Design for Static and Dynamic Loading

Introduction

All the machines and their collective machinery are subjective of some patterns of load which are subdivided into static and dynamic loads. Static loading refers to the process of static load that does not change in any direction, this form of load does not change in magnitude or any direction and it gradually increases in value Whereas dynamic loading refers to the process of loading those changes in the direction or magnitude with respect to time, sometimes it changes in both the direction and magnitude, this type of loading is further subdivided into impact and dynamic load.

Design for static loading

Static loading refers to the process of loading that has a steady flow that does not change in any direction or magnitude, for example, the deadweight of the elements. It is essential to determine the load of the components as available, to determine and enhance their functionality. However, there are failure criteria associated with the loading of the machines which states that the machine would perform poorly in case the load is increased beyond the limit.

• Deformation is one determinant failure criterion as the resultant deformity in the machinery due to excess load will hinder the functionality.
• Due to excess static load, machinery starts yielding and results in deformity, thus yield strength is also a failure criterion.
• Bearing pressure includes bearings, clutches, and gear also experience static load and results in effectivity in the performance of a machine thus these are also failure criteria.

Allowable stress and relative factors

The safety factors are associated with the relative strength of the objects that are reserved in case of any condition that imparts excess load onto the machine. The safety factor is dependent upon the types of loads, selection of materials (ductile or brittle), and the overall quality of the product. Depending upon the criteria of failure, the strength of the factors is analyzed and designed for static loading, and allowable stress is obtained.

Allowable stress, []= Sy  /fos (ductile products); Sut /fos (brittle products)

Where, Sy = yield strength, Sut = tensile strength, fos = factors of safety.

Design for dynamic loading

Dynamic loading is the kind of load that changes in magnitude and direction. Dynamic loading is further subdivided into two categories. 

• Impact load is the kind of load that is imparted with a certain amount of velocity, this load is imparted over a certain period.
• Sudden load refers to the loading that occurs in an instant upon the machines.

In the context of dynamic loading, the machinery subjected to a load over time attains fatigue failure before reaching its limit of yield or tensile strength. It is due to the gradual rate of load included upon the material within a specific magnitude or direction, as it cracks over time under load and then it breaks down. Thus, the endurance factor plays a key role in determining the factors associated with the fatigue point of a machine and thus these factors can help design a modification plan associated with these factors. Depending upon these criteria, the allowable stress is calculated considering factors of safety which will further be used to decide the parameters of the materials used in the machine.

In this case, the endurance limit of a machine is obtained by

Se = [(Ksurf* Ksize*Kload *Krel *Ktemp) / Kf] * S1e

Where Se = Endurance limit of the product, Ksurf = Surface finish factor, Ksize = factor of size, Kload = factor of load, Krel = Factor concerning reliability, Ktemp = factor of temperature, Kf= Factor of fatigue stress concentration

Conclusion

Machines and their parts are subjected to constant functioning with proper output. Thus, it is necessary to determine the factors associated with its strength and durability thus measures are undertaken to determine the limit of fatigue failure of a machine thus static and dynamic loads are conducted upon that determines the yield strength and tensile strength of a machine and in terms of dynamic loading impact and sudden load is conducted to evaluate the fatigue point of a machine.