Microstructure-Aided Analysis of Fatigue Thresholds in Duplex Stainless Steel

2007 ◽  
Vol 567-568 ◽  
pp. 101-104 ◽  
Author(s):  
Jaroslav Pokluda ◽  
Tomáš Podrábský ◽  
Karel Slámečka ◽  
Simona Hutařová ◽  
Guo Cai Chai
Keyword(s):  
Fatigue Cracks ◽  
Fatigue Threshold ◽  
Threshold Region ◽  
Threshold Values ◽  
Duplex Microstructure ◽  
Martensitic Steels ◽  
High Fatigue ◽  
Crack Paths ◽  
Plasticity Induced Crack Closure ◽  
Good Agreement

High fatigue threshold values of duplex ferritic-martensitic steels are interpreted by using a unified model of roughness- and plasticity induced crack closure. Complex metallographical and fractographical analysis was performed in order to obtain characteristics of tortuous crack paths produced by crack deflection and branching mainly at austenite/ferrite interfaces. Calculated values of effective thresholds are in a good agreement with experimental data. The total level of extrinsic toughening (closure + shielding) induced by the duplex microstructure was determined to be as much as 70% of measured fatigue threshold values. This is the main reason for the high resistance to propagation of long fatigue cracks in the near-threshold region.

Computation of Effective Fatigue Thresholds Based on a New Concept of Crack Closure

2006 ◽  
Vol 324-325 ◽  
pp. 803-806 ◽  
Author(s):  
Jana Horníková ◽  
Pavel Šandera ◽  
Jaroslav Pokluda
Keyword(s):  
Crack Closure ◽  
Loading Condition ◽  
Stress Ratio ◽  
Fatigue Cracks ◽  
Theoretical Concept ◽  
Fatigue Threshold ◽  
Threshold Values ◽  
Range Effect ◽  
Plain Strain ◽  
Good Agreement

A new theoretical concept of crack closure under plain strain was applied to assess the effective fatigue threshold under various loading condition for selected aluminium and titanium alloys of different microstructures. The concept is based on the long-range effect of geometrically necessary dislocations remaining in the wake of propagating fatigue cracks. Calculated threshold values FKeff,th for 7475 aluminium alloy are about 1.9 MPa.m1/2 (in vacuum) and 1 MPa.m1/2 (in air), and about 2.5 MPa.m1/2 and 3.3 MPa.m1/2 for c-titanium and Ti-2.5%Cu, respectively. All calculated values are nearly independent on both the microstructure and the applied stress ratio and they are in a good agreement with experimental data.

scholarly journals Microstructure and properties degradation of P/T 91, 92 steels weldments in creep conditions

2012 ◽  
Vol 48 (3) ◽  
pp. 461-469 ◽  
Author(s):  
L. Falat ◽  
V. Homolová ◽  
J. Kepic ◽  
M. Svoboda ◽  
A. Výrostková
Keyword(s):  
Filler Metal ◽  
Light And Electron Microscopy ◽  
Microstructural Change ◽  
Fusion Welding ◽  
Inert Gas ◽  
Martensitic Steels ◽  
Equilibrium Thermodynamic ◽  
Type Iv ◽  
Creep Exposure ◽  
Good Agreement

The studies were performed on dissimilar ferritic/austenitic weldments between 9Cr tempered martensitic steels of the grades either P/T 91 or 92 and unstabilised AISI316H austenitic steel. The welded joints were fabricated using the fusion welding by tungsten inert gas (TIG) method with Ni-based filler metal. Microstructural analyses were performed using light and electron microscopy. Microstructural gradient in heat-affected zone (HAZ) of 9Cr steels remained preserved during creep exposure. All weldments fractured by the type IV failure within their intercritical HAZ (ICHAZ) regions. The most remarkable microstructural change during creep was the precipitation of intermetallic Laves phase. Experimentally determined phases of the samples after creep exposure are in good agreement with equilibrium thermodynamic calculations.

