Strain rate effects on the compressive and tensile behavior of bundle-type polyamide fiber-reinforced cementitious composites

Kim, Hongseop,Kim, Gyuyong,Lee, Sangkyu,Son, Minjae,Choe, Gyeongcheol,Nam, Jeongsoo Elsevier 2019 Composites. Part B, Engineering Vol.160 No.-

<P><B>Abstract</B></P> <P>The compressive and tensile behavior of fiber-reinforced cementitious composites is significantly affected by the bonding and pull-out properties between matrix and reinforced fiber, as well as the fracture properties of the fibers. In addition, an increase in strain rate according to loading conditions influences the fracture behavior between the fiber and matrix. Steel fiber-reinforced cementitious composites with high flexural and tensile strength, toughness, and crack resistance are widely used in tunnels and plant structures. However, the high specific gravity and stiffness of steel fibers can cause rupture of concrete pump tubes, increase the rebound volume of shotcrete, and decrease durability by corrosion of fiber. Therefore, it is necessary to study the development and application of organic fiber which has similar mechanical properties to steel fiber and does not cause corrosion. In this study, polyamide fibers having the same aspect ratio as the hooked steel fibers, which are widely used as reinforcing fibers for concrete, have been developed. And strain rate effect on the compressive and tensile behaviors of bundle-type polyamide fiber-reinforced cementitious composite and hooked steel fiber-reinforced cementitious composite were evaluated. The results showed that the effect of strain rate over different fiber types influenced the tensile behavior more significantly than the compressive behavior. In polyamide fiber-reinforced cementitious composite (PAFRCC), a fracture behavior of fiber was observed regardless of a strain rate, and the tensile behavior of PAFRCC was influenced more by tensile strength of polyamide fiber itself than a bonding stress between fiber and matrix. In hooked steel fiber-reinforced cementitious composite (HSFRCC), a bonding stress between hooked steel fiber and matrix (frictional force at the interface between fiber and matrix, mechanical bond of the hooked part) influenced the tensile behavior significantly. Fracture properties that straightened pulled out the fiber from the matrix were observed at static tensile loading condition. However, non-straightened hooked steel fiber was observed along with the fracture of matrix due to an increase in mechanical bonding force of the hooked part and the bonding stress between the fiber and the matrix.</P>

Study on Assembly and Tensile Performance of Circumferential Anchor Joint for Shield Tunnel Considering Roughness and Size of Structure

Gaole Zhang,Wenjun Zhang,Jiahao Li,Xinnan Zhou,Wang Liu,Jianbing Qi 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.5

Anchor joint is conducive to improving the automation level of the shield tunneling method, whose mechanical behavior is still not fully clear due to the complicated interaction among various structural components. In this paper, a refined FEM model is established and adopted to investigate the anchor joints' assembly and tensile performance. The operation principles of the anchor joint are first introduced for better understanding. Then, a detailed description is presented for the developed refined FEM, including the material properties, structural features, and verification. After that, 76 working conditions in total are set, and an in-depth study is conducted to examine the influence of surface roughness, gap sizes, and strength grades on the assembly and tensile behavior of anchor joints both quantitatively and qualitatively. The results show that the surface roughness mainly influences the maximum assembly load and tensile capacity of anchor joints. The gap size obviously impacts both quantitative and qualitative assembly characteristics and tensile behavior for anchor joints, whose effect is more significant than the surface roughness. The strength grade has a different influence on the distinct mechanical behavior of anchor joints. There is a positive correlation between anchor joints' assembly and tensile behavior. To satisfy the requirement of enough tensile capacity and reasonable assembly difficulty, a good solution should be to reach an appropriate balance between the assembly and tensile behavior of anchor joints.

