Mechanical testing of stainless steel

plates are used to generate data that can be used for design purposes or as part

of the material connection procedure or operator acceptance procedure. The most

important function may be to provide design data, because it is important to

understand the limit value of stainless steel sheet product structure and

ensure that it will not fail.

One other effect of this mechanical test is

the tensile test, which can be used to determine the yield strength of the

steel used for design calculations, or to ensure that the stainless steel plate

meets the strength requirements of the material specifications.

Mechanical tests can be divided into

quantitative or qualitative tests. A quantitative test is a qualitative test

that provides data for design purposes, and the results are used for

qualitative tests such as hardness testing or bend testing.

Tensile testing is used to provide

information used in design calculations, or to prove that materials conform to

the requirements of corresponding specifications, so it may be quantitative or

qualitative testing.

The test is to grasp the end of the

standard sample properly prepared on the tensile testing machine, and then

increase the uniaxial load until failure occurs. Standardized test pieces so

that the results are reproducible and comparable.

The specimen is usually proportionate. When

the gauge length is L 0, it is related to the original cross-sectional area, A

0, as L 0 =k A 0. In the EN standard, the constant k is 5.65, and the ASME

standard is 5. The length of these measurements is about 5 times the diameter

of the sample and 4 times the diameter of the specimen, although this

difference may not be important technically, but it is very important to

declare it in accordance with the specification.

Load (stress) and specimen elongation

(strain) are measured, and engineering stress / strain curves are constructed

from the data. The following aspects can be determined from the curve.

A) the tensile strength, also known as the

ultimate tensile strength, is divided by the original cross section by the load

at the ultimate tensile strength (UTS) and the maximum = P maximum / A 0 when

the fracture is broken. The maximum P = maximum load, A 0 = the original cross

section area. In the EN specification, the parameter is also identified as

“R m”.

B) the yield point (YP), that is, the

stress from the elastic to the plastic deformation, that is, the yield point

below the unloading specimen means that it is restored to the original length,

the permanent plastic deformation at the yield point above the yield point, YP

or sigma y = P YP / A 0, P YP = the yield point load. In the EN specification,

the parameter is also identified as “R e”.

C) in reassembling the broken sample, we

can also measure the elongation, and the El% test piece has been El (%) = (L F

L – 0 / L) = (%) = (L F L = 100), L F = break distance and L 0 = original

distance length. In the EN specification, the parameter is also identified as

“A”.

D) A%= (A 0 -A f / A 0) x 100 and A f =

part of the cross section area, in which the percentage of R is reduced, and

the fracture of the sample in the degree of necking or decrease in diameter. In

the EN specification, the parameter is also identified as “Z”.

A) calculation of elongation, b)

calculation of area reduction rate

(a) and (b) measure the strength of

materials, (c) and (d) indicate the ductility or capacity of materials without

deformation. The slope of the elastic part of a curve is basically a straight

line, which will give young’s modulus of elasticity, which is to measure the

degree of elastic deformation of the structure when it is loaded. Low modulus

means that the structure will be flexible, and the high modulus structure will

be stiff and inflexible.

In order to produce the most accurate

stress / strain curve, additional extensometer should be added to the stainless

steel plate to measure the elongation of the gauge length. The less accurate

way is to measure the movement of the crosshead of the drawing machine.

The above stress-strain curves show

material with good yield point, but only annealed carbon steel shows this

behavior. There must be other ways to determine the “yield point” by

alloying, heat treatment or cold hardening of metal without obvious yielding.

This is measured by measuring yield stress

(yield strength in American terms), that is, a certain amount of stress

required for plastic deformation in the specimen.

The stress is measured by drawing a

straight line parallel to the elastic part of the stress / strain curve at a

specific strain, and the strain is the percentage of the original length of the

standard distance, so 0.2% verification, 1% verification.

For example, in the specimen with a gauge

length of 100mm, the yield strength of 0.2mm is measured by using the permanent

deformation of the 0.2mm. Therefore, it is proved that strength is not a fixed

material property, such as yield point, but depends on the number of plastic

deformation specified. Therefore, when considering the strength of proof, the

percentage must always be quoted. Most steel specifications use 0.2% of the EN

specification, R P0.2.

Some materials such as annealed copper,

gray iron and plastic have no linear elastic part in stress / strain curves. In

this case, similar to the method of determining the strength of the

verification, the usual practice is to define the “yield strength” as

the stress that produces a specified number of permanent deformations.

Source: China Stainless Steel Plates

Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)