam experiments are compared in this study. Results show that for both monotonic and cyclically-loaded specimens, a higher reinforcing ratio and a lower fiber volume introduce more localized cracks, delay steel fracture, and increase R/UHPC deformation capacity. Compared to monotonically-loaded beams, cyclic loading reduces UHPC fiber-bridging capacity, resulting in lower component yield and peak strength as well as more localized cracks. The deformation capacity of cyclically-loaded beams is also lower than that of monotonically-loaded beams due to low cycle fatigue of the reinforcing steel. Differing fiber distributions due to material flow during casting were also found to impact the structural performance under different loading directions. A flexural failure path prediction method for R/UHPC is validated by both the monotonic and cyclic results.
Foreign non‐metallic inclusions can significantly reduce the low‐cycle fatigue (LCF) life of powder metallurgy (PM) superalloy and greatly affect the safety and reliability of aeroengines. In this ...paper, LCF experiments on PM FGH96 superalloy with and without inclusions were conducted. Effects of inclusions on the fatigue life and damage mechanism of FGH96 alloy are discussed by fractography analysis. Parameters related to inclusion characteristics such as strength–inclusion coefficient are proposed. By introducing characteristic parameters of inclusions, the LCF life prediction models are established based on the Manson–Coffin relationship, which significantly improved the prediction accuracy and reduced the scattering band by a factor of 2.
Highlights
By performing strain‐controlled low‐cycle fatigue tests at different strain amplitudes, statistical analyses were carried out to assess the influences of size, location, and type of inclusions on LCF life, with a quantitative relationship established between them.
The change law of LCF life of powder metallurgy superalloy under different inclusion conditions is summarized. Effects of inclusions on the LCF life of FGH96 alloy were clarified and applied to the establishment of fatigue life prediction models considering characteristic parameters of non‐metal inclusions.
A modified Manson–Coffin life prediction model considering inclusion characteristics is proposed to support the safety and reliability assessment of turbine disks made of PM superalloy FGH96.
By introducing characteristic parameters of inclusions, the LCF life prediction models are established based on the Manson–Coffin relationship, which significantly improved the prediction accuracy and reduced the scattering band by a factor of 2.
Low-cycle fatigue (LCF) is studied for a nickel-based single-crystal superalloy in this paper, with a focus on the effect of crystal orientation and temperature. Specifically, cyclic deformation of ...the alloy was compared for 001- and 111-oriented samples tested under strain-controlled conditions at room temperature and 825 °C. Either cyclic hardening or softening was observed during the LCF process, depending on the strain amplitude, crystallographic orientation and temperature. LCF life was also reduced significantly by changing loading orientation from 001 to 111 or increasing temperature to 825 °C. Employing a comprehensive study with transmission electron microscopy (TEM), a connection between microstructure and mechanical behaviour of the alloy is discussed. It was found that the processes of γ′-precipitate dissolution and dislocation recovery were responsible for cyclic softening. Alignments and pile-ups of dislocations in the γ matrix, which prohibited their movement and reduced the interaction of dislocations on different slip systems, contributed to cyclic hardening.
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