Multiaxial High-cycle Fatigue Research Articles

High cycle fatigue strength assessment methodology considering punching effects

Since a decrease of the fatigue strength may result from punching operations, this study proposes a methodology for designing punched parts against high cycle fatigue crack initiation. To reach this goal, high cycle fatigue tests are performed on different specimens configurations with either punched or polished edges. Due to punching effects, the fatigue strength of punched specimens is significantly decreased. Fracture surfaces observations reveal that crack initiation occurs always on a punch defect. Additional investigations are combined to characterize how the edges are altered by the punching operations. High tensile residual stress levels along the loading direction are quantified using X-Ray diffraction techniques. Furthermore, micro-hardness measurements and X-Ray diffraction results reveals a strong hardness gradient due to punching operation. For a better understanding of crack initiation mechanisms, the edge geometries have been scanned with 3D optical microscopy, allowing us to identify the most critical defect (and its real geometry) by comparing the edges before and after fatigue failure. Finally, FEA are performed on identified defects. A non-local high cycle multiaxial fatigue strength criterion has been used as post-processing of FEA to take into account the effect on the HCF strength of defects and the strong stress-strain gradients around them.

Multiaxial high-cycle fatigue life prediction model considering mean shear stress effect under constant and variable amplitude loading

In this paper, load controlled uniaxial, pure torsion, constant and variable amplitude tension–torsion tests on 7075-T651 aluminum alloy tubular specimens were conducted. According to the analysis of the experimental data obtained, a multiaxial high-cycle fatigue life prediction model, based on the critical plane method and considering mean shear stress effect, is proposed. The critical plane is proposed to be determined by a weight average, which is based on the variation of the maximum shear stress. The estimated fatigue lives obtained by applying the proposed model, for the fatigue limits related to 106, 2×106 and 107 cycles, are compared. The results demonstrate that the proposed model shows a good predictive capability.

Numerical assessment of fatigue load capacity of cylindrical crane wheel using multiaxial high-cycle fatigue criteria

The application of multiaxial high-cycle fatigue criteria to the analysis of the subsurface rolling contact fatigue of structures working in contact conditions is discussed. In such objects, an increase in compressive and shear stresses is strongly non-proportional. Therefore, the first part of the paper is devoted to the comparison of the results of six recently used high-cycle fatigue criteria estimating the effort for both different multiaxial proportional and non-proportional loads. In the second part of the paper, the issue of frictionless and tractive rolling contact fatigue is discussed. The fatigue load capacity of a crane wheel has been estimated using recently popular criteria. The orientation of critical planes and location of dangerous points are determined and discussed in detail. It has been found that the Dang Van criterion, which is often proposed in rolling contact fatigue analysis, underestimates the equivalent fatigue stress for such type of loads. Comparison of the results obtained using different multiaxial criteria with the results of the experimental tests enables a selection of criteria suitable for fatigue assessment of machine parts working in cycling rolling contact conditions.

Application of continuum damage mechanics to vibration fatigue life prediction

AbstractIt is pivotal to predict the multiaxial vibration fatigue life during mechanical structural dynamics design. An algorithm of the finite element method implementation for multiaxial high cycle fatigue life evaluation is proposed, on the basis of elastic evolution model of continuum damage mechanics. By considering structural dynamic characteristics, namely, resonant frequencies and mode shapes, this algorithm includes a modal analysis and harmonic analysis, which makes this different from existing fatigue life prediction methods. A 10% decrease in the resonant frequency is regarded as the failure criterion. A critical damage value was obtained, which indicates mesocrack initiation fulfilment. To validate the effectiveness of the algorithm, auto‐phase sine resonance track‐and‐dwell experiments were conducted on notched cantilever beams made of Ti‐6Al‐4V alloy. The life predictions are conservative and in good agreements with the experimental results, which are mainly distributed within a scatter band of 2. This investigation could provide technical support for structural dynamics design and the analysis of reusable spacecraft.

