Table of Contents

Materials and Structure




Materials Modification

Structural materials are seldom used in their pure elemental form. Since the Bronze Age mixtures of elements have been used to improve the performance of a material in a specific application. Bronze is an alloy of copper and tin with a very complex array of possible compositions. Both of the elements are relatively soft and have low melting points. The atoms of one element can substitute for those of the other when they are alloyed to form a bronze. The bronze is less ductile than either of the constituting elements and its properties can be controlled over some range by selecting the composition of the alloy.

The diagram shows the effect of carbon content on a carbon-iron alloy (a carbon steel). The stress-strain curve shows that the addition of carbon to the iron in amounts up to 1% by weight has little effect on the elastic constant (Young's modulus) of the alloys, however, it does have an important effect on the alloy's yield stress,
sy. The yield stress increases in value as the carbon content is increased and additional factors such as heat treatment can also alter its value. (1 ksi = 1000 psi = 6.9 MPa)

From: Hibbeler,
"Statics and Mechanics of Materials,"
Macmillan (1993)