Abstract
It is well known that thermoplastic composite is vulnerable to impact fracture. Submicron glass fiber (sGF) was used to modify the matrix of chopped tape carbon fiber reinforced polypropylene composite. The impact resistance improved 20% and 7.4% coressponding to the dimeter sGF of 0.28 and 0.69 µm used in modified-composite. To shed light upon the mechanism of this improvement, the internal damage statement of post-impact specimens was observed by the CT scanner. The results pointed out that the increase of the impact resistance was due to the enlargement of delamination area under impact load. The micro droplet test and end notch flexure test suggest that the decrease of Mode II fracture toughness in modified-composite comes from narrowing the difference between the interfacial shear strength (IFSS) and the bending strength of matrix thanks to significant improving of IFSS with the addition of sGF while the flexural strength remains the unchanged. Consequently, the failure mode changed from debonding fiber/matrix in unmodified composite into brittle matrix failure in modified composite, resulting in the decrease of the Mode II interlaminar fracture toughness and the enlargement of delamination area. The stress transfer test also indicates that the modified composites is prone to the brittle matrix failure.
Highlights
Compared to thermoset composites, thermoplastic composites offer the potential for short processing time, reparability by melting, less brittle, more tougher and higher damage tolerance (Campbell, Sih, & Akca, 2003)
This indicates that the efficiency of improving impact resistance in chopped carbon fiber tape reinforced PP is dependent on the size of Submicron glass fiber (sGF) modifier. 3.2 Evaluation of Damage State After Impact
The calculation of damage area showed the same tendency with the impact resistance of composites, the delamination area increased 33.7% and 24.6% with the composite modified by sGF in diameter of 0.28 and 0.69 μm, respectively compared to that of the unmodified composite
Summary
Thermoplastic composites offer the potential for short processing time, reparability by melting, less brittle, more tougher and higher damage tolerance (Campbell, Sih, & Akca, 2003). Carbon fiber propylene composite has been widely used in many applications such as automotive, construction, and consumer products (Kim, Gabr, & Koncar, 2018) It is well-known that thermoplastic composite is vulnerable to impact fracture. The structure may fail in a wide variety of modes with the most dominant failure are the complex combinations of energy absorbing mechanisms such as (a) delamination caused by mode II shear, (b) matrix cracking resulted by transverse shear, and (c) translaminar fracture caused by fibre rupture and kinking. Other mentioned methods are toughening matrix by using modifiers of thermoplastic, liquid rubber, polymer blend, hyper-branched polymer (Jang et al, 2003) and Z-pinch technique (Ye at al., 2009) In this investigation, submicron glass fiber was used to improve the impact resistance of chopped carbon fiber thermoplastic (CCT) composite. The mechanism of this improvement was lightened by varieties of mechanical characterized tests
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