Mechanical Properties Terms

Impact toughness index Impact toughness reflects the resistance of metal to external impact loads. It is generally expressed by the impact toughness value (ak) and impact work (Ak), and its units are J/cm2 and J (joule) respectively. Impact toughness or impact work test (referred to as "impact test"), it is divided into three types: room temperature, low temperature and high temperature impact tests due to different test temperatures; if the shape of the sample notch can be divided into "V" shape notch and "U" shape notch impact tests. Impact test: An experiment breaking from the notch when a sample of a certain size and shape (10×10×55mm) (with a "U"-shaped or "V"-shaped notch in the middle of the length direction, with a notch depth of 2mm) on the specified test machine under the impact load. A. Impact absorption work Akv(u)--The work absorbed by the metal pattern with a certain size and shape when it breaks under the impact load. Units are Joule (J) or Kgf. m. B. Impact toughness value akv(u)--the quotient obtained by dividing the impact absorption work by the bottom cross-sectional area at the sample notch. The unit is joules/cm2 (J/cm2) or kilogram force .m/cm2 (Kgf .m/cm2). The calculation formula is: where: Akv(u)--the work absorbed when the sample is broken, Kgf . m(J); S--the area of ​​the bottom cross-section at the sample notch, cm2. The temperature of the normal temperature shock test is 20±5C; the temperature range of the low temperature shock test is <15~-192C; the temperature range of the high temperature shock test is 35~1000C. The cooling medium used in the low-temperature impact test is generally a liquid or gas that is non-toxic, safe, non-corrosive, and does not solidify at the test temperature. Such as anhydrous ethanol (alcohol), solid carbon dioxide (dry ice) or liquid nitrogen atomized gas (liquid nitrogen), etc.

Tensile strength (σb) The force (Fb) that the sample is subjected to during the tensile process is divided by the stress (σ) obtained by dividing it by the original cross-sectional area (So) of the sample, which is called the tensile strength (σb), and is in N/mm2 (MPa). It represents the ability of metal materials to resist damage under tension.

The calculation formula is: where: Fb--the force that the sample is subjected to when it is pulled, N (Newton); So--the original cross-sectional area of ​​the sample, mm2.

The yield point (σs) is a metal material with yield phenomenon. The stress when the sample can continue to elongate without increasing force (keep constant) during the tensile process is called the yield point. If the force decreases, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa). Upper yield point (σsu): stress before the first drop of the force in the sample yields; lower yield point (σsl): small stress in the yield stage when the initial instantaneous effect is ignored.

The formula for calculating the yield point is: where: Fs--yield force (constant), N (Newton); So--the original cross-sectional area of ​​the sample, mm2.

Elongation after break (σ) In tensile test, the percentage of the increase in the length of the gauge distance after the sample is broken and the original gauge distance is called elongation. In σ, the unit is %. The calculation formula is: where: L1--the gauge length after the sample is broken, mm; L0--the original gauge length of the sample is black, mm.

Section shrinkage (ψ) In tensile test, the percentage of the reduction in the cross-sectional area at the shrinkage diameter after the sample is broken and the original cross-sectional area is called the cross-sectional shrinkage. In ψ, the unit is %. The calculation formula is as follows: where: S0--the original cross-sectional area of ​​the sample, mm2; S1--the small cross-sectional area of ​​the sample after being pulled out and shrinked.