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A multi-scale fatigue life prediction methodology of composite pressure vessels subjected to multi-axial loading has been proposed in this paper. The multi-scale approach starts from the constituents, fiber, matrix and interface, leading to predict behavior of ply, laminates and eventually the composite structures. The life prediction methodology is composed of two steps: macro stress analysis and micro mechanics of failure based on fatigue analysis. In the macro stress analysis, multiaxial fatigue loading acting at laminate is determined from finite element analysis (FEM) of composite pressure vessel, and ply stresses are computed using a classical laminate theory (CLT). The micro-scale stresses are calculated in each constituent (i.e. matrix, interface, and fiber) from ply stresses using a micromechanical model. Micromechanics of failure (MMF) was originally developed to predict the strength of composites and now extended to prediction of fatigue life. Two methods are employed in predicting fatigue life of each constituent, i.e. an equivalent stress method for multi-axially loaded matrix, and a critical plane method for the interface. A modified Goodman diagram is used to take into account the generic mean stresses. Damages from each loading cycle are accumulated using Miner’s rule. Each fiber is assumed to follow a probabilistic failure depending on the length. Using the overall micro and macro models established in this study, Monte Carlo simulation has been performed to predict the overall fatigue life of a composite pressure vessel considering statistical distribution of material properties of each constituent and manufacturing winding helical angle.

Welded joints are frequently locations for cracks initiation and propagation that may cause fatigue failure of engineering structures. Biaxial or triaxial stress-strain states are present in the vicinity of welded joints, due to local geometrical constraints, welding processes and/or multiaxial external loadings. Fatigue life evaluation of welded joints under multiaxial proportional (in-phase) cyclic loading can be performed by using conventional hypotheses (e.g. see the von Mises criterion or the Tresca criterion) on the basis of local approaches. On the contrary, the fatigue life predictions of welded joints under non-proportional (out-of-phase) cyclic loading are generally unsafe if these conventional hypotheses are used. A criterion initially proposed by the authors for smooth and notched structural components has been extended to the fatigue assessment of welded joints. In more detail, fatigue life of welded joints under multiaxial stress states can be evaluated by considering a nonlinear combination of the shear stress amplitude (acting on the critical plane) and the amplitude and the mean value of the normal stress (acting on the critical plane). In the present paper, fatigue lifetimes predicted through the proposed criterion are compared with experimental fatigue life data available in the literature, related to fatigue biaxial tests.

The purpose of this paper is to compare with estimation of equivalent fatigue load in time domain and frequency domain and estimate the fatigue life of structure with multi-axial vibration loading. The fatigue analysis with two methods is implemented with various signals like random, sinusoidal signals. Also, an equivalent fatigue life estimated by rainflow cycle counting in time domain is compared with results estimated with probability density function of each signal in frequency domain. In case of frequency domain, equivalent fatigue life can be estimated through Dirlik’s method with probability density function. The work proposed in this paper compared the fatigue damage accumulated under uni-axial loading to that induced by multi-axial loading. The comparison was performed for a simple cantilever beam exposed to vibrations of several directions. For verification of estimation performance of fatigue life, results are compared to those of FEM analysis (ANSYS).

Fatigue life estimation of notched components is mostly dependent on notch stress and strain calculation with non-linear finite element analysis (FEA). For multiaxial cyclic loading, the stress-strain analysis of notch root is rather complex and the non-linear FEA is also very time-consuming. In this paper, a new fatigue life prediction method for notched components under multiaxial loading is proposed. First, a linear elastic solution needs to be solved for notched components under multiaxial cyclic loading. Then, an elastic equivalent parameter is computed using the linear elastic solution. On the basis of the elastic equivalent parameter combined with the Neuber’s rule, an elastic-plastic equivalent parameter is obtained. Finally, the elastic-plastic equivalent parameter is used to estimate fatigue crack initiation life of notched components. The proposed method needs only elastically calculated notch strain history as the basic input and is convenient for engineering application. The method is verified with experimental data of SAE 1045 notched shaft specimens under proportional and non-proportional loading. The results showed that the method can provide good life estimates.

Bone cement is subjected to multi-axial cyclic loading when used to fixate orthopedic prostheses for joint arthroplasty. In this study, tubular specimens of poly(methylmethacrylate) (PMMA) bone cement are subjected to internal pressure and cyclic axial loading to ascertain the influence of multi-axial loading on fatigue life. As expected, it was found that the probability of survival of specimens under multi-axial loading was very much reduced relative to specimens loaded uniaxially. Furthermore, the variability of the fatigue life was increased by multi-axial loading. In conclusion, the results point to the importance of characterizing the behavior of bone cements under the multi-axial fatigue experienced in vivo, and of the importance of accounting for the multi-axial stress state when predicting implant longevity.

The purpose of this paper is to compare with estimation of equivalent fatigue load in time domain and frequency domain and estimate the fatigue life of structure with multi-axial vibration loading. The fatigue analysis with two methods is implemented with various signals like random, sinusoidal signals. Also an equivalent fatigue life estimated by rainflow cycle counting in time domain is compared with results estimated with probability density function of each signal in frequency domain. In case of frequency domain, equivalent fatigue life can estimate through Dirlik’s method with probability density function. And the work proposed in this paper compared the fatigue damage accumulated under uni-axial loading to that induced by multi-axial loading. The comparison is preformed for a simple cantilever beam, which is exposed to vibrations of several directions. For verification of estimation performance of fatigue life, results are compared to those of FEM analysis (ANSYS).

