1,721,985 research outputs found
The effect of defects and notches in quasi-static and fatigue loading of Inconel 718 specimens produced by selective laser melting
No full textAdditively manufactured components are likely to contain defects deriving from the manufacturing process. They are also likely to be designed with high geometric complexity (including notches), due to very few design-limitations. In order to understand the influence of these two types of geometric features, we here investigate as-built Inconel 718 specimens produced by selective laser melting under quasi-static and cyclic loading. Notched and unnotched specimens are considered, and the main emphasis is set on the influence of the defects and on how they influence the failure locations at different load levels. © 2020 The Author(s
Fictitious notch rounding concept applied to V-notches with end holes under mode 3 loading
No full textThe present technical note is aimed to provide a closed form expression for the microstructural support factor and for the fictitious notch radius in plates weakened by V-notches with root end-holes. Taking advantage of some recent closed form expressions for the stress distributions due to V-notches with end holes the fictitious notch rounding approach is applied here to mode 3 loading. The factor s for the V-notch with end holes is found to be strongly influenced by the opening angle and the new values are compared with the previous solution available in the literature and dealing with blunt V-notches. To validate the new expressions a comparison is carried out between the theoretical stress concentration factor (SCF) obtained from a rounded V-notch with a fictitiously enlarged end hole (of radius ρ f ) and the effective stress concentration factor obtained by integrating the relevant stress over the microstructural characteristic length (MCL), ρ *, in a pointed V-notch. A sound agreement is found from the comparison. The range of validity of the present equations are limited to linear elasticity or in those cases where the plastic zone is very small with respect to the MCL of the material. © 2011 Elsevier Ltd. All rights reserved
Some recent results on the fatigue strength of notched specimens made of 40CrMoV13.9 steel at room and high temperature
No full textThe work summarizes a large bulk of experimental data from specimens made of 40CrMoV13.9 steel. The first part of the paper deals with multiaxial fatigue strength of notched round bars tested under combined tension and torsion loading, both in-phase and out-of-phase. The results from multi-axial tests are discussed together with those obtained under pure tension and pure torsion loading from notched specimens with the same geometry. The second part of the paper summarizes data from uniaxial-tension stress-controlled fatigue tests on specimens made of the same steel. Tests are performed varying temperature, from room temperature up to 650°C. Altogether more than 180 new fatigue data are summarised in the present work, corresponding to more than two-years of testing programme. All fatigue data are presented first in terms of nominal stress amplitudes referred to the net area and then re-analysed in terms of the mean value of the strain energy density evaluated over a given, crescent shape volume embracing the stress concentration region. For the specific steel, the radius of the control volume is found to be independent of the loading mode
Tilted lateral V-notches with root hole subjected to in-plane mixed mode loading: Fictitious notch rounding concept
No full textThe fictitious notch rounding concept is applied for the first time to inclined lateral V-notches with root hole subjected to in-plane mixed mode loading. Out-of-bisector crack propagation is taken into account by combining the fictitious notch rounding approach with the maximum tangential stress criterion. Following the guidelines of a previous paper dealing with internal notches, the fictitious notch radius is determined as a function of the real notch radius, the microstructural support length and the notch opening angle. The problem is of formidable complexity and for this reason a simple method based on the normal stress failure criterion is adopted here. The analytical method based on Neuber's procedure proposed for central notches is extended here to tilted lateral notches. The method provides the values of the microstructural support factor as a function of the mode mixity parameter and the notch opening angle. The support factor is considered to be independent of the microstructural support length. To validate the approach about two thousands finite element analyses have been performed varying the notch shape and load configuration. Finally an experimental validation has been performed considering a complete set of data from pointed V-notches made of polymethylmethacrylate
Crack Initiation at V-Notch Tip under In-Plane Mixed Mode Loading: A Review of the Fictitious Notch Rounding Concept
No full textThe fictitious notch rounding concept has been recently applied for the first time to V-notches with root hole subjected to in-plane mixed mode loading. Out-of-bisector crack propagation is taken into account. The fictitious notch radius is determined as a function of the real notch radius (the microstructural support length) and the notch opening angle. Due to the complexity of the problem, a method based on the simple normal stress failure criterion has been used. It is combined with the maximum tangential stress criterion to determine the crack propagation angle. An analytical method based on Neuber’s procedure has been developed. The method provides the values of the microstructural support factor as a function of the mode ratio and the notch opening angle. The support factor is considered to be independent of the microstructural support length. Finally, for comparison, the support factor is determined on a purely numerical basis by iterative analysis of finite element models. The present paper is aimed to give a brief overview of the recent findings on this challenging topic making clear the state of the art