A Study on the Low Cycle Fatigue Behavior of the Steel for Shipbuilding Industry

2005 ◽  
Vol 297-300 ◽  
pp. 10-15 ◽  
Author(s):  
Kyung Su Kim ◽  
Byung Ok Kim ◽  
Young Kwan Kim ◽  
Chang Hwan Lee ◽  
Sung Won Lee
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Published Data ◽  
Cycle Fatigue ◽  
Maritime Industry ◽  
Shipbuilding Industry ◽  
Design Procedures ◽  
Calculation Results ◽  
Good Agreement

Recently, most of fatigue cracks in ship structures are reported within a few years after delivery. This type of fatigue characteristics cannot be explained adequately by the S-N curve based on high cycle fatigue. Calculation results under critical loading conditions reveal that stress magnitude higher than three times the yield stress occurs at some critical locations. It shows the fatigue cracks are related to low cycle fatigue. But the existing recommended design procedures in maritime industry do not properly cover low cycle fatigue problems. This work represents the first step in an effort to develop a design code that addresses low cycle fatigue problems. Low cycle fatigue test for uniform round specimen made of base/weld metal and for cruciform welded joint are carried out under constant amplitude alternating load, controlled by strain. Strain-cycle curves for the base metal and weld joints show good agreement with published data as well as some code recommended design curves.

Experimental Studies of Glass Reinforced Aluminum (GLARE) Bolted Joint

2012 ◽  
Vol 217-219 ◽  
pp. 124-129
Author(s):  
Ji Feng Zhang ◽  
Zi Zhen Cao ◽  
Yong Gang Xie
Keyword(s):  
Impact Resistance ◽  
Experimental Studies ◽  
High Strength ◽  
Geometric Parameters ◽  
Experimental Program ◽  
Bolted Joint ◽  
Threshold Values ◽  
Tightening Torque ◽  
High Fatigue ◽  
Ply Orientation

GLARE laminates with outstanding impact resistance, high fatigue resistance and a number of excellent performances are combined by ductile aluminum layers and high strength FRP layers. An experimental program was conducted to estimate the influence of geometric parameters, ply orientation and tightening torque on the performances of GLARE bolted joint. The study showed that the parameters of GLARE bolted joint have intrinsic properties of metal bolted joint and composite bolted joint. The design threshold values including of geometric parameters, ply orientation and tightening torque were given.

Critical Strain Energy Density along the Curved Front of the Growing Fatigue Crack

2005 ◽  
Vol 482 ◽  
pp. 307-310
Author(s):  
Tomáš Denk ◽  
Vladislav Oliva ◽  
Aleš Materna
Keyword(s):  
Fracture Mechanics ◽  
Fatigue Cracks ◽  
Anomalous Behavior ◽  
Fatigue Threshold ◽  
Stress Constraint ◽  
Short Cracks ◽  
T Stress ◽  
Residual Fatigue ◽  
Two Parameter ◽  
Different Levels

A two-parameter constraint-based fracture mechanics approach is used to explain the effect of the constraint on the apparently anomalous behavior of short fatigue cracks. The different levels of stress constraint are quantified by the T-stress, and microstructurally as well as mechanically short cracks are discussed. Short cracks generally behave more sensitively to the constraint than the long ones. It is shown that in most cases, the existence of short cracks goes hand in hand with an intrinsic loss of the constraint, which contributes to a decrease of their fatigue threshold values and accelerates their growth. In this paper, the above effect is quantified and conclusions concerning the applicability of the fracture mechanics parameters and approaches to the estimation of the residual fatigue life of structures are discussed.

