Search

The fatigue behaviour of notched and unnotched specimens produced by additively manufactured Inconel 718 were analysed in the as‐built and heat‐treated conditions. The surfaces display high roughness and defects acting as fatigue initiation sites. In the as‐built condition, fine subgrains were found, while in in the heat‐treated state, the subgrains were removed and the dislocation density recovered. SN‐curves are predicted based on tensile properties, hardness and defects obtained by fractography, using the urn:x-wiley:ffe:media:ffe13300:ffe13300-math-0001‐method. © 2020 The Authors. Fatigue & Fracture of Engineering Materials & Structures published by John Wiley & Sons Ltd This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Weld quality could have a significant influence on the fatigue strength of welded components. The correlation between weld imperfections and fatigue strength is defined in different guidelines as IIW-recommendations or the German technical bulletin DVS 0705 in a conservative manner. In order to assess the influence of weld porosity on fatigue strength in a more accurate way, experimental and numerical investigations on welded specimens with internal pores were performed. Experimentally, the specimens were tested under cyclic loading until failure and finally, the fracture surfaces were evaluated with respect to the size and location of the defects and the fracture behaviour. Numerically the specimens were simulated including the inner pores and evaluated regarding the number of cycles to c rack initiation and crack propagation, respectively. Besides the conventional approach to fatigue assessment of welded components based on their fatigue classes, the applicability of the fatigue damage parameter according to Fatemi and Socie was examined in order to estimate the fatigue life until the formation of a crack from the initial pore. The remaining life until failure was estimated using fracture mechanics methods in combination with the fatigue crack growth curve da/dN. The results demonstrate that in general the number of cycles until crack formation is larger than the cycles of crack propagation until failure. Therefore, the assumption of the pore as a sharp crack would underestimate the fatigue life significantly. With the combination of both methods, the estimation of crack f ormation using an appropriate damage parameter and crack extension based on fracture mechanics the fatigue life of welded plates with internal pores can be described in accordance with the experiments.

As the older wind farms are slowly reaching their design lifetime, topics like fatigue and lifetime assessment gain importance. To decide on a possible lifetime extension of the turbine and its foundation, an accurate fatigue assessment for every wind turbine in the farm is needed. As the installation of specific sensors needed for a fatigue assessment is too time consuming and costly, the “Fleet Leader Concept” is applied and validated in this paper. Here, a few turbines are instrumented and a fatigue assessment based on rainflow counting and Miner’s rule can be performed. For a farm-wide fatigue assessment, the obtained damage is extrapolated towards the other turbines. Sample based bootstrapping is performed to introduce an uncertainty on the results. A successful extrapolation was obtained for in-field measurements at an older offshore wind farm. In general, relative errors of less than 5% on damage were found.

The fatigue strength of ferritic, pearlitic, and solution strengthened ferritic ductile irons taken from heavy sections and characterized by long solidification times has been assessed. Starting from the idea of Murakami and co‐workers, a new model for the prediction of the fatigue strength is proposed. It allows a sound fatigue assessment of the fatigue strength of as‐cast ductile irons containing solidification defects, such as low nodule count, exploded, chunky and spiky graphite, or microshrinkage porosities. The newly developed equation validated by means of an extensive benchmarking with data taken from the literature has shown a very high potential for applications to thick‐walled components. This is the pre-peer reviewed version of an article, which has been published in final form at [https://doi.org/10.1111/ffe.12815]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.

Orthotropic deck structures are used in many steel bridges. Due to the typical detailing applied as around 1970, a significant number of deck structures constructed in that period suffer from fatigue damage. In many countries cracks have been detected, in particular in the weld between the deck plate and the trapezoidal stiffener. These cracks tend to grow relatively slowly, but are difficult to detect at an early stage because they initiate from inside the trapezoidal stiffener.This paper presents a model with which the growth of these cracks can be predicted. The model is aimed at the growth rate prediction of through-thickness cracks that can be detected by visual inspection, but that do not have a risk of fracture, which would affect the traffic safety. Stresses are extracted from a detailed finite element model of the entire deck. A second, local finite element model including the crack is used as the basis of a fracture mechanics model. The growth rate determined with the model is calibrated and validated with measured cracks in various bridges.The novel model can be used in daily engineering practice. It can serve to determine inspection intervals for orthotropic bridge decks. It can also serve to support decisions of repairing detected cracks or to determine the effectiveness of strengthening measures such as the addition of a high strength concrete overlay. The model has been successfully applied to 6 large existing bridges in The Netherlands.

Orthotropic deck structures are used in many steel bridges. Due to the typical detailing applied as around 1970, a significant number of deck structures constructed in that period suffer from fatigue damage. In many countries cracks have been detected, in particular in the weld between the deck plate and the trapezoidal stiffener. These cracks tend to grow relatively slowly, but are difficult to detect at an early stage because they initiate from inside the trapezoidal stiffener. This paper presents a model with which the growth of these cracks can be predicted. The model is aimed at the growth rate prediction of through-thickness cracks that can be detected by visual inspection, but that do not have a risk of fracture, which would affect the traffic safety. Stresses are extracted from a detailed finite element model of the entire deck. A second, local finite element model including the crack is used as the basis of a fracture mechanics model. The growth rate determined with the model is calibrated and validated with measured cracks in various bridges. The novel model can be used in daily engineering practice. It can serve to determine inspection intervals for orthotropic bridge decks. It can also serve to support decisions of repairing detected cracks or to determine the effectiveness of strengthening measures such as the addition of a high strength concrete overlay. The model has been successfully applied to 6 large existing bridges in The Netherlands.

The fatigue performance of composite joints is one of the major concerns for the extensive application of composites in aircraft structures. Accurate assessment of the fatigue life behaviour is crucial and valuable to this end. A wearout model was used to characterize the fatigue life behaviour of composite joint structures. The fatigue data used were selected from the open literature. A data fitting tool, which could deal with small fatigue data sample cases, was developed. The tool could accurately replicate the fitting parameters for S-N curves of single-piece composite cases and was used to study the fatigue life behaviour of adhesively bonded and bolted composite joint cases. Recommendations are made for improving the fatigue assessment capability in composite joint structures using the wearout model., 26th Annual Technical Conference of the American Society for Composites 2011 and the 2nd Joint US-Canada Conference on Composites, 26 September 2011 through 28 September 2011, Montreal, QC