Crack Angle Increases Research Articles

Reactive molecular dynamics of the fracture behavior in geopolymer: Crack angle effect

Reactive molecular dynamics was applied in this study to construct the sodium aluminosilicate hydrate (N-A-S-H) and tensile fracture models with various crack angles. The impact of crack angle on the behavior of N-A-S-H fractures was explored while considering structural mechanical properties and energy evolution. Furthermore, the fracture toughness and brittleness index for various crack angle models were calculated. The findings indicated that the ultimate strength and elastic modulus of the fracture models grew linearly with the increase in crack angle. The fracture toughness value progressively grew while the model’s elastic energy efficiency and new surface energy efficiency decreased simultaneously. The 45° crack model possessed the largest oblique crack development surface in the fracture process due to the coupling effect of tensile and shear stress. Its elastic energy efficiency decreased as well the most, while the new surface energy efficiency increased and the fracture toughness value dropped sharply. It is crucial to place a stronger emphasis on spotting cracks both in the in-service structures or structures being demolished. This ensures optimal performance and safety by enabling more effective adjustments to the direction of external forces and energy input.

Molecular Dynamics Study on Crack Angle Effect on Amorphous Silica Fracture Performance

To investigate the effect of crack angle on the fracture performance of brittle materials under tensile load, a molecular dynamics simulation method based on ReaxFF is used to establish an amorphous silica model through the high-temperature melting and annealing process. Under the simulation environment of 300 K, 1.013 × 105 Pa and 5 × 109 s−1, the impact of crack angle on the fracture performance of the model from three perspectives is analyzed: material mechanical properties, micro fracture process, and energy evolution. The result indicates that as the crack angle increases, the ultimate strain and stress of the model decrease accordingly. The crack propagation path of the model will exhibit a “Z” shape due to the coupling effect of tensile and shear stress. The elastic energy efficiency and new surface energy efficiency of the model increase with the increase in crack angle, and the most new surface is generated at 45° crack angle. The linear regression model and asymptotic regression model are used to fit the trends of elastic energy efficiency and new surface energy efficiency with crack angle, respectively, with correlation coefficients R2 of 0.986 and 0.994. In the actual comminution process, the input energy required for crushing as well as the surface area and morphology of the material after crushing can be changed by adjusting the angle between the load and the main crack of the material being broken.

Study on mechanical properties and fracture modes of sandstone with cracks under triaxial compression

AbstractThis study examines the mechanical properties and fracture modes of sandstone with single and double cracks under varying confining pressures through triaxial compression tests. The stress–strain curves, mechanical parameters, and fracture modes of both intact and cracked sandstone are analyzed based on experimental results. The study finds that the presence of cracks has a significant impact on the mechanical properties of sandstone, with greater damage observed with an increase in the number of cracks. The peak strength and strain of a cracked rock sample increase with the increase in crack angle. The fracture mode of sandstone is influenced by both crack angle and confining pressure. When the crack angle is small, the fracture mode is a combination of shear and tensile failure, while a large crack angle results in shear failure. Moreover, as the confining pressure increases, the degree of damage to the sandstone also increases.

Hydraulic Fracture Propagation in Fractured Rock Mass

According to fracture mechanics theory, the initial cracking law and wing crack propagation model of compression shear rock cracks subjected to hydraulic pressure and far field stresses are discussed. The results of the theoretical study show that crack initiation strength is inversely related to hydraulic pressure, that hydraulic pressure aggravates the wing crack’s growth, and that the wing crack’s behavior under high hydraulic pressure shifts from stable to unstable expansion. The confining pressure is proportional to the rock mass strength, the wing crack’s stress intensity factor drops as the remote field stress σ3 increases, and the wing crack tends to expand stably. As the crack angle increases, the cracking strength reduces at first, then increases. At the same time, damage fracture mechanics models are established for the occurrence of wing crack-wing crack failure, wing crack-shear crack failure, wing crack-shear crack-wing crack failure, and shear crack-shear crack failure in the compression-shear crack bridge under far-field stress and hydraulic pressure. The link between hydraulic pressure, confining pressure, fracture angle, stress intensity factor, and compression-shear factor λ12 is also clarified. The value of the stress intensity factor increases when the hydraulic pressure decreases, the confining pressure increases, and the crack angle increases, whereas the compression-shear factor decreases. This study lays the groundwork for a quantitative assessment of fractured rock mass destruction under hydraulic pressure.

