Description

Example of a Michaelis’ double-lever machine for testing the tensile strength of concrete or mortar briquette samples (c.1895).

A description of this and some other testing machines can be found at http://chestofbooks.com/architecture/Building-Construction-3-3/Pozzuolana-Mortars-Continued.html#.VXG_AU3bLIU.

This is an example of a Michaelis’ double-lever machine for testing the tensile strength concrete or mortar briquette samples. On a large pillar, about 300 mm in height, are fastened two levers connected to one another. The upper lever has a leverage of 10 to 1 and the lower lever of 5 to 1. In combination, both levers provide a total leverage of 50 to 1. The briquettes are cast in moulds to have a neck of area exactly 1 sq in (645 sq mm).

The upper clip of the clamp for the sample to be tested is fastened to the lower arm; the lower clip is attached to the base of the pillar with a hand wheel for lowering or raising. There is also a counter balance for bringing the levers into exact equilibrium. The weight is applied by means of a stream of shot flowing from a shot tower into a shot bucket attached to the upper lever. The moment the specimen breaks, the bucket drops striking a lever below which closes a trap and shuts off the stream of shot instantly. The shot in the bucket is then weighed and the breaking strain per sq in is thus exactly fifty times the weight of the shot.

See also 1973/040.