Fracture Resistance Evaluation of Fibre Reinforced Brittle Matrix Composites

2005 ◽  
Vol 290 ◽  
pp. 167-174 ◽  
Author(s):  
Ivo Dlouhý ◽  
Zdeněk Chlup
Keyword(s):  
Fracture Toughness ◽  
Fracture Resistance ◽  
Ceramic Materials ◽  
Matrix Composites ◽  
Brittle Matrix ◽  
Loading Mode ◽  
Chevron Notch ◽  
Point Bend ◽  
The Right ◽  
Major Crack

Determination of the fracture toughness using a specimens with straight and/or chevron notch in the three (four) point bend test for monolithic ceramic materials can be taken as standardized techniques. In case of composite materials, mainly of brittle matrix reinforced by unidirectional fibres the crack growth resistance increases as the crack propagates. In addition, the long fibres stimulate delaminations along fibre – matrix interface perpendicularly to the major crack. Fracture toughness determination (in the loading mode I) in cases when delaminations take place is difficult. The chevron notch technique could be the right way to overcome this difficulty and obtain exact fracture toughness characteristics by its natural ability to “keep” the direction of major crack. Based on fractographic analyses some examples are described to show potential of the chevron notch technique for fracture resistance characterisation of the studied composite including comparison of data from chevron and straight notch technique etc.

Fracture toughness and R-Curve behavior of laminated brittle-matrix composites

1998 ◽  
Vol 29 (10) ◽  
pp. 2483-2496 ◽  
Author(s):  
D. R. Bloyer ◽  
R. O. Ritchie ◽  
K. T. Venkateswara Rao
Keyword(s):  
Fracture Toughness ◽  
Matrix Composites ◽  
Brittle Matrix ◽  
Brittle Matrix Composites

Effect of Fiber Extensibility on the Fracture Toughness of Short Fiber or Brittle Matrix Composites

1992 ◽  
Vol 45 (8) ◽  
pp. 377-389 ◽  
Author(s):  
L. K. Jain ◽  
R. C. Wetherhold
Keyword(s):  
Fracture Toughness ◽  
Fracture Energy ◽  
Fiber Orientation ◽  
Crack Opening ◽  
Matrix Composites ◽  
Brittle Matrix ◽  
Pull Out ◽  
General Terms ◽  
Brittle Matrix Composites ◽  
Fiber Orientation Distribution

A micromechanical model based on probabilistic principles is proposed to determine the effective fracture toughness increment and the bridging stress-crack opening displacement relationship for brittle matrix composites reinforced with short, poorly bonded fibers. Emphasis is placed on studying the effect of fiber extensibility on the bridging stress and the bridging fracture energy, and to determine its importance in cementitious matrix composites. Since the fibers may not be in an ideal aligned or random state, the analysis is placed in sufficiently general terms to consider any prescribable fiber orientation distribution. The model incorporates the snubbing effect observed during pull-out of fibers inclined at an angle to the crack face normal. In addition, the model allows the fibers to break; any fiber whose load meets or exceeds a single-valued failure stress will fracture rather than pull out. The crack bridging results may be expressed as the sum of results for inextensible fibers and an additional term due to fiber extensibility. An exact analysis is given which gives the steady-state bridging toughness G directly, but presents a non-linear problem for the bridging stress-crack opening (σb – δ) relationship. An approximate analysis is then presented which gives both G and σb – δ directly. To illustrate the effect of extensibility on bridging stress and fracture energy increment due to bridging fibers, a comparison with the inextensible fiber case is provided. It is found that effect of extensibility on fracture energy is negligible for common materials systems. However, extensibility may have a significant effect on the bridging stress-crack opening relationship. The effect of other physical and material parameters such as fiber length, fiber orientation and snubbing friction coefficient is also studied.

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