Fastener Testing
Many factors must be considered when establishing a threaded fastener bolted joint analysis program, which should include methods for modeling the joint, determining torque-tension characteristics and friction coefficients, and experimental testing of components and assemblies.
Test methods have been established and published for mechanical properties such as hardness, tensile strength, and torsional strength as well as corrosion and hydrogen embrittlement. These provide the baseline information necessary for proper interpretation of the friction coefficient, torque-tension, and angular ductility testing tests that are used to complete the evaluation of bolted joints. Once the basic material strength and friction coefficient information has been determined, an additional method, Torque-Angle Signature Analysis, can provide valuable information on joint strength and performance when applied to testing fasteners in bolted joints.
The basic torque-angle signature can be used as a starting point for all analysis. For example, it can be used to illustrate the influence of underhead and thread friction on the tightening process where an increase in friction, in either the thread or underhead regions, can result in a proportional increase in the slope of the torque-angle signature. The study of the slope of the torque-angle curve when the fastener is tightened is an important component of analyzing the performance of threaded fasteners in bolted joints.
To apply torque-angle signature analysis, a torque-angle recording device is needed for measurement and curve plotting. The recorder can provide curves on-screen for analysis as well as print them out for additional study. Tightening, audit, and release angle signatures for a given bolted joint can be simultaneously displayed and printed. A careful review of the applied torque vs. angle-of-turn plot, signature analysis can be used to evaluate bolted joints for loss of preload due to settling, creep and relaxation, or vibration and dynamic loading. In addition, joint strength problems such as thread strip and embedment of bearing surfaces and material yield within the bolted joint are easily identified.
The following tests are typically conducted in the Fastener Test area:
Torque Tension Testing
Friction Coefficient Testing
Assembly Strategy Testing
Locknut Testing
Bolted Joint Analysis & Troubleshooting
Yield Determination Testing
Bolted Joint Modeling and Analysis
Products and accessories specifically designed for use in all of these Fastener Testing tests, including:
LabMaster Professional, Model 3200
Rotary Torque Transducers, Series PC9000
Fastener Drive System
Force Washer Transducers, Series FT4000
Fastener Tension Load Cells, Series FT9000
Fastener Torque-Tension Load Cells, Series FTA9000
Portable Data Recorder, Model 962
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