Use of plastic models to evaluate thermal strains in diesel-engine pistons

Abstract

The paper presents a low-temperature plastic-model technique for the simulation of thermal strains in diesel-engine pistons. Various difficulties in obtaining accurate thermal-strain measurements from resistance strain gauges attached to plastics are discussed. These difficulties include: the formation of a hot spot under the gauge, caused either by the low-conductivity gauge or by the electrical power dissipated by the grid; the apparent strain characteristics of gauges mounted on plastics; reinforcement of the model by the gauge; irreversible expansion of the plastic causing zero drift. An application of the technique is given, and the service failure of a 19-in diameter piston crown is explained.