Jaime Tupiassú Pinho de Castro

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Pontifical Catholic University of Rio de Janeiro · Department of Mechanical Engineering

Notch sensitivity under sulfide stress corrosion cracking (SSC) conditions is quantified in this work, considering its tolerance to short cracks that start at notch tips and become non-propagating after growing for a short while. The considered material is an UNS S41426 super 13Cr5Ni2Mo martensitic stainless steel, frequently used in pipelines to t...

Elastoplastic (EP) stress gradient factors (SGF) ahead of notch tips are used to evaluate the actual notch effects in fatigue strength due to their tolerance to non-propagating short cracks, which depends on the notch stress concentration factor, on the stress gradient ahead it, and on the material. Considering the significant role of local plastic...

A powerful probabilistic framework is proposed to account for life-dependent data scatter in fatigue crack initiation (FCI) predictions considering mean stress effects. It is applicable to any stress, strain, or energy-based fatigue damage parameter (DP), as long as the logarithm of DP for a given FCI life Nf can be assumed to follow a three-parame...

Strain-life models that include Walker-like products can reproduce the higher mean stress effects in fatigue crack initiation observed in high-strength materials. These models are able to improve Coffin-Manson’s and Smith-Watson-Topper’s strain-life predictions, at the cost of an additional data-fitting exponent. This work reviews and compares seve...

This work aims to improve the modeling of peak/mean normal stress effects on multiaxial fatigue lives, applying a deviatoric strain-life model based on the critical plane approach to predict the initiation of tensile-driven cracks. Based on Kujawski’s deviatoric multiaxial fatigue damage parameter, this model assumes the peak deviatoric stress norm...

This paper presents analyses of noise effects in displacement histories measured by double numerical integration of acceleration data. Since such noise-induced errors tend to be highly random, they must be estimated statistically. The noise root mean square (RMS) value can be used to estimate its effect on the actual resolution of acceleration meas...

Although the strains on a given material depend on its properties and, in general, on the stresses, on the temperature and on the time under load, they may be modeled as a function of the stresses alone in most practical structural analyses at low service-to-fusion temperature ratios. Most metallic and ceramic alloys can be modeled in such a simpli...

It is well known that materials subjected to cyclic loads increase their temperatures, either by elastic or much more intensely by plastic straining mechanisms. Because fatigue damage is a dissipative process associated with cyclic plastic strains, such temperature increments are much larger for loads above the fatigue limit than below it. Since st...

The fatigue limit is an important material property used for design purposes. The thermographic method was developed to determine it in a more optimized way since the traditional techniques are expensive and time consuming. It correlates the temperature increasing with several loading amplitudes and defines the fatigue limit as the stress below whi...

Tests are used to verify the hypothesis “the fatigue crack growth (FCG) driving force is the effective stress intensity factor range ΔKeff”. The tests are performed measuring FCG rates in steel and aluminum C(T) and DC(T) specimens under fixed {ΔK, Kmax} loading conditions and during FCG delays induced by single overloads. Crack-opening loads Pop a...

Relative displacement measurements are needed in many practical applications, in particular to estimate damage from the associated strains and to follow and/or to control paths of moving objects. In many cases, such as monitoring of huge structures like tall bridges or of moving objects like vehicles, it is much easier to indirectly measure displac...

A pure mode-I approach cannot properly analyze many important practical problems that involve combined mode I and II loadings, which in particular may not be sufficient to estimate crack paths and fracture toughness in such cases. Multiaxial crack tip conditions characterized by a crack inclination angle β in a modified mixed-mode single edge tensi...

Engineering problems that involve fatigue crack growth and fracture frequently can be studied by taking into account only mode-I features. However, many important problems that involve combined mode I and II loadings cannot be properly analyzed by a pure mode-I approach, which in particular may not be sufficient to estimate fracture toughness for p...

In this work, DIC analysis is used to assess the cyclic plastic deformation response, Δε, at the near crack-tip region of propagating fatigue cracks and to identify the effects of other phenomena that happen during crack propagation, such as crack closure and partial crack opening on the measured elastoplastic strain loops. The DIC measurements use...

This paper carries out a parametric analysis to evaluate the effect of circular holes on the strength of unidirectional laminae. Stroh Formalism is used to describe the elastic stresses around the border of circular holes in large plates subjected to in-plane loads and Puck failure criterion is applied to estimate the critical load. Finite plates a...

