Ricardo Branco | IFPR - Academia.edu (original) (raw)

Papers by Ricardo Branco

Trauma Case Reports, 2021

Pediatric traumatic hip dislocations (PTHD) are rare and represent around 5% of all pediatric dis... more Pediatric traumatic hip dislocations (PTHD) are rare and represent around 5% of all pediatric dislocations. Associated bony or soft tissue injury can occur as often as 17%-25% of the time. We report a case of an 8-year-old boy presenting a posterior hip dislocation after a low-energy trauma, which was initially managed with closed reduction and bed rest for 1 week. Two days after hospital discharge, he suffered a recurrent posterior hip dislocation. He was now managed with 4 weeks of bed rest and lower limb skin traction followed by 1 week of no weight-bearing on crutches. With 6 months of follow-up, he is asymptomatic, walking autonomously, with complete and painless range of motion of the affected hip and no major radiographic changes. Pediatric traumatic hip dislocation is a rare and challenging injury that should be managed promptly. Currently, there is no protocol concerning treatment in the literature and its largely dependent of patient and parents' cooperation.

Production Engineering Archives, 2020

Modern methods of testing materials require the use of the latest technologies and combining meas... more Modern methods of testing materials require the use of the latest technologies and combining measurement and calculation methods. It is important to find a quantitative way of describing, among other things, the failures so that it can help to design with high accuracy. This paper studies loading orientations on crack shape and fracture surface changes. The advantage of the entire fracture surface method is simplicity and applicability in studies on other materials, shapes and loadings. A higher values of fracture surface parameters (Sx, Vx) was observed in failure specimens with lower σ/τ (B/T) ratios. It has been observed that largest crack lengths with a small number of cycles occur for loading combinations different then B=T. As well as analyzed surface parameters Sx, Vx, are higher for larger number of cycles to crack initiation (Ni) values.

The aim of this paper is to critically evaluate, how well the most common non-linear fracture cri... more The aim of this paper is to critically evaluate, how well the most common non-linear fracture criteria actually describe the general experimental trends, which were confirmed in a large number of fracture tests, conducted over the past fifty years. In particular, we examine the agreement between these general experimental trends and the theoretical predictions based on the critical value of the crack-tip stress at some certain distance, J-integral, crack tip opening displacement and crack-tip-opening angle. All theoretical predictions are derived from the classical strip yield model, which is considered to be adequate for the purpose of the current study.

Fatigue & Fracture of Engineering Materials & Structures, 2021

Mechanics of Materials, 2021

The paper studies the effect of strain-loading sequence on fatigue lifetime and fracture surface ... more The paper studies the effect of strain-loading sequence on fatigue lifetime and fracture surface topographies in 7075-T651 aluminum alloy specimens. Fatigue tests were performed in two ways: (i) constant-amplitude loading and (ii) two series of variable amplitude loading with non-zero mean strain values. The topography of the fatigue fractures was measured over their entire surfaces with the help of an optical confocal measurement system. The results of fatigue tests in the form of equivalent strains, ε aeq , such as the weighted mean of strain components, ε a1 , ε a2 , and fatigue life, N f , were used as the sum of the partial number of cycles N 1 , and N 2. This study indicates, inter alia, that the values of the fracture surface parameter core height Sk, found in the two-step loading program, are linearly dependent on the equivalent strain, and logarithmically dependent on the fatigue life.

Structural Integrity, 2019

The aim of this contribution is to provide a brief review of the latest developments in the area ... more The aim of this contribution is to provide a brief review of the latest developments in the area of 3D Linear-Elastic Fracture Mechanics. The primary focus of this contribution is on the situations where the classical results, which are normally obtained within the framework of plane theory of elasticity, lead to peculiar results. These situations include analysis of stress and displacement fields near vertex points, generation of the coupled fracture mode under shear loading, application of Williams series expansion to 3D problems as well as fracture scaling.

Measurement, 2021

Fracture surfaces after biaxial fatigue tests were compared using fractal dimension for three typ... more Fracture surfaces after biaxial fatigue tests were compared using fractal dimension for three types of metallic materials in smooth and notched specimens made of S355J2 and 10HNAP steels and 2017-T4 aluminium alloy, considering both proportional and nonproportional cyclic loading. High-resolution optical 3D measurement studies were performed on the entire fracture surface. A direct correlation between fractal dimension and fatigue loading was established. This systematic relationship can serve as a basis for obtaining information about fatigue loading from the fracture surfaces of failed materials and structures. Moreover, measurements of the fracture surface with an optical profilometer, quantitative analysis, and fractography contribute to a better comprehension of the fatigue failure processes. Differences in individual zones of fatigue fractures were identified while demonstrating the correctness of the total fracture surface method.

