Статті в журналах: "Contact crack"

1

Kuo, C. H., L. M. Keer, and M. P. Bujold. "Effects of Multiple Cracking on Crack Growth and Coalescence in Contact Fatigue." Journal of Tribology 119, no. 3 (July 1, 1997): 385–90. http://dx.doi.org/10.1115/1.2833499.

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A three-dimensional fracture analysis is applied to investigate the interaction effects of multiple cracking on the crack growth in contact fatigue and to simulate the process of crack coalescence that leads to pitting failure. The rolling contact fatigue is simulated by a cyclic Hertzian contact loading moving across the surface of an elastic half-space containing several planar cracks. The body force method is applied to determine the three modes of stress intensity factors around the three-dimensional crack fronts. The fatigue crack propagation under contact loading is estimated based on the modified Paris law for mixed mode crack growth. For coplanar cracks, the growth rate increases significantly as the adjacent cracks are very close while parallel cracks appear to constrain the cracks from coalescing. A numerical simulation for the propagation of crack fronts versus contact cycles is shown to agree with the pitting cracks observed in gears.

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2

Chen, Yung-Chuan, and Jao-Hwa Kuang. "Partial Slip Rolling Wheel-Rail Contact With a Slant Rail Crack." Journal of Tribology 126, no. 3 (June 28, 2004): 450–58. http://dx.doi.org/10.1115/1.1759339.

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This paper investigates the tip characteristics of an oblique crack in the wheel-rail contact problem. The wheel-rail normal contact pressure and interfacial shear stress distributions, and the stress intensity factors (SIF), are studied for oblique cracks of different inclinations, and the variations in both contact stress distributions near the crack edge are simulated under normal and traction loads, respectively. Contact elements are employed to model the interactions between the wheel-rail contact surfaces and the crack surfaces, respectively. The effects of crack orientation, crack length, and contact distance on the contact stress distributions and stress intensity factors, KI and KII, are investigated. The results indicate that a wheel-rail traction force reduces KII significantly as the contact point travels over the crack edge. Furthermore, fluctuations in KI and KII are very significant with regard to early squat propagation of cracks. The results also demonstrate that applying Carter’s contact model or the full slip contact model to the same wheel-rail contact crack problem yields significantly different stress intensity factor values.

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3

Bower, A. F. "The Influence of Crack Face Friction and Trapped Fluid on Surface Initiated Rolling Contact Fatigue Cracks." Journal of Tribology 110, no. 4 (October 1, 1988): 704–11. http://dx.doi.org/10.1115/1.3261717.

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A two-dimensional model of a surface initiated rolling contact fatigue crack has been developed. The model takes into account the effects of frictional locking between the faces of the crack, and the influence of fluid pressure acting on the crack faces. The model has been used to investigate three possible mechanisms for propagating the cracks: mode II crack growth due to the cyclic shear stresses caused by repeated rolling contact; crack growth due to fluid forced into the crack by the load; and crack growth due to fluid trapped inside the crack. The predictions of the theory are compared with the behaviour of contact fatigue cracks.

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4

Gao, Ruipeng, Mengmeng Liu, Bing Wang, Yiran Wang, and Wei Shao. "Influence of Stress Intensity Factor on Rail Fatigue Crack Propagation by Finite Element Method." Materials 14, no. 19 (September 30, 2021): 5720. http://dx.doi.org/10.3390/ma14195720.

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Wheel rail rolling contact fatigue is a very common form of damage, which can lead to uneven rail treads, railhead nuclear damage, etc. Therefore, ANSYS software was used to establish a three-dimensional wheel–rail contact model and analyze the effects of several main characteristics, such as the rail crack length and crack propagation angle, on the fatigue crack intensity factor during crack propagation. The main findings were as follows: (1) With the rail crack length increasing, the position where the crack propagated by mode I moved from the inner edge of the wheel–rail contact spot to the outer edge. When the crack propagated to 0.3–0.5 mm, it propagated to the rail surface, causing the rail material to peel or fall off and other damage. (2) When the crack propagation angle was less than 30°, the cracks were mainly mode II cracks. When the angle was between 30 and 70°, the cracks were mode I–II cracks. When the angle was more than 70°, the cracks were mainly mode I cracks. When the crack propagation angle was 60°, the equivalent stress intensity factor reached the maximum, and the rail cracks propagated the fastest.

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5

Zhang, Yu, Sanjit Bhowmick, and Brian R. Lawn. "Competing Fracture Modes in Brittle Materials Subject to Concentrated Cyclic Loading in Liquid Environments: Monoliths." Journal of Materials Research 20, no. 8 (August 1, 2005): 2021–29. http://dx.doi.org/10.1557/jmr.2005.0276.

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The competition between fracture modes in monolithic brittle materials loaded in cyclic contact in aqueous environments with curved indenters is examined. Three main modes are identified: conventional outer cone cracks, which form outside the maximum contact; inner cone cracks, which form within the contact; and median–radial cracking, which form below the contact. Relations describing short-crack initiation and long-crack propagation stages as a function of number of cycles, based on slow crack growth within the Hertzian field, are presented. Superposed mechanical driving forces—hydraulic pumping in the case of inner cone cracks and quasiplasticity in the case of median–radials—are recognized as critically important modifying elements in the initial and intermediate crack growth. Ultimately, at large numbers of cycles, the cracks enter the far field and tend asymptotically to a simple, common relation for center-loaded pennylike configurations driven by slow crack growth. Crack growth data illustrating each mode are obtained for thick soda-lime glass plates indented with tungsten carbide spheres in cyclic loading in water, for a range of maximum contact loads and sphere radii. Generally in the glass, outer cone cracks form first but are subsequently outgrown in depth as cycling proceeds by inner cones and, especially, radial cracks. The latter two crack types are considered especially dangerous in biomechanical applications (dental crowns, hip replacements) where ceramic layers of finite thickness are used as load-bearing components. The roles of test variables (contact load, sphere radius) and material properties (hardness, modulus, toughness) in determining the relative importance of each fracture mode are discussed.

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6

Eberhardt, A. W., and B. S. Kim. "Stress Intensity Factors for a Vertical Surface Crack in Polyethylene Subject to Rolling and Sliding Contact." Journal of Biomechanical Engineering 120, no. 6 (December 1, 1998): 778–83. http://dx.doi.org/10.1115/1.2834893.

