Ricardo Branco

University of Coimbra | UC · Department of Mechanical Engineering

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 c...

The present paper focuses on the application of the total strain energy density approach to assess fatigue life in notched samples subjected to multiaxial loading. This approach requires, as a starting point, a fatigue master curve defined in terms of total strain energy density versus number of cycles to failure, which is usually determined from a...

Fatigue crack initiation behaviour of notched 34CrNiMo6 high-strength steel bars with transverse blind holes and lateral U-shaped notches subjected to proportional bending-torsion loading is studied. Crack initiation at the geometric discontinuities is examined in situ using a high-magnification digital camera. Crack initiation mechanisms and failu...

This paper investigates the effect of loading history on cyclic deformation and fatigue behaviour of 7075-T651 aluminium alloy subjected to two-step loading. High-low and low-high sequences, encompassing both symmetrical and asymmetrical steps, are performed under strain-controlled mode for different loading scenarios. An elastic-plastic constituti...

This paper aims at investigating the strain ratio effect on cyclic deformation behaviour of 7050-T6 aluminium alloy. Low-cycle fatigue tests are conducted under strain-controlled conditions at three strain ratios (-1, 0, and 0.5) with strain amplitudes in the range 0.60-1.75%. Microstructure is analysed by optical microscopy, transmission electron...

The objective of this paper is to provide the fatigue life of riveted joints in AA2024 aluminum alloy plates and optimization of riveted joints parameters. At first, the fatigue life of the riveted joints in AA2024 aluminum alloy plates is obtained by experimental tests. Then, an artificial neural network is applied to estimate the fatigue life of...

The cyclic deformation and fracture behaviour of 18Ni300 maraging steel produced by laser beam powder bed fusion is studied under variable-amplitude loading. The tests were conducted under fully-reversed strain-controlled conditions with a loading sequence comprising three ascending cycles and three descending cycles repeated sequentially until fai...

In this paper, the methods of compensation of differences in the results of entire bending-fatigued fracture surface topographies were presented. The roughness evaluation was performed with a focus variation microscope and confocal surface topography measurement techniques. The differences in the ISO 25178 roughness parameters were investigated and...

In this paper, the application of an Autocorrelation Function for the characterisation of surface topography was validated. The roughness evaluation of turned composite surfaces was supported by sophisticated studies of the Autocorrelation Function properties, considering especially the shape of the function. Details were measured with the optical...

Wind turbines of large size pose a challenge to structural engineers in providing suitable supporting structures. Nevertheless, these structures frequently result in complex logistical requirements, raising the expenses of new projects. Hence, the design philosophy is shifting towards lighter and modular towers, which often use tubular components....

In this study, the fractal dimension of fatigue fracture surfaces is investigated in order to find an alternative failure loading indicator. Some of many metrological factors are generalized by reducing the fracture surface structure to one factor and develop an entire fracture surface procedure by analyzing the impact of surface slope and calculat...

Selective laser melting (SLM) is an additive manufacturing powder-bed fusion process that allows producing complex metallic parts with a relative density of up to 99.9%. Nevertheless, the mechanical properties of these components depend on numerous process variables, and there is a lack of systematic studies focused on SLM stainless steels. In the...

The concept of entire fracture surface investigation is helpful in explaining fatigue phenomena. In this paper, this method has been applied for 18Ni300 maraging steel using a 3D measurement system. Before post-mortem analysis, the specimens produced by laser beam powder bed fusion (LB-PBF) were tested under low-cycle fatigue (LCF) for eight strain...

This paper examined the cyclic deformation behaviour of multiphase low-carbon steel that was subjected to austempering heat treatments at four temperatures (190 °C, 230 °C, 275 °C, and 315 °C) below the martensite start temperature (Ms = 353 °C). The tests were conducted at room temperature, under fully reversed strain-controlled conditions, with s...

This study is focused on the anisotropic fatigue crack growth (FCG) behavior of an aluminum AA7050‐T7451 plate. L‐T and S‐T orientations were studied in M(T) samples with W = 50 mm, in mode I loading, with R‐ratio of +0.05. A numerical approach was used, assuming that crack tip plastic strain is the crack driving force. A purely kinematic elastic–p...

In this study, fatigue fracture surfaces of aluminium alloy 2017-T4 notched specimens were investigated under cyclic bending to find an alternative failure loading index.. The surface topographies were measured on the entire fracture area with an optical profilometer for different loading conditions. Fatigue crack initiation life Ni and total fatig...

This study is focused on the anisotropic fatigue crack growth (FCG) behaviour of an aluminium AA7050-T7451 plate. L-T and S-T orientations were studied in M(T) samples with W=50 mm, in mode I loading, with R-ratio of +0.05. A numerical approach was used, assuming that crack tip plastic strain is the crack driving force. A purely kinematic elastic-p...