International Journal of Fatigue, 2021

Abstract This paper deals with the notch fatigue behaviour and crack initiation life estimation i... more Abstract This paper deals with the notch fatigue behaviour and crack initiation life estimation in maraging steel fabricated by laser beam powder bed fusion under multiaxial loading. Tests are conducted in tubular geometries with lateral holes considering different normal stress to shear stress ratios and multiaxial loading levels. The cyclic stress–strain response at the notch-controlled process zone is simulated numerically using two alternative approaches: a generalised isotropic plasticity model with mixed isotropic-kinematic hardening, and a linear-elastic model. Both approaches demonstrated to be suitable for predicting the crack initiation sites, the directions of crack growth, and the fatigue life. Fatigue life was calculated from a SWT-based model combined with the Theory of Critical Distances. Elastic-plastic predictions led to smaller errors but slightly shifted to the non-conservative side.

Applied Sciences, 2020

Carbide-free bainitic steels are an example of high-strength steels that show an excellent combin... more Carbide-free bainitic steels are an example of high-strength steels that show an excellent combination of strength, ductility, toughness and rolling fatigue contact resistance and are progressively being introduced in the production of railways, crossings and automotive components. Although there are Mn-free approaches able to produce carbide-free bainitic steels, those based on the addition of Mn are less expensive. Therefore, it is important to fully understand the mechanical behavior of such materials to develop reliable engineering products. In this paper, three low-carbon bainitic steels, differing in Mn content, namely 0%, 2.3% and 3.2%, designated as steel A, B and C, respectively, were studied in a systematic manner. Low-cycle fatigue tests were conducted under symmetrical strain-controlled conditions for different strain amplitudes (0.6%, 0.7%, 0.8% and 1%). Independent of Mn content, a strong relationship between cumulative strain energy density and number of cycles to fai...

Procedia Structural Integrity, 2020

Abstract The purpose of this paper is to present a mixed mechanical-metrological procedure, based... more Abstract The purpose of this paper is to present a mixed mechanical-metrological procedure, based on a fractographical approach, capable of correlating the fracture deformation behaviour with the fatigue loading history. The degradation mechanisms, which are related to the degree of fatigue damage, are identified from the changes in the dynamic response of the mechanical system. These changes, recorded during the tests by means of uniaxial acceleration sensors, are compared to different surface texture parameters, namely height parameters and material/void parameters, determined for both parts of the fracture surfaces after fatigue damage, and with the force needed for complete failure. The results show a direct relationship between the degree of fatigue damage, accounted for by the changes in the uniaxial acceleration sensors, and the surface texture parameters. This connection between the mechanical system dynamics and the surface metrology can provide a more precise fitness-for-service assessment.

Mechanics of Materials, 2020

Non-destructive methods are powerful tools in modern industry to assess the structural integrity ... more Non-destructive methods are powerful tools in modern industry to assess the structural integrity of engineering critical parts subjected to fatigue loading. This paper proposes a mixed mechanical-metrological approach able to account for the three-dimensional fractographic damage in samples subjected to fatigue bending loading histories based on the system dynamics. The system records the changes in the dynamic response, using uniaxial acceleration sensors, enabling the correlation of the stiffness variations with the crack length and the residual loading capacity. Fracture topologies are analysed via standard surface texture parameters, namely height, material volume and void volume parameters, for different degrees of fatigue damage. The results show a clear relationship between the changes in the recorded accelerations, which are associated with the degree of fatigue damage, and the values of the above-mentioned surface texture parameters.

Procedia Structural Integrity, 2020

The application of damage tolerance to the design of components is based on the ability to predic... more The application of damage tolerance to the design of components is based on the ability to predict fatigue crack growth (FCG) rate precisely. A literature review about analytical models showed a great number of models developed for specific materials and loading conditions. A numerical analysis of a CT specimen made of 304L stainless steel showed the complex influence of material parameters on FCG, which also depends on loading parameters, geometry and environmental conditions. Therefore an alternative to analytical models is proposed here, based on plastic CTOD, assuming that this is the crack driving force. A material law must be first obtained relating da/dN with plastic CTOD range, p, obtained numerically using the finite element method or experimentally using DIC. This law changes with material and includes all material parameters and also environmental conditions (temperature and atmosphere). The design of a specific cracked component is made using numerical tools in order to obtain p for different crack lengths. This second analysis includes the effect of geometrical and loading parameters.

