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The huge impact of kinetic energy released by the breaking of hard roof is one of the important factors that induces dynamic disasters in coal mines. The key to preventing and controlling coal and rock dynamic disasters is the directional fracture of strata at a specific position and reducing the length of hard roof suspension. The multi-hole sleeve fracturing technology has the advantages of simple operation and wide application conditions and has a wide research prospect in the field of hard roof weakening. In order to understand the mechanism of multi-hole sleeve fracturing, the mechanical mechanism of multi-hole sleeve fracturing was studied using theoretical analysis and numerical simulation. The variation law of inter-hole stress under different influencing factors was revealed, and the crack propagation law and force chain distribution characteristics in the fracturing process were obtained. The pre-cracking effect of sleeve fracturing can be improved by changing the drilling structure through grooving. In order to determine the reasonable hole arrangement parameters, a mechanical model of the multi-hole sleeve fracturing with prefabricated cracks was established based on linear elastic fracture mechanics. The calculation equations of stress intensity factor, critical expansion pressure, and critical crack initiation angle of cracks were given, and the variation rules of stress intensity factor, critical expansion pressure, and critical crack initiation angle of cracks under different influencing factors were obtained. The results show that: ① The lateral pressure coefficient k has a significant effect on the minimum crack initiation stress of the borehole. With the lateral pressure coefficient k > 1, the minimum crack initiation stress decreases with the increase of the hole angle. With the lateral pressure coefficient k < 1, the minimum crack initiation stress decreases with the increase of the hole angle. ② The numerical simulation results show that there is a stress superposition effect between the sleeves, and the contact force chain is a 'radial' distribution. The fracturing process of the sleeve is mainly a tensile failure, and the deformation and failure at the connection of the hole center is the most severe, forming a 'banded' fracture surface along the direction of the hole. ③ The stress distribution near the slot end is changed by the slot, and the circumferential tensile stress is larger than that of the seamless slot model. When the slot length is 0.5 times the radius of the hole, the critical expansion pressure is the smallest, and the crack is most likely to expand. ④ The critical initiation angle is determined by KI and KII, which is less than 70.53°. Under the condition that the pump pressure and in-situ stress conditions cannot be changed, the directional fracturing of the rock can be realized by adjusting the hole angle and the length of the prefabricated slot.

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Chongqing University of Technology (Natural Science) is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Through construction of the conformal mapping and with Stroh’s formula, the antiplane problem of 4 secondary cracks at the lip-shaped orifice of 1D hexagonal piezoelectric quasicrystal, was studied. The effects of geometrical parameters and external loads on stress intensity factors and energy release rates were analyzed with numerical examples. The results show that, the crack length growth on either corner side of the orifice or the orifice length increase can promote the crack propagation. The crack length growth on the upper and lower sides has no obvious effect on the crack propagation on the left and right sides. The higher the orifice height is, the more significant the inhibition effect on the crack growth on both corner sides will be; the increase of the external mechanical load and electric load can promote the crack propagation. Some special defects can be derived from the degradation of the relevant parameters of the defects, such as the secondary 2 cracks in the orifice, the lip-shaped crack, and the Griffith crack, etc. [ABSTRACT FROM AUTHOR]