This paper explores the applicability of a new damage parameter combining both fracture surface topography and loading features to estimate the fatigue lifetime under creep pre-strain and low-cycle fatigue loading. Fractures of EN-AW 2024 aluminum alloy caused by mixed creep and low-cycle fatigue loading are experimentally characterized and quantif...

In this study, different fracture surfaces caused by fatigue failure were generated from 18Ni300 steel produced by selective laser melting (SLM). Hollow round bars with a transverse hole were tested under bending-torsion to investigate the crack initiation mechanisms and fatigue life. Next, the post-failure fracture surfaces were examined by optica...

Characterization of surface topography, roughly divided into measurement and data analysis, can be valuable in the process of validation of the tribological performance of machined parts. Surface topography, especially the roughness, can respond straightly to the machining process and, in some cases, is defined as a fingerprint of the manufacturing...

This study presents the numerical evaluation of the compliance in the CCC specimen aiming to assess the crack length inside the specimen. The numerical model considered the elastoplastic behaviour of the specimen, which is modelled using axisymmetric finite elements. The results shown that the propagation of the crack yields a non-linear increase o...

This paper analyses the microstructural and mechanical properties of carbon steel coupons produced by CMT-WAAM. The strategy adopted in the fabrication of the test specimens using a robotised facility is explained. Then, the results of the mechanical characterization performed using as-built and machined samples, extracted in several directions (0°...

This paper aims to quantitatively evaluate the residual stress and fatigue life of T-type welded joints with a multi-pass weld in different direction. The main research objectives of the experimental test were to test the residual stress by changing direction along with multiple wielding passes and determine the fatigue life of the welded joints. T...

Welding processes often produce high levels of tensile residual stress. Low transformation temperature (LTT) welding wires utilise phase transformation strains to overcome the thermal contraction of a cooling weld. In this paper, the residual stress within each weld was quantified using the milling/strain gauge method, being the strain change measu...

The influence of defect features on fatigue behaviour is a complex trivial issue. Although the important advances over the last decades, the dialectical relationship between the defect orientation and durability is not clearly understood. The paper aims at studying the influence of the orientation of elliptical defects on the durability of samples...

Fiber-reinforced polymer composites are frequently used in marine environments which may limit their durability. The development of accurate engineering tools capable of simulating the effect of seawater on material strength can improve design and reduce structural costs. This paper presents a numerical-based approach to predict the stress-strain r...

In the era of internet and robots, sophisticated devices and real‐time simulation, the construction sector remains highly dependent on manual labor which is also the main source of delays, lack of quality, and human injuries. The rapid development in technological areas such as mechatronics, computers, sensors, programming, human interfaces, and ar...

This paper aims to study the effect of asynchronous axial-torsional strain-controlled loading histories on fracture surface behavior of thin-walled tubular X5CrNi18-10 (304/304L) austenitic steel specimens. Tests under pure axial loading and pure torsional loading are also conducted to better segregate the effect of multiaxiality. The fractures sur...

In this paper, the fracture behavior and fatigue crack growth rate of the 2024-T351 aluminum alloy has been investigated. At first, the 2024-T351 aluminum alloys have been welded using friction stir welding procedure and the fracture toughness and fatigue crack growth rate of the CT specimens have been studied experimentally based on ASTM standards...

The current work aims to characterise the fatigue behaviour of an additively manufactured maraging steel, AISI 18Ni300. This is a class of high-strength steel widely used in biomedical, aircraft, aerospace, offshore, and military industries thanks to its good performance in terms of strength, toughness, ductility, dimensional stability, and weldabi...

In this paper, the applicability of the cumulative strain energy density is explored as a fatigue indicator parameter for advanced high-strength steels subjected to strain-controlled conditions. Firstly, the cyclic stress-strain responses of nine steels, selected from three multiphase families, encompassing different elemental compositions and diff...

The effect of L-T and S-T orientations on FCGR is here in studied in 7050-T7451 and 2050-T8 aluminum alloys. The Low-cycle fatigue tests and hardness measurements have shown that specimen orientation has a minor effect on material plastic hardening. Lower FCG rates are obtained for both materials in the L-T orientation, which can be associated to t...

The effect of heat treatment on the cyclic deformation behaviour of AlSi10Mg aluminium alloy manufactured by laser powder bed fusion (LPBF) was investigated. Uniaxial fully-reversed strain-controlled fatigue tests were conducted on polished smooth specimens in the low-cycle and high-cycle fatigue regimes for three material states: no heat treatment...

