Investigation on fatigue crack growth behavior for commercial pure titanium at different crack tip plastic deformed levels

ABSTRACT Fatigue crack growth behavior of carbon black–reinforced natural rubber is investigated. Rubber compounds of Shore A = 70 are prepared by varying the formulation loadings of a wide range of carbon black types based on their structure and surface area properties. The resulting fatigue crack growth behavior shows significant variation in β exponent values, depending on the properties of the carbon black. These variations are rationalized by considering the strain amplification of natural rubber by carbon black aggregates in the region of compound directly ahead of the crack tip. An assumption is made that little networking of the carbon black aggregates exists in this region of very high strain and that hydrodynamic calculations that consider occluded rubber can therefore provide realistic values for strain amplification. A reasonable scaling of power law crack growth parameters to calculated strain amplification factors is found, with the exponent, β, decreasing with increasing strain amplification. The implication here is that enhanced strain amplification promotes the formation of strain-induced crystallites in the crack tip region. Performance tradeoffs resulting from the crossover of crack growth data sets dependent on the carbon black type are discussed. Of practical significance is the fact that the strain amplification factors can be calculated directly from knowledge of carbon black type and loading in rubber formulations.

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Numerical simulation of fatigue crack growth behavior by crack-tip blunting

Engineering Fracture Mechanics ◽

10.1016/j.engfracmech.2009.05.012 ◽

2009 ◽

Vol 76 (13) ◽

pp. 2056-2064 ◽

Cited By ~ 9

Author(s):

J.M. Hunnell ◽

D. Kujawski

Keyword(s):

Numerical Simulation ◽

Fatigue Crack ◽

Fatigue Crack Growth ◽

Crack Growth ◽

Crack Tip ◽

Growth Behavior ◽

Crack Growth Behavior ◽

Fatigue Crack Growth Behavior ◽

Crack Tip Blunting

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In-Situ SEM Testing for Transient Fatigue Crack Growth Behavior Investigation Subjected to a Single Tensile Overload

Volume 9: Mechanics of Solids, Structures and Fluids ◽

10.1115/imece2014-37703 ◽

2014 ◽

Author(s):

Wei Zhang ◽

Yongming Liu

Keyword(s):

Fatigue Crack ◽

Fatigue Crack Growth ◽

Crack Growth ◽

Crack Closure ◽

Crack Tip ◽

Growth Behavior ◽

Crack Growth Behavior ◽

Fatigue Crack Growth Behavior ◽

Single Overload

In this paper, the in-situ scanning electron microscopy (SEM) experiments are performed in the edge-cracked specimen under the single overload in order to investigate transient fatigue crack growth behavior. The specimen is made of Al7075-T6 and under the plane stress condition. During the testing, several loading cycles of interest are selected and divided into a certain number of steps. At each step, high resolution images around the crack tip region are taken under the SEM. Imaging analysis is used to quantify the crack tip opening displacement (CTOD) at each corresponding time instant in a loading cycle. In the current experimental work, the crack closure phenomenon is not only directly observed under constant amplitude loadings, but also under the variable amplitude loading. The experimental results provide the evidence that the crack closure may disappear or become inconsequential right after the single overload. And some observations imply that the crack closure is not the only parameter which controls fatigue crack growth rate, other factors need to be considered. A detailed discussion is given based on the current investigation.

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