Fatigue Life Estimation Method Considering Inelastic Behavior of Ni-Based Directionally Solidified Superalloy With Multiple Holes

2012 ◽  
Author(s):  
Takashi Yokoyama ◽  
Masaru Sekihara
Keyword(s):  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Estimation Method ◽  
Inelastic Strain ◽  
Maximum Tensile Stress ◽  
Fatigue Tests ◽  
Inelastic Behavior ◽  
Cycle Fatigue ◽  
Directionally Solidified ◽  
Element Analysis

Low cycle fatigue tests at high temperature were conducted on test specimens with small holes made of a Ni-based directionally solidified superalloy, which are intended as the cooling structures formed in the components in the fossil fuel power plant. The tests included those cases with and without a strain holding process, i.e., fatigue creep interaction (FCI) tests and low cycle fatigue (LCF) tests, respectively. The number of LCF crack initiation cycles of the one- and seven-hole specimens decreased compared to that of the smooth one. The number of FCI crack initiation cycles of a compressive hold case for the seven-hole specimen decreased compared to that of the LCF test, while that of a tensile hold case decreased further. The test results were evaluated based on the inelastic behavior around the center hole of the specimens, where the most serious inelastic strain occurred, using finite element analysis that takes into account the inelastic anisotropy of material properties. The number of crack initiation cycles of the LCF and the compressive FCI tests correlated with the maximum tensile stress around the hole, while that of all the tests correlated with the frequency-modified strain energy. We propose a method for evaluating cyclic inelastic behavior around a hole using cyclic Neuber’s rule for anisotropic materials to simply evaluate the failure life of actual components.

Low Cycle Fatigue Tests and Simulations on Steel Elbows

2013 ◽  
Author(s):  
Patricia Pappa ◽  
George E. Varelis ◽  
Spyros A. Karamanos ◽  
Arnold M. Gresnigt
Keyword(s):  
Finite Element ◽  
Low Cycle Fatigue ◽  
Local Strain ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Out Of Plane ◽  
Strain Gauge Measurements ◽  
Number Of Cycles

In this paper the low cycle fatigue behaviour of steel elbows under strong cyclic loading conditions (in-plane and out-of-plane) is examined. The investigation is conducted through advanced finite element analysis tools, supported by real-scale test data for in-plane bending. The numerical results are successfully compared with the experimental measurements. In addition, a parametric study is conducted, which is aimed at investigating the effects of the diameter-to-thickness ratio on the low-cycle fatigue of elbows, focusing on the stress and strain variations. Strain gauge measurements are compared with finite element models. Upon calculation of local strain variation at the critical location, the number of cycles to fracture can be estimated.

Detection of the Crack Initiation by Means of AE Method Under Low Cycle Fatigue of Elbow Pipe Having Local Wall Thinning

2010 ◽  
Author(s):  
Naoya Kasai ◽  
Kotoji Ando ◽  
Maki Nishio ◽  
Yoshio Urabe ◽  
Koji Takahashi
Keyword(s):  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Axial Strain ◽  
Wide Band ◽  
Fatigue Tests ◽  
Crack Growth Behavior ◽  
Cycle Fatigue ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Local Wall Thinning

This paper describes the detectability of the crack initiation by means of the AE method under low cycle fatigue of the elbow pipe having local wall thinning to clarify the crack growth behavior for the pipes. Elbow specimens having local wall thinning were prepared, and local wall thinning due to flow accelerated corrosion was simulated by machined pipe wall thinning. Low cycle fatigue tests for the specimens were then carried out. AE method during low cycle fatigue tests was conducted to evaluate the crack initiation and location. In AE measurement, wide band AE sensors of 5mm in diameter were used to attach to the convex surfaces of the specimens. The circumference and axial strain of the specimens and the cross head displacement were also stored to the digital AE system signal. As a result, it is clear that the AE signals indicated the crack initiation in small circumference strain.

INELASTIC STRAIN CONCENTRATION IN DIRECTIONALLY SOLIDIFIED MATERIALS

1995 ◽  
Vol 19 (3) ◽  
pp. 331-346 ◽  
Author(s):  
R.S. Alwar ◽  
Suresh Babu
Keyword(s):  
Strain Energy Density ◽  
Strain Energy ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Engine Performance ◽  
Inelastic Strain ◽  
Equivalent Strain ◽  
Cycle Fatigue ◽  
Directionally Solidified ◽  
Neuber's Rule

The application of Directionally Solidified (DS) materials in the construction of hot section parts (blades, vanes) of a gas turbine results in improvement in the engine performance and durability. Inelastic strain, an important parameter in low cycle fatigue (LCF) life prediction methodology, may be evaluated using simplified methods like Neuber’s rule and Equivalent Strain Energy Density Hypothesis. The objectives of the present investigation are to examine the validity of these methods in case of DS materials and to demonstrate using numerical methods that the low cycle fatigue life of DS materials is superior to isotropic materials.