Energy characteristics of sandstones with different crack angles under true triaxial cyclic loading and unloading

AbstractThe effect of crack angle on energy evolution during sandstone failure subjected to true triaxial cyclic loading and unloading is of great concern. However, the energy consumed in the crack initiation and compaction process is generally referred to the dissipated energy, which is inaccurate. To reveal the energy law in the breaking process of sandstone, a complex cyclic loading and unloading test is carried out on precast angled sandstone samples by employing the triaxial test system. The area integral methodology is exploited to evaluate the evolution of total energy density, elastic energy density, dissipated energy density, and plastic energy density of the rock samples of different crack angles. The variations of these four energy density levels in terms of the number of loading and unloading cycles and the upper limit of stress are explained and discussed. The obtained results reveal that during the entire cycle of loading and unloading, the variations of the above‐mentioned factors of the rock sample fairly do not rely on the crack angle. The energy density increases with the number of cycles, and the total energy density and elastic energy density significantly increase faster than the consumption mode. The growth rate of the dissipative energy density is greater than that of the plastic energy density. Additionally, the aforementioned four energy quantities grow in a quadratic manner as a function of the upper limit of the loading stress. The releasable elastic energy gradually magnifies by increasing the upper limit of the loading stress. The plasticity density first decreases and then increases, reflecting the change law of the irreversible plastic deformation caused by newly developed cracks in the rock sample. The elastic energy density, the fitting coefficient of the dissipated energy density, and the total energy density are employed to define the characteristic coefficients of the rock energy storage and energy dissipation. The results indicate that the larger the rock crack angle, the stronger the energy storage energy and the weaker the energy dissipation capacity. It also explains that how the strength of the rock sample becomes higher as the crack angle increases.

Energy Evolution and Damage Mechanism of Fractured Sandstone with Different Angles

To explore the influence of crack angle on the mechanical properties, energy evolution, and damage evolution of sandstone, uniaxial loading tests were conducted on sandstones with different crack angles. Through the stress–strain curve, the influence of the crack angle on the mechanical properties was analyzed. Based on energy theories and principles, the influence of crack angle on the energy conversion mechanism was analyzed. Based on crack angle and dissipated energy, a damage model considering the initial damage to the fractured sandstones was established. The following conclusions were drawn: (1) The strength and elastic modulus of sandstone decrease with an increase in crack angle, and Poisson’s ratio increases with an increase in crack angle; prefabricated cracks affect the crack initiation position, and accelerate the formation of fracture surfaces. (2) The stress–strain curve was divided into compaction stage, elastic stage, yield stage, and failure stage. The larger the crack angle, the longer the yield stage and the shorter the failure stage. (3) At the peak point, the elastic energy, dissipated energy, and input energy of fractured sandstone always decrease with an increase in crack angle; the energy consumption ratio increases with an increase in crack angle; and the energy storage ratio decreases with an increase in crack angle. (4) The damage variable shows a trend of slow accumulation–steady accumulation–rapid accumulation; the crack angle affects the initial damage of the specimen, and the dissipated energy affects the variation trend of the damage variable.

