Effect of Toe Grinding on Fatigue Strength of Ship Structure

2008 ◽  
Vol 24 (03) ◽  
pp. 152-160 ◽  
Author(s):  
Hong Ryeul Ryu ◽  
Wha Soo Kim ◽  
Woo Il Ha ◽  
Sung Won Kang ◽  
Myung Hyun Kim
Keyword(s):  
Fatigue Life ◽  
Crack Propagation ◽  
Enhancement Factor ◽  
Research Work ◽  
Fatigue Tests ◽  
Special Equipment ◽  
Structural Shape ◽  
Actual Structure ◽  
Weld Toe ◽  
Crack Initiation Life

It is well known that grinding the weld toe is not only effective in increasing the fatigue life at the weld joint by removing the initial defect and by reducing the stress concentration, but also rather convenient to apply and survey at the construction stage without special equipment or techniques. In this research work, comparative fatigue tests have been performed for a total of five types of weld specimens: three types of small welded specimens and two types of small-scaled structural models. According to the results of the fatigue tests, the enhancement factor of fatigue life by toe grinding for small welded specimens is determined to be about 6 to 10. However, the enhancement factor of fatigue life by toe grinding for small-scaled structure is 1.9 to 5.4. In the case of small welded specimens, once the crack is initiated to a certain level, then the crack propagation is accelerated rapidly due to simplicity of structural shape. In the case of actual ship structures, however, even after the crack is initiated to a certain level, the crack propagation is not accelerated as much due to structural redundancy. The toe grinding is only beneficial in extending the crack initiation life. Accordingly, the effect of toe grinding on the fatigue life at the actual structure is not as predominant as the one at the small welded specimen.

Fatigue Behavior of Circumferentially Notched Round Bars of Austenitic Stainless Steel Under Torsional and Axial Loads

2010 ◽  
Author(s):  
Masao Itatani ◽  
Keisuke Tanaka ◽  
Isao Ohkawa ◽  
Takehisa Yamada ◽  
Toshiyuki Saito
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Static Tension ◽  
Cyclic Torsion ◽  
Cyclic Tension ◽  
Crack Initiation Life

Fatigue tests of smooth and notched round bars of austenitic stainless steels SUS316NG and SUS316L were conducted under cyclic tension and cyclic torsion with and without static tension. Fatigue strength under fully reversed (R=−1) cyclic tension once increased with increasing stress concentration factor up to Kt=1.5, but it decreased from Kt=1.5 to 2.5. Fatigue life increased with increasing stress concentration under pure cyclic torsion, while it decreased with increasing stress concentration under cyclic torsion with static tension. From the measurement of fatigue crack initiation and propagation lives using electric potential drop method, it was found that the crack initiation life decreased with increasing stress concentration and the crack propagation life increased with increasing stress concentration under pure cyclic torsion. Under cyclic torsion with static tension, the crack initiation life also decreased with increasing stress concentration but the crack propagation life decreased or not changed with increasing stress concentration then the total fatigue life of sharper notched specimen decreased. It was also found that the fatigue life of smooth specimen under cyclic torsion with static tension was longer than that under pure cyclic torsion. This behavior could be explained based on the cyclic strain hardening under non-proportional loading and the difference in crack path with and without static tension.

RETROFITTING METHODS AGAINST FATIGUE CRACKING IN STEEL GIRDER WEB PENETRATION

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Chihiro Sakamoto ◽  
Masahiro Sakano ◽  
Hideyuki Konishi ◽  
Takashi Fujii
Keyword(s):  
Fatigue Life ◽  
Fatigue Cracking ◽  
Highway Bridges ◽  
Lower Surface ◽  
Strength Properties ◽  
Fatigue Tests ◽  
Stress Distributions ◽  
Steel Girder ◽  
Cracking Behavior ◽  
Weld Toe

Fatigue cracking in steel girder web penetration details is so dangerous that it can break steel girders. Since a number of highway bridges have such web penetration details in Japan, it is of urgent importance to grasp these fatigue strength properties and develop effective retrofitting methods. In a previous report, we investigated the stress distributions around web penetration details, and fatigue cracking behavior, using steel girder specimens with web penetration details. In this study, we investigate effects of retrofitting methods against fatigue cracking in web penetration details through fatigue tests using large girder specimens with web penetration details in which cross beam lower flanges are connected to lower surface of a slot by welding. Principal results obtained through this study are as follows: (1) Weld toe grinding can extend fatigue life more than 5 times, (2) Two-face attachment can extend fatigue life more than 10 times, and (3) Two-face attachment with weld toe grinding can extend fatigue life more than 25 times.

