• International Journal of Concrete Structures and Materials
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• v.18 no.1E
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• pp.11-16
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• 2006

The use of the current ACI 318 stress block parameters has been reported to provide unconservative estimations of the moment capacities for high-strength concrete columns. Accordingly, several concrete stress block parameters have been recently proposed. This paper discusses various concrete stress block parameters for high-strength concrete and their influences on the code provisions. In order to adopt the proposed stress block parameters to the design code, it is necessary to understand the impact of the change of the stress block parameters on various aspects of the code provisions. For this purpose, the influence of using of different stress block parameters on the location of the neutral axis and the tensile strain in extreme tension steel as well as the axial and moment capacities are investigated. In addition, the influence on the prestressed concrete members is also elucididated.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.273-278
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• 2003

Recently, high-performance hybrid composite materials have been used for various industrial fields because of their superior high strength, high stiffness and lower weight. In this study, manufactured hybrid composite materials are composed of two parts. One is hard-anodized Al5083-O alloy as a face material and the other is high strength aramid fiber ($Twaron^{(R)}$ CT709) laminates as a back-up material. Resistance to penetration is determined by protection ballistic limit($V_{50}$, a static velocity with 50% probability for complete penetration) test method. $V_{50}$ tests with $0^{\circ}$obliquity at room temperature were conducted with 5.56mm ball projectiles that were able to achieve near or complete penetration during high velocity impact tests.

• Computers and Concrete
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• v.26 no.3
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• pp.275-283
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• 2020

Reinforced concrete (RC) does not provide sufficient resistance against impacts and blast loads, and the brittle structure of RC fails to protect against fractures due to the lack of shock absorption. Investigations on improving its resistance against explosion and impact have been actively conducted on high-performance fiber-reinforced cementitious composites (HPFRCCs), such as fiber-reinforced concrete and ultra-high-performance concrete. For these HPFRCCs, however, tensile strength and toughness are still significantly lower compared to compressive strength due to their limited fiber volume fraction. Therefore, in this study, the tensile behavior of slurry-infiltrated fiber-reinforced cementitious composites (SIFRCCs), which can accommodate a large number of steel fibers, was analyzed under static and dynamic loading to improve the shortcomings of RC and to enhance its explosion and impact resistance. The fiber volume fractions of SIFRCCs were set to 4%, 5%, and 6%, and three strain rate levels (maximum strain rate: 250 s^-1) were applied. As a result, the tensile strength exceeded 15 MPa under static load, and the dynamic tensile strength reached a maximum of 40 MPa. In addition, tensile characteristics, such as tensile strength, deformation capacity, and energy absorption capacity, were improved as the fiber volume fraction and strain rate increased.

• Korean Journal of Metals and Materials
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• v.48 no.9
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• pp.798-806
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• 2010

The effects of alloying elements and the cooling condition on the microstructure, tensile properties, and Charpy impact properties of high-strength bainitic steel plates fabricated by a controlled rolling process were investigated in the present study. Eight kinds of steel plates were fabricated by varying C, Cr, and Nb additions under two different cooling rates, and their microstructures and tensile and Charpy impact properties were evaluated. The microstructures present in the steels increased in the order of granular bainite, acicular ferrite, bainitic ferrite, and martensite as the carbon equivalent or cooling rate increased, which resulted in a decrease in the ductility and Charpy absorbed energy. The steels containing a considerable amount of bainitic ferrite or martensite showed very high strengths, together with good ductility and Charpy absorbed energy. In order to achieve the best combination of strength, ductility, and Charpy absorbed energy, granular bainite and acicular ferrite were properly included in the high-strength bainitic steels by controlling the carbon equivalent and cooling rate, while about 50 vol.% of bainitic ferrite or martensite was maintained to maintain the high strength.

• Journal of the Korean Wood Science and Technology
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• v.32 no.6
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• pp.67-73
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• 2004

The influence of liquefied wood (LW) on the mechanical and thermal properties of liquefied wood-polymer composites (LWPC) was investigated in this study. The thermal behaviors of LWPC were characterized by means of thermogravimetric (TGA) and differential scanning calorimetric (DSC) analyses. LW showed significant effects on the mechanical strength properties. The increase of flexural MOE and Young's modulus was related to the increase of stiffness of LWPC. The effect of LW was also significant on the flexural and tensile MOR. The impact strength decreased with the increase of LW application level. With the increased stress concentration by the poor bonding between LW and polymer, the impact strength of LWPC decreased, compared with that of high-density polyethylene (HDPE). The thermal stability of LWPC decreased with the increase of LW content up to 40%. The melting temperature of HDPE decreased with the increase of LW loading level. Enthalpy of HDPE also decreased with the addition of LW. This study proves the thermal stability necessary for the consolidation of composition materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.12
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• pp.3748-3758
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• 1996

