Shear-fatigue behavior of high-strength reinforced concrete beams under repeated loading

Kwak, Kae-Hwan,Park, Jong-Gun Techno-Press 2001 Structural Engineering and Mechanics, An Int'l Jou Vol.11 No.3

The purpose of this experimental study is to investigate the damage mechanism due to shear-fatigue behavior of high-strength reinforced concrete beams under repeated loading. The relationship between the number of cycles and the deflection or strain, the crack growths and modes of failure with the increase of number of cycles, fatigue strength, and S-N curve were observed through a fatigue test. Based on the fatigue test results, high-strength reinforced concrete beams failed at 57-66 percent of static ultimate strength for 2 million cycles. The fatigue strength at 2 million cycles from S-N curves was shown as about 60 percent of static ultimate strength. Compared to normal-strength reinforced concrete beams, fatigue capacity of high-strength reinforced concrete beams was similar to or lower than fatigue capacity of normal-strength reinforced concrete beams. Fatigue capacity of normal-strength reinforced concrete beams improved by over 60 percent.

Experimental Investigation on Fatigue Strength of Joints between SRC Beams and Concrete-Filled RHS Columns

Qingjun Xian,Le-Wei Tong,Liying Zhou,Yiyi Chen 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.5

Fatigue behavior, failure mechanism and fatigue strength of joints between steel reinforced concrete (SRC) beams and Concrete Filled Rectangular Hollow Section (CFRHS) columns is discussed in this paper. Three identical beam-to-column joint specimens were designed and tested under static loading and two stages of fatigue loading. In the first stage of fatigue loading, the specimens were subjected to design fatigue load for 2 million cycles, while during the second stage, they were loaded to failure under increased fatigue load in order to know failure mechanism and fatigue strength. It is found that the joints satisfied design requirements when subjected to static loading and design fatigue loading. Fatigue failure occurred after these joints were applied higher-level fatigue loading. The crack initiated at the weld toe of stud or stirrup hole in the upper flange of I-shaped steel in certain SRC beam, and then it propagated along flange width in winding trajectory until fatigue fracture occurred. Stress amplitude of tension flange in SRC beam can be regarded as the parameter representing fatigue strength of the joints. S-N curves in related codes are selected to evaluate fatigue strength of the joints. The design method is suggested to consider fatigue design of the joints.

열적, 기계적 피로응력이 교정용 브라켓의 결합강도에 미치는 영향

김정기,김상철 대한치과교정학회 2000 대한치과교정학회지 Vol.30 No.5

본 연구는 열적 및 기계적 피로응력이 교정용 브라켓의 전단결합강도, 인장결합강도, 전단-인장 복합 결합강도에 미치는 영향과 결합상태에 미치는 영향, 그리고 접착파절 양상을 비교하는데 목적이 있다. 이를 위하여 기저부 형태가 다른 5종의 금속 브라켓을 교정치료를 목적으로 발거한 상 · 하악 소구치에 부착하여, 계면에 200g의 전단-인장 복합 하중을 4주간 가한 기계적 피로시험과, 5,000회의 thermocycling을 시행한 열적 피로시험 후, 전단결합강도, 인장결합강도, 및 전단-인장 복합 결합강도를 측정하고, 파절양상을 분석하여 다음과 같은 결과를 얻었다. 1.정적시험에서 얻은 브라켓 접착부의 결합강도는 Photoetched base가 가장 크고, Integral base가 가장 작았다(p〈0.05). 모든 종류의 브라켓에서 전단결합강도가 가장 컸으며, 전단-인장 복합 결합강도는 전단결합강도의 1/3 수준으로 가장 작았다. 2.4주간 200g의 전단-인장 복합 하중을 가한 후의 결합강도는 Photoetched base가 가장 크고, Integral base가 가장 작았으며(p〈0.05), 기계적 피로시험 후 Photoetched base와 Micro-Etched Foil Mesh base의 전단, 인장, 전단-인장 복합 결합강도가 감소하였고, Chessboard base의 전단결합강도가 감소하였다(p〈0.05). 3.5,000회의 thermocycling 후의 결합강도는 Photoetched base가 가장 컸고, Integral base가 가장 작았으며 (p〈0.05), 열적 피로시험 후 Photoetched base와 Chessboard base, Micro-Etched Foil Mesh base의 결합강도가 모두 감소하였다(p〈0.05). 4.정적시험의 결합강도 측정 후 접착파절은 브라켓/레진 계면에서 일어났으며, thermocycling 후에는 브라켓/레진 계면과, 법랑질/레진 계면, 레진내 파절이 혼합되어 나타나 ARI점수가 높아졌다. 기계적 피로시험 후에는 정적시험 때와 비슷한 ARI 점수를 보였다. 5.모든 브라켓에서 thermocycling 후 브라켓/레진 계면과 법랑질/레진 계면에서 미세 균열이 관찰되었다. The purpose of this study is to evaluate the effects of mechanical and thermal fatigue stress on the shear, tensile and shear-tensile combined bond strengths(SBS, TBS, CBS) in various orthodontic brackets bonded to human premolars with chemically cured adhesive(Ortho-one, Bisco, USA). Five types of commercially available metal brackets with various bracket base configurations of Photoetched base(Tomy, Japan), Non-Etched Foil Mesh base(Dentaunlm, Germany), Micro-Etched Foil Mesh base(Ortho Organizers, USA), Chessboard base(Daesung, Korea), and Integral base(3M United, USA) were used. Samples were divided into 3 groups, the first group was acted with shear-tensile combined loads(45˚) of 200g for 4 weeks(mechanical fatigue stress), the second group was subjected to the 5,000 thermocycles of 15 second dwell time each in 5℃ and 55℃ baths(thermal fatigue stress), and the third group was the control. Bond strengths were measured at the crosshead speed of 0.5mm/min. The cross-section of bracket base/adhesive interface and the fracture surface were examined with the stereoscope and the scanning electron microscope. The resin remnant on bracket base surface was assessed by ARI(Adhesive Remnant Index). The obtained results were summarized as follows ; 1.In static bond strength, Photoetched base bracket showed the maximum bond strength and Integral base bracket showed the minimum bond strength(p〈0.05). In all brackets, shear bond strength(SBS) was in the greatest value and shear-tensile combined strength(CBS) was in the least value(p〈0.05). 2.After mechanical fatigue test, Photoetched base bracket showed the maximum bond strength and Integral base bracket showed the minimum bond strength(p〈0.05). In Photoetched base bracket and Micro-Etched Foil Mesh base bracket, shear bond strength(SBS), tensile bond strength(TBS) and shear-tensile combined strength(CBS) were decreased after mechanical fatigue test(p〈0.05). 3.After thermocycling, Integral base bracket showed the minimum bond strength. The SBS, TBS and CBS of Photoetched base, Chessboard base, and Micro-Etched Foil Mesh base bracket were decreased after 5,000 cycled thermocycling(p〈0.05). 4.In static test, bond failure sites were mainly between bracket and adhesive. After thermocycling, ARI scores were greater than those in static test. 5.SEM micrographs of cross-section of bracket bonding site showed that many micro-cracks in bracket/resin interface and in enamel/resin interface were found in all brackets after thermocycling.

