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

1991 ◽  
Vol 226 ◽  
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.

The Distribution of the Stress Intensity Factor Along the Front of the Growing Crack in an Optical Glass Fiber

1992 ◽  
Vol 114 (4) ◽  
pp. 403-406 ◽  
Author(s):  
M. Muraoka ◽  
H. Abe´ ◽  
N. Aizawa
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Front ◽  
Crack Velocity ◽  
Optical Glass ◽  
Fiber Surface ◽  
Element Analysis ◽  
Growing Crack ◽  
Silica Optical Fiber

The stress intensity factor K1 along the front edge of a growing small crack in a silica optical fiber was evaluated by 3-D boundary element analysis based on the crack geometry observed during the delayed fracture test. The variation of K1 was shown to be little along the front of the growing crack. The crack velocity in the direction normal to the crack front was able to be expressed as a power function of K1 at each position on the crack front. The crack velocity was also shown to be larger at a position closer to the fiber surface for each value of K1.

Subcritical crack growth along epoxy/glass interfaces

1992 ◽  
Vol 7 (9) ◽  
pp. 2621-2629 ◽  
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.

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

1997 ◽  
Vol 12 (3) ◽  
pp. 840-845 ◽  
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.

Fracture Toughness and Subcritical Crack Growth in Polycrystalline Silicon

2005 ◽  
Vol 73 (5) ◽  
pp. 714-722 ◽  
Author(s):  
I. Chasiotis ◽  
S. W. Cho ◽  
K. Jonnalagadda
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Crack Growth ◽  
Critical Stress ◽  
Polycrystalline Silicon ◽  
Subcritical Crack Growth ◽  
Crack Tip ◽  
Critical Stress Intensity Factor ◽  
Mode I ◽  
Intensity Factors

The fracture behavior of polycrystalline silicon in the presence of atomically sharp cracks is important in the determination of the mechanical reliability of microelectromechanical system (MEMS) components. The mode-I critical stress intensity factor and crack tip displacements in the vicinity of atomically sharp edge cracks in polycrystalline silicon MEMS scale specimens were measured via an in situ atomic force microscopy/digital image correlation method. The effective (macroscopic) mode-I critical stress intensity factor for specimens from different fabrication runs was 1.00±0.1MPa√m, where 0.1MPa√m is the standard deviation that was attributed to local cleavage anisotropy and grain boundary effects. The experimental near crack tip displacements were in good agreement with the linearly elastic fracture mechanics solution, which supports K dominance in polysilicon at the scale of a few microns. The mechanical characterization method implemented in this work allowed for direct experimental evidence of incremental (subcritical) crack growth in polycrystalline silicon that occurred with crack increments of 1-2μm. The variation in experimental effective critical stress intensity factors and the incremental crack growth in brittle polysilicon were attributed to local cleavage anisotropy in individual silicon grains where the crack tip resided and whose fracture characteristics controlled the overall fracture process resulting in different local and macroscopic stress intensity factors.

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

1988 ◽  
Vol 110 (3) ◽  
pp. 219-223 ◽  
Author(s):  
M. Yoda
Keyword(s):  
Crack Growth ◽  
Crack Velocity ◽  
Subcritical Crack Growth ◽  
Vickers Microhardness ◽  
Glass Plate ◽  
Crack Plane ◽  
Velocity Data ◽  
Microhardness Indentation ◽  
Loading Axis ◽  
Inclined Cracks

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.

Slow crack-growth behavior of alumina ceramics

2000 ◽  
Vol 15 (1) ◽  
pp. 142-147 ◽  
Author(s):  
M. E. Ebrahimi ◽  
J. Chevalier ◽  
G. Fantozzi
Keyword(s):  
Stress Intensity Factor ◽  
Grain Size ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Crack Velocity ◽  
Slow Crack Growth ◽  
Velocity Versus ◽  
Water Molecules ◽  
Alumina Ceramics

