How To Calculate Fatigue Life

In the actual world, it is not uncommon for loads to be applied from a variety of angles all at once, resulting in strains that can be felt in any direction. The primary trend’s direction shifts with every cycle. These strains are multiaxial and, more significantly, complicated multiaxial.

How To Calculate Fatigue Life

Acquiring information on a material’s fatigue life is useful when developing a new engineering component out of the material. As a general rule, this can be done by deriving an equation that can be used to predict fatigue life from data on fracture toughness and fatigue crack growth.

To calculate fatigue life, one type of equation can be derived by integrating the fatigue crack growth rate equation between the initial crack (flaw) size ao and the critical crack (imperfection) size, which is generated at fatigue failure after a specific number of cycles to loss Nf.

The Fatigue Crack Growth Rate can be calculated using the formula given below.

The Rate of Fatigue-Induced Crack Growth: where m = constants that vary with the type of material, the setting, the frequency of application, the temperature, and the stress ratio, and where K = the range of the stress intensity factor (K = Kmax Kmin), we get an equation for the rate of growth of a fatigue crack in millimeters or inches per cycle: da/dN. MPam.

The KI (pronounced “Kay-one”) stress intensity factor was used in this case.

Thus, the fracture toughness measure ignores the critical stress intensity factor KIC (pronounced “kay-one-see”). That shouldn’t be open to interpretation. This is the point at which understanding begins.

Mode, The degree of stress, in 1 case, has been determined.

KI = Y σ √(πa)

What we’re talking about here is the KI, or stress-intensity factor.

Where = applied nominal stress b = length of edge crack or half of internal through crack a = size of the crack

In geometry, Y is a unitless constant.

Factors of stress intensity can be calculated as

ΔK = Yσ√πa = Y σ π1/2 a1/2

Consequently, it makes sense to assume that.

This is then used in conjunction with the Fatigue Crack Growth Rate calculation to provide

By rearranging the equation above, we integrate the crack size from its initial value of ao to its final value of af upon fatigue failure and the number of fatigue cycles, from zero to the number at fatigue failure Nf. Thus,

When calculating your Fatigue Life Span, what factors should you consider?

The following is the standard integration formula.

An alternative variant of the formula for standard integration is presented here.

Rewriting the preceding equation in terms of the two given formulas is doable.

What factors into your Fatigue Life determination?

The fatigue life, expressed in cycles Nf, can be calculated using the relation mentioned earlier by solving for f.

That’s the prescription for a life of Fatigue. We can use this equation only if m 2 and Y are independent of fracture length.

Thus, it is possible that fatigue, as mentioned earlier, is life expressed in cycles. Nf understates the actual value for the fatigue life of the component.

Similarly to the more general example, when Y = f, the values of K and N must be established for a succession of gradually smaller lengths to account for the fluctuation in Y when calculating Nf (a).

Let’s work out how to deal with the hypothetical scenario where a steel plate is subjected to a never-ending tensile and compressive test in a fatigue testing machine, and we’ll learn how to calculate the fatigue life of the container.


There will be a rising demand for technical professionals in this interdisciplinary subject who can assist with the incorporation of practical experience and newly developed approaches.

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