저온 분사 공정으로 제조된 초고강도 Cu 벌크 소재의 인장 및 압축 변형 거동

김영균,이기안 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.11

In this study, high-strength pure Cu bulk material was manufactured using a cold spray additive manufacturing process, and its microstructure, tensile and compressive deformation behaviors were investigated and compared. The cold spray additive manufactured Cu bulk material showed a heterogeneous grain structure consisting of fine-grains and coarse-grains, and only α – Cu single phase was identified. The cold spray Cu exhibited yield strengths of ~415 MPa in tensile- and compression tests, indicating that it had similar mechanical properties in different deformation modes. The yield strength values were similar to that of Cu manufactured by equal channel angular pressing (ECAP), a severe plastic deformation (SPD) method which enables ultra-high strength. Concerning tensile characteristics, the cold sprayed Cu exhibited partial plastic deformation that has not been reported to date. In addition, some nano-sized dimples, suggesting metallurgical bonding, were also found in the fracture surface. Regarding compression characteristics, the strain softening phenomenon, which is not a general tendency in room temperature deformation, appeared. This unique softening behavior was attributed to dynamic recovery and dynamic recrystallization during compression testing. Based on the above results, we discuss the tensile/compressive deformation behavior of the cold spray Cu bulk material, and predict compressive deformation behavior considering the constitutive equation.

콘크리트 보강용 고연성 하이브리드 FRP 보강근의 인장 및 파괴 특성

박찬기,원종필,Park, Chan-Gi,Won, Jong-Pil 한국농공학회 2004 한국농공학회논문집 Vol.46 No.1

FRP re-bar in concrete structures could be used as a substitute of steel re-bars for that cases in which aggressive environment produce high steel corrosion, or lightweight is an important design factor, or transportation cost increase significantly with the weight of the materials. But FRP fibers have only linearly elastic stress-strain behavior; whereas, steel re-bar has linear elastic behavior up to the yield point followed by large plastic deformation and strain hardening. Thus, the current FRP re-bars are not suitable concrete reinforcement where a large amount of plastic deformation prior to collapse is required. The main objectives of this study in to evaluate the tensile behavior and the fracture mode of hybrid FRP re-bar. Fracture mode of hybrid FRP re-bar is unique. The only feature common to the failure of the hybrid FRP re-bars and the composite is the random fiber fracture and multilevel fracture of sleeve fibers, and the resin laceration behavior in both the sleeve and the core areas. Also, the result of the tensile and interlaminar shear stress test results of hybrid FRP re-bar can provide its excellent tensile strength-strain and interlaminar stress-strain behavior.

High-temperature tensile deformation behavior of hot rolled CrMnFeCoNi high-entropy alloy

Jang, Min Ji,Praveen, S.,Sung, Hyun Je,Bae, Jae Wung,Moon, Jongun,Kim, Hyoung Seop Elsevier 2018 Journal of Alloys and Compounds Vol.730 No.-

<P><B>Abstract</B></P> <P>In the present study, high temperature (700–1100 °C) tensile deformation behavior of hot-rolled CrMnFeCoNi high-entropy alloy was investigated. A single face-centered cubic phase was retained in the hot deformed specimens under different deformation conditions. The flow behavior was significantly influenced by temperature and microstructure evolution. A strong temperature dependence of yield stress was observed with a drastic drop in yield strength from 413 MPa at 700 °C to 94 MPa at 900 °C. A profound increase in ductility was observed above 700 °C and a perceptive decrease in ductility was observed above 900 °C. Electron backscatter diffraction analysis indicates incomplete dynamic recrystallization at 700 °C leading to a significant difference in the flow behavior.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The high-temperature tensile deformation behavior of hot rolled HEA was studied. </LI> <LI> FCC single phase is retained during hot deformation. </LI> <LI> The yield stress strongly depends on the testing temperature. </LI> <LI> A profound increase in ductility was observed at 900 °C due to DRX. </LI> <LI> Steady-state flow stress was observed in the samples tested above 700 °C. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Structural Behavior of 3D Printed Concrete Specimens with Reinforcement