Due to the significant variation of the stress gradient at the opening of ultra-high-pressure vessel, the cubic polynomial usually fitted by the least square method often has a large deviation from the actual stress distribution. To solve this problem, a calculation method based on piecewise interpolation was proposed. Firstly, based on the theory of stress intensity factor and general weight function, the calculation formulas were derived by constant interpolation, linear interpolation and quadratic interpolation. Secondly, combining with an engineering example, based on the elastic stress analysis of a crack free body, the calculation results of the stress distribution characterization accuracy and stress intensity factor of the conventional least square method, constant interpolation, linear interpolation and quadratic interpolation were compared and analyzed, and the reliability of the linear interpolation and quadratic interpolation methods was determined. Then, the influence of data collection on the results of linear interpolation and quadratic interpolation was analyzed, and the practicability of linear interpolation method was determined. Finally, the results of linear interpolation and finite element analysis were analyzed and verified. The results show that the representation accuracy of stress distribution is “ the least square method < constant interpolation < linear interpolation < quadratic interpolation”, and the relative error of calculation results is about 15% . With the increase of the amount of collected data, the calculation results using linear interpolation method can converge faster, which is more suitable for engineering calculation. The results of linear interpolation and finite element method are highly consistent, which proves the reliability of linear interpolation calculation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Mechanical Strength / Jixie Qiangdu is the property of Zhengzhou Research Institute of Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As an important covariate for assessing whether cracks are extended or not, the accuracy of the calculation of the stress intensity factor affects the assessment of material properties. The stress intensity factor at the crack tip was calculated by four numerical cases of a three-point bending beam containing precast cracks, rectangular slab center crack, rectangular slab center oblique crack, and rectangular slab center interface crack models using displacement extrapolation method and extended finite element method, respectively. The computational accuracy of the two methods was verified by comparing the computational results with the analytical solutions or reference solutions of other numerical methods. In addition, the effect of grid density on the accuracy of the stress intensity factor solution and the effect of eliminating the results near the crack tip on the displacement extrapolation method to solve the stress intensity factor was discussed. It is found that the displacement extrapolation method can improve the accuracy by local encryption of the crack tip and removal of the crack tip singularities. The extended finite element method requires a relatively small mesh density, and the mesh density can be increased appropriately considering the comprehensive calculation time. The results can provide a reference for solving the stress intensity factor and calculating the fracture toughness for the experimental-numerical coupling method. [ABSTRACT FROM AUTHOR]

Aiming at the problem of bed plate cracking during the construction of CRTS I double-block ballastless track in high-speed railway tunnels in China, a three-dimensional solid model of tunnel and ballastless track is established by using finite element software. The change law of displacement and uplift of each structure layer of ballastless track in tunnel under the action of groundwater is studied. Combined with FRANC3D software, prefabricated three-dimensional cracks of different shapes are inserted into the most stressed position of the roadbed slab structure, and the influence of water pressure and crack length on the crack growth of the roadbed slab is analyzed. The results show that: ( 1) Although the displacement uplift of the roadbed slab is somewhat decreased when the triangular load is applied compared with the uniform load, the repeated action of underground water pressure will always affect the track structure smoothness, and even lead to the separation of the track bed plate and the invert arch filling. (2) Crack length is the controlling factor of crack instability and growth. When the drainage system is completely blocked, it is recommended that the crack length be controlled within 200 mm. (3) Water pressure is the key influencing factor of crack growth. Under the same conditions, the larger the water pressure is, the more rapid the crack growth will be. The stress intensity factor at the tip of the crack of the roadbed slab under uniform load is 1.2~1.4 times of that under the corresponding triangular load. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Mechanical Strength / Jixie Qiangdu is the property of Zhengzhou Research Institute of Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study the influence of tooth root cracks on the fatigue life of case-hardened gears, taking an involute case-hardened gear as the research object, the mechanism of the tooth root fatigue crack growth is analyzed based on the fracture mechanics method and fatigue crack growth theory. The residual life analysis model of the tooth root crack propagation for case-hardened gears is established, considering the influence of load, initial crack size and initial crack location, etc. The evolution of stress intensity factor and crack propagation mechanism at different root crack propagation stages is studied. According to the bending fatigue test data of an involute case-hardened gear pair, the calculation model is analyzed and verified, and the accuracy of the model is proved. The results indicate that, compared with type Ⅱ and type Ⅲ, type Ⅰ stress intensity factor is the highest, which gradually decreases from the tooth surface to the direction of crack depth. With the increase of factors such as load, crack length, crack width, and initial crack distance from the center position of the tooth width, the residual life of crack propagation decreases accordingly.

