Among the many mechanical properties of plastics materials, tensile properties are probably the most frequently considered, evaluated and use throughout the industry. These properties are important indicators of the strength of a material. Tensile testing provides much useful information - tensile yield strength, tensile strength at break (ultimate tensile strength), tensile modulus (Young's modulus), and elongation at both yield and break. Table 1 below shows a typical tensile curve for a ductile thermoplastic.
Tensile Yield Strength
This is the maximum engineering stress in MPa, at which permanent, non-elastic deformation begins.
The Yield Point
This is the point (load) at which the specimen yields or fails, by separating into two or more pieces, with no increase in load - or where the specimen's cross-sectional area begins to decrease significantly.
Ultimate Tensile Strength
This is the maximum stress (forced divided by cross-sectional area) a material can absorb before yielding or failing, whichever occurs at the higher stress level.
Elongation At Yield
This is the strain which the material undergoes at the yield point, or the percent change in length which occurs while the material is stressed to its yield point.
Elongation at break is the strain at failure, or the percent change in length at failure.
The Tensile Modulus Or Young's Modulus
This ia the ratio of stress to strain within the elastic region of the stress-strain curve (prior to the yield point). A material's stress-strain curve also indicates the overall toughness of the material. The area under the curve, in units of MPa, is a measure of material's toughness. The greater that area is, the tougher the material is, and the greater the amount of energy that will be required to break it.
Additives to thermoplastics, such as those for ignition resistance or mould release, decrease the ultimate tensile strength, elongation at break and tensile modulus values.
Temperature also affects tensile properties - as environmental temperature increases, tensile values decrease.