•The AISI D2 fatigue behaviour is investigated under EDM and grinding surface processing.•EDM produced higher residual stresses and roughness than grinding and lower fatigue resistance.•Surface ...roughness and surface residual stresses were highly correlated.•Walker mean stress correction was able to model data from the different tested surfaces.•Very high fatigue notch sensitivity with Kf factor higher than the apparent Kt is verified.
Non-conventional machining processes, such as the Electrical Discharging Machining (EDM) offers the possibility to machine very hard materials with great potential to generate complex geometries. However, the EDM process involves significant microstructural changes in the as machined surfaces, which are known to have a significant impact on fatigue behaviour of mechanical parts. This study aims at investigating the fatigue behaviour of the AISI D2 tool steel subjected to EDM machining. Both smooth and notched specimens are tested aiming at assessing the fatigue notch sensitivity of this material and results compared with conventional grinding techniques in terms of fatigue resistance and residuals stresses. The AISI D2 steel shows a microstructure composed of large dendritic primary carbides detrimental to the fatigue resistance. Also, the EDM process is responsible for the generation of detrimental tensile residual stresses that justifies the lower fatigue resistance when compared with the ground material that exhibits beneficial compressive residual stresses. The fatigue test data of the notched specimens machined by EDM process show a high fatigue notch sensitivity of the AISI D2 tool steel. The heterogeneous structure of the material, showing large undissolved carbides, leads to a notch fatigue reduction factor that is higher to the apparent theoretical elastic stress concentration factor.
In Reliability-based Multidisciplinary Design Optimization (RBMDO), the key performance functions of wind turbine are usually implicit, which means the performance response can only be obtained ...through time-consuming Physics Experiment (PE) or Finite Element Analysis (FEA). However, for practical engineering, the computational cost of repeatedly using PE or FEA is prohibitive. To tackle this challenge, in this study, an adaptive Kriging-model-assisted RBMDO strategy is proposed. The novel updated-strategy for performance function in RBMDO is discussed to find effective training samples of active learning for Kriging model. Also, a powerful decoupling strategy of RBMDO is introduced and combined with the proposed method to enhance computational efficiency further. Two case studies, including a mathematic example and a hydraulic turbine rotor bracket design example, are utilized to illustrate the advantage of the given strategy. Finally, the proposed method is applicated into an engineering design of 5 MW offshore wind turbine tower to ensure its reliability and safety.
•A novel Kriging-model-assisted RBMDO strategy.•An updated strategy for Kriging model to find effective training samples.•A powerful decoupling strategy of RBMDO is combined with the proposed method.•Two case studies are utilized to illustrate the advantage of the given strategy.•The proposed method is applied to an RBMDO problem for offshore wind turbine tower.
•A new nonlinear fatigue damage accumulation model based on isodamage curves.•A damage function related to isodamage curves and remaining life aspects.•Fatigue damage modelling and life prediction ...considering the influence of loading history.•Proposed model yields better predictions of three materials under eight types of load spectra than others.
Cumulative fatigue damage analysis and life prediction of engineering structures/components is vital for ensuring their structural integrity and operational reliability under variable amplitude loadings. In this regard, a new nonlinear fatigue damage accumulation model is proposed by introducing a damage function related to the isodamage curves and remaining life aspects. Specifically, its damage exponent is refined by considering effects of loading history. Experimental data from tests available in literature are utilized for model validation and comparison. Compared with four existing models, the proposed model shows higher precision for cumulative damage modelling and fatigue life prediction than others. Moreover, it improves the deficiencies inherent in other rules under the promise of maintaining its simplicity in practice.
•The fatigue behaviour of bolted joints is researched using various test conditions.•Snug-tight concept is explored (used in the industry, lacking in the literature).•The zinc-coated thin steel ...plates used result in a very low friction coefficient.•Innovative global and local approaches are used for the fatigue life prediction.•A master S-N curve based on peak elastic maximum principal stresses was generated.
This work presents global and local fatigue approaches for snug-tight (common in rack structures) and preloaded bolted joints using thin hot-dip galvanized steel plates, where the zinc coating results in a low friction coefficient. Moreover, S-N data supporting the current revision of Eurocode 3 (EN 1993-1-9) is generated by considering remote and net stresses computed directly or by numerical analysis. Additionally, a master S-N curve based on elastic peak stresses is obtained encompassing the effects of the various tested conditions. Finally, a local fatigue life prediction based on the modified Morrow model combined with elastoplastic numerical analysis returns satisfactory results.
•Mixed modes fracture test were perform using rectangular specimens.•The change of the angle of loading effect on fatigue life of the specimens.•The MTS criterion predicts the initial fatigue crack ...curving direction correctly.•The fatigue crack paths under mixed mode conditions were investigated.•The fractography analysis of crack surfaces was performed.
This paper presents the results of an experimental investigation about fatigue crack paths and fatigue crack growth on S355J0 steel subjected to I + II and I + III mixed mode conditions both under load ratios R = 0 and 0.1 and different mode mixities. In particular, compact specimens with distinct notch inclinations were exposed to mixed mode I + II (tension and shear) whereas prismatic specimens provided with an external one-sided sharp notch were subjected to mixed mode I + III under distinct bending to torsion ratios. The influences of distinct load mixities on fatigue crack growth rates and fatigue crack growth directions are analysed and discussed in relation to existing theories. Also the influence of each loading mode for the resulting mixed mode fatigue crack propagation is also discussed.
