Search

The present study investigates the vibration analysis of cylindrical shells composed of fiber metal laminate (FML) with embedded piezoelectric layers, undergoing fluid-structure interaction (FSI) and resting on a Pasternak elastic foundation based on the principles of three-dimensional elasticity theory. Using the state space approach, the equations of motion were derived under simply supported boundary conditions. The natural frequencies of the FML cylindrical shell, accounting for the presence of a moving fluid, were computed by solving the eigenfrequency equations. The study examined the influence of various parameters, including boundary conditions, length-to-radius ratio, fluid type, fluid velocity, circumferential wave number, and radius-to-thickness ratio, on glass-reinforced aluminum laminate (GLARE), aramid-reinforced aluminum laminate (ARALL), and carbon-reinforced aluminum laminate (CARALL). A constant composite/metal volume ratio was assumed. The results obtained were validated by comparing with natural frequency values from the existing literature, confirming the agreement and convergence with previous studies. The results confirm that the highest natural frequency values are assigned to the CARALL, ARALL and GRALE structures in descending order. Furthermore, an increase in fluid flow velocity through the cylindrical shell correlates with a reduction in natural frequency. [ABSTRACT FROM AUTHOR]

There are two methods for determining the fracture energy (Gf) of hot mix asphalt (HMA) composites at intermediate temperatures: (i) load–crack mouth opening displacement (CMOD) and (ii) load–load line displacement (LLD) curves. The effects of these two methods on the Gf values of different HMA mixtures are investigated at different loading rates and temperatures. A large number of semicircular bend (SCB) specimens were tested under mode I at different temperatures of 5°C, 15°C, and 25°C and loading rates of 1, 5, 10, and 50 mm/min. The three‐dimensional (3D) fracture energy surface plots obtained from the tests revealed that both temperature and loading rate have noticeable effects on the fracture energy, such that Gf values generally increased by increasing the loading rate and reducing the temperature. Also, the Gf values measured by the LLD method were higher than those by the CMOD method for lower temperatures and lower loading rates (i.e., below 10 mm/min). For the higher loading rates, the Gf values determined by the CMOD method were higher than those by the LLD method. Furthermore, the HMA type had meaningful influences on the variations of Gf at different temperatures and loading rates. Highlights: Fracture energy (Gf) dependency of HMA mixtures to the force–CMOD or force–LLD methods was demonstrated.The Gf value increases by increasing the loading rate and decreasing the temperature.At higher loading rates, the CMOD method provided a higher Gf value.Gf was the function of mixture types and environmental and testing conditions. [ABSTRACT FROM AUTHOR]

In this paper, mixed mode I/II and I/III fracture toughness of preplaced aggregate concrete was studied using an edge‐notched disc bend specimen. The results showed the dependency of the fracture toughness value on the mode mixity. The values of modes I, II, and III fracture toughness were obtained to be equal to 0.67MPam, 0.72MPam, and 0.42MPam, respectively. Several theoretical fracture criteria were examined for predicting the trends of experimental data in the tested preplaced aggregate concrete material. The 3D averaged strain energy density criteria provided the best predictions for the KIIIc/KIc ratio. Mixed mode I/III fracture toughness data were between the predicted envelopes of the maximum tensile stress and 3D maximum tangential strain theories. The generalized maximum tangential stress criterion provided accurate predictions for pure mode II and mixed mode I/II fracture data among the investigated mixed mode fracture criteria. By comparing the preplaced aggregate concrete fracture results with those of other types of concrete, it is observed that preplaced aggregate concrete has acceptable and in‐the‐range fracture resistance. Highlights: The compressive and tensile strengths of preplaced aggregate concrete were obtained.Pure mode I, II, and III and mixed mode I/II and I/III fracture toughness of preplaced aggregate concrete mixtures were obtained using ENDB specimen.The accuracy of the data relevant to the experimental results was examined by standard prediction criteria.The fracture parameters (equivalent fracture toughness and work of fracture trend) for mode mixities I/II and I/III were investigated. [ABSTRACT FROM AUTHOR]