Changbin Joh(조창빈),Jungwoo Lee(이장우),In-Hwan Yang(양인환) 한국건설순환자원학회 2018 한국건설순환자원학회 논문집 Vol.6 No.3

본 연구에서는 프린트 층 사이에 부착에 초점을 두고 3D 프린팅 콘크리트의 구조거동 연구를 수행하였다. 3D 프린팅 콘크리트의 부착 및 인장강도 실험을 수행하고 일괄 타설 콘크리트 실험결과와 비교하였다. 실험변수는 콘크리트 층 사이의 프린트시간차와 철근 보강 여부이다. 콘크리트 층 사이에는 공극이 존재하고 이에 따라, 강도 감소가 발생한다. 층 사이 대부분의 인장부착 강도 감소는 응력 집중과 프린트 시간차에 기인한다. 프린트 시간차가 24시간을 초과할 때 인장부착 강도의 감소는 구조거동에 영향을 미친다. 층 사이 철근 보강은 연성거동 증진에 유용하고 구조물의 갑작스런 파괴를 예방한다. 또한, 공극이 유발한 응력 집중에 기인한 휨 강도 감소는 횡방향 하중을 받는 3D 프린트 벽체 구조물 설계시에 고려되어야 한다. This paper examines the structural behavior of 3D printed concrete specimens with focus on the bond between the layers. The tensile bond and flexural strengths were investigated experimentally and compared with those of specimens made by conventional mold casting. The test parameters were the time gap between printing layers and the reinforcement between vertical layers. The results showed the 3D printed specimens had voids between layers and confirmed the strength reduction due to printing time gap and the stress concentration caused by the voids. Most of the reduction in tensile bond strength between layers was due to the stress concentration at least up to certain printing time gap. Moreover, beyond a certain printing time gap (24hours), the additional reduction in tensile bond strength reached a level that could affect the structural behavior. The reinforcement between layers was helpful to increase the ductile behavior which is essential to prevent the sudden collapse of the structure. In addition, the reduction in flexural strength due to the stress concentration by the voids was observed and should be considered in the design of 3D printed wall structures against the lateral load.

Deformation behavior and tensile properties of an austenitic Fe-24Mn-4Cr-0.5C high-manganese steel: Effect of grain size

Lee, Sang-In,Lee, Seung-Yong,Han, Jeongho,Hwang, Byoungchul Elsevier 2019 Materials science & engineering. properties, micro Vol.742 No.-

<P><B>Abstract</B></P> <P>Deformation behavior and tensile properties of an austenitic Fe-24Mn-4Cr-0.5C high-manganese steel with different grain sizes were discussed in this study. Effective grain size including annealing twins and stacking fault energy increased with increasing annealing temperature from 800 °C to 1200 °C. Room-temperature tensile test results indicated that the yield and tensile strengths increased, but the total elongation decreased with decreasing the effective grain size. According to electron back-scattered diffraction and transmission electron microscopy analyses, the deformed microstructure of all the specimens having stacking fault energy between 24.0 mJ/m<SUP>2</SUP> and 31.6 mJ/m<SUP>2</SUP> showed deformation twinning. However, the formation of the deformation twinning was suppressed with decreasing the grain size, resulting in different work hardening behaviors. Experimental and calculated twinning stress increased with decreasing the grain size because dislocation activity and the movement of partial dislocations required for form the deformation twinning were further inhibited by interaction of relatively high dislocation density in specimens with finer grain size.</P>

하이브리드 FRP 리바의 역학적 특성

박찬기 ( Park Chan Gi ),원종필 ( Won Jong Pil ) 한국농공학회 2003 韓國農工學會誌 : 전원과 자원 Vol.45 No.2

