Tensile test of all kinds of materials can be done with universal material testing machine. Its operation steps are the same. Taking low carbon steel as an example, the steps of tensile test are introduced in detail.
1. Measuring specimen size
Using vernier calipers, the diameter d0 of three sections at both ends and in the middle is measured within the distance L0 of the specimen. Each cross section is measured once vertically and six times in three places. The average diameter d0 of the smallest of the three points is used to calculate the cross-section area A0.
According to L0=10d0, two points are drawn by hammer and punching nail as the distance points within the distance length of the specimen.
2. Selective dial: Estimate the maximum load (Pmax=A0*b) according to the section size of the specimen, and select the appropriate measuring dial. Configuration of the corresponding ballast (pendulum) and adjustment of the corresponding oil return buffer calibration.
3. Zero pointer adjustment: turn on the power supply, press the (green) oil pump start button, close the return valve (feel good, do not screw too tight), open the intake valve (at the beginning there may be no hydraulic oil in the working cylinder, need to open a larger amount of oil, so that hydraulic oil quickly into the working cylinder, so that the moving platform accelerates the rise). When the movable platform rises about 5-10 mm, the oil inlet valve is closed (if the movable platform is in the right position, it is not necessary to open the oil inlet valve first, just close the oil inlet valve; if the movable platform rises too high, the specimen can not be clamped, the oil return valve should be opened, and the movable platform can be lowered to the right position and closed). Moving the balance hammer keeps the pendulum bar perpendicular (the standard of perpendicularity is that the right side of the pendulum bar is aligned with the line of the sign). Then gently rotate the screw to actively target the zero point on the calibration plate, and gently press the dial hook to pull the driven needle close to the active needle. Pay attention to making the driven needle close to the right side of the active needle. At the same time, the automatic plotter is adjusted, the paper and pen are packed and the drawing pen is laid.
4. Installation specimens:
Firstly, the specimen is installed in the upper chuck of the hydraulic universal testing machine, then the lower chuck lifting motor (or the lower chuck lifting handwheel) is activated to reach the appropriate position, and then the lower end of the specimen is clamped. The chuck should clamp the whole head of the specimen.
The specimen is slowly and evenly deformed by slow loading. When the pointer rotates faster, turn down the oil inflow and increase the oil inflow when the pointer rotates slowly.
Attention should be paid to observing the rotation of the dynamometer pointer and the trajectory of P-L curve on the automatic plotter in the process of specimen tension. When the force-measuring pointer goes backward (sometimes it shows that the pointer swings back and forth, indicating that the material has entered the yield stage, pay attention to the observation of yield phenomenon, at this time do not increase the oil quantity and do not reduce the oil quantity, let the material yield slowly, pay attention to observation, record the minimum load Ps (lower yield point) when the pointer swings back and forth, that is, the minimum value when the pointer swings back and forth.
When the active needle starts to drive the driven needle forward, it indicates that the material has passed the yield stage and entered the strengthening stage. At this time, the amount of oil can be increased appropriately, that is, loading at a faster speed until the specimen breaks. Before the specimen breaks, pay attention to the movement of the pointer. When the active needle moves back, the material has entered the necking stage. Pay attention to the necking phenomenon of the specimen. At this time, some oil intake can be reduced appropriately. When the sound of fracture is heard, close the intake valve immediately and record the maximum load Pb indicated by the driven needle.
6. End of Work
Remove the specimen and turn off the power supply. Re-docking the specimens. Measure the length L1 (the distance between the two marking lines after the break) with vernier calipers. And the diameter D1 at the fracture. (Measure the two perpendicular directions at the fracture once each other). Finally, observe whether the fracture shape and the drawing curve on the automatic plotter are consistent with the theory.
Matters needing attention:
(1) After the specimen is clamped, the lifting motor of the lower chuck shall not be activated. Otherwise, the motor will burn out.
(2) Loading should start slowly to prevent the throttle from opening too large, causing sudden increase of load impact and causing accidents.
(3) When conducting the test, special personnel must be responsible for it and stick to the position. If abnormal sound of the machine occurs, the machine will stop immediately.
(4) After the test, remember to close the intake valve, remove the specimen, open the return valve and close the power supply.