Experimental Investigation of Porous and Mechanical Characteristics of Single-Crack Rock-like Material under Freeze-Thaw Weathering

Freeze-thaw weathering changes the pore structure, permeability, and groundwater transportation of rock material. Meanwhile, the change in rock material structure deduced by frost heaving deteriorates mechanical properties of rock material, leading to instability and insecurity of mine slopes in cold regions. In this paper, rock-like specimens containing prefabricated cracks at different angles and having undergone various freeze-thaw cycles are used as the object. Their pore structure, compressive mechanical properties, strain energies, failure characteristics, and the connection between pore structure and mechanical properties are analyzed. Results show that the porosity, spectrum area of mesopores, and spectrum area of macropores increase with the increase in freeze-thaw cycles, while crack angle shows no obvious influence on pore structure. Peak stress and elastic modulus drop with the increase in freeze-thaw cycles, while peak strain shows an increasing trend. Peak stress and elastic modulus decrease in the beginning, and then increase with the increase in crack angle, while peak strain shows a reverse trend. Elastic strain energy and pre-peak strain energy drop with the increase in freeze-thaw cycles. Elastic strain energy decreases first, and then increases with the increase in crack angle. The correlation between the spectrum area of macropores and elastic modulus is the strongest among different pores. Elastic modulus and peak stress decrease with the increase in macropore spectrum area, and peak strain increases with the increase in macropore spectrum area.

A study on the ultimate strength of ship plate with coupled corrosion and crack damage

Under fatigue loading, crack damage shaped by stress concentration of pitting corrosion in the steel plate adversely affects the strength of ship structure. A nonlinear finite element study is carried out in this paper to investigate how coupled corrosion and crack damage influences the ultimate strength of ship plate. The parameters such as the length, angle and transverse position of cracks, corrosion density and depth and the plate slenderness ratio are taken into account in the present study. It is presumed that the crack is through-thickness and symmetrically distributed inside and on both sides of the corrosion pits, and no contact of crack faces occurs at the ultimate limit state. Reasonable crack gap and a shape of semicircular tip are employed based on numerical results. The crack propagation is not considered in this paper. It is found that the major crack impacts on the ultimate strength depend on the interactions between the length and location as well as the plate slenderness ratio. In addition, the effect of different corrosion factors can be attributed to the corrosion volume. When the crack and corrosion exist together in the plate, their reduction for the ultimate strength is less than their superposition when they exist alone. Moreover, the difference of these two reductions becomes larger as the crack angle increases. Based on numerical results, two mathematical formulas for predicting the residual ultimate strength of steel unstiffened plates with coupled corrosion and crack damage are proposed for longitudinal cracks, transverse and inclined cracks, respectively.

Theoretical study on extension of crack tip plastic zone by remote simple tensile considering crack interaction

In many cases, crack coalescence could be due to the contact of crack tip plastic zone of two cracks. Thus, it is an important work to study the extension of crack tip plastic zone considering interaction of two cracks. Based on the basic theories of famous Kachanov method and with the widely used Mises yield criterion, the extension of crack tip plastic zone by far-field simple tensile considering interaction of two collinear unequal cracks has been researched. And the theoretical equations of the crack tip plastic zone radius under both plane stress and plane strain conditions have been derived. At last, the influence of some factors (main crack length, secondary crack length, crack space and crack angle) on the extension of crack tip plastic zone have been analyzed comprehensively. The results show that, as the increase of the main crack length, the crack tip plastic zone size of the main crack decreases, and while that of the secondary crack increases. As the secondary crack length increases, the crack tip plastic zone size for main crack increases, and that for secondary crack decreases. As the crack space decreases, the crack tip plastic zone size for two cracks develops very quickly, and the cracks extend quickly. Moreover, as the crack angle increases, the effect of crack space on the crack tip plastic zone size decreases.

The crack propagation path under multiple moving contact loads in rolling contact fatigue

This paper proposes a model which considers multiple moving loads to calculate the remaining life of a surface under the rolling contact fatigue. This model is based on the linear fracture mechanics for determining the characteristics of cyclic crack growth. The body under the rolling contact is modeled by a half-plane with an edge crack. Rolling contact is simulated by a translational motion of concentrated forces along the half-plane boundary. The fracture mechanics problem is formulated based on the singular integral equations method and these equations are solved at each step of crack growth, resulting in the stress intensity factors at each step. Then, the crack growth is modeled using the mixed mode fracture criterion for finding the crack path during the growth and the Paris equation for determining the amount of fatigue crack propagation. The effect of the number of moving loads with similar and different speeds applied on the edge of the half-plane, the value of coefficient of friction and the distance between the moving loads with the similar speeds on the crack propagation path and the remaining life have been investigated. It is seen that by increasing the number of the moving loads with the similar speeds on the boundary of the half-plane, increasing the distance between the two and three concentrated moving loads and when two concentrated moving loads move with different speeds, the crack propagation angle compared to the initial crack angle increases and the crack is distracting more inside the surface. As a result, the surface cracks join together and grow towards the surface, causing pitting be reduced.

