Abstract
In engineering practice, the service life of cemented carbide shield tunneling machines in uneven soft and hard strata will be seriously reduced due to thermal stress. When carbon nanotubes (CNTs) and graphene nano-platelets (GNPs) are added to WC–Co carbide as enhanced phases, the thermal conductivity of carbide is significantly improved. Research should be performed to further understand the mechanism of enhancement in composites and to find ways to assist the design and optimization of the structure. In this paper, a series of finite element models were established using scripts to find the factors that affect the thermal conduction, including positions, orientations, interface thermal conductivity, shapes, sizes, and so on. WC–Co carbide with CNTs (0.06%, 0.12%, and 0.18% vol.), GNPs (0.06%, 0.12%, and 0.18% vol.) and hybrid CNTs–GNPs (1:1) were prepared to verify the reliability of finite element simulation results. The results show that the larger the interface thermal conductivity, the higher the composite phase thermal conductivity. Each 1%vol of CNTs increased the thermal conductivity of the composite phase by 7.2%, and each 1% vol. of GNPs increased the thermal conductivity of the composite phase by 5.2%. The proper curvature (around 140°) of CNTs and GNPs with a proper diameter to thickness ratio is suggested to lead to better thermal conductivity.
Highlights
Carbide has the advantages of high hardness, high wear resistance, and good toughness for avoiding brittle fracture, and is a common material for shield blades
Junjie Chen et al introduced graphene oxide into metals and polymers and investigated the thermal properties of graphene oxide using nonequilibrium molecular dynamics, and the results showed that the degree of oxidation has a significant effect on the thermal conductivity
The thermal conductivity of cemented carbides with graphene and carbon nanotubes has been improved to some extent, and through EDS energy spectrum analysis it has been concluded that graphene and carbon nanotubes are mainly distributed in the Co phase of WO–Co carbide [26]
Summary
Carbide has the advantages of high hardness, high wear resistance, and good toughness for avoiding brittle fracture, and is a common material for shield blades. When a shield machine digs in the bottom layer of uneven soft and hard strata, the life of the tool will be seriously reduced due to thermal stress and other reasons. The current research shows that the main failure forms of carbide tools in shield machines are fracture and wear. The reason for failure is that, under the simultaneous action of mechanical stress and thermal stress, micro cracks are formed and extended until the carbide tool fails [3,4]. The cause of carbide tool failure is due to thermal stress-induced cracking, but little research has been completed on how to improve the thermal conductivity of carbide to solve this problem. The addition of graphene and carbon nanotubes to cemented carbide may be a good solution to the low thermal conductivity of cemented carbide [5]
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