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Pitting wear is a dominant form of polyethylene surface damage in total knee replacements, and may originate from surface cracks that propagate under repeated tribological contact. In the present study, stress intensity factors, KI, and KII, were calculated for a surface crack in a polyethylene-CoCr-bone system in the presence of rolling or sliding contact pressures. Variations in crack length and load location were studied to determine probable crack propagation mechanisms and modes. The crack tip experienced a wide range of mixed-mode conditions that varied as a function of crack length, load location, and sliding friction. Positive KI values were observed for shorter cracks in rolling contact and for all crack lengths when the sliding load moved away from the crack. KII was greatest when the load was directly adjacent to the crack (g/a = ±1), where coincidental Mode I stresses were predominantly compressive. Sliding friction substantially increased both KImax and KIImax. The effective Mode I stress intensity factors, Keff, were greatest at g/a = ±1, illustrating the significance of high shear stresses generated by loads adjacent to surface cracks. Keff trends suggest mechanisms for surface pitting by which surface cracks propagate along their original plane under repeated reciprocating rolling or sliding, and turn in the direction of sliding under unidirectional sliding contact.

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7

Nishimura, T. "Contact Analysis for Collinear Multiple Cracks in Residual Stress Field." Journal of Pressure Vessel Technology 116, no. 2 (May 1, 1994): 169–74. http://dx.doi.org/10.1115/1.2929571.

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A method is proposed for analyzing stress intensity factors and crack profiles for collinear multiple cracks perpendicular to welded joints in an infinite plate. Using the basic solution of a single crack and taking unknown density of fictitious tractions, Fredholm integral equations and algebraic equations are formulated based upon traction-free conditions and crack face displacements, respectively. These equations are solved simultaneously, considering the contact effect of crack surfaces. Using the derived density of fictitious tractions, the stress intensity factors and displacements of multiple cracks are determined. Some numerical examples are analyzed.

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8

Fletcher, D. I., and J. H. Beynon. "Equilibrium of crack growth and wear rates during unlubricated rolling-sliding contact of pearlitic rail steel." Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit 214, no. 2 (March 1, 2000): 93–105. http://dx.doi.org/10.1243/0954409001531360.

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It is generally accepted that large rolling contact fatigue cracks in rails do not develop during unlubricated rolling-sliding contact, and damage under these conditions is restricted to wear of the rail steel. However, close examination of a worn rail steel surface reveals the presence of a multitude of wear flakes, the roots of which closely resemble shallow rolling contact fatigue cracks. Experiments have been conducted under unlubricated rolling-sliding conditions to examine the early development of flakes, or cracks, using a laboratory-based, twin-disc test machine to simulate the contact pressure and slip characteristic of the contact between a rail and a locomotive driving wheel. Small defects were found after as few as 125 unlubricated contact cycles. It was found that an equilibrium between crack growth rate and surface wear rate was established after approximately 10 000 cycles, leading to a shallow steady state crack depth. Initial crack growth by ratchetting (accumulation of unidirectional plastic strain until the critical failure strain of the material is reached), followed by shear stress-driven crack growth described by fracture mechanics, was found to be a sequence of mechanisms in qualitative agreement with the observed crack growth and steady state crack depth.

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9

Fedelinski, Piotr. "Analysis of closed branched and intersecting cracks by the boundary element method." Acta Mechanica 233, no. 3 (March 2022): 1213–30. http://dx.doi.org/10.1007/s00707-022-03158-x.

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AbstractThe boundary element method (BEM) and a computer code for the analysis of plates with closed branched and intersecting cracks are developed. The BEM enables simple and accurate modelling of cracked plates by using boundary elements. Contact tractions between crack surfaces are computed using an iterative procedure. Stress intensity factors (SIFs) are determined using the path-independent integral. Three numerical examples are studied: a star-shaped crack in a square plate, multiple interacting cracks in an infinite plate and randomly distributed and intersecting cracks in a square plate. The examples demonstrate the simplicity of numerical modelling, the accuracy of the method and the possible applications. The influences of load directions, distances between cracks and the contact of the crack surfaces on SIF are investigated. For the plate with randomly distributed cracks, the effective elastic properties are additionally computed by considering or neglecting contact of crack surfaces. The results show that the importance of the contact procedure depends on how the cracked material is loaded.

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10

Graciani, Enrique, Vladislav Mantič, and Federico París. "Effect of Friction on the Size of the Near-Tip Contact Zone in a Penny-Shaped Interface Crack." Key Engineering Materials 618 (July 2014): 179–201. http://dx.doi.org/10.4028/www.scientific.net/kem.618.179.

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Relations between different solutions of an interface crack in a neighborhood of the crack tip given by the open model, frictionless and frictional contact models of interface cracks are analyzed numerically for a penny-shaped interface crack subjected to remote tension. A new analytic expression for the size of the near-tip contact zone in presence of Coulomb friction between crack faces is proposed in the so-called case of the contact zone field embedded in the oscillatory field.

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11

Kida, Katsuyuki. "Flaking Failure in Silicon Nitride under Reciprocating Rolling Contact Fatigue." Advanced Materials Research 217-218 (March 2011): 866–73. http://dx.doi.org/10.4028/www.scientific.net/amr.217-218.866.

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Previous researchers investigated the failures of ball surfaces of silicon nitride bearings from the viewpoint of the ring crack model. They explained the process of flaking failures in terms of surface semi-circular cracks which grew by the stresses around the circumference of the contact circle. However, contrary to their explanation, we found that the ring crack model did not explain the process of the flaking failure of plates. In the present work we compare the growth directions of surface and subsurface cracks in order to find out which crack is more dominant in the process of the flaking failure. We carried out reciprocating-rolling contact fatigue (RCF) tests and concluded that the directions of arcs formed by the semi-circular surface cracks were dominated by subsurface crack growth direction.

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12

Dubourg, M. C., and B. Villechaise. "Analysis of Multiple Fatigue Cracks—Part I: Theory." Journal of Tribology 114, no. 3 (July 1, 1992): 455–61. http://dx.doi.org/10.1115/1.2920905.

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This paper analyzes the effects of multiple cracks situated in the contact zone vicinity of an elastic isotropic component, modeled as a half-plane. Friction between the crack faces is taken into account using Coulomb’s law. Straight arbitrarily oriented cracks are considered. Any contact condition can be modeled between the crack faces as well as any loading condition over the half-plane surface, including complete loading cycles. The method has been tested for up to 5 cracks and shows no limitation in crack number. Further, the method is general as no prior assumptions concerning the state of the crack, i.e., the slip-stick-open configurations along the crack are required. The stress intensity factors (SIFs) calculated for two crack configuration are compared with those obtained for single cracks.

