• Journal of Ocean Engineering and Technology
• /
• v.1 no.2
• /
• pp.123-129
• /
• 1987

Corrosion fatigue fracture of dual phase steel(SS41) and raw material steel(SS41) were investigated in 3.5% NaCl aqueous solution at PH 4,6,9 and 11. The fatigue limit of dual phase steel is increased approximately 1.8 times larger than that of raw material in air. The corrosion fatigue life of dual phase steel is about 5-10 times larger than that of raw material in 3.5% NaCl aqueous solution. The reduction of fatigue life is larger for the acidsalt solution than for the alkali salt solution. The reduction of stress level on the reduction ratio of corrosion fatigue life is large as pH 6-11. The reduction ratio of corrosion fatigue life of dual phase steel and raw material is nearly coincided at pH 2. While at pH4-2 the reduction ratio of corrosion fatigue life only depends on the corrosion effect. It has been found that the corrosion resistance effect of dual phase steel is smaller than that of raw material in corrosion fatigue crack propagation rate. As pH below 6 is changed, it can be clearly observed from raw material that the brittle intergranular fracture is characterized, and from the above result, the influence of corrosion of dual phase steel is small.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2000.11a
• /
• pp.79-83
• /
• 2000

Interfacial and microfailure properties of carbon liber/bismaleimide (BMI) composites were evaluated using both tensile fragmentation and compressive Broutman tests with acoustic emission (AE). Since BMI is rather difficult matrix to apply for the conventional fragmentation test because of its too low elongation and too brittle and high modulus properties, dual matrix composite system was applied. After carbon fiber/BMI composite was prepared for rod shape by controlling differing curing stage, composites rod was embedded in toughened epoxy as outer matrix. The typical microfailure modes including fiber break, matrix cracking, and interlayer failure were observed during tensile testing, whereas the diagonal slippage in fiber ends was observed during compressive test. On the other hand, AE amplitudes of BMI matrix fracture were higher than carbon fiber tincture under tensile test because BMI matrix has very brittle and high modulus. The waveform of signals coming from BMI matrix fractures was consistent with AE amplitude result under tensile tests.

• Composites Research
• /
• v.16 no.1
• /
• pp.42-49
• /
• 2003

Brittle matrix composites often have interfacial debonding between the fiber and matrix which may lead to strength and stiffness degradation. The effect of interfacial debonding and fiber volume fraction on the mechanical properties of composite material were studied by using finite element method. Firstly, the modelling of fiber and matrix constituting the composite material was simplified under some assumptions. Traction and displacement continuity conditions were imposed along the boundary of adjacent representative volume elements. In order to obtain the effective material properties of composite material, stiffness constants were inverted. Numerical values of longitudinal moduli in case of perfect bonding were compared with theoretical values obtained by rule of mixtures and yielded consistency. Material properties of composite with large debonding an81e were found to decrease even though the fiber volume fraction increased.

• Structural Engineering and Mechanics
• /
• v.26 no.3
• /
• pp.263-276
• /
• 2007

Steel frame structures have been widely used in multi-storey and high-rise buildings and the connections in these structures are critical. In the Northridge and Kobe Earthquake, beam-column connections suffered damage due to brittle fracture. According to seismic design codes, ductility of the beam to column connection is also necessary. A study on the behavior of a beam to column connection with the aim of improving ductility as well as preventing brittle failure was carried out. In order to control the position of a plastic hinge on the beam, a connection with a hole in the beam web was developed. Five specimens with different parameters under cyclic load were assessed. The results are presented in terms of the stress distribution of the beam, hysteretic behavior, and ultimate capacity. Furthermore, the finite element method was also used to analyze the model, and the results were compared with those obtained from the experiment. It is shown from the analysis and experimental results that this type of connection is effective in terms of improving ductility for a beam to column connection in low-rise buildings.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.11 no.6
• /
• pp.107-114
• /
• 2012

Fracture of brittle material due to dynamic load such a particle impact has been reported by many researchers as the fracture behavior by variation of stress for a short minute. Especially, the brittle material, such a ceramic, applied to the structural component of machine, is considered as the important project. In order to evaluate the improvement of impact resistance, the particle impact test for the $Al_2O_3-TiO_2$ coated glass is practiced. And then, the damage variation according to the impact energy of steel ball was evaluated. There was a large improvement by the ceramic coating on the surface of a glass substrate. The damage volume was especially imported to evaluate damage behavior in quantity. These data were plotted on logarithmic coordinate and experimental equations were induced by data analysis based on test results. And the variation of critical energy for crack initiation was analyzed with critical impact energy when each crack occurs.