In the practical application process, due to the different properties of the materials on both sides of the composite interface and the defects in the manufacturing process, under the action of external load, a large number of initial microcracks are generated at the interface, which then expand and intersect to form macrocracks and finally expand and penetrate, resulting in structural failure. Therefore, the analysis of interfacial cracks is very important for optimizing composite materials and improving their application performance and reliability. An extended two-phase hybrid stress finite element method was proposed. The fracture mechanics analysis of interface cracks was carried out by constructing an extended two-phase hybrid stress finite element model of two-phase materials including boundary cracks, horizontal center cracks and inclined cracks. The Lagrange multiplier method was used to introduce the zero boundary condition of the surface force of each interface crack and the continuous condition of the surface force of the unbroken interface into the modified complementary energy functional. The high-order polynomial stress function was assumed in each phase material domain, and the influence of the interface shape was fully considered. The interaction stress function was constructed, and the singular stress field function near the crack tip of the bimaterial interface crack was introduced. The element stress field was obtained based on Fortran program, and the stress intensity factor of interface crack was calculated by least square method. The numerical simulation results obtained by this method are compared with the numerical results of traditional finite element analysis to verify the effectiveness and accuracy of the method. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Light Industry Machinery is the property of Light Industry Machinery Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the gradual development of mines, tunnels, and other underground constructions, theoretical research on the influence of internal defects in rock structure on rock dynamic fracture behavior and related engineering practices are of great importance. In this paper, a digital laser dynamic caustics experimental system is used to conduct three-point bending drop hammer impact tests on three groups of polymethyl methacrylate specimens with different angles of bedding (30°, 45°, and 60°). The fracture process of the specimens and the shape change process of the dynamic caustic speckle at the crack tip were recorded using a high-speed camera. The characteristics of dynamic stress intensity factors Ⅰ and Ⅱ were obtained, and the crack tip displacement and velocity curves were analyzed. Combined with the discrete lattice spring model (DLSM), the fracture morphology of the specimens was analyzed, and the variation law of the stress field and field at the crack tip was obtained. The transmission and reflection characteristics of stress waves were studied at stratification. Finally, the impact of the fracture characteristic stratification parameters of the medium was analyzed using DLSM. The results show that the fracture characteristics of the specimens, the initiation time of the crack, and the propagation speed of the crack in the bedding plane vary with the bedding angle. With increasing bedding angle, the initiation time of the crack advances, the propagation speed of the crack increases along the weak bedding plane after extending to the bedding plane, and the crack is more inclined to extend along the weak bedding plane to complete specimen fracture. With the crack expansion, the type Ⅱ stress intensity factor appears, and the specimen fracture shows the characteristics of tension–shear composite failure. Before arriving at a particular bedding speed, cracks fluctuate up and down, and attenuation in the aftermath of the bedding generally has lower volatility change; the elastic modulus and bedding thickness affect the dynamic fracture characteristics of the specimens. If the bedding elastic modulus is less than 0.1 GPa, the crack extension in the bedding plane distance increases with the elastic modulus. If it is more than 0.1 GPa, when the bedding for the organic glass bonding effect increases, the crack goes directly through the bedding. The propagation distance of cracks along the weak plane of the bedding increases with the bedding thickness.

In order to accurately predict the effect of crack on the rockmass compression mechanical property such as strength and stiffness, a more reasonable compression damage model for the cracked rockmass is needed to be established. On basis of the relevant experimental data and mechanical behavior of the cracked rockmass under uniaxial compression, some deficiencies in the existing compression damage models for the rockmass with intermittent cracks are analyzed in detail. Three improvements are made to improve the existing methods, e.g., the crack deformation parameter is not taken as a constant, the negative first stress intensity factor KI produced by the normal stress on the crack face is considered, and KI produced by the effective shear stress on the crack face is considered. A revised uniaxial compression damage model for rockmass considering the crack deformation parameter is proposed and the validity of the proposed model is verified with the experimental data. The results show that the prediction of the rockmass elastic modulus and damage under uniaxial compression with the proposed model are more accurate than those obtained with the existing models. Especially, when the crack dip angel is 0°, the rockmass elastic modulus obtained with the proposed model is 4.306 MPa, which is nearly equal to its tested value 4.310 MPa. The proposed model can perfectly describe the rockmass mechanical behavior under uniaxial compression, which also indicates that it is very necessary to consider the effect of the crack deformation parameter on the rockmass uniaxial compression mechanical property. This study can provide references for accurately predicting the rockmass mechanical behavior under uniaxial compression.

