keresztmetszetcsökkenést

Keresztmetszetcsökkenés, often translated as cross-sectional reduction or necking, is a phenomenon observed in ductile materials during tensile testing. It refers to the localized decrease in the cross-sectional area of a specimen as it is subjected to increasing tensile stress. This reduction begins after the material has reached its ultimate tensile strength and before fracture occurs.

The process of necking is a visual indicator of plastic deformation. As the material elongates beyond its elastic limit, the deformation becomes non-uniform. A particular region of the specimen starts to thin down more rapidly than the rest. This localized thinning concentrates the stress in that area, further accelerating the deformation and reduction in cross-sectional area.

The extent of necking is a characteristic property of ductile materials. Materials that exhibit significant necking are considered to have good ductility. The presence and magnitude of the necking phenomenon are often analyzed in stress-strain curves derived from tensile tests. The point at which necking begins is typically associated with the ultimate tensile strength of the material, which is the maximum stress a material can withstand before it starts to neck. Following necking, the engineering stress (force divided by original cross-sectional area) decreases, even though the true stress (force divided by instantaneous cross-sectional area) continues to increase until fracture.