Measuring and understanding the mechanical response is critical for material research, product development, and process control. The mechanical response of these materials is dependent on the application scenarios as well as material chemistry. The main parameters that are considered to measure these mechanical properties are, load (P), loading rate (Ṗ) or strain rate (ἐ), time of loading (t).
Traditionally, mechanical properties were determined from a stress-strain curve generated by an applied load but nanoindentation has proved to be much more advanced providing multiple properties such as hardness, modulus from a single test in less than a second. Some common terms used in mechanicsl tests are stress, strain, yield stress. Stress (σ) is the instantaneous load applied to a specimen divided by its cross-sectional area before any deformation. Strain (ε) is the change in gauge length of a specimen divided by its original gauge length. Yield stress (σy) is the stress at the point where the material no longer responds elastically, referred to as the yield point.
From fundamental data, mechanical properties are determined:
- Elastic modulus
- Complex modulus for viscoelastic materials
- Fracture toughness
Schematic of a stress-strain curve with elastic and plastic regions before fracture