Aplikasi Size Effect Law Pada Beton Marine dengan Pola Bukaan Tarik

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

The Size Effect and Microstructure Changes of Granite after Heat Treatment

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.

Crack Propagation Modeling of Strengthening of RC Deep Beams With CFRP Plates

Fracture analysis of reinforced concrete deep beam strengthened with carbon fiber-reinforced polymer (CFRP) plates was carried out. The present research aims to find out whether the crack propagation in a strengthened deep beam follows linear elastic fracture mechanics (LEFM) theory or nonlinear fracture mechanics theory. To do so, a new energy release rate based on nonlinear fracture mechanics theory was formulated on the finite element method and the discrete cohesive zone model (DCZM) was developed in deep beams. To validate and compare with numerical models, three deep beams with rectangular cross-sections were tested. The code results based on nonlinear fracture mechanics models were compared with experimental results and ABAQUS results carried out based on LEFM. The predicted values of initial stiffness, yielding point and failure load, energy absorption, and compressive strain in the concrete obtained by the proposed model were very close to the experimental results. However, the ABAQUS software results have greater differences with the experimental results. For example, the predicted failure load for the shear-strengthened deep beam using the proposed model has only 6.3% differences compared to the experimental result. However, the predicted failure load using ABAQUS software based on LEFM has greater differences (25.1%) compared to the experimental result.

Study of the Rock Crack Propagation Induced by Blasting with a Decoupled Charge under High In Situ Stress

The high in situ stress can significantly affect the blast-induced rock fragmentation and cause difficulties in deep mining and civil engineering where the drilling and blasting technique is applied. In this study, the rock crack propagation induced by blasting under in situ stress is first analyzed theoretically, and then a numerical model with a decoupled charge in LS-DYNA is developed to reveal how the initiation and propagation of rock cracks are under high in situ stress. Through simulation, the mechanisms of blast-induced crack evolution under various hydrostatic pressures and nonhydrostatic pressures are investigated, and the differences in crack evolution with specific decoupling coefficients are compared. According to the simulation, three damage zones, i.e., the crushed zone, the nonlinear fracture zone, and the radial crack propagation zone, are formed, and the radial crack evolution is greatly suppressed by the high in situ stress which has no much influence on the crack propagation in the crushed and the nonlinear fracture zones. The velocity of crack propagation is slightly reduced, and the process of crack propagation is stopped early when the rock is subjected to high in situ stress. Furthermore, the numerical analysis indicates that the crack grows preferentially in the direction of maximum principal stress, and the radial crack propagation is predominantly controlled by the preloaded pressure, which is vertical to the crack propagation direction. Based on the numerical results, it is suggested that the optimal decoupling coefficients for rock cracking are 2.65, 1.87, 1.37, and 1.22 for 0, 10, 20, and 30 MPa, respectively. This study provides not only an analysis of the rock crack evolution under high in situ stress but also a reference for resolving excavation difficulties in deep mining.

Kinetics of the multidirectionality of elastic-plastic fracture with allowance for anisotropy of the material properties

Survivability, service life and operational safety of the engineering structures are determined by their damage rate which is mainly regulated by the presence and development of the crack-like defects in the material. Kinetic dependences describing the development of multidirectional semi-elliptic surface cracks with allowance for the anisotropy of the material properties are proposed proceeding from experimental data and numerical solutions. The obtained results are required in studying kinematic problems in nonlinear mechanics of a continuous anisotropic medium. Refining parametric equations for elastoplastic deformation anisotropy are proposed. Functional dependences of the parameters of the kinetic diagrams of low-cycle fracture on the mechanical properties of the material are presented for a wide class of welded joints of austenite stainless cyclically stable steels (12Kh18N10T). The processes of developing inclined semi-elliptic surface cracks in the continuums of welded joints under non-linear boundary loading conditions are studied. We have carried out combined computational, experimental and numerical studies of the stress-strain state in the vicinity of the contour of stationary and growing surface semi-elliptic cracks randomly oriented in space under elastoplastic nominal cyclic loading taking into account the anisotropy of the material properties. The functional distribution of the inhomogeneity parameter of the mechanical properties of the material, which affects accumulation of the local plastic strains and direction of developing the elastoplastic fracture is obtained and presented in the form of the kinetic equation of nonlinear fracture mechanics. Comparison of the experimental results and numerical calculations of the stress-strain state along the contour of the cracks under study in nonlinear boundary loading conditions revealed a good agreement between the intensities of relative elastoplastic deformations at their surface points with allowance for the deformation anisotropy. Calculations of the elastoplastic fracture resistance of the critical elements of the equipment with allowance for considered factors of nonlinear fracture mechanics and heterogeneity of the properties can improve the accuracy of evaluation of their strength, service life and survivability.