• Proceedings of the Korea Concrete Institute Conference
• /
• 2009.05a
• /
• pp.531-532
• /
• 2009

This paper presents crack spacing which quantitatively considers the fiber distribution and prediction of uniaxial tensile behavior of ECC on the basis of crack spacing and fiber distribution. The predictions exhibit similar tensile stess-strain curves to the test results within 10% error.

• Journal of Ocean Engineering and Technology
• /
• v.7 no.2
• /
• pp.57-67
• /
• 1993

The fracture behavior of plain woven glass/epoxy composite plates with a crack is investigated under static tensile loading. It is shown in this paper that the characteristic length associated with the point stress criterion depends on the crack length. To predict the not ched tensile strength, the point stress criterion proposed by Whitney and Nuismer are modified. An excellent agreement is found between the experimental results and the analytical prediction of the modified point stress criterion. The condition of unstable crack growth in the presence of a per-existing flaw(machined notch) is examined by means of the maximum stress intensity factor $K_max$ using maximumload P$_max$. The values of $K_max$ evaluated from energy release rate G$_max$(the compliance me thod) indicate a wide difference. Therefore in regard to anisotropy and heterogeneity of the composite materials studied, the modified shape correction factor f(a/W) is obtained. $K_max$evaluated by the compliance method a little or insignificantly depends on the initial crack length a, the specimen thickness B, the crack angle .theta. and the specimen geometry.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.22 no.1
• /
• pp.67-73
• /
• 2009

The stress-strain behavior and its effects on the crack initiation and growth of ITO film on PET substrate with a sheet resistance of 45 ohms/sq were investigated. Electrical resistance increased gradually at the strain of 0.7% in the elastic to plastic transition region of the stress strain curves. Numerous cracks were observed after 1% strain and the increase of the resistance can be linked to the cracking of ITO thin films. The onset strain for the increase of resistance increased with increasing strain rate, suggesting the crack initiation is dependent on the strain rate. Upon loading, the initial cracks perpendicular to the tensile axis were observed and propagated the whole sample width with increasing strain. The spacing between horizontal cracks is thought to be determined by the fracture strength and the interfacial strength between ITO and PET. The crack density increased with increasing strain. The spacing between horizontal cracks (perpendicular to the stress axis) increased with decreasing strain rate, The increase of crack density with decreasing strain rate can be attributed to the higher fraction of the plastic strain to the total strain at a given total strain. As the strain increased over 5% strain, cracks parallel to the stress axis were developed and increased in number with strain, accompanied by drastic increases of resistance.

• Journal of the Korean Society of Safety
• /
• v.27 no.6
• /
• pp.99-108
• /
• 2012

Ultra High Performance Concrete(UHPC) has compressive strength higher than 180 MPa. The use of steel fibers in the dense UHPC matrix increases tensile strength, ductility and bond strength between UHPC and rebars. However, to apply the advance material behavior of UHPC to the design of a structure, we need design formulas. The crack formula is one of them. This paper investigated experimentally the bond behavior of a rebar and K-UHPC, the UHPC developed by Korea Institute of Construction Technology, and, modified CEB-FIP crack formula based on the test. In addition, this paper tested the crack behavior of K-UHPC reinforced with rebars to verify the modified crack formula. The result showed that the modified formula is reasonable to predict the width of cracks in the reinforced K-UHPC structures.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.1754-1759
• /
• 2007

Propagation of a mixed-mode crack in Soda-Lime silica glass using Movable Cellular Automata (MCA) method is demonstrated in this study. In MCA method, special fracture criterion is used to describe the process of crack initiation and propagation. Comparison between MCA and other crack initiation criteria results are made. The crack resistance curves and bifurcation angles under different loading angles are found. In comparisons with results of maximum circumferential tensile stress criterion, MCA result showed the sufficient agreement.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1998.03a
• /
• pp.178-183
• /
• 1998