New specimen and horn design for combined tension and torsion ultrasonic fatigue testing in the very high cycle fatigue regime

Fatigue damage has special relevance on the life span of mechanical components and structures, as it takes responsibility for the majority of the registered structural failures. Although its mechanisms have been the subject of continuous research, the growing need for greater lifespans forced the understanding of the behavior of materials under the very high cycle regime, also known as Very High Cycle Fatigue. This field of research, which studies the mechanical behavior of materials for fatigue lives beyond 1E7 cycles, only recently gained notoriety, largely due to the appearance of ultrasonic fatigue testing machines, working at 20kHz and due to the acquisition and control equipment capable of handling signals at very high frequencies. On the other hand the behavior of materials under multiaxial fatigue has been the subject of research and development, but not in the region of very high cycles, due to the inexistence of appropriate testing machine to perform these tests. The authors of this work have already a large experience on the performance of multiaxial fatigue tests under axial/torsion loading under servo-hydraulic fatigue testing machines and on very high cycle fatigue tests. In this paper, and using a new developed multiaxial fatigue testing machine operating at 20kHz frequency, experimental results, using strain gauges and axial and shear stresses determined by finite element modelling on a new specimen design tested with biaxial loadings, tension/torsion at 20kHz, are discussed and analyzed. Results show that it is possible to carry out multiaxial (axial/torsion loading) fatigue tests at very high frequencies which will allow to perform reliable very high cycle multiaxial fatigue tests.

Size optimization of rectangular cross section members subject to fatigue constraints

Although in the scientific literature there are studies regarding optimization of structural members subject to static loads or even cyclic in-phase loads, the optimization of structures subject to cyclic, out-of-phase multiaxial loads is still an unexplored issue. In this paper, we present an approach to the problem of size optimization of rectangular cross-section members subject to multiaxial in-phase and out-of-phase cyclic loads. The objective of the optimization is to minimize the cross sectional area of such elements while retaining their fatigue endurance. Under the proposed methodology, optimum values of the area are achieved for six loading cases and for three values of the height to width ratio of the cross section, and these values are reported. The novelty of the approach lies in the inclusion of two multiaxial high cycle fatigue criteria, i.e., Dang Van and Vu-Halm-Nadot ones, as constraints for size optimization problems, fully integrated within an in-house developed tool, capable of handling non-proportional stresses. A plot of the feasible solution space for this optimization problem is also obtained.

多軸一定応力振幅下の高サイクル疲労寿命予測

Multiaxial high cycle fatigue life prediction under constant stress amplitude is proposed. This new criterion, which extends the proposed fatigue limit criterion by the authors in the previous papers, uses the unified equivalent shear stress amplitude. The material properties for the proposed criterion are the axial fatigue limit and the true fracture strength. The multiaxial high cycle fatigue tests for life prediction accuracy verification was carried out with S45C and SCM440. The fatigue tests were conducted under combined axial and torsion stresses with mean stress and phase difference. The criterion error is better than that of the Susmel criterion. The proposed criterion predicted the experimental fatigue life to be within a factor of 3.

Comparison of Equivalent Stress Methods with Critical Plane Approaches for Multiaxial High Cycle Fatigue Assessment

Several equivalent stress methods and more advanced critical plane criteria are compared in terms of their performance in fatigue life estimations under uniaxial and biaxial loadings in which the effect of phase is investigated. For this purpose a MATLAB code is written which transforms the multiaxial cyclic stress state into a uniaxial cyclic stress to use with the equivalent stress based methods. For critical plane approaches the program searches a damage parameter on all material planes. The maximum damage parameter is then compared with a material allowable obtained from uniaxial fatigue tests for life estimation. In addition, various methods for calibration of the material coefficient k and prominent stress history enclosure methods to calculate the shear stress amplitude are also studied for determining their effect on the performance of critical plane approaches.

Fatigue behaviour of defective cast iron

With the analysis example of a cast iron component a Finite Element Analysis (FEA) based modelling and post-processing methodology is proposed for the multiaxial high-cycle fatigue assessment of surface defects. Methods are proposed for the measurement and mechanical description of surface defects using an ellipsoid simplification and the well-known size parameter from Murakami (2002). Different methods are compared for the stress-computation near surface defects: elastic FEA, elastic-plastic FEA with nonlinear kinematic hardening material model, and analytical calculations with the Equivalent Inclusion Method from Eshelby (1957). The Defect Stress Gradient (DSG) approach from Vincent et al. (2014) is applied to predict crack initiation, whereby a new method is proposed for the estimation of the stress gradient, which allows the presentation of the DSG utilisation factor results field.

