Experimental Research on Size Effect of Mode II Fracture Toughness of Concrete

2013 ◽  
Vol 438-439 ◽  
pp. 229-234
Author(s):  
Shao Wei Hu ◽  
Liang Hu
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Size Effect ◽  
Fracture Energy ◽  
Experimental Research ◽  
Shear Fracture ◽  
Concrete Strength ◽  
Displacement Curve ◽  
Fracture Parameters ◽  
Mode Ii Fracture Toughness

Based on specimen size, which is the main reason of the shear fracture toughness of concrete, experimental research was carried out by 5 groups including 40 symmetrically loading specimens with different length and height. Through load and crack tip sliding displacement curve P-CTSD, load and strain curve P-ε and load and time curve P-t, the effects of length and height of specimens to shear fracture toughness were studied. Specimen stability is strengthened with increasing of length and weakened with increasing of height. Size effect of fracture toughness is weakened with increasing of length, is strengthened with the increasing of height. Fracture toughness increases with the increasing of length, decreases with the increasing of height. Research Background The size effect exists in parameters of concrete, such as concrete strength, modulus of elasticity, fracture toughness, fracture energy and so on [1-. In 1961, the theory of fracture mechanics was applied to concrete structure for the first time by Kaplan [. A vast majority of research work about concrete fracture mechanics was carried out by international scholars [6-. As the development of fracture theory of concrete, the size effect of fracture parameters became the focal point in theory study. Karihaloo [ pointed out that the size effect of concrete strength strengthens with the increasing of components size, however, the size effect weakens when crack length decreased relative to the size of specimens. Hu [3, 10, 11] accounted for the size effect by applying the theory of boundary effect and carried out the concept of local fracture energy which changes with width of fracture process zone. Based on the fictitious crack model, an analytical method [12, 13] for predicting the effective fracture toughness of concrete of three-point bending notched beams is proposed and the effects of initial seam height ratio and height on fracture parameters were carried out by Wu and Xu. At present, research on shear fracture toughness of concrete is immature and there are almost no papers about the size effect of shear fracture toughness of concrete. Aiming at the issue, this paper conducts a study on the size effect of shear fracture toughness of concrete by using symmetrically single-edge notched specimen.

scholarly journals Fracture Properties of Concrete in Dry Environments with Different Curing Temperatures

2020 ◽  
Vol 10 (14) ◽  
pp. 4734
Author(s):  
Zhengxiang Mi ◽  
Qingbin Li ◽  
Yu Hu ◽  
Chunfeng Liu ◽  
Yu Qiao
Keyword(s):  
Fracture Toughness ◽  
Growth Rate ◽  
Fracture Energy ◽  
Elevated Temperatures ◽  
High Growth ◽  
High Growth Rate ◽  
Growth Speed ◽  
Crossover Effect ◽  
Fracture Properties ◽  
Fracture Parameters

This paper investigated the fracture properties of concrete in dry environments with different curing temperatures (5, 20, 40, and 60 °C). For each curing condition, the key fracture parameters of concrete were tested using wedge splitting specimens at five different ages (3, 7, 14, 28, and 60 d). The results show that in dry environments, the effective fracture toughness and fracture energy of concrete exposed to elevated temperatures increased at a relatively high growth rate at an early age. Nevertheless, the growth speed of effective fracture toughness and fracture energy decreased more quickly at elevated temperatures in the later stages. As a result, the concrete cured at higher temperature exhibited lower ultimate values of fracture parameters, and vice-versa. Namely, a temperature crossover effect was found in the effective fracture toughness and fracture energy of concrete under dry environments. Considering the early growth rate and ultimate values of fracture parameters, the optimum temperature suitable for concrete fracture properties development under dry condition was around 40 °C.

Mode I and Mode II fracture toughness of densified Sitka spruce fabricated in an airtight atmosphere with high-temperature steam

Holzforschung ◽  
2008 ◽  
Vol 62 (1) ◽  
pp. 82-85 ◽  
Author(s):  
Hiroshi Yoshihara ◽  
Kyohei Nobusue
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Sitka Spruce ◽  
Treatment Method ◽  
Mode I ◽  
Mode Ii ◽  
Mode Ii Fracture Toughness ◽  
Point Bend ◽  
High Temperature Steam ◽  
Compression Treatment

Abstract Mode I and Mode II initiation fracture toughness was examined by DCB (double cantilever beam) and 3ENF (three-point bend end notched flexure) tests on specimens of compressed Sitka spruce. The compressed wood was fabricated by varying the compression ratio, and the effectiveness of the compression treatment was examined in view of improving the fracture mechanics properties. In both cases, the fracture toughness did not show a significant increase after the compression treatment. Thus, it would be necessary to develop a new compression treatment method to improve the fracture mechanics properties.