This paper examines the crack growth behavior of 7075-T651 and 5052-H32 aluminum alloys for variable load within tensile load range 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 ratio is R=0.3 and variable load are R=0.65, 0.46. Crack length, stress intensity factor range, ratio of effective stress intensity factor range and crack growth rate etc. are inspected with fracture mechanics estimate.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1998.10a
• /
• pp.279-286
• /
• 1998

Fatigue crack propagation behavior for variable load in high strength aluminum alloys was investigated in this study. The materials used in this study are aluminum 7075-T651 and 5052-H32 alloys. Crack length was measured from calibration curve, which was plotted by known crack length and resistance of standard specimens. Load was obtained from linear regression formula. Unloading elastic compliance method was ap;ied to check the crack closure and cracked area.

• Computers and Concrete
• /
• v.13 no.1
• /
• pp.49-70
• /
• 2014

Steel fiber-reinforced concrete (SFRC) is known as one of the efficient modern composites that can greatly enhance the material performance of cracked concrete in tension. Such improved tensile resistance mechanism at crack interfaces in SFRC members can be heavily influenced by methodologies of treatments of crack direction. While most existing studies have focused on developing the numerical analysis model with the rotating-angle theory, there are only few studies on finite element analysis models with the fixed-angle model approach. According to many existing experimental studies, the direction of principal stress rotated after the formation of initial fixed-cracks, but it was also observed that new cracks with completely different angles relative to the initial crack direction very rarely occurred. Therefore, this study introduced the direct tension force transfer model (DTFTM), in which tensile resistance of the fibers at the crack interface can be easily estimated, to the nonlinear finite element analysis algorithm with the fixed-angle theory, and the proposed model was also verified by comparing the analysis results to the SFRC shear panel test results. The secant modulus method adopted in this study for iterative calculations in nonlinear finite element analysis showed highly stable and fast convergence capability when it was applied to the fixed-angle theory. The deviation angle between the principal stress direction and the fixed-crack direction significantly increased as the tensile stresses in the steel fibers at crack interfaces increased, which implies that the deviation angle is very important in the estimation of the shear behavior of SFRC members.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.1
• /
• pp.46-54
• /
• 2013

Two different UHPCCs having different fiber lengths and volume fractions are considered to be applied to bridge decks. The objective of this study is to estimate cracking resistance of the two UHPCCs. The notched beam tests were performed with the UHPCCs, and the relationships between load and CMOD(Crack Mouth Opening Displacement) were obtained from the tests. The tensile stress and crack opening relationships optimally fitting the measured load-CMOD curves were found through the inverse analyses. The UHPCC with 2% volume fraction of 13 mm long fiber has lower fracture energy than the UHPCC with 0.5% and 1.0% volume fractions of 16.3 mm and 19.5 mm long fibers, respectively. It indicates that the latter UHPCC is more effective in uniformly distributing crack formation and reducing crack width.

• Journal of the Korean Wood Science and Technology
• /
• v.18 no.3
• /
• pp.6-16
• /
• 1990

The objectives of this study were to investigate the relative effects of specific gravity and particle size on internal bond and tensile strengths and fracture toughness of particleboard and to compare mechanical strength with fracture toughness. The particleboard was manufactured with three different particle sizes at specific gravity levels of 0.6, 0.7, and 0.8 with a resin content of 10% based on oven dry weight. The results were summarized as follows: 1. Internal bond strength. fracture toughness in internal bond test. maximum tensile strength, and fracture toughness in tension test increased with the increase of specific gravity of particleboard. 2. As partcle size increased, internal bond strength, fracture toughness. maximum tensile strength. and fracture toughness in tension test increased. 3. The maximum tensile strength and fracture toughness appeared to be in a direct relationship, and then maximum tensile strength could be used for predicition of fracture toughness for tension test. 4. The fracture toughness in internal bond test was somewhat independent on induced crack length.