Numerical simulation of tensile failure of concrete using Particle Flow Code (PFC)

Hadi Haeri,Vahab Sarfarazi 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.18 No.1

This paper considers the tensile strength of concrete samples in direct, CTT, modified tension, splitting and ring tests using both of the experimental tests and numerical simulation (particle flow code 2D). It determined that which one of indirect tensile strength is close to direct tensile strength. Initially calibration of PFC was undertaken with respect to the data obtained from Brazilian laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, validation of the simulated models in four introduced tests was also cross checked with the results from experimental tests. By using numerical testing, the failure process was visually observed and failure patterns were watched to be reasonable in accordance with experimental results. Discrete element simulations demonstrated that the macro fractures in models are caused by microscopic tensile breakages on large numbers of bonded discs. Tensile strength of concrete in direct test was less than other tests results. Tensile strength resulted from modified tension test was close to direct test results. So modified tension test can be a proper test for determination of tensile strength of concrete in absence of direct test. Other advantages shown by modified tension tests are: (1) sample preparation is easy and (2) the use of a simple conventional compression press controlled by displacement compared with complicate device in other tests.

섬유가 혼합된 시멘트 페이스트의 인장강도 특성에 관한 연구

박성식,호우 야오롱 한국지반공학회 2015 한국지반공학회논문집 Vol.31 No.3

The characteristics of tensile strength of fiber-reinforced grouting (cement paste) injected into rocks or soils werestudied. A tensile strength of such materials utilized in civil engineering has been commonly tested by an indirect splittingtensile test (Brazilian test). In this study, a direct tensile testing method was developed with built-in cylinder insidea cylindrical specimen with 15 cm in diameter and 30 cm in height. The testing specimen was prepared with 0%, 0.5%,or 1% (by weight) of a PVA or steel fiber reinforced mortar. A specimen with 5 cm in diameter and 10 cm in heightwas also prepared and tested for the splitting tensile test. Each specimen was air cured for 7 days or 28 days beforetesting. The tensile strength of built-in cylinder test showed 96%-290% higher than that of splitting tensile test. The3D finite element analyses on these tensile tests showed that the tensile strength from built-in cylinder test had was3 times higher than that of splitting tensile test. It is similar to experimental result. As an amount of fiber increasedfrom 0% to 1%, its tensile strength increased by 119%-190% or 23%-131% for 7 days or 28 days-cured specimens,respectively. As a curing period increased from 7 days to 28 days, its strength decreased. Most specimens reinforcedwith PVA fiber showed tensile strength 14%-38% higher than that of steel fiber reinforced specimens.

Measurement of tensile strength of brittle rocks using a half ring shaped specimen

최병희,이연규,박철환,류창하,박찬 한국지질과학협의회 2019 Geosciences Journal Vol.23 No.4

A tensile test using a half ring (HR) shaped specimen is attempted for the determination of the tensile strength of rock materials. The HR test is a 3-point bend test similar to the semicircular bend (SCB) test. However, the HR specimen is a curved prismatic bar. The theoretical tensile strength of this special bar can be obtained by an analytical formula derived from a basic theory of strength of materials. Owing to the eccentricity of the HR specimen, the possibility for a single tensile fracture to begin at the intended location can increase. This may give results that are more accurate than the conventional bending tests. In this paper, after the concept and formula of the HR test are introduced, its applicability to brittle rocks is investigated by FEM simulations and laboratory tests. In the processes, the theories of the Brazilian test and a special SCB test, which is an alternative to the Brazilian test, are used to examine the accuracy of the HR test.

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.

수압파쇄시험 해석을 위한 중공원통 인장시험과 압열인장시험 화강암 인장강도 비교

조영욱(Yeonguk Jo),장찬동(Chandong Chang),이태종(Tae Jong Lee),김광염(Kwang-Yeom Kim) 한국암반공학회 2013 터널과지하공간 Vol.23 No.5

수압파쇄법으로 최대수평주응력 크기 규명에 필요한 요소 중 하나인 암반의 인장강도를 측정하는 방법에 대해 연구하였다. 석모도 시추공에서 회수한 화강암 시료에 대해 두 가지 실내시험(중공원통 인장시험 및 압열인장시험)으로 인장강도를 측정하고 두 결과가 차이를 보이는지 비교하였다. 중공원통 인장시험에서는 높은 수압증가율 상태에서 더 높은 인장강도를 보여, 현장의 수압파쇄시험에서 보인 수압 증가율 상태에서 측정된 인장강도나 그 증가율로 보정된 인장강도를 이용해야한다는 점을 보였다. 인장강도에 대한 수압 증가율 효과와 크기 효과를 보정하면 중공원통 인장시험 결과는 압열인장시험 결과와 유사하게 나타났으며 이는 수압파쇄 인장강도를 위해 압열인장강도를 이용할 수도 있다는 점을 시사한다. We conducted hollow cylinder tensile strength tests and Brazilian tests in Seokmo granite to measure tensile strength necessary for estimating the magnitude of the maximum horizontal principal stress in hydraulic fracturing stress measurements. Two different pressurization rates were used in hollow cylinder tests. Tensile strengths were determined to be higher at higher pressurization rate, which suggests that tensile strength should be measurement at the same rate used in actual in situ hydraulic fracturing tests. Considering the effect of pressurization rate and specimen size on tensile strength, the hollow cylinder tests and Brazilian tests yield similar results each other. This demonstrates that Brazilian tests can be utilized to produce representative tensile strengths for interpretation of hydraulic fracturing test results.

