Destructive testing of adhesively bonded joints under static tensile loading

Ochsner, A.,Gegner, J. The Society of Adhesion and Interface 2004 접착 및 계면 Vol.5 No.2

Several in-situ testing methods of adhesively bonded joints under static short-time tensile loading are critically analyzed in terms of experimental procedure and data evaluation. Due to its rather homogeneous stress state across the glue line, the tensile-shear test with thick single-lap specimens, according to ISO 11003-2, has become the most important test process for the determination of realistic materials parameters. This basic method, which was improved in both, the experimental part by stepped adherends and easily attachable extensometers and the evaluation procedure by numeric substrate deformation correction and test simulation based on the finite element method (FEM), is therefore demonstrated by application to several kinds of adhesives and metallic adherends. Multi-axial load decreases the strength of a joint. This effect, which is illustrated by an experimental comparison, impedes the derivation of realistic mechanical characteristics from measured force-displacement curves. It is shown by numeric modeling that tensile-shear tests with thin plate substrates according to ISO 4587, which are widely used for quick industrial quality assurance, reveal an inhomogeneous stress state, especially because of relatively large adherend deformation. Complete experimental determination of the elastic properties of bonded joints requires independent measurement of at least two characteristics. As the thick-adherend tensile-shear test directly yields the shear modulus, the tensile butt-joint test according to ISO 6922 represents the most obvious complement of the test programme. Thus, validity of analytical correction formulae proposed in literature for the derivation of realistic materials characteristics is verified by numeric simulation. Moreover, the influence of the substrate deformation is examined and a FEM correction method introduced.

강섬유 보강 초고성능 콘크리트의 전단 전달 모델

이지형,홍성걸,Lee, Ji-Hyung,Hong, Sung-Gul 한국공간구조학회 2015 한국공간구조학회지 Vol.15 No.2

Ultra High Performance Fiber Reinforced Concrete (UHPFRC) has a outstanding tensile hardening behaviour after a crack develops, which gives ductility to structures. Existing shear strength model for fiber reinforced concrete is entirely based on crack opening behavior(mode I) which comes from flexural-shear failure, not considering shear-slip behavior(mode II). To find out the mode I and mode II behavior on a crack in UHPFRC simultaneously, maximum shear strength of cracked UHPFRC is investigated from twenty-four push-off test results. The shear stress on a crack is derived as variable of initial crack width and fiber volume ratio. Test results show that shear slippage is proportional to crack opening, which leads to relationship between shear transfer strength and crack width. Based on the test results a hypothesis is proposed for the physical mechanics of shear transfer in UHPFRC by tensile hardening behavior in stead of aggregate interlocking in reinforced concrete. Shear transfer strength based on tensile hardening behavior in UHPFRC is suggested and this suggestion was verified by comparing direct tensile test results and push-off test results.

Bond behaviour at concrete-concrete interface with quantitative roughness tooth

Ayinde, Olawale O.,Wu, Erjun,Zhou, Guangdong Techno-Press 2022 Advances in concrete construction Vol.13 No.3

The roughness of substrate concrete interfaces before new concrete placement has a major effect on the interface bond behaviour. However, there are challenges associated with the consistency of the final roughness interface prepared using conventional roughness preparation methods which influences the interface bond performance. In this study, five quantitative interface roughness textures with different roughness tooth angles, depths, and tooth distribution were created to ensure consistency of interface roughness and to evaluate the bond behaviour at a precast and new concrete interface using the splitting tensile test, slant shear test, and double-shear test. In addition, smooth interface specimens and two separate the pitting interface roughness were also utilized. Obtained results indicate that the quantitative roughness has a very limited effect on the interface tensile bond strength if no extra micro-roughness or bonding agent is added at the interface. The roughness method however causes enhanced shear bond strength at the interface. Increased tooth depth improved both the tensile and shear bond strength of the interfaces, while the tooth distribution mainly influenced the shear bond strength. Major failure modes of the test specimens include interface failure, splitting cracks, and sliding failure, and are influenced by the tooth depth and tooth distribution. Furthermore, the interface properties were obtained and presented while a comparison between the different testing methods, in terms of bond strength, was performed.

