Experimental Study on Electric-Current Induced Damage Evolution at the Crack Tip in Thin Film Conductors

1998 ◽  
Vol 120 (4) ◽  
pp. 354-359 ◽  
Author(s):  
A.-F. Bastawros ◽  
K.-S. Kim
Keyword(s):  
Electric Current ◽  
Crack Growth ◽  
Gold Film ◽  
Pure Aluminum ◽  
High Vacuum ◽  
Crack Tip ◽  
Negative Electrode ◽  
Initial Crack ◽  
Time Dependent ◽  
Current Intensity

The time dependent temperature distribution induced by electric current heating in a double edge cracked, unpassivated thin aluminum or gold film interconnect lines is monitored using a high resolution infrared imaging system. A pure aluminum or gold film, with a thickness of 0.2 μm, is deposited by high vacuum evaporation coating and patterned into test structures of varying widths. The operative mechanisms of mass transport are assessed in view of the monitored temperature profile. The pre-cracked aluminum film shows fine crack growth towards the positive electrode, which originates from the initial crack tips. The crack-tip temperature is close to melting, during propagation. After the initial crack propagation, a hot spot is formed between the two elongated cracks, and leads to failure. The crack growth generates a backward mass flow towards the negative electrode. The gold film shows a different pattern, in which the original cracks propagate towards each other with a slight tilt towards the negative electrode. The tip temperature is lower than the melting temperature. These time dependent failure mechanisms are rationalize using a proposed critical current intensity factor and a normalized current intensity rate, similar to the fracture toughness KIC for brittle fracture.

scholarly journals In-situ SEM and optical microscopy testing for investigation of fatigue crack growth mechanism under overload

2018 ◽  
Vol 165 ◽  
pp. 13013
Author(s):  
Wei Zhang ◽  
Liang Cai
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Optical Microscopy ◽  
Crack Growth ◽  
Load Condition ◽  
Crack Tip ◽  
Initial Crack ◽  
Crack Growth Behavior ◽  
Single Overload

In this paper, the in-situ scanning electron microscope (SEM) and optical microscopy experiments are performed to investigate the crack growth behavior under the single tensile overload. The objectives are to (i) examine the overload-induced crack growth micromechanisms, including the initial crack growth acceleration and the subsequent retardation period; (ii) investigate the effective region of single overload on crack growth rate. The specimen is a small thin Al2024-T3 plate with an edge-crack, which is loaded and observed in the SEM chamber. The very high resolution images of the crack tip are taken under the simple variable amplitude loading. Imaging analysis is performed to quantify the crack tip deformation at any time instant. Moreover, an identical specimen subjected to the same load condition is observed under optical microscope. In this testing, fine speckling is performed to promote the accuracy of digital imaging correlation (DIC). The images around the crack tip are taken at the peak loads before, during and after the single overload. After that, the evolution of local strain distribution is obtained through DIC technique. The results show that the rapid connection between the main crack and microcracks accounts for the initial crack growth acceleration. The crack closure level can be responsible for the crack growth rate during the steady growth period. Besides that, the size of retardation area is larger than the classical solution.

scholarly journals Crack Tip Radius Effect on Fatigue Crack Growth and Near Tip Fields in Plastically Compressible Materials

2021 ◽  
Vol 71 (2) ◽  
pp. 248-255
Author(s):  
S. Singh ◽  
D. Khan
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Strain Softening ◽  
Crack Tip ◽  
Initial Crack ◽  
Strain Fields ◽  
Tip Radius ◽  
Compressible Materials ◽  
Structural Polymers

Motivated by the prospective uses of plastically compressible materials such as, metallic and polymeric foams, transformation toughened ceramics, toughened structural polymers etc., the present authors investigate the crack-tip radius effect on fatigue crack growth (FCG) of a mode I crack and near-tip stress-strain fields in such plastically compressible solids. These plastically compressible materials have been characterised by elastic-viscoplastic constitutive equations. Simulations are conducted for plane strain geometry with two different hardness functions: one is bilinear hardening and the other one is hardening-softening-hardening. It has been observed that plastic compressibility as well as strain softening lead to significant deviation in the amount of crack growth. It has further been revealed that the nature of FCG is appreciably affected by initial crack-tip radius. Even though it may look from outside that the increase in tip radius will lead to decrease in FCG, but the nature of FCG variation with respect to tip radius is found to be a combined effect of tip radius, plastic compressibility and work or strain softening etc.

Does the Process Zone Control Crack Growth?

