• 제목/요약/키워드: Impact toughness

Search Result 365, Processing Time 0.078 seconds

A Study on the Impact Fracture Behavior of Side Plate for G/T 35ton Class FRP Vessel (35톤급 FRP선박 외판자재의 충격파괴거동에 관한 연구)

  • Lee, Jin-Jeong
    • Journal of Korea Ship Safrty Technology Authority
    • /
    • no.7
    • /
    • pp.64-76
    • /
    • 2008
  • This paper describes the failure mechanism and Charpy impact test of Fiber glass Reinforced Plastic composites which it was actually used for side plate of vessel. There are two examinations. The examination I, the specimens which it given temperature range $-25^{\circ}C$-$50^{\circ}C$ and with different initial notch length did impact test and then it compared impact energy(Uc) and impact fracture toughness(GIC). The examination II, the specimens which it putted into fresh water and sea water for scheduled hours did impact test and it compared impact energy(Uc) and impact fracture toughness(GIC). From examination I, it showed that impact energy(Uc) and impact fracture toughness(GIC) were peak at ambient temperature and decrease as temperature reduced. Fracture toughness(GIC) showed increase as initial notch length reduced. From examination II, impact energy(Uc) and impact fracture toughness(GIC) tended to increase which specimens putted in fresh water compared with sea water and maximum tolerance rate tend to decrease as permeation hours will be long.

  • PDF

Low Heat Input Welding to Improve Impact Toughness of Multipass FCAW-S Weld Metal

  • Bang, Kook-soo;Park, Chan;Jeong, Ho-shin
    • Journal of Ocean Engineering and Technology
    • /
    • v.28 no.6
    • /
    • pp.540-545
    • /
    • 2014
  • Multipass self-shielded flux cored arc welding with different heat inputs (1.3–2.0 kJ/mm) was conducted to determine the effects of the heat input on the proportion of the reheated region, impact toughness, and diffusible hydrogen content in the weld metal. The reheated region showed twice the impact toughness of the as-deposited region because of its fine grained ferritic-pearlitic microstructure. With decreasing heat input, the proportion of the reheated region in the weld metal became higher, even if the depth of the region became shallower. Accordingly, the greatest impact toughness, 69 J at −40℃, was obtained for the lowest heat input welding, 1.3 kJ/mm. Irrespective of the heat input, little difference was observed in the hardness and diffusible hydrogen content in the weld metal. This result implies that low heat input welding with 1.3 kJ/mm can be performed to obtain a higher proportion of reheated region and thus greater impact toughness for the weld metal without the concern of hydrogen cracking.

An Evaluation of Notch Shpae for Estimation of Available $K_{1d}$ by Instrumented Charpy Impact Test (유효 $K_{1d}$ 산정을 위한 샬피 충격시험편의 노치형상에 관한 연구)

  • 우창기;강동명;이하성
    • Transactions of the Korean Society of Automotive Engineers
    • /
    • v.7 no.6
    • /
    • pp.135-143
    • /
    • 1999
  • This investigation evaluates effects of notch depth, fatigue precrack length and side groove in impact specimen for estimation of a valid K1d by instrumented Charpy impact test. Specimen material is 6005-T6. for notch depth 2.0mm and 2.5mm specimens or within about 2mm fatigue precrack length with notch depth 2.0mm and 2.5mm specimens or within about 2mm fatigue precrack length with notch depth 2.0mm , dynamic fracture toughness [$K_{1d,(1)}$] obtained by crack initiation load($P_m$) should be used. Dynamic fracture toughness of side grooved specimens are overestimated to that of standard impact specimen about 15 %-20%. It is confirmed that the formula of dynamic fracture toughness obtained by impact absorbed energy is inappropriate for ductile materials.

