Scope of Application This standard applies to aerospace and aerospace products, especially for the connection of carbon fiber reinforced resin matrix composite structural parts, to avoid serious galvanic corrosion problems between fasteners and carbon fiber reinforced resin matrix composites. At the same time, in the structural connection of the composite material, the high-locking bolt and the high-lock nut can be used to effectively control the pre-tightening force of the joint, thereby controlling the compressive strength of the connected member (composite material).
The main content of this series of standards has two standard components: QJ2825-965MJ threaded titanium small countersunk head tight tolerance high lock bolt 6 and QJ2826-965MJ threaded titanium alloy flat head tight tolerance high lock bolt 6. Two specifications specified in the standard The high lock bolt diameter tolerances are tight tolerances (f9) and are suitable for structural connections subjected to shear loads. In general, use flat-headed bolts; use small countersunk bolts only if the bolt heads are not required to be raised and one of the thicknesses is thin.
Materials and heat treatment standards stipulate that the material for manufacturing high-lock bolts is titanium alloy TB3 according to the specifications of titanium and titanium alloy rods (wire) of GJB22195 fasteners. The technical conditions are titanium and titanium for GJB2189-945 fasteners. Specification for alloy rod (wire) material specification 6. At present, there are mainly two types of titanium alloy materials available for manufacturing fasteners in China, namely B type TB2 and TB3; A+B type TC4.TC4 is a duplex alloy, which can only be heated or machined. Forming, and destroying the fiber of the material, the machining efficiency is also low, the cost is high, and the heat is limited by the equipment, and the space system cannot be produced. Therefore, it can only be selected from B alloy. TB2 is mainly used to manufacture rivets, and TB3 has been widely used in the manufacture of screws and bolts, and is used on satellite models. The density of TB3 is 4184g/mm3, which has the general characteristics of titanium alloy. Although its thermal stability is slightly worse than TC4, it can meet the design requirements of the model. The tensile strength of the material in the solid solution state is 840MPa940MPa, which has good cold heading performance. The ratio of cold head to rake ratio (the ratio of the height of the radon before the height of the crucible to the height of the crucible) can reach 218, and after aging treatment, the tensile strength can be Up to 1100MPa, the shear strength is above 690MPa, which can fully meet the design strength requirements.
The thread standard stipulates that the thread of the high lock bolt is the MJ thread commonly used in the international aerospace industry. The main advantage of this thread is its good fatigue resistance, which means that its ability to withstand dynamic loads is greatly improved compared to conventional threads. In addition, due to the high precision of the MJ thread (external thread is 4h6h), the anti-loose effect will also be significantly improved.
According to the relevant resolution of ISO/TC20/SC4 Aerospace Fasteners Subcommittee, the specifications of MJ fasteners are indicated by code. For example, 050024 indicates that the diameter specification (050) is MJ5 and the length specification (024) is 24mm. This specification is fully in line with international standards.
The mechanical properties of the high-lock bolts are the same as those of ordinary bolts. Therefore, the technical conditions of this standard all refer to the technical conditions of QJ2602-945MJ thread 1100MPa titanium alloy bolts. 6. It should be noted that the loading value and head strength of the bolt fatigue test Related to, the head is small, the head is thin, and the load is large. The strength of the heads of these two bolts is weak, so when selecting the fatigue load, the data is selected according to the no-slot small countersunk head in QJ2602.
When the slope of the surface of the material structural member exceeds 015b, a special gasket with a slope should be used under the head of the high-lock bolt, otherwise the head strength of the high-lock bolt will be greatly weakened. Determination of the length of the high-lock bolts Considering the unevenness of the thickness of the composite material, the thickness of the bolt holes should be measured using the thickness gauge of the interlayer (using the thickness gauge of the interlayer). If the detection point is in the middle of the two-line, the reading is compared. Great value. The polished rod length is the sum of the detection point reading value and the gasket thickness.
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