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13

Xu, Yan Hai, and Yong Xiang Zhao. "Modelling the Behavior of Short Fatigue Cracks under Variable Amplitude Loading Using FEM." Key Engineering Materials 353-358 (September 2007): 985–88. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.985.

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The behavior of short fatigue cracks under variable amplitude loading (VA) was investigated by FEM. The crack closure induced by the crack surface roughness was taken into consideration by using the contact between these crack surfaces. The effects of variable amplitude loading on the performance of short cracks are demonstrated with factors such as grain orientation and misorientation, crack length and the friction efficient between the contacted crack surfaces. Through the two indicators, crack tip opening displacement represented by "CTOD and "CTSD and the plastic strain range of crack tip, the characteristics of short cracks affected by loading blocks are discussed in detail. It is shown from the numerical results that the significance of the design of loading blocks in the fatigue experiments is evident and the performance of short cracks from the variable amplitude loading is more effective due to the closer to practice.

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14

Daves, Werner, Wei Ping Yao, and Stephan Scheriau. "Crack Growth Tendency of Surface Shear Cracks in Rolling Sliding Contact." Key Engineering Materials 592-593 (November 2013): 250–53. http://dx.doi.org/10.4028/www.scientific.net/kem.592-593.250.

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Surface cracks arising during rolling sliding contact of a wheel and a rail are investigated. A two-dimensional crack model is proposed which calculates the crack driving force using the configurational force concept. The numerical applicability of the configurational force concept for surface shear cracks under cyclic contact loading is discussed and compared to the J-integral concept. A single inclined crack in a rail loaded by an accelerated wheel is investigated. The material of the rail is described by a cyclic plastic kinematic hardening model. The evolution of the crack driving force during several cycles is investigated.

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15

Takahashi, Koji, Keita Takahashi, and Kotoji Ando. "Improvement in Contact Strength of Si3N4/SiC Composite by Crack Healing." Journal of Powder Technology 2013 (June 11, 2013): 1–6. http://dx.doi.org/10.1155/2013/598024.

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Ceramics have been used as bearing and cutting tool components, which are subjected to contact loading during their operation. The presence of surface cracks on these components decreases their contact strength. Thus, the reliability of ceramic components can be increased by improving their contact strength through crack healing. In the present study, the effects of crack healing on the contact strength of a silicon carbide-(SiC-) reinforced silicon nitride (Si3N4) composite subjected to various machining processes were investigated. The contact strength of this composite was evaluated using a sphere indentation test in which acoustic emission was used. The results showed that the contact strength of the composite improved when it was subjected to crack healing in combination with rapping; this was true even when the composite had cracks due to a heavy machining process.

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16

Kim, Ki-Chai, Jong-Woo Kim, Jae-Yong Kwon, and No-Weon Kang. "Non-contact Crack Detection in Metals Using a Cutoff-Cavity Probe." Journal of Electromagnetic Engineering and Science 21, no. 3 (July 31, 2021): 167–76. http://dx.doi.org/10.26866/jees.2021.3.r.23.

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This paper presents a non-contact method for the detection of surface cracks in metal materials through a forced-resonance microwave method (FRMM) using a cutoff cavity-backed narrow slot as a crack detection probe without using a vector network analyzer (VNA) at microwave frequencies. The FRMM uses the deviations in the ammeter or voltmeter readings of the forcefully obtained resonance of a cutoff-cavity probe for a metal material with or without cracks. The cutoff cavity-backed narrow slot on metal with no cracks produces a series resonance (maximum current) or a parallel resonance through an external control element located on a post inside the cutoff cavity. Cracks were detected by a change in this forced-resonance state (maximum current) when the cutoff-cavity probe was scanned over a crack. The characteristic crack signal was derived from the resonance current deviation on the ammeter located on a post inside the cavity probe. Galerkin’s method of moments was used to obtain a forced-resonance state from which the crack signal of the FRMM was calculated. The experimental measurements for non-contact (remote or lift-off) crack detection are also presented.

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17

Shi, Zhifeng, Jing Liu, and Shaojiang Dong. "A numerical study of the contact and vibration characteristics of a roller bearing with a surface crack." Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications 234, no. 4 (January 30, 2020): 549–63. http://dx.doi.org/10.1177/1464420720903075.

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Roller bearings are key parts in different machineries. As one of the major incipient failure models in the bearings, the surface crack will be enlarged to be a large spalling failure. Moreover, the abrupt changes in the contact characteristics caused by the crack zone would produce unacceptable impulses, which can affect the bearing vibrations. Thus, a study of the contact characteristics and vibrations of the bearings including the surface crack could be conducive for the incipient fault monitoring methods. To overcome this issue, a finite element model is proposed to obtain the influences of the depth and slope angle of a surface crack on the contact characteristics in a roller bearing. The relationships between the contact characteristics (contact deformation, width and stiffness) and crack sizes (depth and slope angle) are established. To study the influences of the surface crack sizes on the bearing vibrations, a dynamic model of the roller bearing considering the surface crack is also proposed. An experiment is introduced to verify the proposed method. It seems that the crack depth and slope angle can greatly affect the contact and vibration characteristics of the bearing. This study provides a helpful numerical approach for understanding the contact and vibration characteristics of roller bearings with various surface cracks.

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18

CHEN, Y. Z., X. Y. LIN, Z. X. WANG, and N. M. A. NIK LONG. "SOLUTION OF CONTACT PROBLEM FOR AN ARC CRACK USING HYPERSINGULAR INTEGRAL EQUATION." International Journal of Computational Methods 05, no. 01 (March 2008): 119–33. http://dx.doi.org/10.1142/s0219876208001418.

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This paper investigates the contact problem for an arc crack, for example, under a remote compression. A hypersingular integral equation (HSIE) for curved cracks in plane elasticity is suggested. It is found that the direct usage of HSIE cannot solve the mentioned contact problem. For the contact problem, one must take necessary modifications for solving the HSIE. The main modified points are as follows. First, one should assume some portion along the crack under contact. The margin or the end of the contacted portion is determined by the vanishing normal contact stress at the margin point. In addition, it is found that a suggested quadrature rule in conjunction with the curve length method provides a very effective way to solve the HSIE. Finally, several numerical examples are given.

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19

Lamacq, V., M. C. Dubourg, and L. Vincent. "Crack Path Prediction Under Fretting Fatigue—A Theoretical and Experimental Approach." Journal of Tribology 118, no. 4 (October 1, 1996): 711–20. http://dx.doi.org/10.1115/1.2831599.

