The connection of composite parts is an important aspect in various fields ranging from materials to engineering structures [1
]. In addition to the most common mechanical connections, the adhesive bonding of composite materials is a joint connection technique that uses adhesives to bond together composite components. Compared with traditional mechanical connections, the use of adhesive bonding technology for composite materials not only avoids the damage and stress [2
] caused by punching on the components, but also enhances the integrity of the materials. Adhesive bonding technology enables the strength of the structure to be equal to or higher than that of traditional connections, which saves costs and reduces the weight of the bond. The structure of the adhesively bonded joint is simple, with good sealing performance, high specific strength, and low cost. It is widely used in the aerospace, mechanical manufacturing, and automobile fields [3
]. More than 100 kinds of aircraft with adhesive structures exist around the world. The leading edge and nose cone of the B-58 supersonic bomber [5
] are composed of carbon fiber reinforced composites, and the adhesive honeycomb structure is used widely for the bomber, replacing half a million rivets.
Adhesively bonded joints nonetheless have some disadvantages due to their processing and associated overlapping. The bearing capacity of adhesively bonded joints is considerably affected by the manufacturing process, application environment, geometric dimensions, and the gap between adhesive layers. In particular, for bonded composite structures used in extreme environments such as high temperature and high humidity, joint strength presents an obvious dispersion. The strength of the adhesive changes with the temperature, resulting in changes in the bearing capacity of the joint. Although an adhesive layer has a strong shear capacity, its peeling resistance is poor. A reasonable structure should be designed based on the direction of the maximum load so that the joint can transfer the load as much as possible in the form of shearing. For example, in an adhesively bonded single-lap structure, the peeling stress at both ends of the adhesive layer increases due to secondary bending [6
], resulting in failure of the adhesive layer. To reduce the torque generated by an eccentric load, the thin plate is usually selected as the adherend of an adhesively bonded single-lap structure. However, for materials with high brittleness such as C/C composite materials and C/SiC materials, the composite material undergoes brittle fracture if the adhesive strength is large when a thin plate is used for the single-lap joint. Therefore, in practical applications, a scarf joint [7
] is used, or alternately the single-lap structure of brittle materials is reinforced along the thickness direction of the overlapped plate to fully take advantage of the shear performance of the adhesive. With the rapid development of the national defense industry, civil construction industry, automobile industry, and so on, the bearing capacity of the connection structure of high-temperature resistant composite materials must be increased.
Many reports have been published on the bearing capacity and failure modes of the adhesively bonded single-lap structures of composite materials. In-depth and extensive studies have been conducted on the factors influencing the properties of adhesively bonded structures of composite materials, such as thickness of the adhesive layer [8
], gaps in the adhesive layers [9
], temperature [10
], and loading forms [13
], and even reports on nanoscales have been produced [15
]. The methods used have included experimental tests [17
], finite element simulations [20
], and analytical methods [22
]. However, most objects employed in the research have been limited to the connection structures of resin-based fiber reinforced composite materials at temperatures below 400 °C [12
]. Studies are lacking on the connection structures of high-temperature resistant materials (C/C composite materials and high-temperature ceramics) at a temperature resistance above 400 °C because (1) the connection technology of high-temperature-resistant composite materials involves military cutting-edge technologies with few published research results, and (2) because the preparation process of high-temperature-resistant composite materials is complicated [23
] and expensive. Appropriate antioxidant measures should be taken as materials are oxidized easily at high temperatures [24
]. These issues have posed challenges for the experimental study of connection structures of composite materials at high temperatures.
With support from the National Natural Science Foundation of China, we studied the compression shear properties of the adhesively bonded single-lap structures of high-temperature-resistant composite materials (C/C composite materials) at high temperatures by combining experimental tests and finite element simulations. Specifically, we examined the influences of ambient temperature, overlapped length, and gap position of adhesive layers on the joint bearing capacity.