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to characterize the Ⅰ-Ⅱ mixed-mode fracture performance of 2D-C/SiC composites, Arcan butterfly specimens with unilateral cracks were used, and the mode-Ⅰ and mode-Ⅱ fracture shape factors of the specimen were calibrated through finite element model. The Arcan disc device was used to carry out mode-Ⅰ, mode-Ⅱ and Ⅰ-Ⅱ mixed-mode fracture tests upon 2D-C/SiC butterfly specimens, and the macroscopic and microscopic fracture modes and strength properties of the specimens under different loading paths were investigated. The results show that the fracture toughness of mode-II of 2D-C/SiC material is higher than that of mode-I. With increasing of the loading angle, the influence of shear stress on the crack propagation path increases, and meanwhile the fracture resistance of the specimens presents a tendency to increase. The applicability of several fracture criteria is demonstrated, and an Ⅰ-Ⅱ mixed-mode fracture criterion for 2D-C/SiC composites is suggested.

Due to the influence of geological structures, various forms of joint structural planes are present in rock mass engineering. The undulating structural planes, such as a torsional fold surface, are unique geological structures. These structures affect the stability of rock masses and cause potential hazards to rock mass engineering. Because of their shape complexity, the research on the fracture and damage constitutive law of rock mass with undulating joints is not thoroughly conducted. Undulating joints with various dip angles were fabricated using three-dimensional printing technology. The uniaxial compression test and digital image correlation (DIC) technology were used to study the mechanical and fracture characteristics of undulating joint specimens. Based on the principle of fracture mechanics, an idea was proposed to use the DIC displacement field for solving the stress intensity factor (SIF：type one KI and type two KII) at the joint tips and to study the damage constitutive law. The results show that the upper limit of undulating joint damage to specimens is determined with 46.6% through the minimum strength analysis. The sensitivity of uniaxial strength to a joint dip angle of undulating joint specimen is greater than that of a straight joint specimen. The fracture initiation occurs near peak stress. The fracture process can be divided into the initiation and synchronous penetration of microcracks on the fracture path. Additionally, the fracture mode shows a combination of multiple tension and shear fractures. The SIF increases with loading at the prepeak stage, and the cracks propagate in shear fracture at the joint left and right tips in the postpeak stage because KII>KI under the same stress. The undulating joint damage to the specimen with the dip angle is in a sinusoidal curve form. The relationships between the total damage coupled by joint and load with strain are all “S” curves.

Taking 42CrMo steel for wind turbine pitch bearing as the research object, a three-dimensional finite element CT specimen model of initial crack is established by using ABAQUS and degenerated singular element, and the stress intensity factor at the crack front is calculated. A hexahedral mesh is used for the part far from the crack front. The stress intensity factor distribution of the crack front is extracted by the method of contour integration, and the numerical calculation results are compared with the theoretical calculation results. The distribution law of stress intensity factor at the crack front and the change law of stress intensity factor at the crack front under different loads and crack lengths are obtained. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Mechanical Strength / Jixie Qiangdu is the property of Zhengzhou Research Institute of Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study explores the full-field strain and dynamic fracture characteristics of a linear shaped charge under different initiation positions. The explosion dynamic caustic line experiment system is employed to examine the characteristics of the blast crack propagation of the linear shaped charge at different initiation positions and capture the dynamic information of the crack tip propagation speed and stress intensity factor. Furthermore, the digital image correlation method was used to show the strain evolution law of the linear shaped charge at different initiation positions, as well as the medium strain response of the charge near the explosion zone caused due to detonation transmission. The results show that in end-initiation, the wing crack length at the initiation point is the smallest, and the wing crack propagation length increases with the detonation propagation of the explosive. Conversely, in center-initiation, the propagation length of the wing cracks at the center is less than those at both ends. The propagation length of the wing cracks in the noninitiation end is the longest for end-initiation, where the velocities of the wing crack initiation and propagation are minimum. For center-initiation, the wing crack initiation and propagation velocities are the smallest, i.e., irrespective of the initiation position, the wing crack initiation and propagation velocities at the initiation point are lower than that at other locations. Based on the dynamic stress intensity factor analysis, irrespective of the initiation position, the center wing cracks are type Ⅰ cracks with the largest crack toughness, the stress intensity factor value is the maximum, and the wing cracks at the ends are type Ⅰ−Ⅱ composite cracks dominated by type Ⅱ. Based on the full-field strain analysis of the linear shaped charge, at end-initiation, the range of tension and strain action is mainly along the direction of explosive transmission, and the tension and strain action area at the noninitiation end is larger than that at the initiation end. The corresponding position of the maximum compressive strain is 0.67–0.83 times the charge length from the initiation point. When the center detonates, the action process of tension and compression strain propagates symmetrically from the center to both ends of the initiation, and the strain at the center is the largest. The compressive stress concentration at the end occurs under both initiation modes because the explosive transmission is the process of energy accumulation; thus, the effect of the explosive explosion on the medium grows increasingly stronger along the direction of explosive transmission.

