Black & Decker Canada Ltd. is considering alternate materials for the mower blades supplied with their electric lawnmowers. However, for safety and liability reasons, before Black & Decker uses any new material for their lawnmower blades it must be proven that the new blades can withstand typical lawnmower operating loads without failure. Black & Decker requires a test that can be used to qualify, or disqualify, alternate materials for lawnmower blade usage.

A standard Black & Decker 19" Convertible Mulching / Rear Bagging Electric Lawnmower was instrumented with strain gauges on the lawnmower blade. A finite element model of the lawnmower blade was used to determine optimal strain gauge locations on the lawnmower blade. Lawnmower blade strain and rotational speed were simultaneously recorded for a variety of grass cutting conditions and for the same blade rotating without grass interaction. The results of these trials were then compared so that the effect of grass cutting could be discerned from the effects of rotation alone.

The results of this research reveal that the primary effect of grass cutting on the lawnmower blade is a reduction in the rotational speed of the blade. This, in turn, causes a reduction in centrifugal load on the blade. Since the effects of centrifugal load are difficult to simulate outside the rotating environment, a rotating test using varying rotational speeds to simulate grass loads is recommended.