• 대한기계학회논문집A
• /
• 제27권7호
• /
• pp.1185-1192
• /
• 2003

Governing parameters for determination of the location of crack initiation and direction of crack initiation were investigated by performing fretting fatigue tests and analysis on Al 2024-T351. Fatigue tests were carried out using biaxial fatigue machine. It was shown that the dominant fatigue crack tended to initiate at the outer edge of one of the four bridge pads, growing at an angle beneath a pad, before turning perpendicular to the orientation of the axial load. Distribution of stresses generated during fretting fatigue loading along the interface was calculated by elastic FE simulation. It can be known that the location of crack initiation can be predicted by using the maximum tangential stress range. Futhermore, the crack initiation direction can also be predicted by a maximum tangential stress range.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.156-161
• /
• 2004

To predict the direction of the fatigue crack initiated from a hole under various types of biaxial fatigue loads with different phase difference and biaxiality, fatigue parameters were investigated. Axial and torsional biaxial fatigue loads were selected with the respective combination of five different phase differences of 0, 45, 90, 145 and 180 degrees and five biaxialities of 0, $1/{\sqrt{3}}$, 1, ${\sqrt{3}}$, ${\infty}$. Directions of the fatigue crack initiation around the hole were found to approach to the circumferential direction of the specimen with increment of the phase difference for fatigue tests with phase differences less than $90^{\circ}$. Whereas directions for tests with phase differences greater than $90^{\circ}$ went away from the circumferential direction and those were symmetric to the directions for tests with phase difference less than $90^{\circ}$. With increase of biaxilities, the fatigue crack initiated more apart from the circumferential direction of the specimen. These crack initiation direction were predicted using maximum tangential stress range and maximum shear stress range obtained at far-field and around the hole. Comparing these two stress parameters, The crack initiation direction can be successfully explained by using the direction of the maximum tangential stress range obtained around the hole and at far-field.

• 터널과지하공간
• /
• 제28권5호
• /
• pp.426-441
• /
• 2018

일반화된 Hoek-Brown (GHB) 파괴조건식은 최근 각종 암반공학적 계산에 활발히 이용되고 있지만 Mohr 파괴포락선이 해석적 수식으로 표시되지 않아 적용범위를 넓히는데 어려움이 있다. 이러한 단점을 극복하기 위해 이 연구에서는 GHB 파괴함수에 내포된 수직응력 - 접선마찰각 관계식을 다항식으로 최적 근사시켜 접선마찰각을 수직응력의 명시적 근사함수로 표시하는 새로운 방법을 제안하였다. 이 수직응력 - 접선마찰각 관계식을 직선 또는 2차 다항식으로 최적 근사시킬 경우 접선마찰각에 대한 해석적 해가 존재한다. 이 해를 전단응력 - 접선마찰각 관계식에 대입하면 GHB 파괴함수의 근사적 Mohr 파괴 포락선을 유도하는 것이 가능하다. 유도한 근사 Mohr 파괴포락선은 GSI 값 전체 범위에서 정해와 매우 근사함이 입증되었다.

• Journal of Mechanical Science and Technology
• /
• 제17권6호
• /
• pp.796-804
• /
• 2003

The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failures occur from cracks subjected to mixed-mode loading. Hence, it is necessary to evaluate the fatigue behavior under mixed-mode loading. Under mixed-mode loading, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. In modified range 0.3$\leq$a/W$\leq$0.5, the stress intensity factors (SIFs) of mode I and mode II for the compact tension shear (CTS) specimen were calculated by using elastic finite element analysis. The propagation behavior of the fatigue cracks of cold rolled stainless steels (STS304) under mixed-mode conditions was evaluated by using K$\_$I/ and $_{4}$ (SIFs of mode I and mode II). The maximum tangential stress (MTS) criterion and stress intensity factor were applied to predict the crack propagation direction and the propagation behavior of fatigue cracks.

• Journal of the Korean Wood Science and Technology
• /
• 제36권2호
• /
• pp.20-28
• /
• 2008

This study was carried out to provide the so-called circumferential slicing method for investigating radial distributions of the tangential strains and of moisture contents within the log cross section (LC) of Kalopanax pictus during indoor drying it. While the heartwood showed an almost uniform moisture content distribution in the range of about 50~55% in case of the green wood, it has gradually decreased toward the outer side, showing about 19% of moisture content difference from the innermost slice. Although the moisture gradient along the radial direction has gradually become gentle as drying progresses, the sapwood of the outer side represented the moisture contents below the fiber saturation point after 24 hours of drying while the heartwood in the inner part showed the moisture contents higher than the fiber saturation point. The pith side was laid under the tensile stress after 24 hours of drying, and then gradually decreasing toward the bark side, and showed the distribution being switched again to the tensile stress on the bark side. As the drying has progressed, this trend got more intensified, and finally showed the U-shaped distribution model after 48 hours of drying. The circumferential slice test is considered to be suitable in quantitatively determining the tangential strains and moisture content within a LC.