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In this paper, the direction of crack growth under fretting fatigue loading is studied through an experimental and theoretical approach. The experimental work enabled the fretting conditions to be known and the site of initiation and crack trajectory to be viewed; theoretical work permitted a prediction of those processes. Fretting wear and fretting fatigue loadings induce non-proportional mixed mode loading at the tip of the cracks initiated within the contact zone. The classical criteria predicting the direction of crack growth cannot account for the non-proportional loading. Tests were carried out to study the cracking phenomena under cumulative effects of contact and external loadings, i.e., fretting fatigue loading. The fretting contact between the two contacting bodies is modeled to evaluate the operating contact loading conditions. The response of the cracked body is determined in terms of stress intensity factors using the continuous distribution of dislocations theory coupled with a unilateral contact analysis with friction. The angle of crack extension is then predicted, at different stages of crack life, according to a new approach. The correlation of the predicted angle of crack extension with the experimental observation enables the conclusion that, under fretting fatigue loading, cracks propagate by a mode I process.

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20

Daves, Werner, and Michal Kráčalík. "Cracks Loaded by Rolling Contact - Influence of Plasticity around the Crack." Solid State Phenomena 258 (December 2016): 221–24. http://dx.doi.org/10.4028/www.scientific.net/ssp.258.221.

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For the description of cracks in rolling/sliding contacts many overlapping interactions has to be regarded and most of them are non-linear phenomena. This paper emphasis the aspect of plasticity around cyclically loaded shear cracks which is omitted very often in the common literature. It is shown that this plasticity can be calculated and regarded in computed crack driving forces; however, the problem is not solved after doing this. It is a first estimate only to regard the crack driving force calculated in the finite elements surrounding the crack tip as a relevant measure.

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21

Chen, Shao Hua, Guang Xu, and Cong Yan. "Subsonic Interface Crack with Crack Face Contact." Advanced Materials Research 33-37 (March 2008): 307–14. http://dx.doi.org/10.4028/www.scientific.net/amr.33-37.307.

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A steady-state subsonic interface crack propagating between an elastic solid and a rigid substrate with crack face contact is studied. Two cases with respective to the contact length are considered, i.e., semi-infinite and finite crack face contact. Different from a stationary or an open subsonic interface crack, stress singularity at the crack tip in the present paper is found to be non-oscillatory. Furthermore, in the semi-infinite contact case, the singularity of the stress field near the crack tip is less than 1/2. In the finite contact case, no singularity exists near the crack tip, but less than 1/2 singularity does at the end of the contact zone. In both cases, the singularity depends on the linear contact coefficient and the crack speed. Asymptotic solutions near the crack tip are given and analyzed. In order to satisfy the contact conditions, reasonable region of the linear contact coefficient is found. In addition, the solution predicts a non-zero-energy dissipation rate due to crack face contact.

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22

Lei, T. S., V. Bhargava, G. T. Hahn, and C. A. Rubin. "Stress Intensity Factors for Small Cracks in the Rim of Disks and Rings Subjected to Rolling Contact." Journal of Tribology 108, no. 4 (October 1, 1986): 540–44. http://dx.doi.org/10.1115/1.3261258.

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The influence of the residual stresses attending the plastic deformation of a rim on the cyclic crack growth driving force produced by repeated two-dimensional rolling contacts is evaluated. The residual stresses are estimated for disks and rings with different geometries. Values of the Mode II and Mode I stress intensity range, ΔKI and ΔKII, are derived for small, subsurface cracks from the variations in the stress intensity factors with position of the contact for rolling in the absence of surface shear tractions. The calculations take into account (i) steady-state contact stresses generated by a relative peak pressure of po/k = 5; (ii) the radial and circumferential residual stresses, (iii) the frictional resistance on the crack faces; (iv) the crack inclination, and (v) the relative ratios of the inner and outer ring radii. A prediction of the crack initiation and growth rate for high strength steel is illustrated.

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23

Chen, Yung-Chuan, and Jao-Hwa Kuang. "Elastic-Plastic Partial Slip Rolling Wheel-Rail Contact with an Oblique Rail Crack." Journal of Tribology 127, no. 4 (March 29, 2005): 705–12. http://dx.doi.org/10.1115/1.2033006.

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This study employs an elastic-plastic finite element model to investigate the effect of oblique rail surface crack on the wheel-rail contact stress distribution under partial slip rolling conditions. Numerical simulations are performed to explore the effects of the contact distance and tractive force on the contact pressure and tangential stress distributions, tip plastic energy, and critical wheel applied load. Contact elements are used to simulate the interaction between the surfaces of the wheel rail and the crack. The numerical results indicate that the contact stress distributions are influenced significantly by the presence of oblique cracks in the rail. The results also indicate that a higher friction force is induced on the crack surfaces when a greater tractive force is applied to the wheel. This increased crack surface friction force reduces the sliding between the crack surfaces and hence causes a reduction in the tip plastic energy.

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24

Hiraoka, Kazuhiko, Takeshi Fujimatsu, Kazuya Hashimoto, Shinji Fukumoto, and Atsushi Yamamoto. "Crystallographic Analyses on Cracks Initiated by Rolling Contact Fatigue in High Carbon Chromium Bearing Steel." Materials Science Forum 561-565 (October 2007): 2151–54. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.2151.

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Crack formation by a rolling contact fatigue in a high carbon chromium bearing steel has been discussed. Newly developed method for preparing specimens including pre-existing voids enabled one to observe the early stage of fatigue crack formation. Many fatigue cracks were formed around the voids. The positions of crack formation and the direction of the cracks were consistent with those forecasted by finite element analysis. Fatigue crack formation was followed by formation of the WEAs.

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25

Feng, Li Chun, Da Peng Chen, Zhi Zeng, and Ning Tao. "Composite Evaluation Using Contact and Non-Contact Ultrasound Excited Thermography." Applied Mechanics and Materials 268-270 (December 2012): 1627–31. http://dx.doi.org/10.4028/www.scientific.net/amm.268-270.1627.

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In ultrasound excited thermography method, high energy ultrasound is used as exciting source which can stimulate the defects such as crack and disband to produce heat. The heat excited would lead to temperature increase. The surface temperature would be captured and recorded by a thermal camera and further analysis would done. In this method, the defect is selectively stimulated, which makes this method suitable for small crack detection. Compared to contact ultrasound excited thermography method in which the sample to be tested is contacted with the high energy ultrasound source, in non-contact ultrasound excited thermography method, the sample has no contact with the horn of the high energy source and the energy is coupled by air. The non-contact method is suitable for the application in which even and not very high ultrasound energy is required or the sample is fragile. CFRPs with impact damage and a composite component with cracks were inspected with these two methods, the results show that ultrasound excited thermography method is suitable for composite evaluation.