터진고리 형태의 암석시편에 대한 인장강도 시험의 이론과 실제

최병희 ( Byung-hee Choi ),이연규 ( Youn-kyou Lee ),박찬 ( Chan Park ),박철환 ( Chulwhan Park ) 대한화약발파공학회 2020 화약발파 Vol.38 No.1

본 연구에서는 암석의 인장강도를 측정하는 데 터진고리(split ring; SR) 형태의 시편(NX 코어)을 이용하는 굽힘시험법의 적용성을 검토하였다. SR 시험법은 반고리(half ring; HR) 형태의 시편을 이용하는 HR 시험법(Choi et al., 2019)과 개념적으로는 동일하지만 파괴면이 하중방향과 직교하는 특징이 있다. 이 직교성 때문에 SR 시험법은 HR 시험법보다 더 높은 정확성을 발휘할 수 있을 것으로 예상되었다. HR 시편과 마찬가지로 SR 시편은 균일단면을 가진 굽은 각봉이다. 이 특수한 각봉의 이론적 인장강도는 재료강도학의 굽힘이론으로부터 계산할 수 있다. 일련의 LS-DYNA 수치해석을 수행한 결과, 예상대로 인장형 및 압축형 SR 시험법의 강도오차는 1% 및 5%로서 HR 시험법의 오차(12%)에 비해 매우 낮게 나타났다. 두 SR 시험법의 성능을 확인하기 위하여 실내실험을 실시하였다. 비교를 위하여 HR 시험과 Brazilian 시험도 함께 수행하였다. 실험 결과, Brazilian 강도에 대한 인장형 및 압축형 SR 시험의 강도비는 각각 1.2∼1.4 및 1.1∼1.2로 나타났는데, 이는 통상적인 굽힘시험의 경험치에 비해 너무 작은 수치였다. 결과적으로 SR 시험은 NX 코어로 성형한 암석시편에 대해서는 실용성이 없는 것으로 판단하였다. 반면, HR 시험의 강도비는 선행연구와 본 연구를 통해 1.7~2.0의 범위에 속하여 높은 일관성을 보였다. In this study the split ring (SR) test was investigated for its applicability to the measurement of the tensile strength of rock specimen of NX size. The concept of the SR test is the same as the half ring (HR) test (Choi et al., 2019) except that the expected fracture plane is perpendicular to the loading direction. Because of this perpendicularity, however, it was believed that the SR test could be more accurate than the HR test. Like the HR specimen, the SR specimen is a curved prismatic bar with a uniform section. Appealing to a basic bending theory in strength of materials, the tensile strength for the special bar can be calculated analytically. Numerical simulations using LS-DYNA revealed, as expected, that the strength errors were 1% and 5% for the tensional and compressional SR tests, respectively, which were much lower than that (12%) of the HR test. To identify the performance of the two SR tests, laboratory experiments were conducted. The HR and Brazilian tests were also performed for comparison. The experiments showed that the ratios of the tensional and compressional SR to Brazilian strengths were 1.2∼1.4 and 1.1∼1.2, respectively, which are too small compared to empirical values in ordinary bend tests. Consequently, it is concluded that the SR test is not appropriate for use in tensile strength test of rock specimen of NX size. But the ratio of the HR to Brazilian strengths was within 1.7~2.0 for both the previous and present studies, showing a good consistency in their test results.

Inconel 617 노치시편의 상온 및 고온 인장실험 해석

오창식(Chang-Sik Oh),마영화(Young-Wha Ma),윤기봉(Kee-Bong Yoon),김윤재(Yun-Jae Kim) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5

In this paper, notched bar tensile tests of Inconel 617 were performed at room (20℃) and elevated (800℃) temperature. Finite element analyses are also performed. It is found that, at the room temperature, smooth bar tensile test results could be used to simulate notched bar tensile tests. However, at the elevated temperature, notched bar tensile test results can not be simulated from smooth bar tensile test results. Metallurgical examination reveals that strength weakening results from many cavities over the specimens for smooth bar test at the elevated temperature. “True” tensile properties at the elevated temperature is found using FE simulations. It also suggests that cautious should be taken to determine tensile properties of Inconel 617 at elevated temperatures using smooth bar tests.