Metals, Jun 5, 2018

Bainitic steels play an important role in the modern automotive and rail industries because of th... more Bainitic steels play an important role in the modern automotive and rail industries because of their balanced properties. Understanding the relationship between the bainitic microstructure features and the fatigue performance is a fundamental ingredient in developing safer and durable products. However, so far this relationship is not sufficiently clear. Therefore, there is the need to strengthen the knowledge within this field. The present paper aims at comparing the uniaxial cyclic behaviour of carbide-bearing and carbide-free bainitic steels. To meet this goal, fully-reversed strain-controlled tests at various strain amplitudes were performed. After the final failure, fracture surfaces were observed by transmission electron microscopy to relate the bainitic morphology to the fatigue performance. The main findings of this work show that the carbide-free lower bainite has superior fatigue performance compared to the carbide-bearing lower bainite. This is explained by the presence of stable carbides and thick bainite ferrite plates.

International Journal of Rock Mechanics and Mining Sciences, 2017

The channel fracturing technique aims for discontinuous placement of proppant particles along the... more The channel fracturing technique aims for discontinuous placement of proppant particles along the length of a hydraulic fracture in a way that a network of open channels or voids can be created between the proppant-filled regions of the fracture. In this paper, a simple theoretical model is developed to identify the optimal proppant volume fraction that maximises the effective conductivity of the partially-filled fracture while reducing the amount of proppant used. The fracture geometry is idealised as two-dimensional and a regular arrangement of proppant columns is considered. The residual opening profile of the fracture is determined as a function of the proppant column width and spacing, the mechanical properties of the rock and the proppant pack as well the magnitude of the compressive in-situ stress acting normal to the fracture plane. The effective fracture conductivity is then determined as a function of its residual opening profile. Some optimal estimates are provided for the conductivity enhancement and reduction in proppant use which can be useful for the application of the channel fracturing technique.

Theoretical and Applied Fracture Mechanics, 2019

This paper presents a new analytical method for the analysis of fatigue growth of surface cracks ... more This paper presents a new analytical method for the analysis of fatigue growth of surface cracks in various structural components. The method is based on a governing equation describing the front evolution of surface cracks of elliptical and part-elliptical shapes. This method avoids the need for various numerical schemes for the calculation of the incremental crack front advance, which were used in all previous studies. Plasticity-induced crack closure models can also be incorporated into the method or these models can be deducted from a correlation of experimental data and the method predictions. When the plastic constraint conditions change significantly along the crack front, the implementation of the plasticity induced crack closure models can significantly improve the accuracy of fatigue life predictions. The method is validated against previous theoretical and experimental studies.

Frattura ed Integrità Strutturale, 2017

Fatigue crack growth (FCG) is associated with irreversible and non-linear processes happening at ... more Fatigue crack growth (FCG) is associated with irreversible and non-linear processes happening at the crack tip. This explains different problems observed in the use of da/dN-K curves, namely the inability to explain stress ratio and load history effects. The replacement of K by nonlinear crack tip parameters, namely the crack tip opening displacement (CTOD) is an interesting alternative. However, the determination of CTOD, using the finite element method, depends on different numerical parameters, not sufficiently studied so far. The objective here is to study the effect of these parameters on plastic CTOD, and therefore on da/dN-CTODp curves. A transient behaviour was found at the beginning of numerical crack propagation which is linked to the formation of residual plastic wake. Therefore, a minimum number of crack increments is required to obtain stabilized values. On the other hand, the predicted CTOD p decreases with the distance to crack tip. Close to the crack tip, sensitivity to the measured values is much higher, but it also exists at remote positions. In addition, the mesh has a relatively low influence on CTODp. Finally, the effect of the number of load cycles between crack increments greatly depends on material properties.

