In the present paper, by definition of a damage parameter, a new mixed mode I/II fracture criterion is presented for predicting the initiation and propagation of cracks in orthotropic materials. ...Damage parameter can be obtained with respect to micromechanics consideration that inferred from the residual tensile and shear strength of fracture process zone at crack tip vicinity. Numerical and experimental approaches are employed for estimation of material properties in damage zone. A new approach named in this research as “Representative Circular Elements (RCEs)” is proposed for simulation of variety in directions and dimensions of damage zone micro-cracks. Comparison with experimental results is demonstrated the capability of the presented criterion.
When mechanical components are subjected to multiaxial cyclic loading during operation, the additional strengthening effect is easy to occur. Using uniaxial fatigue life calculation formula to ...predict their life will produce large errors. However, the existing multiaxial fatigue life prediction models are not convenient for engineering applications because it contains a large number of material constants. To solve the above problems, based on the initiation and promotion mechanism of fatigue microcracks under different stresses, combined with the shear damage model, a new expression of damage parameters is proposed, and the corresponding multiaxial fatigue life prediction model is derived combined with the Manson-Coffin-Basquin equation. The test data of two materials under the non-proportional loading and proportional loading path are used to verify the proposed life prediction model, and compared with the prediction results of the FS model. The results show that the proposed model has a good prediction effe
•A novel energy-based equivalent damage parameter based on uniaxial fatigue data is proposed.•The Moment Of Inertia method and a weighting factor are introduced in the parameter.•Incremental ...plasticity algorithms are avoided in the prediction of non-proportional multiaxial fatigue life.•A series of multiaxial fatigue tests validate the prediction capability of the proposed parameter.
Energy-based damage parameters are widely used, due to their availability, in the prediction of multiaxial fatigue life, usually by integrating the product of stress and strain range into a single scalar quantity. However, in most engineering applications, stress and the strain histories cannot be known simultaneously. Although incremental plasticity methods can be used to estimate the response from measured or specifically designed loads, these processes are too complicated to be employed. In this paper, a novel energy-based Equivalent Damage Parameter (EDP) based on uniaxial fatigue data is proposed to predict the fatigue life under multiaxial fatigue loadings. In this way, the augmentation of uniaxial tensile elastoplastic work can be estimated thanks to the non-proportional (NP) hardening factor FNP and the energy-based material constant αw. Moreover, the contributions to total elastoplastic work from different loading components can be separated and quantified by using the Moment Of Inertia (MOI) method and weighting factor ξ, introduced as a parameter. The efficiency of the proposed parameter is validated by reasonable correlations with the experimental fatigue data of 316L steel tubular specimens subjected to various proportional or NP loadings.
•A strain hardening rule combined with a defined fatigue damage parameter is introduced to represent prior fatigue damage.•The proposed model is capable of capturing effects of various prior fatigue ...loadings.•Satisfactory prediction of various tensile deformations is achieved.
Reliable constitutive models are necessary for the precise design and manufacture of complicated components. This study is devoted to developing a modified constitutive model to capture the effects of prior fatigue loading on subsequent tensile deformation of 9%Cr steel. In the proposed model, a strain hardening rule combined with a defined fatigue damage parameter was introduced to represent prior fatigue damage. The defined fatigue damage parameter based on the inelastic strain range of each cycle is capable of describing the evolution of tensile strength, recovery of martensite laths and decline of dislocation density, regardless of the variation in fatigue loading conditions. To validate the predictive capacity of the proposed model, experimental tensile results at different strain amplitudes, lifetime fractions and hold times of prior fatigue loading were compared with the predicted results. Good agreement between experimental and predicted results indicates that the proposed model is robust in describing the tensile behaviour under prior fatigue loading. Moreover, few determined material parameters are required, which makes the proposed model convenient for practical applications.
