Wohler diagram

Fig. 1.5 S -N curve, cyclic stress (T versus number of cycles to failure N, also known as Wohler diagram, showing the three regions that characterize fatigue behavior...

This time, the cycles required to produce final fracture have grown to 8,548, but also the allowable cycle Nf obtained from the Wohler diagram of Fig. 10.44 increased to 770,000. Therefore the ratio Nf / Ni t becomes... 

For the characterization of the fatigue properties of polymers and polymer composites, Wohler experiments to establish S-N diagrams are usually employed (Fig. 3). 

There are three closely related reactions by which narcotine may be cleaved into two fragments which still contain all of the carbon atoms. Wohler (4) observed that when narcotine is heated in dilute sulfuric acid it yields two substances, a base, cotarnine, and an acid, opianic acid. Hydrolysis with water at 150° or with boiling dilute acids results in hydro-cotarnine and opianic acid, whereas heating with zinc and hydrochloric or sulfuric acid generates hydrocotarnine and meconin. These reactions are restated in the following diagram. 

The cylinder is subjected to a repetitive stress by the hydraulic pressure. Approx. 40 strokes are performed per hour so that after an assumed life of the press of 30 years, and two 8-hour shifts per working day, and 300 working days per year, the number of load alternations = 30 X 300 X 2 X 8 X 40 = 5,760,000 is attained. Therefore, the fatigue limit has to be calculated as per Wohler s diagram. 

Fig. 5.31 Wohler s curves or 5-A diagram obtained on a 2024-T351 aluminum alloy for various R ratios (data from [33])...

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