Material Design & Processing Communications, 2019

Advanced high-strength steels are outstanding materials to meet the current demands of automotive... more Advanced high-strength steels are outstanding materials to meet the current demands of automotive industry, including the reduction of vehicle weight. These high value-added products, which operate generally under adverse service conditions, are highly susceptible to fatigue failure. Modern fatigue design approaches, namely, those based on the strain energy density concept, require detailed information about the energy-life relationship. This paper proposes a straightforward methodology to generate energy-life fatigue master curves on the basis of only two uniaxial low-cycle fatigue tests and two elastic-plastic finite-element models. The methodology is successfully tested in an advanced high-strength steel. KEYWORDS fatigue master curve, low-cycle fatigue, strain energy density 1 | INTRODUCTION Advanced high-strength steels are outstanding materials to meet the current demands of automotive industry, namely, the reduction of vehicle weight and also reduction of fuel consumption. These steels, which pose superior properties in terms of strength and ductility, have been developed to compete with various lightweight materials on the basis of cost, performance, and manufacturability. 1 However, due to the combination of stress concentration phenomena and timevarying loading, these high value-added products are susceptible to fatigue failure. 2-4 Therefore, detailed information on the fatigue response of these materials is pivotal to ensure a safe long-term life. Modern fatigue design models are generally formulated based on local stress-based, strain-based, and energy-based approaches. 5,6 Within the energy-based formulations, those based on the strain energy density concept have gained increased popularity. 7-9 This can be explained by the fact that they can handle different materials, loading scenarios, and geometries and because they require a balanced number of material properties. 9-14 Despite this, the determination of such properties is time-consuming and expensive. In this sense, the development of faster and low-cost approaches would be of great importance to simplify the procedures and to make these energy-based prediction models even more attractive. In this paper, it is proposed a straightforward methodology to generate energy-life fatigue master curves from only two uniaxial low-cycle fatigue tests. Here, two fully reversed strain-controlled tests, with strain amplitudes of 0.6% and 2.0%, were performed using standard cylindrical specimens made of a DIN 34CrNiMo6 high-strength steel. From these two tests, the Basquin and Coffin-Manson relationships were determined by linear regression, aiming at obtaining a strain-life relationship. Parallelly, two independent elastic-plastic numerical models were developed to describe the cyclic behaviour of the material for each strain-amplitude. These two models were then used to generate stable

Genome Medicine, 2018

Background: Studies have shown that complex structural variants (cxSVs) contribute to human genom... more Background: Studies have shown that complex structural variants (cxSVs) contribute to human genomic variation and can cause Mendelian disease. We aimed to identify cxSVs relevant to Mendelian disease using short-read whole-genome sequencing (WGS), resolve the precise variant configuration and investigate possible mechanisms of cxSV formation. Methods: We performed short-read WGS and analysis of breakpoint junctions to identify cxSVs in a cohort of 1324 undiagnosed rare disease patients. Long-read WGS and gene expression analysis were used to resolve one case. Results: We identified three pathogenic cxSVs: a de novo duplication-inversion-inversion-deletion affecting ARID1B, a de novo deletion-inversion-duplication affecting HNRNPU and a homozygous deletion-inversion-deletion affecting CEP78. Additionally, a de novo duplication-inversion-duplication overlapping CDKL5 was resolved by long-read WGS demonstrating the presence of both a disrupted and an intact copy of CDKL5 on the same allele, and gene expression analysis showed both parental alleles of CDKL5 were expressed. Breakpoint analysis in all the cxSVs revealed both microhomology and longer repetitive elements. Conclusions: Our results corroborate that cxSVs cause Mendelian disease, and we recommend their consideration during clinical investigations. We show that resolution of breakpoints can be critical to interpret pathogenicity and present evidence of replication-based mechanisms in cxSV formation.

Theoretical and Applied Fracture Mechanics, 2017

The main purpose of this paper is the fatigue assessment in lateral U-shaped notched round bars u... more The main purpose of this paper is the fatigue assessment in lateral U-shaped notched round bars under bending-torsion loading. Despite its importance in the context of mechanical design, very little work has been done in this field. The fatigue life prediction model relies on the assumption that both the smooth and the notched samples fail when a critical value of the total strain energy density is reached. The modus operandi, in a first instance, consists of developing a fatigue master curve that relates the total strain energy density and the number of cycles to failure using smooth specimens subjected to strain-controlled conditions. In a second stage, the total strain energy density of the notched samples is computed from representative hysteresis loops obtained through a three-step procedure: reduction of the multiaxial stress state to an equivalent stress state using a linear-elastic finite-element model; definition of an effective stress range on the basis of the Theory of Critical Distances; and generation of a hysteresis loop applying the Equivalent Strain Energy Density concept in conjunction with the calculated effective stress range. The comparison between the experimental and the predicted lives has shown a very good correlation, with all points within a factor of 2.