강섬유 보강 초고성능 콘크리트 전단 전달 모델

이지형,홍성걸 한국공간구조학회 2015 한국공간구조학회지 Vol.15 No.2

Ultra High Performance Fiber Reinforced Concrete (UHPFRC) has a outstanding tensile hardening behaviour after a crack develops, which gives ductility to structures. Existing shear strength model for fiber reinforced concrete is entirely based on crack opening behavior(mode I) which comes from flexural-shear failure, not considering shear-slip behavior(mode II). To find out the mode I and mode II behavior on a crack in UHPFRC simultaneously, maximum shear strength of cracked UHPFRC is investigated from twenty-four push-off test results. The shear stress on a crack is derived as variable of initial crack width and fiber volume ratio. Test results show that shear slippage is proportional to crack opening, which leads to relationship between shear transfer strength and crack width. Based on the test results a hypothesis is proposed for the physical mechanics of shear transfer in UHPFRC by tensile hardening behavior in stead of aggregate interlocking in reinforced concrete. Shear transfer strength based on tensile hardening behavior in UHPFRC is suggested and this suggestion was verified by comparing direct tensile test results and push-off test results.

음향방출을 이용한 저항 점용접의 용접 품질평가

조대희(Dae-Hee Jo),이장규(Zhang-Kyu Rhee),박성완(Sung-Oan Park),조진호(Jin-Ho Cho),김봉각(Bong-Gag Kim),우창기(Chang-Ki Woo) 한국생산제조학회 2006 한국생산제조학회지 Vol.15 No.4

In this paper, for the purpose of investigation the acoustic emission(AE) behaviors during resistance spot welding process and tension test of SPCC steels. As the results present the resistance spot welding method that can get suitable welding qualities or structural integrity estimating method. The resistance spot welding process consists of several stages: set-down of the electrodes; squeeze; current flow; forging; hold time; and lift-off. Various types of AE signals are produced during each of these stages. For tensile-shear test and cross tensile test in resistance spot welded specimens, fracture patterns are produced: tear fracture; shear fracture; and plug fracture. Tensile-shear specimens strength appeared higher than cross tensile specimens one. In case of tensile-shear specimen happened tear fracture that crack happens in most lower plate. Also, in case of cross tensile specimens, upper plate and lower plate are detached perfect fracture was exposed increases a little as acting force is lower than ordinary welding condition. Therefore, the structure which is combined by resistance spot welding confirmed that welding design must attain so that shear stress may can interact mainly.

Numerical simulations of fracture shear test in anisotropy rocks with bedding layers

Haeri, Hadi,Sarfarazi, Vahab,Zhu, Zheming,Nejati, Hamid Reza Techno-Press 2019 Advances in concrete construction Vol.7 No.4

In this paper the effect of bedding layer on the failure mechanism of rock in direct shear test has been investigated using particle flow code, PFC. For this purpose, firstly calibration of pfc2d was performed using Brazilian tensile strength. Secondly direct shear test consisting bedding layer was simulated numerically. Thickness of layers was 10 mm and rock bridge length was 10 mm, 40 mm and 60 mm. In each rock bridge length, bedding layer angles changes from $0^{\circ}$ to $90^{\circ}$ with increment of $15^{\circ}$. Totally 21 models were simulated and tested. The results show that two types of cracks develop within the model. Shear cracks and tensile cracks. Also failure pattern is affected by bridge length while shear strength is controlled by failure pattern. It's to be noted that bedding layer has not any effect on the failure pattern because the layer interface strength is too high.