• Proceedings of the KSR Conference
• /
• 2002.05a
• /
• pp.183-188
• /
• 2002

In locations where the cost or concrete is relatively high, or in situations where the weight or concrete members is to be kept to a minimum, it may be economical to use hollow reinforced concrete vertical members. Hollow reinforced concrete columns with low axial load, moderate longitudinal steel percentage, and a reasonably thick wall were found to perform in a ductile manner at the flexural strength, similar to solid columns. However, hollow reinforced concrete columns with high axial load, high longitudinal steel percentage, and a thin wall were found to behave in a brittle manner at the flexural strength, since the neutral axis is forced to occur away from the inside face of the tube towards the section centroid and, as a result, crushing of concrete occurs near the unconfined inside face of the section. If, however, a steel tube is placed near the inside face of a circular hollow column, the column can be expected not to fail in a brittle manner by disintegration of the concrete in the compression zone. Design recommendation and example by moment-curvature analysis program for curvature ductility are presented. Theoretical moment-curvature analysis for reinforced concrete columns, indicating the available flexural strength and ductility, can be conducted providing the stress-strain relation for the concrete and steel are known. In this paper, a unified stress-stain model for confined concrete by Mander is developed for members with circular sections.

• Journal of the Korean Society for Precision Engineering
• /
• v.25 no.1
• /
• pp.138-144
• /
• 2008

Micro-machining of a brittle material such as glass, silicon, etc., is important in micro fabrication. Particularly, micro-abrasive jet machining (${\mu}-AJM$) has become a useful technique for micro-machining of such materials. The ${\mu}-AJM$ process is mainly based on the erosion of a mask which protects brittle substrate against high velocity of micro-particle. Therefore, fabrication of an adequate mask is very important. Generally, for the fabrication of a mask in the ${\mu}-AJM$ process, a photomask based on the semi-conductor fabrication process was used. In this research a rapid mask fabrication technology has been developed for the ${\mu}-AJM$. By scanning the focused UV laser beam, a micro-mask pattern was fabricated directly without photolithography process and photomask. Two kinds of mask patterns were fabricated using SU-8 and photopolymer (Watershed 11110). Using fabricated mask patterns, abrasive-jet machining of Si wafer were conducted successfully.

• Steel and Composite Structures
• /
• v.8 no.5
• /
• pp.389-402
• /
• 2008

In December 2005, one(A) of the two pre-engineered warehouse buildings in the port of K City of Korea was completely destroyed and the other(B) was seriously damaged to be demolished. Over-loaded snow and unexpected blast of wind were the causes of the accident and destructive behavior was brittle fracture caused by web local buckling and lateral torsional buckling at the flange below rafter. However, the architectural design technology of today based on material non-linear method does not consider the tolerances to solve the problem of such brittle fracture. So, geometric non-linear evaluation which includes initial deformation, width-thickness ratio, web stiffener and unbraced length is required. This study evaluates the structural safety of 4 models in terms of width-thickness ratio and unbraced length using ANSYS 9.0 with parameters such as width-thickness ratio of web, existence/non-existence of stiffener and unbraced length. The purpose of this study is to analyze destructive mechanism of the above-mentioned two warehouse buildings and to provide ways to promote the safety of pre-engineered buildings.

• Journal of the Korean Society of Safety
• /
• v.24 no.1
• /
• pp.1-6
• /
• 2009

In machining of ceramic materials, they are very difficult-to cut materials because of there high strength and hardness. Machining of ceramics are characterized by cracking and brittle fracture. Generally, ceramics are machined using conventional method such as grinding and polishing. However these processes are generally costly and have low MRR(material removal rate). This paper focuses on machinability evaluation of machinable ceramics for products with CNC machining center. Thus, in this paper, experiment applying cutting parameters is performed based on experimental design method. A design and analysis of experiments is conducted to study the effects of these parameters on the surface roughness by using the S/N ratio, analysis of ANOVA, and F-test. And multiple linear regression analysis is applied to compare experimental with predicted data in consideration of surface roughness. Cutting parameters, namely, feed, cutting speed and depth of cut are used to accomplish purpose of this paper. Required experiments are performed, and the results are investigated.

• Journal of Welding and Joining
• /
• v.7 no.4
• /
• pp.56-67
• /
• 1989

In this study, the possibility of evaluating the peculiar fracture strength of weldment in high strength steels was investigated by means of a small punch(SP) test. In order to obtain the ductile-brittle transition temperature(DBTT) of SP energy by which the fracture strength of weldment in structural steels such as SS41 and SM53B steels had been evaluated in our preceding publication, the effects of notches and loading rates on SP energy were discussed. It was found that the correspondence of SP energy to critical COD at test temperature -196.deg. C showed a linear relation with some deviation. The empirical correlation with scatter band, Esp/(Esp)p = 1.67[.delta./(.delta./sub c//(.delta./sub c/)/sub p/]-0.55, was developed between the SP energy ratio and critical COD ratio of each weld structure compared with parent material at test temperature -196.deg. C. In addition, there did not appear to be a significant effect of test materials and specimen size etc. on the correlation.