Trauma Case Reports, 2021

Pediatric traumatic hip dislocations (PTHD) are rare and represent around 5% of all pediatric dis... more Pediatric traumatic hip dislocations (PTHD) are rare and represent around 5% of all pediatric dislocations. Associated bony or soft tissue injury can occur as often as 17%-25% of the time. We report a case of an 8-year-old boy presenting a posterior hip dislocation after a low-energy trauma, which was initially managed with closed reduction and bed rest for 1 week. Two days after hospital discharge, he suffered a recurrent posterior hip dislocation. He was now managed with 4 weeks of bed rest and lower limb skin traction followed by 1 week of no weight-bearing on crutches. With 6 months of follow-up, he is asymptomatic, walking autonomously, with complete and painless range of motion of the affected hip and no major radiographic changes. Pediatric traumatic hip dislocation is a rare and challenging injury that should be managed promptly. Currently, there is no protocol concerning treatment in the literature and its largely dependent of patient and parents' cooperation.

Production Engineering Archives, 2020

Modern methods of testing materials require the use of the latest technologies and combining meas... more Modern methods of testing materials require the use of the latest technologies and combining measurement and calculation methods. It is important to find a quantitative way of describing, among other things, the failures so that it can help to design with high accuracy. This paper studies loading orientations on crack shape and fracture surface changes. The advantage of the entire fracture surface method is simplicity and applicability in studies on other materials, shapes and loadings. A higher values of fracture surface parameters (Sx, Vx) was observed in failure specimens with lower σ/τ (B/T) ratios. It has been observed that largest crack lengths with a small number of cycles occur for loading combinations different then B=T. As well as analyzed surface parameters Sx, Vx, are higher for larger number of cycles to crack initiation (Ni) values.

The aim of this paper is to critically evaluate, how well the most common non-linear fracture cri... more The aim of this paper is to critically evaluate, how well the most common non-linear fracture criteria actually describe the general experimental trends, which were confirmed in a large number of fracture tests, conducted over the past fifty years. In particular, we examine the agreement between these general experimental trends and the theoretical predictions based on the critical value of the crack-tip stress at some certain distance, J-integral, crack tip opening displacement and crack-tip-opening angle. All theoretical predictions are derived from the classical strip yield model, which is considered to be adequate for the purpose of the current study.

Fatigue & Fracture of Engineering Materials & Structures, 2021

Mechanics of Materials, 2021

The paper studies the effect of strain-loading sequence on fatigue lifetime and fracture surface ... more The paper studies the effect of strain-loading sequence on fatigue lifetime and fracture surface topographies in 7075-T651 aluminum alloy specimens. Fatigue tests were performed in two ways: (i) constant-amplitude loading and (ii) two series of variable amplitude loading with non-zero mean strain values. The topography of the fatigue fractures was measured over their entire surfaces with the help of an optical confocal measurement system. The results of fatigue tests in the form of equivalent strains, ε aeq , such as the weighted mean of strain components, ε a1 , ε a2 , and fatigue life, N f , were used as the sum of the partial number of cycles N 1 , and N 2. This study indicates, inter alia, that the values of the fracture surface parameter core height Sk, found in the two-step loading program, are linearly dependent on the equivalent strain, and logarithmically dependent on the fatigue life.

Structural Integrity, 2019

The aim of this contribution is to provide a brief review of the latest developments in the area ... more The aim of this contribution is to provide a brief review of the latest developments in the area of 3D Linear-Elastic Fracture Mechanics. The primary focus of this contribution is on the situations where the classical results, which are normally obtained within the framework of plane theory of elasticity, lead to peculiar results. These situations include analysis of stress and displacement fields near vertex points, generation of the coupled fracture mode under shear loading, application of Williams series expansion to 3D problems as well as fracture scaling.

Measurement, 2021

Fracture surfaces after biaxial fatigue tests were compared using fractal dimension for three typ... more Fracture surfaces after biaxial fatigue tests were compared using fractal dimension for three types of metallic materials in smooth and notched specimens made of S355J2 and 10HNAP steels and 2017-T4 aluminium alloy, considering both proportional and nonproportional cyclic loading. High-resolution optical 3D measurement studies were performed on the entire fracture surface. A direct correlation between fractal dimension and fatigue loading was established. This systematic relationship can serve as a basis for obtaining information about fatigue loading from the fracture surfaces of failed materials and structures. Moreover, measurements of the fracture surface with an optical profilometer, quantitative analysis, and fractography contribute to a better comprehension of the fatigue failure processes. Differences in individual zones of fatigue fractures were identified while demonstrating the correctness of the total fracture surface method.