1992 ◽  
Vol 45 (8) ◽  
pp. 367-376 ◽  
Author(s):  
H. Abe´ ◽  
M. Saka ◽  
S. Ohba ◽  
T. Hashida
Keyword(s):  
Crack Growth ◽  
Main Crack ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Crack Tip ◽  
Compact Tension ◽  
Initial Crack ◽  
Zone Control ◽  
Notch Length

Fracture toughness tests were carried out by using small compact tension specimens of Westerly granite. Relation between the load-line displacement and the initial crack-tip separation changed from linear to nonlinear and then to linear again with increasing loading. The onset of the main crack growth was found to occur in a loading level at which the relation was nonlinear. This result disclosed that the onset of main crack growth in granite occurred without experience of the complete area under the tension-softening curve. The critical value of the initial crack-tip separation for onset of the main crack growth was obtained independently of the initial notch length. Also monitoring of the growth of the fracture process zone by ultrasonic technique showed that its length related with the crack-tip separation independently of the initial notch length. By combining the results just mentioned, it was concluded that the fracture process zone controlled the onset of the main crack growth.

Strip-Yield Modeling of Load-Time-Temperature Effects on Crack Growth in Engine Materials

2020 ◽  
Author(s):  
James C. Newman ◽  
Rani Sullivan
Keyword(s):  
Stress Relaxation ◽  
Crack Growth ◽  
Test Data ◽  
Crack Front ◽  
Crack Tip ◽  
Time Dependent ◽  
Yield Model ◽  
Linear Superposition ◽  
Strip Yield Model ◽  
Creep Deformations

Abstract Plastic and creep deformations around a crack front and in the wake of a moving crack under cyclic loading are implemented into the life-prediction code, FASTRAN (a strip-yield model). Creep deformations are modeled by stress relaxation around the crack-tip location, since the crack-front material is under displacement control due to the surrounding elastic material. Sinusoidal and trapezoidal loading are considered. A modified linear superposition model was used to compute the cyclic- and time-dependent damage, which was based on the stress-intensity-factor concept for creep-brittle materials. Application of the modified strip-yield model was made on two sets of test data on Inconel-718 alloy. The environments were laboratory air or helium gas. From the literature, the “environment” had been shown to be a major contributor to damage magnitudes. Thus, the time-dependent crack-growth constants were selected to match the test data. In addition, the effects of a small overload on time-dependent damage, and the effects of stress relaxation and varying temperatures on crack-opening stresses and cyclic crack-tip-opening displacements, were studied.

Fracture mechanics in design and service: ‘living with defects’ - Subcritical crack growth: fatigue, creep and stress corrosion cracking

1981 ◽  
Vol 299 (1446) ◽  
pp. 31-44 ◽  
Keyword(s):  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Crack Extension ◽  
Subcritical Crack Growth ◽  
Practical Interest ◽  
Crack Tip ◽  
Corrosion Cracking ◽  
Time Dependent ◽  
Crack Advance

Subcritical crack growth can occur under steady or varying loads. In the former it is precipitated by specific environmental conditions that encourage the operation of time-dependent processes controlling crack advance. These include aggressive environments leading to stress corrosion cracking, or elevated temperature conditions leading to creep cavitation. The result is a time-dependent maintenance of a sharp crack profile during crack extension. Under varying loads such a sharp profile is readily achieved by plastic deformation on load reduction. Net crack advance in fatigue therefore occurs in each load cycle by this blunting-resharpening process, and empirical crack growth laws reflect this physical basis. Parameters such as K and J, which define crack tip deformation, are useful for correlating fatigue crack growth. In that they define crack tip stress-strain fields under load, they also partly describe crack advance for steady load creep and stress corrosion cracking. In particular they can define a threshold state for crack extension by all three processes. Under varying loads, if fatigue conditions are combined with an aggressive or high-temperature environment the description of crack growth can be complex. These areas of corrosion fatigue and creep fatigue are of considerable current practical interest.

scholarly journals Time Dependent Crack Initiation and Growth in Ceramic Matrix Composites

1997 ◽  
Author(s):  
Matthew R. Begley ◽  
Brian N. Cox ◽  
Robert M. McMeeking
Keyword(s):  
Crack Growth ◽  
Crack Tip ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Cracking ◽  
Time Dependent ◽  
Small Scale ◽  
Matrix Composites ◽  
Fine Grained ◽  
Growth Initiation