This comprehensive new ASTM publication examines state-of-the-art multiaxial testing techniques and methods for characterizing the fatigue and deformation behaviors of engineering materials. 25 analytical, peer-reviewed papers, written by experts from academia, industry, and government, are divided into the following sections: Multiaxial Strength of Materials--addresses multiaxial strength, stress, and failure modes of materials. Multiaxial Deformation of Materials--investigates constitutive relationships and deformation behavior of materials under multiaxial loading conditions. Fatigue Life Prediction under Generic Multiaxial Loads--examines the challenging task of estimating fatigue life under general multiaxial loads. Fatigue Life Prediction under Specific Multiaxial Loads--describes biaxial and multiaxial fatigue and life estimation under combinations of cyclic loading conditions, such as axial tension/compression, bending, and torsion. Multiaxial Fatigue Life and Crack Growth Estimation--covers crack growth monitoring under cyclic mulitaxial loading conditions and determination of fatigue life. Multiaxial Experimental Techniques--explores state-of-the-art experimental methods to generate mulitaxial deformation and fatigue data to develop and verify both constitutive models used to describe the flow behavior of materials and fatigue life estimation models. The International Standards contained in the Handbook set out the practical methodology which a user requires in order to be able to process and interpret, statistically, testing and inspection results whenever goods are assessed from a sample. This fifth edition of the ISO Standards Handbook Statistical Methods for Quality Control is published in two volumes: Volume 1 includes standards on vocabulary and symbols, and the two basic tools used in sampling throughout the world -- sampling by attributes and by variables. Volume 2 presents interpretation of statistical data, process control charts, the newly revised and expanded standards on the precision of measurement methods. The volumes compliment the ISO 9000 Compendium, containing International Standards for quality management, and ISO/IEC Compendium of Conformity Assessment Documents, containing guides on the testing, inspection and certification of products, processes and services, and on the assessment of quality systems, testing laboratories, inspection bodies, certification bodies and their operation and acceptance.

Description This comprehensive new ASTM publication examines state-of-the-art multiaxial testing techniques and methods for characterizing the fatigue and deformation behaviors of engineering materials. 25 analytical, peer-reviewed papers, written by experts from academia, industry, and government, are divided into the following sections: Multiaxial Strength of Materials--addresses multiaxial strength, stress, and failure modes of materials. Multiaxial Deformation of Materials--investigates constitutive relationships and deformation behavior of materials under multiaxial loading conditions. Fatigue Life Prediction under Generic Multiaxial Loads--examines the challenging task of estimating fatigue life under general multiaxial loads. Fatigue Life Prediction under Specific Multiaxial Loads--describes biaxial and multiaxial fatigue and life estimation under combinations of cyclic loading conditions, such as axial tension/compression, bending, and torsion. Multiaxial Fatigue Life and Crack Growth Estimation--covers crack growth monitoring under cyclic mulitaxial loading conditions and determination of fatigue life. Multiaxial Experimental Techniques--explores state-of-the-art experimental methods to generate mulitaxial deformation and fatigue data to develop and verify both constitutive models used to describe the flow behavior of materials and fatigue life estimation models.

Stochastic fatigue life prediction of Fiber-Reinforced laminated composites by continuum damage Mechanics-based damage plastic model

The dislocation-based fatigue deformation mechanism of a RAFM steel under multi-axial loadings

A multi-axial and high-cycle fatigue life prediction model based on critical plane criterion

On plastic deformation and fatigue under multiaxial loading

The influence of loading conditions on fatigue life and stress concentration, on ferritic nodular graphite cast iron material, undergoing multi-axial proportional cyclic loading, is investigated experimentally and numerically. The studies are conducted under a controlled maximum amplitude stress (induced Von Mises stress) of 158 Mpa which is close to the fatigue limit of the studied material. Good agreements are reported between numerical and experimental results. It is found that fatigue life and Von Mises stress concentration depend strongly on cyclic loading amplitude ratio 'R'. Fatigue life is less for proportional loading than for simple torsion or simple axial loading. The ultimate number of cycles, in the studied interval of 'R' (-1 to +1), increases in a linear fashion. It has a minimum value at R equals to-1. This effect is directly related to the maximum Von Mises stress. The latter increases in a linear fashion as R increases from-1 to +1, and exhibits a maximum value at R equals to-1. Also, it is found that fatigue life and Von Mises stress are highly dependent on the induced stress ratio (σ/τ). Von Mises stress increases as stress ratio increases. In a reverse manner, fatigue life increases slowly as the ratio /increases. This result concludes the strong effect, on fatigue life, of the presence of the axial load within the multi-axial cyclic loading. In fact, axial loading favors the mode I crack which propagates rapidly perpendicularly to the axis of axial loading.

A numerical investigation on multiaxial fatigue assessment of Nitinol peripheral endovascular devices with emphasis on load non-proportionality effects

A crystal plasticity model for multiaxial cyclic deformation of U75V rail steel