PFRP 복합재의 전단탄성계수 예측

김수영,서재훈,김학군,김선희,윤순종 한국복합신소재구조학회 2018 복합신소재구조학회 학술발표회 Vol.2018 No.04

In this study, we investigated the shear properties of pultruded fiber reinforced polymer plastic (PFRP) composites. Especially, we focused on the relationship between the shear properties of PFRP and other mechanical properties of PFRP composites by comparing the experimental results with the theoretical results. We compared the shear characteristics obtained by the tensile test and calculated from the theoretical equation proposed in previous work. It was found that the shear modulus of elasticity predicted by using the theoretical formula is close to the shear modulus of elasticity obtained by the 45° off-axis tensile test.

구조보강용 FRP 함침·접착수지의 역학적 특성 분석을 위한 시험방법 비교 연구

유영찬,최기선,김긍환 한국구조물진단유지관리공학회 2008 한국구조물진단유지관리공학회 논문집 Vol.12 No.2

FRP와 콘크리트의 접착강도를 평가하기 위해 현장에서 일반적으로 사용되는 Pull-off 실험방법은 FRP 복합체의 손상을 초래하며 더욱이 FRP의 최대 pull-off 강도가 콘크리트의 인장강도에 의해 제한 되는 단점을 지니고 있다. 이에 따라 구조보강용 접착제의 역학적 특성을 1차적으로 평가할 수 있는 간접적인 실험방법의 개발이 요구된다. 본 연구에서는 여러나라에서 각기 제안되고 있는 실험규격에 대한 비교실험을 통하여 구조보강용 접착제의 역학적 특성을 개략적으로 예측할 수 있는 표준화된 실험방법 및 평가기준을 제안하고자 하였다. 본 연구결과를 바탕으로 인장전단접착강도 시험의 접착제 두께, 압축/휨강도 시험체의 제원 등이 통일되어 표준시험체 제원을 도출할 수 있었다. Pull-off test is generally used to evaluate bond strength of FRP composite with concrete at job site. However, some damages on FRP composites can not be avoided during pull-off test and moreover test range of pull-off strength is limited by maximum tensile strength of concrete. Accordingly, it is required to set-up a test method that can evaluate mechanical properties of structural adhesive indirectly prior to pull-off test. In this study, the standard test methods for structural adhesive which can simply evaluate mechanical performance of adhesive were suggested through comparative experiments from each different standard in various countries. Particularly, gluing thickness of adhesive in tensile lap-shear tests, the section dimension of compression and bending test specimens become unified, and standard test specimen size is achieved by test results.

고강성 탄소섬유 복합재료 단층 설계허용값 개발

이명건,장세용,김상용,조숙경 한국항공우주학회 2012 한국항공우주학회 학술발표회 논문집 Vol.2012 No.11

1990년대 고강성/고강도 탄소섬유 복합재료 IM7/977-3 프리프레그(군용항공기, Cytec/미국)와 T800H/3900-2 프리프레그(민수항공기, Toray/일본)가 개발되면서 본격적으로 항공기 1차구조물에 적용되었다. 군용항공기(F-22, F-35, 유로파이터), 민간항공기(Boeing 787, A350/A380) 및 무인기(Global Hawk, Predetor)에 적용된 탄소섬유 복합재료는 수출허가(Expert License)품목으로 분류되어 국내 수입이 제한되고 있으며, 기 개발된 복합재료 물성값과 설계허용값 획득은 거의 불가능한 실정이다. 이러한 실정 하에서 항공기 1차구조물에 탄소섬유 복합재료를 적용하기 위하여 복합재료 설계개발시험을 수행하였다. 복합재료 설계개발시험은 MIL-HDBK-17 Building Block Approach에 따라 수행하였다. 시험은 물리적 특성시험과 기계적 특성시험으로 분류하여 약 8,000개 시편 시험을 하였다. 본 논문은 탄소섬유 복합재료 8,000개 시편 시험 중 단층의 인장/압축시험 및 전단특성시험 결과와 기계적 특성값과 설계허용값 개발내용을 포함하였다. High Modulus/Strength Carbon/Epoxy prepreg has been applied in the primary structure of aircraft since IM7/977-3(military aircraft, Cytec/USA) and T800H/3900-2(commercial aircraft, Toray/Japan) had been developed in 1990’s. Carbon/Epoxy composite materials which have been used in military aircraft (F-22, F-35 and Eurofighter), commercial aircraft (Boeing 787 and A350/A380) and UAV (Global Hawk and Predetor) were classified as Expert License. The distribution of both material properties and design allowable values have not been allowed to a foreign country. Under this situation the composite material DDT(Design Development Test) has been performed and the design allowable values as DDT results were applied to the primary structures of aircraft. The DDT has been performed according to MIL-HDBK-17 Building Block Approach. The tests were categorized by physical property tests and mechanical property tests with approximately 8,000 specimens. This report contained the mechanical properties and the design allowable values as results of the tensile/compression tests and in-plane shear property tests for Carbon/Epoxy composite lamina materials among 8,000 specimen tests.