The present study attends to the effect of tensile pre-strain histories and strain ratio on cyclic deformation behavior of 6061 aluminum alloy and 2024 aluminum alloy. Low-cycle fatigue tests performed in this study covered two areas; Under fully reversed conditions, with 8% tensile pre-strain, 4% tensile pre-strain, and 0% tensile pre-strain, at s...

The paper focuses on researching the effect of fatigue loading on metallic structure, lifetime, and fracture surface topographies in AISI H13 steel specimens obtained by selective laser melting (SLM). The topography of the fracture surfaces was measured over their entire area, according to the entire total area method, with an optical three-dimensi...

In this paper, the cumulative strain energy density, also called fatigue toughness, was used to predict the fatigue life of notched members subjected to multiaxial loading. The relationship between the total energy absorbed to fracture and the number of cycles to failure was established from uniaxial strain-controlled fatigue tests. Multiaxial fati...

Fatigue and fracture are pivotal issues in structural integrity [...]

The unusual premature failure of a heavy-duty truck engine crankshaft has been the subject of a rigorous study, and this manuscript describes it in detail. The failure was happened to begin with the growth of the crack from the surface defects, in the form of the clusters of non-metallic inclusions, in the lubrication hole zone of the first main jo...

The aim of this contribution is to provide a brief overview of three-dimensional linear-elastic fracture mechanics (3D LEFM) as well as the latest advances in this area. The primary focus of this review is on the situations where the classical LEFM, which largely relies on plane stress or plane strain simplifications, provides peculiar or misleadin...

This paper presents an analytical-based approach to simulate fatigue growth of surface cracks in round bars subjected to cyclic tension and/or bending. The proposed approach assumes a part-elliptical crack front shape, and it is capable to incorporate plasticity-induced crack closure models. In addition, it is mesh-insensitive, easy to implement, a...

This paper studies the fatigue crack initiation and fatigue crack propagation of notched cylindrical bars made of 7050-T6 aluminium alloy subjected to multiaxial bending-torsion loading. The sites of crack initiation and the angles of crack initiation were successfully predicted from the distribution of the first principal stress at the notch surfa...

The current work aims at characterizing the fatigue behaviour of an additively manufactured maraging steel. This is a class of high-strength steels widely used in aircracft, aerospace, offshore and military industries thanks to its good performance in terms of strength, toughness, ductility, dimensional stability and weldability. Fabrication of suc...

This work presents the effect of elliptical defects orientation on the durability of specimens made of C45 steel. Three kinds of specimens with elliptical defects in the form of a one-sided notch oriented at different angles 45, 60, and 90 degrees were subjected to cyclic bending (R=-1). The stress state analysis was performed using local and non-l...

This paper studies the cyclic deformation behaviour of AlSi10Mg aluminium alloy manufactured by laser-beam powder bed fusion for different processing states, namely in the as-built, stress-relieved, and T6 conditions. Low-cycle fatigue tests (R =-1) are performed using the single step test method, at room temperature, with a constant strain rate,...

The objectives of this study were to investigate the fracture surface topography of X8CrNiS18-9 austenitic stainless-steel specimens for different loadings and notch radii and to supplement the knowledge about the fracture mechanisms for fatigue performance. Cases with three different values of the notch radius ρ and the stress amplitude σa were an...

Mode I and mode I+II fatigue crack growth experiments are performed using compact tension shear specimens made of Ti-6Al-4V by additive manufacturing for various loading angles. The performance of various methodologies used to determine the equivalent stress intensity factor were studied, obtaining good results in simpler methods when the crack def...

This paper aims at predicting the fatigue crack initiation life in maraging steel manufactured by selective laser melting under in-phase bending-torsion loading. Three relationships between the bending moment and the torsion moment were studied, namely B/T=2, B/T=1, and B/T=2/3. The tested geometries consisted of hollow cylindrical specimens with l...

Fatigue behaviour of SLM 18Ni300 steel under proportional bending-torsion loading is studied. The fatigue tests are conducted under pulsating loading conditions using tubular specimens with a transversal circular hole. Three ratios of the normal stress to shear stress are considered, namely \(\sigma /\tau = {4},\sigma /\tau = {2}\) and \(\sigma /\t...

In this study, fracture surface topography parameters were measured to investigate the effects of multiaxial loading. In order to assess the metrological aspects of fracture for notched specimens made of high-strength steels processed by both conventional and additively manufacturing (AM) techniques, an optical surface profilometer was used. Three...

Current research has demonstrated that the tempering temperature affects the martensitic transformation of medium-carbon high-strength steels. This temperature plays an important role in the final microstructure, percentage ratios of martensite to ferrite phases and, consequently, in the mechanical properties and the fatigue response. So far, the r...