Distinguishing oil and water layers in a porous cracked medium by interpreting acoustic logging data on the basis of Hudson Theory

During surveys, water layers may interfere with the detection of oil layers. In order to distinguish between oil and water layers in a porous cracked medium, research on the properties of cracks and oil and water layers and their relation to acoustic logging rules is essential. On the basis of Hudson’s crack theory, we simulated oil and water layers in crack-porous medium with different crack parameters corresponding to the well-field response. We found that in a cracked medium with high crack angle or low number density of cracks, compressional and shear wave velocities are sensitive to crack characteristics; further, these velocities are more sensitive to crack characteristics when the waves propagate through the water layer than when they propagate through the oil layer. Compressional and shear wave velocities increase with an increase in crack angle: in the water layer, the increase is approximately linear. On comparing the full waveforms observed in the oil and water layers, we find that the amplitudes of most waves are higher in the water layer. Among the considered waves, the Stoneley wave suffers maximum amplitude attenuation in the oil layer. The maximum excitation intensity for oil layer is greater than that for the water layer. These results can guide further cracked media logging field exploration work.

Detection and monitoring of side crack in a rectangular plate using mobility

Here, forced vibration of a rectangular plate with a side crack of arbitrary length, orientation and position is studied by the Ritz method. Simply supported and clamped boundary conditions are used in the analysis. Numerical results obtained from the Ritz method are validated by finite element method software (ABAQUS). Good matching was found for first five modes. Mobility curves are presented for variation in force location, crack length, crack orientation and crack position in a square plate. Normalized mobility is found to increase with an increase in crack length ratios and decrease with an increase in crack angle. Again, it is observed that a change in crack position from side towards middle increases the normalized mobility. The results can be used for mobility-based crack detection.

The Strength Effect of Pre-Cracked Rocks at Different Angles

In this paper pre-cracked rock is used to study the strength affect by the coal rock internal fissures, through uniaxial compression tests to observe the different perspectives cracks on rock strength by using the precast specimens. The experimental results show that: the strength of specimens with crack angle increases, decreases and then increases, till reaches a maximum at 90°. Based on the force divided, destruction of different angles of prefabricated crack growth path can be divided into: shear failure, tensile failure and tensile shear composite damage.

Experimental and numerical investigation in failure of cracked aluminum plates repaired with bonded FML composite patch, under impact loading

Abstract In this paper, Charpy impact tests were conducted on cracked aluminum plates repaired with FML composite patches. The effects of the crack characteristics and patch lay-up sequence on the energy absorption of the specimens were investigated experimentally. In order to reduce the test numbers, the design of experiments method was used, and the results were predicted by response surface method. The effect of repairing on the fracture parameters [stress intensity factor (SIF), J-integral, and crack propagation direction (CPD)] at the crack front was calculated using three-dimensional (3D) finite element analysis. The results show that the value of the energy absorption increases when the crack angle increases and that the patch lay-up sequence has a significant role on the efficiency of the repair. When the location of the metal layer of the patch is near the repaired surface of the specimen, the value of the energy absorption increases.

The plastic limit load of circumferentially cracked thin-walled pipes under axial force, internal pressure and asymmetrical bending

This paper presents plastic limit load solutions for thin-walled pipes with off-centre inner and outer circumferential surface cracks, embedded cracks and through-wall cracks under tensile force, an asymmetrical bending moment and internal pressure. Formulae for these cracks are also presented for any combinations of these loads. The analytical results show that, when the cracks are off-centred, the plastic limit loads are larger than those for symmetrically centred cracks. As the off-centre crack angle increases, the load-carrying capacity of the pipes increases.