Papers by Keyword: Constant Amplitude Loading

Abstract: Loading history makes fatigue crack propagation modelling complex. This article focus on life prediction models which take into consideration the variability of fluctuating loads. In particular it emphases on the comparative studies of prediction models involving the significance of one model’s over another. The paper studies models based on multifarious loadings (constant amplitude load, variable amplitude load, overload/underload etc.). The major parameters of load interaction modelling are plasticity, crack closure, effective stress intensity, effective stress ratio and damage accumulation. For large deformation, elasto-plastic fracture mechanics based models are also included. The complexity of models, their features and focusing on their limitation and strengths are stated with various conditions and also validation of models with experimental data are reported. The paper speculates on the directions the study of crack propagation will take in future.

Abstract: Through series of dynamic triaxial tests, the relationships of soil deformations under irregular seismic loading and fixed-number constant amplitude loading are analyzed. The effect of loading amplitudes on the relationships is presented. The results shows: (1) soil deformation under irregular seismic loading obviously differs from that under constant amplitude sinusoidal loading, and the strain history is mainly controlled by the performance of ground motion; (2) if 20 cycles of constant amplitude loading is employed instead of irregular seismic loading to correct residual deformation under real seismic loading, loading amplitudes have no effect on soil deformation under irregular waves and fix-number waves.

Abstract: In this paper, the fracture toughness of materials, , effects on fatigue crack propagation that can be quantified using the dynamical coefficient mechanics (DCM) model. And we can not only change the material with high value, but also should take other methods into consideration to decrease the fatigue crack growth (FCG) rate when replacing material can’t obviously decrease the FCG rate, which were examined objectively by the test results from literature.

Abstract: Durability assessment of automotive lower suspension arm has been studied under service loadings. The fatigue tests were conducting for the SAE 1045 steel based strain-controlled. To specify the material mechanical properties of the used material, a fatigue test under constant amplitude loading has been carried out then the results were provided for the finite element code. The finite element fatigue life were evaluated and compared with the experimental results. The accuracy and efficiency of the numerical models are demonstrated. This tool cannot be considered as a powerful alternative prior to the further experimental process. Instead, suitable fatigue prediction models under service loadings need to be developed.

Abstract: This paper applies the fracture-mechanics-based analysis and the crack-closure concept to naturally occurring small cracks and large crack growth, and to make total fatigue life predictions solely based on crack growth from the assumed initial materials defect. The equation of total fatigue crack propagation life under constant amplitude loading is presented. And the total fatigue propagation lives of LY12-BCZYU aluminium alloy SENT specimens by this equation and validated by experimental results. Validation against calculations by the model and experimental data shows a good agreement.

Abstract: The effect of the load ratio, R, or the mean-stress on fatigue life has been recognized for more than a hundred years. In this paper we first describe a novel mechanics model for fatigue crak growth (FCG) under constant amplitude (CA) loading based on static fracture mechanics with thinking about the inertial effect coefficient and its impact to crack tip, and then discuss the relation between R-ratio and fatigue crak growth rate. Comparison of the present analysis with experimental data taken from the literature demonstrates that R-ratio has a greater impact to the fatigue crack propagation.

Abstract: This paper presents methodologies for damage tolerance evaluation of tubular T- and Y-joints by using linear elastic fracture mechanics (LEFM) principles. The damage tolerance evaluation is in terms of crack growth analysis and remaining life prediction of tubular joints. Stress intensity factor (SIF) for T-butt plates which can be used for computation of SIF for tubular joints has been evaluated as per BS: 7910. It is observed from the literature that the expressions given in BS: 7910 for computation of SIF have not been used for remaining life prediction of tubular joints. In this paper, these expressions have been used for analytical prediction of remaining life of tubular T- and Y- joints subjected to constant amplitude loading (CAL) and variable amplitude loading (VAL). Wheeler residual stress model has been employed to represent the retardation effects due to tensile overloads. It is observed that remaining life predicted for T- and Y-joints under CAL are found to be in good agreement with those of experimental values reported in the literature. In the case of VAL, it is observed that crack growth retardation increases with increase of OLR resulting in higher predicted remaining life. It has also been observed that the predicted remaining life is influenced by the number of OLs and occurrence of OL. Early occurrence of OL causes the higher remaining life compared to later OLs.

Abstract: The equation of fatigue crack propagation rate is indispensable to precisely predict the fatigue life of structure containing three-dimensional crack under constant amplitude loading. Considering the crack closure effects and thickness effects in real structures, the equation of fatigue crack propagation rate under tri-axial stress state is presented. And the fatigue propagation lives of LY12-BCZYU aluminium alloy plate specimens with central through crack are predicted by this equation and validated by experimental results. Validation against calculations by the model and experimental data shows a good agreement.

Abstract: The crack closure phenomenon has attracted great attention in the prediction of fatigue crack growth. The finite element analysis of fatigue crack growth has been conducted by many researchers mainly emphasized on the technique implementation of the simulation. In this paper the behavior of plasticity induced fatigue crack closure was analyzed by the elastic-plastic finite element method for middle crack tension (MT) specimen. The material was assumed as linear-kinematic hardening. The crack growth was simulated by releasing the “bonded” node pairs ahead of crack tip in stepwise. The calculations focused on the effects of load cases and crack length on crack opening/closure levels. For constant amplitude cyclic loadings with different load ratios, the crack opening/closure levels increases for a while and then decreases continuously, with the increase of crack length. For the loadings with invariable maximum stress intensity factors (briefly the constant-K loading), however, the crack tip plastic zone sizes at different crack lengths remain unchanged and the crack opening and closing load levels normalized by the maximum load levels keep constants as well. The results indicate that the crack length does not affect the relative opening and closure levels and numerical analysis for the constant-K loading case should play a key role in characterizing the fatigue crack growth behavior.

Abstract: Externally bonded carbon fiber reinforced polymer (CFRP) materials are well suited to the rehabilitation and reinforcement of civil engineering structures due to their high specific strength, specific stiffness and corrosion resistance. To probe the fatigue behavior of CFRP strengthened concrete structures, three point bending experiments of reinforced concrete (RC) beams strengthened with carbon fibre laminate (CFL) under constant amplitude loading were performed. The histories of midspan flexibility and bending stiffness of strengthened beams were recorded automatically. And the linear curve between fatigue strength and the logarithm of fatigue life was obtained. The failure modes go through concrete cracking, CFL debonding from concrete and steel bars yielding and fracture with increasing cycles of fatigue loading. Bonded CFL increases the ductility of strengthened RC beam and results in dense distribution of cracks compared with normal RC beam, and it’s bending stiffness at damage state as well. The fatigue damage evolvement shows three stages of nucleation, steady expansion and failure. Then the failure mechanism was studied and a cumulative damage model was proposed to describe the fatigue damage and fracture process of CFL strengthened RC beams under constant amplitude loading.