Experimental Investigation on Mode II Fracture Toughness KIIC of Concrete and Fracture Behavior

2006 ◽  
Vol 324-325 ◽  
pp. 1149-1152 ◽  
Author(s):  
Shi Lang Xu ◽  
Hong Bo Gao ◽  
Xiu Fang Zhang
Keyword(s):  
Fracture Toughness ◽  
Crack Length ◽  
Fracture Behavior ◽  
Shear Fracture ◽  
Discontinuity Point ◽  
Fracture Load ◽  
Mode Ii ◽  
Mode Ii Fracture ◽  
Double Edge ◽  
Mode Ii Fracture Toughness

Using the double-edge notched geometry proposed by Xu and Reinhardt recently, the dimension of 200 mm×200 mm×100mm concrete cube specimens, of which the crack length are 10 mm, 20 mm, 30mm, 40mm, 50mm respectively, are designed to experimentally measure mode II fracture toughness KIIC of concrete. For almost all specimens, typical shear fracture features i.e. approximately 0º initial cracking angle as well the following crack forwards propagation along the direction of ligament is phenomenally observed. This fact strongly confirms that this double-edge notched geometry is validly and capable of being utilized as a mode II fracture geometry to evaluate mode II fracture behavior. Then, from the discontinuity point of the measured load-displacement plot, the critical shear fracture load Pc is determined and the corresponding mode II fracture toughness KIIC is also calculated using the formula developed by Xu and Reinhardt. The computed results show that KIIC has no dependency on initial crack length, about 3.36MPa·m1/2 for the tested specimens.

scholarly journals Aplikasi Size Effect Law Pada Beton Marine dengan Pola Bukaan Tarik

2021 ◽  
Vol 28 (2) ◽  
pp. 143-154
Author(s):  
Fella Supazaein ◽  
Resmi Bestari Muin
Keyword(s):  
Fracture Mechanics ◽  
Size Effect ◽  
Fracture Energy ◽  
High Performance ◽  
High Performance Concrete ◽  
Actual Performance ◽  
Nonlinear Fracture Mechanics ◽  
Nonlinear Fracture ◽  
Sample Height ◽  
Marine Concrete

AbstrakPengembangan infrastruktur di bidang maritim adalah salah satu strategi untuk mengembangkan perekonomian. Beton marine banyak digunakan sebagai material struktur  pada pembangunan infrastruktur di bidang maritim tersebut. Beton marine harus menggunakan beton high performance concrete (HPC). Dengan berkembangnya teknologi beton HPC pengoptimalan efisiensi komponen struktur menjadi lebih signifikan.Pada perencanaan pelaksanaan pembangunan khususnya pada tahap analisa struktur, jarang sekali direncanakan kekuatan terhadap mekanika fraktur yang seharusnya juga didesain agar keruntuhan secara fraktur bisa diatasi. penelitian ini mengkaji aplikasi size effect law pada beton HPC pada balok  dengan berbagai ukuran yang sudah ditentukan (small, medium dan high) untuk memperoleh nilai energy fraktur (Gf). Hasil penelitian ini dapat berkontribusi dalam penerapam metode untuk mendapatkan nilai parameter dari kinerja fraktur. selain itu, data parameter dapat digunakan dalam mengkalibrasi analisa numerik elemen struktur berbasis fraktur energi agar dapat dipastikan kinerja struktur yang sesungguhnya.Hasil pengujian menunjukkan energi fraktur pada benda uji set II (rasio takik terhadap tinggi sample = 1/6) lebih besar 8,4% dari benda uji set I (rasio takik terhadap tinggi sample = 1/3). Factor geometri  dan kemiringan pada garis regresi (A) menurun selaras dengan menurunnya rasio takik. Dari angka keruntuhan nilai  berada pada range 0,1 <  < 10 yang menandakan material didesain harus dengan kriteria nonlinear fracture mechanic.Kata-kata Kunci: Beton marine, mekanika fraktur, size effect law, nonlinear fracture mechanics AbstractInfrastructure development in the maritime sector is one strategy for developing the economy. Marine concrete is widely used as a structural material in infrastructure development in the maritime sector. Marine concrete must use high performance concrete (HPC). With the development of HPC concrete technology, optimization of the efficiency of structural components has become more significant.In the construction implementation planning, especially at the structural analysis stage, it is rare to plan the strength of the fracture mechanics which should also be designed so that fracture collapse can be overcome. This study examines the application of size effect law on HPC concrete on beam of various predetermined sizes (small, medium and high) to obtain the fracture energy value (Gf). The results of this study can contribute to the application of the method to obtain parameter values of fracture performance. In addition, parameter data can be used in calibrating the numerical analysis of energy fracture based structural elements in order to ascertain the actual performance of the structure.The results showed that fracture energy in specimen set II (ratio of notches to depth = 1/6) was 8.4% greater than specimen set I (ratio of notches to sample height = 1/3). The geometric factor  and slope of the regression line (A) decreased in line with the decreasing notch ratio. From the brittleness number, the value of β is in the range 0.1 <β <10 which indicates that the material should  designed with nonlinear fracture mechanic criteria.Key words: marine concrete, fracture mechanics, size effect law, nonlinear fracture mechanics