This paper analytically studies how elliptical holes affect the resistance of unidirectional laminate plates. Although local stress and strain concentration effects induced by notches are well known in isotropic materials, the same cannot be said about anisotropic materials. Stroh formalism is used to describe the elastic stresses around the border...

Elber assumed that the actual driving force for fatigue crack growth (FCG) is the effective stress intensity factor ΔKeff. To verify this hypothesis, both DC(T) and C(T) specimens are cut from a 6351-T6 Al alloy circular bar with two different thicknesses, 2 and 30mm, tested under fixed ΔK and Kmax to simulated plane stress and plane strain FCG con...

A stereo microscope coupled to a 3-D Digital Image Correlation system is used to measure strain ranges on the cyclic plastic zone ahead of a fatigue crack-tip. First, a very refined speckle pattern is applied on the surface of a disk-shaped compact tension specimen of 1020 low-C steel by spraying toner powder over a layer of white paint, a suitable...

The fatigue limit is an important material property used for design purposes. The thermographic method was developed to evaluate this parameter in an optimized way, since the traditional techniques are expensive and time consuming. This technique correlates temperature increments with several loading amplitudes and estimates the fatigue limit as th...

Part-through surface or corner 2D cracks are commonly found in structural components, even because practically all fatigue cracks tend to start this way. It is a reasonable hypothesis to model them assuming the shape of their 2D fronts can be approximated by an elliptical arc, as supported by many fractographic observations. However, their transiti...

Elber's assumed long ago that the effective stress intensity factor (SIF) range ΔK eff = K max − K op is the actual driving force for fatigue crack growth (FCG), where K op is the SIF that fully opens the crack, and his idea still is widely used to predict residual lives of cracked components. However, although crack closure can affect the FCG proc...

Stress concentration effects in unavoidable notches reduce fatigue strengths and lives of most structural components, so they must be properly quantified when designing and analyzing them. The Stress Gradient Method (SGM), based on classic Fracture Mechanics concepts and on short crack ideas, can be used to calculate Stress Gradient Factors (SGF) a...

Plastic zones (pz) ahead of crack tips are obtained by incremental elastoplastic (EP) finite element (FE) 3D calculations for cracked components with relatively high and low transversal constraints, considering all effects associated with their geometry and loading conditions. Contrary to what is assumed in traditional Fracture Mechanics estimates,...

This paper focuses on the modeling of fatigue lives of L-shaped cracks obtained by unusual crack tests performed in plates first loaded under tensile loads and then under out-of-plane pure bending loads. To ensure life predictions accuracy, the paper compares two different methodologies. The first uses three points from the measured crack fronts an...

A fast algorithm is presented to implement a multiaxial version of the racetrack amplitude filter, improved upon the authors’ previous works. The algorithm only requires a single user-defined scalar filter amplitude to eliminate noise and potentially non-damaging events from arbitrary non-proportional multiaxial stress or strain histories, while pr...

Traditional fatigue limit measurements are expensive and time consuming, requiring a large number of specimens and a long time to be completed. An alternative approach is used in this work to obtain the fatigue limit of a cold drawn steel, in a rotating bending machine, by monitoring temperature variations induced by different load range levels in...

Part-through surface or corner 2D cracks are commonly found in structural components. To model them assuming that the shape of their fronts is approximately elliptic is a quite reasonable hypothesis supported by fractographic observations, but their transition to a 1D through-crack normally is not properly addressed in fatigue life predictions. Alt...

The study of thermography and its use as a characterization tool is essential in order to develop a reliable, faster and less expensive procedure to measure and determine the fatigue properties of a specific material. Through the temperature increment analysis on the external surface of a tested specimen during the application of a cyclic load, it...

This work analyzes the applicability of the ASME Boiler and Pressure Vessel Code procedures to calculate fatigue crack initiation under multiaxial stresses and/or strains, in particular when caused by non-proportional loads that lead the principal directions at the critical point to vary with time, e.g. due to out-of-phase bending and torsion loads...

Traditional fatigue limit measurements are expensive and time consuming, requiring a large number of specimens and a long time to be completed. An alternative approach is used in this work to obtain the fatigue limit of a cold drawn steel, in a rotating bending machine, by monitoring temperature variations induced by different load range levels in...

