Comparison between SSF and Critical-Plane models to predict fatigue lives under multiaxial proportional load histories (original) (raw)
Related papers
Stress scale factor and critical plane models under multiaxial proportional loading histories
Engineering Fracture Mechanics, 2017
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 analysis or fatigue damage evaluations. Most of multiaxial fatigue models use an SSF, and materials can be classified as shear sensitive (low SSF values) or tensile sensitive (large SSF values), depending on the main fatigue microcrack initiation process under multiaxial loadings. The use of SSF is quite common in many multiaxial fatigue criteria based on the critical plane approach. Such criteria adopt a SSF value assumed constant for a given material, sometimes varying with the fatigue life (in cycles) but not with the SAR (Stress Amplitude Ratio), the stress amplitude level, or the loading path shape. In this work, in-phase proportional tensiontorsion tests related to 42CrMo4 steel specimens for several values of SAR are presented. The SSF approach is then compared with critical-plane models, based on their predicted fatigue lives and the observed ones for the studied tension-torsion histories.
Interaction of shear and normal stresses in multiaxial fatigue damage analysis.PDF
Due to the abundance of engineering components subjected to complex multiaxial loading histories, being able to accurately estimate fatigue damage under multiaxial stress states is a fundamental step in many fatigue life analyses. In this respect, the Fatemi-Socie (FS) critical plane damage parameter has been shown to provide excellent fatigue life correlations for a variety of materials and loading conditions. In this parameter shear strain amplitude has a primary influence on fatigue damage and the maximum normal stress on the maximum shear plane has a secondary, but important, influence. In this parameter, the maximum normal stress is normalized by the material yield strength in order to preserve the unitless feature of strain. However, in examining some literature data it was found that in certain situations the FS parameter can result in better fatigue life predictions if the maximum normal stress is normalized by shear stress range instead. These data include uniaxial loadings with large tensile mean stress, and some non-proportional axial-torsion load paths with different normal-shear stress interactions. This modification to the FS parameter was investigated by using fatigue data from literature for 7075-T651 aluminum alloy, as well as additional data from 2024-T3 aluminum alloy fatigue tests performed in this study.
Frattura ed Integrità Strutturale, 2016
Most of the prior studies on the prediction of fatigue lives have been limited to uniaxial loading cases, whereas real world loading scenarios are often multiaxial, and the prediction of fatigue life based upon uniaxial fatigue properties may lead to inaccurate results. A detailed exploration of multiaxial fatigue under constant amplitude loading scenarios for a range of metal alloys has been performed in this study, and a new methodology for the accurate prediction of fatigue damage is proposed. A wide variety of uniaxial, torsional, proportional and non-proportional load-paths has been used to simulate complex, real-world loading scenarios. Test data have been analyzed and a critical-plane based fatigue damage parameter has been developed. This fatigue damage parameter contains stress and strain terms, as well as a term consisting of the maximum value of the product of normal and shear stresses on the critical plane. The shear-dominant crack initiation phenomenon and the combined effect of shear and tensile stresses on micro-crack propagation have been modeled in this work. The proposed formulation eliminates many of the shortcomings of the earlier developed critical-plane fatigue damage models. It is mathematically simple with substantially fewer material dependent constants, and provides design engineers with a tool to predict the fatigue life of machine parts with minimal computational effort. This life prediction methodology is intended for a wide variety of LCF and HCF loadings on machine parts made of metals including advanced alloys.
Strain-based multiaxial fatigue damage modelling
Fatigue <html_ent glyph="@amp;" ascii="&"/> Fracture of Engineering Materials and Structures, 2005
A B S T R A C T A new multiaxial fatigue damage model named characteristic plane approach is proposed in this paper, in which the strain components are used to correlate with the fatigue damage. The characteristic plane is defined as a material plane on which the complex threedimensional (3D) fatigue problem can be approximated using the plane strain components. Compared with most available critical plane-based models for multiaxial fatigue problem, the physical basis of the characteristic plane does not rely on the observations of the fatigue crack in the proposed model. The cracking information is not required for multiaxial fatigue analysis, and the proposed model can automatically adapt for different failure modes, such as shear or tensile-dominated failure. Mean stress effect is also included in the proposed model by a correction factor. The life predictions of the proposed fatigue damage model under constant amplitude loading are compared with a wide range of metal fatigue results in the literature.
Development of a multiaxial fatigue damage parameter and life prediction metho.PDF
Most of the prior studies on the prediction of fatigue lives have been limited to uniaxial loading cases, whereas real world loading scenarios are often multiaxial, and the prediction of fatigue life based upon uniaxial fatigue properties may lead to inaccurate results. A detailed exploration of multiaxial fatigue under constant amplitude loading scenarios for a range of metal alloys has been performed in this study, and a new methodology for the accurate prediction of fatigue damage is proposed. A wide variety of uniaxial, torsional, proportional and non-proportional load-paths has been used to simulate complex, real-world loading scenarios. Test data have been analyzed and a critical-plane based fatigue damage parameter has been developed. This fatigue damage parameter contains stress and strain terms, as well as a term consisting of the maximum value of the product of normal and shear stresses on the critical plane. The shear-dominant crack initiation phenomenon and the combined effect of shear and tensile stresses on micro-crack propagation have been modeled in this work. The proposed formulation eliminates many of the shortcomings of the earlier developed critical-plane fatigue damage models. It is mathematically simple with substantially fewer material dependent constants, and provides design engineers with a tool to predict the fatigue life of machine parts with minimal computational effort. This life prediction methodology is intended for a wide variety of LCF and HCF loadings on machine parts made of metals including advanced alloys.