The crack tip stress intensity factor is an important criterion for judging crack extension and structural failure. Investigating the crack tip stress intensity factor for the interaction between circular hole and crack under tensile loading is of great significance for material fracture criterion and residual strength analysis. Based on the superposition principle and the initial solution of elastodynamics, the integral equation of the stress intensity factors of the crack at the edge of a uniaxially tensile circular hole plate was obtained by using the Westergaard stress function, and the approximate solution of the integral equation was obtained by using Chebyshev polynomials, and the approximate solution was modified by using the exponential function to obtain the modified solution of the stress intensity factors at the crack tip. The same problem was simulated using Abaqus and compared with the corrected solution results. The effects of crack size, circular hole radius, crack location angle, and crack inclination on the stress intensity factor at the crack tip were analyzed. The results show that the modified solution and the Abaqus simulation solution basically agree. The stress intensity factors increases with the increase of crack size and circular hole radius, and decreases with the increase of crack location angle and crack inclination angle. [ABSTRACT FROM AUTHOR]

Centrifugal impeller blades are prone to fracture failure due to crack propagation when rotating at high speed. Due to the complex blade geometry and load, there is an error in calculating the stress intensity factor of mode-I crack by formula. Due to the complex blade geometry and load, errors are generated inevitably in calculating the stress intensity factor of mode I crack using theoretical formulae. Although extended finite element method can be used to obtain stress intensity factors with good accuracy, the computation is generally time consuming, and sometimes hard to converge. Firstly, the stress intensity factors at the crack tips of the blade were simulated considering different crack start positions and crack lengths using ABAQUS's XFEM module, and their relationship with crack length and starting position was obtained. Next, the accuracy of the formulaic estimate on the stress intensity factor was tested based on the theory of fracture mechanics. Finally, a multi-layer back propagation artificial neural network (BP-ANN) with the stress intensity factor of the crack tip was established using the simulation results of the extended finite element method as the training data and the crack position and crack length of the blade as the input parameters. The example shows that the predicting accuracy of BP-ANN is better than that of the formulaic method. With the BP-ANN, the simulation times of the extended finite element method can be effectively reduced which is beneficial to promoting the application of fracture mechanics in the reliability design of centrifugal impellers. [ABSTRACT FROM AUTHOR]

The inner wall of the quartz crucible for continuous Czocharlski will form more bubbles with the increase of Czocharlski times, and it is easy to generate dislocations in the crystal and the erosive silicon melt, which will cause the crucible to dissolve and corrode over time. In order to study the effect of the interaction of erosive silicon melt with bubbles on the crucible, in situ observations of the performance of quartz crucibles are expected. However, the extremely high temperature environment inside single crystal furnaces makes it difficult to investigate their interiors experimentally. In this paper, the pore-crack on the inner surface of the quartz crucible are taken as the research object, and the finite element simulation is used to obtain the stress intensity factor values of different pore shapes, crack shapes and crack inclination angles of the quartz crucible under high temperature cyclic loading at different Czocharlski stages. The results show that with the increase of the crack inclination angle, the KΙ value shows a trend of gradually decreasing, the Kâ...¢ value shows a trend of first increasing and then decreasing, and the Kâ...¢ value is symmetrical distributed along 45°; furthermore, with the increase of the pore depth/diameter ratio, KΙ value shows a decreasing trend, and the rate of reduction when the depth/diameter ratio is equal to 1 as the boundary has a significant increase, Kâ...¢ is much smaller than KΙ value, indicating that the dominant form of cracking is type â...; the crack shape ratio has a significant impact on the value of KΙ or Kâ...¢, and the smaller the shape ratio, the greater the value of the stress intensity factor at the crack tip; when the inclination angle is 0°, the total stress intensity factor K value is the largest, which will make the crack most likely to expand and the most harmful to the quartz crucible. Finally, in the case of continuous Czocharlski, the total stress intensity factor of the crown growth process is always greater than that of the equal diameter growth, cone and cooling growth process. Simulation results bring certain theoretical guiding significance for production. [ABSTRACT FROM AUTHOR]

