Question 6.5: Design of a Cantilever Bracket for Fluctuating Bending Probl...
Design of a Cantilever Bracket for Fluctuating Bending
Problem A feed-roll assembly is to be mounted at its ends on support brackets cantilevered from the machine frame as shown in Figure 6-47. The feed rolls experience a total fluctuating load that varies from a minimum of 200 lb to a maximum of 2 200 lb, split equally between the two support brackets. Design a cantilever bracket to support a fluctuating bending load of 100- to 1 100-lb amplitude for 10^{9} cycles with no failure. Its dynamic deflection cannot exceed 0.02 in.
Given The load-time function shape is shown in Figure 6-47. The operating environment is room air at a maximum temperature of 120°F. The space available allows a maximum cantilever length of 6 in. Only ten of these parts are required.
Assumptions The bracket can be clamped between essentially rigid plates bolted at its root. The normal load will be applied at the effective tip of the cantilever beam from a rod attached through a small hole in the beam. Since the bending moment is effectively zero at the beam tip, the stress concentration from this hole can be ignored. Given the small quantity required, machining of stock mill-shapes is the preferred manufacturing method.
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