Abstract
The fracture mechanics of random discontinuous Carbon Fiber Sheet Molding Compound (C-SMC) materials compared to traditional carbon fiber composites are not well understood. An experimental study was carried out to characterize the fracture behavior of such C-SMC materials. Mode I tests, using double cantilever beam specimens, and mode II tests, adopting the four-point bend, end-notched flexure configuration, were performed. Results show high variations in the forcedeflection responses and scatter in the fracture toughness properties GIc and GIIc, due to the complex mesostructure defined by random oriented carbon fiber chips. To investigate the influence of the mesostructure, tensile tests with varying specimen width and thickness were assessed by stochastic measures to find the representative specimen size.
Highlights
The exceptional strength to weight ratios presented by many advanced composite materials are desirable for industries that constantly fight to improve efficiency [1]
Random discontinuous Carbon Fiber Sheet Molding Compound (C-SMC) is a special type of SMC material, where a unidirectional carbon fiber prepreg is slit and chopped into chips, randomly distributed in a mold and finished in a single-stage compression and curing process
Research employing microscopical analysis of tensile, compressive and flexural tested specimens conducted by Feraboli et al [2] showed that failure in random discontinuous C-SMC materials is a matrixdominated event with two prevalent failure modes of intralaminar chip cracking and interlaminar chip delamination, with little or no fiber breakage
Summary
The exceptional strength to weight ratios presented by many advanced composite materials are desirable for industries (automotive, aerospace, . . . ) that constantly fight to improve efficiency [1]. Random discontinuous C-SMC is a special type of SMC material, where a unidirectional carbon fiber prepreg is slit and chopped into chips, randomly distributed in a mold and finished in a single-stage compression and curing process. This material and process technology can be used to produce geometric complex, lightweight applications in an industrial (automated) and cost efficient way. The authors point out that delamination failure initiates in chips perpendicular to the load direction and propagates until delamination of other chips with higher alignment is involved In another recently published work by Kravchenko et al [4] the tensile failure behavior of discontinuous C-SMC with unidirectional aligned chips was investigated by numerical analysis. In random discontinuous CSMC materials, the effective load transfer between the chips is greatly reduced because of a wide distribution of overlapping lengths caused by the stochastic distribution of the chips
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