This study is to investigate experimentally relationships between the impact energy and moisture absorption characteristies vs.the residual bending strength with the variation of stacking seqences. When Carbon-fiber reinforced plastics(CFRP) impact-induced laminates are subjected to the high temperatures and hygrothermal effects, it is found that what CFRP laminates are impacted by a steel ball (5 mm in diametar) ; thus, the generated delamination is observed by the ultrasonic microscope. And the residual bending strength is evaluated by a three-point bending test. Also, a thermostat is used in test with the unimpacted and impacted specimens for the moisture experimentaiton. The percision electro lever scles is used to measure the moisture content(1/10, 000g).

• Journal of the Korean Society for Precision Engineering
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• v.23 no.9 s.186
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• pp.149-155
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• 2006

This paper is concerned with the weight reduction of front side member of a vehicle considering the application of high strength steel sheet. The influence of steel sheet grade and thickness on the energy absorption, impact load and deformed shape of front side member is investigated by using reverse engineering and FE-analysis. The reverse engineering is applied to obtain 3D model of front side member from B.I.W for the FE simulation. FE analysis is carried out with commercial crash analysis SW PAM-CRASH. The crashworthiness of front side member is considerably improved with steel sheet strength and thickness increase. From the result of this study the weight reduction in automotive parts for the improvement of the fuel efficiency can be easily achieved with replacing high strength steel without deterioration of crashworthiness.

• Architectural research
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• v.18 no.4
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• pp.179-184
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• 2016

The structure must be periodically checked and measures must be taken to prevent deterioration in building construction. From this point of view, a nondestructive test is essential to estimate whether the construction of buildings is proper, and whether the dimension of depositing concrete is consistent and without damage. This study estimated the thickness of the concrete component of construction framework using the ultrasonic velocity method and the impact echo method, in order to investigate reliability of the estimation of the thickness of normal strength concrete and high strength concrete, leading to the following conclusions. In the estimation of the thickness of the concrete structures, specimens of normal strength of 24MPa and specimens of high strength of 40MPa demonstrated an average error rate of 5.1% and 2.2%, respectively. The impact-echo method, one of the non-destructive tests, is verified as an efficient diagnostic technique. With this information, we will determine specific standards for the maintenance of structures, and the re-creation of lost building blueprints.

• Journal of Powder Materials
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• v.1 no.2
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• pp.181-189
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• 1994

The compacts of pure and phosphorus-coated iron powder with 0~0.8%C were sintered at $1100^{\circ}C$ for 40 min. in cracked ammonia gas atmosphere. The tensile and impact strengths were measured and the relationship of the results with carbon content, phosphorus, quenching and tempering was investigated. The results obtained can be summarized as follows : (1) The tensile strength of sintered compacts increased slowly with carbon content. Increase in tensile strength by heat treatment was evident especially in the low carbon specimen. The specimen with phosphorus showed higher strength compared to pure iron compacts value. (2) No inflection point of elasticplastic deformation on stress-strain curve was observed in sintered steel. The elastic modulus of sintered steel had the same tendency as tensile strength. But the elongation showed the opposite tendency. (3) The impact absorption energy of sintered steel without addition of phosphorus decreased successively with carbon content and by quenching and tempering. On the contrary, addition of phosphorus resulted in an increase of the impact absorption energy. Quenching and tempering did not affect the impact energy especially in high carbon content. (4) The main fracture source was pore in specimen and the propagation of crack occured mostly along the grain boundaries. But the intragranular fracture was also observed in high carbon, quenched and tempered specimen, and especially in the specimen with phosphorus.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.3
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• pp.1-9
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• 2001

Impact tests are performed on the high strength structural steel that is being developed for the submarine material. Especially, the impact characteristics of this structural steels at low temperatures are investigated by charpy impact testing. Hyperbolic tangent curve fitting method is used to evaluate the LSE(lower shelf energy), USE(upper shelf energy) and DBTT(ductile-brittle transition temperature). Proportional equations between charpy impact energy and lateral expansion are obtained using the test results. Effect of temperature on the fracture appearance is investigated by using SEM.