•The vibration fatigue behavior of DZ125L alloy under different stress levels were investigated.•A vibration fatigue life prediction model based on the phase transformation theory is developed.•The ...fatigue crack growth mechanism of DZ125L alloy under vibration load is proved by experiments and simulations.
Directionally solidified nickel base superalloy DZ125L is the main material that has been widely used to manufacture aviation gas turbine blades and hot-end structural parts. Aeroengine is under vibration load for a long time in the service process, which makes vibration fatigue become one of the main failure modes of aero-engine structures. In this study, vibration fatigue behavior and excitation frequency response curves of DZ125L alloy under different stress levels were investigated through vibration fatigue tests. The fatigue crack initiation and growth mechanism of DZ125L alloy under vibration load is studied based on the results of the vibration fatigue test and finite element simulation. A vibration fatigue life prediction model based on the phase transformation theory is developed. Each parameter has clear physical significance in the model. The comparison between the model prediction results and the test results shows that the theoretical prediction results have reasonable accuracy.
•DSOLSP processing is proposed for the small-sized blisk.•DSOLSP causes a two-way bending deformation of the blade.•The gradient microstructure and full-thickness CRS are induced by DSOLSP.•The ...vibration fatigue strength of the DSOLSPed blades increased by 25.9%.•The anti-fatigue mechanism of DSOLSP is elucidated.
Double-sided symmetric oblique laser shock peening (DSOLSP) was adopted to experiment on a small-sized blisk with restricted space. The influences of different laser energies on the shape deviation, surface roughness, microhardness, and residual stress of the blades were studied. The optimum process parameters were selected based on the shape deviation results of the blades and the microstructural evolution of the surface layers was investigated. The strengthening effect of DSOLSP treatment on notched blades was evaluated by vibration fatigue tests. It was found that DSOLSP can effectively cover the fatigue vulnerable regions without interference. Two-way bending deformation was formed after DSOLSP, and the shape deviation of the blades could be controlled within ±0.02 mm. With the increase of laser energy, the surface roughness and the depth of work-hardened layer increased. The full-thickness compressive residual stress (CRS) field was induced. A gradient microstructure was generated on the surface of the blade, and the size of average nanograins on the topmost surface is approximately 36.5 nm. The fatigue strength of the DSOLSP treated blades with notches was increased by 25.9 %. The enhancement can be attributed to the synergistic strengthening of CRS and gradient microstructure.
In this paper, a comparative review between time- and frequency-domain methods for fatigue damage assessment is performed. The principal steps of a fatigue study are described in detail: Material ...Characterization, Definition of the Reference Parameter, Treatment of Loading History, Cycle Counting Algorithm and Damage Model. Furthermore, for each of them the main differences found between the advances made in the time- and frequency-domains are highlighted. As a conclusion, this comparative literature review allows us to identify some important lights and shadows in both approaches: several efforts have been made in the development of advanced material characterization models in S-N field in the time-domain methods, either deterministic or probabilistic, but in the frequency-domain methods only the linear Basquin model is currently used. Also the ongoing discussion about the reference parameter in material characterization (stress, strain, energy, etc.) is not present in the frequency-domain methods, which are mainly based on the stress range. Contrarily, the frequency-domain methods show an advanced treatment of the rainflow histogram with different proposed statistical distributions together with theoretical and analytical relationships between the power spectral density and the expected fatigue damage, leading to a simpler and easier methodology to be applied for fatigue damage assessment than those based on time-domain.
•A comparative review between time- and frequency-domain methods for fatigue damage assessment is performed.•The development of material characterization models is more prolific in time-domain.•The selection of a suitable reference parameter is an ongoing topic in time-domain.•A vast different proposed models to define analytically the rainflow cycle has been formulated in frequency-domain.
Vibration is the main factor causing high cycle fatigue. The macro-response stress and strain of the structure under the excitation of vibration load are generally in the elastic stage. However, ...fatigue failure still occurs due to long-term cyclic load, which is unexplainable by the macro-plastic accumulation method. Therefore, a two-scale nonlinear damage accumulation model is proposed for vibration fatigue based on the physical characteristics of multi-scale fatigue damage evolution. In this model, two-scale elastic-plastic constitutive equations based on the equivalent inclusion theory are built, and a two-stage damage accumulation strategy with two critical damages is designed. A resonance fatigue life prediction algorithm is established based on the proposed model, and a validation test is carried out using the cantilever beam made of GH4169 alloy. The results show that the deviation between the vibration fatigue life prediction and test results is within a scatter band of factor 2, indicating that the two-scale nonlinear damage accumulation model is effective in the vibration fatigue region.
