Experimental determination of tensile strength and K_Ic_ of polymer concretes using semi-circular bend(SCB) specimens

M.R.M. Aliha,M. Heidari-Rarani,M.M. Shokrieh,M.R. Ayatollahi 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.43 No.6

An experimental method was suggested for obtaining fracture toughness (KIc) and the tensile strength (σt) of chopped strand glass fiber reinforced polymer concretes (PC). Semi-circular bend (SCB) specimens subjected to three-point bending were used for conducting the experiments on the PC material. While the edge cracked SCB specimen could be used to evaluate fracture toughness, the tensile strength was obtained from the un-cracked SCB specimen. The experiments showed the practical applicability of both cracked and un-cracked SCB specimens for using as suitable techniques for measuring KIc and σt in polymer concretes. In comparison with the conventional rectangular bend beam specimen, the suggested SCB samples need significantly less material due to its smaller size. Furthermore, the average values of σt and KIc of tested PC were approximately 3.5 to 4.5 times the corresponding values obtained for conventional concrete showing the improved strength properties of PC relative to the conventional concretes.

Experimental determination of tensile strength and K_Ic of polymer concretes using semi-circular bend (SCB) specimens

Aliha, M.R.M.,Heidari-Rarani, M.,Shokrieh, M.M.,Ayatollahi, M.R. Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.43 No.6

An experimental method was suggested for obtaining fracture toughness ($K_{Ic}$) and the tensile strength (${\sigma}_t$) of chopped strand glass fiber reinforced polymer concretes (PC). Semi-circular bend (SCB) specimens subjected to three-point bending were used for conducting the experiments on the PC material. While the edge cracked SCB specimen could be used to evaluate fracture toughness, the tensile strength was obtained from the un-cracked SCB specimen. The experiments showed the practical applicability of both cracked and un-cracked SCB specimens for using as suitable techniques for measuring $K_{Ic}$ and ${\sigma}_t$ in polymer concretes. In comparison with the conventional rectangular bend beam specimen, the suggested SCB samples need significantly less material due to its smaller size. Furthermore, the average values of ${\sigma}_t$ and $K_{Ic}$ of tested PC were approximately 3.5 to 4.5 times the corresponding values obtained for conventional concrete showing the improved strength properties of PC relative to the conventional concretes.

Crack tip plastic zone under Mode I, Mode II and mixed mode (I+II) conditions

Ayatollahi, M.R.,Sedighiani, Karo Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.5

The shape and size of the plastic zone around the crack tip are analyzed under pure mode I, pure mode II and mixed mode (I+II) loading for small scale yielding and for both plane stress and plane strain conditions. A new analytical formulation is presented to determine the radius of the plastic zone in a non-dimensional form. In particular, the effect of T-stress on the plastic zone around the crack tip is studied. The results of this investigation indicate that the stress field with a T-stress always yields a larger plastic zone than the field without a T-stress. It is found that under predominantly mode I loading, the effect of a negative T-stress on the size of the plastic zone is more dramatic than a positive T-stress. However, when mode II portion of loading is dominating the effect of both positive and negative T-stresses on the size of the plastic zone is almost equal. For validating the analytical results, several finite element analyses were performed. It is shown that the results obtained by the proposed analytical formulation are in very good agreements with those obtained from the finite element analyses.

Crack tip plastic zone under Mode I, Mode II and mixed mode (I+II) conditions

M.R. Ayatollahi,Karo Sedighiani 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.5

The shape and size of the plastic zone around the crack tip are analyzed under pure mode I, pure mode II and mixed mode (I+II) loading for small scale yielding and for both plane stress and plane strain conditions. A new analytical formulation is presented to determine the radius of the plastic zone in a non-dimensional form. In particular, the effect of T-stress on the plastic zone around the crack tip is studied. The results of this investigation indicate that the stress field with a T-stress always yields a larger plastic zone than the field without a T-stress. It is found that under predominantly mode I loading, the effect of a negative T-stress on the size of the plastic zone is more dramatic than a positive T-stress. However, when mode II portion of loading is dominating the effect of both positive and negative Tstresses on the size of the plastic zone is almost equal. For validating the analytical results, several finite element analyses were performed. It is shown that the results obtained by the proposed analytical formulation are in very good agreements with those obtained from the finite element analyses.

