• Title/Summary/Keyword: stress-relaxation

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Fatigue Life Evaluation by ${\sigma}-N$ and ${\epsilon}-N$ Approaches Considering Residual Stresses (잔류응력을 고려한 국부변형률과 공칭응력 기준 피로수명 평가)

  • Goo, Byeong-Choon;Yang, Sung-Yong;Seo, Jung-Won;Jun, Hung-Chai
    • Proceedings of the KSME Conference
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    • 2004.11a
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    • pp.342-347
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    • 2004
  • To evaluate the fatigue lives of welded joints taking into residual stress relaxation, two approaches are applied. One is based on the conventional local strain analyses. The other is based on a model developed by the authors. In the first approach, the Ramberg-Osgood relation, Lawrence model and S.W.T. parameter are used. In the second approach, The S-N curve for a welded joint is deduced from that of the parent material. Residual stress relaxation obtained by finite element analysis is considered. Finally, we evaluate the fatigue lives for four weld details using the two approaches.

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Thermal Residual Stress Relaxation Behavior of Alumina/SiC Nanocomposites (Alumina/SiC 나노복합재료에서의 잔류 열응력 완화거동에 관한 연구)

  • Choa, Y.H.;Niihara, K.;Ohji, T.;Singh, J.P.
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2002.04b
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    • pp.11-11
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    • 2002
  • Plastic deformation was observed by TEM around the intragranular SiC particles in the $Al_2O_3$ matrix for $Al_2O_3/SiC$ nanocomposite system. The dislocations are generated at selected planes and there is a tendency for the dislocations to form a subgrain boundary structure with low-angel grain boundaries and networks. In this study, dislocation generated in the $Al_2O_3$ matrix during cooling down from sintering temperatures by the highly localized thermal stresses within and/or around SiC particles caused from the thermal expansion mismatch between $Al_2O_3$ matrix and SiC particle was observed. In monolithic $Al_2O_3$ and $Al_2O_3/SiC$ microcomposite system. These phenomena is closely related to the plastic relaxation of the elastic stress and strain energy associated with both thermal misfitting inclusions and creep behaviors. The plastic relaxation behavior was explained by combination of yield stress and internal stress.

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Estimation of Viscoelastic Properties of Trabecular Bone Using An Inverse Method (역추기법을 이용한 해면골의 점탄성 특성 해석)

  • Kang, Shin-Ill;Lee, Won-Hee;Hong, Jung-Hwa
    • Journal of Biomedical Engineering Research
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    • v.18 no.3
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    • pp.211-216
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    • 1997
  • An inverse method with regularization has been developed to determine the viscoelastic properties of trabecular bone. A series of stress relaxation experiments were performed under the condition of uniaxial compression stress state. Optimization has been formulated within the framework of nonlinear least-squares and a modified Gauss-Newton method with a zeroth-order regularization technique. The stress relaxation behavior of trabecular bone was analyzed using a standard viscoelastic model. The present study clearly shows that trabecular bone exhibits typical viscoelastic stress relaxation behavior, and the obtained material parameters well represent the viscoelastic behavior of trabecular bone.

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In-situ Analysis on the Effect of Mo Underlayer on Hillock Formation Behavior in Al Thin Films (Al 박막의 힐록 형성에 미치는 Mo 하부층의 영향에 관한 실시간 분석)

  • Lee, Yong-Duck;Hwang, Soo-Jung;Lee, Je-Hun;Joo, Young-Chang;Park, Young-Bae
    • Korean Journal of Materials Research
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    • v.17 no.1
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    • pp.25-30
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    • 2007
  • The in-situ scanning electron microscopy observation of real-time hillock evolution in pure hi thin films on glass substrate during Isothermal annealing was analyzed quantitatively to understand the compressive stress relaxation mechanism by focusing on the effect of Mo interlayer between Al film and glass substrate. There is a good correlation between the hillock-induced stress relaxation by in-situ scanning electron microscopy observation ana the measured stress relaxation by wafer curvature method. It is also clearly shown that the existence of Mo interlayer plays an important role in hillock formation probably due to the large difference in interfacial diffusivity of Al films.

