You have built the majority of the tension testing machine, but much of the instrumentation is still being assembled. To test the machine, you perform a test on a steel specimen with known properties. The machine provides you with the given load data, and you manually record the lengths between the marks on the specimen at each point using an extensometer to obtain the table of data shown below. L (in) 2.2804 2.4774 2.0012 3.51 2.0025 7.09 2.0350 7.87 2.0798 8.83 2.1313 9.84 P (kip) 11.77 12.37 Use these results to calculate the stress and strain at the yield point, the ultimate strength point, and the fracture point. 2.1937 10.80 2.5791 11.80 2.6657 10.81 2.7281 9.81 2.7497 9.42
Design Against Fluctuating Loads
Machine elements are subjected to varieties of loads, some components are subjected to static loads, while some machine components are subjected to fluctuating loads, whose load magnitude tends to fluctuate. The components of a machine, when rotating at a high speed, are subjected to a high degree of load, which fluctuates from a high value to a low value. For the machine elements under the action of static loads, static failure theories are applied to know the safe and hazardous working conditions and regions. However, most of the machine elements are subjected to variable or fluctuating stresses, due to the nature of load that fluctuates from high magnitude to low magnitude. Also, the nature of the loads is repetitive. For instance, shafts, bearings, cams and followers, and so on.
Design Against Fluctuating Load
Stress is defined as force per unit area. When there is localization of huge stresses in mechanical components, due to irregularities present in components and sudden changes in cross-section is known as stress concentration. For example, groves, keyways, screw threads, oil holes, splines etc. are irregularities.
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