International Journal of Fatigue, 2021

Abstract This paper deals with the notch fatigue behaviour and crack initiation life estimation i... more Abstract This paper deals with the notch fatigue behaviour and crack initiation life estimation in maraging steel fabricated by laser beam powder bed fusion under multiaxial loading. Tests are conducted in tubular geometries with lateral holes considering different normal stress to shear stress ratios and multiaxial loading levels. The cyclic stress–strain response at the notch-controlled process zone is simulated numerically using two alternative approaches: a generalised isotropic plasticity model with mixed isotropic-kinematic hardening, and a linear-elastic model. Both approaches demonstrated to be suitable for predicting the crack initiation sites, the directions of crack growth, and the fatigue life. Fatigue life was calculated from a SWT-based model combined with the Theory of Critical Distances. Elastic-plastic predictions led to smaller errors but slightly shifted to the non-conservative side.

Applied Sciences, 2020

Carbide-free bainitic steels are an example of high-strength steels that show an excellent combin... more Carbide-free bainitic steels are an example of high-strength steels that show an excellent combination of strength, ductility, toughness and rolling fatigue contact resistance and are progressively being introduced in the production of railways, crossings and automotive components. Although there are Mn-free approaches able to produce carbide-free bainitic steels, those based on the addition of Mn are less expensive. Therefore, it is important to fully understand the mechanical behavior of such materials to develop reliable engineering products. In this paper, three low-carbon bainitic steels, differing in Mn content, namely 0%, 2.3% and 3.2%, designated as steel A, B and C, respectively, were studied in a systematic manner. Low-cycle fatigue tests were conducted under symmetrical strain-controlled conditions for different strain amplitudes (0.6%, 0.7%, 0.8% and 1%). Independent of Mn content, a strong relationship between cumulative strain energy density and number of cycles to fai...

Procedia Structural Integrity, 2020

Abstract The purpose of this paper is to present a mixed mechanical-metrological procedure, based... more Abstract The purpose of this paper is to present a mixed mechanical-metrological procedure, based on a fractographical approach, capable of correlating the fracture deformation behaviour with the fatigue loading history. The degradation mechanisms, which are related to the degree of fatigue damage, are identified from the changes in the dynamic response of the mechanical system. These changes, recorded during the tests by means of uniaxial acceleration sensors, are compared to different surface texture parameters, namely height parameters and material/void parameters, determined for both parts of the fracture surfaces after fatigue damage, and with the force needed for complete failure. The results show a direct relationship between the degree of fatigue damage, accounted for by the changes in the uniaxial acceleration sensors, and the surface texture parameters. This connection between the mechanical system dynamics and the surface metrology can provide a more precise fitness-for-service assessment.

Mechanics of Materials, 2020

Non-destructive methods are powerful tools in modern industry to assess the structural integrity ... more Non-destructive methods are powerful tools in modern industry to assess the structural integrity of engineering critical parts subjected to fatigue loading. This paper proposes a mixed mechanical-metrological approach able to account for the three-dimensional fractographic damage in samples subjected to fatigue bending loading histories based on the system dynamics. The system records the changes in the dynamic response, using uniaxial acceleration sensors, enabling the correlation of the stiffness variations with the crack length and the residual loading capacity. Fracture topologies are analysed via standard surface texture parameters, namely height, material volume and void volume parameters, for different degrees of fatigue damage. The results show a clear relationship between the changes in the recorded accelerations, which are associated with the degree of fatigue damage, and the values of the above-mentioned surface texture parameters.

Procedia Structural Integrity, 2020

The application of damage tolerance to the design of components is based on the ability to predic... more The application of damage tolerance to the design of components is based on the ability to predict fatigue crack growth (FCG) rate precisely. A literature review about analytical models showed a great number of models developed for specific materials and loading conditions. A numerical analysis of a CT specimen made of 304L stainless steel showed the complex influence of material parameters on FCG, which also depends on loading parameters, geometry and environmental conditions. Therefore an alternative to analytical models is proposed here, based on plastic CTOD, assuming that this is the crack driving force. A material law must be first obtained relating da/dN with plastic CTOD range, p, obtained numerically using the finite element method or experimentally using DIC. This law changes with material and includes all material parameters and also environmental conditions (temperature and atmosphere). The design of a specific cracked component is made using numerical tools in order to obtain p for different crack lengths. This second analysis includes the effect of geometrical and loading parameters.