  • PDF

Evaluation of Fracture Toughness and Microstructure on FCA Weldment According to Heat Input (입열량에 따른 FCAW용접부 파괴인성에 미치는 미세조직의 영향)

  • Shin, Yong-Taek;Kang, Sung-Won;Kim, Myung-Hyun
    • Journal of Welding and Joining
    • /
    • v.26 no.3
    • /
    • pp.51-60
    • /
    • 2008
  • This paper is to evaluate fracture characteristics of API 2W Gr.50 TMCP steel weldment typically applied for offshore structures, with the focus on the influence of heat input arising from flux cored arc welding. Based on the results and insights developed from this study, it is found that the toughness for both CTOD and impact exhibits a tendency to decrease as the weld heat input increases. The reheated zone of weldmetal exhibit lower hardness than solidified zone and microstructure that are liable to affect the toughness are acicular ferrite and martensite-austenite constituents (M-A). In particular, M-A is a more effective micro-phase for CTOD toughness than impact toughness.

Effect of oxygen content on impact toughness of austenitic-and duplex stainless steel weld metal (오스나이트계 및 이상계스테인레스강 용착부의 산소가 충격인성에 미치는 영향)

  • 문영훈;김환태;허성도
    • Journal of Welding and Joining
    • /
    • v.5 no.3
    • /
    • pp.38-45
    • /
    • 1987
  • An investigation was conducted to find out the factors influencing on the impact toughness of austenitic-and duplex stainless steel weld metal. Various welding process with commerically available consumables was adopted to get weld doposited metal. The oxygen content of each weld metal was very sensitiive to welding process, involving flux composition, shielding gas and structural features. The results of this study show tat the content of oxygen as an oxide inclusion significantly affects impact toughness, and .delta.-ferrite distribution is also correlated with resultant toughness value.

  • PDF

Effects of Heat Input and Preheat/interpass Temperature on Strength and Impact Toughness of Multipass Welded Low Alloy Steel Weld Metal (다층용접한 저합금 용접금속의 강도와 인성에 미치는 입열량 및 예열/패스간 온도의 영향)

  • Bang, Kook-soo;Jung, Ho-shin;Park, Chan
    • Journal of Ocean Engineering and Technology
    • /
    • v.29 no.6
    • /
    • pp.481-487
    • /
    • 2015
  • The effects of the heat input and preheat/interpass temperatures on the tensile strength and impact toughness of multipass welded weld metal were investigated and interpreted in terms of the recovery of the alloying elements and microstructure. Increases in both the heat input and preheat/interpass temperatures decreased the tensile strength of the weld metal. A lower recovery of alloying elements, especially Mn and Si, and smaller area fraction of acicular ferrite in the weld metal were observed in higher heat input welding, resulting in a lower tensile strength. In contrast, only a microstructure difference was observed at a higher preheat/interpass temperature. The impact toughness of the weld metal gradually increased with an increase in the heat input because of the lower tensile strength. However, it decreased again when the heat input was larger than 45 kJ/cm because of the much smaller area fraction of acicular ferrite. No effect of the preheat/interpass temperature on the impact toughness was observed. The formation of a weld metal heat-affect zone showed little effect on the impact toughness of the weld metal in this experiment.

Effect of Microstructural Factors on Room- and Low-Temperature Impact Toughness of Hypoeutectoid Steels with Ferrite-Pearlite Structure (페라이트-펄라이트 조직 아공석강의 상온 및 저온 충격 인성에 미치는 미세조직적 인자의 영향)

  • Lee, Seung-Yong;Jeong, Sang-Woo;Hwang, Byoungchul
    • Korean Journal of Materials Research
    • /
    • v.25 no.11
    • /
    • pp.583-589
    • /
    • 2015
  • This paper presents a study on the room- and low-temperature impact toughness of hypoeutectoid steels with ferrite-pearlite structures. Six kinds of hypoeutectoid steel specimens were fabricated by varying the carbon content and austenitizing temperature to investigate the effect of microstructural factors such as pearlite volume fraction, interlamellar spacing, and cementite thickness on the impact toughness. The pearlite volume fraction usually increased with increasing carbon content and austenitizing temperature, while the pearlite interlamellar spacing and cementite thickness mostly decreased with increasing carbon content and austenitizing temperature. The 30C steel with medium pearlite volume fraction and higher manganese content, on the other hand, even though it had a higher volume fraction of pearlite than did the 20C steel, showed a better low-temperature toughness due to its having the lowest ductile-brittle transition temperature. This is because various microstructural factors in addition to the pearlite volume fraction largely affect the ductile-brittle transition temperature and low-temperature toughness of hypoeutectoid steels with ferrite-pearlite structure. In order to improve the room- and low-temperature impact toughness of hypoeutectoid steels with different ferrite-pearlite structures, therefore, more systematic studies are required to understand the effects of various microstructural factors on impact toughness, with a viewpoint of ductile-brittle transition temperature.

