Poisson’s Ratio = coeficiente de Poisson (v). For elastic deformation, it is the negative ratio between lateral and axial strains resulting from the application of axial stress. This coefficient relates to Young’s modulus to the shear modulus. The term razão de Poisson is an incorrect literal translation. Unit: dimensionless (coefficient);

Yield Strength ou Yield point = limite de escoamento (σe). Stress requires a very small but defined amount of plastic deformation. Due to the difficulty in precisely determining this point in the stress-strain diagram during instrumented testing, the proportional limit is often adopted without compromising the concept, this is the point at which the linear proportionality between stress and strain ends. It defines the elastic region of the material. Beyond this point, the material undergoes plastic or permanent deformation (Figure 2A). Unit: pressure (Pa).

Ultimate Strength = limite de resistência (σr). Maximum stress level that a material can withstand under uniform plastic deformation (Figure 2A). In ductile metallic materials under tensile testing, this limit separates uniform plastic deformation from localized plastic deformation (necking), which leads to material failure that may be catastrophic. It is important to note that in compression there is no ultimate strength limit, as necking does not occur, and therefore the fracture mode differs from that observed in tension. Unit: pressure (Pa).

Stress riser = concentrador de tensão. Geometric features such as sharp corners, defects (voids, fissures, or cracks), or any structural discontinuity-internal or superficial-where externally applied stress becomes concentrated (Figure 1A). This phenomenon may be associated with the weakest link theory, in which a material will fail at its weakest point, i.e., at the largest stress concentrator present. The term stress concentration is equivalent. The radius and size of the concentrator are critical factors. In the case of a crack, the radius is much smaller than that of a sharp corner, thus requiring less stress to propagate and cause failure. The concentration factor is measurable by a material property known as fracture toughness (KIC), which corresponds to the energy a material can absorb before fracturing in the presence of a stress concentrator. Unit: Pa.m1/2.

Stiffness = rigidez. Resistance of a material to deformation. It is represented in the load-displacement diagram by the slope of the curve in its linear (elastic) region and is determined by the strength of the chemical bonds between atoms in the material (Figure 2B). The term “rigidity” is also synonymous. Unit: N/mm.

Displacement = deslocamento. Movement of a body in the direction of the applied force. In mechanical testing, it may refer to the displacement of the actuator or crosshead of the testing machine and is used as a simple and indirect way to infer the deformation of the tested specimen (Figure 2B). Unit: length (mm).

Resilience = resiliência (Ur). Total energy or work absorbed by a specimen in the elastic regime during a tensile test. Unit: energy per volume (J·m⁻³);

Toughness = tenacidade (Ut). Total energy or work absorbed by a specimen during a tensile test. The term toughness is used in a wide range of contexts. Unit: energy per volume (J·m⁻³).