Internal Crack Initiation in Low-Cycle Fatigue of Stainless Steel

2010 ◽  
Author(s):  
Masayuki Kamaya ◽  
Masahiro Kawakubo
Keyword(s):  
Stainless Steel ◽  
Crack Initiation ◽  
Strain Amplitude ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Internal Crack ◽  
Surface Cracks ◽  
Cycle Fatigue ◽  
Type Specimens ◽  
316 Stainless Steel

Internal cracks were observed on the fracture surface of Type 316 stainless steel specimens subjected to a low-cycle fatigue test, in which the strain amplitude was more than 1%. In some cases the specimens fractured due to these internal cracks. In this study, the reason and conditions for the internal crack initiation were examined. Fatigue experiments were conducted using Type 316 stainless steel. In order to enhance the internal crack initiation, the specimens were subjected to pre-damaging and surface cracks were removed before the start of the fatigue tests. It was shown that specimens fractured due to internal cracks when the strain amplitude of pre-damaging was more than 1% and hourglass-type specimens were used. The fatigue life was reduced largely due to the internal cracks and the magnitude of reduction was more significant for the smaller strain amplitude of the fatigue tests. Inclusions were observed at the origin of some internal cracks. It was deduced that the hourglass geometry of the specimen enhanced the internal crack initiation. Namely, the multi-axial field was one of the factors promoting the internal crack initiation.

Microstructural Effects in the Low-Cycle Fatigue of Fe-Ni-Cr Austenite

1977 ◽  
Vol 99 (1) ◽  
pp. 29-35 ◽  
Author(s):  
N. F. Fiore ◽  
D. R. Diercks
Keyword(s):  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Hold Time ◽  
Weight Percent ◽  
Fatigue Tests ◽  
304 Stainless Steel ◽  
Cycle Fatigue ◽  
Cyclic Life ◽  
Localized Deformation ◽  
Cast Alloys

A series of low-cycle fatigue tests was performed at 593 deg C on Fe-20 Cr-10 Ni and Fe-20 Cr-20 Ni (in weight percent) austenitic alloys in both the cast and wrought conditions. The as-cast alloys exhibited substantially longer cyclic lives than the wrought alloys or wrought Type 304 stainless steel. An effect of Ni content on fatigue life was noted for the cast alloys, but not for the wrought. Striation, measurements indicated that the majority of the cyclic life was spent in crack initiation and early growth in all cases, and the superiority of the cast alloys was almost entirely due to a greater resistance to crack initiation. Macroscopic crack-growth rates were found to be essentially independent of composition and microstructure. A 1-min tension hold time per cycle produced a significant reduction in cyclic life in all cases except for the as-cast high Ni alloy. The decrease in life appeared to be associated with the initiation of cracks from localized deformation at grain boundaries.

Low Cycle Fatigue Analysis of after Treatment Device Induced due to Thermal Load by Using Finite Element Analysis

2014 ◽  
Vol 592-594 ◽  
pp. 1104-1108 ◽  
Author(s):  
Swapnil Vitthal Kumbhar ◽  
Vilas Kulkarni ◽  
R.M. Tayade
Keyword(s):  
Crack Initiation ◽  
Thermal Fatigue ◽  
Thermal Loading ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Analysis ◽  
Von Mises Stress ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Von Mises

Cyclic thermal loading causes cyclic thermal stress and thermal fatigue in the component. The goal of this paper is to characterize the thermal fatigue behavior of after-treatment (AT) device, i.e. Exhaust Gas Processor (EGP) and prediction of crack initiation cycles. The paper contains transient thermal analysis to map temperature on EGP model. By taking temperature distribution as input, Elasto-plastic structural analysis is done. Based on stress-strain data and fatigue material property, crack initiation cycles are estimated. For low cycle fatigue analysis, strain based approach, i.e. Brown-Miller Criteria with Morrow mean stress correction factor [1] is used. The von-Mises stress and crack initiation cycles are investigated and S-N curve and Ɛ-N curve are compared with standard graphs.

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