•Two-scale equations with equivalent inclusion theory are built for vibration fatigue.•Cross-scale damage accumulation strategy with two critical damages is first proposed.•Vibration life predictions and test results are within a scatter band of factor 2.
Vibration fatigue by spectral methods relates the theory of structural dynamics to high-cycle vibration fatigue. An ideal spectral method should perform well and consistently, regardless of the ...response spectrum and the material being analyzed. The primary aim of this review is to develop a common theoretical and open-source-code framework for a side-by-side comparison of more than 20 spectral methods, which will help a future spectral-domain vibration-fatigue research. The reviewed spectral methods are structured in terms of the damage-estimation concept: narrowband approximation, narrowband correction factor (Wirsching–Light, Ortiz–Chen, α0.75, Tovo–Benasciutti (two versions)), rainflow probability-density-function approximation (Dirlik, Zhao–Baker, Park, Jun–Park) and combined fatigue damage, where the damage is combined according to the cycle types (Jiao–Moan, Sakai–Okamura, Fu–Cebon, modified Fu–Cebon, Low’s bimodal, Low 2014, Gao–Moan) and the narrowband damage combination criterion (Lotsberg, Huang–Moan, single moment, bands method). All the reviewed methods are implemented in the supporting open-source Python package FLife, with the comparison being fully reproducible using the package documentation. The accuracy of the spectral methods is investigated in terms of a time-domain rainflow analysis, where three different materials are considered: steel, aluminium and spring steel. The comparison is based on typical PSD defined signals, with the focus on: spectral width, background noise, close modes, number of modes and typical vibration profiles used in accelerated automotive tests. In addition, a bimodal spectrum is formulated to examine a specific group of spectral methods that are developed for bimodal random processes. This research shows that other methods, besides the well-established ones, such as the Dirlik and Tovo-Benasciutti methods, should be considered when the fatigue load is broadband: Ortiz–Chen, α0.75, Park, Jun–Park and Huang–Moan methods. Furthermore, as the fatigue analysis of bimodal random processes has become well established, the applicability of bimodal methods is inspected. Among the reviewed spectral methods, Low’s bimodal and Low 2014 method show exceptional accuracy that can be attained using the bimodal formulation.
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•21 different methods are compared for broadband loads.•8 different methods are compared for bimodal loads.•Typical structural dynamics response spectra in vibration-fatigue are analysed.•Fully reproducible comparison with open-source package.
•The effect of FCHs on the vibration fatigue performance of DZ125L alloy was studied.•The crack propagation mechanism of FCH specimens under vibration was proposed.•Two new models enhance the ...applicability of frequency domain method to FCHs.
Film cooling represents a critical protective measure for turbine blades, yet the presence of film cooling holes (FCHs) under vibrational loads can significantly impact structural strength and integrity. This study conducts random fatigue tests on DZ125L directionally solidified superalloy specimens with FCHs. It investigates how various FCH types and vibration signal intensities influence the vibration fatigue behavior of DZ125L alloy. Characterization of vibration fatigue fracture and surface cracks of FCH specimens utilizes ultra depth of field microscopy and scanning electron microscopy. Additionally, the crack propagation mechanism for FCH specimens under random processes is proposed based on finite element stress distribution and fracture morphology. Results reveal the generation of two types of cracks, namely hole cracks and edge cracks, under vibration load in FCH specimens. The crack propagation process produces water wave-like fatigue striations. Notably, a low stress zone exists between the two dangerous holes in the multi-hole specimen, mitigating the expansion trend of hole cracks between the FCHs compared to cracks expanding towards the edges. Furthermore, two novel models, New1 and New2, are introduced to enhance the applicability of the frequency domain method for predicting the fatigue life of FCH specimens under random processes. Accuracy and error analyses of the models suggest that New2, incorporating the FCH stress concentration coefficient KT and intensity function f(ξ), exhibits superior accuracy and stability.