2E12 is a new aluminum alloy material made in China. It is to be used in aircraft fuselage skin structure. Damage tolerance performance is one of its key indicators for the material. According to the requirement of damage tolerance design, this paper designs three typical test pieces of fuselage panel structure, including single-span crack, double-span crack and crack repair. Firstly, the numerical analysis of crack propagation and residual strength is completed, and then the verification test is carried out. The results are compared with those of 2024 aluminum alloy. The results show that the damage tolerance of 2E12 aluminum alloy material can meet the design requirements. Compared with single crack propagation, the existence of multi-crack increases the crack growth rate significantly, and the total life of multi-cracks is shortened by about 30%. The error of crack propagation analysis and test results is less than 10%. The residual strengths of all test pieces are in good agreement, and the difference between the analytical results and the experimental results is about 2.3%. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Some thin-walled structures in aircraft structures inevitably bear out-of-plane bending,affecting the safety of aircraft significantly.The FRACN3D-ABAQUS simulation method is adopted to carry out such research work.Effects of boundary restraint and initial crack shape on this kind of fatigue crack propagation are studied.The applicability of the simulation method is evaluated.Results show that weaker boundary constrains in simulations will increase the calculated stress intensity factor(SIF);the initial hole corner crack has a higher crack propagation rate than the initial surface crack around the hole;the FRACN3D-ABAQUS simulation method cannot simulate the crack propagation in the compressed surface,where the crack is unable to propagate.

In order to study the fracture characteristics of semi-disc specimens with circular defects under different impact speeds, Hopkinson rod is used to dynamically load the semi-disc specimen, and the fracture process of the semi-disc specimen is observed by the dynamic caustics test system, Through the combination of the two test systems, the fracture characteristics of the semi-disc specimens are studied, the research results show that: before the crack initiation, the focal speckle radius jumps, which is caused by the repeated loading of the incident rod. With the increase of the impact velocity, the peak stress intensity factor of the crack passing through the circular defect increases, and the propagation speed of the crack passing through the circular defect also increases significantly, which shows that the impact velocity contributes to the crack propagation. With the increase of the radius of the circular defect, the stress intensity factor of the second crack initiation at the circular defect becomes larger.

In this paper, an isogeometric analysis method is proposed to obtain the notch tip stress intensity factor for the plane fracture problem with V-notch. Based on the isogeometric analysis, which discretizes the overall structure and constructs the stiffness matrix of the structure, obtains the equilibrium equation, and simultaneously obtains the coordinate information of the nodes. Combined with the displacement expression of the plane with sharp notch in polar coordinate system, the node coordinate information of the whole field is substituted into the analytical expression after coordinate conversion to obtain a transformation matrix, and the isogeometric equilibrium equation is converted into a smaller-dimensional equation. The coefficients of the analytical solution of the displacement field can be calculated, and the stress field and the stress intensity factor of the notch are obtained at the same time. This method unifies numerical modeling and numerical calculation into one platform, which improves the efficiency of numerical analysis; avoids the grid-sensitive problem of iso-geometric analysis fracture problems, and the stress intensity factors can be directly solved without any post-processing program, and avoids the problem of inconsistency in the calculation of isogeometric equations.

Through studying the cracking and propagation law of compressive-shear cracks in rock under remote stress field， a new calculation model for the mode-I stress intensity factor at wing crack tip was proposed by considering the interaction of wing cracks. Based on the modified wing crack propagation model， considering the damage evolution on the number of the activated microcracks， a microcrack propagation-based damage model for rock was established by combining the relationship between macro-micro definition of rock damage. Finally， the theoretical curves of proposed damage model were compared with the experimental curves. The results showed that the modified wing crack propagation model can not only accurately predict the cracking angle of wing crack， but also simulate the whole range of variation of wing crack length from being extremely short to very long. The microcrack propagation-based damage model can not only continuously describe the stress-strain curves under different confining pressures， but also predict the peak strength well. [ABSTRACT FROM AUTHOR]