Elber assumed a long time ago that Δ. Keff is the driving force for fatigue crack growth (FCG), and his hypothesis is the basis for strip-yield models widely used to predict residual lives of cracked components. However, this hypothesis cannot explain many load sequence effects observed in practice. Hence, it is at least worth to verify if FCG mode...

The closure and crack growth behaviors of a fatigue cracked DC(T) 4340 steel specimen before and after a single 100% overload on the stress intensity factor (SIF) peak, applied over an otherwise mode I loading with quasi-constant SIF range and load ratio, was studied using Digital Image Correlation (DIC) and strain gage techniques. A significant re...

In this paper, crack shape evolution under out-of-plane pure bending loads in plates with an initial through-thickness edge crack is investigated experimentally and computationally. Such cracks were numerically simulated by a step-by-step 3D finite element technique as an attempt to reproduce the evolving geometry of the crack front for the present...

Three analytical-experimental hybrid approaches for determining the range of stress intensity factors (SIF) and the pseudo-SIFs of fatigue cracks on the presence of crack closure, crack tip plasticity and blunting are presented and evaluated. These approaches use the Digital Image Correlation (DIC) technique to measure cyclic-varying displacement f...

The behavior of short cracks that depart from elastoplastic notch tips is modeled to estimate the stresses required to initiate and to propagate cracks in notched structural components, and to evaluate the size of tolerable crack-like defects under general loading conditions. This analysis can model both fatigue and environmentally assisted crackin...

The recently proposed multiaxial racetrack filter (MRF) is able to deal with general non-proportional multiaxial load histories. While only requiring a single user-defined scalar filter amplitude, the MRF is able to synchronously eliminate non-damaging events from any noisy multiaxial load history without changing the overall shape of its original...

Fatigue design routines and computer codes must use some damage accumulation rule to deal with variable amplitude loadings (VAL), usually Palmgren-Miner (or Miner’s) linear rule for lack of a clearly better option. Nevertheless, fatigue lives are intrinsically sensitive to the order of VAL events, which may e.g. induce residual stresses and thus ch...

Elber's hypothesis that ΔKeff can be assumed as the driving force for fatigue crack growth (FCG) is the basis for strip-yield models widely used to predict fatigue lives under variable amplitude loads, although it does not explain all load sequence effects observed in practice. To verify if these models are indeed intrinsically better, the mechanic...

Elber found in the early 70’s that fatigue cracks can close under tensile loads, and assumed that fatigue crack growth (FCG) would be controlled by ΔKeff =Kmax - Kop, where Kmax and Kop are the maximum and opening values of the stress intensity factor. This hypothesis can rationalize many transient effects observed under service loads, but it canno...

Este trabalho apresenta o uso da técnica de correlação de imagens digitais (DIC) para medir o fechamento de uma trinca propagada por fadiga em modo I, antes e após uma sobrecarga de 100%. Para isto, um corpo de prova tipo disco circular tracionado DC(T) de aço 4340 com espessura de 4,4 mm foi testado em ensaio de fadiga sob condições de carregament...

Redundant data obtained under quasi-constant {∆K, Kmax} loading conditions is used to verify if the effective stress intensity factor (SIF) range ∆Keff = ∆Kmax - ∆Kop is indeed the fatigue crack driving force. The crack opening SIF Kop is measured along the entire crack path on DC(T) low carbon steel specimens by a series of strain gages bonded alo...

The DIC technique was used to determine displacement and strain fields surrounding the tip of a fatigue crack in DC(T) (disk compact tension) specimen of normalized AISI 4340 steel, before and after an 120% overload was applied over otherwise fixed loading conditions in mode I ΔK = 31 MP√m and R = Kmin/Kmax = 0.1. The specimen has thickness of 4.6...

Digital image correlation (DIC) techniques are used to obtain the stress intensity factor (SIF) via experimental J-integral evaluations in an AISI 4340 steel disk-shaped compact-tension (DC(T)) specimen subjected to mode I loading conditions. The combined analytical and experimental methodology is based on the computation of the J-integral over an...

This paper focuses on the prediction of crack nucleation under fretting fatigue loadings via multiaxial fatigue models for a couple of steel. In this work, a numerical model of a two-dimensional cylinder on flat contact, which allows applying fretting and fatigue efforts was built using the Abaqus application. Kujawaski’s critical-plane tensile-bas...

