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The way of reshaping the crack growth rate formulae in the form enablingtheir use in fatigue design at non-stationary loading is demonstrated. This new derivedformula suggests an additional damage increase when crossing from one stress block toanother. Herein, the reshaped crack growth rate formula is applied for the fatigue design ofaircraft components made of titanium alloy Ti-6Al-4V and subjected to combinedHCF/LCF loading. For the stress history simplified in the way that it consists of one LCFstress block at load ratio r = 0, followed by one HCF stress at load ratio r > 0, the closedform expression is derived for estimating the crack propagation life at combined HCF/LCFloading. Smith and Haigh diagrams as design tools for estimating the fatigue strengths fordesigned fatigue life, known load ratio and various number of HCF cycles per onecombined stress block, are obtained and presented for the parts made of titanium alloy Ti-6Al-4V and subjected to combined HCF/LCF loading.