Matrix cracking in ceramic matrix composites with fine grained fibers at high temperatures will be governed by fiber creep, as relaxation of the fibers eliminates crack tip shielding. Using a time dependent bridging law which describes the effect of creeping fibers bridging a crack in an elastic matrix, crack growth initiation and history have been modeled. For a stationary crack, crack tip stress intensity factors as a function of time are presented to predict incubation times before subcritical crack growth. Two crack growth studies are reviewed: a constant velocity approximation for small-scale bridging, and a complete velocity history analysis which can be used to predict crack length as a function of time. The predictions are summarized and discussed in terms of identifying various regimes of crack growth initiation, subcritical growth, and catastrophic matrix cracking.

scholarly journals Synergism Between Fatigue and Cyclic-Stress Corrosion-Cracking

2020 ◽  
Author(s):  
Meryl Hall, Jr
Keyword(s):  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Crack Tip ◽  
Cyclic Stress ◽  
Corrosion Cracking ◽  
Time Dependent ◽  
Stress Cycles ◽  
Cycle Dependent ◽  
Crack Growth Rates

For 50 years, researchers have considered how time-dependent environmental effects can be included in cycle-dependent corrosion fatigue (CF) crack growth rate (CGR) models. Common assumptions are that cycle- and time-dependent contributions are separable, operate in parallel, are non-interacting and that total environmental CGR can be obtained by linear summation of cycle-dependent fatigue and time-dependent (SCC) CGRs. However, considered here are data and analyses that show that environmental CGRs may be greater than predicted by superposition models. A phenomenological model is developed to quantify the effect of crack-tip strain-rate due to fatigue stress-cycles on electrochemical activity at a crack tip and thereby synergistically increase crack growth rates by a cyclic-stress corrosion-cracking (C-SCC) mechanism.

scholarly journals Role of Initial Crack Tip Shape, Plastic Compressibility and Strain Softening on Near-Tip Stress-Strain State in Fatigue Cracks during Simulation of a Finite Deformation based Elastic-Viscoplastic Constitutive Model

2021 ◽  
Author(s):  
Md Intaf ALAM ◽  
Debashis KHAN ◽  
Satyabrat PANDEY ◽  
Sandeep KUMAR
Keyword(s):  
Crack Growth ◽  
Strain Softening ◽  
Fatigue Cracks ◽  
Crack Tip ◽  
Initial Crack ◽  
Small Scale ◽  
Curvature Radius ◽  
Stress Strain ◽  
Initial Shape ◽  
Hardening Material

This paper deals with the effect of initial crack tip shape, plastic compressibility, and strain softening on near-tip stress-strain fields for a mode I crack subjected to fatigue loading under plane strain and small scale yielding. A finite strain-based elastic-viscoplastic constitutive equation with bilinear hardening and hardening-softening-hardening hardness functions is taken up for simulation. It is observed that plastic compressibility and strain softening have a significant impact on crack tip opening displacement (CTOD) and tip propagation. Furthermore, it has been viewed that the initial shape of a crack tip can significantly influence both the CTOD and the crack tip extension for the bilinear hardening material; however, with identical conditions for the hardening-softening-hardening material, the initial crack tip shape affects the fatigue crack growth much lesser though the CTOD is influenced considerably. In comparison to the crack growth in the plastically incompressible hardening-softening-hardening solids, the variation of the crack growth (with respect to the tip curvature radius) is more and peculiar in the corresponding plastically compressible solid. To explain and to get a better insight of the crack tip deformation, the near-tip plastic strain and hydrostatic stress have been illustrated.

Time-Dependent Crack Initiation and Growth in Ceramic Matrix Composites

1998 ◽  
Vol 120 (4) ◽  
pp. 808-812
Author(s):  
M. R. Begley ◽  
B. N. Cox ◽  
R. M. McMeeking
Keyword(s):  
Crack Growth ◽  
Crack Tip ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Cracking ◽  
Time Dependent ◽  
Small Scale ◽  
Matrix Composites ◽  
Fine Grained ◽  
Growth Initiation

Matrix cracking in ceramic matrix composites with fine grained fibers at high temperatures will be governed by fiber creep, as relaxation of the fibers eliminates crack tip shielding. Using a time dependent bridging law that describes the effect of creeping fibers bridging a crack in an elastic matrix, crack growth initiation and history have been modeled. For a stationary crack, crack tip stress intensity factors as a function of time are presented to predict incubation times before subcritical crack growth. Two crack growth studies are reviewed: a constant velocity approximation for small-scale bridging, and a complete velocity history analysis which can be used to predict crack length as a function of time. The predictions are summarized and discussed in terms of identifying various regimes of crack growth initiation, subcritical growth, and catastrophic matrix cracking.

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