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What is the difference between toughness and rigidity of injection molded parts?

Injection molded parts usually mention their toughness and rigidity, what is the difference?

Toughness refers to the ability of a material to absorb plastic deformation work and fracture work before fracture, characterizing its ability to resist crack propagation. It can usually be measured by the area under the engineering stress-strain curve. The larger the area, the higher the toughness, and the stronger the fracture resistance. Only when the horizontal and vertical coordinates of the stress-strain curve (i.e. strength and strain) are relatively large, can toughness be high. If the strength is too low, even if the ductility is large, Resilience will not be too high. So toughness is a comprehensive indicator of strength and plasticity.

That is to say, toughness refers to the amount of energy absorbed by a material before failure, as well as its plastic deformation ability, which is opposite to brittleness. Therefore, those with large deformation and fracture work on the tensile curve have good toughness. Impact strength is usually used for evaluation, as it is generally expressed in terms of fracture energy.

Plasticity is a material property in which a material undergoes permanent deformation under a given load. For most engineering materials, the stress-strain relationship is linear when the stress is below the proportional limit. In addition, most materials exhibit elastic behavior when their stress is below the yield point, meaning that their strain also completely disappears when the load is removed. Plasticity is usually measured by elongation and reduction of area.

Tensile strength: It may seem to be related to bond energy, but for polymers, tensile damage is mostly not related to bond damage, but rather to changes in slip and aggregation states between molecular chains, so it is mainly related to intermolecular forces and crystallinity.

Rigidity is usually measured by bending strength. Polymers are usually evaluated in terms of strength, hardness, softness, and brittleness.

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