Engineering strain is defined as the change in length divided by what?

• A. Change in length over current length
• B. Change in length over original length
• C. Force divided by original cross-sectional area
• D. Change in area over original area

Answer: (B)

Engineering strain measures how much a specimen length changes relative to its starting length. It is defined as the change in length divided by the original length: epsilon = (L − L0) / L0. This reference length in the denominator makes the quantity dimensionless and it’s usually expressed as a fraction or percent. For small deformations, this linear measure works well; for larger deformations, true strain uses the natural logarithm of L over L0, which can differ from engineering strain. The other forms involve either using the current length in the denominator, or refer to stress (force over area) or to area change, none of which describe the longitudinal elongation relative to the original length.