After repeated assembly and disassembly, the assessment of thread wear and connection reliability of aluminum alloy nuts needs to be conducted from multiple dimensions, encompassing visual inspection, dimensional measurement, mechanical property testing, microstructure analysis, non-destructive testing, connection strength verification, and actual working condition simulation, to ensure that they still meet design requirements.
Visual inspection is the foundation of the initial assessment. After repeated assembly and disassembly, aluminum alloy nuts may exhibit defects such as scratches, burrs, deformation, or cracks on their surface. Significant wear on the thread profile, such as rounded tooth crests and flattened tooth flanks, indicates that the thread has undergone plastic deformation or abrasive wear. Furthermore, the presence of oxide layer peeling or corrosion spots on the nut surface may accelerate the thread wear process, requiring further comprehensive judgment using other testing methods.
Dimensional measurement is crucial for quantifying thread wear. Using a thread measuring machine or coordinate measuring machine, parameters such as the thread pitch diameter, major diameter, minor diameter, and pitch can be accurately measured. If the pitch diameter exceeds the tolerance range, it may lead to excessive thread clearance, causing loosening or stripping; accumulated pitch errors will affect the smoothness of thread engagement and increase assembly and disassembly resistance. Simultaneously, the height and hexagonal dimensions of the nut must be measured to confirm whether deformation is preventing the wrench from applying force properly.
Mechanical property testing verifies the load-bearing capacity of the aluminum alloy nut. Hardness testing of the nut's surface and core is performed using a hardness tester. A significant decrease in hardness may indicate material softening and reduced wear resistance. During tensile testing, if the nut's tensile strength or yield strength does not meet standard requirements, its connection reliability cannot be guaranteed. Furthermore, residual clamping force testing is crucial. The effective clamping force provided by the nut after multiple assembly and disassembly is assessed using marking or residual torque methods to ensure it meets anti-loosening requirements.
Microstructural analysis reveals the intrinsic mechanisms of thread wear. Observing the metallographic structure of the thread surface using a metallographic microscope reveals coarse grains, abnormal second-phase precipitation, or microcracks, indicating material degradation. Scanning electron microscopy analysis of the thread wear surface morphology can distinguish different failure modes such as abrasive wear, adhesive wear, or fatigue wear, providing a basis for optimizing assembly and disassembly processes or material selection. For example, pitted wear may indicate aluminum alloy oxide buildup due to fretting wear.
Non-destructive testing (NDT) can detect hidden defects within the threads. Penetrant testing is suitable for inspecting open cracks on the nut surface, while ultrasonic or eddy current testing can detect internal cracks or porosity. For aluminum alloy nuts in critical applications such as aerospace or automotive, NDT is essential to ensure their internal quality is defect-free and prevent connection failures caused by potential defects.
Connection strength verification is a direct means of assessing reliability. After assembling the aluminum alloy nut with matching bolts, a static tensile test is performed. If the connection slips or breaks before reaching the design load, it indicates that thread wear has severely affected the connection strength. Dynamic fatigue testing simulates alternating loads under actual operating conditions to evaluate the nut's fatigue resistance after repeated assembly and disassembly. Furthermore, vibration testing verifies the nut's anti-loosening effect, ensuring stable connection under vibration.
Actual operating condition simulation is the final stage of the evaluation. Depending on the specific application scenarios of the aluminum alloy nut, such as high temperature, high humidity, or corrosive environments, accelerated aging tests are designed to simulate its performance degradation after long-term use. For applications requiring frequent assembly and disassembly, multiple cyclic assembly and disassembly tests are conducted to record the wear rate of the nut and changes in connection performance. Through simulation of actual working conditions, the overall reliability of the aluminum alloy nut after multiple assembly and disassembly can be comprehensively evaluated, providing a basis for determining maintenance cycles or replacement strategies.
