Wei-Xing Yao

Evaluation and comparison of several multiaxial fatigue criteria

In this paper several multiaxial fatigue criteria are reviewed. The criteria are divided into three groups, according to the parameters used to describe the fatigue life or fatigue strength of materials. They are stress criteria, strain criteria and energy criteria. Their predictive capabilities are checked against the experimental data of six materials under proportional and nonproportional loading. Among the stress criteria, the criterion of Lee is in the best agreement with the test data. Among the strain criteria, the Kandil, Brown and Miller’s criterion has the best correlation with the experimental data of the materials employed. The Farahani’s criterion yields the most satisfactory result among the energy criteria. Its fatigue life correlation for 1045HR steel and 304 stainless steel fell within factors of 2 and 3, respectively.  2003 Elsevier Ltd. All rights reserved.

A nonlinear damage cumulative model for uniaxial fatigue

On the basis of the continuum fatigue damage theory, according to the varying behavior of the material ductility in the process of fatigue damage, a new nonlinear fatigue damage cumulative model is proposed, which considered the fatigue limit, the mean stress and the unseparable characteristic for the damage variables and the loading parameter, and the effect of the loading sequence may also be included. The recurrence formula of fatigue damage model was derived under multilevel loading. The fatigue test data for two kinds of materials were used to verify the model proposed in this paper. The results show that good agreements are achieved with this model to predict fatigue life.

A new approach to the determination of fatigue crack initiation size

Abstract In this paper, the definition of fatigue crack initiation size and determining method were presented on the basis of the non-propagating cracks behaviour. The physical significance of fatigue crack initiation size was explained from the point of view of the fatigue damage. Fatigue crack initiation size is obtained by predicting a non-propagating crack at the notch root under fatigue limit loading. On the basis of the fatigue crack initiation size determined in this paper, the fatigue crack initiation life was predicted by means of the local stress–strain approach, under both constant amplitude and random loading, and good agreement is demonstrated with experimental data.

Local stress–strain field intensity approach to fatigue life prediction under random cyclic loading

Abstract According to the characteristic of the local behavior of fatigue damage, on the basis of stress field intensity approach, a theory of local stress–strain field intensity for fatigue damage at the notch is developed in this paper, which can take account of the effects of the local stress–strain gradient on fatigue damage at the notch. In order to calculate the local stress–strain field intensity parameters, an incremental elastic-plastic finite element analysis under random cyclic loading is used to determine the local stress–strain response. A local stress–strain field intensity approach to fatigue life prediction is proposed by means of elastic-plastic finite element method for notched specimens. This approach is used to predict fatigue crack initiation life, and good correlation was observed with U-shape notched specimens for normalized 45 steel.

Multi-directional stiffness degradation induced by matrix cracking in composite laminates

A model was developed for predicting the stiffness degradation of fiber reinforced plastics (FRP), with ply configuration [0 m /±θ n ] S , induced by matrix cracking under in-plane tension. The model assumes that the cracks in off-axis plies are uniformly distributed and a damage variable D is defined. Based on the theory of fracture mechanics, the elastic moduli of cracked matrix are obtained and indicated by the damage variable D, then the reduction of elastic moduli of laminates caused by the matrix cracks was studied. Comparison with experimental values for the glass/epoxy [90 3 /0] S , [0/90] S and [0/±45] S laminates shows good agreement with the theoretical prediction given by the presented model.

A verification of the assumption of anti-fatigue design

Abstract In this paper, the approaches of anti-fatigue design are briefly reviewed and are classified into three groups: nominal stress approach, local stress–strain approach and stress field intensity approach. Two types, each with two notches, are specially designed and a total of 30 specimens with 4 dimensions are tested under different constant–amplitude loading. These specimens are also analysed with elasto-plastic FEM to obtain stress–strain distributions and stress concentration factors. Fatigue life is estimated based on the different approaches. Experimental and analytical results show that the assumption of stress field intensity is more reasonable than that of the other approaches.

Statistical analysis of data from truncated fatigue life and corresponding residual strength experiments for polymer matrix composites

Abstract A statistical analysis method for the evaluation of data from truncated fatigue life experiments and corresponding residual strength tests of polymer matrix composites is presented. This method is based on the conclusion that under a given fatigue stress S0 the conditional probability of specimen survival at a given fatigue life N0 is equal to the conditional probability that the residual strength of specimens at the fatigue life N0 is greater than S0. This conclusion is deduced from the assumption that for a given specimen, the residual strength decreases monotonously as the fatigue life increases. Some experimental data are applied to demonstrate the analytical ability of the analysis method from which satisfactory results have been obtained.