Metals, Jun 5, 2018

Bainitic steels play an important role in the modern automotive and rail industries because of th... more Bainitic steels play an important role in the modern automotive and rail industries because of their balanced properties. Understanding the relationship between the bainitic microstructure features and the fatigue performance is a fundamental ingredient in developing safer and durable products. However, so far this relationship is not sufficiently clear. Therefore, there is the need to strengthen the knowledge within this field. The present paper aims at comparing the uniaxial cyclic behaviour of carbide-bearing and carbide-free bainitic steels. To meet this goal, fully-reversed strain-controlled tests at various strain amplitudes were performed. After the final failure, fracture surfaces were observed by transmission electron microscopy to relate the bainitic morphology to the fatigue performance. The main findings of this work show that the carbide-free lower bainite has superior fatigue performance compared to the carbide-bearing lower bainite. This is explained by the presence of stable carbides and thick bainite ferrite plates.

International Journal of Rock Mechanics and Mining Sciences, 2017

The channel fracturing technique aims for discontinuous placement of proppant particles along the... more The channel fracturing technique aims for discontinuous placement of proppant particles along the length of a hydraulic fracture in a way that a network of open channels or voids can be created between the proppant-filled regions of the fracture. In this paper, a simple theoretical model is developed to identify the optimal proppant volume fraction that maximises the effective conductivity of the partially-filled fracture while reducing the amount of proppant used. The fracture geometry is idealised as two-dimensional and a regular arrangement of proppant columns is considered. The residual opening profile of the fracture is determined as a function of the proppant column width and spacing, the mechanical properties of the rock and the proppant pack as well the magnitude of the compressive in-situ stress acting normal to the fracture plane. The effective fracture conductivity is then determined as a function of its residual opening profile. Some optimal estimates are provided for the conductivity enhancement and reduction in proppant use which can be useful for the application of the channel fracturing technique.

Theoretical and Applied Fracture Mechanics, 2019

This paper presents a new analytical method for the analysis of fatigue growth of surface cracks ... more This paper presents a new analytical method for the analysis of fatigue growth of surface cracks in various structural components. The method is based on a governing equation describing the front evolution of surface cracks of elliptical and part-elliptical shapes. This method avoids the need for various numerical schemes for the calculation of the incremental crack front advance, which were used in all previous studies. Plasticity-induced crack closure models can also be incorporated into the method or these models can be deducted from a correlation of experimental data and the method predictions. When the plastic constraint conditions change significantly along the crack front, the implementation of the plasticity induced crack closure models can significantly improve the accuracy of fatigue life predictions. The method is validated against previous theoretical and experimental studies.

Frattura ed Integrità Strutturale, 2017

Fatigue crack growth (FCG) is associated with irreversible and non-linear processes happening at ... more Fatigue crack growth (FCG) is associated with irreversible and non-linear processes happening at the crack tip. This explains different problems observed in the use of da/dN-K curves, namely the inability to explain stress ratio and load history effects. The replacement of K by nonlinear crack tip parameters, namely the crack tip opening displacement (CTOD) is an interesting alternative. However, the determination of CTOD, using the finite element method, depends on different numerical parameters, not sufficiently studied so far. The objective here is to study the effect of these parameters on plastic CTOD, and therefore on da/dN-CTODp curves. A transient behaviour was found at the beginning of numerical crack propagation which is linked to the formation of residual plastic wake. Therefore, a minimum number of crack increments is required to obtain stabilized values. On the other hand, the predicted CTOD p decreases with the distance to crack tip. Close to the crack tip, sensitivity to the measured values is much higher, but it also exists at remote positions. In addition, the mesh has a relatively low influence on CTODp. Finally, the effect of the number of load cycles between crack increments greatly depends on material properties.

