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Engineering stress-strain curve describes the relationship between engineering stress and engineering strain for a material when subjected to tensile or compressive forces. Engineering stress is defined as the applied load divided by the original cross-sectional area of the material. Engineering strain is the change in length divided by the original length. This curve is a fundamental tool in materials science and engineering for characterizing the mechanical behavior of materials.

The initial portion of the curve typically exhibits a linear elastic region. In this region, stress is directly proportional to strain, and the material will return to its original shape when the load is removed. The slope of this linear section is known as Young's modulus or the modulus of elasticity, which quantifies the material's stiffness.

Beyond the elastic limit, the material enters the plastic deformation region. Here, the strain is no longer proportional to the stress, and permanent deformation occurs. The curve may show a yield point, where plastic deformation begins, or a gradual yielding. Ductile materials exhibit a significant amount of plastic deformation before fracturing, characterized by a peak stress (ultimate tensile strength) followed by a decrease in stress as the material necks down. Brittle materials, on the other hand, fracture with little or no plastic deformation. The area under the stress-strain curve represents the energy absorbed by the material before fracture.