2. Chain Dynamics
2.2.2 Repeated Load Tension, Fatigue Failure In Basics Section 2.2.1, we looked at the case of rotating chains without load. In this section, we’ll examine rotating chains with load, a typical use of chains. In Figure 2.15, the left sprocket is the driving side (power input) and the right sprocket is the driven side (power output). If we apply counterclockwise rotation power to the driving sprocket while adding resistance to the driven sprocket, then the chain is loaded in tension mainly at the D~A span, and ten- sion is smaller in the other parts. Figure 2.16 shows this relation.
Figure 2.15 ATypical Chain Drive with the Driving Side on the Left
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Figure 2.16 Chain Load with the Addition of Resistance
Chains in most applications are typically loaded by cyclical tension. Chain fatigue is tested under pulsating tension via a fixture. The fatigue limit will occur between 10 6 to 10 7 times. Figure 2.17 shows the concept of repeated load tension, where P a represents the amplitude. NOTE: If the minimum force is zero, the chain is free to move during testing. Therefore, JIS provides P min =P max 3 1/11, as in Figure 2.17. When a chain that is more than five links and of linear configuration receives
repeated load, it can be shown as a solid line (as in Figure 2.17). JIS B 1801-1990 defines the breakage load in 5 3 10 6 times:
P max = P m + P a = 2.2 P a
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