Material Design & Processing Communications, 2019

Advanced high-strength steels are outstanding materials to meet the current demands of automotive... more Advanced high-strength steels are outstanding materials to meet the current demands of automotive industry, including the reduction of vehicle weight. These high value-added products, which operate generally under adverse service conditions, are highly susceptible to fatigue failure. Modern fatigue design approaches, namely, those based on the strain energy density concept, require detailed information about the energy-life relationship. This paper proposes a straightforward methodology to generate energy-life fatigue master curves on the basis of only two uniaxial low-cycle fatigue tests and two elastic-plastic finite-element models. The methodology is successfully tested in an advanced high-strength steel. KEYWORDS fatigue master curve, low-cycle fatigue, strain energy density 1 | INTRODUCTION Advanced high-strength steels are outstanding materials to meet the current demands of automotive industry, namely, the reduction of vehicle weight and also reduction of fuel consumption. These steels, which pose superior properties in terms of strength and ductility, have been developed to compete with various lightweight materials on the basis of cost, performance, and manufacturability. 1 However, due to the combination of stress concentration phenomena and timevarying loading, these high value-added products are susceptible to fatigue failure. 2-4 Therefore, detailed information on the fatigue response of these materials is pivotal to ensure a safe long-term life. Modern fatigue design models are generally formulated based on local stress-based, strain-based, and energy-based approaches. 5,6 Within the energy-based formulations, those based on the strain energy density concept have gained increased popularity. 7-9 This can be explained by the fact that they can handle different materials, loading scenarios, and geometries and because they require a balanced number of material properties. 9-14 Despite this, the determination of such properties is time-consuming and expensive. In this sense, the development of faster and low-cost approaches would be of great importance to simplify the procedures and to make these energy-based prediction models even more attractive. In this paper, it is proposed a straightforward methodology to generate energy-life fatigue master curves from only two uniaxial low-cycle fatigue tests. Here, two fully reversed strain-controlled tests, with strain amplitudes of 0.6% and 2.0%, were performed using standard cylindrical specimens made of a DIN 34CrNiMo6 high-strength steel. From these two tests, the Basquin and Coffin-Manson relationships were determined by linear regression, aiming at obtaining a strain-life relationship. Parallelly, two independent elastic-plastic numerical models were developed to describe the cyclic behaviour of the material for each strain-amplitude. These two models were then used to generate stable

Genome Medicine, 2018

Background: Studies have shown that complex structural variants (cxSVs) contribute to human genom... more Background: Studies have shown that complex structural variants (cxSVs) contribute to human genomic variation and can cause Mendelian disease. We aimed to identify cxSVs relevant to Mendelian disease using short-read whole-genome sequencing (WGS), resolve the precise variant configuration and investigate possible mechanisms of cxSV formation. Methods: We performed short-read WGS and analysis of breakpoint junctions to identify cxSVs in a cohort of 1324 undiagnosed rare disease patients. Long-read WGS and gene expression analysis were used to resolve one case. Results: We identified three pathogenic cxSVs: a de novo duplication-inversion-inversion-deletion affecting ARID1B, a de novo deletion-inversion-duplication affecting HNRNPU and a homozygous deletion-inversion-deletion affecting CEP78. Additionally, a de novo duplication-inversion-duplication overlapping CDKL5 was resolved by long-read WGS demonstrating the presence of both a disrupted and an intact copy of CDKL5 on the same allele, and gene expression analysis showed both parental alleles of CDKL5 were expressed. Breakpoint analysis in all the cxSVs revealed both microhomology and longer repetitive elements. Conclusions: Our results corroborate that cxSVs cause Mendelian disease, and we recommend their consideration during clinical investigations. We show that resolution of breakpoints can be critical to interpret pathogenicity and present evidence of replication-based mechanisms in cxSV formation.

Theoretical and Applied Fracture Mechanics, 2017

The main purpose of this paper is the fatigue assessment in lateral U-shaped notched round bars u... more The main purpose of this paper is the fatigue assessment in lateral U-shaped notched round bars under bending-torsion loading. Despite its importance in the context of mechanical design, very little work has been done in this field. The fatigue life prediction model relies on the assumption that both the smooth and the notched samples fail when a critical value of the total strain energy density is reached. The modus operandi, in a first instance, consists of developing a fatigue master curve that relates the total strain energy density and the number of cycles to failure using smooth specimens subjected to strain-controlled conditions. In a second stage, the total strain energy density of the notched samples is computed from representative hysteresis loops obtained through a three-step procedure: reduction of the multiaxial stress state to an equivalent stress state using a linear-elastic finite-element model; definition of an effective stress range on the basis of the Theory of Critical Distances; and generation of a hysteresis loop applying the Equivalent Strain Energy Density concept in conjunction with the calculated effective stress range. The comparison between the experimental and the predicted lives has shown a very good correlation, with all points within a factor of 2.