. "Energy per Area"@en . "Energy per unit area is a measure of the energy either impinging upon or generated from a given unit of area. This can be a measure of the \"toughness\" of a material, being the amount of energy that needs to be applied per unit area of a crack to cause it to fracture. This is a constant for a given material.." . . . . . . . . . . . . . . "http://www.calculator.org/property.aspx?name=energy%20per%20unit%20area"^^ . . . .