From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Investigation into inertia and temperature stresses on pedestal type pistons.
| Identifier | WestWitteringFiles\Q\2April1927-June1927\ 104 | |
| Date | 18th May 1927 | |
| Hs{Lord Ernest Hives - Chair}/Tsn1/LG18.5.27. INVESTIGATION OF STRESSES IN PEDESTAL TYPE PISTONS - E.75540. (A) Inertia stresses. At 3000 r.p.m. the inertia force will produce a pull in the bolts (E.75186) of 498 lbs., the weight of the piston and rings being 1.462 lbs. The area of seating under the head of the bolt is .0651 sq.ins. The bearing pressure is therefore 7,660 lbs/sq.in. or 3.42 tons/sq.in. The tensile stress in the thin parts of the bolt will be 15,850 lbs/sq.in. (B) Temperature stresses. To find the increase in the bolt tension when hot, under the following circumstances: Temperature 250°C - uniform throughout. Co-efficients of linear expansion: Magnesium .00002225 (assume same as alum:) Steel .0000072 per °C Length of magnesium surrounding bolt 1.625" Strain in bolt = increase in length of magnesium - increase in length of same length of bolt: = .0064" Strain per unit length of bolt = .00266" approximate stress = 79,800 lbs/sq.in. It will be seen from this that the total bearing (compressive) stress under the bolt head will be excessive as well as the stress in the bolt. The above calculation of the stress in the bolt assumes no deflection in the piston material. Actually this will occur locally, and cannot be calculated. It appears though that the area beneath the bolt head is very much too small. Hs{Lord Ernest Hives - Chair}/S.S.Tresilian. | ||