Evaluation of Fatigue Strength Based on Dissipated Energy for Laser Welds

To optimize welding conditions that ensure the safety and reliability of laser welds, this study established an evaluation method of the fatigue strength for the laser welds of steel sheets over a short period of time. This study focuses on a fatigue limit estimation based on dissipated energy which is caused by micro plastic deformation. As a result, the area at which the temperature changes, due to dissipated energy, is locally high is the fracture origin of the laser welds. The fatigue limit of the laser welds is almost the same as the stress amplitude at which a temperature change occurs due to dissipated energy.

Download Full-text

Bending Fatigue Strength Evaluation of Notched Structural Steel Sheet Repaired by Bolt

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.452-453.25 ◽

2010 ◽

Vol 452-453 ◽

pp. 25-28

Author(s):

Li Sha He ◽

Nobusuke Hattori

Keyword(s):

Plastic Deformation ◽

Fatigue Strength ◽

Stress Concentration ◽

Structural Steel ◽

Fatigue Limit ◽

Steel Sheet ◽

Bending Fatigue ◽

Steel Sheets ◽

Bending Fatigue Strength ◽

Working Method

The present investigation attempts to evaluate the improvement of working by bolt on the fatigue limit of structural steel sheets with drilling a circular hole. The material used in this study is structural steel (JIS SM400A). And the specimens are identified to two types of the non-worked specimen and the worked specimen. The results obtained in this study can be summarized as follows: (1) The fatigue limit of worked specimens increases than that of non-worked specimen. Futhermore, there has a suitable value of the torque for improving the fatigue limits. (2) The reasons of enhancing the fatigue strength of the worked specimens are due to the elastic deformation, the plastic deformation and the changing of stress concentration part. Our investigations confirm the advantages of this working method which repaired the structural steel sheets by bolt.

Download Full-text

Effect of micro-notches on fatigue strength of electrodeposited nanocrystalline nickel thin films

MATEC Web of Conferences ◽

10.1051/matecconf/201816504011 ◽

2018 ◽

Vol 165 ◽

pp. 04011

Author(s):

Keisuke Tanaka ◽

Yuta Murase ◽

Hirohisa Kimachi

Keyword(s):

Thin Films ◽

Fatigue Strength ◽

Fatigue Limit ◽

Stress Ratio ◽

Fatigue Crack Initiation ◽

Fatigue Tests ◽

Fine Grained ◽

Nickel Thin Films ◽

Nano Crystalline ◽

Fictitious Crack

The effect of micro-notches on the fatigue strength of nickel thin films was studied. Two types of thin films with 10 μm thickness were produced by electrodeposition using sulfamate solution without and with brightener: ultra-fine grained film (UFG) with the grain size of 384 nm and nano-crystalline grained film (NCG) with that of 17 nm. Micro-sized notches introduced by FIB had the width of 2 μm and various depths from 8 to 150μm. Fatigue tests were conducted under the stress ratio of 0.1. The fatigue strength decreased with increasing depth of notches. NCG had much higher strength than UFG compared at the same notch depth. Notches as small as 8μm did reduce the fatigue strength of both UFG and NCG. The fatigue limit was controlled by the initiation of cracks and no non-propagating crack was observed in specimens fatigued below the fatigue limit. A model of fictitious crack successfully predicted the reduction of the fatigue limit due to micro-notches. The characteristic crack length of NCG was much smaller than the UFG, while the fatigue strength of defect-free NCG was larger than that of UFG. SEM observation of fracture surfaces was conducted to reveal micromechanisms of fatigue crack initiation.

Download Full-text

Spot Weldability Assessment of Similar and Dissimilar Steel Sheets for Light Weight Automobile Body

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.306-308.899 ◽

2006 ◽

Vol 306-308 ◽

pp. 899-904

Author(s):

Dong Ho Bae ◽

Won Seok Jung ◽

J.B. Heo

Keyword(s):

Stainless Steel ◽

Fatigue Strength ◽

Lap Joints ◽

Vehicle Body ◽

Rolled Steel ◽

Cold Rolled Steel ◽

Steel Sheets ◽

Automobile Body ◽

Cold Rolled ◽

Spot Welded

An effective way to reduce the weight of vehicle body seems to be application of new materials, and such trend is remarkable. Among the various materials for automobile body, stainless steel sheets and cold rolled steel sheets are under the interests. However, in order to guarantee reliability of new material and to establish the long life fatigue design criteria for body structure, it is necessary to assess spot weldability and fatigue strength of spot welded lap joints fabricated under optimized spot welding condition. In this paper, spot weldability of stainless steel sheets, STS301L and STS304L, and cold rolled steel sheets, SPCC and SPCD. Fatigue strength of lap joints spot welded between similar and dissimilar materials were also assessed.

Download Full-text

Fatigue Strength Analysis of S34MnV Steel by Accelerated Staircase Test

Open Engineering ◽

10.1515/eng-2020-0048 ◽

2020 ◽

Vol 10 (1) ◽

pp. 394-400 ◽

Cited By ~ 2

Author(s):

I. M. W. Ekaputra ◽

Rando Tungga Dewa ◽

Gunawan Dwi Haryadi ◽

Seon Jin Kim

Keyword(s):

Standard Deviation ◽

Fatigue Strength ◽

Fatigue Limit ◽

Fatigue Testing ◽

Reliability Estimation ◽

Test Method ◽

Strength Analysis ◽

Staircase Method ◽

Staircase Test ◽

Number Of Cycles

AbstractThis paper presents the reliability estimation of fatigue strength of the material used for crank throw components. The material used for crank throw components is forged S34MnV steel and subsequently heat-treated by normalising and tempering. High cycle fatigue testing under fully reversed cycling (R = −1) was performed to determine the fatigue limit of the material. The staircase test method is used to obtain accurate values of the mean fatigue limit stress until a number of cycles up to 1E7 cycles. Subsequently, the fatigue test results depend strongly on the stress step and are evaluated by the Dixon-Mood formula. The values of mean fatigue strength and standard deviation predicted by the staircase method are 282 MPa and 10.6MPa, respectively. Finally, the reliability of the design fatigue strength in some selected probability of failure is calculated. Results indicate that the fatigue strength determined from accelerated staircase test is consistent with conventional fatigue testing. Furthermore, the proposed method can be applied for the determination of fatigue strength and standard deviation for design optimisation of S34MnV steel.

Download Full-text