publications | Andrea Chiocca

2024

A Comparative Analysis: Time vs. Frequency Domain Definitions of the Fatemi-Socie Criterion

Adam Niesłony, Michał Böhm, Michele Sgamma, Andrea Chiocca, Francesco Bucchi, and 1 more author

In VAL5 - Fifth International Conference on Material and Component Performance under Variable Amplitude Loading, 2024

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In the realm of multiaxial fatigue analysis, the Fatemi-Socie criterion stands as a well-established and validated tool, having undergone rigorous experimental scrutiny with consistently favorable outcomes across a wide spectrum of materials [1]. Prior evaluations have predominantly involved comparisons under constant amplitude, both in proportional and non-proportional loading scenarios, with less frequent exploration of variable amplitude or random loadings [2]. Notably, there has been a gap in employing this criterion, particularly in the context of frequency domain and algorithms utilizing the power spectral density function. In this study, the authors introduce a comprehensive adaptation of the Fatemi-Socie criterion to the frequency domain and compare the resulting fatigue assessments with those obtained in the time domain. The comparative analysis extends to critical plane identification, critical plane amplitudes and maxima analysis, and overall fatigue life determination. The findings reveal a compelling similarity in fatigue life predictions between computational algorithms operating in both the time and frequency domains, underscoring the criterion’s versatility and robustness.
@inproceedings{Niesony, dimensions = {true}, author = {Nies{\l}ony, Adam and B{\"{o}}hm, Micha{\l} and Sgamma, Michele and Chiocca, Andrea and Bucchi, Francesco and Frendo, Francesco}, doi = {10.48447/VAL5-2024-037}, booktitle = {VAL5 - Fifth International Conference on Material and Component Performance under Variable Amplitude Loading}, title = {{A Comparative Analysis: Time vs. Frequency Domain Definitions of the Fatemi-Socie Criterion}}, year = {2024} }
A closed-form solution for evaluating the Findley critical plane factor

Andrea Chiocca, Michele Sgamma, and Francesco Frendo

European Journal of Mechanics, A/Solids, 2024

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The fatigue assessment of structural components is a significant topic investigated both in the academia and industry. Despite the significant progress in comprehension over the past few decades, fatigue damage remains a significant challenge, often leading to unexpected component failures. One commonly used approach for fatigue assessment is the critical plane analysis, which aids in identifying the critical location and early crack propagation direction in a component. However, the conventional method for calculating critical plane factors is computationally demanding and is typically utilized only when the critical regions of the component are already known. In situations where the critical areas are difficult to be identified due to complex geometry, loads, or constraints, a more efficient method is required for evaluating critical plane factors. This research paper introduces an analytical algorithm to efficiently evaluates the widely used Findley critical plane factor. The algorithm operates within the framework of linear-elastic material behavior and proportional loading conditions, relying on tensor invariants and coordinate transformation laws. The algorithm has been tested on different component geometries, including a box-welded joint and a tubular specimen, subjected to proportional loading conditions such as tension, torsion, and a combination of them. The analytical method allowed a significant reduction in computation time while providing the exact solution of critical plane factor and critical plane orientations.
@article{Chiocca2024a, dimensions = {true}, author = {Chiocca, Andrea and Sgamma, Michele and Frendo, Francesco}, doi = {10.1016/j.euromechsol.2024.105274}, file = {::}, issn = {09977538}, journal = {European Journal of Mechanics, A/Solids}, keywords = {Algorithm optimization,Computational efficiency,Critical plane,Findley,Material fatigue}, pages = {105274}, publisher = {Elsevier Masson}, title = {{A closed-form solution for evaluating the Findley critical plane factor}}, volume = {105}, year = {2024} }
Fatigue assessment of structural components through the Effective Critical Plane factor

Andrea Chiocca, and Francesco Frendo

International Journal of Fatigue, Aug 2024

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The integrity assessment of structural components under complex loading conditions relies on the evaluation of the fatigue damage typically arising from stress concentrations, such as geometric irregularities, notches, weld beads, grooves etc. Various methodologies, including the Notch Stress Approach (NSA), the Theory of Critical Distances (TCD), the Strain Energy Density (SED), and the Critical Plane (CP) concept, have been pivotal in assessing fatigue strength for notched and welded components. Recent works combine some of the above mentioned methodologies, while other works propose to vary the embedded parameters accounting for the loading type or the fatigue lives, trying to improve the accuracy of the fatigue assessment process. This paper introduces a novel approach, the Effective Critical Plane (ECP), which is founded on the critical plane concept. The CP factor is, however, calculated starting from an averaged, over a small volume, stress–strain field. The size of the averaging volume is assumed to be a material parameter and is determined by a best fitting procedure over different experimental data sets. The novel approach is illustrated by means of the Fatemi-Socie and the Smith-Watson-Topper CP damage factors. Its potential application to other CP formulations is straightforward, as well. Literature experimental data for low carbon steel specimens possessing different notches and loading conditions are used to validate the method’s capability in accurately determining the fatigue life and to set the radius of the averaging volume for the given material and CP parameter. A spherical volume or circular area are used in case of fully 3D or 2D numerical models, respectively. Results are compared to those of some of already existing methods, namely SED, TCD and the Modified Wöhler Curve Method.
@article{Chiocca2024b, dimensions = {true}, author = {Chiocca, Andrea and Frendo, Francesco}, doi = {10.1016/j.ijfatigue.2024.108565}, file = {::}, issn = {01421123}, journal = {International Journal of Fatigue}, keywords = {Computational cost,Control volume,Critical plane method,Fatigue assessment,Notched component,Volumetric average}, month = aug, pages = {108565}, publisher = {Elsevier}, title = {{Fatigue assessment of structural components through the Effective Critical Plane factor}}, volume = {189}, year = {2024}, }
How many critical planes? A perspective insight into structural integrity

