Crack Propagation and Simulation of Thermal Fatigue

2012 ◽  
Vol 217-219 ◽  
pp. 2287-2292
Author(s):  
Hui Yu ◽  
Xin Liang Zang ◽  
Li Gang Liu
Keyword(s):  
Fatigue Crack ◽  
Thermal Stress ◽  
Crack Propagation ◽  
Fatigue Damage ◽  
Thermal Fatigue ◽  
Damage Mechanics ◽  
Fatigue Crack Initiation ◽  
Temperature Fields ◽  
Thermal Fatigue Crack ◽  
Initiation And Propagation

In this paper, the thermal fatigue damage phenomenon in the comprehensive temperature environment is studied by means of thermal fatigue damage mechanics and FEM technology, the thermal-stress analysis modal under the comprehensive thermodynamic boundary conditions is established, the regularities of distribution of temperature fields, thermal stress fields effected by the comprehensive coupled variables are investigated. According to the modify of material characteristics under the high-temperature alternating thermal impact conditions and the integrated influences of environment, mechanical parameter and material microstructure to the fatigue fracture, numerical modal of thermal fatigue crack initiation and propagation are developed, so the characteristics of thermal fatigue crack propagation are studied, which are verified by the experiments, it is very significant to study thermal damage question of working equipments in the similar conditions.

High-Cycle Thermal Fatigue Crack Initiation and Growth Behavior in a Semi-Infinite Plate Model

2001 ◽  
Vol 123 (3) ◽  
pp. 305-309 ◽  
Author(s):  
Makoto Hayashi
Keyword(s):  
Fatigue Crack ◽  
Thermal Stress ◽  
Crack Initiation ◽  
Thermal Fatigue ◽  
Temperature Fluctuation ◽  
Cold Water ◽  
Fatigue Crack Initiation ◽  
Infinite Plate ◽  
Plate Model ◽  
Thermal Fatigue Crack

At a T-junction in piping system, hot and cold water mixes in a whirl. The vibrating mixing boundary between the hot and cold water causes a temperature fluctuation on the inner surface of the pipe just after the connection point at the T-junction, and this temperature fluctuation yields a cyclic thermal stress near the pipe surface, resulting in crack initiation. In this study, the thermal stress distribution was analyzed for a semi-infinite plate model. The allowable water temperature range for the fatigue crack initiation was determined based on the mechanical fatigue test results. The thermal fatigue crack arrest behavior was analyzed based on the distributions of the stress intensity factor. The arrested crack depth is found to be in proportion to the reciprocal root of the frequency of the temperature fluctuation and is 3.8 mm for the frequency of 1 Hz.

Modeling of Fatigue Crack Propagation

2004 ◽  
Vol 126 (1) ◽  
pp. 77-86 ◽  
Author(s):  
Yanyao Jiang ◽  
Miaolin Feng
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Fatigue Crack Propagation ◽  
Fatigue Crack Initiation ◽  
Cyclic Plasticity ◽  
R Ratio

Fatigue crack propagation was modeled by using the cyclic plasticity material properties and fatigue constants for crack initiation. The cyclic elastic-plastic stress-strain field near the crack tip was analyzed using the finite element method with the implementation of a robust cyclic plasticity theory. An incremental multiaxial fatigue criterion was employed to determine the fatigue damage. A straightforward method was developed to determine the fatigue crack growth rate. Crack propagation behavior of a material was obtained without any additional assumptions or fitting. Benchmark Mode I fatigue crack growth experiments were conducted using 1070 steel at room temperature. The approach developed was able to quantitatively capture all the important fatigue crack propagation behaviors including the overload and the R-ratio effects on crack propagation and threshold. The models provide a new perspective for the R-ratio effects. The results support the notion that the fatigue crack initiation and propagation behaviors are governed by the same fatigue damage mechanisms. Crack growth can be treated as a process of continuous crack nucleation.

Effect of Heat Treatment on Microstructure and Thermal Fatigue Properties of Al-Si-Cu-Mg Alloys

2018 ◽  
Vol 37 (4) ◽  
pp. 289-298
Author(s):  
Wei Chao ◽  
Liu Guang-lei ◽  
Wan Hao ◽  
Li Yu-shan ◽  
Si Nai-chao
Keyword(s):  
Heat Treatment ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
Grain Boundary ◽  
Crack Propagation ◽  
Thermal Fatigue ◽  
Fatigue Crack Initiation ◽  
Fatigue Properties ◽  
Eutectic Si ◽  
Al Matrix

AbstractThe effect of heat treatment on the microstructure and thermal fatigue properties were studied by means of optical microscope (OM) and scanning electron microscope (SEM). Energy dispersive X-ray detector (EDX) was used to analyze the role of phase composition in fatigue crack propagation. The results show that after heat treatment, the ultimate tensile strength increased from 285 MPa to 368 MPa and the elongation increased from 5.8 % to 6.5 %. During the initiation of fatigue crack, the crack was mainly propagated through eutectic Si area. With the long needles of eutectic Si particles spherodized after heat treatment, the split action from brittle Si particles to α-Al matrix was reduced and prolonged the fatigue crack initiation period. After aging for 6 h, the dispersed precipitation of secondary phases (Al2Cu, Mg2Si) elevated the driving force of crack propagation, blocked the spread of crack in the grain boundary, decreased the rate of fatigue crack growth and improved the fatigue resistance of alloy at the same time. In the process of crack initiation, the surplus-phase around the grain boundary fell off from α-Al matrix under thermal cycling stresses. The combination of interfaces was weaken by cycling stress and the fatigue crack was finally grown up in the weakness area between matrix and secondary phase.

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