Fatigue strength coefficient

Here As/2 = total strain amplitude, Ase/2 = elastic strain amplitude = a/(IE), Asp/2 = plastic strain amplitude = As/2 - AsJ2 = Ae/2 - a/(2E), Si = fatigue ductility coefficient (related to fracture strain in a monotonic tensile test), and cTf = fatigue strength coefficient (related to fracture stress in a mono tonic tensile test). 

The fatigue strength coefficient is related to the tensile strength. In plain carbon and low-alloy steels, a rule of thumb states cr( = 1.5i m in aluminium and titanium alloys, = 1.67i m holds approximately [113]. The fatigue strength exponent a depends on the material and the specimen geometry in many materials, it takes values between 0.05 and 0.12 if smooth specimens are used [8,113]. 

Fig. 6.9 Fatigue strength coefficient o /vs. true traction strength <7 /of several metal alloys [12]...

If the independence of the ratio EjEp of is restored it introduces an effect of mean stress in the plastic domain that experience does not confirm. As to the Morrow correction (6.17), Walcher, Gary and Manson [20] observed that in alloys like Ti-6Al-4 V the fatigue strength coefficient a fCm be so high as to mask the mean stress effect. Therefore, they proposed a correction to the fatigue strength coefficient of the type... 

Strain hardening exponent of the material n is needed together with the fatigue strength coefficient a f and the fatigue ductility coefficient f. these last two coefficient have been already calculated in sample problem 1. of Sect. 5.3 and are... 

S-N curve in terms of stress amplitude. The Basquin line contain a parameter, the fatigue strength coefficient a f, that is the true stress at failure (see Sect. 5.2.2). Its value is normally measured with standard specimens of 10 mm diameter and 10 cm length. Therefore, its process volume, that we will assume as reference volume, is Vref — 7853 mm. Therefore... 

Table 4.19 Partial safety coefficient, y m,4, for fatigue strength.

Mechanical property n. Any property of a material that defines its response to a particular mode of stress or strain. Such properties include elastic moduli, strength, and ultimate strain in several modes, impact strength, abrasion resistance, creep, ductility, coefficient of friction, hardness, cychc fatigue strength, tear strength, and ma-chinability. Many ASTM tests in Section 08 are devoted to the mechanical properties of plastics. 

Alloy Yield Strength 0.2% Offset (ksi) Elongation in 50 mm (%) Modulus of Elasticity XIO (psi) Brinell Hard- ness Impact (ft-lb) Fatigue Strength XIO (psi) Electrical Conductivity (% lACS) Thermal Conduc- tivity (W/mK) Coefficient of Thermal Expansion (10- /°F)... 

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