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Outstanding mechanical properties and high thermal conductivity epoxy composites are being developed and are becoming urgent in the electronic and aerospace industries. Boron nitride nanosheet (BN), a nanomaterial with high thermal conductivity, and its epoxy composite adhesive have high thermal conductivity. However, due to its characteristics, the mechanical properties of BN/epoxy will decrease when more BN is added. Therefore, this study graphene platelet and carbon nanotube are selected and packed epoxy/BN composite adhesives to develop adhesives with excellent mechanical properties and thermal conductivity at the same time. In this study, an enhancement effect between a graphene platelet (GnP) and a carbon nanotube (CNT) within an epoxy/BN composite is reported. In the three-phase composite adhesive, the 2 D graphene platelets and 1D carbon nanotubes form a global bearing force network, and the boron nitride nanosheets provide high heat conduction inside the epoxy. They both complement each other in developing thermal conductive and high mechanical energy epoxy composite adhesives. At filler ranging from 0 to 1.0 wt%, epoxy/BN-CNT can improve the fracture toughness (K1c), critical stress-energy release rate (G1c) and Young's modulus of pure epoxy, are 89, 484, and 67% compared to 52, 286, and 42% in epoxy/BN-GnP composites, respectively. When adding 5.0 wt% of BN-CNT, the epoxy composites' thermal conductivity is up to 0.8 W/m%K, 400% higher than pure epoxy. This article also tested the electrical conductivity of epoxy/BN-CNT and epoxy/BN-GnP composites and found that the electrical conductivity was increased by 12 and 10 orders of magnitude, respectively, and it could be used as an antistatic material. Investigating the enhanced mechanism of epoxy/BN/CNT and epoxy/BN/GnP composites by scanning electron microscopy analysis. Lap shear strength tests on epoxy composite adhesives confirm the reinforcement effect of GnP and CNT of epoxy/BN composites. [ABSTRACT FROM AUTHOR]

In the electronics and aerospace industries, epoxy resins are generally regarded as economical and efficient adhesives and have a high status. However, epoxy resins are highly crosslinked polymers and are very brittle adhesives where they are prone to fast crack propagation under dynamic loads. Therefore, it is very necessary to enhance the toughness of epoxy resin adhesives. Nano-rubber has been proved to be an important toughening agent for epoxy resin, which can significantly improve the fracture toughness of epoxy resin. However, increasing the toughness of epoxy resin by adding nanomaterials is often accompanied by decreasing the strength and stiffness of resin. Therefore, in this work, rigid nano-silica particles were added to improve the rigidity and tensile strength reduction caused by the addition of rubber particles. And further increase the toughness of the epoxy resin to obtain an epoxy adhesive with balanced stiffness-toughness. As a result, it can be found that the addition of silica particles can significantly improve the decrease in stiffness caused by the addition of rubber particles. For example, Young's modulus and tensile strength are increased by 28%, and 23%, respectively, with 4% silica is added based on rubber particles. Through the single lap shear experiment, it is found that the shear strength of the epoxy/RnP/silica composite adhesive has increased, which further proves that the addition of nano-silica particles can increase the stiffness of the epoxy composite. The dynamic mechanical analysis experiment found that after adding nano-silica particles, the storage modulus of epoxy composites increased, which also shows that adding nano-silica particles can improve the stiffness of epoxy composites. Scanning electron microscopy analysis was performed to study the reinforcement mechanism of epoxy/RnP/silica composite materials. The thermal stability of epoxy composites was characterized by Dynamic mechanical analysis and thermogravimetric analysis. [ABSTRACT FROM AUTHOR]

Graphene platelets (electrically conductive 2D filler) and rubber nanoparticles (0D soft filler) can work together to develop electrically conductive and toughened epoxy composite adhesives. In this study, complementing effect between graphene platelets (GnPs) and rubber nanoparticles (RnPs) within an epoxy matrix is reported. In the 3‐phase composite adhesive, the 2D graphene platelets form global conductive network and rubber nanoparticles provide a viscoelastic phase inside the epoxy, both complementing each other to develop electrically conductive and toughened epoxy composite adhesives. Fracture toughness (K1c) and critical strain energy release rate (G1c) of the epoxy were augmented by 422% and 872%, respectively by adding 1 wt% RnPs and it recorded electrical percolation threshold at 0.78 vol% GnP. Also, the Young's modulus and strength of epoxy/1 wt% RnP composite were promoted from 1.57 to 2.32 GPa when 1 wt% GnP is added. Scanning electron microscopy analysis was conducted to investigate the toughening mechanism of epoxy/RnP/GnP and epoxy/GnP composites. Lap shear strength tests on epoxy composite adhesives confirm the reinforcement effect of GnPs and toughness effect of RnPs. [ABSTRACT FROM AUTHOR]

Composite sandwich panels with pyramidal lattice truss cores (CSPPLTCs) were manufactured employing waterjet-cutting technology and interlocking assembly. The effect of high-low temperature environments on the out-of-plane compressive and shear performance of the panels was studied using theoretical and experimental methods. In particular, the out-of-plane compressive stiffness, strength of sandwich panels with pyramidal lattice truss cores, their shear stiffness, and strength in high-low temperature environments were predicted using theoretical equations. The study found that in low-temperature environments, the movement of molecular chain segments in the epoxy is hindered, futhermore, the mismatched thermal expansivity of carbon fiber and epoxy resin leads to the improvement of interface bonding performance, thus improving the out-of-plane compressive and shear performance of CSPPLTCs; in high temperature environments, the movement of molecular chain segments in the epoxy gets more active and tends to move freely, so the resin turns into a flexible state with high elasticity from the stiff glass state, which finally causes a deterioration in out-of-plane compressive and shear performance of CSPPLTCs. According to observations, the failure mode depends on temperature environments. Brittle fracture and crushing failure happen in the composite struts at low temperature; plastic microbuckling may happen in the composite struts at high temperature. [ABSTRACT FROM AUTHOR]