Engineering stress ([latex]sigma[/latex]) is the applied load divided by the original cross-sectional area ([latex]A_0[/latex]), while engineering strain ([latex]epsilon[/latex]) is the change in length ([latex]Delta L[/latex]) divided by the original length ([latex]L_0[/latex]). These definitions, [latex]sigma = frac{F}{A_0}[/latex] and [latex]epsilon = frac{Delta L}{L_0}[/latex], are fundamental for plotting stress-strain curves but assume the specimen’s dimensions remain constant during the test.
