The Machine Under Operational Stress

A part, a component, or even the entire installation will only fail in such instances where it has been subjected to a stress of intolerable magnitude. 

Future stress conditions should therefore be known as accurately as possible during the planning phase and should be taken into consideration accordingly. 

While the installation is operational, parts or components, constantly or alternately, are usually either under excessive or insufficient stress. Therefore, after starting the machine, the determination and evaluation of operational stress for the purpose of matching planning and operational data is of the utmost importance. Under operational conditions it is vital that the stress factor be limited in such a way that the design configuration matches the application configuration. 

For a systematic survey it is expedient to limit the determination of the possible types of stress in a machine to only a few categories. The above-described method deals with stresses of a primary nature which are directly connected to the operation of the installation and can thus be anticipated with relative ease. These include operational pressures and vibrations. 

Other types of stresses are the result of specific operational conditions which cannot be fully taken into consideration during the planning stage. These include the influence of media of different types as well as environmental influence factors. 

---

The shear stress in the equation represents the level of stress required to perform the machining operation. Therefore, this stress is equal to the shear strength of the work material under the conditions at which cutting occurs (Groover 2010). 

Actually, machine parts or components, for reasons of simplification, are often designed for static operation only, although a fluctuating stress pattern may be expected. Therefore, instead of a static stress, pressures whose amplitudes and frequencies are subject to fluctuations will occur. These may be displayed with the help of stress-time functions. Given the above-described conditions, components subjected to dynamic stresses will fail earlier than those under static stresses. The following is meant to show how examinations of components in such cases may be conducted with maximum expediency. 

Gertman, D. I., Haney, L. N., Jeirkins, J. P., Blackman, H. S. (1985). Operator Decision Making Under Stress. In G. Johannsen, G. Mancini, L. Martensson (Eds.). Analysis Design and Evaluation of Man-Machine Systems (Proceedings of the 2nd IFAC/IFIP/IFORS Conference, Varese, Italy). 

The lubrication of leadscrews is similar in essence to that of slideways, but in some instances may be more critical. This is especially so when pre-load is applied to eliminate play and improve machining accuracy, since it tends to squeeze out the lubricant. Leadscrews and slideways often utilize the same lubricants. If the screw is to operate under high unit stresses - due to pre-load or actual working loads - extreme-pressure oil should be used. 

Cobalt is a component of the so-called superalloys used to make critical parts of jet engines, gas-turbines, and of other machines operating under stress at high temperatures. It is also a component of the so-called stellites. These alloys are composed of 50-60% cobalt, 30-40% chromium and 8-20% tungsten, and are valued for their extreme hardness, strength, and heat resistance. In addition, cobalt is a component of magnetic steels and aluminum alloys with superior ferromagnetic properties. In 1975,... 

---