Influence of the depth and location of perforation, direction and magnitudes of in situ stresses, wellbore angle, and pumping pressure is investigated numerically for the hydraulic fracture. 3D models of rock formation with vertical, inclined or horizontal wells containing semi‐circular crack are analyzed to obtain both KI and the minimum pumping pressure. By computing the magnitude and sign of the T‐stress it is demonstrated that hydraulic fracture path is generally stable except for a very limited situations in which the vertical well is subjected to the lowest in situ stresses. The minimum horizontal in situ stress has the most dominant role in controlling the hydraulic fracture. A direct relationship between KI and T was obtained for different ranges of in situ stresses and some relations were presented for estimating the critical stress intensity factor at the onset of hydraulic fracture and minimum injection pressure in terms of the applied in situ stresses. Highlights: Influence of in situ stresses, well orientation and perforation size on KI and T values.Determining the minimum pumping pressure in terms of in situ stresses and well type.Stability analysis of hydraulic fracture path for vertical‐oblique‐horizontal wellbores.Obtaining direct relationships between KI and T by changing in situ stresses. [ABSTRACT FROM AUTHOR]

Opening mode fracture behavior of asphalt mixture is studied experimentally and theoretically using three full disk‐shaped specimens, namely, edge‐notched disk bend (ENDB), disk‐shaped compact tension (DCT), and center‐cracked Brazilian disk (CCBD). While the ENDB sample is subjected to pure bending, the BD and DCT specimens are loaded by diametral compression and pin loading tension, respectively. The experimental results showed the noticeable role of loading type on the cracking resistance of asphaltic mixtures such that the specimen loaded in diametral compression showed significantly smaller fracture toughness than the DCT specimen (that is loaded under tension). The KIc results determined from the ENDB also lie between the KIc of DCT and CCBD testing methods. The discrepancies observed between the experimental results of the three specimen types were related to different signs and magnitudes of T‐stress in these test samples. Accordingly, by taking into account the effect of such stress term via employing modified maximum normal strain theory, the mode I test data were predicted theoretically. Finally, the test data obtained from the CCBD and DCT samples were estimated in terms of the KIc of the ENDB specimen (as the reference sample). Highlights: Significant effect of loading type (tensile, compression, and bending) on mode I fracture toughness of disk‐shaped asphaltic mixture.Variations of determined KIc values with the sign and magnitude of T‐stress in the tested disk‐shaped samples.Utilization of maximum normal strain model for predicting the mode I fracture toughness ratios.ENDB specimens can provide a more accurate KIc value compared to the CCBD and DCT samples. [ABSTRACT FROM AUTHOR]

Understanding the cracking resistance of ballast rock materials is key parameter for designing the ballast rock crushing machines or estimating the onset of fracture in the ballast rocks of railway tracks. In this research, mode I fracture toughness (KIc) and mode I fracture energy (GIc) values were determined experimentally for the red andesite ballast rock obtained from the Shahryar mine (Tehran province). Two disc-shaped samples subjected to three-point bending, namely semi-circular bend (SCB) and edge-notched disc bend (ENDB) are selected for conducting the tests and for each specimen 14 replicates were tested. Although a natural scatter was observed for the experimental results the failure probability curves of SCB and ENDB samples showed meaningful difference demonstrating the effect of testing method on mode I fracture behavior. Two- and three-parameter Weibull distribution curves were fitted to the fracture toughness and fracture energy results of andesite ballast rock tested with both specimens. By relating the Weibull distribution curves obtained for the ENDB and SCB samples to their geometries, the statistical fracture behavior curves of SCB were estimated theoretically in terms of the Weibull statistical curves of the ENDB specimen. In addition, the relationship between the statistical fracture toughness and fracture energy data obtained from the tested SCB and ENDB specimens made of andesite ballast rock was examined and it was shown that these two parameters are correlated well to each other as suggested by the framework of linear elastic fracture mechanics. Highlights: Two different mode I configurations were used for rock fracture studies. The effect of specimen geometry on KIc and GIc of andesite ballast rock was studied using Weibull statistical analysis. Two and three-parameter Weibull distribution curves were obtained for the fracture toughness and fracture energy results. The relationship between fracture toughness and strain energy release rate of tested rock samples was investigated statistically. [ABSTRACT FROM AUTHOR]