침탄 두께에 따른 피로강도 영향 특성 평가

최현민,박용하,신용택,김명현,Choi, Hyun Min,Park, Yong Ha,Shin, Yong Taek,Kim, Myung Hyun 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.4

Carburizing treatments are the important way to developing fatigue strength and wear resistance. It is well known that the case depth is one of the most significant parameters determining fatigue strength. In this study, 3-point bending fatigue test was conducted to evaluate fatigue strength for the carburized depth with 18CrNiMo7-6 steel. As a result, fatigue strength increased with effective case depth decreased. It is shown that hardness in case hardened layer played principal role in the fatigue strength.

선체구조 판부재에서 해수부식현상에 기인하는 부식층의 피로강도분담효과에 관한 연구

김원범(Kim, Won-Beom) 한국산학기술학회 2013 한국산학기술학회논문지 Vol.14 No.5

해양환경에서 사용되는 선박이나 해양구조물은 해수환경에서 쉽게 부식이 발생한다. 본 연구에서는 구조용 강재에서 부식생성물의 존재가 피로강도에 미치는 영향에 대하여 조사하였다. 이를 위하여 부식생성물을 제거한 시험 편과 부식생성물이 부착된 시험편의 피로강도를 비교하고 부식생성물의 강도분담에 대하여 고찰하였다. 본 연구에서 부식생성물은 피로강도분담효과가 있으며, 부식생성물을 제거한 시험편의 피로강도는 부식생성물이 부착되어 있는 시 험편보다 피로강도감소계수가 18.1% 감소하였다. 이상의 연구에서 부식생성물 내에서 강도상 유해물질이 없는 한 부 식생성물은 피로강도에 유익함을 알 수 있었다. Ship and offshore structures, those are to be used under the seawater conditions are prone to corrosion. In this research, the effect of rust existence on the fatigue strength at structural member of ship and offshore structure was investigated. For this purpose, fatigue tests for the rust removed specimen were conducted. In addition, the comparison of fatigue strength between rust removed specimen and rusted specimen was conducted. With these test results, fatigue strength share effect was investigated. Finally, at this research, it was found that there is fatigue strength share effect on the rust. In comparison of fatigue strength reduction factor, fatigue strength of the rust removed specimen is 18.1% lower than that of the rusted specimen. From the above, it was known that as far as there are not any harmful ingredients in it, rust on the steel plate is beneficial in an aspect of fatigue strength.

