The correct answer is: B. Strength and toughness.
A composite sleeper is a type of railway sleeper made from a composite material, such as glass fiber reinforced polymer (GFRP). Composite sleepers are designed to be stronger and more durable than traditional wooden or concrete sleepers.
The composite sleeper index is a measure of the strength and toughness of a composite sleeper. It is calculated by dividing the sleeper’s ultimate tensile strength by its strain at failure. The higher the composite sleeper index, the stronger and more tough the sleeper is.
The other options are incorrect because they do not accurately reflect the purpose of the composite sleeper index. Hardness is a measure of a material’s resistance to indentation, while wear resistance is a measure of a material’s resistance to abrasion. Neither of these properties are directly related to the strength or toughness of a material.