• Steel and Composite Structures
• /
• v.22 no.2
• /
• pp.387-398
• /
• 2016

In order to evaluate the effects of U shape ultra high performance concrete (UHPC) permanent form on the behaviors of Reinforced Concrete (RC) beam, a full scale RC composite beam is designed and tested with U shape UHPC permanent form and a reference RC beam with same parameters is tested simultaneously for comparison. The effects of the permanent form on the failure mode, cracking strength, ultimate capacity and deformation are studied. Test results shows that the contributions of the U shape UHPC permanent form to the flexural cracking behaviors of RC beam are significant. This study may provide a reference for the design of sustainable RC beam with high durable UHPC permanent form.

• Journal of Welding and Joining
• /
• v.18 no.2
• /
• pp.86-94
• /
• 2000

This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7N01 spot-welded by pulse Nd : YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed : center line crack({TEX}$C_{C}${/TEX}), diagonal crack({TEX}$C_{D}${/TEX}), and U shape crack({TEX}$C_{U}${/TEX}). Also, HAZ crack({TEX}$C_{H}${/TEX}) was observed in the HAZ region, furthermore, mixing crack({TEX}$C_{M}${/TEX}) consisting of diagonal crack and HAZ crack was observed. White film was formed at th hot crack region in the fractured surface after it was immersed to 10% NaOH water. In the case of A5083 alloy, white films in {TEX}$C_{C}${/TEX} crack and {TEX}$C_{D}${/TEX} crack region were composed of low melting phases, {TEX}$Fe_{2}SiAl_{8}${/TEX} and eutectic phases, $Mg_2$Al$_3$ and $Mg_2$Si. Such films observed $CuAl_2$, {TEX}$Mg_{32}(Al,Zn)_{3}${/TEX}, MgZn$_2$, $Al_2$CuMg and $Mg_2$Si were observed in the whitely etched films near {TEX}$C_{C}${/TEX} crack and {TEX}$C_{D}${/TEX} crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Sim in the case of A7N01 alloy, respectively. The {TEX}$C_{C}${/TEX} and {TEX}$C_{D}${/TEX} cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of {TEX}$C_{M}${/TEX} crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The {TEX}$C_{U}${/TEX} crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification.

• Journal of Welding and Joining
• /
• v.18 no.2
• /
• pp.213-213
• /
• 2000

This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7NO1 spot-welded by pulse Nd: YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed: center line crack($C_{C}$), diagonal crack($C_{D}$), and U shape crack($C_{U}$). Also, HAZ crack($C_{H}$), was observed in the HAZ region, furthermore, mixing crack($C_{M}$), consisting of diagonal crack and HAZ crack was observed.White film was formed at the hot crack region in the fractured surface after it was immersed to 10%NaOH water. In the case of A5083 alloy, white films in C crack and $C_D crack region were composed of low melting phases, Fe₂Si$Al_8$ and eutectic phases, Mg₂Al₃ and Mg₂Si. Such films observed near HAZ crack were also consist of eutectic Mg₂Al₃. In the case of A7N01 alloy, eutectic phases of CuAl₂, $Mg_{32}$ (Al,Zn) ₃, MgZn₂, Al₂CuMg and Mg₂Si were observed in the whitely etched films near $C_{C}$ crack and $C_{D}$ crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Si in the case of A7N01 aooly, respectively.The $C_{D}$ and $C_{C}$ cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of $C_{M}$ crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The $C_{U}$ crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification. (Received October 7, 1999)

• Structural Engineering and Mechanics
• /
• v.63 no.5
• /
• pp.575-583
• /
• 2017

The study covers the behavior of reinforced concrete deep beams loaded under 4-point bending, failed by shear and repaired using bonding glass fiber reinforced plastics fabrics (GFRP) patches. Two rehabilitation methods have been used to highlight the influence of the composite on the ultimate strength of the beams and their failure modes. In the first series of trials the work has been focused on the reinforcement/rehabilitation of the beam by following the continuous configuration of the FRP fabric. The patch with a U-shape did not provide satisfactory results because this reinforcement strategy does not allow to increase the ultimate strength or to avoid the abrupt shear failure mode. A second methodology of rehabilitation/reinforcement has been developed in the form of SCR (Strips of Critical Region), in which the composite materials reinforcements are positioned to band the inclined cracks (shear) caused by the shear force. The results obtained by using this method lead a superior out come in terms of ultimate strength and change of the failure mode from abrupt shearing to ductile bending.

• Korean Journal of Materials Research
• /
• v.8 no.8
• /
• pp.766-774
• /
• 1998

32$0^{\circ}C$, 40%NaOH 용액의 autoclave에서 약 300wppm의 탄소를 함유하고 있는 15Cr-9Fe-balanced Ni 합금 판상시편에 대해 응력부식 저항성을 조사하였다. 부식시편은 $700^{\circ}C$, 100시간 동안의 열처리로 합금내부에 석출될 수 있는 가능한 한 많은 양의 크롬계 탄화물을 석출시킨 후, 다시 재용해에 의해 크롬계 탄화물의 형태를 조절하는 $800^{\circ}C$-$950^{\circ}C$범위의 최종열처리를 시행하고 급냉시킨 다음 U-자형으로 응력을 가하여 준비되었다. 최종열처리 온도가 올라감에 따라 시편들의 입계응력부식균열(IGSCC ) 전파속도는 $900^{\circ}C$까지는 거의 직선적으로 증가하다가 $950^{\circ}C$에서는 $700^{\circ}C$에서 얻은 값보다도 더 낮게 감소하였다. 즉, 크롬계 탄화물이 재용해되어 그 밀도가 감소함에 따라 IGSCC저항성이 감소하다가 완전히 재용해된 $950^{\circ}C$ 열처리 조건에서 오히겨 가장 큰 IGSCC 저항성을 나타내었다. 이와같은 최조열처리 온도에 따른 니켈계 합금 600의 부식거동은 입계에 존재하는 크롬계탄화물의 형태변화 때문이 아니라 입계에서 탄소-크롬계 탄화물-크롬간의 상평형에 의해 이루어지는 탄소의 입계편석량이 크롬계탄화물이 존재할 때에는 열처리 온도에 따라 증가하다가 그것이 완전히 재용해 되었을 때 가장 낮아지기 때문인 것으로 생각된다.