Comparison between SSF and Critical-Plane models to predict fatigue lives unde.PDF
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 parameter. Low SSF values are associated with a shear-sensitive material, while a large SSF indicates that a tensile-based multiaxial fatigue damage model should be used instead. For tension-torsion histories, a recent published approach combines the shear and normal stress amplitudes using a SSF polynomial function that depends on the stress amplitude ratio (SAR) between the shear and the normal components. Alternatively, critical-plane models calculate damage on the plane where damage is maximized, adopting a SSF value that is assumed constant for a given material, sometimes varying with the fatigue life (in cycles), but not with the SAR, the stress amplitude level, or the loading path shape. In this work, in-phase proportional tension-torsion tests in 42CrMo4 steel specimens for several values of the SAR are presented. The SSF approach is then compared with critical-plane models, based on their predicted fatigue lives and the observed values for these tension-torsion histories.
2014
It is generally accepted that the additional hardening of materials could largely shorten multi-axis fatigue life of engineering components. To consider the effects of additional hardening under multi-axial loading, this paper summarizes a new multi-axial low-cycle fatigue life prediction model based on the critical plane approach. In the new model, while critical plane is adopted to calculate principal equivalent strain, a new plane, subcritical plane, is also defined to calculate a correction parameter due to the effects of additional hardening. The proposed fatigue damage parameter of the new model combines the material properties and the angle of the loading orientation with respect to the principal axis and can be established with Coffin-Manson equation directly. According to experimental verification and comparison with other traditional models, it is clear that the new model has satisfactory reliability and accuracy in multi-axial fatigue life prediction. KEYWORDS additional hardening, critical plane approach, fatigue life prediction, multi-axial fatigue, nonproportional loading NOMENCLATURE: α max , direction angle of critical plane; Δα t , deviation of the plane with maximum shear strain from critical plane; Γ t , statistical parameter considering additional hardening at time t; Γ T , statistical parameter considering additional hardening in 1 cycle; γ, applied shear strain; γ −1 , shear strain fatigue limit; γ' f , torsional fatigue ductility coefficient; γ αmax , maximum shear strain on critical plane; γ t,α , shear strain on the plane with angle α and at the time t; Δγ, Δγ e , Δγ eq , shear strain, shear elastic strain, and equivalent shear strain range; ε, applied normal strain; ε −1 , normal strain fatigue limit; ε' f , axial fatigue ductility coefficient; ε n * , normal strain excursion; ε αmax , normal strain amplitude on critical plane; ε t,αt , normal strain on the plane with angle α t and at the time t; Δε, Δε e , Δε eq , normal strain, normal elastic strain, and equivalent normal strain range; U, error index; μ(U), Δμ(U), σ(U), average values, relative average value, and standard deviations of U; ν e , ν p , ν eff , elastic, plastic, and effective Poisson's ratio; σ y , yield strength; σ n,max , maximum normal stress; Φ, non-proportionality factor; L, non-proportional hardening coefficient; φ, phase angle between the applied tension and torsion strain; b, b γ , axial and torsional fatigue strength exponent; c, c γ , axial and torsional fatigue ductility coefficient; E, E * , G, elastic modulus, secant modulus, and shear modulus; E s , stacking fault energy; K′, cyclic strength coefficient; N f , number of cycles to failure; N E , N P , experimental life and predicted life; n′, cyclic strain hardening exponent; t, T, loading time and cycle
Including the normal to shear stresses ratio in fatigue life estimation for cyclic loadings
MATEC Web of Conferences, 2019
The paper presents the estimation of the fatigue life under multiaxial cyclic loading of two construction materials. The main aim of this paper is to present a new method which allows evaluation of fatigue life during the design and construction phase of machine elements. In paper three well known multiaxial fatigue criteria based on the critical plane approach verified. This paper contains a proposition to define a new way of determining an orientation angle of the critical plane. The comparison between experimental and theoretical results varying the critical plane orientation appears to be satisfactory.
Effect of Tension/Torsion Load Sequences on Multiaxial Fatigue Life Prediction
2009
The objective of this paper is to evaluate the effect of sequences of tension and torsion loads (proportional, non-proportional and sequential) on the fatigue lives of specimens made of 42CrMo4 steel. A series of biaxial load controlled fatigue tests are carried out using a biaxial servo-hydraulic testing machine. Different sequential biaxial loading paths are applied, fatigue performances are observed and both fatigue lives and fracture surfaces are analysed. The results show that the axial/torsion load sequences have significant effects on both fatigue life and fractography. Multiaxial fatigue life prediction models are applied for sequential biaxial loadings, such as the von Mises approach and the MCE methodology applied to the Sines approach.