Experimental Study on the Fatigue Performance of Roof and U-rib Welds of Orthotropic Steel Bridge Decks

Zhongqiu Fu,Bohai Ji,Chengyi Zhang,Di Li 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.1

The fatigue performance of a roof-U rib weld on orthotropic steel bridge decks was studied by fatigue experiments on 40 specimens, considering the influences of amplitude, penetration rate, loading position, and steel strength. Influences of different factors on the fatigue life of crack initiation and specimen failure were studied by analysis of crack propagation in the weld and changes in stress amplitude. In addition, nominal stress amplitudes and hot spot stress amplitudes of the welds were compared and the suggested values of fatigue strength were proposed according to the test results. The study shows that increase of penetration rate can decrease the crack propagation rate and extend failure fatigue life. A larger steel strength can increase the fatigue strength of crack initiation. Under the same loading conditions, the fatigue life of crack initiation is about half of the failure fatigue strength. A nominal stress of 70 MPa and a hot spot stress of 75 MPa are recommended for fatigue strength of roof-U rib welds under the manufacturing process investigated here.

High-cycle and very high-cycle bending fatigue strength of shot peened spring steel

NohJun Myung,Liang Wang,Nak-Sam Choi 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.11

This paper examined bending fatigue strength of shot-peened spring steel under the high cycle fatigue (HCF) and very high cycle fatigue (VHCF), and analyzed the effects of shot-peening on the high strength spring steel through service life. Hourglass shape specimens made of spring steel (Si-Cr alloys) were prepared for the rotary bending fatigue test. Actual local stresses were quantitatively calculated to compensate for the applied stress amplitudes, through which it was clarified that the shot-peening had strongly positive effects on the HCF strength, but rather negative effect on the VHCF strength. The fracturing process examination confirmed that most fish-eye fractures arose at sites deeper than the compressive residual stress zone, which did not prevent the creation of the fish-eye. The fatigue strength improvement in the VHCF range was scarcely expected as a result of the shot-peening treatment.

Analysis of fatigue resistance of continuous and non-continuous welded rectangular frame intersections by finite element method

M. L. McCoy,R. Moradi,H. M. Lankarani 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.5

Agricultural and construction equipment are commonly implemented with rectangular tubing in their structural frame designs. A typical joining method to fabricate these frames is by welding and the use of ancillary structural plating at the connections. This aids two continuous members to pass through an intersection point of the frame with some degree of connectivity, but the connections are highly unbalanced as the tubing centroids exhibit asymmetry. Due to the practice of welded continuous member frame intersections in current agricultural equipment designs, a conviction may exist that welded continuous member frames are superior in structural strength over that of structural frame intersections implementing welded non-continuous members where the tubing centroids lie within two planes of symmetry, a connection design that would likely fabricating a more fatigue resistant structural frame. Three types of welded continuous tubing frame intersections currently observed in the designs of agricultural equipment were compared to two non-continuous frame intersection designs. Each design was subjected to the same loading condition and then examined for stress levels using the Finite Element Method to predict fatigue life. Results demonstrated that a lighter weight, non-continuous member frame intersection design was two magnitudes superior in fatigue resistance than some current implemented frame designs when using Stress-Life fatigue prediction methods and empirical fatigue strengths for fillet welds. Stress-Life predictions were also made using theoretical fatigue strength calculations for the fatigue strength at the welds for comparison to the empirical derived weld fatigue strength.

Effects of Solidification Structure on Fatigue Crack Initiation and Fatigue Strength in Al-Si-Mg Cast Alloys

Han, Sang-Won,Lee, Ui-Jong,Kim, Sug-Won 대한금속학회 2002 METALS AND MATERIALS International Vol.8 No.5

Rotating-bending uniaxial fatigue tests and micro-fatigue crack initiation tests were carried out using a permanent mold cast (PMC) and semi-solid die cast (SDC) with Al-7%Si-0.35%Mg composition in order to examine the relationship between solidification structures and fatigue behaviors. The crack length was measured using a replication method. Fatigue strength was improved in SDC, which was almost consistent with the predicted fatigue strength using the size of Si particle cluster. Resistance to fatigue crack initiation and fatigue strength were improved in SDC owing to the finer Si cluster and to higher ultimate tensile strength. Fatigue crack in PMC was preferentially initiated at pores. For SDC, the fatigue crack was initiated at the Si particle/matrix interface, and then sucessively grew along eutectic cell boundaries.

세라믹 용사된 S45C강재의 기계적 특성 및 피로강도

오맹종(Maeng-jong Oh),오창배(Chang-bae Oh),김귀식(Gui-shik Kim) 한국해양공학회 1998 韓國海洋工學會誌 Vol.12 No.1

This paper is to investigate of microhardness, adhesive strength, tensile strength, and fatigue strength of ceramic sprayed steel. Rotary bending fatigue tests have been conducted at room temperature in air and 3% NaCl solution using specimens of carbon steel(S45C) with sprayed coating layers of Ni-4.5%Al(under coating) and TiO₂ (top coating). The microhardness has been improved at 800℃ heat treatment and 150㎜ spraying distance. Tensile strength of the sprayed steel is dependent on the substrate strength. The fatigue strength of the sprayed steel is larger than that of substrate due to blasting and constraint surface of plastic deformation effect. In low stress level, the corrosion fatigue strength of the sprayed steel were lower than that of fatigue strength in air by corrosion