In this paper, A356/B4C composites were fabricated using the friction stir processing (FSP) method. The process's input parameters, including rotational and transverse speed, were optimized using the response surface methodology (RSM). Three factors and three levels with nine experimental runs made up the design of the experiments. An analysis of variance (ANOVA) was employed to determine whether the constructed model was adequate at a 95% confidence level. This study found that transverse speed was the most critical variable affecting the composites' silicon (Si) particle size, UTS, and force. The findings demonstrate that the Si particle size of the parent material and the dispersion quality of B4C particles in the aluminum matrix are considerably influenced by the FSP factors, such as rotating speed and transverse speed. Second, tests for tensile strength were conducted to examine the composites' mechanical properties. Then, using a specially designed fixture to measure force during the process, the forces on the tool, which play a decisive role in determining the tool's life, were measured in different input parameters. The findings demonstrate that FSP transforms the mechanism of the fracture from brittle to extremely ductile in composites from the as-received metal. [ABSTRACT FROM AUTHOR]

Environmental issues and high prices of bitumen justify the use of reclaimed asphalt pavement (RAP) as a raw material in asphalt production. However, the high stiffness of the aged bitumen in RAP material often causes different problems such as lower workability and lower fatigue and cracking resistance which can be solved by using recycling agents (RA). In this research study, asphalt mixtures containing 0%, 25%, 50%, 75% and 100% of RAP material and two oil-based RAs were investigated in terms of moisture, rutting, fatigue and cracking resistance. It was concluded that the mixtures containing RAP material had high resistance against rutting, moisture damage, and low-temperature cracking. Using RAs had a slight adverse effect on these parameters. On the other hand, fatigue and intermediate-temperature crack resistance of asphalt mixtures were impaired by using RAP material. Recycling agents used in this study could improve fatigue and intermediate-temperature cracking performance of the mixtures depending on the RAP content and testing conditions. [ABSTRACT FROM AUTHOR]

Crack growth and brittle fracture is one of the major failure modes in bone materials and therefore understanding the fracture behavior and affecting parameters on the crack growth resistance of bone is necessary for biomechanics researchers. In this paper, mode I fracture toughness value for the left and right femur bones of same bovine were measured experimentally using several single edge notch bend beam specimens (SENB) subjected to three-point bend loading in dry condition. The SENB specimens were cut along the longitudinal axis of bone but from different hoop directions. Fracture toughness results of sample prepared from the frontal part of bone were higher than the back or side sections. Depending on the location of sample, the fracture toughness of femur bone was varied from 5 to 10 MPa √m . Furthermore, the results obtained for similar location of both left and right femur bones were nearly identical. The fracture energy (Gf) of the tested specimens was also measured and it was found that a linear relation can be fitted to the (KIc)² versus Gf results of the tested bovine bone. [ABSTRACT FROM AUTHOR]

Abstract: In this research, fracture of dissimilar friction stir welded (FSWed) joint made of Al 7075‐T6 and Al 6061‐T6 aluminum alloys is investigated in the cracked semi‐circular bend (CSCB) specimen under mixed mode I/II loading. Due to the elastic‐plastic behavior of the welded material and the existence of significant plastic deformations around the crack tip at the propagation instance, fracture prediction of the FSWed specimens needs some failure criteria in the context of the elastic‐plastic fracture mechanics which are very complicated and time‐consuming. For this purpose, the Equivalent Material Concept (EMC) is used herein by which the tensile behavior of the welded material is equated with that of a virtual brittle material. By combining EMC with the 2 brittle fracture criteria, namely the maximum tangential stress (MTS) and mean stress (MS) criteria, the load‐carrying capacity (LCC) of the FSWed CSCB specimens is predicted. Comparison of the experimental results and theoretical predictions from the 2 criteria showed that both criteria could accurately predict the LCC of the cracked specimens. Moreover, as the contribution of mode II loading increases, the size of the plastic region around the crack tip at failure increases, leading to increasing the LCC. [ABSTRACT FROM AUTHOR]