Fatigue Crack Growth Thresholds of Deflected Mixed-Mode Cracks in PWA1484

2005 ◽  
Vol 127 (1) ◽  
pp. 2-7 ◽  
Author(s):  
K. S. Chan ◽  
J. Feiger ◽  
Y.-D. Lee ◽  
R. John ◽  
S. J. Hudak,
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Mixed Mode ◽  
Fatigue Cracks ◽  
Symmetry Plane ◽  
Crystallographic Analysis ◽  
Mode I ◽  
Test Technique ◽  
Crack Paths

The fatigue crack growth (FCG) behavior of PWA1484 single crystals was characterized in air under mixed-mode loading at 593°C as a function of crystallographic orientation using an asymmetric four-point bend test technique. Most mixed-mode fatigue cracks deflected from the symmetry plane and propagated as transprecipitate, noncrystallographic cracks, while self-similar fatigue crack growth occurred on the (111) planes in (111)/[011] and 111/[112]¯ oriented crystals. The local stress intensity factors and the crack paths of the deflected mixed-mode cracks were analyzed using the finite-element fracture mechanics code, FRANC2D/L. The results indicated that the deflected crack path was close to being normal to the maximum tensile stress direction where the Mode II component diminishes. Crystallographic analysis of the deflected crack paths revealed that the Mode I and the deflected mixed-mode cracks were usually of different crystallographic orientations and could exhibit different Mode I FCG thresholds when the crystallography of the crack paths differed substantially. These results were used to identify the driving force and conditions for cracking mode transition.

Evaluation of Fatigue Crack Growth Rates and Threshold Conditions in an Al 2124-T851 Alloy at Different Load Asymmetry Considering Microstructure Orientation

2013 ◽  
Vol 577-578 ◽  
pp. 321-324
Author(s):  
Ivo Černý
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stable Crack Growth ◽  
Repeated Measurements ◽  
Stress Intensity Factor Range ◽  
Threshold Region ◽  
Artificial Ageing ◽  
Threshold Values ◽  
Load Asymmetry

Results of a fairly comprehensive experimental programme aimed at evaluation of fatigue crack growth (FCG) rates in an aircraft Al 2124 alloy in T851 state, after hot rolling, solution annealing, small plastic strain and artificial ageing are presented and discussed. Measurement was performed not only in the region of stable crack growth, but also in the threshold region enabling to estimate threshold values of stress intensity factor range using method of regression analyses. FCG rates were evaluated in both L-T and T-S directions to evaluate sensitivity of FCG resistance on different microstructure orientation. Different load asymmetry conditions R = Fmin / Fmax were used, namely R = 0.1 and 0.6. Repeated measurements in more than one specimen at each condition enabled to evaluate reproducibility, scatter of measurement and to perform eventually probabilistic assessment. The reproducibility of measurement was particularly good for L-T orientation. In this case, threshold values were somewhat higher and FCG rates lower in comparison with the T-S orientation. In the contrary, cyclic fracture toughness in T-S orientation was slightly higher. The results are discussed form the viewpoint of residual fatigue life in aircraft components considering probabilistic aspects.

scholarly journals MASS SHELL SMEARING EFFECTS IN TOP PAIR PRODUCTION

2012 ◽  
Vol 27 (13) ◽  
pp. 1250072 ◽  
Author(s):  
V. I. KUKSA ◽  
R. S. PASECHNIK ◽  
D. E. VLASENKO
Keyword(s):  
Pair Production ◽  
Cross Sections ◽  
Top Quark ◽  
Preliminary Analysis ◽  
Mass Shell ◽  
Threshold Region ◽  
Suggested Approach ◽  
Unstable Particles ◽  
Higher Order Corrections ◽  
Good Agreement

The top quark pair production and decay are considered in the framework of the smeared-mass unstable particles model. The results for total and differential cross-sections in vicinity of [Formula: see text] threshold are in good agreement with the previous ones in the literature. The strategy of calculations of the higher order corrections in the framework of the model is discussed. Suggested approach significantly simplifies calculations compared to the standard perturbative one and can serve as a convenient tool for fast and precise preliminary analysis of processes involving intermediate timelike top quark exchanges in the near-threshold region.

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