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26

Seo, Jung Won, Seok Jin Kwon, Hyun Kyu Jun, and Dong Hyung Lee. "Microstructure Features and Contact Fatigue Crack Growth on Rail." Materials Science Forum 654-656 (June 2010): 2491–94. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.2491.

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Rolling Contact Fatigue (RCF) damage on the surface of rails such a head check, squats is a growing problem. Since rail fractures can cause derailment with loss of life and property, the understanding of rail fracture mechanism is important for reducing damages on the rail surface. In this study, we have investigated RCF damage, fatigue growth and fracture surface morphology on the surface of broken rail using failure analysis and finite element (FE) analysis. The investigation indicates that the crack grows at about 20° to the depth of 8mm from the surface and branches into two cracks. One crack propagates downward at about 47°, the other propagates upward. Since the crack growth rate of the downward crack was faster than that of upward crack, rail eventually was broken. Since the downward branches lead to fracture of the rail, they are more dangerous to the integrity of rails. It has been observed that White Etching Layer (WEL) occurs within the surface of broken rail. It was found that the fatigue crack initiation and propagation was accelerated by WEL.

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27

Hannes, Dave, and B. Alfredsson. "Rolling Contact Fatigue Crack Growth Prediction by the Asperity Point Load Mechanism." Key Engineering Materials 488-489 (September 2011): 101–4. http://dx.doi.org/10.4028/www.scientific.net/kem.488-489.101.

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The crack path and growth life of surface initiated rolling contact fatigue was investigated numerically based on the asperity point load mechanism. Data for the simulation was captured from a gear contact with surface initiated rolling contact fatigue. The evolvement of contact parameters was derived from an FE contact model where the gear contact had been transferred to an equivalent contact of a cylinder against a plane with an asperity. Crack propagation criteria were evaluated with practically identical crack path predictions. It was noted that the trajectory of largest principal stress in the uncracked material could be used for the path prediction. The mode I fracture mechanism was applicable to the investigated rolling contact fatigue cracks. The simulated path agreed with the spall profile both in the entry details as in the overall shape, which suggested that the point load mechanism was valid not only for initiation but also for rolling contact fatigue crack growth. Different equivalent stress intensity factor ranges were used to estimate the fatigue life, which agreed with the life of the investigated gear wheels.

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28

Kaneta, M., and Y. Murakami. "Propagation of Semi-Elliptical Surface Cracks in Lubricated Rolling/Sliding Elliptical Contacts." Journal of Tribology 113, no. 2 (April 1, 1991): 270–75. http://dx.doi.org/10.1115/1.2920616.

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In this paper the three-dimensional mixed mode stress intensity factors for semi-elliptical inclined cracks formed on elliptical Hertzian contact surfaces are calculated. This analysis accounts for both the frictional forces between the contact surfaces and between the crack faces, as well as including fluid pressure acting on the crack faces. Various factors affecting the crack growth are discussed and possible growth modes are investigated. In particular, the analytical results predict that the crack has a faster growth rate when the major axis of the contact ellipse is in the direction of motion of the load as compared to the minor axis being in the direction of motion of the load.

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29

Mizozoe, Syunsuke, and Katsuyuki Kida. "Internal Shear Stress Distribution and Subsurface Cracks of PPS Thrust Bearings under Rolling Contact Fatigue in Water." Key Engineering Materials 858 (August 2020): 101–5. http://dx.doi.org/10.4028/www.scientific.net/kem.858.101.

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In this study, crack propagation in PPS thrust bearings under rolling contact fatigue (RCF) in water was observed, and relation between subsurface crack and internal shear stress parallel to the surface was investigated. It was found the cause of flaking was subsurface crack. They were evaluated in terms of contact stress and friction between their faces. It was discovered that subsurface cracks distributed around shear stress peak, and flaking failure was dominated by subsurface shear stress.

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30

Yu, Hai Liang, Xiang Hua Liu, Chang Sheng Li, and Li Qing Chen. "Research on Behavior of Slab Surface Defects in Forward Slip Zone during V-H Rolling Process." Materials Science Forum 575-578 (April 2008): 243–48. http://dx.doi.org/10.4028/www.scientific.net/msf.575-578.243.

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Behavior of the transversal crack and the longitudinal crack on slab surface during V-H rolling was simulated by the FEM. The contact pressure on crack surfaces and the crack-tip stress change rules during rolling were analyzed. Results show that the contact pressure on crack surfaces decreases and the tensile stress appears at crack tip in the zone of slippage on the delivery side, which may make the cracks propagation. For the phenomenon, the stress distribution along rolling direction and along width direction in rolling are analyzed, and the influence of forward slip on the closure and growth of the surface transversal crack and the surface longitudinal crack are discussed. Results support some significant information for researching the behavior of the slab surface defects in rolling process.

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31

Tomczyk, Adam. "Friction Effect in a Plane Problem of Punch Acting on A Half-Space Weakened by Cracks." Acta Mechanica et Automatica 8, no. 2 (August 15, 2014): 107–14. http://dx.doi.org/10.2478/ama-2014-0020.

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Abstract This work makes use of singular integral equations method to solve plane contact problem for a half-space containing cracks. This method is based on complex variables. Relationships are presented which help find the contact pressure under the punch and the value of stress intensity factors at the crack tips. A detailed solution is presented for the problem of a punch pressed to the surface of a half-space weakened by a single straight crack. It includes both a situation where the punch has a flat and parabolic base. The influence of friction and the position of the crack on the distribution of the values of stress intensity factors i in the functions of crack length and distance from the contact zone was analyzed in detail.

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32

Yuan, Zhe, Bohan Wang, Chao Liu, Zhan Wang, Xiaochen Zhang, and Yu Zhang. "The Crack Propagation Trend Analysis in Ceramic Rolling Element Bearing considering Initial Crack Angle and Contact Load Effect." Shock and Vibration 2021 (July 29, 2021): 1–12. http://dx.doi.org/10.1155/2021/5559296.

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Silicon nitride ceramic bearings are widely used for their excellent performance. However, due to their special manufacturing method, cracks will occur on ceramic ball surface, and this initial surface crack will propagate under the action of cyclic stress, which will lead to material spalling. This will greatly limit its service life in practical applications, especially under heavy load at high speed. Therefore, it is necessary to study the surface crack propagation of silicon nitride ceramic bearings. In this paper, the effect of initial crack angle and contact load on crack growth is analysed by the finite element method (FEM). A three-dimensional finite element model of a silicon nitride bearing ball containing an initial crack is created by the FEM. The cracks are initially classified based on the angle between the crack and the bearing ball surface, and the location of the most dangerous load for each type of crack is known by theoretical analysis. The stress intensity factors (SIFs) are calculated for the crack front to investigate the effect of load position on crack growth. Subsequently, the SIFs are calculated for each type of crack angle subdivided again to investigate the effect of crack angle on crack propagation.

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33

He, Chenggang, Jihua Liu, Wenjian Wang, and Qiyue Liu. "The Tribo-Fatigue Damage Transition and Mapping for Wheel Material under Rolling-Sliding Contact Condition." Materials 12, no. 24 (December 10, 2019): 4138. http://dx.doi.org/10.3390/ma12244138.

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The purpose of this work is to construct a tribo-fatigue damage map of high-speed railway wheel material under different tangential forces and contact pressure conditions through JD-1 testing equipment. The results indicate that the wear rate of the wheel material varies with tangential force and contact pressure. The wear mapping of the wheel material is constructed and divided into three regions: slight wear, severe wear, and destructive wear, based on the wear rate under each test condition. With an increase in tangential force and contact pressure, the maximum crack length and average crack length of the wheel material increases. According to the surface damage morphologies and corresponding statistical results of average crack length of wheel material under each experiment condition, a tribo-fatigue damage map is constructed and divided into three regions: slight fatigue damage region, fatigue damage region, and severe fatigue damage region. Fatigue cracks initiate on the wheel specimen surface. Some cracks may propagate into material and fracture under cyclic rolling contact; some cracks may grow into inner material with a certain depth, and then turn toward the surface to form material flaking; some cracks may always propagate parallel to the wheel roller surface.

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34

Bhowmick, Sanjit, Juan José Meléndez-Martínez, and Brian R. Lawn. "Contact fatigue of silicon." Journal of Materials Research 23, no. 4 (April 2008): 1175–84. http://dx.doi.org/10.1557/jmr.2008.0149.

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Macroscopic cracks in bulk silicon are generally considered to be immune to fatigue. Here, evidence for pronounced fracture-related fatigue damage in cyclic contact loading of (001) monocrystalline silicon with hard spheres of millimeter-scale radius is presented. The periodic indentation field generates ring cracks around the contact, which proliferate with continued cycling. Copious debris in the form of slabs and particulates is ejected from within the crack walls onto the specimen surface. Continued ejection leads ultimately to large-scale surface removal. The fatigue damage progressively degrades the material strength, more rapidly at higher contact load. Implications concerning the function of silicon devices, including microelectro-mechanical systems, will be briefly discussed.

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35

Shimizu, Kenichi, Tashiyuki Torii, and YouLi Ma. "Crack Opening/Sliding Morphology and Stress Intensity Factor of Slant Fatigue Crack." Key Engineering Materials 297-300 (November 2005): 697–702. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.697.

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For an actual crack growth in structures subjected to the applied stress from the various directions, it is important to study about the fatigue crack propagation behavior under mixed-mode condition. In particular under the condition, crack surfaces tend to contact when the load is applied because of the compressive residual stress distributed near the crack and the zigzag crack surface morphology. In this study, using slant cracks with compressive residual stress induced in mode I fatigue crack propagation under the stress ratio of R= –1 and 0, stress intensity factors (KI)est and (KII)est were evaluated from the measured crack opening and sliding displacements. As a result, the stress intensity factor (KII)est for the crack made under the stress ratio of R= –1 with the slant angle of 45 deg. was decreased owing to the crack surface contact, while (KI)est showed relatively large values in spite of compressive residual stress.

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36

Bartley, John M., Drew S. Coleman, and Allen F. Glazner. "Incremental pluton emplacement by magmatic crack-seal." Transactions of the Royal Society of Edinburgh: Earth Sciences 97, no. 4 (December 2006): 383–96. http://dx.doi.org/10.1017/s0263593300001528.

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ABSTRACTA growing body of evidence indicates that some, and perhaps most, plutons are highly composite. However, the geometrical forms of increments and the processes by which they are added are poorly known. Magmatic crack-seal probably is an important incremental assembly process, particularly in the upper crust where wall-rock fracture is important. Evidence for magmatic crack-seal is clearest where it is antitaxial, i.e., new fractures form at the contact between wall rock and a growing intrusion. Local deviation of antitaxial cracks into wall rocks isolates wall-rock bodies that therefore mark increment contacts. Wall rock isolated by this process remains in situ and thus is likely to preserve a ghost stratigraphy. Previously described plutons are identified, and interpreted to have grown by antitaxial magmatic crack-seal. In contrast, it remains unclear what observable geological record may remain in plutons formed by syntaxial crack-seal, in which new cracks form in the middle of the growing pluton. Several plutons are identified that preserve possible indirect evidence for growth by syntaxial crack seal, but conclusive identification of a direct record of the process remains elusive. However, plutons with sharp discordant contacts but few xenoliths may have been emplaced incrementally by syntaxial magmatic crack-seal.

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37

Nakai, Yoshikazu, Daiki Shiozawa, Shoichi Kikuch, Hitoshi Saito, Takashi Nishina, Taizo Makino, and Yutaka Neishi. "Observation of Flaking Process in Rolling Contact Fatigue by Laminography Using Ultra-bright Synchrotron Radiation." MATEC Web of Conferences 165 (2018): 11002. http://dx.doi.org/10.1051/matecconf/201816511002.

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The flaking failure in rolling contact fatigue (RCF) results from crack initiation and propagation has been believed to originate from non-metallic inclusions located beneath the surface. With conventional microscopies, however, damage process in the internal region of materials could not be observed, then RCF crack initiation and propagation behaviours were observed by using synchrotron radiation computed laminography (SRCL) in the brightest synchrotron facility in Japan, and the effect of the inclusion orientation on the RCF property was examined. In our previous studies, crack initiation and propagation behaviours caused by extended MnS inclusions distributed in depth or transverse (width) direction was observed by the SRCL. In the present study, the fracture mechanism under RCF was discussed on specimens with MnS inclusions distributed in the rolling direction. As a result, vertical cracks were initiated on the surface, parallel to the ball-rolling direction in specimens. The crack propagation direction was then changed perpendicular to the rolling direction. Thereafter, similar with our previous studies, vertical cracks caused the horizontal cracks beneath the surface, when the vertical cracks reached to a critical length. The ratio of the vertical crack initiation life to the flaking life was higher than specimens with other inclusion orientation.

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38

Navarro, C., S. Muñoz, and J. Domínguez. "Analysis of crack evolution in fretting fatigue with spherical contact." Journal of Strain Analysis for Engineering Design 44, no. 6 (August 1, 2009): 503–15. http://dx.doi.org/10.1243/03093247jsa487.

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This paper analyses various procedures for predicting crack growth as a function of the number of cycles in fretting fatigue tests with spherical contact. The evolution of the crack is calculated using fracture mechanics starting from an initial defect. Different growth laws are considered, including the behaviour of small cracks, by modifying either the threshold or the effective stress intensity factor value. Theoretical results are compared with those obtained in tests on Al 7075 T651. Results show that, although the final lives predicted by the different laws are similar, the predicted crack evolution does vary, and the most precise law is the one that modifies the growth threshold.

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39

Dubourg, M. C., M. Godet, and B. Villechaise. "Analysis of Multiple Fatigue Cracks—Part II: Results." Journal of Tribology 114, no. 3 (July 1, 1992): 462–68. http://dx.doi.org/10.1115/1.2920906.

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A semianalytical model of multiple fatigue crack analysis in sliding contact is developed. Linear elastic fracture mechanics is applied. Frictional resistance between crack faces is taken into account. Five crack interaction mechanisms have been identified. Load transfer between cracks can cause both significant increases and drops in stress intensity factors both in mode I and II. The interaction depends on the distance between cracks, their relative position with respect to the loading zone, and the interfacial crack coefficient of friction.

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40

Yang, Mingfa, and Kyung-Suk Kim. "The behavior of subinterface cracks with crack-face contact." Engineering Fracture Mechanics 44, no. 1 (January 1993): 155–65. http://dx.doi.org/10.1016/0013-7944(93)90088-a.

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41

Zhao, Yang, Yang Xiao, Hao Sun, Wenhao Huo, Chuan Wu, Song Feng, and Yong Liao. "A lubrication contact pair model for simulating gear micro-pitting damage characteristics based on contour integral." Advances in Mechanical Engineering 13, no. 8 (August 2021): 168781402110394. http://dx.doi.org/10.1177/16878140211039431.

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A new two-dimensional finite element model of a lubricated contact pair, based on a contour integral, is proposed to investigate the formation of micro-pitting on gear tooth surfaces. Meanwhile, the contact properties and elasto-hydrodynamic lubrication (EHL) conditions of the gears are considered in the lubricated contact pair model. Then, the stress intensity factors (SIFs) KI and KII and the propagation angle θ C at the crack tip are analyzed by ABAQUS software. Next, the equivalent SIF Kσ can be calculated according to the maximum tangential stress (MTS) criterion, which is often used as the criterion for crack propagation. Considering the effect of a moving contact, the crack more easily propagates under the load x0/ b = −0.895. Furthermore, the pit shapes and variation of stress intensity factor are determined for various combinations of initial crack length a0 and angle β. The results show that longer germinated cracks propagate in areas that are deeper below the tooth surface. And the total length of final crack increases with the initial length and germination angle. These research results provide theoretical support for contact fatigue life analysis and meshing stiffness calculations of micro-pitting gears.

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42

Liu, C. H., and I.-Feng Chen. "Interface Cracks in a Layered Solid Subjected to Contact Stresses." Journal of Applied Mechanics 63, no. 2 (June 1, 1996): 271–77. http://dx.doi.org/10.1115/1.2788860.

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A boundary element technique has been developed to analyze interface cracks in a layered solid. The loading applied on the solid may be tension, compression, shear, or an arbitrary combination of these. Crack surfaces may be open, closed, or partially open and partially closed. In all these cases, energy release rates can always be determined by using this technique. Crack-tip conditions are determined by an iterative procedure so that they themselves are parts of the solutions of a problem. The numerical technique is utilized to analyze subsurface interface cracks in a layered solid. Results are shown for various materials and under various loading conditions.

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43

Akama, Makoto, and Akira Kiuchi. "Fatigue Crack Growth under Non-Proportional Mixed Mode Loading in Rail and Wheel Steel Part 2: Sequential Mode I and Mode III Loading." Applied Sciences 9, no. 14 (July 18, 2019): 2866. http://dx.doi.org/10.3390/app9142866.

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Rolling contact fatigue cracks in rail and wheel undergo non-proportional mixed mode I/II/III loading. Fatigue tests were performed to determine the coplanar and branch crack growth rates on these materials. Sequential and overlapping mode I and III loading cycles were applied to single cracks in round bar specimens. Experiments in which this is done have been rarely performed. The fracture surface observations and the finite element analysis results suggested that the growth of long (does not branch but grown stably and straight) coplanar cracks was driven mainly by mode III loading. The cracks tended to branch when increasing the material strength and/or the degree of overlap between the mode I and III loading cycles. The equivalent stress intensity factor range that can consider the crack face contact and successfully regressed the crack growth rate data is proposed for the branch crack. Based on the results obtained in this study, the mechanism of long coplanar shear-mode crack growth turned out to be the same regardless of whether the main driving force is in-plane shear or out-of-plane shear.

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44

Li, Wen, Ri Dong Liao, Li Tao Liu, and Zheng Xing Zuo. "Analysis of Fretting Crack Propagation Behavior with X-FEM Method." Applied Mechanics and Materials 157-158 (February 2012): 1162–66. http://dx.doi.org/10.4028/www.scientific.net/amm.157-158.1162.

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Fretting fatigue cracks always initial at the tralling of contact region, because the stresses in the vicinity of the contact zone exhibit steep gradients. A fracture mechanics approach is usually used to estimate fretting fatigue propagation life. In this paper, extended finite element method combined with fracture mechanics is used to study fretting crack propagation behaviors. The computation results reveal that fretting crack nucleation is mainly decided by fretting, and the cycle bulk stress is the main reason for crack propagation. Also the X-FEM exhibits merits in fretting fatigue problem.

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45

Keer, Leon M. "Mechanics of Contact Fatigue." Applied Mechanics Reviews 47, no. 6S (June 1, 1994): S194—S198. http://dx.doi.org/10.1115/1.3124405.

