• 한국해양공학회지
• /
• 제8권2호
• /
• pp.141-150
• /
• 1994

In designing, the strength of tubular joint has been an important problem for integrity of steel structures in which many tubular members are used. This paper presents the results of FEM analysis on stress concentration and fatigue crack initiation life for two types of tubular joints. One is circular and rectangular T type joints which consist of circular brace and rectangular chord. Another is circular and circular T type joints which consist of circular brace and circular chord. FEM analyses were performed under the axial load and in-plane bending moment. The fatigue crack initiation life can be estimated by using $\varepsilon$-N curve and by applying the Palmgren-Miner linear damage rule. According to the results, the stress concentration factor(SCF) of circular and rectangular joints is higher than that of circular and circular joints. The fatigue crack initiation lives of circular-circular joints and circular-rectangular joints were calculated.

• Steel and Composite Structures
• /
• 제18권6호
• /
• pp.1465-1478
• /
• 2015

The effect of cutting off fibers on transient load in a polymeric matrix composite lamina was studied in this paper. The behavior of fibers was considered to be linear elastic and the matrix behavior was considered to be linear viscoelastic. To model the viscoelastic behavior of matrix, a three parameter solid model was employed. To conduct this research, finite difference method was used. The governing equations were obtained using Shear-lag theory and were solved using boundary and initial conditions before and after the development of break. Using finite difference method, the governing integro-differential equations were developed and normal stress in the fibers is obtained. Particular attention is paid the dynamic overshoot resulting when the fibers are suddenly broken. Results show that considering viscoelastic properties of matrix causes a decrease in dynamic load concentration factor and an increase in static load concentration factor. Also with increases the number of broken fibers, trend of increasing load concentration factor decreases gradually. Furthermore, the overshoot of load in fibers adjacent to the break in a polymeric matrix with high transient time is lower than a matrix with lower transient time, but the load concentration factor in the matrix with high transient time is lower.

• 한국자동차공학회논문집
• /
• 제4권2호
• /
• pp.80-89
• /
• 1996

Fatigue life of a notched shaft was evaluated in order to estimate the durability and integrity of the notched shaft in design stage. Cumulative fatigue dama- ge analysis was performed using local strain approach based on the assumption that the fatigue life of a notched component is approximately same as that of a smooth specimen is subjected to the same strain at the notched component. In this paper, shafts with different notch root radius of 1, 2㎜ resulting in different values of stress concentration factors were tested under||rotating bending fatigue loading condition. Theoretical stress concentration factor for each notch type was calculated using finite element method. Fatigue life prediction program, FALIPS, written in C language was developed using the strain-life curve, and the local strain approach integrating Neuber's rule, cyclic stress-strain, and hysteresis loop equations. The fatigue life evaluated using the fatigue notch factor obtained from the experimentally determined fatigue strength showed very large scattering with nonconservatism, but the fatigue notch factors derived from the stress concentration factors and Peterson's equation reduced the considerablely accurate fatigue life evaluation within a factor of three.

• Structural Engineering and Mechanics
• /
• 제34권2호
• /
• pp.143-157
• /
• 2010

This paper presents theoretical solutions for the three-dimensional (3D) stress field in an infinite isotropic elastic plate containing a through-the-thickness circular hole subjected to far-field in-plane loads by using Kane and Mindlin's assumption. The dangerous position, where the premature fracture or failure of the plate will take place, the expressions of the tangential stress at the surface of the hole and the out-of-plane stress constraint factor are found in a concise, explicit form. Based on the present theoretical solutions, a comprehensive analysis is performed on the deviated degree of the in-plane stresses from the related plane stress solutions, stress concentration and out-of-plane constraint, and the emphasis has been placed on the effects of the plate thickness, Poisson's ratio and the far-field in-plane loads on the stress field. The analytical solution shows that the effects of the plate thickness and Poisson's ratio on the deviation of the 3D in-plane stress components is obvious and could not be ignored, although their effects on distributions of the in-plane stress components are slight, and that the effect of the far-field in-plane loads is just on the contrary of that of the above two. When only the shear stress is loaded at far field, the stress concentration factor reach its peak value about 8.9% higher than that of the plane stress solutions, and the out-of-plane stress constraint factor can reach 1 at the surface of the hole and is the biggest among all cases considered.

• 한국기계가공학회지
• /
• 제6권1호
• /
• pp.20-26
• /
• 2007

In this study, fatigue strength of load-carrying cruciform fillet welded joints were evaluated using a new method proposed by Yamada, for geometric or structural stress in welded joint, that is, one-millimeter stress below the surface in the direction corresponding to the expected crack path. Validity of the method is verified by analyzing fatigue test results for load-carrying cruciform welded specimens has different size of weld toe radius, leg length and plate thickness reported in literature. Structural stress concentration factor for 1mm below the surface was calculated by finite element analysis for each specimen respectively. When compared to the basic fatigue resistance curve offered by BS7608, the one-millimeter stress method shows conservative evaluation for load-carrying cruciform fillet welded joints.

