Abstract
A modified rule of mixtures is required to account for the experimentally observed nonlinear variation of tensile strength. A modified Halpin–Tsai model was presented to predict the Young’s modulus of multiscale reinforced composites with both micron-sized and nano-sized reinforcements. In the composites, both micron-sized fillers—carbon fibers—and nano-sized fillers—rubber nanoparticles and carbon nanotubes—are added into the epoxy resin matrix. Carbon fibers can help epoxy resins increase both the tensile strength and Young’s modulus, while rubber nanoparticles and carbon nanotubes can improve the toughness without sacrificing other properties. Mechanical experiments and scanning electron microscopy observations were used to study the effects of the micron-sized and nano-sized reinforcements and their combination on tensile and toughness properties of the composites. The results showed that the combined use of multiscale reinforcements had synergetic effects on both the strength and the toughness of the composites.
Highlights
Direct extrusion fabrication (DEF), a new branch of solid freeform fabrication (SFF),[1] is an automated fabricating process that builds three-dimensional (3D) complex structures layer by layer directly according to computer-aided design (CAD) files without specific tooling of part, heating, and human intervention
In the ideal rule of mixtures (ROM), fibers in the composite are unidirectionally aligned and uniformly distributed, but in reality the fibers have some nonhomogeneity of spread and misalignment of orientation
A new type of epoxy resin (EP)-based composite materials, which is modified by multiscale reinforcements, for DEF is developed
Summary
Direct extrusion fabrication (DEF), a new branch of solid freeform fabrication (SFF),[1] is an automated fabricating process that builds three-dimensional (3D) complex structures layer by layer directly according to computer-aided design (CAD) files without specific tooling of part, heating, and human intervention. EPs have a few drawbacks, such as brittle fracture properties and poor crack propagation resistance, which restrict their applications.[9] a number of researchers have presented some modification methods to improve the mechanical performance of EP-based composites These methods include micron-sized modification and nano-sized reinforcing modification.[9,10,11]. Zhang et al.[28] and Sharma and Lakkad[29] stated that multiscale carbon reinforcements had synergetic effects on both the strength and fracture properties of EPs. In this study, short CFs, RNPs, and CNTs were used to modify the EP matrix.
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