GFRP보강적층목재핀의 휨강도 및인장형 전단내력 성능평가

송요진,정홍주,김대길,김상일,홍순일 韓國木材工學會 2014 목재공학 Vol.42 No.3

목구조물 접함부에 기존 드리프트핀(Drift pin)을 대체하고자 단판이나 합판을 유리섬유강화플라스틱(GFRP: Glass fiber reinforced plastic)과 복합 적층시킨 GFRP보강적층목재핀을 세작하였다. 더불이 GFRP보강적층목재핀을 사용하여 집성재 접합부의 인장형 전단내력 시험을 실시하였다. GFRP 배열에 따른 보강적층목재핀의 휨강도 시험결과 GFRP를 각층에 l장씩 삽입한 시험편(Type-A)이 가장 양호한 성능을 발휘하였다. 또한 압체압력 1.96 N/mm2, 온도 150℃에서 한 시간 열압하여 고밀화한 시험편이 고밀화하지 않은 시험편과 비교하여 휨장도 성능이 1.57배 향상됨을 확인히였으며, 하중방향에 따라 Edgewise가 Flatwise보다 3.51배 높은 성능을 발휘하였다. 시험을 통해 가장 양호한 성능을 보인 Type-A 보강적층목재핀을 이용하여 전단내력 시험을 실시하였다. 접합구의 종류와 접합판의 종류를 달리하여 시험한 결과 드리프트핀과 강판을 적용한 시험체(Type-DS)와 비교하여 GFRP보강적층목재핀과 GFRP보강목재적층판을 적용한 시험체(Type-WL)가 1.12배 높은 전단내력이 측정되었으며 최대하중 이후에도 매우 양호한 인성이 관찰 되었다. By replacing the previous metal connector on the joints of timber structure, the GFRP reinforced laminated wooden pin was produced using a wooden material and Glass fiber reinforced plastic(GFRP) composite laminate. In addition, using the reinforced wooden pin, the tensile type shear strength test was conducted. Based on the result of the bending strength test of the reinforced laminated wooden pin according to the GFRP arrangement, a specimen(Type-A) with a single insertion of GFRP for each layer have shown the most favorable performance. Also, it was verified that densified specimen hot pressed for an hour at the temperature of 150℃ and with the oppression pressure 1.96 N/mm2 have shown the improved performance of 1.57 times than the specimen without the densification. And in the bending strength test considering the load direction, edgewise have shown a higher performance of 3.51 times than the flatwise. A shear strength test was conducted using the Type-A reinforced laminated wooden pin which have shown a moderate performance on the test. Based on the test conducted by differentiating the type of the joint plate and the connector, compared to the specimen(Type-DS) applied with the drift pin and steel plate, the speci-men(Type-WL) applied with the GFRP reinforced laminated wooden pin and GFRP reinforced wooden laminated plate have shown 1.12 times higher shear strength and also have shown an excellent toughness even after the maximum load.