Application of the modal superposition technique combined with analytical elastoplastic approaches to assess the fatigue crack initiation on structural components

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Local fatigue approaches, such as, the stress-life, strain-life or energetic approaches defines a framework to estimate the fatigue crack initiation from notches of structural details. Various engineering structures, such as, bridges, wind towers, among others, are subjected to cyclic dynamic loadings which may substantially reduce the strength of these structures. Nowadays, the structural systems tend to be more complex being necessary to find computationally efficient solutions to perform their fatigue analysis, accounting for dynamic actions corresponding to long complex loading events (e.g. diversity of trains crossing a bridge), mainly if local approaches are envisaged. Thus, this paper aims at presenting and validating a generalization of a methodology based on modal superposition technique, for fatigue damage parameters evaluation, which can be applied in fatigue analysis using local approaches. This technique was applied recently in the context of fatigue crack propagation based on fracture mechanics, although it can be extended to compute the history of local notch stresses and strains at notches. A very important conclusion is that the technique can be explored for the case of local confined plasticity at notches whenever the global elastic behaviour of the component prevails. Local submodelling can be explored with this technique to avoid the necessity of large computational models. Local models are only needed to be run under linear elastic conditions for the selected modal shapes of the structure, being the local time history of fatigue damage variable computed by modal superposition for each loading event. That time history may be further post-processed for elastoplastic conditions using Neuber or Glinka's analyses. Comparisons with direct integration elastoplastic dynamic analysis confirmed the feasibility of the proposed approach.Authors acknowledge the Portuguese Foundation for Science and Technology for the funding, particularly through the iRail doctoral program and the grants PD/BD/114101/2015 and SFRH/BPD/107825/2015. Authors gratefully acknowledge the funding of SciTech – Science and Technology for Competitive and Sustainable Industries (NORTE-01-0145-FEDER-000022), R&D project co-financed by Programa Operacional Regional do Norte

Osteochondral Grafting: Effect of Graft Alignment, Material Properties, and Articular Geometry

Osteochondral grafting for cartilage lesions is an attractive surgical procedure; however, the clinical results have not always been successful. Surgical recommendations differ with respect to donor site and graft placement technique. No clear biomechanical analysis of these surgical options has been reported. We hypothesized that differences in graft placement, graft biomechanical properties, and graft topography affect cartilage stresses and strains. A finite element model of articular cartilage and meniscus in a normal knee was constructed. The model was used to analyze the magnitude and the distribution of contact stresses, von Mises stresses, and compressive strains in the intact knee, after creation of an 8-mm diameter osteochondral defect, and after osteochondral grafting of the defect. The effects of graft placement, articular surface topography, and biomechanical properties were evaluated. The osteochondral defect generated minimal changes in peak contact stress (3.6 MPa) relative to the intact condition (3.4 MPa) but significantly increased peak von Mises stress (by 110%) and peak compressive strain (by 63%). A perfectly matched graft restored stresses and strains to near intact conditions. Leaving the graft proud by 0.5 mm generated the greatest increase in local stresses (peak contact stresses = 6.7 MPa). Reducing graft stiffness and curvature of articular surface had lesser effects on local stresses. Graft alignment, graft biomechanical properties, and graft topography all affected cartilage stresses and strains. Contact stresses, von Mises stresses, and compressive strains are biomechanical markers for potential tissue damage and cell death. Leaving the graft proud tends to jeopardize the graft by increasing the stresses and strains on the graft. From a biomechanical perspective, the ideal surgical procedure is a perfectly aligned graft with reasonably matched articular cartilage surface from a lower load-bearing region of the knee

Railway traffic characterisation data based on weigh-in-motion and machine learning: A case study in Portugal

Metallic railway bridges built during the 20th century are ageing, but their continued operation is essential for enhancing the capacity of the network. Structural degradation phenomena are a cause for concern, particularly fatigue, which requires accurate knowledge of service railway loads for structural integrity assessment in order to avoid unnecessary strengthening or premature bridge replacement. Quantifying present traffic scenarios is, therefore, critical and provides a basis for deriving past and future scenarios, given the challenges of implementing permanent weighing systems. Weigh-In-Motion (WIM) approaches are used to periodically collect data on train loads and geometry, generating large datasets containing information such as axle loads, axle spacings, and train speeds. However, identifying train types in these data is often a manual and laborious task, with this information being crucial not only for structural assessment, such as fatigue analysis, but also for broader considerations within the railway sector, including economic and social impacts. This paper presents the outcomes from a WIM system installed on the Alc & aacute;cer do Sal bridge in Portugal to capture real-time train data, which was then post-processed through an automated Machine Learning (ML) approach for train classification. The resulting information is valuable not only for the national context but also for other countries with com-parable traffic characteristics. (c) 2025 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/

Application of the modal superposition technique combined with analytical elastoplastic approaches to assess the fatigue crack initiation on structural components

Local fatigue approaches, such as, the stress-life, strain-life or energetic approaches defines a framework to estimate the fatigue crack initiation from notches of structural details. Various engineering structures, such as, bridges, wind towers, among others, are subjected to cyclic dynamic loadings which may substantially reduce the strength of these structures. Nowadays, the structural systems tend to be more complex being necessary to find computationally efficient solutions to perform their fatigue analysis, accounting for dynamic actions corresponding to long complex loading events (e.g. diversity of trains crossing a bridge), mainly if local approaches are envisaged. Thus, this paper aims at presenting and validating a generalization of a methodology based on modal superposition technique, for fatigue damage parameters evaluation, which can be applied in fatigue analysis using local approaches. This technique was applied recently in the context of fatigue crack propagation based on fracture mechanics, although it can be extended to compute the history of local notch stresses and strains at notches. A very important conclusion is that the technique can be explored for the case of local confined plasticity at notches whenever the global elastic behaviour of the component prevails. Local submodelling can be explored with this technique to avoid the necessity of large computational models. Local models are only needed to be run under linear elastic conditions for the selected modal shapes of the structure, being the local time history of fatigue damage variable computed by modal superposition for each loading event. That time history may be further post-processed for elastoplastic conditions using Neuber or Glinka's analyses. Comparisons with direct integration elastoplastic dynamic analysis confirmed the feasibility of the proposed approach