Subcritical Crack Growth of Glass Under Combined Modes I and II Loading

The glass plate specimens with inclined cracks introduced by Vickers microhardness indentation were subjected to sustained bend stress in water. Subcritical crack growth behaviors were investigated under combined Modes I and II loading. The crack velocity dc/dt can be described as a function of coplanar energy release rate G. The experimental results show that the dc/dt which is initially high decreases and thereafter increases with G. The crack velocity data are found to be influenced by the residual stress and the presence of a lateral crack. Inclined cracks in the increasing region tend to show the crack velocity higher than would be expected from the Mode I results of β = 90 deg on the basis of G as the β between the loading axis and the crack plane decreases. The dc/dt-G curves in this region have a steeper portion at low velocities and thereafter tend to a shallower portion.

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Subcritical crack growth along epoxy/glass interfaces

Journal of Materials Research ◽

10.1557/jmr.1992.2621 ◽

1992 ◽

Vol 7 (9) ◽

pp. 2621-2629 ◽

Cited By ~ 10

Author(s):

K.M. Conley ◽

J.E. Ritter ◽

T.J. Lardner

Keyword(s):

Energy Release Rate ◽

Energy Release ◽

Crack Growth ◽

Power Law ◽

Release Rate ◽

Strain Energy ◽

Crack Velocity ◽

Subcritical Crack Growth ◽

Strain Energy Release Rate ◽

Strain Energy Release

Subcritical crack growth behavior along polymer/glass interfaces was measured for various epoxy adhesives at different relative humidities. A four-point flexure apparatus coupled with an inverted microscope allowed for observation in situ of the subcritical crack growth at the polymer/glass interface. The specimens consisted of soda-lime glass plates bonded together with epoxy acrylate, epoxy (Devcon), or epoxy (Shell) adhesives. Above a threshold strain energy release rate, the subcritical crack velocity was dependent on the strain energy release rate via a power law relationship where the exponent was independent of the adhesive tested and the test humidity (n = 3). However, the multiplicative constant A in the power law relation varied by over three orders of magnitude between the various adhesives with epoxy (Shell) having the smallest value and the epoxy (Devcon) the greatest value; in addition, A was very sensitive to humidity, decreasing by over two orders of magnitude from 80% to 15% relative humidity. At high strain energy release rates, the subcritical crack velocity reached a plateau at approximately 10−6 m/s. The use of this subcritical crack velocity data in predicting thin film delamination is discussed.

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A four-point bending technique for studying subcritical crack growth in thin films and at interfaces

Journal of Materials Research ◽

10.1557/jmr.1997.0122 ◽

1997 ◽

Vol 12 (3) ◽

pp. 840-845 ◽

Cited By ~ 115

Author(s):

Qing Ma

Keyword(s):

Crack Growth ◽

Growth Velocity ◽

Crack Velocity ◽

Subcritical Crack Growth ◽

Beam Theory ◽

Velocity Versus ◽

Displacement Curve ◽

Load Displacement ◽

Corrosion Mechanisms ◽

Crack Growth Velocity

A technique was developed to obtain the subcritical crack growth velocity in a 4-point bending sample by analyzing the load-displacement curve. This was based on the observation that the compliance of a beam increases as the crack grows. Beam theory was used to analyze the general configuration where two cracks propagated in the opposite directions. A simple equation relating the crack velocity to the load and displacement was established, taking advantage of the fact that the compliance was linearly proportional to the crack lengths; thus the absolute crack length was not important. Two methods of obtaining crack velocity as a function of load were demonstrated. First, by analyzing a load-displacement curve, a corresponding velocity curve was obtained. Second, by changing the displacement rate and measuring the corresponding plateau load, a velocity value was calculated for each plateau load. While the former was capable of obtaining the dependence of crack velocity versus load from a single test, the latter was found to be simpler and more consistent. Applications were made to a CVD SiO2 system. In both cases of crack propagation either inside the SiO2 layer or along its interface with a TiN layer, the crack growth velocity changed with the stress intensity at the crack tip exponentially. As a result, a small crack will grow larger under essentially any tensile stresses typically existing in devices, provided that chemical agents facilitating stress corrosion mechanisms are also present.

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A New Approach to Evaluate the Delayed Fracture Behavior of an Optical Glass Fiber

MRS Proceedings ◽

10.1557/proc-226-369 ◽

1991 ◽

Vol 226 ◽

Cited By ~ 4

Author(s):

M. Muraoka ◽

H. AbÉ

Keyword(s):

Stress Intensity Factor ◽

Crack Growth ◽

Crack Velocity ◽

Fracture Behavior ◽

Subcritical Crack Growth ◽

Optical Glass ◽

Delayed Fracture ◽

New Approach ◽

Silica Optical Fiber ◽

Optical Glass Fiber

AbstractThe method for the direct measurement of subcritical crack growth in silica optical fiber with 125μm in diameter was developed. The obtained crack velocity da/dt as a function of stress intensity factor KI was expressed by means of log da/dt vs log KI linear relation with slope n. The obtained value of n showed 22.6 (25 °C,60%r.h.) with small standard deviation 0.7. These results indicate that the postulated crack growth law used for the lifetime prediction is valid and the present approach can solve the problem in the conventional method for evaluating the value of n where the evaluated value has been widely scattered.

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Examination of Fracture Interfaces in Silicon Nitride

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113925 ◽

1975 ◽

Vol 33 ◽

pp. 60-61

Author(s):

Nancy J. Tighe

Keyword(s):

Silicon Nitride ◽

Grain Boundary ◽

Crack Growth ◽

Subcritical Crack Growth ◽

Slow Crack Growth ◽

Ceramic Materials ◽

Grain Boundary Sliding ◽

Boundary Phase ◽

Turbine Engines ◽

Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

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