• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.1 no.1
• /
• pp.54-62
• /
• 1998

This study measured the shearing resistance of the roots of the Sasamorpha purpurascens, Miscanthus sinensis, Lespedeza cyrtobotrya by the tensile strength gained through their individual tensile test for the Root Reinforcement Model. The results to have measured this stress by experiment are as follows. 1) The mean root diameter of the Lespedeza cyrtobotrya used for this experiment was 2.19mm and the mean tensile stress was calculated as $929.489kgf/cm^2$. As for the Sasamorpha purpurascens, its mean root diameter was 1.727mm, and the mean tensile stress was $292.069kgf/cm^2$. And as for the Miscanthus sinensis, its mean root diameter was 0.814mm, and the mean tensile stress was $696.947kgf/cm^2$. And so, it was grasped that Lespedeza cyrtobotrya was highest in tensile stress. 2) ${\Delta}Cr(kg/cm^2)$ of the shearing resistance calculated by estimating the areal ratio of roots at $10^{-3}$ is $1.069kg/cm^2$ in Lespedeza cyrtobotrya, $0.336kg/cm^2$ in Sasamorpha purpurascens, and $0.801kg/cm^2$ in Miscanthus sinensis. That is, Lespedeza cyrtobotrya has the highest shearing resistance. However, since a precise analysis of the controlled factors of the slope analyses are demanded for more accurate dynamic analyses, the future demands a study on this.

• Proceedings of the KWS Conference
• /
• 2002.10a
• /
• pp.145-150
• /
• 2002

It has been well known that ductile fracture of steels is accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameters criterion based on equivalent plastic strain and stress triaxiality. It has been demonstrated by authors using round-bar specimens with circumferential notch in single tension that the critical strain to initiate ductile crack from specimen center depends considerably on stress triaxiality, but surface cracking of notch root is in accordance with constant strain condition. In order to evaluate the stress/strain state in the specimens, especially under dynamic loading, a thermal, elastic-plastic, dynamic finite element (FE) analysis considering the temperature rise due to plastic deformation has been carried out. This study provides the fundamental clarification of the effect of strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, loading mode and loading rate on critical condition to initiate ductile crack from notch root using equivalent plastic strain and stress triaxiality based on the two-parameter criterion obtained on homogeneous specimens under static tension. The critical condition to initiate ductile crack from notch root for strength mismatched bend specimens under both static and dynamic loading would be almost the same as that for homogeneous tensile specimens with circumferential sharp notch under static loading.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1995.05a
• /
• pp.771-776
• /
• 1995

Tensile and J-R tests were carried out to estimate the effects of dynamic strain aging(DSA) on SA106Gr.C piping steel. Tensile tests were performed under temperature range RT to $400^{\circ}C$ md strain rates from $1.39{\times}10^{-4}\;to\;6.95{\times}10^{-2}/s$. Fracture toughness was tested in the temperature range RT to $350^{\circ}C$ and load-line displacement rates 0.4 and 4mm/min. The effects of DSA on the tensile properties were clearly observed for phenomena such serrated flow, variation of ultimate and yield stress, and negative stram rate sensitivity. However, the magnitude of serration and strength increase by DSA was relatively small. this may be due to high ratio of Mn to C. In addition, crack initiation resistance, Ji and crack growth resistance, dJ/da were reduced in the range of $200-300^{\circ}C$, where DSA appeared as serrated flow and UTS hardening. The temperature corresponding to minimum fracture resistance was shifted to higher temperature with increasing loading rate.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.47 no.1
• /
• pp.25-32
• /
• 2005

This study was performed to evaluate strengths and non-destruction properties of super flow concrete using recycled coarse aggregate. At the curing age of 28 days, the compressive strength was 22.7-37.5 MPa, the splitting tensile strength was $2.65\~3.73$ MPa, the flexural strength was $5.78\~6.86$ MPa, the ultrasonic pulse velocity was $3,103\~3,480$ mis, the dynamic modulus of elasticity was $3.401{\times}104\~4.521{\times}104$MPa, respectively. The strengths, ultrasonic pulse velocity and dynamic modulus of elasticity of super flow concrete were decreased with increasing the content of recycled coarse aggregate. The super flow concretes using recycled coarse aggregate were improved by substitution in the range of less than the fly ash content 30010 and recycled coarse aggregate content $75\%$.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.9 no.1
• /
• pp.24-29
• /
• 2000

This paper is experimental study of machining characteristics about martensitic heat resisting steel STR11. Machining characteristics are different according to internal quality(chemical compositions, microscopic structure and nonmetallic inclusion) mechanical properties(tensile strength value impact value and hardness) and dynamic cutting force. Following are the results : 1. In analyzing internal quality test materials have typical martensite structure and a minute needle-shaped structure. 2. Tensile strength and reduction of area and hardness are larger. But values of elongation and impact values are smaller. Fracture surface of tensile specimen is ductile. 3, Cutting force is decreasing with cutting speed increasing 4. Cutting force is increasing with feed speed increasing.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.12 no.1
• /
• pp.106-113
• /
• 2004