• 대한기계학회논문집A
• /
• 제21권11호
• /
• pp.1965-1971
• /
• 1997

The relaxation of stress concentration in notched members can be very significant in the improvement of notched strength and fatigue life. This paper investigated the relationship of stress concentration factor, and notched strength and fatigue life. The stress concentration factors were analyzed by FEM. Uniaxial tensile and fatigue tests were carried on plain woven composite specimens which have a main hole and two defence holes. From experimental results, the notched strength and the fatigue limit increased up to about 50% and 30% respectively due to the reduction in stress concentration. The fatigue lives predicted by Juvinall's approach were underestimated than test results and this trends were remarkable as nothed strength increased. This is because of the underestimation of a coefficient. A in S-N curve (.sigma.$_{ar}$ =A $N_{f}$ $^{B}$). Therefore, considering notched strength the coefficient A was modified. The fatigue lives by this process were agreed well with the experimental results.sults.

• Biomolecules & Therapeutics
• /
• 제32권1호
• /
• pp.77-83
• /
• 2024

Alzheimer's disease (AD) is a neurodegenerative disease characterized by neuronal cell death and memory impairment. Corticosterone (CORT) is a glucocorticoid hormone produced by the hypothalamic-pituitary-adrenal axis in response to a stressful condition. Excessive stress and high CORT levels are known to cause neurotoxicity and aggravate various diseases, whereas mild stress and low CORT levels exert beneficial actions under pathophysiological conditions. However, the effects of mild stress on AD have not been clearly elucidated yet. In this study, the effects of low (3 and 30 nM) CORT concentration on Aβ_25-35-induced neurotoxicity in SH-SY5Y cells and underlying molecular mechanisms have been investigated. Cytotoxicity caused by Aβ_25-35 was significantly inhibited by the low concentration of CORT treatment in the cells. Furthermore, CORT pretreatment significantly reduced Aβ_25-35-mediated pro-apoptotic signals, such as increased Bim/Bcl-2 ratio and caspase-3 cleavage. Moreover, low concentration of CORT treatment inhibited the Aβ_25-35-induced cyclooxygenase-2 and pro-inflammatory cytokine expressions, including tumor necrosis factor-α and interleukin-1β. Aβ_25-35 resulted in intracellular accumulation of reactive oxygen species and lipid peroxidation, which were effectively reduced by the low CORT concentration. As a molecular mechanism, low CORT concentration activated the nuclear factor-erythroid 2-related factor 2, a redox-sensitive transcription factor mediating cellular defense and upregulating the expression of antioxidant enzymes, such as NAD(P)H:quinone oxidoreductase, glutamylcysteine synthetase, and manganese superoxide dismutase. These findings suggest that low CORT concentration exerts protective actions against Aβ_25-35-induced neurotoxicity and might be used to treat and/or prevent AD.

• Nuclear Engineering and Technology
• /
• 제54권1호
• /
• pp.401-413
• /
• 2022

This paper provides a simple method by which to estimate the cross-section stress profiles for nozzles designed according to ASME Code Section III. Further, this method validates the effectiveness of earlier work performed by the authors on standard nozzles. The method requires only the geometric information of the pressure vessel and the attached nozzle. A PWR direct vessel injection nozzle, a PWR outlet nozzle, a PWR inlet nozzle and a BWR recirculation outlet nozzle are selected based on their corresponding specific designs, e.g., a varying nozzle radius, a varying nozzle thickness and an outlet nozzle boss. A cross-section stress profile comparison shows that the estimates are in good agreement with the finite element analysis results. Differences in stress intensity factors calculated in accordance with ASME BPVC Section XI Appendix G are discussed. In addition, a change in the dimensions of an alternate nozzle design relative to the standard values is discussed, focusing on the stress concentration factors of the nozzle inside corner.

• Journal of Advanced Marine Engineering and Technology
• /
• 제36권1호
• /
• pp.85-93
• /
• 2012

본 연구에서는 용접부의 형상을 고려하여 머플러의 피로수명을 예측하는 프로세스를 개발하였다. 피로수명 예측 프로세스 개발을 위해 머플러의 굽힘 피로시험을 진행한 후 M-N선도를 획득하고, 파손이 발생한 용접부의 형상을 모델링 한 후 정적하중해석을 실시하고, 해석결과를 이용하여 응력집중계수를 구하였다. 응력집중계수는 피로노치계수를 구하는데 사용되며, 이를 바탕으로 피로수명을 예측하였다. 시험결과와 예측결과의 비교를 통해서 피로수명 예측의 타당성을 검증하였다.

• 대한조선학회지
• /
• 제4권1호
• /
• pp.55-58
• /
• 1967

It is investigated that in what shape the stress concentration factor of a notched strip under pure bending changes due to unsymmetrically varying notch angle. Four models made of CR-39, having parameters of r/d-0.225, h/r=4; r/d=0.225, h/r=2; r/d=0.4, h/r=4 and r/d=0.4, h/r=2 respectively as shown in Fig.1, Fig.2 and Table are tested with the use of polariscope. For each model, notch angle is unsymmetrically varied from $0^{\circ}$ to $180^{\circ}$ at intervals of $15^{\circ}$ as shown in Fig. 1 and Fig. 2. The results of this experiment are Fig. 7 and Fig. 8 and the following are deduced. As notch angle increases 1) from $0^{\circ}$ to $50^{\circ}$, the decrement of concentration factor is slight. 2) from $50^{\circ}$ to 90, the decrement of concentration factor is a little steeper. 3) from $30^{\circ}$ to $140^{\circ}$, the decrement of concentration factor is slight. 4) from $140^{\circ}$ to $180^{\circ}$, the decrement is very steep with an abrupt with an abrupt change in the neighborhood of $140^{\circ}$.