Search results for "Fatigue"
showing 10 items of 651 documents
Empirical model for stress ratio effect on fatigue delamination growth rate in composite laminates
2004
An empirical model is proposed for the stress ratio effect on the fatigue delamination growth rate in composite laminates under single-mode loading, intending to provide a simple and accurate description tool in engineering application. The model is based on heuristic considerations of damage accumulation ahead of the crack. Linear cumulative assumption is used for damage estimation. Comparison of the prediction based on the proposed model with the test results for different carbon, glass, and alumina fibre-reinforced composites at several stress ratios shows reasonable agreement.
Energy models for fatigue life estimation under uniaxial random loading. Part I: The model elaboration
2001
The paper contains analysis of the energy models for the fatigue life assessment under uniaxial stress state. From the simulation tests it appears that taking into account the stress and strain signs during determination of the energy density allows one to distinguish the strain energy density at the tension and compression path. Under random loading with the zero expected values for Gaussion processes it leads to the centered stochastic process. A new (basic for damage cumulation) material characteristic can be easily determined by rescaling the widely used standard stress and strain characteristics of cyclic fatigue. A new model of the fatigue life determination has been proposed. This mo…
Fatigue delamination experiments on GFRP and CFRP specimens under single and mixed fracture modes
2011
This paper deals with the experimental analysis of the delamination phenomena in composite materials under different loading conditions. Quasi-static and fatigue tests are performed on specimens made of glass-fibre (GFRP) and carbon-fibre (CFRP) reinforced plastic. In particular, experiments have been carried out under single fracture modes I and II (using standard DCB and ENF test configurations) and mixed modes I+II (using the MMB test configuration) with several mode mixtures. Results obtained for the two materials have been compared paying attention on the relationship between the parameters that describe the fatigue behaviour and the mode mixture acting during the crack propagation. © …
Effect of Cold Working and Ring Indentation on Fatigue Life of Aluminum Alloy Specimens
2013
The article deals with the fatigue life of plates with hole made of aluminum alloy. Specifically, the combined effect of cold working expansion and ring indentation on improved fatigue life performance was investigated. Multiple fatigue tests were performed to determine the cycles to failure and the corresponding W¨ ohler diagram. Experimental results were compared with those of nontreated specimens. The conclusion was that cold working expansion and indentation create a delay on crack formation and fatigue failure.
Damage accumulation under variable amplitude loading of welded medium- and high-strength steels
2004
Abstract The paper presents the calculation of cumulative damage for two types of welded joints (butt weld and transverse stiffeners) of four steels (medium to high strength): S355N, S355M, S690Q and S960Q. This calculation is based on experimental data obtained under axial loading and bending with constant and variable amplitudes (Gaussian distribution and Gauss with overload spectrum). The experiments were performed under fully reversed ( R =−1) and pulsating ( R =0) loading. The fatigue life is calculated using the modifications of the Palmgren–Miner–Original rule, according to the Palmgren–Miner–Elementary method, as well as to Haibach’s suggestion. The fatigue life does not depend on t…
A theoretical and experimental study to point out the notion of loading mode in damage mechanicsApplication to the identification and validation of a…
2002
A model of fatigue-induced intralaminar cracking in strongly anisotropic laminates is presented. The features of the microscopic phenomenon are explicitly taken into account at the macroscopic level by the use of two variables, which define a new concept in Damage Mechanics that results not only in a coherent model of crack density evolution, but also in a coherent treatment of damage deactivation. Damage evolution indeed is strongly dependent on the local loading mode in each ply where cracking occurs. Experiments on complex lay-ups provided sufficient data for complete calibration of the model. These tests also allowed to validate the theoretical choice of the damage variable. Finally, nu…
Critical Planes in Multiaxial Fatigue
2005
The paper includes a review of literature on the multiaxial fatigue failure criteria based on the critical plane concept. The criteria were divided into three groups according to the distinguished fatigue damage parameter used in the criterion, i.e. (i) stress, (ii) strain and (iii) strain energy density criteria. Each criterion was described mainly by the applied the critical plane position. The multiaxial fatigue criteria based on two critical planes seem to be the most promising. These two critical planes are determined by different fatigue damage mechanisms (shear and tensile mechanisms).
Criteria of multiaxial random fatigue based on stress, strain and energy parameters of damage in the critical plane
2005
In this paper generalized criteria of multiaxial random fatigue based on stress, strain and strain energy density parameters in the critical plane have been discussed. The proposed criteria reduce multiaxial state of stress to the equivalent uniaxial tension–compression or alternating bending. Relations between the coefficients occurring in the considered criteria have been derived. Thus, it is possible to take into account fatigue properties of materials under simple loading states during determination of the multiaxial fatigue life. Presented models have successfully correlated fatigue lives of cast iron GGG40 and steel 18G2A specimens under constant amplitude in-phase and out-of-phase lo…
A critical plane approach based on energy concepts: application to biaxial random tension-compression high-cycle fatigue regime
1999
Abstract In this paper the energy parameter, defined for random loadings, is analysed. Under uniaxial loading this parameter distinguishes between the strain energy density for tension (positive) and the strain energy density for compression (negative). As a consequence, if there is no mean component in the random loading, we obtain a random history of strain (elastic and plastic) energy density with zero expected value. Under multiaxial loadings the normal strain energy density in the critical plane (i.e. the plane of the maximum damage) is understood as the energy parameter. The history of strain energy density is schematized with use of the rain-flow algorithm. Fatigue damage is accumula…
Critical and Fracture Planes of 18G2A Steel Under Nonproportional Combined Bending and Torsion
2008
Many multiaxial fatigue failure criteria of materials are based on the critical plane approach [1, 2, 3]. In these criteria, it is assumed that the fatigue failure of material is caused by stresses and/or strains acting in one plane (called critical) within the material. The proper orientation of that plane in fatigue failure criteria based on the critical plane concept must be established for fatigue life calculation. In the paper the damage accumulation method was used to determine the critical plane orientations. In this method, the critical plane is the plane where the maximum damage degree, computed according to the selected fatigue failure criterion, is the highest. The critical plane…