• Geomechanics and Engineering
• /
• 제10권2호
• /
• pp.125-135
• /
• 2016

Adhesion in geotechnical engineering is the interaction between cohesive soil and a solid surface which can cause clogging in mechanized tunnelling through clayey formations. Normal piston pull out and modified direct shear tests were performed on clayey soil samples to determine which type of adhesion stress, normal or tangential, could be most effectively measured. Measured values for normal adhesion ranged from 0.9 to 18 kPa. The range of tangential adhesion was 2.4 to 10 kPa. The results indicate normal adhesion results were more accurate than those for the modified direct shear test that measure tangential adhesion. Direct shear test on identical samples did not show any correlation between measured cohesion and normal adhesion values. Normal adhesion values have shown significantly meaningful variation with consistency index and so are compatible with the base of field clogging assessment criteria. But tangential adhesion and cohesion were not compatible with these assessment criteria.

• 대한기계학회논문집A
• /
• 제27권10호
• /
• pp.1695-1702
• /
• 2003

Fatigue crack initiation around a hole subjected to biaxial fatigue loads with a phase difference was investigated. Axial and torsional biaxial fatigue loads with different phase differences and biaxiality of 1/√3 were applied to thin-walled tubular specimens. Five phase differences of 0, 45, 90, 145 and 180 degrees were selected. Directions of the fatigue crack initiation around the hole were found to approach to the circumferential direction of the specimen with increment of the phase difference for fatigue tests with phase differences less than 90$^{\circ}$. Whereas directions for tests with phase differences greater than 90$^{\circ}$ got away from the circumferential direction and those were symmetric to the directions for tests with phase difference less than 90. . Furthermore, it was shown that the fatigue initiation life decreased with increment of phase difference for fatigue tests with phase differences less than 90$^{\circ}$, but it increased for tests with phase difference greater than 90$^{\circ}$. The crack initiation direction can be successfully explained by using the direction of the maximum tangential stress range obtained around the hole and at far-field.

• Geomechanics and Engineering
• /
• 제25권4호
• /
• pp.341-345
• /
• 2021

1D sand compression response to ko-loading experiences volume contraction from low to high effective stress regimes. Previous study suggested compressibility model with physically correct asymptotic void ratios at low and high stress levels and examined only for both remolded clays and natural clays. This study extends the validity of Enhanced Terzaghi model for different sand types complied from 1D compression data. The model involved with four parameters can adequately fit 1D sand compression data for a wide stress range. The low stress obtained from fitting parameters helps to identify the initial fabric conditions. In addition, strong correlation between compressibility and the void ratio at low stress facilitates determination of self-consistent fitting parameters. The computed tangent constrained modulus can capture monotonic stiffening effect induced by an increase in effective stress. The magnitude of tangent stiffness during large strain test should not be associated with small strain stiffness values. The use of a single continuous function to capture 1D stress-strain sand response to ko-loading can improve numerical efficiency and systematically quantify the yield stress instead of ad hoc methods.

• 터널과지하공간
• /
• 제32권5호
• /
• pp.312-326
• /
• 2022

암반의 표준 파괴기준식의 하나로 인정받고 있는 일반화된 Hoek-Brown (GHB) 식은 암반공학적 활용에 특화되어 있으며 넓은 범위의 암반조건을 고려할 수 있다. 이에 따라 암반 구조물의 안정성 해석과정에서 GHB 식을 적극적으로 활용하기 위한 많은 연구 노력이 진행 중이다. 이 연구에서는 탄소성 해석법의 일종인 slip-line 해석법을 GHB 파괴기준식과 결합하여 원형터널 주변의 소성반경과 응력분포를 간편하게 계산할 수 있는 해석적 수식들을 유도하였다. 관련 수식 유도과정에서는 파괴 후 거동으로 완전 소성 거동을 가정하였고, 초기지압은 정수압 상태로 가정하였다. 이 연구를 통하여 소성반경은 터널 벽면과 탄성-소성 경계면에 대응되는 두 접선 마찰각을 이용하여 해석적으로 계산할 수 있음을 밝혔다. 또한 유도한 해석 식들을 이용하여 계산한 소성반경과 응력분포는 2008년에 발표된 Lee & Pietruszczak의 수치해석적 방법의 결과와 일치함을 보였다. 이 논문의 후반부에서는 유도한 해석 식을 활용하여 암반의 양호도가 소성영역의 크기, 응력분포, 접선마찰각의 변화에 미치는 영향을 분석하였다.

• 대한기계학회논문집A
• /
• 제24권6호
• /
• pp.1446-1455
• /
• 2000

Fatigue crack initiation and propagation behavior under cyclic biaxial loading has been investigated using thin-walled tubular specimen with a hole. Two types of biaxial loading system, i.e. cyclic tensile loading with super-imposed static torsional load and cyclic torsional loading with superimposed static tensile load, with various values of the biaxial loading ratio, $\tau$ s/ $\sigma$ max (or $\tau$ max/ $\sigma$s) were employed. Fatigue tests show that fatigue crack near the hole initiates and propagates at 900 and 450 direction to the longitudinal direction of the specimen under cyclic tensile and torsion loading with static biaxial stress, respectively, and the static biaxial stress doesn't have any great influence on fatigue crack initiation and growth direction. Stress analysis near the hole of the specimen shows that the crack around the hole initiates along the plane of maximum tangential stress range. Fatigue crack growth rates were evaluated as functions of equivalent stress intensity factor range, strain energy density factor range and crack tip opening displacement vector, respectively. It is shown that the biaxial mode fatigue crack growth rates can be relatively consistently predicted with these cyclic parameters.