MINER’S EQUATION AND FLUCTUATING LOAD STUDY
MINER’S EQUATION : INTRODUCTION TO CUMULATIVE DAMAGE IN FATIGUE
MINER’S EQUATION :Till now, we dealt with stresses that acted on the system in a single stress cycle. In practical analysis, especially in high stress applied tasks, the stress acts in PARTICULAR levels.
Here, a particular mechanical component gets subjected to different stress levels , AND each stress level acting at different parts of the work cycle.
So, MINER developed an EQUATION in order to solve this problem.
MINER’S EQUATION : FORMULA AND IT’S STUDY
Suppose we take a component ; subjected to various completely reversed stresses , each stress cycle acting for various no. of work cycles.
Now, suppose no. of cycles (n1,n2,n3,……) at respective stress levels (σ1,σ2,σ3,……) are unknown.
Now, suppose no. of cycles (n1,n2,n3,……) at respective stress levels (σ1,σ2,σ3,……) are unknown.
Application of Miner’s Rule:
Miner’s rule can analysis gear drives cumulative fatigue damage. It is important factor in operation of equipment with various loading. When various manufacturers’ options are available, especially when the specifications are unknown, it can be difficult to confirm that the device is suitable for the application. However, if the amount and duration of the load is known to the application, the cumulative fatigue analysis, such as the Miner’s rule, can be used to accurately determine the life of the gear drive. For example, wind turbine meets many conditions for measuring cumulative fatigue damage due to unpredictable continuous oscillations [2]. According to Miner’s rule, load and acceleration tests on the shaft of the wind turbine can be used to analyse the fatigue failure phenomenon through the load and acceleration test of the gear of the machine [3]. Other example is railway vehicles. Structural integrity of railway vehicles should last for a long period against various and continuous fatigue loadings, and the body structures of railway vehicle are manufactured by applying multiform welding types for each material. The damage caused by the fatigue load of the railway car body occurs mostly on the basis of the welded part, and various fatigue strength evaluations should be made. Those phenomena are able to analysis cumulative fatigue damage and it is possible to become one of examples [4].
Limitations:
Miner’s Rule does not take into account the sequencing or order in which in the cyclic loads are applied, however the order greatly affects fatigue life. In some specific situations, the high and low cycles of stress are possible to cause more damage than the damage tally predicted by Miner’s rule [5]. This hypothesis did not take into account the effect of delaying crack growth by inducing compressive residual stress at high stresses. However, the material could have less damage in high stress and low stress, when the residual stress is stayed in the material. Miner’s linear damage rule can be regarded as a relatively good evaluation method when the applied stress is mainly within elastic range of the material and the load range is wide, the stress above the fatigue limit is mostly.
To know more: