Effect of Fiber Reinforcement on Dynamic Crack Growth in Brittle Matrix Composites

1993 ◽  
Vol 115 (1) ◽  
pp. 140-145 ◽  
Author(s):  
Arun Shukla ◽  
Sanjeev K. Khanna
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Velocity ◽  
Dynamic Crack ◽  
Matrix Composites ◽  
Dynamic Photoelasticity ◽  
Brittle Matrix Composites ◽  
Fiber Matrix Interface ◽  
Crack Faces

An experimental investigation is conducted to study the interaction of a running crack with embedded fibers. Dynamic photoelasticity is used to evaluate the crack velocity and the instantaneous stress intensity factor, KID, as the crack propagates across the fibers. Fractography is used to explain the interaction of the dynamic crack front with the fiber. The results show that fibers significantly reduce the stress intensity factor and also the crack velocity. The effect of a weak fiber-matrix interface on crack velocity and KID is studied. A weak interface reduces KID but has no effect on the crack velocity. The crack closing forces applied by fibers bridging the crack faces have been determined for both the strong and weak interfaces and their effect on KID is explained.

Stability Analysis of Bridged Cracks in Brittle Matrix Composites

1993 ◽  
Vol 115 (1) ◽  
pp. 127-138 ◽  
Author(s):  
R. Ballarini ◽  
S. Muju
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Opening ◽  
Matrix Crack ◽  
Matrix Composites ◽  
Brittle Matrix ◽  
Matrix Cracks ◽  
Brittle Matrix Composites ◽  
Propagating Crack

The bridging of matrix cracks by fibers is an important toughening mechanism in fiber-reinforced brittle matrix composites. This paper presents the results of a nonlinear finite element analysis of the Mode I propagation of a bridged matrix crack in a finite size specimen. The composite is modeled as an orthotropic continuum and the bridging due to the fibers is modeled as a distribution of tractions that resist crack opening. A critical stress intensity factor criterion is employed for matrix crack propagation, while a critical crack opening condition is used for fiber failure. The structural response of the specimen (load-deflection curves) as well as the stress intensity factor of the propagating crack is calculated for various constituent properties and specimen configurations for both tensile and bending loading. By controlling the length of the bridged crack, results are obtained that highlight the transition from stable to unstable behavior of the propagating crack.

Stability Analysis of Bridged Cracks in Brittle Matrix Composites

1991 ◽  
Author(s):  
Roberto Ballarini ◽  
Sandeep Muju
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Opening ◽  
Matrix Crack ◽  
Matrix Composites ◽  
Brittle Matrix ◽  
Matrix Cracks ◽  
Brittle Matrix Composites ◽  
Propagating Crack

The bridging of matrix cracks by fibers is an important toughening mechanism in fiber reinforced brittle matrix composites. This paper presents the results of a non-linear finite element analysis of the Mode-I propagation of a bridged matrix crack in a finite size specimen. The composite is modeled as an orthotropic continuum and the bridging due to the fibers is modeled as a distribution of tractions which resist crack opening. A critical stress intensity factor criterion is employed for matrix crack propagation while a critical crack opening condition is used for fiber failure. The structural response of the specimen (load-deflection curves) as well as the stress intensity factor of the propagating crack are calculated for various constituent properties and specimen configurations for both tensile and bending loading. By controlling the length of the bridged crack results are obtained which highlight the transition from stable to unstable behavior of the propagating crack.

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.

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