Development of Bending and Torsion Fatigue Testing Machine for Multiaxial Non-Proportional Loading

This study presents a newly developed multiaxial high cycle fatigue testing machine which can load a cyclic bending loading and a reversed torsion loading onto an hour-glass shaped solid bar specimen. This testing machine can perform the fatigue tests with a high frequency under a proportional and a non-proportional loading conditions. In the non-proportional loading, principal directions of stress and strain are changed in a cycle. In the testing machine, the loading is generated by centrifugal force caused by the revolving weights attached to rotational wheels. The maximum frequency of the testing machine is 50Hz. A material tested was a type 304 stainless steel. In the test, two types of loading paths are employed, a proportional loading and a non-proportional loading. The former is a cyclic bending loading and the latter a combining cyclic bending and reversed torsion loading in the developed testing machine. In this study, an applicability of the testing machine is evaluated by carrying out the tests under these loading conditions.

Modeling the high cycle fatigue behavior of T-joint fillet welds considering weld-induced residual stresses based on continuum damage mechanics

A nonlinear continuum damage mechanics (CDM) model for multiaxial high cycle fatigue which incorporates the cyclic plasticity constitutive equation is developed in the finite element (FE) framework. FE simulation of T-joint fillet welding is first performed to identify welding residual stresses employing sequentially coupled three-dimensional (3-D) thermo-mechanical FE formulation. The high cycle fatigue damage model is then applied to the T-joint fillet welds subjected to cyclic fatigue loading to compute the fatigue life considering the residual stresses. The calculated total fatigue life which includes the fatigue crack initiation and the propagation is compared with the test result. The FE results demonstrate that the high cycle fatigue damage model proposed in this work gives a correct prediction of the fatigue life of the welds, and welding residual stresses cannot be disregarded in an estimation of the fatigue life of the welds.

Multiaxial high-cycle fatigue life prediction model based on the critical plane approach considering mean stress effects

The aim of this paper is to propose a modified multiaxial high-cycle fatigue criterion based on the critical plane approach. The proposed criterion contains three parameters, that is, shear stress amplitude, normal stress amplitude and mean normal stress. In order to take into account the mean shear stress effects, the critical plane is determined by the maximum shear stress. In the proposed multiaxial fatigue criterion, the influence of mean normal stress on fatigue damage is also considered. Based on the proposed criterion, the multiaxial fatigue life is predicted, and the results showed a good agreement with experimental data obtained from some literatures.

Continuum approach for modelling transversely isotropic high-cycle fatigue

Abstract A continuum approach is proposed for modelling multiaxial high-cycle fatigue of solids which exhibit transversely isotropic fatigue properties. The approach is an extension of the original isotropic model proposed by Ottosen, Stenstrom and Ristinmaa in 2008, which model is based on the concept of a moving endurance surface in the stress space and on an evolving damage variable. The theory is formulated in a rate form within continuum mechanics framework without the need to measure damage changes per loading cycles. Capability of the approach is illustrated by several examples with different uni- and multiaxial loading histories.

Multiaxial high-cycle fatigue criteria and life prediction: Application to gas turbine blade

A recent work conducted by the authors (Maktouf and Saï, 2015) demonstrated that the root cause of the premature blade failure was caused by high-cycle fatigue (HCF) mechanism initiated at a localized carbon-rich area inducing grain boundary brittleness. The blade was subject to multiaxial cyclic loadings during its service life and any attempt to assess component fatigue strength leads to the question of choosing an appropriate fatigue design criterion. In this paper several multiaxial fatigue models are applied as post-processing step of the Finite Element Analysis (FEA) output results and the estimated fatigue lifetimes were assessed under different loading conditions. The material fatigue parameters, required as an input to the selected fatigue models were determined through a series of bending and torsion tests on specimens made of aged Inconel 718. A numerical post-processing algorithm was developed for Fatemi-Socie fatigue criterion and included as additional post-computation model in the used computer aided fatigue damage evaluation tool. The authors point out that the majority of the multiaxial fatigue studies available in the literature are conducted mainly for correlating the experimental laboratory results on specimens while they have been used in the frame of this study to investigate their application to an industrial case.