Brittle fracture analysis of the offset-crack DCDC specimen

M.R. Ayatollahi,S. Bagherifard 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.29 No.3

Applications of fracture mechanics in the strength analysis of ceramic materials have been lately studied by many researchers. Various test specimens have been proposed in order to investigate the fracture resistance of cracked bodies under mixed mode conditions. Double Cleavage Drilled Compression (DCDC) specimen, with a hole offset from the centerline is a configuration that is frequently used in subcritical crack growth studies of ceramics and glasses. This specimen exhibits a strong crack path stability that is due to the strongly negative T-stress term. In this paper the maximum tensile stress (MTS) criterion is employed for investigating theoretically the initiation of brittle fracture in the DCDC specimen under mixed mode conditions. It is shown that the T-stress has a significant influence on the predicted fracture load and the crack initiation angle. The theoretical results suggest that brittle fracture in the DCDC specimen is controlled by a combination of the singular stresses (characterized by KI and KII) and the non-singular stress term, T-stress.

New formulation for vibration analysis of Timoshenko beam with double-sided cracks

M.R. Ayatollahi,R. Hashemi,H. Rokhi 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.4

It is the intention of this study to synthesize the effects of double-edge cracks on the dynamic characteristics of a beam. The stiffness matrix is first determined for a Timoshenko beam containing two same-line edge cracks. The presented model is then developed for elements with two parallel double-sided cracks, considering the interaction between the stress fields of adjacent cracks. Finally, a finite element code is implemented, to examine the influence of depth and location of double cracks, on the natural frequencies of the damaged system.

Brittle fracture analysis of the offset-crack DCDC specimen

Ayatollahi, M.R.,Bagherifard, S. Techno-Press 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.29 No.3

Applications of fracture mechanics in the strength analysis of ceramic materials have been lately studied by many researchers. Various test specimens have been proposed in order to investigate the fracture resistance of cracked bodies under mixed mode conditions. Double Cleavage Drilled Compression (DCDC) specimen, with a hole offset from the centerline is a configuration that is frequently used in subcritical crack growth studies of ceramics and glasses. This specimen exhibits a strong crack path stability that is due to the strongly negative T-stress term. In this paper the maximum tensile stress (MTS) criterion is employed for investigating theoretically the initiation of brittle fracture in the DCDC specimen under mixed mode conditions. It is shown that the T-stress has a significant influence on the predicted fracture load and the crack initiation angle. The theoretical results suggest that brittle fracture in the DCDC specimen is controlled by a combination of the singular stresses (characterized by KI and KII) and the non-singular stress term, T-stress.

Effects of mixed contents of carbon nanoreinforcements on the impact resistance of epoxy-based nanocomposites

M.R. Ayatollahi,A.R. Naeemi,E. Alishahi 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.56 No.2

The impact behavior of epoxy-based nanocomposites reinforced with carbon nano tube (CNT), carbon nano fiber (CNF) and mixed contents of these nanoparticles was investigated using Izod impact test. The results showed that while the impact strength of nanocomposites containing 1 wt% of CNT and 1 wt% of CNF increased 19% and 13% respectively, addition of mixed contents of these nanofillers (0.5-0.5 wt%) demonstrated higher improvement (21%) in the impact resistance. The trend of the results is explained on the basis of different fracture mechanisms of nanocomposites. Furthermore, the fracture surface of specimens and the dispersion state of nanoenhancers have been studied using scanning electron microscopy (SEM) photographs.

Experimental verification of RV-MTS model for fracture in soda–lime glass weakened by a V-notch

M. R. Ayatollahi,A. R. Torabi 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.10

Fracture phenomenon was experimentally investigated in a soda–lime glass weakened by a V-notch under tensile-shear loading. Fracture tests were conducted using a new test sample called the V-notched Brazilian disc (V-BD) specimen. The fracture resistance and fracture initiation angle were obtained initially from the test results. Afterward, a fracture model was utilized to estimate the experimental results. Very good correlation was found between the experimental and theoretical results both for the fracture resistance and the fracture initiation angle in notches having different notch angles and various notch tip radii. Experimental results revealed that for a constant notch tip radius, the failure load under pure tensile loading conditions decreases as the notch angle increases. For a constant notch angle,as the notch tip radius increases, the fracture load in the soda–lime glass V-BD specimens enhances in the whole domain from pure tensile to pure shear loading. Moreover, for a constant notch tip radius, the notch angle has almost no effect on the fracture initiation angle when the specimen is predominantly under tensile loading conditions.

New formulation for vibration analysis of Timoshenko beam with double-sided cracks

Ayatollahi, M.R.,Hashemi, R.,Rokhi, H. Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.4

It is the intention of this study to synthesize the effects of double-edge cracks on the dynamic characteristics of a beam. The stiffness matrix is first determined for a Timoshenko beam containing two same-line edge cracks. The presented model is then developed for elements with two parallel double-sided cracks, considering the interaction between the stress fields of adjacent cracks. Finally, a finite element code is implemented, to examine the influence of depth and location of double cracks, on the natural frequencies of the damaged system.