Tensile Properties of a ZnS Nanowire Determined with a Nano-manipulator and Force Sensor

장훈식,남승훈,이학주,Jung Han Kim,오규환 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.3

Tensile tests of an individual ZnS nanowire with a cubic structure were performed with a nanomanipulator inside a scanning electron microscope (SEM). To perform the tensile test of ZnS nanowires, a mechanical testing system was installed in the SEM. A nano-manipulator was set up in the SEM, and a cantilever force sensor was mounted on the nano-manipulator. The force sensor could be controlled with the nano-manipulator. The ZnS nanowires were dispersed on the transmission electron microscope (TEM) grid; then, the ends of the ZnS nanowires were welded to the TEM grid and the tip of force sensor by exposing them to the E-beam of the SEM. The tensile tests of the ZnS nanowires were performed by controlling the nano-manipulator in the SEM. The load response during the tensile tests was obtained with a force sensor. The strain-stress curve was obtained from the tensile load-displacement curve after the tensile test. The tensile strengths for nanowires 1, 2, and 3 were 364.7 ± 5.2, 146.2 ± 5.2, and 234.4 ± 5.2 MPa, respectively, and the elastic moduli for nanowires 1, 2, and 3 were 39 ± 5.2, 33.4 ± 5.2, and 37.4 ± 5.2 GPa, respectively.

Direct and indirect methods for determination of mode I fracture toughness using PFC2D

Vahab Sarfarazi,Hadi Haeri,Alireza Bagher Shemirani 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.20 No.1

In this paper, mode I fracture toughness of rock was determined by direct and indirect methods using Particle Flow Code simulation. Direct methods are compaction tension (CT) test and hollow centre cracked quadratic sample (HCCQS). Indirect methods are notched Brazilian disk (NBD) specimen, the semi-circular bend (SCB) specimen, hollow centre cracked disc (HCCD), the single edge-notched round bar in bending (SENRBB) specimen and edge notched disk (END). It was determined that which one of indirect fracture toughness values is close to direct one. For this purpose, initially calibration of PFC was undertaken with respect to data obtained from Brazilian laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, the simulated models in five introduced indirect tests were cross checked with the results from direct tests. By using numerical testing, the failure process was visually observed. Discrete element simulations demonstrated that the macro fractures in models are caused by microscopic tensile breakages on large numbers of bonded discs. Mode I fracture toughness of rock in direct test was less than other tests results. Fracture toughness resulted from semi-circular bend specimen test was close to direct test results. Therefore semi-circular bend specimen can be a proper test for determination of Mode I fracture toughness of rock in absence of direct test.

Investigation of the tensile behavior of joint filling under experimental test and numerical simulation

Jinwei Fu,Hadi Haeri,Vahab Sarfarazi,Mohammad Fatehi Marji,Mengdi Guo 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.81 No.2

In this paper, tensile behavior of joint filling has been investigated under experimental test and numerical simulation (particle flow code). Two concrete slabs containing semi cylinder hole were prepared. These slabs were attached to each other by glue and one cubic specimen with dimension of 19 cm×15 cm×6 cm was prepared. This sample placed in the universal testing machine where the direct tensile stress can be applied to this specimen by implementing a special type of load transferring device which converts the applied compressive load to that of the tensile during the test. In the present work, two different joint filling thickness i.e., 3 mm and 6 mm were prepared and tested in the laboratory to measure their direct tensile strengths. Concurrent with experimental test, numerical simulation was performed to investigate the effect of hole diameter, length of edge notch, filling thickness and filling length on the tensile behavior of joint filling. Model dimension was 19 cm×15 cm. hole diameter was change in four different values of 2.5 cm, 5 cm, 7.5 cm and 10 cm. glue lengths were different based on the hole diameter, i.e., 12.5 cm for hole diameter of 2.5 cm, 10 cm for hole diameter of 5 cm, 7.5 cm for hole diameter of 7.5 cm and 5 cm for hole diameter of 10 cm. length of edge notch were changed in three different value i.e., 10%, 30% and 50% of glue length. Filling thickness were changed in three different value of 3 mm, 6 mm and 9 mm. Tensile strengths of glue and concrete were 2.37 MPa and 6.4 MPa, respectively. The load was applied at a constant rate of 1 kg/s. Results shows that hole diameter, length of edge notch, filling thickness and filling length have important effect on the tensile behavior of joint filling. In fixed glue thinks and fixed joint length, the tensile strength was decreased by increasing the hole diameter. Comparing the results showed that the strength, failure mechanism and fracture patterns obtained numerically and experimentally were similar for both cases.