In this paper, we investigated the impact of manual drilling in the actual production process on the structural material properties of the airframe. Specifically, we focused on elliptical and inclined holes and studie...
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In this paper, we investigated the impact of manual drilling in the actual production process on the structural material properties of the airframe. Specifically, we focused on elliptical and inclined holes and studied the effects of different parameters on the fatigue life of 2198-T8 skin sheets using digitalimagecorrelation. Through our experimental tests, we found significant correlations between the shape of the holes and the structural properties of the airframe. The results indicate that the fatigue life is somewhat enhanced when the long-axis direction of the elliptical hole and inclined direction of the inclined hole align with the direction of external load, leading to weakened stress concentration. Nevertheless, when the direction is not aligned, the fatigue performance considerably decreases, resulting in a minimum life that is just 46.5% of that of a standard hole. When the fatigue crack in the slanted aperture widens, there is a marked discrepancy in the length of the two sides of the sheet, and the damage is not readily observable in the initial stages. This leads to a formidable potential issue. ABAQUS and FRANC3D were employed to simulate the progression of the fatigue crack, and these simulations were then integrated with Fe-Safe for fatigue longevity forecasting. The outcomes obtained from the simulations correlate well with the empirical data.
Discontinuous joints are prevalent in engineered rock masses and play a significant role in the stability of the rock mass. This study aims to analyze the impact of the inclination angle and number of prefabricated fl...
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Discontinuous joints are prevalent in engineered rock masses and play a significant role in the stability of the rock mass. This study aims to analyze the impact of the inclination angle and number of prefabricated flaws on the crack evolution and failure pattern of sandstone specimens. Uniaxial compression tests, along with acoustic emission technology and digitalimage technology, were employed to monitor and analyze the effects. The findings indicate that: (1) With the increase in the flaw inclination angle, the damage mode of the specimen transitions from tensile to compressive-shear failure. The localized high-strain region on the surface of the specimen predicts the propagation path for the formation of macroscopic cracks. (2) When the number of prefabricated flaws is small, the flaws mainly expand through tensile wing cracks. As the number of flaws increases, the inner flaw tip does not produce cracks. Instead, the failure of the entire specimen occurs along the direction of the outer flaw's tensile wing crack, with the inner flaw running through it. (3) The winged tensile crack is the first crack to appear in all rock samples, regardless of the flaw initiation angles. Finally, the stress intensity factor at the crack tip under uniaxial compression conditions, without considering the closure effect, was expressed based on fracture mechanics theory. The crack initiation angle was then calculated. The results of the theoretical calculation of the initiation angle were found to be consistent with the test results. These research findings can serve as theoretical references and provide insights into the failure mechanisms of cracked rocks and the development of disaster control methods in rock engineering. The increase in the number of flaws of sandstone specimens reduces the ultimate propagation length of the wing crack, leading to through failure and a reduced load carrying capacity of the specimen at lower compressive stresses. As the inclination angle of the
Triaxial state of stress experienced by structural components due to complex geometry, discontinuities, or type of loading can be studied by tensile testing of notched specimens. Herein, assessment of tensile deformat...
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Triaxial state of stress experienced by structural components due to complex geometry, discontinuities, or type of loading can be studied by tensile testing of notched specimens. Herein, assessment of tensile deformation of 316LN austenitic stainless under the uniaxial and triaxial stresses is presented based on finite element (FE) analysis and digitalimagecorrelation (DIC). To study their effects, notches of different root radii are incorporated in flat smooth specimens. The strength of the material increases in the presence of notch. Among the various constitutive expressions, the Swift equation provides a better representation of the tensile response for the smooth specimen. The analysis is further extended by incorporating Swift equation parameters as the deformation model in the FE analysis for notched specimens. The tensile response of the notched specimens is predicted well using the FE analysis. The in-house algorithm is developed for DIC and used to estimate the strain in smooth and notched specimens by speckle-pattern image analysis. The total displacement of smooth and notched specimens obtained from the FE analysis and DIC technique is comparable to the experimental results. Both the techniques complemented each other in understanding the deformation behavior of the steel.
