Abstract
Mechanical properties of metals are remarkably affected by the grain size. Petch found the quantitative relationship between the yield stress, σ, and the grain size, d, to be in the following formula σ=σ0+k·d−1⁄2. As this equation is significant theoretically and practically, it has been studied by many workers. In an attempt to examine Petch’s equation from an entirely different angle, the authors investigated how the dimensions of specimens would affect the relationship between mechanical properties and grain size. The variations of flow stress against grain size are divided in to three parts, i.e., the part obeying Petch’s equation, that affected with the specimen dimensions and that to be dealt with as a single crystal. In the part affected with the test-piece dimensions, it is found that the flow stress, (σ) is related to the grain size, (d) and constant values (A,B) determined by the thickness and width of specimens as follows: σ=σ_0+A(log1/d-logB).