Andrea Chiocca, Michele Sgamma, and Francesco Frendo

In Procedia Structural Integrity, Aug 2024

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The topic of material fatigue is a subject extensively investigated within both scientific and industrial worlds. Fatigue-induced damage remains a critical concern for a variety of components, encompassing both metallic and non-metallic materials, often leading to unexpected failures during their operational lifecycle. In cases necessitating the assessment of multiaxial fatigue, critical plane methodologies have emerged as a valuable approach. These methodologies offer the means to pinpoint the component’s critical regions and anticipate early-stage crack propagation. Nevertheless, the conventional technique (i.e., plane scanning method) for computing critical plane factors is a time-intensive process, reliant on nested iterations, predominantly suited for research purposes. In numerous cases, where the critical area within a component is unknown in advance (i.e., primarily due to complex geometries and loading conditions) the method proves impractical. Furthermore, the plane scanning method does not provide a deep comprehension of the critical plane concept; indeed, it is just a numerical artifice for calculating stress and strain quantities on different planes. Recently, the authors introduced an efficient algorithm for evaluating critical plane factors. This algorithm is based on a closed form solution and is applicable to all instances where the maximization of a specific parameter, based on stress or strain components, is required. The methodology relies on tensor invariants and coordinates transformation principles thus enhancing the investigation of various critical plane methods. The paper addresses two formulations of the Fatemi-Socie critical plane factor and discusses how the number of critical planes depend on the loading conditions the component is subjected to. By the use of a closed form solution a deep insight of critical planes orientation can be achieved.
@inproceedings{Chiocca2024c, dimensions = {true}, author = {Chiocca, Andrea and Sgamma, Michele and Frendo, Francesco}, booktitle = {Procedia Structural Integrity}, doi = {10.1016/j.prostr.2024.05.007}, issn = {24523216}, keywords = {algorithm efficiency,computational cost,critical plane,fatigue assessment,finite element analysis,multiaxial fatigue}, pages = {42--47}, publisher = {Elsevier}, title = {{How many critical planes? A perspective insight into structural integrity}}, volume = {58}, year = {2024} }
Fatigue assessment of a FSAE car rear upright by a closed form solution of the critical plane method

Andrea Chiocca, Michele Sgamma, Francesco Frendo, Francesco Bucchi, and Giuseppe Marulo

Frattura ed Integrità Strutturale, Aug 2024

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Material fatigue is extensively discussed and researched within scientific and industrial communities. Fatigue damage poses a significant challenge for both metallic and non-metallic components, often resulting in unexpected failures of in-service parts. Within multiaxial fatigue assessment, critical plane methods have gained importance due to their ability to characterize a component’s critical location and detect early crack propagation. However, the conventional approach to calculate critical plane factors is time-consuming, making it primarily suitable for research purposes or when critical regions are already known. In many real-world scenarios, identifying the critical area of a component is difficult due to complex geometries, varying loads, or time limitations. This challenge becomes particularly crucial after topological optimization of components and in the context of lightweight design. Recently, the authors proposed an efficient method for evaluating critical plane factors in closed form, applicable to all cases that necessitate the maximization of specific parameters based on stress and strain components or their combination. This paper presents and validates the proposed methodology, with reference to a rear upright of a FSAE car, which is characterized by a complex geometry and is subjected to non-proportional loading conditions. The efficient algorithm demonstrated a substantial reduction in computation time compared to the standard plane scanning method, while maintaining solution accuracy.
@article{Chiocca2024, author = {Chiocca, Andrea and Sgamma, Michele and Frendo, Francesco and Bucchi, Francesco and Marulo, Giuseppe}, doi = {10.3221/IGF-ESIS.67.11}, issn = {1971-8993}, journal = {Frattura ed Integrit{\`{a}} Strutturale}, keywords = {3D Finite element analysis,Computational analysis,Critical Plane Approach,Fatigue damage,Multiaxial fatigue}, number = {67}, dimensions = {true}, pages = {153--162}, title = {{Fatigue assessment of a FSAE car rear upright by a closed form solution of the critical plane method}}, volume = {18}, year = {2024}, }

Rapid and accurate semi-analytical method for the fatigue assessment with critical plane methods under non-proportional loading and material plasticity

Michele Sgamma, Andrea Chiocca, and Francesco Frendo

International Journal of Fatigue, May 2024

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@article{Sgamma2024a,
  author = {Sgamma, Michele and Chiocca, Andrea and Frendo, Francesco},
  doi = {10.1016/J.IJFATIGUE.2024.108191},
  issn = {0142-1123},
  journal = {International Journal of Fatigue},
  month = may,
  pages = {108191},
  publisher = {Elsevier},
  dimensions = {true},
  title = {{Rapid and accurate semi-analytical method for the fatigue assessment with critical plane methods under non-proportional loading and material plasticity}},
  volume = {182},
  year = {2024},
}