•A fatigue life prediction method for non-stationary vibration is proposed.•Non-stationary pavement excitations are generated by data augmentation methods.•The LSTM surrogate model can accurately ...predict the response of the structure.•The representative time required for fatigue analysis is estimated.•The fatigue life of automobile control arm is predicted.
Automotive components are prone to fatigue failure as a result of the long-term effects of vibration loads. Due to the significant non-stationarity of irregular excitations from various road surfaces, the classical frequency-domain method struggles to accurately estimate the fatigue life of automotive components. Based on long short-term memory (LSTM) networks, an efficient time-domain method for non-stationary vibration fatigue life prediction is proposed. Firstly, the data augmentation method for simulating long-time non-stationary loads is studied. Short-time histories are transformed into time–frequency spectrograms, and then the time–frequency spectrums are warped and masked to reconstruct the long-time non-stationary loads. Furthermore, employing only short-time loads and responses as training samples, the LSTM network is trained to construct a surrogate model for calculating structural stress time histories. Finally, the responses of varying-length long-time loads are calculated, and fatigue life is predicted by the combination of rainflow counting and Miner rule. Additionally, the representative response durations required for the fatigue analysis are estimated. Numerical simulation of control arms shows that the fatigue life prediction results using the LSTM surrogate model are within 1.9% difference compared to transient dynamics analysis results based on finite element method, and the calculation efficiency is improved by orders of magnitude.
•We present a data-driven framework to establish spectral multiaxial fatigue criteria.•The method can be used for multiaxial fatigue analysis in the frequency domain.•The method explicitly addresses ...the non-proportional multiaxial stress effect.•Different time-domain multiaxial fatigue criteria can be adopted into their spectral equivalent.•Various data-driven models can be incorporated into the framework.
Random vibration fatigue of structures is intrinsically multiaxial, driven by complex stress states. Non-proportional multiaxial stresses exacerbate fatigue damage compared to proportional stresses. Frequency domain fatigue analysis is generally more efficient for structures operating near natural frequencies. However, handling non-proportional multiaxial stress effects in the frequency domain remains challenging. This paper introduces a data-driven framework that reformulates time domain multiaxial fatigue failure criteria into their frequency domain counterparts, explicitly addressing non-proportional effects. The method introduces a non-proportional correction factor into the power spectral density of equivalent stress, determined through a data-driven approach, converting various time domain multiaxial fatigue criteria into their frequency domain equivalents. Combined with modal decomposition analysis, this approach efficiently evaluates multiaxial vibration fatigue for engineering structures, effectively accounting for non-proportional stress effects.
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•We present a frequency domain procedure to model multiaxial fatigue of welded structures.•Mesh insensitive traction stress method is applied to address the stress singularity at the ...welds.•Traction stress mode shape and modal decomposition is used to compute the weld line dynamic stress.•A correlation coefficient function can address non-proportional multiaxial stress effects.•The method can identify the most detrimental mode in terms of fatigue for optimizing fatigue design.
Modeling of vibration fatigue of welded structures in the frequency domain can be particularly challenging. For instance, the stress singularity at weld locations causes finite element size sensitivity in stress determination. Furthermore, the interactions of multiple vibration modes at a weld location can generate non-proportional multiaxial stresses. Here we present a comprehensive procedure for modeling multiaxial fatigue behaviors of welded structures in the frequency domain to address some of these issues. The procedure utilizes a robust mesh-insensitive method and modal decomposition approach to determine the normal and shear traction stress responses. We proposed a non-proportionality correlation function to interrelate the resulting power spectrum density (PSD) of normal and shear traction stresses and their cross-PSD (CPSD) for establishing an effective stress parameter. The correlation function is determined and validated based on the well-established time-domain path-dependent maximum range (PDMR) method through a small-scale data-driven approach.
In this paper, a fatigue life prediction model based on the amplitude probability density function under broadband multimodal stochastic vibration response is presented. An analysis method is ...proposed to address the dispersion of the third- and fourth-order normalized moments of rain-flow amplitude distributions. The unified relationships between the first four-order normalized moments of rain-flow amplitude distributions and the spectral parameters are established to determine the model parameters. Through comparison with other frequency-domain methods and based on the tail probability density distribution of rain-flow amplitude, the proposed model offers more precise and stable fitting results under broadband multimodal response power spectra.