Fracture Toughness Measurement of Asphalt Concrete by Nanoindentation

2017 ◽  
Author(s):  
Zafrul Khan ◽  
Hasan M. Faisal ◽  
Rafiqul Tarefder
Keyword(s):  
Fracture Toughness ◽  
Energy Release Rate ◽  
Fracture Energy ◽  
Energy Release ◽  
Release Rate ◽  
Asphalt Concrete ◽  
Nanoindentation Test ◽  
Displacement Curve ◽  
Macro Scale ◽  
Load Displacement

Fracture toughness and fracture energy release rate are two important parameters to understand the crack propagation within any material. Fracture toughness of asphalt concrete (AC) is vital to explain the fatigue cracking and low temperature cracking of asphalt pavement. These two types of distresses are still unsolved issues for asphalt researchers. Measuring fracture toughness of AC is not a new phenomenon. Recently, researchers have used several techniques to measure the fracture toughness of AC. Tests like semi-circular bending (SCB) and disk-shaped compact specimen (DCT) testing have been used to measure the fracture toughness of the AC. From the SCB or DCT tests, past researchers have shown that crack in AC propagates through mainly binder and mastic phase. All these conventional tests are carried out in macro scale. It is important to understand that before propagation of these macro scale cracks, the cracks initiates at the nano/micro scale level. With the increment of the loads these nanoscale cracks become macro scale cracks and propagates through the sample. Therefore, it is important to understand the cracks at nanoscale. In this study, nanoindentation test was introduced to measure the fracture toughness of the asphalt concrete. In a nanoindentation test, the sample surface is indented with a loaded indenter. For this test, Berkovich indenter with load control method was used. A field cored asphalt concrete sample was used for this study. The sample was collected by coring at interstate 40 (I-40) near Albuquerque, New Mexico. The sample was field aged for four years. The maximum load applied in this study was 5-mn and the unloading was done at a faster rate than the loading rate. From the load-displacement curves of the nanoindentation tests, fracture toughness of the samples was measured. The unloading curve of the nanoindentation test was further used to obtain reduced modulus of the asphalt concrete using Oliver-Pharr method. In this study, fracture energy is thought of as a portion of irreversible energy. This irreversible energy is comprised of plastic energy and energy required for propagation of crack. By analyzing the load displacement curve along with the maximum indentation depth, energy release rate and mode I fracture toughness of asphalt concrete was measured.

scholarly journals The Size Effect and Microstructure Changes of Granite after Heat Treatment

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Zhongping Guo ◽  
Jian Li ◽  
Yongqi Song ◽  
Chengqian He ◽  
Fuyu Zhang
Keyword(s):  
Fracture Toughness ◽  
High Temperature ◽  
Fracture Mechanics ◽  
Size Effect ◽  
Mineral Composition ◽  
Fracture Morphology ◽  
Optical Microscope ◽  
High Temperature Treatment ◽  
Nonlinear Characteristics ◽  
Nonlinear Fracture