Impact Toughness and Softening of the Heat Affected Zone of High Heat Input Welded 390 MPa Yield Strength Grade TMCP Steel (항복강도 390 MPa급 가공열처리강 대입열용접 열영향부 충격인성 및 연화현상)

  • Bang, Kook-Soo;Ahn, Young-Ho;Jeong, Hong-Chul
    • Korean Journal of Metals and Materials
    • /
    • v.56 no.11
    • /
    • pp.796-804
    • /
    • 2018
  • The Charpy impact toughness of the heat affected zone (HAZ) of electro gas welded 390 MPa yield strength grade steel, manufactured by a thermo mechanically controlled process, was investigated. The effects of added Nb on the toughness of the steel and the factors influencing scatter in toughness are discussed in the present work. It was observed that adding Nb to the steel led to the deterioration of HAZ toughness. The presence of soluble Nb in the HAZ increased its hardenability and resulted in a larger amount of low toughness bainitic microstructure. Microstructural observations in the notch root area revealed the significant role of different microstructures in the area. In the presence of a larger amount of bainitic microstructures, the HAZ exhibited a lower Charpy toughness with a larger scatter in toughness. A softened zone with a lower hardness than the base metal was formed in the HAZ. However, theoretical analysis revealed that the presence of the zone might not be a problem in a real welded joint because of the plastic restraint effect enforced by surrounding materials.

Impact Toughness and Fracture Behavior in Non-Heat Treating Steels Containing Bainite (베이나이트 함유 비조질강의 충격인성 및 파괴거동)

  • Cho, Ki-Sub;Kwon, Hoon
    • Journal of the Korean Society for Heat Treatment
    • /
    • v.32 no.4
    • /
    • pp.161-167
    • /
    • 2019
  • Impact toughness and fracture behavior were studied in five kinds of non-heat treating steels containing bainite; standard(0.25C-1.5Mn-0.5Cr-0.2Mo-0.15V), high V(0.3V), Ni(0.5Mn-2Ni), W(0.4W instead of Mo), and high C-Ni(0.35C-0.5Mn-2Ni) steels. The good hardness and impact toughness balance was exhibited in the $1100^{\circ}C$-rolled condition, while the impact toughness was deteriorated due to coarse grained microstructure in the $1200^{\circ}C$-rolled condition. The impact toughness decreased with increasing the hardness in all steels studied. The fracture behavior was also basically identical, that is, the fracture area was divided into 3 zones; shear and fibrous zone, fracture transition zone with ductile dimples and cleavage cracks, where the cracks initiate and grow to critical size, unstable cleavage fracture propagation zone. The energy absorbed for the critical crack formation through the plastic deformation inside the plastic zone in front of the notch root contributed to a mostly significant portion of the total impact energy.

Fracture Toughness and AE Behavior of Impact-Damaged CFRP (탄소섬유복합재료의 충격 손상에 따른 파괴 인성과 AE 특성)

  • Lee, S.G.;Nam, K.W.;Oh, S.K.
    • Journal of the Korean Society for Nondestructive Testing
    • /
    • v.17 no.2
    • /
    • pp.81-88
    • /
    • 1997
  • Impact behavior of carbon fiber reinforced plastics (CFRP) laminates were evaluated with tension test and compact tension test. A steel ball launched by an air gun collides against CFRP laminates to generate impact damage of relatively low energy. The static tensile and fracture toughness tests were performed to evaluate the residual strength and the AE behavior of impact-damaged laminates. As a results, it was found that the static strength, the fracture toughness and the AE-event count were decreased with increasing of impact velocity and delamination area, and to have a different strength ratio and fracture toughness ratio for each stacking method. And also, it was confirmed that strength and fracture toughness of impact-damaged CFRP laminates could be evaluated and analyzed quantitatively by AE techniques.

  • PDF