scholarly journals Study on the Prediction Method of the Ultra-Low-Cycle Fatigue Damage of Steel

2020 ◽  
Vol 10 (2) ◽  
pp. 679
Author(s):  
Qin Tian ◽  
Yanhua Liao ◽  
Xu Xie ◽  
Hanqing Zhuge
Keyword(s):  
Weld Metal ◽  
Base Metal ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Large Strain ◽  
Prediction Method ◽  
Continuum Damage Mechanics ◽  
Uniaxial Tensile ◽  
Cycle Fatigue ◽  
Strain Threshold

Cyclic void growth model (CVGM) and continuum damage mechanics (CDM) model are suitable for predicting the damage of ultra-low-cycle fatigue (ULCF) theoretically. However, studies on the prediction of ultra-low-cycle fatigue (ULCF) damage is lacking. To determine which method is better, we used the two methods to predict the damage of ULCF. Firstly, uniaxial tensile and large strain cycle tests were performed on the base metal, weld metal and heat-affected zone and the material parameters were calibrated respectively. The uniaxial plastic strain threshold and toughness parameter of weld metal were minimum, and the dispersion was maximum. The finite element models of the base metal and weld specimens were established based on the calibrated parameters, and the ULCF damage was predicted. Compared with the CVGM model, the CDM model can predict the fatigue life and the relationships among the fatigue and fracture lives, the post-fracture path and the number of cycles to initial damage. The parameter calibration is simple. CDM is superior to CVGM in predicting the ULCF damage of steel and its weld joints.

scholarly journals Prediction of the Ultra-Low-Cycle Fatigue Damage of Q345qC Steel and its Weld Joint

Materials ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 4014 ◽  
Author(s):  
Qin Tian ◽  
Hanqing Zhuge ◽  
Xu Xie
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Plastic Strain ◽  
Weld Metal ◽  
Base Metal ◽  
Weld Joint ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Experimental Values ◽  
Strain Threshold

Based on the continuum damage mechanics model (CDM) for monotonic tension, a new CDM for ultra-low-cycle fatigue (ULCF) is put forward to predict ULCF damage of steel and its weld joint under strong earthquakes. The base metal, heat-affected zone and weld metal of Q345qC steel were considered as research objects, and the uniaxial plastic strain threshold of the CDM model was calibrated via tensile testing combined with finite element analysis of notched round bar specimens. ULCF tests of the base metal and weld specimens were carried out to analyse their fatigue life, fracture life and post-fracture path. Based on the calibrated uniaxial plastic strain threshold, the finite element models of base metal and weld specimens suitable for CDM model were established by ABAQUS. The calibration results of material parameters show that the weld metal has the lowest plastic strain threshold and the largest dispersion coefficient at the plastic strain threshold. Prediction results under cyclic loading with a large strain were compared with experimental values, and results showed that the predicted crack initiation and fracture lives of the base metal and weld specimens are lower than their corresponding experimental values. The predicted errors of crack initiation life and fracture life decrease with increasing strain level. The development law of the damage variable reveals exponential growth combined with a stepped pattern. The CDM model can also accurately predict the number of cycles to initial damage. Taking the results together, the CDM of the ULCF of the base metal and weld specimens could successfully predict post-fracture paths.

Fatigue Crack Modeling and Simulation Based on Continuum Damage Mechanics

2006 ◽  
Vol 129 (1) ◽  
pp. 96-102 ◽  
Author(s):  
Masakazu Takagaki ◽  
Toshiya Nakamura
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Continuum Damage Mechanics ◽  
Fatigue Loading ◽  
Present Theory ◽  
Continuum Damage ◽  
Cycle Fatigue

Numerical simulation of fatigue crack propagation based on fracture mechanics and the conventional finite element method requires a huge amount of computational resources when the cracked structure shows a complicated condition such as the multiple site damage or thermal fatigue. The objective of the present study is to develop a simulation technique for fatigue crack propagation that can be applied to complex situations by employing the continuum damage mechanics (CDM). An anisotropic damage tensor is defined to model a macroscopic fatigue crack. The validity of the present theory is examined by comparing the elastic stress distributions around the crack tip with those obtained by a conventional method. Combined with a nonlinear elasto-plastic constitutive equation, numerical simulations are conducted for low cycle fatigue crack propagation in a plate with one or two cracks. The results show good agreement with the experiments. Finally, propagations of multiply distributed cracks under low cycle fatigue loading are simulated to demonstrate the potential application of the present method.

CDM Approach Applied to Crack Initiation and Propagation under Variable Amplitude

2016 ◽  
Vol 829 ◽  
pp. 55-60
Author(s):  
Jin Yang Chu ◽  
Jian Xing Mao
Keyword(s):  
Crack Initiation ◽  
Damage Accumulation ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Fatigue Crack Initiation ◽  
Continuum Damage Mechanics ◽  
Cycle Fatigue ◽  
Variable Amplitude ◽  
Crack Initiation Life ◽  
Initiation Stage

In this paper, the low cycle fatigue crack initiation life was regarded as a process of damage accumulation and a damage accumulation model was established based on the Continuum Damage Mechanics. By the model, we analyzed how the variable amplitude applied at the crack initiation stage influenced the low cycle fatigue life of high temperature materials. With the parameters of GQGH4169 alloy at room temperature, we determined the specific values of damage parameters by finite element method and numerical analysis method. Then, the crack initiation life predictions were carried out. The results show that using this approach can not only predict the crack initiation life of CT specimen accurately, but also reflect a definite influence of variable amplitude on the crack propagation life combining with the Paris Law, and the test costs reduced consequently.

Identification and Validation of a Low Cycle Fatigue Damage Model for Al 7075-T6 Alloy

2015 ◽  
Vol 137 (1) ◽  
Author(s):  
Saeed Masih ◽  
Mohammad Mashayekhi ◽  
Noushin Torabian
Keyword(s):  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Damage Model ◽  
Fatigue Crack Initiation ◽  
Life Time ◽  
Continuum Damage Mechanics ◽  
Material Behavior ◽  
Cycle Fatigue ◽  
Explicit Finite Element ◽  
Al 7075

In this paper, the behavior of 7075-T6 aluminum alloy under low cycle fatigue (LCF) loading is experimentally and numerically investigated using continuum damage mechanics (CDM). An experimental procedure is established to identify the damage parameters for Al 7075-T6. A damage-coupled explicit finite element code is developed using the experimentally extracted damage parameters to study the material behavior under LCF loading. Moreover, fractographic examinations are conducted to identify the fatigue crack initiation locations and propagation mechanisms. The model is employed for life-time assessment of stringer-skin connection of a fuselage and the results are compared with the data available in the literature.

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