2023

A Novel Digitized Method for the Design and Additive Manufacturing of Orthodontic Space Maintainers

Francesco Tamburrino, Andrea Chiocca, Beatrice Aruanno, Alessandro Paoli, Lisa Lardani, and 5 more authors

Applied Sciences, May 2023

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Primary dentition is crucial in influencing the emergence of permanent teeth. Premature primary tooth loss can result in undesired tooth motions and space loss in the permanent dentition. Typically, fixed or removable dental appliances are adopted to maintain edentulous space until the eruption of permanent teeth. However, traditional space maintainers have limitations in terms of variability in tooth anatomy, potential allergic reactions in some individuals (i.e., nickel sensitivity), difficulties in maintaining oral hygiene, and patient acceptance. The present study introduces a fully digital framework for the design and manufacturing of customized pediatric unilateral space maintainers using generative algorithms. The proposed approach overcomes the current challenges by using a biocompatible resin material and optimizing the device’s size, design, and color. The methodology involves intraoral scanning, surface selection, and trim, generative 3D modeling, finite element analysis (FEA), and additive manufacturing (AM) through vat photopolymerization. FEA results demonstrate the device’s mechanical performance and reliability, while additive manufacturing ensures design freedom, high resolution, surface finishing, dimensional accuracy, and proper fit. The mechanical interlocking system facilitates easy and effective positioning of the device. This digital approach offers the potential for wider usage of space maintainers and can be further validated through experimental assessments and clinical studies.
@article{Tamburrino2023, author = {Tamburrino, Francesco and Chiocca, Andrea and Aruanno, Beatrice and Paoli, Alessandro and Lardani, Lisa and Carli, Elisabetta and Derchi, Giacomo and Giuca, Maria Rita and Razionale, Armando V. and Barone, Sandro}, doi = {10.3390/app13148320}, issn = {20763417}, journal = {Applied Sciences}, number = {14}, pages = {8320}, publisher = {Multidisciplinary Digital Publishing Institute}, title = {{A Novel Digitized Method for the Design and Additive Manufacturing of Orthodontic Space Maintainers}}, volume = {13}, year = {2023}, dimensions = {true}, }

Rapid and accurate fatigue assessment by an efficient critical plane algorithm: application to a FSAE car rear upright

Andrea Chiocca, Michele Sgamma, Francesco Frendo, and Francesco Bucchi

Procedia Structural Integrity, Jan 2023

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@article{Chiocca2023a,
  author = {Chiocca, Andrea and Sgamma, Michele and Frendo, Francesco and Bucchi, Francesco},
  doi = {10.1016/J.PROSTR.2023.07.044},
  issn = {2452-3216},
  journal = {Procedia Structural Integrity},
  month = jan,
  pages = {749--756},
  publisher = {Elsevier},
  title = {{Rapid and accurate fatigue assessment by an efficient critical plane algorithm: application to a FSAE car rear upright}},
  volume = {47},
  year = {2023},
  dimensions = {true},
}

Frequency analysis of random fatigue: Setup for an experimental study

Michele Sgamma, Andrea Chiocca, Francesco Bucchi, and Francesco Frendo

Applied Research, Jan 2023

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The frequency-domain approach to fatigue life estimation in random loading has been largely investigated due to its computational advantages, and several methods for the frequency translation of the most common time-domain methods have been proposed. Between the most known frequency methods, there are Bendat’s method, valid for narrow-band signals, and Dirlik’s formula, which ifis considered the best result for wide-band signals. However, a great part of the frequency methods takes the rainflow count as a reference time-domain method and uses the rainflow damage computation as the exact value to emulate. Therefore, very few experimental data for the fatigue life of mechanical components subject to random loads are available in the literature. This work presents the setup for a series of experimental tests for specimens subjected to random loads, aiming at achieving experimental data to compare with the results provided by frequency methods. After a brief description of the materials used for the setup, the two-step test concept is described: first, the specimen will be subjected to random loads obtained by a certain power spectral density for an amount of time which should nominally cause a 30% of damage; then, the fatigue test will be ended on a resonance testing machine to compute the actual residual fatigue life of the specimen; this two-step testing also allows to reduce the time requested for the tests. The test bench developed for the experimental investigation is described in the paper, together with the results of some preliminary tests, aimed at verifying the feasibility of the conceived procedure.
@article{Sgamma2023, author = {Sgamma, Michele and Chiocca, Andrea and Bucchi, Francesco and Frendo, Francesco}, doi = {10.1002/appl.202200066}, issn = {2702-4288}, journal = {Applied Research}, keywords = {durability,experimental tests,frequency analysis,random fatigue,structural analysis}, pages = {e202200066}, publisher = {John Wiley {\&} Sons, Ltd}, title = {{Frequency analysis of random fatigue: Setup for an experimental study}}, year = {2023}, dimensions = {true}, }
Closed-form solution for the Fatemi-Socie extended critical plane parameter in case of linear elasticity and proportional loading

Andrea Chiocca, Michele Sgamma, and Francesco Frendo

Fatigue & Fracture of Engineering Materials & Structures, Oct 2023

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Fatigue damage remains a significant issue for both metallic and non-metallic components, being the main cause of in-service failures. Among the different assessment methodologies, critical plane methods have gained significance as they enable identifying the critical location and the early crack propagation orientation. However, the standard plane scanning method used for calculating critical plane factors is computationally intensive, and as a result, it is usually applied only when the component’s critical region is known in advance. In the presence of complex geometries, loads, or constraints, a more efficient method would be required. This work presents a closed‐form solution to efficiently evaluate a critical plane factor based on the Fatemi‐Socie criterion, in the case of isotropic linear‐elastic material behavior and proportional loading conditions. The proposed algorithm, based on tensor invariants and coordinate transformation laws, was tested on different case studies under various loading conditions, showing a significant reduction in computation time compared to the standard plane scanning method.
@article{Chiocca2023b, author = {Chiocca, Andrea and Sgamma, Michele and Frendo, Francesco}, doi = {10.1111/FFE.14153}, issn = {1460-2695}, journal = {Fatigue {\&} Fracture of Engineering Materials {\&} Structures}, keywords = {Fatemi,Socie,closed,computational cost,critical plane,fatigue analysis,form solution,speed,up calculation}, month = oct, publisher = {John Wiley {\&} Sons, Ltd}, title = {{Closed-form solution for the Fatemi-Socie extended critical plane parameter in case of linear elasticity and proportional loading}}, year = {2023}, dimensions = {true}, }
An efficient algorithm for critical plane factors evaluation

Andrea Chiocca, Francesco Frendo, and Giuseppe Marulo

International Journal of Mechanical Sciences, Oct 2023

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Fatigue of structural components is a widely discussed subject on which extensive research is still being carried out, both in the scientific and industrial communities. Fatigue damage still represents a major issue for both metallic and non-metallic components, sometimes leading to unforeseen failures for in-service parts. Among all the assessment methodologies, critical plane methods gained a lot of relevance, as they allow the identification of the component’s critical location and the direction of early crack propagation. However, the standard method employed for calculating critical plane factors is very time-consuming as it makes use of nested for/end loops and, for that reason, it is usually applied in a research context, or when the critical areas of the component are known. Very often, however, the critical regions cannot be identified, due to complex geometries, loads or constraints, or the fatigue assessment has to be carried out with tight time scheduling, which is typical of the industry. In this work, an efficient algorithm for calculating critical plane factors, useful to speed up the fatigue assessment process, is presented. The algorithm applies to all critical plane factors that require the maximization of a specific parameter based on stress and strain components or a combination of them. The methodology maximizes the parameter utilizing tensor invariants and coordinates transformation law. In order to validate the proposed methodology, without loosing generality, the Fatemi-Socie critical plane factor was considered. The new algorithm was tested on different geometries (i.e. hourglass, notched and welded joint geometries) under different loading conditions (i.e. proportional/non-proportional, uniaxial and multiaxial loading) and showed a significant reduction in computation time respect the standard plane scanning method, without any loss of solution accuracy.
@article{Chiocca2023, author = {Chiocca, Andrea and Frendo, Francesco and Marulo, Giuseppe}, doi = {10.1016/j.ijmecsci.2022.107974}, issn = {00207403}, journal = {International Journal of Mechanical Sciences}, keywords = {Algorithm efficiency,Computational cost,Critical plane approach,Finite element analysis,Multiaxial fatigue,Uniaxial fatigue}, pages = {107974}, publisher = {Pergamon}, title = {{An efficient algorithm for critical plane factors evaluation}}, volume = {242}, year = {2023}, dimensions = {true}, }

Numerical-experimental characterization of the dynamic behavior of PCB for the fatigue analysis of PCBa

Francesco Fontana, Andrea Chiocca, Michele Sgamma, Francesco Bucchi, and Francesco Frendo

Procedia Structural Integrity, Oct 2023

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@article{Fontana2023,
  author = {Fontana, Francesco and Chiocca, Andrea and Sgamma, Michele and Bucchi, Francesco and Frendo, Francesco},
  doi = {10.1016/J.PROSTR.2023.07.043},
  issn = {2452-3216},
  journal = {Procedia Structural Integrity},
  pages = {757--764},
  publisher = {Elsevier},
  title = {{Numerical-experimental characterization of the dynamic behavior of PCB for the fatigue analysis of PCBa}},
  volume = {47},
  year = {2023},
  dimensions = {true},
}

2022

Dataset of dimensionless operating conditions for welding and metal additive manufacturing

Mattia Moda, Andrea Chiocca, Giuseppe Macoretta, Bernardo Disma Monelli, and Leonardo BERTINI

Oct 2022

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@article{Moda2022a,
  author = {Moda, Mattia and Chiocca, Andrea and Macoretta, Giuseppe and Monelli, Bernardo Disma and BERTINI, Leonardo},
  doi = {10.17632/B2437352KY.2},
  publisher = {Mendeley Data},
  title = {{Dataset of dimensionless operating conditions for welding and metal additive manufacturing}},
  volume = {2},
  year = {2022},
}

Rapid evaluation of notch stress intensity factors using the peak stress method with 3D tetrahedral finite element models: Comparison of commercial codes

Giovanni Meneghetti, Alberto Campagnolo, Alberto Visentin, Massimiliano Avalle, Matteo Benedetti, and 20 more authors

Fatigue and Fracture of Engineering Materials and Structures, Apr 2022

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The peak stress method (PSM) allows a rapid application of the notch stress intensity factor (NSIF) approach to the fatigue life assessment of welded structures, by employing the linear elastic peak stresses evaluated by FE analyses with coarse meshes. Because of the widespread adoption of 3D modeling of large and complex structures in the industry, the PSM has recently been boosted by including four-node and ten-node tetrahedral elements of Ansys FE software, which allows to discretize complex geometries. In this paper, a Round Robin among eleven Italian Universities has been performed to calibrate the PSM with seven different commercial FE software packages. Several 3D mode I, II and III problems have been considered to investigate the influence of (i) FE code, (ii) element type, (iii) mesh pattern, and (iv) procedure to extrapolate stresses at FE nodes. The majority of the adopted FE software packages present similar values of the PSM parameters, the main source of discrepancy being the stress extrapolation method at FE nodes.
@article{Meneghetti2022, author = {Meneghetti, Giovanni and Campagnolo, Alberto and Visentin, Alberto and Avalle, Massimiliano and Benedetti, Matteo and Bighelli, Andrea and Castagnetti, Davide and Chiocca, Andrea and Collini, Luca and {De Agostinis}, Massimiliano and {De Luca}, Alessandro and Dragoni, Eugenio and Fini, Stefano and Fontanari, Vigilio and Frendo, Francesco and Greco, Alessandro and Marannano, Giuseppe and Moroni, Fabrizio and Pantano, Antonio and Pirondi, Alessandro and Rebora, Alessandro and Scattina, Alessandro and Sepe, Raffaele and Spaggiari, Andrea and Zuccarello, Bernardo}, doi = {10.1111/ffe.13645}, issn = {14602695}, journal = {Fatigue and Fracture of Engineering Materials and Structures}, keywords = {FE analysis,coarse mesh,notch stress intensity factor (NSIF),peak stress method (PSM),tetrahedral element}, month = apr, number = {4}, pages = {1005--1034}, publisher = {John Wiley {\&} Sons, Ltd}, title = {{Rapid evaluation of notch stress intensity factors using the peak stress method with 3D tetrahedral finite element models: Comparison of commercial codes}}, volume = {45}, year = {2022}, dimensions = {true}, }

Effects of coating on the fatigue endurance of FDM lattice structures

Andrea Chiocca, Francesco Tamburrino, Francesco Frendo, and Alessandro Paoli

Procedia Structural Integrity, Apr 2022

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@article{Chiocca2022a,
  author = {Chiocca, Andrea and Tamburrino, Francesco and Frendo, Francesco and Paoli, Alessandro},
  doi = {10.1016/j.prostr.2022.12.101},
  issn = {24523216},
  journal = {Procedia Structural Integrity},
  pages = {799--805},
  publisher = {Elsevier},
  title = {{Effects of coating on the fatigue endurance of FDM lattice structures}},
  volume = {42},
  year = {2022},
  dimensions = {true},
}

Influence of residual stresses on the fatigue life of welded joints. Numerical simulation and experimental tests

Andrea Chiocca, Francesco Frendo, Francesco Aiello, and Leonardo Bertini

International Journal of Fatigue, Apr 2022

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@article{Chiocca2022,
  author = {Chiocca, Andrea and Frendo, Francesco and Aiello, Francesco and Bertini, Leonardo},
  doi = {10.1016/j.ijfatigue.2022.106901},
  issn = {01421123},
  journal = {International Journal of Fatigue},
  pages = {106901},
  publisher = {Elsevier},
  title = {{Influence of residual stresses on the fatigue life of welded joints. Numerical simulation and experimental tests}},
  volume = {162},
  year = {2022},
  dimensions = {true},
}

Technological implications of the Rosenthal solution for a moving point heat source in steady state on a semi-infinite solid

Mattia Moda, Andrea Chiocca, Giuseppe Macoretta, Bernardo Disma Monelli, and Leonardo Bertini

Materials & Design, Jul 2022

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@article{Moda2022,
  author = {Moda, Mattia and Chiocca, Andrea and Macoretta, Giuseppe and Monelli, Bernardo Disma and Bertini, Leonardo},
  doi = {10.1016/j.matdes.2022.110991},
  issn = {02641275},
  journal = {Materials {\&} Design},
  month = jul,
  pages = {110991},
  publisher = {Elsevier},
  title = {{Technological implications of the Rosenthal solution for a moving point heat source in steady state on a semi-infinite solid}},
  year = {2022},
  dimensions = {true},
}

2021

Representative structure elements for the fatigue assessment of additively manufactured components

