• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1997.10a
• /
• pp.120-126
• /
• 1997

This paper examines the crack growth behavior of 7075-T651 aluminum alloy under high-low block loading condition. The cantilever beam type specimen with a chevron notch is used in this study. The crack growth and closure are investgated by compliance method. The applied initial stress ratios are R=-0.5, R=0.0 and R=0.25 Crack length($\alpha$), effective stress intensity factor range(ΔKeff), ratio of effective stress intensity factor range(U) and crack growth rate(d$\alpha$/dN) etc. are inspected fracture mechanics estimate.

• International Journal of Precision Engineering and Manufacturing
• /
• v.2 no.3
• /
• pp.19-26
• /
• 2001

In order to investigate the effect of single tensile overload on the short crack growth behavior under the out-of-plane cyclic bending moment, crack opening stresses were continuously measured by an elastic compliance method using strain gages. The characteristics of short crack growth after the single tensile overload are analyzed by the effective stress range ratio. Futhermore, the investigation was carried out with respect to various fatigue crack growth behaviors such as the plastic zone size effect on crack retardation, the retarded crack length and the number of cycles.

• Journal of Ocean Engineering and Technology
• /
• v.4 no.1
• /
• pp.110-119
• /
• 1990

This study is concerned about the stress concentration factor measurement by photoelastic method, for the case of two circular holes arrangement in 3mm semi-infinite plate under tensile load, the ratio of those two circular holes diameter, the ratio of distance apart from circular holes to breadth and the two holes arrangement angle with loading direction were varied. Besides, the measured stress concentration by photoelastic method around one circular hole was compared with that by strain-gage method.

• Journal of the Korean Institute of Gas
• /
• v.4 no.1 s.9
• /
• pp.33-39
• /
• 2000

Stress intensity factor after penetration was discussed experimentally using long surface pre-cracked specimens of aluminum alloy 5083. The propagation behavior evaluation of long surface crack by equation proposed at penetration of short surface crack could be need modification to evaluate precisely because the error was high as aspect ratio is little. The modification of stress intensity factor with consideration of aspect ratio at penetration of long surface crack can be analyzed the behavior of crack penetration quantitatively.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2001.04a
• /
• pp.740-743
• /
• 2001

Sandwich structure is widely used in various fields of industry due to its excellent strength and stiffness compared with weight. We studied the sandwich structure which has honeycomb core type. We are concerned about its buckling and bending stress with respect to its side length, thickness and the height ratio of its unit core. After obtaining the buckling critical load of unit core, we applied it to the sandwich structure to observe the bending behavior. When we compared the buckling with bending stress under buckling critical load, we observed that models of which length ratio of unit honeycomb core, A, is lower than 0.04 and the thickness of core, t, is thicker than 0.09 mm, is subjected to the ultimate stress by bending before buckling.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.04a
• /
• pp.127-131
• /
• 2008

This paper deals with the performance evaluation of piezoelectric unimorph actuator. In the unimorph design, the thickness ratio of substrate to piezoelectric material and the elastic modulus ratio of substrate to piezoelectric material are important parameters. There exists only one structural configuration that satisfies the optimal condition among them, and actuators using that configuration exhibit better actuating displacements. Another design parameter is the piezoelectric coefficient which can be improved due to the induced tensile stress and voltages. The application of the tensile stress to the piezoelectric material makes it get higher piezoelectric coefficient and the total displacement performance of the unimorph actuator is improved. Finally, the piezoelectric actuator system with spring elements is fabricated and it shows higher actuating displacement capability.

• Biomedical Science Letters
• /
• v.19 no.1
• /
• pp.55-60
• /
• 2013

This study was to know the effects of massage on the back region in order to reduce stress in middle age women. To investigate the effects of massage to the stress levels of middle aged women, we evaluated blood pressure (BP), heart rate variability (HRV), and ultrasonography before and after back massage. The blood pressure after massage was reduced when compared to that of pre-massage. The HRV spectrum analysis was used Frequency domain analysis such as Mean HRV, normalized low frequency (norm LF), norm high frequency (norm HF), and LF/HF ratio. Post-massage BP tended to be low, but not statistical significant. After Massage, the Mean HRV, norm LF, and LF/HF ratio were significantly reduced, while norm HF was significantly increased as compared with pre-massage. The muscle layer and fat layer were significantly diminished by massage. The study was suggested that massage may be an effective treatment for relief of stress.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1997.10a
• /
• pp.653-658
• /
• 1997

Recently, carbon Fiber sheet (CFS) is frequently used for strengthening deteriorated concrete structures. To strengthening damaged structures, the property and characteristic of the bond between CFS and the concrete surface must be understood. The tensile test of single lap shear specimen was performed to study bond strength, bond stress distribution and stress transfer between CFS and concrete surface according to the bond length. Based on the test results, there were ultimate influence length (UIL) in which bond stress was distributed, and ultimate strain reduction ratio (USRR) by which strain was reduced linearly. Bond resisting force (BRF) was estimated by UIL and USRR, and which was compared with ultimate loads. According to the results of comparison, it was shown that ultimate bond strength could be estimated reasonablely by BRF.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2004.10a
• /
• pp.92-97
• /
• 2004

The aim of this study is to estimate the strength of injection molded plastic stepped gear. We considered stepped gear as plate model which are fixed by two edges. While, on the other sides are free. Normal gear is calculated by Lewis formula which can be derived quite simply from the equation for the stress at the root of a cantilever beam. Stress ratio(step factor) is represented for the ratio of the bending stress of normal and the bending stress of stepped gear, and it is plotted by face width factor. This study is propose the step factor added in Dupont equation which are strength estimation of step gear

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.15 no.3
• /
• pp.17-23
• /
• 2006

The strength estimation is carried out for injection molded plastic stepped gear. The stepped gear is considered as a plate model which is fixed by two edges and freed on the other sides. The stress of common normal gear is calculated by Lewis formula which can be derived quite simply from the equation fur the stress at the root of a cantilever beam. Stress ratio(step factor) between the common normal gear and stepped gear is proposed for the ratio of the bending stress of normal gear and that of stepped gear. This study proposes the step factor added in Dupont equation which is used for strength estimation of injection molded plastic stepped gear.