Advanced Approaches Applied to Materials Development and Design Predictions

This thematic issue on advanced simulation tools applied to materials development and design predictions gathers selected extended papers related to power generation systems, presented at the XIX International Colloquium on Mechanical Fatigue of Metals (ICMFM XIX), organized at University of Porto, Portugal, in 2018. In this issue, the limits of the current generation of materials are explored, which are continuously being reached according to the frontier of hostile environments, whether in the aerospace, nuclear, or petrochemistry industry, or in the design of gas turbines where efficiency of energy production and transformation demands increased temperatures and pressures. Thus, advanced methods and applications for theoretical, numerical, and experimental contributions that address these issues on failure mechanism modeling and simulation of materials are covered. As the Guest Editors, we would like to thank all the authors who submitted papers to this Special Issue. All the papers published were peer-reviewed by experts in the field whose comments helped to improve the quality of the edition. We also would like to thank the Editorial Board of Materials for their assistance in managing this Special Issue

A brief review of fatigue design criteria on offshore wind turbine support structures

In this paper, a brief review of the main fatigue design criteria and some advanced fatigue approaches applied to offshore structures (e.g. offshore wind turbines) are presented. It is extremely important to understand the fatigue phenomenon and how it affects structures since offshore structures are constantly submitted to cyclic loading and corrosive attacks that aggravate the problem. All the influencing factors and approaches used during the design phase are also discussed

Literature review of mobile learning systems

This paper presents a research about the monotonic and failure behaviours of bolted joints made of thin plates of S350GD and S355MC steels grades, which are used for rack structures. A full factorial test matrix was performed considering two joints configurations (1+1 and 4+4 double shear bolted joints), two material thicknesses (2 and 3mm), three coatings (“black steel”, zinc coating, zinc plus paint) and two preload levels (25%×70%Fu and 70%Fu). Tests were performed under static monotonic loading until failure. Slip tests were also performed according to the EN 1090-2 standard to evaluate joint slip factors for the three material surface conditions. In addition to the experimental tests, numerical simulation of static tests were performed using elastoplastic material behaviour, based on Mises yield theory and isotropic hardening identified with experimental tensile testing data. The models were able to reproduce conveniently the ultimate loads of the joints and failure modes, including clamping and friction effects

A comparison between S-N Logistic and Kohout-Věchet formulations applied to the fatigue data of old metallic bridges materials

A new formulation of a Logistic deterministic S-N curve is applied to fatigue data of metallic materials from ancient Portuguese riveted steel bridges. This formulation is based on a modified logistic relation that uses three parameters to fit the low-cycle- (LCF), finite-life- and high-cycle-fatigue (HCF) regions. This model is compared to the Kohout-Věchet fatigue model, which has a refined adjustment from very low-cycle fatigue (VLCF) to very high-cycle fatigue (VHCF). These models are also compared with other models, such as, Power law and fatigue-life curve from the ASTM E739 standard. The modelling performance of the S-N curves was made using the fatigue data considering the stress fatigue damage parameter for the materials from the Eiffel, Luiz I, Fão and Trezói riveted steel bridges. Using a qualitative methodology of graphical adjustment analysis and another quantitative using the mean square error, it was possible to evaluate the performance of the mean S-N curve formulation. The results showed that the formulation of the S-N curve using the Logistic equation applied to the metallic materials from the old bridges obtained superior performance to the analysed models, both in the estimation of fatigue behaviour in the low-cycle fatigue (LCF) region and in the lowest mean square error

Fracture evaluation of ultra-high-performance fiber reinforced concrete (UHPFRC)

The development of numerical simulation for Ultra-high-performance concrete (UHPC) and Ultra-high-performance fiber-reinforced concretes (UHPFRC) is fundamental for the design and construction of related structures. The simplified engineering stress-strain relationship and the input values are necessary in the finite element modeling. Four-linear curves and modified Kent–Park model were proposed to describe the engineering tensile and compressive stress-strain relationship, respectively. An attempt was made to simulate the fracture of UHPC and UHPFRC using concrete damaged plasticity model and element deletion strategies. The predicted tensile and compressive behaviors of UHPC and UHPFRC were successfully validated by the test results in the literature. For a better understanding of the mechanical behavior of UHPC and UHPFRC exposed to biaxial loadings, mixed-mode crack propagation simulation on the double-notched specimens exposed to combined shear-tensile and shear-compressive forces was discussed.</p

