Measurement of residual stresses in cast aluminium engine blocks

Aluminium engine blocks require the use of grey iron liners to resist wear from sealings mounted in pistons. Liners can be inserted into the piece after machining or can be cast-into the block. The latter method allows for higher productivity, but has the disadvantage to promote the development of residual stresses in critical areas such as the cylinder bridges. These stresses arise from the differences in the thermal expansion coefficient of iron and aluminium and, if high enough, may promote the failure of the block. This work describes the procedure followed to measure the residual stresses that develop in the cylinder bridges in type A319 aluminium–silicon–copper engine blocks with cast-in grey iron liners. The measurements were obtained by extensometric means. It was found that the stresses can be higher than 150 MPa in tension, depending on the geometry and size of the piece. It is concluded that these types of analyses provide for an early advice when changes take place in design, processing or material.