Over the last decade fiber-reinforced polymer (FRP) reinforcement consisting of glass, carbon, or aramid fibers embedded in a resin such as vinyl ester, epoxy, or polyester has emerged as one of the most promising and affordable solutions to the corrosion problems of steel reinforcement in structural concrete. But reinforcing rebar for concrete made of FRP rebar has linear elastic behavior up to tensile failure. For safety a certain plastic strain and an elongation greater than 3% at maximum load is usually required for steel reinforcement in concrete structures. The same should be required for FRP rebar. Thus, the main object of this study was to develop new type of hybrid FRP rebar Also, this study was evaluated to the mechanical properties of Hybrid FRP rebar. The Manufacture of the hybrid FRP rebar was achieved by pultrusion, and braiding and filament winding techniques. Tensile and interlaminar shear test results of Hybrid FRP rebar can provide its excellent tensile strength-strain behavior and interlaminar stress-strain behavior.

UV 폭로 및 동결융해 시험을 거친 FRP Hybrid Bar의 인장거동 평가

윤용식(Yong-Sik Yoon),박재성(Jae-Sung Park),박기태(Ki-Tae Park),권성준(Seung-Jun Kwon) 한국건설순환자원학회 2017 한국건설순환자원학회 논문집 Vol.5 No.2

본 연구에서는 UV 폭로 및 동결융해 환경이 FRP Hybrid Bar의 인장거동 및 표면 열화에 미치는 영향을 평가하기 위해 FRP Hybrid Bar를 대상으로 UV 폭로 및 동결융해 시험을 실시하였다. FRP Hybrid Bar의 경우 UV 폭로 및 동결융해 180cycle 시험 전/후 외관적인 열화가 거의 발생하지 않았다. 또한 FRP Hybrid Bar의 주요 장점 중 하나인 인장경화특성은 동결융해시험을 거친 이후에도 유지되었는데, 이는 UV 폭로시험을 거친 FRP Hybrid Bar에도 유효하게 평가되었다. UV 폭로시험을 거친 FRP Hybrid Bar는 일반 FRP Hybrid Bar와 거의 비슷한 인장거동을 나타내었으며, 동결융해 180cycle의 진행에도 불구하고 일반철근, FRP Hybrid Bar, UV 폭로를 거친 FRP Hybrid Bar의 인장거동은 큰 변화를 나타내지 않았다. 본 연구에서는 UV 폭로 및 동결융해 환경이 FRP Hybrid Bar의 외관 및 인장 특성에 큰 영향을 미치지 못하는 것으로 판단되지만, 충격에 따른 규사코팅의 박락은 콘크리트와의 부착력에 영향을 미치므로 이에 대한 고려가 필요하다. The present work is for an evaluation of tension behavior and surface deterioration of FRP Hybrid Bar due to UV exposure and freezing/thawing(F/T) actions. For the work, FRP Hybrid Bar is subjected to UV exposure test, then F/T test is performed successively to 180 cycles. In FRP Hybrid Bar, no significant surface deterioration is evaluated after UV exposure. Tension hardening performance, a unique engineering advantage of FRP Hybrid Bar, is still maintained after F/T test. The performance in FRP Hybrid Bar exposed to UV is still effective. FRP Hybrid Bar exposed to UV have almost similar tension behavior of FRP Hybrid Bar without UV exposure. Although F/T cycles increase to 180, steel rebar, FRP Hybrid Bar, and FRP Hybrid Bar exposed to UV show no significant changes in tension behavior. In the work, UV exposure and F/T actions are evaluated to have little negative effect on surface deterioration and tensile performance in FRP Hybrid Bar, however spalling of silica coating due to impact should be considered since it affects bonding strength to outer concrete.

항복함수에 따른 이방성 경화거동의 근사성능 평가

배기현(G. H. Bae) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.10

This paper evaluates performance of anisotropic yield function to approximate the uni-axial hardening behavior with respect to the loading angle from the rolling direction. Three yield functions, such as Hill48, YJd89 and Yld2000-2d, are selected to approximate the anisotropic hardening behavior. The test material is 340ES steel sheet with the thickness of 0.65 ㎜. The results show that more advanced material model is required to describe the anisotropy change with the increase of the plastic strain.