Most fatigue models must somehow identify and count individual load events before quantifying the damage induced by each one of them, making multiaxial fatigue damage calculations under non-proportional variable amplitude loadings a challenging and laborious task in practical applications. Moreover, to apply such models it is usually necessary to u...

It has been experimentally proven that the shear stress level needed to cause fatigue failure is lower than the axial one. This fact has led to consider a Stress Scale Factor (SSF) between shear and axial stress to reduce different applied stresses to the same shear stress space or principal stress space, consequently facilitating the yielding anal...

There are several methods or rules to estimate elastoplastic (EP) notch-tip stresses and strains from simpler linear elastic calculations, an almost indispensable step for practical fatigue damage calculations. Neuber’s and Molski-Glinka’s rules are perhaps the most popular for fatigue analyses of uniaxial load histories. Their use in such elementa...

Nonproportional (NP) strain hardening is caused by multiaxial load histories that induce variable principal stress/strain directions, activating cross-slip bands in several directions, due to the associated rotation of the maximum shear planes. This effect increases the strain-hardening behavior observed under proportional loads, those with fixed p...

Several models have been proposed in the literature to account for fatigue damage under multiaxial load histories. Most of them require some measure of an equivalent stress or strain amplitude, in the sense of causing the same damage as the original history, which may be difficult to obtain for generic non-proportional multiaxial variable amplitude...

Several methods can be used to estimate elastoplastic (EP) notchtip stresses and strains from linear elastic calculations, providing EP stress and strain concentration factors. For uniaxial load histories, Neuber’s and Glinka’s rules are perhaps the most used. For non-proportional multiaxial histories, such corrections require incremental plasticit...

The Moment-Of-Inertia (MOI) method has been proposed by the authors to solve some of the shortcomings of convex-enclosure methods, when they are used to calculate path-equivalent ranges and mean components of complex non-proportional (NP) multiaxial load histories. In the proposed 2D version for use with critical-plane models, the MOI method consid...

Materials can be classified as shear or tensile sensitive, depending on the main fatigue microcrack initiation process under multiaxial loadings. The nature of the initiating microcrack can be evaluated from a stress scale factor (SSF), which usually multiplies the hydrostatic or the normal stress term from the adopted multiaxial fatigue damage par...

Filtering techniques have been proposed for multiaxial load histories, usually aiming to filter out non-reversals, i.e. sampling points that do not constitute a reversal in any of its stress or strain components. However, the path between two reversals is needed to evaluate the equivalent stress or strain associated with each event. Filtering out t...

Multiaxial fatigue damage calculations under non-proportional variable amplitude loadings still remains a quite challenging task in practical applications, in part because most fatigue models require cycle identification and counting to single out individual load events before quantifying the damage induced by them. Moreover, to account for the non...

Notches induce localized stress concentration effects that can affect many failure mechanisms, in particular the initiation and growth of short cracks under fatigue loads, significantly reducing the strength of structural components under service loads. To decrease such nocive effects, notches are usually designed with as large as possible circular...

Amplitude filters are a most important tool in practical fatigue analyses to manage their computational cost when, as usual, the measured load history is noisy, oversampled, too long, and/or contains too many non-damaging low-amplitude cycles or events. To reduce the calculation burden, such filters should not only eliminate noise and remove redund...

The calculation of elastoplastic strains from stress histories, or vice-versa, is an important computational step in low-cycle fatigue analyses. This step is a challenging task for general multiaxial non-proportional (NP) loading histories, where the principal stress directions are not constant, requiring 6D incremental plasticity calculations to c...

Part I of this work introduced efficient reduced-order five-dimensional (5D) stress and strain spaces that can be used to predict ratcheting and mean stress relaxation phenomena at a much lower computation cost than in traditional 6D formulations. These 5D spaces were then applied to the qualitative study of uniaxial ratcheting, multiaxial ratcheti...

Multiaxial variable amplitude histories usually require a rainflow algorithm to identify individual cycles. A computationally- efficient 5D multiaxial rainflow algorithm that can deal with any 1D to 6D history has been proposed by the authors, based on the representation of 6D stresses and strains in 5D deviatoric sub-spaces that use a von Mises me...