High temperature can change the mechanical properties of granite, with significant nonlinear characteristics, and at the same time change its microstructure. Therefore, two kinds of granites are used in this paper: one is normal temperature granite and the other is granite treated at 600°C, and a detailed comparative study is made. The fracture toughness of two kinds of rocks was tested by fracture tests, and the results were analyzed by a nonlinear fracture mechanics model (SEL). At the same time, in order to understand the influence of high temperature on the mineral composition and microstructure of granite, XRD, optical microscope, and SEM were used to observe the mineral composition, microcracks, and fracture morphology of granite. The results show the following: (1) high temperature significantly changes the fracture mechanics parameters of granite. The fracture toughness of granite treated at 600°C is significantly lower than that of untreated granite, which is reduced by more than 60%. (2) No obvious size effect was found in the untreated granite, while the size effect of the granite after treatment at 600°C was significant. (3) The granite after high-temperature treatment showed strong nonlinear characteristics, and the SEL can reasonably describe and explain its nonlinear fracture characteristics. (4) The brittleness of the granite treated at 600°C decreased and the ductility increased. The microscopic morphology of the fracture was rough, with obvious steps and rivers. The microcracks and porosity had increased significantly, but the main components did not change significantly.

scholarly journals Tensile Properties, Fracture Mechanics Properties and Toughening Mechanisms of Epoxy Systems Modified with Soft Block Copolymers, Rigid TiO2 Nanoparticles and Their Hybrids

2018 ◽  
Vol 2 (4) ◽  
pp. 72 ◽  
Author(s):  
Ankur Bajpai ◽  
Arun Alapati ◽  
Andreas Klingler ◽  
Bernd Wetzel
Keyword(s):  
Fracture Toughness ◽  
Tensile Strength ◽  
Block Copolymers ◽  
Fracture Mechanics ◽  
Fracture Energy ◽  
Tio2 Nanoparticles ◽  
Plastic Zone Size ◽  
Hybrid Nanocomposites ◽  
Tensile Fracture ◽  
Toughening Mechanisms

The effect of the hybridization of a triblock copolymer and a rigid TiO2 nanofiller on the tensile, fracture mechanics and thermo-mechanical properties of bisphenol F based epoxy resin were studied. The self-assembling block copolymer, constituted of a center block of poly (butyl acrylate) and two side blocks of poly (methyl) methacrylate-co-polar co-monomer was used as a soft filler, and TiO2 nanoparticles were employed as rigid modifiers. Toughening solely by block copolymers (BCP’s) led to the highest fracture toughness and fracture energy in the study, KIc = 2.18 MPa·m1/2 and GIc = 1.58 kJ/m2. This corresponds to a 4- and 16-fold improvement, respectively, over the neat reference epoxy system. However, a reduction of 15% of the tensile strength was observed. The hybrid nanocomposites, containing the same absolute amounts of modifiers, showed a maximum value of KIc = 1.72 MPa·m1/2 and GIc = 0.90 kJ/m2. Yet, only a minor reduction of 4% of the tensile strength was observed. The fracture toughness and fracture energy were co-related to the plastic zone size for all the modified systems. Finally, the analysis of the fracture surfaces revealed the toughening mechanisms of the nanocomposites.

Nanoindentation Assessed Fracture Toughness of Cement Paste

2016 ◽  
Vol 368 ◽  
pp. 186-189 ◽  
Author(s):  
Jiří Němeček ◽  
Vladimír Hrbek
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Fracture Energy ◽  
Cement Paste ◽  
Quantitative Data ◽  
Brittle Materials ◽  
Fracture Properties ◽  
Micro Scale ◽  
Energetic Approach

This paper deals with fracture properties of microlevel components of hydrated cementpaste. Determination of fracture energy and fracture toughness for quasi-brittle materials hasbecome a challenge for many years on both macro- and micro-scales. Limited number of quantitative data can be found in the literature for the micro-scale. This work uses energetic approach and decomposition of work of indentation into plastic and other parts. Based on simplified assumptions fracture energy and fracture toughness are calculated for individual microstructural phases of cement paste with the aid of nanoindentation, statistical deconvolution and fracture mechanics.

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