Multiaxial fatigue criterion based on parameters from torsion and axial S-N curve

Multiaxial high cycle fatigue is a topic that concerns nearly all industrial domains. In recent years, a great deal of recommendations how to address problems with multiaxial fatigue life time estimation have been made and a huge progress in the field has been achieved. Until now, however, no universal criterion for multiaxial fatigue has been proposed. Addressing this situation, this paper offers a design of a new multiaxial criterion for high cycle fatigue. This criterion is based on critical plane search. Damage parameter consists of a combination of normal and shear stresses on a critical plane (which is a plane with maximal shear stress amplitude). Material parameters used in proposed criterion are obtained from torsion and axial S-N curves. Proposed criterion correctly calculates life time for boundary loading condition (pure torsion and pure axial loading). Application of proposed model is demonstrated on biaxial loading and the results are verified with testing program using specimens made from S355 steel. Fatigue material parameters for proposed criterion and multiple sets of data for different combination of axial and torsional loading have been obtained during the experiment.

The Influence of Multiaxial Superimposed Static Mean Stress on High-Cycle Fatigue Life of Cu-ETP Copper

High–cycle multiaxial fatigue tests under proportional and non-proportional loading conditions with various combinations of superimposed static mean stresses was carried out on Cu-ETP copper. The results show differences in fatigue life between various ratios of mean stresses. These results are similar to others described in the literature.

Fatigue assessment of notched specimens by means of a critical plane-based criterion and energy concepts

A strain-based multiaxial fatigue criterion previously proposed for fatigue assessment of unnotched specimens is here extended to the case of notched ones. Such a criterion is a reformulation of the stress-based multiaxial High-Cycle Fatigue (HCF) criterion by Carpinteri and Spagnoli. The extension herein presented considers as the critical point, where to perform the fatigue assessment, the material point located at a certain distance from the notch tip, depending such a distance on both the biaxiality ratio (defined as the ratio between the applied shear stress amplitude and the normal stress amplitude) and the control volume radii R1 (related to Mode I) and R3 (related to Mode III). Some multiaxial fatigue data related to specimens made of titanium grade 5 alloy (Ti–6Al–4V) and weakened by sharp notches are examined to validate the extended criterion.

A probabilistic method for multiaxial HCF based on highly loaded regions below the threshold depth

For High Cycle Fatigue (HCF) assessment of structural components, a variety of evaluation methods that take important factors into account are available. The application of probabilistic evaluation methods is not always straightforward. Investigations show that the methods have limited predictive capability and most often poor transferability of fatigue test results for more complex geometries. Here, a new probabilistic HCF model based on the concept of highly loaded region is proposed. A depth parameter is taking on an important role in the proposed model. Different local stress criteria in combination with the new model and two other evaluation methods are studied. The purpose is to determine the combination of criteria and evaluation method that gives the best transferability. The results show that the new model has superior predictive capability than other models regardless the choice of fatigue stress criteria.

Implementation of multiaxial high cycle fatigue criterion in finite element analysis

Multiaxial high cycle fatigue analyses concern many mechanical components in several industries (aircraft, automobile, railway...). Many multiaxial fatigue criteria have been proposed in the literature for metals. This study deals with the integration of fatigue criteria in finite element code by using APDL (ANSYS Parametric Design Language) scripting language. Three criteria have been implemented including Crossland, Dang Van and Vu et al. [6] criteria. The predictions of Vu et al. criterion are in good accordance with the experimental data.

曲げ・ねじり組合せ疲労試験装置を用いたSUS304の非比例多軸高サイクル疲労寿命

曲げ・ねじり組合せ疲労試験装置を用いたSUS304の非比例多軸高サイクル疲労寿命