Study on the Fatigue Properties of the TIG Weld Joint with the Stainless Steel Conduit in Aircraft

2015 ◽  
Vol 664 ◽  
pp. 104-110
Author(s):  
Ying Liu ◽  
Dong Jie Li ◽  
Xiao Hong Li
Keyword(s):  
Stainless Steel ◽  
Stress Concentration ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Weld Joint ◽  
Fatigue Cracks ◽  
Fatigue Properties ◽  
Research Focus ◽  
Weld Toe ◽  
Crack Initiation Life

The research focus on the material of the stainless steel thin conduit in aircraft, named 1Cr18Ni9Ti , and the TIG weld joint of which was investigated to analysis the fatigue properties. The fracture mechanics was used to analysis the crack initiation life and crack propagation life, and the fatigue surface was characterized with scanning electron microscope (SEM). The experimental and analytical results show that, the origin position of fatigue crack is the surface of the conduit. The stress concentration at the weld toe, the crystal structure is not uniform and Stress concentration in the heat affected zone (HAZ) and fusion line, so the fatigue cracks are easily generated in these locations. Delta K increases to a certain value, the HAZ has become one of the most dangerous position. The crack initiation life of HAZ in the total fatigue life is far higher than the proportion of crack propagation life.

Experimental Study on Fatigue Life of Steel Beams Strengthened with a CFRP Plate

2008 ◽  
Vol 33-37 ◽  
pp. 163-168 ◽  
Author(s):  
Jun Deng ◽  
Marcus M.K. Lee ◽  
Pei Yan Huang
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Test ◽  
Interfacial Stress ◽  
Steel Beams ◽  
Test Results ◽  
Load Range ◽  
Cfrp Plate ◽  
Crack Initiation Life

The adhesive bonding between the steel beam and carbon fibre reinforced polymer (CFRP) plate is the weakest link and fatigue performance is a major consideration. This paper gives details of a fatigue test programme of a series of small-scale steel beams bonded with a CFRP plate. Two phases of the fatigue life, including crack initiation life and crack propagation life, are considered. Backface-strain technique was applied to monitor crack initiation. An S-N curve was developed from the test results. The curve correlates the maximum principal interfacial stress at the plate end to the crack initiation life. The fatigue limit of the S-N curve was found to be about 30% of the ultimate static failure stress. In accordance with Paris Law, moreover, an equation was developed to predict the number of cycles during the crack propagation. The empirical coefficients of the equation were obtained from the fatigue test results. This equation can correctly predict the crack propagation life. The fatigue load range affects the fatigue life, but its significance is much less than the magnitude of the maximum load in the load range.

Research on Contact Fatigue Properties of Some Materials Used for Heavy Load Gear

2010 ◽  
Vol 139-141 ◽  
pp. 360-363
Author(s):  
Ying Xia Yu ◽  
Bo Lin He ◽  
Er Yu Shao
Keyword(s):  
Fatigue Life ◽  
Crack Propagation ◽  
Maximum Shear Stress ◽  
Contact Fatigue ◽  
Fatigue Tests ◽  
Experimental Results ◽  
Fatigue Properties ◽  
Heavy Load ◽  
Contact Fatigue Life ◽  
Materials Used

The contact fatigue tests were carried out using three kind of steel(45, 42CrMo, 40CrNi2Mo) which were quenched and tempered to the same medium hardness(HRC37±1). The experimental equipment is JPM-1 type contact fatigue tester. During the experiment process, the contact stress is 1600MPa and the surface roughness is 0.4 um. The crack initiation and the crack propagation direction were observed by using SEM. The contact fatigue failure mechanism was also analyzed. The experimental results were analyzed by using Weibull distribution. The experimental results show that the contact fatigue crack was initiated in the roller surface. With increasing of the cycle, the initiated crack propagates into subsurface and becomes to pitting. The pitting becomes bigger and bigger and leads to failure finally. The maximum shear stress is the main driving force for the crack propagation. The contact fatigue life increases in sequence of 45, 42CrMo, 40CrNi2Mo. The contact fatigue life has the relationship with the shearing resistant stress Тk. About the same carbon content, the value of the shearing resistant stress Тk becomes greater with increasing the alloying elements. The best material used for making heavy duty gear is 40CrNi2Mo steel.