The Effects of Acupuncture Stimulation and Progressive Relaxation Therapy on Examination Stress of Students -Using Heart Rate Variability and Pupil Size Variability - (침자극과 이완요법이 시험 스트레스에 미치는 영향 - 심박변이도와 동공크기변이도를 사용하여 -)

  • Kwak, Sun;Lee, Seung-Gi;Park, Kyung-Mo;Choi, Woo-Jin
    • Korean Journal of Acupuncture
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    • v.21 no.2
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    • pp.161-176
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    • 2004
  • Objectives : The purpose of this study was to investigate the effects of acupuncture stimulation and relaxation therapy on autonomic nervous system for students with examination stress by HRV, PSV and to find out relationship with anti-stress effect. Methods : The study group consists of 42 students were classified into three groups randomly : acupuncture stimulation group(male n=8, female n=6), relaxation therapy group(male n=8, female n=6) and rest group(male n=8, female n=6). Using heart rate variability and pupil size variability, we measured the value of HRT, SDNN, SDSD, LF norm, HF norm, LF/HF ratio, Pupil area, and compared the changes the sympathetic- parasympathetic activity. Measurement value were compared before and after, during midterm examination and normal times. Results : 1. HRT, LF/HF ratio, LF norm of acupuncture group was significantly decreased and HF norm were significantly increased in HRV after acupuncture stimulation at a term of examination. While variables of the other group were no significantly different. 2. SDNN of acupuncture group were significantly increased in HRV after acupuncture stimulation at normal times. 3. Pupil area, LF norm, HF norm of three group were no significantly different in PSV at a term of examination. 4. Pupil area of relaxation group were significantly decreased in PSV at normal times. While variables of the other group were no significantly different. 5. HRT of rest group were significantly decreased in HRV between three groups at a term of examination and normal times. 6. Pupil area of relaxation group were significantly decreased in PSV between three groups at a term of examination and normal times. Conclusion : The results suggest that acupuncture stimulation is associated with changed activity in the sympathetic and parasympathetic nervous system. Measurement values of HRV and PSV are suitable to estimate the activity of automatic nervous system.

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Development of a SRP(Stress Relaxation Program) Game using HRV(Heart Rate Variability) (심장박동수 변이성을 이용한 스트레스 이완용 게임개발)

  • Choi, Sam-Ha;Joe, Young-Sin;Kim, Kyung-Sik
    • Journal of Korea Game Society
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    • v.2 no.1
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    • pp.77-83
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    • 2002
  • Cases of applying game in the medical area are increasing thesedays. This game has been developed to prevent disease in self-nervous system through the control of respiration after monitoring the mental stress and physical stress from the heart rate variability (HRV) of the game user. The game is a kind of a stress relaxation program (SRP) designed not to avoid boring or rejecting mind of users by traditional simple training of continuous repetition, but to increase interaction which is a unique feature of games.

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Early Stage Growth Structure and Stress Relaxation of CoCrPt Thin Films on Spherically Modulated Polymer Surface

  • Kim, Sa-Rah;Jeong, Jun-Ho;Shin, Sung-Chul;Son, Vo Thanh;Jeon, Bo-Geon;Kim, Cheol-Gi;Jeong, Jong-Ryul
    • Journal of Magnetics
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    • v.15 no.1
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    • pp.12-16
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    • 2010
  • Combined study of in-situ stress measurements and atomic force microscopy (AFM) revealed drastic stress relaxation in the CoCrPt and PS(styrene)-PVP(vinyl pyridine) polymer hybrid structure that was closely related to the growth structure of the film. We have observed not only no large initial growth stress at the initial stages of film growth but also twice smaller stress in magnitude with opposite sign in the CoCrPt/PS-PVP/Si sample. The microstructural studies using AFM at the various film growth stages revealed that the film growth structure plays an important role in the stress relaxation mechanism of CoCrPt films on a corrugated polymer surface.

