Project Introduction

Yield strength: It is the yield limit when the metal material yields, that is, the stress that resists the slight plastic deformation. For metallic materials without obvious yield, the stress that produces 0.2% residual deformation is defined as its yield limit, which is called the conditional yield limit or yield strength. An external force greater than this limit will permanently deform the part and cannot be recovered.

experiment method

There are generally two methods for measuring the upper and lower yield strengths: the graphic method and the pointer method.

· Graphic method

During the test, an automatic recording device was used to draw the force-chuck displacement diagram. It is required that the ratio of the force axis is less than 10N/mm2 per mm, and the curve must be drawn at least to the end of the yield stage. Determine the constant force Fe on the yield platform, the maximum force Feh before the force first falls in the yield stage, or the minimum force FeL that is less than the initial transient effect on the curve.

The yield strength, upper yield strength and lower yield strength can be calculated according to the following formula:

Yield strength calculation formula: Re=Fe/So; Fe is the constant force at yield.

The formula for calculating the upper yield strength: Reh=Feh/So; Feh is the maximum force before the force drops for the first time in the yield stage.

The calculation formula of the lower yield strength: ReL=FeL/So; FeL is the minimum force FeL less than the initial transient effect.

· Pointer method

During the test, the constant force when the pointer of the force measuring disc stops rotating for the first time or the maximum force before the pointer turns for the first time or the minimum force less than the initial instantaneous effect corresponds to the yield strength, upper yield strength, and lower yield strength, respectively.

Guideline

Yield strength testing and sample preparation requirements

Normal temperature and high temperature stretching: 1. Wire and round bar samples: d≥10mm, length L≥200mm 3mm≤d≤10mm, length L≥200mm d≤3mm, length L≥1000mm (minimum wire 300mm, minimum bar 80mm ) 2. Rectangular sample: ≥16*200mm (L min 120mm) 3. Tubular sample: OD ≤ 30mm, L ≥ 300mm (min 150) OD> 30mm, general requirement L ≥ 300mm and OD ≤ 55mm, can be used for whole tube Stretching 4. The shrinkage rate of the cross section requires the length of the detection interval d ≥ 5mm.