At intermediate service temperatures hot mix asphalt (HMA) concretely are subjected to different loading rates due to movement of vehicles which can significantly affect their mechanical characteristics and final service load. Hence, in this paper the effect of loading rate on intermediate temperature fracture resistance of HMA materials is investigated experimentally in different modes of cracking. Different hot mix asphalt mixtures made of various compositions were subjected to asymmetric threepoint bend loading in the form of edge cracked semi-circular bend (SCB) specimens. The effect of aggregate type and air void were studied on the fracture energy values for three mode mixities (including pure mode I, mixed mode I/II and pure mode II) and at different temperatures of 5°C, 15°C and 25°C. Trends of change in fracture energy values revealed noticeable influence of loading rate on the low and intermediate temperature cracking behavior of tested asphalt mixtures with different air void contents and aggregate types subjected to mixed mode I/II loading. Also, a change observed in fracture resistance of asphalt mixtures at nearly zero (5°C) and intermediate temperatures (25°C) that was due to change in the behavior of bitumen from elastic to viscoelastic. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of the first non-singular stress terms on the fracture assessment of sharp V-notches under mixed mode loading. First, numerical studies have been performed on a fracture test configuration called single V-notched ring (SVR) specimen. Then, the notch stress intensity factors as well as the coefficients of the first non-singular stress terms, which are vital parameters in brittle fracture of V-notched components, were calculated via a finite element over-deterministic algorithm for a wide range of loading and geometry conditions. The obtained results demonstrate that the SVR specimen is able to provide a complete range of mode mixities from pure mode I to pure mode II loading conditions. The numerical results, next, have been converted to dimensionless parameters and are illustrated in several graphs. Indeed, these graphs can be easily employed by the engineers for rapid calculation of the corresponding notch stress intensity factors and the coefficients of the first non-singular stress terms in the SVR specimen. The obtained fracture parameters are then submitted to the maximum tangential stress criterion to assess the effects of the first non-singular terms on fracture behaviour of the specimen. Finally, an experimental study has been performed on the SVR specimen made of Nayriz Marble rock for two notch angles with a complete range of mode mixities. The obtained experimental data confirm the significant role of the first non-singular stress terms. In fact, these results show that considering only the singular stress terms may induce an average error of 38% in the predicted fracture loads, which can be decreased to about 12% just by adding the contribution of the first non-singular terms to the maximum tangential stress criterion. [ABSTRACT FROM AUTHOR]

Brittle fracture of asphalt mixtures at low temperatures is one of the main deterioration modes of pavements. Hence as an important design parameter, it is required that a reliable value for fracture toughness of asphalt mixtures is known. However, because of natural inhomogeneity of asphalt mixtures and inherent sources of scatters such as random distribution of ingredients and preparation process, the use of statistical analyses might provide better estimations for the crack growth resistance of asphalt mixtures. In this paper by conducting several low temperature fracture toughness experiments on three types of asphalt mixtures with different air void contents, the effects of air void percentage on mode I fracture toughness are studied statistically. Fifty six edge cracked semi-circular bend specimens containing 4, 5 and 7% air voids were tested, and the corresponding two and three-Weibull distribution parameters were determined for each set of data. It was shown that the Weibull model can be used successfully for predicting the statistical nature of tensile cracking phenomenon in asphalt mixtures. The mean fracture toughness values and the Weibull parameters were reduced by increasing the air void content. Furthermore, the distribution parameters obtained experimentally for the mixtures containing 4% and 5% voids were also predicted quite well in terms of the Weibull parameters of a reference mixture containing 7% air void. [ABSTRACT FROM AUTHOR]