Borehole destabilization damage is an important factors affecting gas extraction efficiency. To derive the fracture development law, strain, and energy evolution characteristics of different borehole diameters, uniaxi...
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Borehole destabilization damage is an important factors affecting gas extraction efficiency. To derive the fracture development law, strain, and energy evolution characteristics of different borehole diameters, uniaxial compression experiments were conducted on prefabricated rock specimens with different borehole diameters. The results showed that the elastic energy and dissipation energy of the specimens with different pore diameters changed with the compression process, and the energy distribution inside the specimens. The results show that as the pore size of the specimen increases, the strain area damaged by tensile fracture gradually decreases and the strain area damaged by shear fracture gradually increases, and the damage of the dominant specimen gradually evolves from tensile fracture as the dominant factor to tensile fracture and shear fracture together as the dominant factor and finally to shear fracture as the dominant factor. For the whole compression process of pore size rock specimens, the total energy curve shows a nonlinear growth trend, and the elastic energy curve shows a nonlinear growth trend before the specimen damage and a cliff-type decrease after the specimen damage. From the perspective of energy distribution, the elastic energy storage limit of the specimen decreases with the increase of the specimen pore size, the energy distribution law inside the rock specimen with pores changes, and the total energy absorbed from the outside gradually changes to the dissipated energy, resulting in an increasing proportion of dissipated energy, indicating that the larger the pore size, the larger the plastic deformation, and the more obvious ductile damage characteristics of the specimen with pores will be shown. The research analyzes the causes of destabilization of rock samples with different hole diameters and provides some theoretical guidance for the study of gas extraction drilling stability.
Present work is aimed at performing fatigue tests on notched C-Mn steel tubes. Tests were conducted on different sizes of notches under remote axial strain-controlled conditions. Individual effects of peak equivalent ...
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Present work is aimed at performing fatigue tests on notched C-Mn steel tubes. Tests were conducted on different sizes of notches under remote axial strain-controlled conditions. Individual effects of peak equivalent strain amplitude and strain gradient are brought out on experimental fatigue life. The localized measured strains are compared with corresponding outcome of FE analyses. Fatigue life for notched specimens was predicted based on peak equivalent strain amplitude/existing critical plane model considering stress/strain information at peak/characteristic distance locations. The characteristic distance location with critical plane model and peak equivalent strain amplitude results in improved fatigue life predictions.
Fractures are prevalent in engineering rock, necessitating the study of initiation laws and energy evolution characteristics for ensuring rock engineering stability. This study uses theoretical analysis to predict cra...
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Fractures are prevalent in engineering rock, necessitating the study of initiation laws and energy evolution characteristics for ensuring rock engineering stability. This study uses theoretical analysis to predict crack initiation at fracture tips, complemented by experiments and numerical simulation to investigate the deformation and fracture processes of sandstones containing single and double fractures under uniaxial compression. The research assesses strength, deformation, failure modes, internal microcrack propagation, and energy evolution. The results indicate that this study introduces a new parameter, the initiation factor Z, based on theoretical derivation. The condition for crack tip propagation in rocks is that the Z must be greater than or equal to the square of the fracture toughness factor (K-IC), and the greater the value of |Z-K-IC(2) |, the easier it is for the crack tip to initiate. Theoretical calculations predict the sequence of crack tip initiation in rocks with single and double fractures, and these predictions are consistent with experimental and numerical simulation results. The presence of fractures decreases the maximum strength of rocks by 36.2%. As the inclination angle increases in single-fractured rock, the peak strength often exhibits an "increase-decrease-increase" pattern. Double-fractured rock generally exhibits higher peak strength as the angle between fractures increases. The internal elastic energy of rocks shows a positive correlation with rock strength, dissipative energy, and rock fractal damage. This study improves understanding of the mechanical response mechanisms and energy evolution in fractured rock, offering a theoretical basis for assessing the potential impacts of fractures in underground engineering at a microscopic scale.
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