The Effect of Residual Stress on Fatigue Life of Welded Cruciform Joints of 16MnR for Train Bogie

2013 ◽  
Vol 815 ◽  
pp. 695-699 ◽  
Author(s):  
Ying Xia Yu ◽  
Bo Lin He ◽  
Jian Ping Shi ◽  
Jing Liu
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Fatigue Life ◽  
Load Ratio ◽  
Fatigue Tests ◽  
Residual Tensile Stress ◽  
Cruciform Joints ◽  
Weld Toe ◽  
Deformation Layer ◽  
Cruciform Joint

The weld toe surface and its nearby area of welded cruciform joints were treated by ultrasonic impact. Under the same stress concentration and after heat treatment to eliminate residual stress, the effect of residual stress on the fatigue life of joint was researched. The fatigue tests are performed on the joints of 16MnR both for the un-treated and treated joints by using EHF-EM200K2-070-1A type fatigue tester when the load ratio is 0.1, frequency is 10Hz. The experimental results indicate that the severe plastic deformation in the vicinity of weld toe surface was formed by impact treating for 2 minutes, the thickness of the plastic deformation layer is about 60μm. Residual tensile stress in the weld toe surface can be changed to residual compressive stress by impact treatment. The fatigue life of welded joint is 0.260×106cycle, and the fatigue life of treated joint is 0.499×106cycle. Compared to the un-treated joint, the fatigue life of treated joint has been increased by 91.92%. The residual stress contributed to fatigue life is about 16%. Residual stress has great effect on the fatigue life of welded cruciform joint.

A Calculation Method of Vibration Fatigue Life with Coupling Effect

2011 ◽  
Vol 338 ◽  
pp. 411-414
Author(s):  
Wen Guang Liu ◽  
Hong Lin He
Keyword(s):  
Fatigue Life ◽  
Crack Propagation ◽  
Calculation Method ◽  
Coupling Effect ◽  
Element Model ◽  
Test Results ◽  
Engineering Structures ◽  
Vibration Fatigue ◽  
Crack Initiation Life ◽  
Total Life

There are different modes of damage in any engineering structures, and most of them are cracks. In order to study the influence of coupling effect on the fatigue life, a calculation method of structure vibration fatigue life with crack propagation is proposed. In analysis, a series of finite element model with crack of different length is built to simulate the crack propagation, and Paris equation is employed to calculate the vibration fatigue life by stepwise method. The crack initiation life is got based on the change law of natural frequency from test results, and the total life is calculated in the end. Results indicate that the simulation results identical with the experimental results well.

Fatigue Life Prediction for Short Dents in Petroleum Pipelines

2002 ◽  
Author(s):  
Adam J. Rinehart ◽  
Peter B. Keating
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Propagation ◽  
External Force ◽  
Life Prediction ◽  
Fatigue Behavior ◽  
Contact Region ◽  
Fatigue Cracking ◽  
Fatigue Life Prediction ◽  
Crack Initiation Life

Pipeline dent fatigue behavior has been shown to be strongly dependent upon dent length and external force dent restraint characteristics. Full-scale laboratory tests have shown that short dents that are unrestrained by an external force typically experience fatigue cracking in the dent periphery outside of the dent contact region. A fatigue life prediction method for short dents is presented here. In order to assess method accuracy, predictions are made for cases in which fatigue life has been measured experimentally. The predictions account for both crack initiation life and crack propagation life. Stress concentration values used in the predictions are determined using finite element modelling on a case-by-case basis for comparison purposes. Appropriate crack initiation life estimates, stress intensity factor predictions, and crack propagation models are taken from existing literature. Predicted and measured fatigue lives are compared for the cases studied.

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