Experimental study on influence of bolt tightening torque on joint strength of composites
Composite materials are a new class of materials that emerged in the 1960s. They have high strength, high stiffness, light weight, and have a series of advantages such as anti-fatigue, vibration reduction, high temperature resistance and design. They have shown strong strength once they are published. vitality. At present, advanced composite materials have been widely used in aerospace, energy, transportation, construction, biology, medical and other fields. Compared with metal materials, advanced composite materials have many excellent characteristics such as high specific strength and specific modulus, performance design and easy integral forming. They are used in aircraft structures and can reduce weight by 25% to 30% compared with conventional metal structures. Therefore, more and more composite structures are used in aerospace and structural design in various fields. Especially in the civil aviation field, the Boeing 787 has a composite material usage of 50%. The newly developed Airbus A350 aircraft composite materials will be used. More than 50%. Due to the limitation of the technical level of composite molding technology and the inevitable connection of composite components with metal components, there are still a large number of connection problems in the composite structure, and due to the particularity of the composite materials, the connection analysis is largely Dependent on experimental research. The bolt tightening torque is one of the factors affecting the joint strength of composite materials. This paper gives the connection failure load of the same type of laminated carbon fiber composite under different tightening torques, which can provide a basis for the formulation of composite tightening torque standards. 1 Test type and test conditions 2 test results and analysis (1) In the case of double shear connection, as the tightening torque increases, the final breaking load gradually increases until the tightening torque reaches 8 N·m, and the joint strength decreases. The 4% deformation load decreases with the increase of the tightening torque. (2) In the case of single shear connection, as the tightening torque increases, the final breaking load also gradually increases, showing the same trend as the double shear connection. (3) Comparing the 4% deformation load of the same bolt tightening torque in the case of double shear and single shear connection, the double shear connection is smaller than the single shear connection load. (4) Comparing the breaking load of the same bolt tightening torque in the case of double shear and single shear connection, when the fastener is 2 N·m tightening torque, the double shear connection is increased by 8.7% compared with the single shear connection; the fastener is 4 N·m tightening torque, the double shear connection is reduced by 7.8% compared to the single shear connection. (5) The failure mode of the double-shear lap test piece is mainly the extrusion failure of the hole in the middle plate, the single-shear lap test piece is crushed at the edge of the lower laminate, and the bolt rod is bent at 2 N·m tightening torque. , 4 N・m, the bolt rod is sheared. 3 Conclusion The connection form and the fastener form are the same. When the tightening torque is different, the final breaking load increases gradually as the tightening torque increases, but there is an extreme value. After the extreme value is exceeded, the tightening torque increases. The load will decrease. In the case of double shear and single shear connection, the same bolt tightening torque is 4% deformation load, double shear connection is smaller than single shear connection load; double shear and single shear connection is the same bolt tightening torque breaking load, fastener is 2 N・m tightening torque, double shear connection is larger than single shear connection load, when the fastener is 4 N·m tightening torque, double shear connection is smaller than single shear connection load; double shear joint test piece failure mode is mainly middle When the hole edge extrusion failure occurs, the single shear lap test piece is crushed at the edge of the lower laminate, and the bolt rod is bent when the torque is 2 N·m, and the bolt rod is sheared at 4 N·m. The above data only shows the influence of tightening torque on the joint strength under partial connection. More research in this area will be carried out later, and more data will be obtained for the study of bolt tightening torque. references [1] Wang Hai, Xie Mingjiu. Experimental study on bonding strength of composite material laminate titanium bolts, Proceedings of the 9th National Conference on Composite Materials [C]. Beijing: World Book Publishing Company. 1996. [2] Jia Purong, Jiao Guiqiong, Pan Wenge, et al. Experimental study on nail hole extrusion strength of carbon fiber composites, Proceedings of the Ninth National Conference on Composite Materials [C]. Beijing: World Book Publishing Company. 1996. [3] Jin Hui. Research on Determination Method of Environmental Factors for Static Test of Civil Aircraft Composite Structure[J]. Civil Aircraft Design and Research, 2012(S1): 34-37. Pvc Fence,Vinyl Fence,Privacy Fence,Plastic Fencing HeBei Fortune Trade Co.,Ltd. , https://www.gardfence.com