Tianxi Tang

VARIABLE-NOTCH ONE-SIZE TEST METHOD FOR FRACTURE ENERGY AND PROCESS ZONE LENGTH

Based on the generalized theory of the size effect law allowing dissimilar specimens, this paper proposes a new version of the size effect method for determining the fracture energy Gr and effective process zone length cr, which permits using specimens of only one shape and one size, but with different notch lengths. Cutting notches of different lengths on specimens of the same shape and size is an easy way to obtain specimens of different brittleness numbers, as required by the size effect method. Either linear or nonlinear regression of measured maximum loads of these specimens can give the material parameters G~ and cr. An experimental program is conducted to verify the proposed method. The notched holed split-tension cylinder is found to be a suitable specimen shape, while the notched eccentric compression specimen is found to provide a barely sufficient range of brittleness numbers. The analysis in the paper also indicates that there exists an upper limit of notch (or initial crack) length for some specimen geometries as the limit for validity of the definition of brittleness number. Copyright

Splitting tension tests to determine concrete fracture parameters by peak-load method

Abstract An experimental program confirms that the peek-load method can be successfully applied to splitting tension tests to determine fracture parameters KIcS and CTODc of the two-parameter fracture model from the measured peak loads. The peak-load method requires distinct specimens. It is found that a hole drilled at the axis of splitting tension cylinder can largely expand the specimen distinction. Combination of tests on splitting tension cylinders with and without a hole raises the reliability of the KIcS and CTODc values determined by the peak-load method.

Determination of Fracture Energy and Process Zone Length by Using Variable-Notch One-Size Specimens

A new test method for determining fracture energy and process zone length, defined by the size effect law and its generalized theory, has been proposed. It allows the use of specimens of the same size and shape but with different notch lengths. This paper proposes test and data analysis procedures for using this variable-notch one-size method. By filling in a programmed spreadsheet, the measured maximum loads of the specimens, fracture energy and process zone length are output instantly. Tests have been conducted to verify the proposed method. It is shown that either eccentric compression prisms or split-tension cylinders can be applied to obtain accurate results. Since the method requires the maximum loads of several specimens of the same size and shape, it makes specimen preparation and testing very simple.

Bimaterial brazilian specimen for determining interfacial fracture toughness

Abstract The test specimen proposed in this study, named the bimaterial Brazilian specimen, is a cylindrical specimen consisting of two dissimilar materials with a cross-section through a diameter of the cylinder as their interface. Stress intensity factors for the tip of the crack in the interface were calibrated with the finite element method for several different moduli combinations and loading directions. Specimens consisting of mortar and rock were prepared and tested to simulate the mortar-aggregate interface in concrete. Test results show that apparent mortar-limestone interfacial fracture toughness increases with the phase angle and also that specimen size has significant effects on the apparent interfacial toughness. The possibility of investigating the effect of specimen size in the interfacial toughness is particularly important in the study of a heterogeneous medium (such as concrete) since the size of inclusions (such as aggregate in concrete) is known to affect the strength of the medium.

STRAIN AND AGE EFFECTS ON BEHAVIOR OF A CONCRETE PAVEMENT JOINT SEALANT MATERIAL

A one-part self-leveling silicone joint sealant material was experimentally investigated in the laboratory. It was found that strain and age had apparent effects on the relaxation modulus of the material. Relaxation tests were conducted under different strain levels. The test samples were exposed to ultraviolet radiation and moisture for artificial aging before testing. For this largely deformable material, finite strain formulas were used in analysis of experimental data. Strain and age effects were successfully normalized in the relaxation master curve by using the superposition principle. On the basis of the master curve, a material model of the generalized Maxwell model in parallel type was constructed. The real time was scaled to the reduced time by time-strain shift and time-age shift factors so as to characterize the strain and age effects. This model is mathematically simple and can be easily applied in finite element programs for concrete pavement joint analysis.

A SYSTEMATIC METHOD TO DETERMINE OPTIMAL SPECIMEN GEOMETRY FOR MEASURING CONCRETE FRACTURE PROPERTIES BY THE PEAK-LOAD METHOD

The peak-load method is a simple method for determining the fracture properties of critical stress intensity factor (K) and crack-tip opening displacement at the peak load (CTOD) of the two-parameter fracture model of concrete. With this method, the fracture properties can be determined from the measured peak loads of several different (or distinct) specimens. Specimens can be made distinct in specimen shape, size, notch length, and loading configuration. To quantitatively identify the degree of specimen distinction, a variable named specimen distinction number is proposed. When test specimens are considerably distinct, random experimental errors have negligible effect, and determination of K and CTOD is of high accuracy. Thus, test specimens can be optimized to obtain the most accurate values of the fracture properties. A previous experimental program found that change in specimen shape, such as a hole drilled at the axis of a splitting tension cylinder, can largely expand the specimen distinction. An experimental program reported in this paper shows that changing loading configurations of beams or prisms from bending to eccentric compression can also largely enhance the specimen distinction and therefore provide K and CTOD determination of high accuracy.