In order to study the damage form and mechanism of coal mine roof, the stress distribution state in the stacked beam model was analyzed by using the stacked beam model and introducing the stress ...potential function; the model was simplified by using horizontal and vertical joints all over, and the damage range of coal seam roof was analyzed by combining Mohr-Coulomb strength criterion. The results show that the main factors of coal seam roof damage are layer separation caused by horizontal joints and fractures caused by vertical joints; the separation failure zone has a “hyperbolic-like” distribution with steep top and flat bottom, and the fracture damage zone has an “arch-shaped” distribution; with the increase of inter-bed friction coefficient with the increase of the interlayer friction coefficient, the height and width of the layer separation damage zone of the top plate decrease significantly, while the increase of the elastic modulus has less effect on the damage range of the top plate; meanwhile, with t
The effects of pre-tension on the fatigue properties of a rolled Mg-3Al-1Zn (AZ31) alloy were investigated by imposing 2%, 5%, and 10% tensile strains along the rolling direction before low-cycle ...fatigue tests. The investigation showed that the applied pre-tension increased the dislocation density and introduced a small number of twins into the material. Although the as-rolled sample and all the pre-tensioned samples exhibited asymmetric hysteresis loops owing to the alternation of twinning and detwinning during each cycle, the tensile and compressive peak stresses increased with an increase in the amount of pre-tension during the first cycle. With an increase in the number of cycles, however, the flow stress, mean stress, plastic strain energy density, and hysteresis loop of the samples became similar irrespective of the amount of pre-tension, which is attributed to cyclic strain softening or hardening behavior depending on the initial dislocation density. Despite the relatively large pre-deformation, the pre-tensioned samples exhibited a fatigue life equivalent to that of the as-rolled sample because of an early extinction of the difference in the cyclic stress-strain response caused by pre-tension. This result demonstrates that the pre-tension process can improve the yield strength of rolled Mg alloys without a loss of their low-cycle fatigue resistance.
•We propose experiment and modeling of uniaxial fatigue for filled natural rubbers.•We study the relationship between tension fatigue and damage parameters.•All damage parameters discussed can ...correlate with tension fatigue life well.•The relation of tension fatigue and damage parameters is independent on specimens.
A tension fatigue model of filled natural rubbers is investigated to study the contributions of two key factors, namely, the damage parameter and the specimen geometry used in the fatigue experiment. The uniaxial tension fatigue experiments were carried out for three filled natural rubber specimens with different geometry: a dumbbell simple tension specimen (STS), a dumbbell cylindrical specimen (DCS), and a hollow cylindrical specimen (HCS). The commonly used damage parameters for fatigue life prediction are discussed. The fatigue life prediction models are formulated using the measured tension fatigue life of the STS together with different damage parameters. The effectiveness of the models is established in terms of a correlation coefficient characterizing the error between the measured and predicted fatigue lives. It is concluded that all the damage parameters considered in the study can effectively estimate the tension fatigue life with correlation coefficients exceeding 0.9. The fatigue life model formulated for the STS was also found to be appropriate for predicting the fatigue life of specimens with different geometry (DCS and HCS) suggesting that the relationship between the tension fatigue life and the damage parameters is independent of the specimen geometry. One may thus conduct tension fatigue tests with STS alone in order to model the tension fatigue life of rubbers with alternate geometry.
It is known that a local deformation mode affects the fracture behavior. First, a parameter that represents the deformation mode is defined for a fracture criterion that can consider the deformation ...mode in ordinary state-based peridynamics. This parameter is analogous to stress triaxiality in conventional continuum mechanics. The calculated values of the parameter agree well with the theoretical values under uniaxial compression, pure shear, uniaxial tension, and equi-biaxial tension. Then, modified fracture strain by a function using the parameter is proposed as a fracture criterion. The intended fracture strains of uniaxial tensioned cubes and those of equi-biaxial tensioned cubes were well reproduced by calculations with the criterion. Further, the intended ratio of fracture strain of a uniaxial tensioned round bar to that of an equi-biaxial tensioned thin plate was reproduced by calculations with the criterion. In a pipe bending simulation, the crack propagation behavior was reproduced by the proposed criterion.
This paper describes a study of recycled concrete under compressive loads. The study was conducted in two main parts. In the first part, experimental tests were carried out on concrete samples with ...varying levels of substitution (25%, 50%, and 75%) with recycled aggregate in order to measure the mechanical properties of the recycled concrete. In the second part of the study, a nonlinear homogenization model was developed on the basis of a classical secant approach to predict the behavior of recycled concrete. In this model, we assume that the behavior of the mortar phase, the concrete, and the recycled aggregates follow Mazars damage law. Comparison with the experimental data shows that the proposed homogenization model is accurate and efficient in predicting the correct nonlinear behavior of the recycled concrete. By better understanding the properties and behavior of recycled concrete, it will be possible to develop more effective methods for incorporating recycled materials into concrete structures.
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