Rainer Wagener, and Andrea Chiocca

In Procedia Structural Integrity, Jan 2021

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The fatigue life estimation of additively manufactured structures can be a very challenging task, because the component behaviour will be influenced by many parameters, such as surface roughness, imperfections and inhomogeneous properties. Furthermore, the loading conditions and the component geometry have to be taken into account. The problem of considering the singular influences adequately is intensified by their interactions, which invokes a simultaneous treatment of all relevant influencing factors. Without predefinition of the fatigue approach, properties to describe the cyclic aspects of component behaviour and the fatigue life are required. Even in the case of using small sized specimens, it is not possible to produce a defect-free material for studying the behaviour of sound material in order to derive cyclic material properties as a requirement for the local strain-based fatigue concept, or in order to derive a reference SN-curve and knock-down factors for load-based concepts. Analysing the microstructure offers additional information about the local material state, because, depending on the lightening strategy, the material can be divided into different areas (up-skin, down-skin, contour, core, etc.) with characteristic distributions of imperfections. In order to use a conventional fatigue approach method, this information is not sufficient, because the interaction of statistically distributed imperfections is superimposed on the effect of singular defects. Due to these reasons and after introducing a new interpretation of the measured stress and strain, a fatigue approach will be discussed, which is based on a combined experimental and numerical derivation of the required local properties of the so-called representative structure elements. In addition to the reduced numerical effort compared to the conventional approaches, a combined experimental and numerical derivation of RSE properties is enabled.
@inproceedings{Wagener2021, author = {Wagener, Rainer and Chiocca, Andrea}, booktitle = {Procedia Structural Integrity}, doi = {10.1016/j.prostr.2021.12.037}, issn = {24523216}, keywords = {Additive manufacturing,Fatigue strength,Incremental step test,Material defects,Representative strucutre elements}, month = jan, pages = {259--265}, publisher = {Elsevier}, title = {{Representative structure elements for the fatigue assessment of additively manufactured components}}, volume = {34}, year = {2021}, dimensions = {true}, }
Residual stresses influence on the fatigue strength of structural components

Andrea Chiocca, Francesco Frendo, and Leonardo Bertini

In Procedia Structural Integrity, Jan 2021

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Several production processes, both conventional and innovative, may result in residual stresses arising in critical areas of a component. The main issues include high distortion, reduced fatigue life, fracturing or delamination. In this context, standard fatigue design codes traditionally consider residual stresses through conservative assumptions, leading to either sub-optimal design or unexpected failures. Recently, innovative computational techniques have been developed to address residual stresses in a more comprehensive way. As a result, a more effective material utilisation and a more accurate fatigue life assessment can be achieved. The present work examines the influence of residual stresses on the fatigue endurance of S355JR structural steel components. Both welded and notched components were analysed, carrying out numerical and experimental analyses. In the case of welded components, residual stresses resulting from the welding process were numerically evaluated by means of an uncoupled thermal-structural simulation, while for notched specimens a preload causing limited yielding was used to induce a local residual stress field comparable to that obtained for welded specimens nearby the critical locations. Even if he work is still in progress, tests carried out with different specimens under different loading conditions allowed to understand the effect of residual stresses on the fatigue life.
@inproceedings{Chiocca2022b, author = {Chiocca, Andrea and Frendo, Francesco and Bertini, Leonardo}, booktitle = {Procedia Structural Integrity}, doi = {10.1016/j.prostr.2022.03.045}, issn = {24523216}, keywords = {S355JR,fatigue,residual stresses,thermal-structural simulation,welding}, month = jan, number = {C}, pages = {447--456}, publisher = {Elsevier}, title = {{Residual stresses influence on the fatigue strength of structural components}}, volume = {38}, year = {2021}, dimensions = {true}, }
Influence of residual stresses on the fatigue life of welded joints

