Fatigue (material)#Miner.27s rule

The linear damage accumulation is used to assess the influence of a load spectrum on the life of a component and goes to the engineers Arvid Palmgren (1924 ), B. F. Langer ( 1937) and Milton Miner ( 1945) back.

Description

Normally, a component is not only subject to a cyclic loading with constant amplitude, that is, a rectangular load cycle as used for example in the SN test, but the load is variable in height. To calculate the lifetime of the collective amplitude is divided into individual rectangular collectives with a constant amplitude and a part number of cycles ( A stepped ). According to the method of linear damage accumulation is a partial damage is now calculated by the part number of cycles is divided by the maximum tolerable number of cycles at a SN curve for each part of the collective. The partial damage of all sub-collectives are summed up and give the total damage D of the component.

Exceeds the injury to the value 1, is expected to break or crack initiation in the component under the considered load spectrum.

Figuratively speaking, it is according to the linear damage accumulation not matter what load level, a certain fraction of the maximum tolerable number of cycles spent. The damage to a part of the collective can be converted into a different part of the collective through

If you imagine a two-stage load, it does not matter in which order the loads according to the linear damage accumulation. Thus, sequence effects can not be explained.

Modifications of Miner's rule

There are numerous modifications of Miner's rule assess the damage from vibrations below the so-called fatigue strength. This is always the course of the SN curve, which are compared with the sub-collectives, modified.

The original Miner's rule is known as the original Miner and does not consider part of their collective load amplitudes below the fatigue limit. A laying out components with this rule may lead to an under-dimensioning, as well as load cycles can cause damage below the so-called fatigue strength.

As a conservative variant applies the elementary Miner rule according to Palmgren. This kinking of the SN curve is completely neglected, so that all sub-collectives have a harmful effect.

Another important modification is the Miner's rule modified Haibach. Here, a decrease in the fatigue strength is accounted for by a change in slope:

From J. Liu and H. Zenner ( Miner's rule modified after Liu - Zenner ), a rotation of the SN curve at the level of collective maximum value and then continuing with the slope:

Proposed. An additional factor is the slope of the crack growth life curve "m" added. Furthermore, the beginning of the fatigue strength range is characterized by: