Development of the Outer Surface Irradiated Laser Stress Improvement Process

Tsubota, Shuho; Kamo, Kazuhiko; Ohta, Takahiro; Ishide, Takashi; Nakamura, Yasuo; Ueda, Takeshi; Onitsuka, Hironori; Akaba, Takashi

doi:10.7791/jhts.35.199

Cited by 4 publications

(1 citation statement)

References 2 publications

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“…In the case of small cracks, which are less than 1 mm, shot‐peening can make the crack harmless (Takahashi et al , 2011). Meanwhile for large cracks, it is reported that induction heating stress improvement (IHSI) (Ohtaka et al , 2007) and laser stress improvement process (L‐SIP) (Tsubota et al , 2009) make large size cracks harmless.…”

Section: Introductionmentioning

confidence: 99%

Analytical investigation of effect of stress ratio on threshold stress intensity factor range improved by overload

Houjou

Takahashi

Ando

2012

International Journal of Structural Integrity

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PurposeThe purpose of this paper is to describe the effects of stress ratio (R) on the threshold stress intensity factor range (ΔKth) by applied overload and to conduct an analytical investigation of the effect of the stress ratio.Design/methodology/approachTensile overload was applied to a compact tension specimen, and fatigue tests were performed at R=0.1 or 0.5.FindingsThe value of ΔKth increased as the tensile overload was increased, and the nominal threshold values were given by the equation ΔNKth,R = C+ DKov, where C represents ΔKth, and D is a proportional constant. Experimental results showed that the value of D showed good agreement with theoretical value.Originality/valueThe paper proposes a new model that arrests crack growth or makes cracks harmless by utilizing the overload effect.

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Section: Introductionmentioning

confidence: 99%

Analytical investigation of effect of stress ratio on threshold stress intensity factor range improved by overload

Houjou

Takahashi

Ando

2012

International Journal of Structural Integrity

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Residual Stress Improvement on Inner Surface of Pipes Using Pipe Outer Surface Irradiated Laser Heating

Ohta¹,

Kamo²,

Muroya³

et al. 2009

QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY

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The new process called L-SIP(outer surface irradiated Laser Stress Improvement Process) is developed to improve the tensile residual stress of the inner surface near butt weld joint of pipes. In L-SIP, the pipe outside temperature rises locally at short time by a laser beam moving in the circumferential direction. If the heating time is short enough, the temperature of the pipe inner surface dose not rise, and a temperature difference occurs between the outer surface and the inner surface. By the thermal expansion difference between the outer surface and the inner surface, the thermal stress occurs in the pipe and the new plastic deformation is produced. After cooling, the compressive residual stress is produced near the inner surface of the pipe with the effect of this plastic deformation. In order to verify the stress improvement mechanism of L-SIP, thermo-elastic-plastic FEM analysis is conducted for austenitic stainless steel pipe (SUS304TP 4B Sch160; O.D. =114.3mm, thickness=13.5mm). It is showed that the residual stress on the pipe inner surface change to the compressive stress like the axial-symmetry model. The experiment is done for butt weld joint of the same pipe as FEM analysis. The welding residual stress is improved from +200MPa (tensile) to less than -100MPa (compression) on the pipe inner surface. Material qualification tests of welding joint are done after L-SIP. It is verified that L-SIP has no bad influence on the welding joint of the stainless steel pipe.

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Study of Temperature Distribution of Pipes Heated by Moving Rectangular Gauss Distribution Heat Source

Ohata¹,

Kamo²,

Asada³

et al. 2009

QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY

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The new process called L-SIP (outer surface irradiated Laser Stress Improvement Process) is developed to improve the tensile residual stress of the inner surface near the butt welded joints of pipes in the compression stress. The temperature gradient occurs in the thickness of pipes in heating the outer surface rapidly by laser beam. By the thermal expansion difference between the inner surface and the outer surface, the compression stress occurs near the inner surface of pipes.In this paper, the theoretical equation for the temperature distributions of pipes heated by moving rectangular Gauss distribution heat source on the outer surface is derived. The temperature histories of pipes calculated by theoretical equation agree well with FEM analysis results. According to the theoretical equation, the controlling parameters of temperature distributions and histories are q/2a y , vh, a x /h and a y /h, where q is total heat input, a y is heat source length in the axial direction, a x is Gaussian radius of heat source in the hoop direction, v is moving velocity, and h is thickness of the pipe. The essential variables for L-SIP, which are defined on the basis of the measured temperature histories on the outer surface of the pipe, are Tmax, F 0 =k 0 /h 2 , vh, W Q and L Q , where Tmax is maximum temperature on the monitor point of the outer surface, k is thermal diffusivity coefficient, 0 is the temperature rise time from 100 to maximum temperature on the monitor point of the outer surface, W Q is 0 v, and L Q is the uniform temperature length in the axial direction. It is verified that the essential variables for L-SIP match the controlling parameters by the theoretical equation.

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Development of the Outer Surface Irradiated Laser Stress Improvement Process

Cited by 4 publications

References 2 publications

Analytical investigation of effect of stress ratio on threshold stress intensity factor range improved by overload

Analytical investigation of effect of stress ratio on threshold stress intensity factor range improved by overload

Residual Stress Improvement on Inner Surface of Pipes Using Pipe Outer Surface Irradiated Laser Heating

Study of Temperature Distribution of Pipes Heated by Moving Rectangular Gauss Distribution Heat Source

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