Impact of Applied Progressive Deep Muscle Relaxation Training on the Level of Depression, Anxiety and Stress among Prostate Cancer Patients: A Quasi-Experimental Study

  • Isa, Mohamad Rodi;Moy, Foong Ming;Razack, Azad Hassan Abdul;Zainuddin, Zulkifli Md.;Zainal, Nor Zuraida
    • Asian Pacific Journal of Cancer Prevention
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    • v.14 no.4
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    • pp.2237-2242
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    • 2013
  • Background: The aim of this study was to determine the impact of applied progressive muscle relaxation training on the levels of depression, anxiety and stress among prostate cancer patients. Materials and Methods: A quasi-experimental study was conducted at the University Malaya Medical Centre (UMMC) and Universiti Kebangsaan Malaysia Medical Centre (UKMMC) over six months. Prostate cancer patients from UMMC received the intervention and patients from UKMMC were taken as controls. The level of depression, anxiety and stress were measured using Depression, Anxiety Stress Scales - 21 (DASS-21). Results: A total of 77 patients from the UMMC and 78 patients from the UKMMC participated. At the end of the study, 90.9% and 87.2% of patients from the UMMC and UKMMC groups completed the study respectively. There were significant improvements in anxiety (p<0.001, partial ${\eta}^2$=0.198) and stress (p<0.001, partial ${\eta}^2$=0.103) at the end of the study in those receiving muscle training. However, there was no improvement in depression (p=0.956). Conclusions: The improvement in anxiety and stress showed the potential of APMRT in the management of prostate cancer patients. Future studies should be carried out over a longer duration to provide stronger evidence for the introduction of relaxation therapy among prostate cancer patients as a coping strategy to improve their anxiety and stress.

A Study on the Distribution of Residual Stress in Fillet Welds for Thick Mild Steel Plate (두꺼운 연강판(軟鋼板) 필렛 용접(熔接)이음부의 잔류응력분포(殘留應力分布)에 대한 연구(硏究))

  • Dong-Suk,Um;Sung-Won,Kang
    • Bulletin of the Society of Naval Architects of Korea
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    • v.20 no.4
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    • pp.17-24
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    • 1983
  • In this study, it was investigated the distribution of residual stress in the direction of loading between the root and toe the load fillet welds for thick steel plate. Residual stress distributions are measured by sectioning method which is one of stress-relaxation technique in welded joint, and analyzed by two dimensional finite element method on thermo-elasto-plastic theory under plane stress condition. These are compared the results of F.E.M analysis with the experimental result by stress-relaxation techniques. As a results, the following conclusion were obtained. (1) In the no penetration fillet welded joint specimen using mild steel plate with 25mm in thickness, the residual stress of loading direction near the root was about $10kg/mm^2$ tensile. (2) The tensile residual stress has been observed in fillet region of the fillet joint by F.E.M. analysis method. (3) The range of compressive residual stress distribution from the root was largest in the case of 5mm root penetration.

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Evaluation of Thin Film Residual Stress through the Theoretical Analysis of Nanoindentation Curve (나노 압입곡선의 이론적 분석을 통한 박막의 잔류응력 평가)

  • Lee, Yun-Hee;Jang, Jae-Il;Kwon, Dong-Il
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.7
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    • pp.1270-1279
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    • 2002
  • Residual stress is a dominant obstacle to efficient production and safe usage of device by deteriorating the mechanical strength and failure properties. Therefore, we proposed a new thin film stress-analyzing technique using a nanoindentation method. For this aim, the shape change in the indentation load-depth curve during the stress-relief in film was theoretically modeled. The change in indentation depth by load-controlled stress relaxation process was related to the increase or decrease in the applied load using the elastic flat punch theory. Finally, the residual stress in thin film was calculated from the changed applied load based on the equivalent stress interaction model. The evaluated stresses for diamond-like carbon films from this nanoindentation analysis were consistent with the results from the conventional curvature method.