A review on coupled modes in V-notched plates of finite thickness: A generalized approach to the problem
No full textMode 1, 2 and 3 cannot exist in isolation. One mode provokes the existence of a coupled mode which, in some conditions, can be more dangerous than the generating mode itself. This means that three-dimensional problems are automatically at least dual scale. While for a crack this effect was known to exist for a long period of time, it was largely ignored in theoretical studies of V-shaped notches subjected to in-plane and out-of-plane loading as well as in practical fracture problems associated with such geometries. Only recently, some numerical investigations confirmed that highly localized coupled modes do exist in the close vicinity of the notch tip. The present paper is aimed to briefly review important features of these recently identified singular coupled modes. The most significant results from a comprehensive three-dimensional numerical study are presented here to describe the contribution of these modes into the overall stress state in the close vicinity of the notch tip and discuss the implementation of these new results to the failure and integrity assessment of plate structures with sharp notches
Fatigue and fracture assessment of notched components by means of the Strain Energy Density
No full textBrittle failure of components weakened by cracks or sharp and blunt V-notches is a topic of active and continuous research. It is attractive for all researchers who face the problem of fracture of materials under different loading conditions and deals with a large number of applications in different engineering fields, not only with the mechanical one. This topic is significant in all the cases where intrinsic defects of the material or geometrical discontinuities give rise to localised stress concentration which, in brittle materials, may generate a crack leading to catastrophic failure or to a shortening of the assessed structural life. Whereas cracks are viewed as unpleasant entities in most engineering materials, U- and V-notches of different acuities are sometimes deliberately introduced in design and manufacturing of structural components. Dealing with failure of notched components and summarising some recent experimental results reported in the literature, the main aim of the present contribution is to present a short review of the research work developed by Professor Paolo Lazzarin dealing with the Strain Energy Density approach. The approach, which is based on the volume Strain Energy Density (SED), has been recently applied to assess the failure of a large number of materials. The main features of the SED approach are outlined in the paper and its peculiarities and advantages accurately underlined. Some examples of applications are reported, as well
A Brief Review of Some Local Approaches for the Failure Assessment of Brittle and Quasi-Brittle Materials
Full text linkBrittle failure of components weakened by cracks and notches is a topic of active and continuous research. It is a key topic for all researchers who face the problem of fracture of materials under different loading conditions and deals with a large number of applications in different engineering fields. This topic is significant in all the cases where intrinsic defects of materials or geometrical discontinuities give rise to localized stress concentration which, in brittle materials, may generate a crack leading to catastrophic failure or to a shortening of the assessed structural life. Whereas cracks are viewed as unpleasant entities in most engineering materials, U- and V-notches of different acuities are sometimes deliberately introduced in design and manufacturing of structural components. The main aim of the present contribution is to present a short review of some local approaches applicable near stress raisers both sharp and blunt allowing the reader to have an update state of the art for the considered criteria
Notch-Defect Interaction in Additively Manufactured Inconel 718
No full textPowder bed fusion based additively manufactured components are known to have poor surface quality, especially when building downward facing surfaces. These surfaces can contain defects, from which fatigue cracks can be initiated. In this work the notched fatigue behaviour of Inconel 718 specimens produced by selective laser melting is investigated. The main focus is set on the interaction between notch geometries and local defects due to the amount of overhang in the notch region. Four different geometries are considered, with different amount of notch acuities and degree of downward facing surfaces. A variation in failure sites, with respect to the notch bisector line, was fond in the specimens, and the position was found to be dependent on the amount of overhang and notch acuity. The fatigue life was found to be dependent on the size of surface defects measured in fracture surfaces. Further, the use of average strain energy density as a failure criteria in additively manufactured metals is discussed
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