Many fatigue cracks can be derived from tank under long-term working conditions. These cracks not only affect the structural strength and service life of tank, but also threaten the personal safety of operators. Therefore, the analysis and research on the dynamic expansion of fatigue cracks in tank materials and the life mechanism were carried out. The semi-elliptical crack specimens with different length-to-depth ratios were prefabricated by Franc3 D crack analysis software to study the change of dynamic stress intensity factor of cracks under fatigue tensile loading, and to investigate the crack expansion path, rate and life time. The results show that the distribution law of the dynamic stress intensity factor at the tip of the semi-elliptic cracks with different length-depth ratios is basically the same, and the magnitude of the intensity factor at the near surface is the highest. The final crack morphology is still semi-oval in final. At the beginning of crack growth, crack propagation rate is almost equal, the growth distance increases exponentially with the increase of the number of load cycles, and the propagation rate at the near surface is the highest, but the crack propagation rate at the near surface of the crack with length-depth ratio less than or equal to 1 is basically the same. [ABSTRACT FROM AUTHOR]

In order to study the mechanical behavior characteristics of dynamic crack initiation and propagation of surrounding rock of adjacent roadway under impact load, with the help of a new digital laser dynamic caustics experimental system, a rock-like medium material PMMA was used to make a double-section roadway model for impact tests, and the crack propagation simulation was carried out based on the ABAQUS numerical simulation platform. The results show that when the pre-crack deflection angle α of adjacent sections is 45°, 22. 5°, 0°, -22. 5°, -45°, the dynamic stress intensity factor are different when the cracks were initiated. The dynamic stress intensity factor change after crack initiation has a "platform section" with a duration of about 160 μs. When the right crack gradually moves away from the left cross-section, the crack propagation speed of left crack after initiation will increase. When the dynamic crack initiation and propagation of the double-section roadway, the adjacent sections will affect the dynamic stress intensity factor and propagation speed to a certain extent. When the tip of the right crack is close to the left crack, the latter's crack initiation toughness is reduced, that is, it is easier to crack.

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As an important equipment for offshore oil and gas exploration, development and production, with its service life approaching the design value, the offshore platform has various forms of crack defects under the presence of complex loads. The effective measures to reduce cost, increase efficiency and improve quality are to carry out repair and reinforcement to prolong the service life. With its excellent mechanical properties, carbon fiber reinforced plastic (CFRP) can be applied to the repair and reinforcement technology of marine structures to achieve the goal of prolonging the duration of service. To research the repair performance of CFRP repair technology on cracked steel plates, the finite element model was determined. Combined with linear elastic fracture mechanics, the dependability of the model was verified. Considering the influence of prestress on the repair effect, the simulation analysis was implemented with crack tip stress (CTS) and stress intensity factor ( SIF) as evaluation indexes. The relationship between prestress on CFRP and SIF was fitted. The results demonstrate that CFRP can reduce the crack-tip stress and SIF of the plate, which shows that the CFRP repair technology has a good repair effect on the steel plate with cracks. The SIF decreases with the increase of prestress on CFRP, which proves that the application of prestress can enhance the repair performance of CFRP repair technology. Furthermore, it is found that there is a linear relationship between prestress and SIF. [ABSTRACT FROM AUTHOR]

Service with cracks is the normal state of engineering structures. Due to the fluid invading into the crack, the crack surface is loaded directly, which makes the crack further expand, and even affects the safety of the structure. In the analysis of fracture problems, according to the Williams element with generalized degrees of freedom (W element), the Williams series was used to establish the displacement field of the singular zone around the crack tip, and the stress intensity factors (SIFs) can be directly obtained by solving the generalized stiffness equation with high precision and high efficiency. However, the W element needs to satisfy the free boundary condition of the crack surface in the singular zone, so it is limited in the analysis of crack surface loading. Based on the SIFs reciprocity, the loading on the crack surface is equivalent to the concentrated force on the crack surface at the periphery of the equivalent singular zone, so the loading on the crack surface in the singular zone can be avoided, and the W element can be easily used for calculation. The numerical examples show that, the size of the equivalent singular zone is 1/20 of the crack length, the suggested equivalent load coefficient P is 2.0, and the calculation accuracy of the W element meets the error limit of 1%. The equivalent treatment method for the analysis of crack surface loading in the singular zone is reasonable and universal, and overcomes the limitation on the W element in analysis of the loading problem on crack surface. [ABSTRACT FROM AUTHOR]