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Contact fatigue between typical machine elements such as gears, roller followers, bearings and other components involves many complex interacting features. There are the effects of geometry, mechanical properties, material properties and surface chemistry. The present discussion will center around analytical prediction techniques that are concerned only with the mechanical aspects of contact fatigue between two elements. Aspects related to the initiation of a crack under repeated loading will be discussed. The application of an approach developed by Mura, analogous to Griffith’s criterion for fracture, will be used to show how estimates of initiation life can be made and how these estimates are related to currently used ones. Once a crack has been initiated, then issues related to crack propagation become important. Some fracture mechanics based methods developed to calculate crack growth will be described along with estimates of crack propagation life.

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46

Oki, Tomoya, Hiroki Yamamoto, Toshio Osada, and Koji Takahashi. "Improvement of the Contact Strength of Al2O3/SiC by a Combination of Shot Peening and Crack-Healing." Journal of Powder Technology 2013 (May 16, 2013): 1–5. http://dx.doi.org/10.1155/2013/946984.

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Al2O3/SiC composite ceramics with high crack-healing ability were subjected to shot peening (SP) using zirconium oxide shots with several peening pressures and shot diameters. Specimens subjected to SP were heat-treated in air to heal the surface cracks induced by SP. The residual stress, the apparent fracture toughness, and the Weibull distribution of the contact strength were investigated, revealing that the combination of SP and crack-healing is effective for increasing the contact strength and decreasing the scatter of the contact strength of Al2O3/SiC.

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47

Xu, Yazhou, Zhen Sun, and Yuqing Zhang. "Experimental and Numerical Investigations of Fretting Fatigue Behavior for Steel Q235 Single-Lap Bolted Joints." Advances in Materials Science and Engineering 2016 (2016): 1–10. http://dx.doi.org/10.1155/2016/6375131.

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This work aims to investigate the fretting fatigue life and failure mode of steel Q235B plates in single-lap bolted joints. Ten specimens were prepared and tested to fit theS-Ncurve. SEM (scanning electron microscope) was then employed to observe fatigue crack surfaces and identify crack initiation, crack propagation, and transient fracture zones. Moreover, a FEM model was established to simulate the stress and displacement fields. The normal contact stress, tangential contact stress, and relative slipping displacement at the critical fretting zone were used to calculate FFD values and assess fretting fatigue crack initiation sites, which were in good agreement with SEM observations. Experimental results confirmed the fretting fatigue failure mode for these specimens. It was found that the crack initiation resulted from wear regions at the contact surfaces between plates, and fretting fatigue cracks occurred at a certain distance away from hole edges. The proposed FFD-Nrelationship is an alternative approach to evaluate fretting fatigue life of steel plates in bolted joints.

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48

Karaszewski, Waldemar. "Analysis of Ceramic Elements with Ring-Crack Defects in Lubricated Rolling Contact." Solid State Phenomena 250 (April 2016): 43–49. http://dx.doi.org/10.4028/www.scientific.net/ssp.250.43.

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Анотація:

The properties of ceramics, specifically low density, high hardness, high temperature capability and low coefficient of thermal expansion are of most interest to rolling element manufacturers. Surface ring cracks on lubricating rolling contact fatigue failure has been studied using numerical fracture analysis. Such cracks are very often found on ceramic bearing balls and decrease fatigue life rapidly. The numerical calculations are based on a three-dimensional model of the ring crack. The stress intensity factors along crack front are analyzed using a finite element analysis. The numerical analysis is verified by experimental studies.

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49

Menshykov, Oleksandr, Vasyl Menshykov, and Olga Kladova. "NONLINEAR PROBLEM OF FRACTURE MECHANICS OF AN INTERFACE CRACK SUBJECTED TO SHEAR WAVE." Bulletin of the National Technical University "KhPI". Series: Mathematical modeling in engineering and technologies, no. 2 (November 30, 2021): 55–64. http://dx.doi.org/10.20998/2222-0631.2021.02.07.

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Solution for the problem for an interface crack under the action of a harmonic shear wave in normal direction is presented. The contact of the crack faces is put into consideration. The problem is solved by the boundary integral equations method, the vector components in the boundary integral equations are presented by Fourier series. The unilateral Signorini boundary conditions are involved to prevent the interpenetration of the crack faces and the emergence of tensile forces in the contact zone. Amonton-Coulomb Friction Law included allows to put into consideration relative resting of the crack opposite faces or their relative motion when one crack face is slipping or sliding across another face. The contact boundary restrictions are implemented using the iterative correction algorithm. The mathematical model adequacy is checked by comparing with classical model solution for statics problems that takes into account the crack faces contact. Numerical researches of friction influence on the displacement and contact forces distribution, size of contact zone are carried out. Influence of the faces contact and value of the friction coefficient on the distribution of stress intensity coefficients of normal rupture and transverse shear, which are the parameters of the biomaterial fracture, are presented and analyzed. It is shown that the nature of change in the distribution of the stress intensity coefficients for the conditions of tensile and shear waves is fundamentally different. It is concluded that it is possible to extend the approach proposed to the problems of three-dimensional fracture mechanics for composites with interfacial cracks at arbitrary dynamic loading.

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50

Yang, Faming, Yongmin Yang, Haifeng Hu, Fengjiao Guan, Guoji Shen, Suiyu Chen, and Zifang Bian. "Extraction of Features due to Breathing Crack from Vibration Response of Rotated Blades considering Tenon Connection and Shroud Contact." Shock and Vibration 2019 (July 29, 2019): 1–20. http://dx.doi.org/10.1155/2019/8729620.

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Анотація:

Cracks are common failures of aeroengine rotated blades. Online monitoring of rotated blades through their vibration to identify cracks early in various working conditions is significant for operational safety. Breathing crack is a practical form of early cracks and results in nonlinear vibration response. Tenon connection and shroud contact are common structures in aeroengine rotated blades, which can also lead blades to vibrate nonlinearly and seriously interfere online identification of early cracks. Thus, it is important to extract vibration features due to breathing crack considering these two structures. Firstly, a blade with tenon and shroud is simplified and a lumped parameter model of the bladed disk is built. Then, dry friction and coupling force on a blade are analyzed and dynamics equations of the lumped parameter model are established. Next, the stiffness of the blade trunk with a breathing crack is analyzed. Finally, the vibration response of blade trunks with the occurrence of breathing crack is analyzed in time and frequency domains by numerical simulation. Effective features due to breathing crack for online identification are extracted. 2x components of spectrums can be the criterion to judge whether breathing crack occurs. Besides, by comparing the changes in vibration amplitudes with 1x component peaks of spectrums, the cracked blade trunk can be distinguished. These findings can provide important theoretical guidance for online identification of early cracks in aeroengine rotated blades.

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