PurposeThe purpose of this scientific work is to simulate the fatigue damage under random loading, taking into account the mean stress effect on fatigue lifetime and using the Rainflow counting ...technique to assess the fatigue damage by the Ansys software. The used material is aluminum alloy 6082-T6. A comparison with literature results has confirmed this investigation in this paper.Design/methodology/approachThe study of fatigue under random loading is based on the same concepts as constant loading with the addition of damage summation. The proportion of damage caused by a stress cycle depends not only on the alternating stress but also on the mean stress.FindingsAnalysis of the fatigue damage shows that the number of relative damage due to each cycle.Originality/valueThis paper aims to simulate the fatigue damage under random loading for aluminum alloys.
Due to the high abrasiveness and anisotropic nature of composites, along with the need to machine different materials at the same time, drilling multi-materials is a difficult task, and usually ...results in material damage, such as uncut fibres and delamination, hindering hole functionality and reliability. Image processing and analysis algorithms can be developed to effectively assess such damage, allowing for the calculation of delamination factors essential to the quality control of hole inspection in composite materials. In this study, a digital image processing and analysis algorithm was developed in Python to perform the delamination evaluation of drilled holes on a carbon fibre reinforced polymer (CFRP) and aluminium (Al) multi-material. This algorithm was designed to overcome several limitations often found in other algorithms developed with similar purposes, which frequently lead to user mistakes and incorrect results. The new algorithm is easy to use and, without requiring manual pre-editing of the input images, is fully automatic, provides more complete and reliable results (such as the delamination factor), and is a free-of-charge software. For example, the delamination factors of two drilled holes were calculated using the new algorithm and one previously developed in Matlab. Using the previous Matlab algorithm, the delamination factors of the two holes were 1.380 and 2.563, respectively, and using the new Python algorithm, the results were equal to 3.957 and 3.383, respectively. The Python results were more trustworthy, as the first hole had a higher delamination area, so its factor should be higher than that of the second one.
•Fatigue crack growth (FCG) data from puddled iron specimens was analysed.•A statistical analysis based on linear regression model for the experimental FCG data was made.•Fatigue tests on double ...shear constructional detail specimens in puddled iron were carried out.•A statistical evaluation of fatigue tests based on the Castillo & Fernández-Canteli model was carried out.•A comparison between experimental fatigue data, statistical models and construction norms is proposed.
The maintenance of old riveted bridges has become a major concern for railroad managers across Europe. These metallic structures, built on their majority on the second half of the 19th century, are indeed submitted to ever increasing traffic loads (augmentation in weight and speed of rolling stock).
To assess the remaining life of these metallic bridges, some critical structural details have been identified and associated to S-N curves to be used in damage estimation (using Palmgren-Miner's rule for cumulative damage, for example). These constructional details are often described in construction standards, such as the EN 1993-1-9, the BS 5400 and the AASHTO standards. The particularity of older hot-riveted bridges is that their numerous geometric configurations are often under-represented, thus, limiting the accuracy of damage estimation.
To compensate the absence of hot riveted assemblies in the standards, numerous research groups have performed extensive experimental campaigns. However, the heterogeneity and rarity of the material (no longer produced nowadays), as well as the very diverse geometrical configurations used at the time of the construction of the bridges (given the novelty proposed by the introduction of metal as a new material in monumental construction), makes difficult the comparison of experimental data.
In order to facilitate interpretation and differentiation of fatigue data of a particular type of constructional detail, experimental data from double shear assemblies manufactured from three different metallic ancient bridges is considered (French and Portuguese puddled iron bridges). Then, through statistical analysis (linearized boundaries and the Fernández-Canteli model), the S-N curves corresponding to their structural configuration are identified. Comparisons to the EN 1993-1-9, the BS 5400 and the AASHTO standards are also proposed.
The combination of the S-N curves and Fracture Mechanics approaches can be used to evaluate the residual life of the old riveted metallic bridges. Thus, a statistical analysis and discussion of experimental fatigue crack propagation data available for materials from the ancient riveted metallic bridges are made. This analysis is important for the application of the Fracture Mechanics approaches to predict the residual life of structural details.
The present paper proposes a combined tribo-mechanical methodology for assessing friction under conditions representative of metal cutting, without resorting to machining process monitoring. The ...purpose is to withdraw the size effect’s contribution due to tool edge radius to the well-known overestimation of the friction coefficient. Comparative numerical analysis of several tribological tests led us to conclude that the ring compression test is one of the most suitable for reproducing the frictional conditions at the chip–tool interface. Two distinct metallic alloys were selected to demonstrate the application of the proposed methodology (UNS L51120 lead alloy and 18Ni300 maraging steel in conventional and additively manufactured conditions). The results help to better explain the influences of process parameters on the friction coefficient value under high temperature and high strain rate conditions. Results showed a typical increase in the coefficient of friction of up to 20% due to both temperature and strain rate parameters for 18Ni300. The results are of interest because they allow considering potential sources of error in the numerical simulation of metal cutting when the same friction coefficient value is considered for a wide range of cutting parameters.
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