The rock bridge in the slope rock mass has a controlling effect on the slope stability. In order to explore the deformation and failure characteristics and crack expansion mechanism of the jointed rock bridge, in this paper, the crack initiation, propagation, penetration and microscopic damage evolution characteristics of rock bridge are analyzed by prefabricating cracks at the end of complete specimen to form middle rock bridge combined with digital image correlation technology. The crack initiation, propagation and penetration mechanism of rock bridge is revealed by using the theory of fracture mechanics. The results show that the fracture process of rock bridge specimen can be divided into five stages and the strain-strain curve shows the characteristics of “pre-peak fluctuation” and “post-peak step” decline. The failure process of the rock bridge specimen is as follows: first, the crack initiation of the lower inclined crack, and then the deflection extends upward at a certain angle, and the crack expansion extends step by step; the failure of rock bridge samples is caused by the accumulation of damage in the early stage. The local high strain region formed at the crack tip indicates the propagation path of macro fracture; the expression of stress intensity factor at the crack tip is derived, and the crack initiation angle is calculated. The theoretical calculation is consistent with the experimental results.

During the service of pressure vessels, a variety of structural damage will occur, among which the corrosion pit formed by the corrosion of the loaded materials is the most important defect. In addition, cracks are formed due to the stress concentration in the pit position, which may propagate and result in fracturing and leakage. Stress intensity factor, as an important parameter to characterize the cracks, is widely used in engineering to judge the safety and reliability of the mechanical structures. Thereby, with reference to the two-parameter pit-crack model, the change rule of the nominal stress intensity factor of crack in the presence of pit-crack was discussed with ANSYS finite element software. The results show that the existence of pit-crack increases the nominal stress intensity factor of crack, but the effect decreases with the increase of pit-crack spacing and trends to be stable. Moreover, the effects of the pit parameters and the length-depth ratio of cracks on the stress intensity factor have obvious interval characteristics. Generally, the research results could provide reference for the failure evaluation of pressure vessels with pit-cracks.

Copyright of Journal of Henan University of Science & Technology, Natural Science is the property of Editorial Office of Journal of Henan University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to overcome the significant settlement difference between the road and the bridge and to essentially solve the bridge head jumping problem, a five-layer system three-dimensional finite element model was established by ABAQUS through the stiffness coordination analysis method, and the change law of the road and bridge transition section surface pavement performance under the action of single and multi-factor was analyzed based on fracture mechanics, and then a multi-factor fatigue life prediction model was established for the structural combination and mechanical control index. The results show that the stress intensity factor KⅡ decreases with the decrease of the stiffness difference between the surface layer and the subgrade, the surface layer and the lap layer, and the surface layer and the soil base. The fatigue life of surface layer decreases with the increase of surface layer modulus and axle load, and increases with the increase of surface layer thickness, base layer thickness, base layer modulus, lap layer thickness, lap layer modulus, soil base modulus and vehicle speed. the order of sensitivity to fatigue life of pavement is surface layer thickness > vehicle speed > soil base modulus > axle load > lap layer thickness > base layer thickness > surface layer modulus > base layer modulus > lap plate modulus. The research results can provide the corresponding theoretical support for the rational design of asphalt pavement at the bridge head lap in China, and also provide a new method for the fatigue life research in China. [ABSTRACT FROM AUTHOR]

The prediction model of leaf springs fatigue crack growth under variable amplitude loads is mainly Schütz phenomenological model. However, the effect of the crack closure effect on fatigue crack propagation and the relationship between the parameters and the stress ratio wasn’t considered. The threshold value of the fatigue crack was only suitable for the special working conditions where the stress ratio is 0. Therefore, the Schütz fatigue crack propagation phenomenological model was improved, which caused the physical parameters meaning more accurate, suitable for different working conditions. The stress measured by the actual vehicle test was applied to the modified model to describe the progress of leaf spring fatigue crack growth under the variable amplitude load. The results show that the crack growth rate increases with the loading amplitude. The test results are in good agreement with the model prediction results, which provides a theoretical basis for the calculation of fatigue crack growth rate under variable amplitude load.