Dynamic Fracture Under Normal Impact Loading of the Crack Faces

1985 ◽  
Vol 52 (3) ◽  
pp. 585-592 ◽  
Author(s):  
K.-S. Kim
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Impact Loading ◽  
Crack Tip ◽  
Time Behavior ◽  
Crack Face ◽  
Copper Strip ◽  
Transient Stress ◽  
Crack Faces

Results of experiments on crack-face impact are presented. The transient stress-intensity factor variation of a crack has been traced by the Stress-Intensity Factor Tracer (SIFT) [1] under time-stepwise uniform pressure loading of the crack faces. To see the effects of various waves generated by the loading, part of the crack faces was left free of traction within the distance l0 from the crack tip. The crack-face impact loading was produced by an electromagnetic force induced by a square pulse of an electric current flowing through a copper strip inserted in the saw-cut crack of a Homalite 100 plate specimen. The current flowed in opposite directions in the two portions of the copper strip, between the crack faces, causing them to repel each other. The short-time and the long-time behavior of the transient stress-intensity factor variation under the impact loading have been carefully investigated. Brittle dynamic initiation of crack extension and the stress-intensity variation of a running crack have been also examined. The experimental results have been compared with theoretical predictions based on Freund’s crack-face concentrated load solution [2]. The agreement between the theory and the experiment is excellent. In this study, the various waves generated by the loading are shown to play different roles in transmitting the load to the crack tip. In addition, confirmation is given that the SIFT is excellent in tracing the stress-intensity factor regardless of the crack-tip motion.

Influences of Crack Face Bridging Stress and Microstructure on Fracture Toughness of Toughened Alumina Ceramics

2011 ◽  
Vol 462-463 ◽  
pp. 972-978
Author(s):  
Yoshihisa Sakaida ◽  
Hajime Yoshida ◽  
Shotaro Mori
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Opening ◽  
Stress Shielding ◽  
Crack Tip ◽  
Shielding Effect ◽  
Hot Press ◽  
Crack Face

Three types of polycrystalline alumina, one pressureless and two hot press sintered Al2O3, were used to examine the effects of the characteristics of microstructure and crack face bridging on fracture toughness. The crack opening displacements and microstructures along the pop-in crack of single edge precracked beam (SEPB) specimens were observed in situ at a constant applied stress intensity factor by scanning electron microscopy (SEM). The bridging stress distribution could be determined from the measured crack opening displacement by three-dimensional finite element analysis, and then the stress intensity factor and stress shielding effect at the crack tip could also be determined. Intergranular microcracks of toughened Al2O3 were deflected by a complicated microstructure, and crack closure due to bridging grains was observed near the crack tip. Bridging stress of Al2O3 was compressive perpendicular to the crack face and was distributed behind the crack tip. The maximum bridging stress of two hot press sintered Al2O3 was about twice as large as that of pressureless sintered Al2O3. The fracture toughness of hot press sintered Al2O3 was, therefore, higher than that of pressureless sintered Al2O3, because the total amount of bridging stress and stress shielding effect increased with increasing magnitude of microcrack deflection and the number of interlocking grains.

scholarly journals Experimental Study on the Caustics of Moving Cracks and Elliptical Curvature under Impact Loading

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Haohao Luo ◽  
Renshu Yang ◽  
Yanbing Wang ◽  
Guoliang Yang ◽  
Chengxiao Li ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Impact Loading ◽  
Crack Tip ◽  
Test System ◽  
Moving Crack ◽  
Linear Elastic ◽  
Elastic Fracture ◽  
Crack Tip Stress

A dynamic caustics test system was used, and different moving cracks were analysed to study the interaction between the crack growth rate, stress intensity factor, and curvature of the elliptical end of a moving crack under impact loading. Based on the linear elastic fracture mechanics theory, linearly fitting of the crack tip stress intensity factor and the elliptical curvature were employed to obtain the specific functional expressions. ABAQUS software was used to numerically simulate the moving crack fracture process passing through different elliptical curvatures. The crack tip stress intensity factor was calculated by the stress extrapolation method. The stress intensity factor obtained from the numerical calculation and the caustics test was consistent. The test and numerical simulation results showed that the direction of moving cracks entering and passing through the elliptical defects shows a certain regularity. As the ellipse curvature increased, the moving crack stress intensity factor passing through the ellipse gradually decreased, and the moving crack also passed easily through oval defects.

The Extent of the Stress Intensity Factor Field During Crack Growth Under Dynamic Loading Conditions

1986 ◽  
Vol 53 (2) ◽  
pp. 303-310 ◽  
Author(s):  
C. C. Ma ◽  
L. B. Freund
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Singular Term ◽  
Dynamic Pressure ◽  
Fracture Initiation ◽  
Fracture Plane ◽  
Crack Face ◽  
Crack Faces

The phenomenon considered is fracture initiation and crack growth in a plate due to dynamic pressure loading on the faces of a pre-existing crack. The problem is formulated within the framework of two-dimensional elastodynamics, and the system is viewed as a semi-infinite crack in an otherwise unbounded body. At a certain instant of time, a spatially uniform pressure begins to act on the crack faces. The pressure magnitude increases linearly in time for a certain period (the rise time T), and it is constant thereafter. The crack begins to extend at constant speed at some time after the pressure begins to act (the delay time τ). The pressure acts only over the original crack faces, and both τ > T and τ < T are considered. The ratio of the normal stress on the fracture plane to the value due to the singular term in the stress field alone is computed for some point at a small fixed distance ahead of the crack tip, with a view toward establishing the conditions under which the stress intensity factor controlled singular term accurately describes the near tip stress distribution in this highly transient process. Measured and calculated histories compare very well for relatively low crack face pressures, but there is significant disagreement beyond crack growth initiation for higher pressures. Possible reasons for the discrepancies are discussed.

