Template:Weibull Distribution Definition

The Weibull distribution is a general purpose reliability distribution used to model material strength, times-to-failure of electronic and mechanical components, equipment or systems. In its most general case, the 3-parameter Weibull [math]\displaystyle{ pdf }[/math] is defined by:

[math]\displaystyle{ f(t)=\frac{\beta}{\eta } \left( \frac{t-\gamma }{\eta } \right)^{\beta -1}{e}^{-(\tfrac{t-\gamma }{\eta }) ^{\beta}} }[/math]

where β = shape parameter, η = scale parameter and γ = location parameter.

If the location parameter, γ , is assumed to be zero, then the distribution becomes the 2-parameter Weibull or:

[math]\displaystyle{ f(t)=\frac{\beta}{\eta }( \frac{t }{\eta } )^{\beta -1}{e}^{-(\tfrac{t }{\eta }) ^{\beta}} }[/math]

One additional form is the 1-parameter Weibull distribution, which assumes that the location parameter, γ, is zero, and the shape parameter is a known constant, or β = constant = C, so:

[math]\displaystyle{ f(t)=\frac{C}{\eta}(\frac{t}{\eta})^{C-1}e^{-(\frac{t}{\eta})^C} }[/math]

For a detailed discussion of this distribution, see The Weibull Distribution.