Recent studies have reached some antagonist conclusions regarding the benefits of post-processing treatments on fatigue performance of AlSi10Mg aluminium alloy processed by laser powder bed fusion (LPBF). Thus, this paper aims to explore the triangular relationship between post-processing routes, microstructure, and cyclic properties. In order to r...

Purpose Additive manufacturing (AM) is a rapidly evolving manufacturing process, which refers to a set of technologies that add materials layer-by-layer to create functional components. AM technologies have received an enormous attention from both academia and industry, and they are being successfully used in various applications, such as rapid pro...

The present study evaluates the fracture surface response of fatigued 34CrNiMo6 steel bars with transverse blind holes subjected to bending with torsion loading. The analysis of the geometric product specification was performed by means of height parameters Sx, functional volume pa-rameters Vx, and fractal dimension Df. Surface topography measureme...

In the work presented herein, the structural integrity of polymeric functional components made of Nylon-645 and Polylactic acid (PLA) produced by additive manufacturing (Fused Deposition Modelling, FDM) is studied. The PLA component under study was selected from the production line of a brewing company, and it was redesigned and analyzed using the...

This paper studies the effect of seawater immersion on the fatigue behavior of notched carbon/epoxy laminates. Rectangular cross-section specimens with a central hole were immersed in natural and artificial seawater for different immersion times (0, 30 and 60 days), being the water absorption rate evaluated over time. After that, fatigue tests were...

This work aims to compare the mechanical behavior of an AISI H13 steel obtained by additive manufacturing with that obtained by conventional manufacturing methods. The average values of the ultimate tensile strength (UTS) and ductility obtained for the specimens produced by the conventional method were equal to 658 MPa and 18%, respectively, which...

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...

The relationship between tempering temperature and low cycle fatigue (LCF) is not clear. New low-carbon martensitic steels under different tempering temperatures (320 °C, 350 °C, 380 °C) are tested for tensile mechanical properties, LCF, and microstructure. The results show that the monotone mechanical properties of martensite steels decrease with...

Advanced high-strength steels play an essential role in many industries and engineering applications because of their excellent combination of mechanical properties important for design, e.g., strength, fatigue, fracture, wear, and manufacturability [...]

This paper aims to compare the predictive capabilities of different one-parameter damage laws and local stress-strain approaches to assess the fatigue lifetime in notched components subjected to proportional bending-torsion loading. The tested fatigue damage parameters are defined using well-known stress-based, strain-based, SWT-based and energy-ba...

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...

Modern industry, driven by the recent environmental policies, faces an urgent need for the production of lighter and more environmentally friendly components [...]

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...

More than forty years ago, several researchers suggested a hypothesis that the front of a fatigue crack must intersect the free surfaces at a certain (critical) angle to ensure the finite energy flux at the terminal (vertex) point(s). Since its formulation, this hypothesis was under scrutiny in many studies, which utilised various materials, cyclic...

This paper presents the influence of multiaxial loading and fatigue behavior on a fracture surface in the context of its topography. For analysis were taken fracture surfaces obtained in experimental tests of S355J2 steel subjected to non-proportional bending with torsion. A high-resolution optical 3D profilometer was used in the examination and su...

Fatigue failure of structural components due to cyclic loading is a major concern for engineers. Although metal fatigue is a relatively old subject, current methods for the evaluation of fatigue crack growth and fatigue lifetime have several limitations. In general, these methods largely disregard the actual shape of the crack front by introducing...

This paper studies the multiaxial fatigue behaviour of maraging steel samples produced by selective laser melting. Hollow cylindrical specimens with transverse circular holes are subjected to different in-phase bending-torsion loading scenarios. Fatigue crack initiation sites and fatigue crack angles are predicted from the first principal stress fi...

The paper describes the analysis of crack surface morphology of S355J2 steel specimens after bending-torsion fatigue. These experimental investigations of the surface topography were carried out using the focus variation microscope, an optical 3D measurement device. Selected results of measured fracture surfaces for S355J2 steel were analysed accor...

The aim of the article is to build-up a simplified model of the effect of atmospheric plasma spraying process parameters on the deposits' functional properties. The artificial neural networks were employed to elaborate on the model and the Matlab software was used. The model is crucial to study the relationship between process parameters, such as s...

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 orien-tations on crack shape and fracture surface ch...

This paper studies the effect of multiaxial loading scenario on surface topography in notched samples made of high-strength steels processed by both conventional and additively manufacturing techniques. In a first stage, combined bending-torsion fatigue tests are performed for three bending-to-torsion ratios. In a second stage, based on the entire...