The fracture behavior of high-purity alumina ceramics with grain sizes ranging from 2 to 13 μm is studied by means of the double torsion method. Crack-propagation tests conducted in air, water, and silicon oil, for crack velocities from 10−7 to 10−2 m/s, show that slow crack growth is due to stress corrosion by water molecules. An increase of the grain size leads to enhanced crack resistance, which is indicated by a shift of the V–KI (crack velocity versus applied stress intensity factor) plot toward high values of KI. Moreover, the slope of the curve is apparently higher for coarse grain alumina. However, if the R-curve effect is substracted from the experimental results, a unique V–KItip (crack velocity versus stress intensity factor at the crack tip) law is obtained for all alumina ceramics, independently of the grain size. This means that the crack-growth mechanism (stress corrosion by water molecules) is the same and that the apparent change of the V–KI law with grain size is a direct effect of crack bridging.

scholarly journals Comparative study of creep and fatigue crack growth in Poly (Vinyl chloride) pipe

2012 ◽  
Vol 9 (2) ◽  
pp. 359-366
Author(s):  
Baghdad Science Journal
Keyword(s):  
Experimental Data ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Crack Velocity ◽  
Rate Theory

The Rate theory of crack growth in PVC pipe has been studied for creep and fatigue crack propagation. Rate theory function parameters, (RTFP), were estimated theoretically from exponential function parameters, (EFP), to experimental data of crack velocity versus stress intensity factor ,(V-K) diagram, to creep crack propagation . Also (RTFP) were estimated theoretically from (EFP) to experimental data of (V-?K) diagram to fatigue crack propagation. Temperature effect with (RTFP) was discussed. Crack velocity function denoted with stress intensity factor and temperature degrees has been determined to fatigue and creep crack propagation theoretically and comparative results this function with experimental data of (V-K or ?K) diagram .

Influence of the initial damage on fracture toughness and subcritical crack growth in a granite rock

2020 ◽  
Author(s):  
Salvatore D'Urso ◽  
Lucas Pimienta ◽  
François Passelègue ◽  
Federica Sandrone ◽  
Sergio Vinciguerra ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Thermal Damage ◽  
Internal Damage ◽  
Initial Damage

<p>Fracture mechanics is an important tool to assess the slope stability, since this approach offers a methodology to study the fracture stress field in the neighborhood of the joint tips and accurately predict propagation of the joints over time. While the fracture toughness of material has been extensively studied in the past, low interest was given to the influence of initial damage on the subcritical crack growth, despite of its relevance to assess long term slope stability. Here we report new experimental results that address this question.</p><p>Starting from the real case of unstable rock mass of “Madonna del Sasso” (Colombero et al., 2015), a series of Cracked Chevron Notched Brazilian Disc (CCNBD) (Fowell, 1995) specimens were failed in a standard Mode I tensile test to investigate the effects of thermal damage on fracture toughness and subcritical crack growth on samples of granite of Alzo.</p><p>The degree of initial damage was imposed using slow heat treatment (1°C/min) up to 100, 200, 300 and 400°C, to emulate different levels of rock degradation. The samples were equipped with strain gauges close to the tips of the notch, an extensometer for the Crack Mouth Opening Displacement (CMOD) and twelve Acoustic Emission recorders.</p><p>Our results show that fracture toughness decreases with increasing thermal damage, in agreement with previous studies (Nasseri, Schubnel, & Young, 2007). The fracture toughness of undamaged granite is 1.04 MPa m<sup>1/2</sup>, but 0.65 MPa m<sup>1/2</sup> after treatment up to 400°C.</p><p>Subcritical crack growth behaviour has been studied for samples treated from 100°C up to 400°C through creep tests on CCNBD specimens. The overall effect of heat treatment is to increase the crack growth rate in granite for a given stress intensity factor. The slopes of stress intensity factor versus crack velocity curves are sensitive to modifications of initial damage’s degree. Trend drops substantially with increase of the temperature of the heat treatment. This shows a substantial increase of the internal damage index n, and a decrease of the time to failure of the CCNBD specimens.</p><p>The study highlights the importance of considering both the time-dependent slope behaviour and effects of rocks internal damage, since these conditions could lead to an unexpected premature failure.</p>

Examination of Fracture Interfaces in Silicon Nitride

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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