Andrea Chiocca

University of Pisa, Jan 2021

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A deep knowledge of the production process is needed, in order to achieve quality and safety requirements in a structural component. As a matter of fact, manufacturing processes can introduce defects such as residual stresses, internal and superficial imperfections. Together with the inherent geometric variations, such as notches, cracks or defects in general, it is often difficult to precisely characterise the structural strength of such parts. In this context, residual stresses play an important role, especially in welded structures. The evaluation of residual stresses is typically performed using both experimental and numerical methods. Both present strengths and drawbacks which demand their combined usage to achieve a consistent and meaningful evaluation of the residual stresses. Within this scope, this PhD thesis presents an evaluation of residual stresses in a pipe-to-plate welded joint and studied their influence on the fatigue life of torsionally and bending loaded components. In the first part, the finite element method was used to assess the capability of different thermal methods used to simulate a single pass of the gas metal arc welding process in reproducing the temperature distribution around the weld bead. Results of the simulations were compared to experimental measurements of the surface temperature close to the weld region. The considered thermal techniques adopted different levels of complexity, from the basic implementation of a constant initial temperature assigned to a given material volume, to the more comprehensive and widespread Goldak’s double-ellipsoid model. The study shows that, close to the weld seam, very similar thermal behaviours can be achieved by employing each one of the analysed methods. Secondly, considering the constant initial temperature method, the comparison between experimental measurements and numerical simulations showed a fairly good agreement, suggesting that a relatively simple method (i.e., requiring the setting of only one parameter) can be used to efficiently reproduce the thermal history of a welding process. In the second part, the study of residual stresses for a S355JR carbon steel pipe-to-plate welded joint is presented. Numerical simulations and experimental tests were both employed in order to gain wide-ranging knowledge. Numerical simulations were performed with the software Ansys through uncoupled thermal-structural simulations in order to evaluate the stresses, strains and temperature at each node of the finite element model for each phase of the simulation. Temperature-dependent elastic-plastic material properties were adopted in combination with the \backslashtextit{element birth \backslash& death} method to simulate the welding process. Two different numerical approaches were implemented for reproducing the weld seam solidification process. The obtained results were discussed and compared with experimental data, in terms of relaxed radial strains measured nearby the seam weld, due to a material removal procedure. The third part investigates the influence of residual stresses on the fatigue life of the welded joints. Influencing factors such as geometric discontinuities and the material heterogeneous microstructure were considered. Experimental tests on as-welded and stress relieved specimens with fully reversed torsion and bending loading conditions were carried out. Experimental results showed how residual stresses exhibited an influence mainly on torsionally loaded components. Numerically, the uncoupled thermal-structural finite element simulation presented in the chapters before was used to assess the complete residual stress field within the specimens. Secondly, residual stresses were mapped and included as initial condition in numerical models intended for fatigue damage factors calculation. Finally, experimental results were then used to corroborate numerical models and verify their efficacy in assessing fatigue endurance. In the last part of this work, a preliminary numerical study of a notched specimen geometry is presented. The work attempts to reproduce residual stress conditions comparable to those found on the welded joint critical notch section on notched specimens thus in order to explain the results observed on welded specimens. Indeed, by varying notch radius and opening angle of a cylindrical specimen, it is possible to obtain a stress gradient similar to that obtained after the welding process at the weld notches. The use of simplified geometry allows easier analysis and a possible improved understanding of the processes taking place within the material.
@phdthesis{ChioccaPHD, author = {Chiocca, Andrea}, doi = {10.13131/unipi/etd/10252021-122902}, pages = {97}, school = {University of Pisa}, title = {{Influence of residual stresses on the fatigue life of welded joints}}, year = {2021}, dimensions = {true}, }
Evaluation of residual stresses in a pipe-to-plate welded joint by means of uncoupled thermal-structural simulation and experimental tests

Andrea Chiocca, Francesco Frendo, and Leonardo Bertini

International Journal of Mechanical Sciences, Jun 2021

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Fatigue of structural components is a widely discussed subject on which extensive research is still being carried out, both in the scientific and industrial communities. Fatigue damage remains a major issue for both metallic and non-metallic components, sometimes resulting in unforeseen failures for in-service parts. Among all the assessment methodologies, critical plane methods have gained relevance as they allow the identification of the component’s critical location and the direction of early crack propagation. However, the standard method for calculating critical plane factors is time-consuming, typically involving nested loops, and is mainly used in a research context or when the critical areas of the component are known. Often, though, critical regions cannot be identified due to complex geometries, loads, constraints, or the need for rapid industry-based fatigue assessments. In this work, an efficient algorithm for calculating critical plane factors, aimed at expediting the fatigue assessment process, is presented. The algorithm applies to all critical plane factors that require the maximization of a specific parameter based on stress and strain components or their combinations. The methodology maximizes the parameter using tensor invariants and coordinate transformation laws. To validate the proposed methodology, without losing generality, the "Fatemi-Socie" critical plane factor was considered. The new algorithm was tested on different geometries (e.g., hourglass, notched, and welded joint geometries) under various loading conditions (e.g., proportional/non-proportional, uniaxial, and multiaxial loading) and demonstrated a significant reduction in computation time compared to the standard plane scanning method, without compromising solution accuracy.
@article{Chiocca2021, author = {Chiocca, Andrea and Frendo, Francesco and Bertini, Leonardo}, doi = {10.1016/j.ijmecsci.2021.106401}, issn = {00207403}, journal = {International Journal of Mechanical Sciences}, month = jun, pages = {106401}, publisher = {Elsevier BV}, title = {{Evaluation of residual stresses in a pipe-to-plate welded joint by means of uncoupled thermal-structural simulation and experimental tests}}, volume = {199}, year = {2021}, dimensions = {true}, }

2020

Fatigue life assessment of welded joints under sequences of bending and torsion loading blocks of different lengths

Francesco Frendo, Giuseppe Marulo, Andrea Chiocca, and Leonardo Bertini

Fatigue and Fracture of Engineering Materials and Structures, Jun 2020

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In this work, the nominal stress concept, the notch stress approach and two critical plane approaches are used to analyse the fatigue endurance of a pipe-to-plate welded joint subjected to complex loading histories. Both the pipe and the plate were made of S355JR steel. Starting from already known fatigue endurance curves obtained for the same specimens under pure bending and pure torsion, a first series of tests was conducted, in which specimens were loaded in bending for a given fraction of the estimated life and then in torsion until failure. A similar series of tests was then carried out by changing the loading order: specimens were firstly loaded in torsion for a given fraction of the estimated endurance and then in bending until failure. The whole test campaign was repeated for two different fractions of the estimated life, that is, 0.3 and 0.45, respectively. After that, additional three series of tests were carried out, in which the specimens were subjected to consecutive sequences of bending and torsion blocks of different lengths (short, medium and long, respectively); the relative length of the bending and torsion block in each series was determined in order to produce the same damage. The experimental results, in terms of total damage at failure, were analysed using the Palmgren–Miner hypothesis. For all the assessment methods, the characteristic endurance curves were firstly calibrated on the basis of finite element (FE) analyses and of the experimental results obtained under pure bending and pure torsion loadings. The observed damage at failure resulted always greater than 0.5 for all the employed methods and greater than 1 for most of the tests. The different methods gave similar results, with the critical plane methods giving a slightly more stable damage at failure and a correct determination of the failure location. For all the methods, the damage at failure slightly reduces as the block length shortens.
@article{Frendo2020, author = {Frendo, Francesco and Marulo, Giuseppe and Chiocca, Andrea and Bertini, Leonardo}, doi = {10.1111/ffe.13223}, issn = {14602695}, journal = {Fatigue and Fracture of Engineering Materials and Structures}, keywords = {critical plane,loading blocks,multiaxial fatigue,nominal stress,notch stress,welded joints}, number = {6}, pages = {1290--1304}, publisher = {Blackwell Publishing Ltd}, title = {{Fatigue life assessment of welded joints under sequences of bending and torsion loading blocks of different lengths}}, volume = {43}, year = {2020}, dimensions = {true}, }

