Analiza fraktalna pękania betonów.

• Autorzy: Halbiniak J. , Prokopski G.

Warianty tytułu

EN

Fractal analysis of fracture in concretes.

• Języki publikacji: PL

Abstrakty

PL

Przedstawione w artykule badania wykazały, że wymiar fraktalny D oraz wskaźnik rozwinięcia linii profilowych RL powstającego w procesie pękania betonów przełomu są zależne od wartości krytycznych współczynnika intensywności naprężeń. Większym wartościom współczynnika intensywności naprężeń odpowiadały mniejsze wartości zarówno wymiaru fraktalnego D, jak również wskaźnika rozwinięcia linii profilowych RL.

EN

The article presents examination results for profile line development index, RL, and the fractal dimension, D, of concrete specimen fractures obtained in fracture toughness tests performed according to Mode I (tension at bending). Test according to Mode I of fracture were carried out using test specimens with dimensions as given in the RILEM Draft Recommendations: W=150 mm, B=80 mm, L=700 mm, S=600 mm, and ao=50 mm. During the tests, a diagram of the loading force as a function of crack mouth opening displacement (CMOD) was recorded for each specimen. Critical values of stress intensity factor was calculated. The results of the concrete fracture toughness tests are given. Subjected to fracture morphology tests were 3 fractures selected randomly from each series of concretes made from: natural-state gravel aggregate, paraffinated gravel aggregate, natural-state gravel aggregate with a 10% silica fume addition and paraffinated gravel aggregate with a 10% silica fume addition. White gypsum paste was poured over the obtained fracture surfaces. After the paste had set, a gypsum replica was taken from the concrete fracture, onto which coloured gypsum paste was then poured. The replicas were mechanically cut vertically to the mapped fracture surface. The images of replica layers were input to a computer in the form of bitmaps using a scanner. Then, the printout of particular layers was done at a five-time magnification. Data for the coordinates of profile line generating points were entered to the computer using a COSMO GRAPHIC digitizer. The digitization process was accomplished using the "operator's point selection" method. Based on the obtained examination results, the relationships of fractal dimensions, D, and profile line development indices, RL, have been established as a function of stress intensity factors. Microstructural examinations were carried out using a JOEL 5400 scanning microscope. On the photographs of the microstructures of natural-state gravel concrete, chiefly the occurrence of microcracks within the cement paste and the aggregate-cement paste interface were observed. The fractures of the specimens occured with the avoidance of coarse gravel grains; the so called "over-grain" fracture formed. In the concrete with the silica-fume addition, the microcracks prpagated, as a rule, through the gravel aggregate grains; the transgranular fracture formed. The examinations of the fracture morphology of gravel concrete specimens have shown that the fractal dimension, D, and profile line development index, RL, of the fracture occuring in the fracture process are closly dependent on the fracture toughness of concrete. It was found that with increasing stress intensity factor, both fractal dimension, D, and profile line development index, RL, decreased.

Słowa kluczowe

PL

analiza fraktalna; beton; linia profilowa; wymiar fraktalny; odporność na pękanie; obciążenie-rozwarcie szczeliny; CMOD; współczynnik intensywności naprężeń

EN

fractal analysis; concretes; profile line; fractal dimension; fracture toughness; crack mouth opening displacement; CMOD; stress intensity factor

• Wydawca: Wydawnictwo SIGMA-NOT
• Czasopismo: Inżynieria Materiałowa
• Rocznik: 2000
• Tom: R. XXI, nr 1
• Strony: 37--40
• Opis fizyczny: Bibliogr. 11 poz. tab., rys.

Twórcy

autor

Halbiniak J.

• Politechnika Częstochowska

autor

Prokopski G.

• Politechnika Rzeszowska

• Politechnika Częstochowska

Bibliografia

• [1] Carpinteri A., Chiaja B., Nemati K. M.: Complex fracture Energy dissipation in concreto under different loading conditions, Mechanics of Materials, 26, 1997.
• [2] Carpinteri A.: Fractal nature of material microstructure and size effects on apparent mechanical properties. Mechanics of Materials, 18, 1994.
• [3] Manderblot B. B.: Les objects fractals. Forme, hasard et dimension. Flammarion, Paris, 1975.
• [4] Brandt A.M., Prokopski G.; On the fractal dimension of fracture surfaces of concrete elements. Journal of Materials Science, 28, 1993.
• [5] Winslow D. N.: The fractal nature of the surface of cement paste. Cem. Concr. Res. 15, 1985.
• [6] Saouma V.E., Barton C.C., Gamaledin N.A.: Fractal characterization of concreto crack surfaces. Eng. Fract. Mech., 35(1), 1990.
• [7] Przerada I.; Fraktalny opis powierzchni przełomu, związki ze strukturą i odpornością na pękanie, praca doktorska, Politechnika Częstochowska 1995.
• [8] Pickens J.R., Gurland J.: Fourth International Congress of Stereology, Gaithersburg, Maryland (NBS Special Publication), 1976.
• [9] Gokhale A. M., Underwood E. E.: A new parametric roughness equation for quantitative fractography. Acta Stereol., 8/1, 1989.
• [10] Determination of fracture parameters (K and CTODC) on plain concreto using three-pointbend test.RILEM Recommendations, TC 89-FMT Fracture Mechanics of Concrete Test Methods, Materials and Structures, 23, 1990.
• [11] Wojnar L.: Fraktografia ilościowa. Podstawy i komputerowe wspomaganie badań. Zeszyty Naukowe Politechniki Krakowskiej, seria Mechanika, zeszyt nr 2, Kraków 1990.