Most of mechanical structures are composed of many substructures connected to one another by various types of mechanical joints. In automotive engineering, it is important to study these connected structures under various dynamic forces for the evaluations of fatigue life and stress concentration exactly. In this study, the dynamic response of vehicle structure to external forces is classified an inverse problem involving strains from the experiment and the analysis. The practical dynamic forces are determined by the combination of the analytical and experimental method with analyzed strain by quasi-static finite element analysis under unit force and with measured strain by a strain gage under driving load, respectively. In a stressed body, inter-molecular chemical bonds are failed beyond the certain magnitude. The failure of molecular structure in material is considered as a time process of which rate is determined by mechanical stress. That is, the failure of inter-molecular chemical bonds is the fatigue lift of material. This kinetic concept is expressed as lethargy coefficient. And S-N curve is obtained with the lethargy coefficient from quasi-static tensile test. Equivalent practical dynamic force is obtained from the identification of practical dynamic force for one loading point. Using the practical dynamic force and S-N curve, fatigue life of a window pillar is analyzed with FEM under the identified force by the procedure of above mentioned.

• Journal of Radiation Industry
• /
• v.4 no.3
• /
• pp.271-276
• /
• 2010

Epoxy resin has wide application in various industrial fields because of their good mechanical strength, superiority adhesion and low shrinkage etc. And the typical curing method for epoxy resins is thermal and press compaction. However, a curing method was used electron beam process in this study. Epoxy acrylate was fabricated from mixture of epoxy, acrylic acid, tetraphenylporphyrin (TPP) and hydroquinone monomethyl ether (MEHQ) with mole ratios. Then electron beam irradiation effect on the curing of the epoxy acrylate resin was investigated various absorption dose in nitrogen atmospheres at room temperature. The dynamic mechanical and thermal properties of the irradiated epoxy acrylate resins were characterized using dynamic mechanical analysis (DMA) and thermogravimetric analyzer (TGA). And the tensile and flexural strength were measured by an universal tensile machine (UTM).

• Journal of The Korean Society of Agricultural Engineers
• /
• v.54 no.6
• /
• pp.151-158
• /
• 2012

This study will not only prove experimental dynamic properties which are classified to slump, compressed strength, bending strength and toughness index blast-furnace cement concrete with polypropylene (PP) fiber that refer properties and volume of it, but also establish a basic data in order to use PP fiber reinforced blast-furnace cement concrete. The slump didn't changed by PP fiber volume $5kgf/m^3$ because of flexibility of fiber in despite of loose mixing. The reason why the slump decreased steadily by PP fiber volume $3kgf/m^3$ was rising contact surface of water. The compressed strength indicated a range of 19.49~26.32 MPa. The tensile strength indicated a range of 2.10~2.44 MPa. The bending strength was stronger about 3~16 % in case of mixing with PP fiber volume than normal concrete. The flexure strength indicated a range of 4.30~4.83 MPa. The toughness indicated a range of $0{\sim}19.88N{\cdot}mm$ and was stronger about 6.7 times in case of PP fiber volume $9kg/m^3$ than PP fiber volume $1kg/m^3$. The pavement with PP fiber volume over such a fixed quantity in the roads of a respectable amount load can have a effect to prevent not only resistance against clack but also rip off failures.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2015.11a
• /
• pp.118-119
• /
• 2015

Fracture behavior of concrete subjected to dynamic loading is affected by loading rate and strain rate. In this study, compressive strength properties according to strain rate of fiber reinforced cement composites by rapid loading with 500Ton rapid loading test machine was analyzed.

• Polymer(Korea)
• /
• v.26 no.3
• /
• pp.335-343
• /
• 2002

Blend resin (PET/PETG 70/30 blend) of poly (ethylene terephthalate) (PET) and poly (ethylene terephthalate glycol) (PETG) of weight percent 70/30 was prepared by a twin-screw extruder. Undrawn films of the blend and pure PETG were made by melt-press in hot press. Drawn films were made by capillary rheometer. Crystallinity, shrinkage, thermal, dynamic mechanical, and mechanical properties of these blends and PETG drawn films were investigated by wide angle X-ray diffractometer, dry oven, DSC thermal analyzer, and tensile tester. The crystallinity and density of these films increased with increasing draw ratio and draw rate but decreased with increasing draw temperature. The crystallinity and density of the blend films were higher than those of PETG films. The tensile strength and tensile modulus of these drawn alms increased with increasing draw ratio and draw rate but decreased with increasing draw temperature. The tensile strength and tensile modulus of blend films were higher than those of PETG films. Shrinkage of PETG md blend films decreased with draw ratio and draw rate. Shrinkage of undrawn blend film was 600% higher than that of pure PET film.