Experimental evaluation of relaxed strains in a pipe-to-plate welded joint by means of incremental cutting process

Andrea Chiocca, Francesco Frendo, and Leonardo Bertini

Procedia Structural Integrity, Jan 2020

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@article{Chiocca2020,
  author = {Chiocca, Andrea and Frendo, Francesco and Bertini, Leonardo},
  doi = {10.1016/j.prostr.2020.11.043},
  issn = {24523216},
  journal = {Procedia Structural Integrity},
  month = jan,
  pages = {2157--2167},
  publisher = {Elsevier},
  title = {{Experimental evaluation of relaxed strains in a pipe-to-plate welded joint by means of incremental cutting process}},
  volume = {28},
  year = {2020},
  dimensions = {true},
}

2019

Evaluation of residual stresses in a tube-to-plate welded joint

Andrea Chiocca, Francesco Frendo, and Leonardo Bertini

MATEC Web of Conferences, Jan 2019

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A deep understanding of the manufacturing process is needed in order to achieve safety and quality requirements for parts and components; to this regard, residual stresses play an important role in welded structures. Residual stresses are mainly caused by the extremely severe thermal cycle to which the welded metal and base material are subjected to during welding process and their knowledge leads to a better static and fatigue assessment of welded joints. This work deals with the study of residual stresses for a tube to plate T-joint, made of S355JR carbon steel. The work was carried out by both numerical simulations and experimental tests. The numerical simulations were performed by Ansys FE code through a structural-thermal full transient analysis to evaluate stress, strain and temperature in each node at each step of the simulation. The “birth and death” method was employed, together with temperature-dependent material properties.A2Danda3D simulation were performed, in order to evaluate possible diﬀerences due to the welding process. Numerical results were compared to some preliminary measurements obtained through an incremental cut made on the plate.
@article{Chiocca2019c, author = {Chiocca, Andrea and Frendo, Francesco and Bertini, Leonardo}, doi = {10.1051/matecconf/201930019005}, journal = {MATEC Web of Conferences}, keywords = {chemistry,conference,engineering,materials,open access,proceedings}, pages = {19005}, publisher = {EDP Sciences}, title = {{Evaluation of residual stresses in a tube-to-plate welded joint}}, volume = {300}, year = {2019}, dimensions = {true}, }
Evaluation of heat sources for the simulation of the temperature distribution in gas metal arc welded joints

Andrea Chiocca, Francesco Frendo, and Leonardo Bertini

Metals, Jan 2019

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Residual stresses can affect both the static strength and the fatigue endurance of welded joints. Residual stresses can be assessed by numerical simulation; however, the simulation of the welding process is a complex task that requires knowledge of several parameters, many of which can only be estimated with some uncertainty. The reduction in the number of these parameters can lead to a more feasible and efficient study. In this work, the finite element method is used to assess the capability of different thermal methods used to simulate a single pass of the gas metal arc welding process in reproducing the temperature distribution around the weld. Results of the simulations are compared to experimental measurements of the surface temperature close to the welding area. The thermal techniques analyzed adopt different levels of complexity, from the basic implementation of a constant initial temperature assigned to a given material volume, to the more comprehensive and widespread Goldak’s double-ellipsoid model. The study shows that, close to the weld seam, very similar thermal behaviors can be achieved by employing each one of the analyzed methods. Secondly, considering the constant initial temperature method, the comparison between experimental measurements and numerical simulations showed a fairly good agreement, suggesting that a relatively simple method (i.e., requiring the setting of only one parameter) can be used to efficiently reproduce the thermal history of a welding process.
@article{Chiocca2019b, author = {Chiocca, Andrea and Frendo, Francesco and Bertini, Leonardo}, doi = {10.3390/met9111142}, issn = {20754701}, journal = {Metals}, keywords = {Constant initial temperature,Element birth and death,FE simulation,GMAW,Goldak's double ellipsoid,Numerical analysis,Residual stress,Steel,Thermo-mechanical analysis,Welded joints}, number = {11}, pages = {1142}, publisher = {MDPI AG}, title = {{Evaluation of heat sources for the simulation of the temperature distribution in gas metal arc welded joints}}, volume = {9}, year = {2019}, dimensions = {true}, }