A FCG Model and the Graphical User Interface Under Matlab for Predicting Fatigue Life: Parametric Studies

The focus of this research work was predicting the fatigue life of mechanical components used for industrial and transport systems. To understand how the phenomenon of fatigue occurs in a material, the fatigue crack growth is studied. The purpose of this work was to create a graphical user interface (GUI) under Matlab to allow researchers to conduct the parametric studies of fatigue crack propagation to predict fatigue life. In this work, three models for fatigue crack propagation were used: those of Paris, Walker and Forman in order to study the three parameters: the Paris exponent m, load ratio R and hardness KIC, respectively. In addition, a novel model FCG was developed to study the influence of the hardening parameters (K′, n′) on fatigue crack propagation. The comparison of the simulation results with those in the literature shows good agreement

Fracture evaluation of ultra-high-performance fiber reinforced concrete (UHPFRC)

The development of numerical simulation for Ultra-high-performance concrete (UHPC) and Ultra-high-performance fiber-reinforced concretes (UHPFRC) is fundamental for the design and construction of related structures. The simplified engineering stress-strain relationship and the input values are necessary in the finite element modeling. Four-linear curves and modified Kent–Park model were proposed to describe the engineering tensile and compressive stress-strain relationship, respectively. An attempt was made to simulate the fracture of UHPC and UHPFRC using concrete damaged plasticity model and element deletion strategies. The predicted tensile and compressive behaviors of UHPC and UHPFRC were successfully validated by the test results in the literature. For a better understanding of the mechanical behavior of UHPC and UHPFRC exposed to biaxial loadings, mixed-mode crack propagation simulation on the double-notched specimens exposed to combined shear-tensile and shear-compressive forces was discussed.Concrete Structure

Ductile fracture locus identification using mesoscale critical equivalent plastic strain

The ductile performance of high strength steel (HSS) from different steel grades, producers, manufacturing processes varies a lot. It is also difficult to conduct all kinds of reliable experiments to generate different stress status through different initial specimen geometries or by applying different load combinations in the civil engineering sector. One of the common issues for HSS structures is to identify the parameters of the ductile fracture model conveniently from the uniaxial stress–strain relationship obtained from common coupon specimens. An attempt is made in this paper to use the proposed mesoscale critical equivalent plastic strain (MCEPS) to calibrate the fracture locus of the uncoupled phenomenological model based only on the engineering stress–strain relationship. The proposed method is successfully validated by the Sandia fracture challenge in 2014.</p

Three-dimensional fatigue crack propagation simulation using extended finite element methods for steel grades S355 and S690 considering mean stress effects

The assessment of fatigue crack propagation of steel structures is essential and important especially to improve the application of high strength steel in construction. The load ratio R, reflecting mean stress effects, will be changed with crack extension in the steel structures with complicated geometry. In this paper, the Walker equation is employed to fit the fatigue crack propagation rate of steel grades S355 and S690 based on experimental data in the literature to incorporate the mean stress effects. The material fatigue crack propagation parameters with 95%, 97.7%, and 99% guarantee of Walker equation were obtained by a stochastic analysis using the Monte Carlo method. The fatigue life was firstly predicted by the analytical method and was used as a baseline for numerical fatigue crack propagation simulation. A user-defined fatigue crack propagation subroutine based on the Walker equation was developed using phantom nodes-based extended finite element method (PN-XFEM) and Virtual Crack Closure Technique (VCCT) to consider the mean stress effects. The proposed three-dimensional fatigue crack propagation simulation subroutine is successfully validated of both steel grades, S355 and S690.Concrete StructuresSteel & Composite Structure