scholarly journals Transient Analysis for Antiplane Crack Subjected to Dynamic Loadings

1991 ◽  
Vol 58 (3) ◽  
pp. 703-709 ◽  
Author(s):  
Chien-Ching Ma ◽  
Ying-Chung Hou
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Shear Wave ◽  
Dynamic Stress Intensity Factor ◽  
Crack Tip ◽  
Point Load ◽  
Crack Face ◽  
Kinked Crack ◽  
Kink Angle

The problem considered here is the antiplane response of an elastic solid containing a half-plane crack subjected to suddenly applied concentrated point forces acting at a finite distance from the crack tip. A fundamental solution for the dynamic dislocation is obtained to construct the dynamic fracture problem containing a characteristic length. Attention is focused on the time-dependent full-field solutions of stresses and stress intensity factor. It is found that at the instant that the first shear wave reaches the crack tip, the stress intensity factor jumps from zero to the appropriate static value. The stresses will take on the appropriate static value instantaneously upon arrival of the shear wave diffracted from the crack tip, and this static value is thereafter maintained. The dynamic stress intensity factor of a kinked crack from this stationary semi-infinite crack after the arrival of shear wave is obtained in an explicit form as a function of the kinked crack velocity, the kink angle, and time. A perturbation method, using the kink angle as the perturbation parameter, is used. If the maximum energy release rate is accepted as the crack propagation criterion, then the crack will propagate straight ahead of the original crack when applying point load at the crack face.

Suddenly Arrested Intersonic Shear Crack

2001 ◽  
Author(s):  
Y. Huang ◽  
H. Gao
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Fundamental Solution ◽  
Shear Crack ◽  
Auxiliary Problem ◽  
Dynamic Stress Intensity Factor ◽  
Crack Tip ◽  
Crack Face ◽  
Static Crack

Abstract We study a mode II crack suddenly stopping after propagating intersonically for a short time. The solution is obtained by superposing the fundamental solution and the auxiliary problem of a static crack emitting dynamic dislocations such that the relative crack face displacement in the fundamental solution is negated ahead of where the crack tip has stopped. We find that, after the crack stops moving, the stress intensity factor rapidly rises to a finite value and then starts to change gradually toward the equilibrium value for a static crack. A most interesting feature is that the static value of stress intensity is reached neither instantaneously like a suddenly stopping subsonic crack nor asymptotically like a suddenly stopping edge dislocation. Rather, the dynamic stress intensity factor changes continuously as the shear and Rayleigh waves catch up with the stopped crack tip from behind, approaches negative infinity when the Rayleigh wave arrives, and then suddenly assumes the equilibrium static value when all the waves have passed by. This study is an important step toward the study of intersonic crack propagation with arbitrary, non-uniform velocities.

A new type of cracks adding to Griffith–Irwin cracks

2019 ◽  
Vol 485 (2) ◽  
pp. 162-165
Author(s):  
V. A. Babeshko ◽  
O. M. Babeshko ◽  
O. V. Evdokimova
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Tip ◽  
Stress Concentrations ◽  
New Type

The distinctions in the description of the conditions of cracking of materials are revealed. For Griffith–Irwin cracks, fracture is determined by the magnitude of the stress-intensity factor at the crack tip; in the case of the new type of cracks, fracture occurs due to an increase in the stress concentrations up to singular concentrations.

scholarly journals Optimisation Method for Determination of Crack Tip Position Based on Gauss-Newton Iterative Technique

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Bing Yang ◽  
Zhanjiang Wei ◽  
Zhen Liao ◽  
Shuwei Zhou ◽  
Shoune Xiao ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Plastic Zone ◽  
Relative Error ◽  
Crack Tip ◽  
Image Correlation ◽  
Preconditioned Conjugate Gradient ◽  
Loading Process ◽  
Tip Position

AbstractIn the digital image correlation research of fatigue crack growth rate, the accuracy of the crack tip position determines the accuracy of the calculation of the stress intensity factor, thereby affecting the life prediction. This paper proposes a Gauss-Newton iteration method for solving the crack tip position. The conventional linear fitting method provides an iterative initial solution for this method, and the preconditioned conjugate gradient method is used to solve the ill-conditioned matrix. A noise-added artificial displacement field is used to verify the feasibility of the method, which shows that all parameters can be solved with satisfactory results. The actual stress intensity factor solution case shows that the stress intensity factor value obtained by the method in this paper is very close to the finite element result, and the relative error between the two is only − 0.621%; The Williams coefficient obtained by this method can also better define the contour of the plastic zone at the crack tip, and the maximum relative error with the test plastic zone area is − 11.29%. The relative error between the contour of the plastic zone defined by the conventional method and the area of the experimental plastic zone reached a maximum of 26.05%. The crack tip coordinates, stress intensity factors, and plastic zone contour changes in the loading and unloading phases are explored. The results show that the crack tip change during the loading process is faster than the change during the unloading process; the stress intensity factor during the unloading process under the same load condition is larger than that during the loading process; under the same load, the theoretical plastic zone during the unloading process is higher than that during the loading process.

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