Impact test
Impact Machine
A specimen with one slot at the middle
In place: The slot must be in line with the edge of the hammer
Details of specimens: 10x10x
- one mm. depth one slot at the middle
- two mm. depth one slot at the middle
- one mm. depth for one slot at the middle and with one mm
slots at 5mm. both sides
Three slots one mm. depth
Lift up the hammer to the assigned angle(input)
A typical broken specimen:
Read the output:
Assign lifted angles and after-strike angles
In an untidy note!
A typical broken three slots specimen
Some very useful calculations:
Plot E vs V(h)
An example:
Anyone does notice something wrong up there!
Explanation of the results:
Firstly, the specimen is treated as simple beam with ball supported at
both sides.
Secondly, the impact force is huge due to small interval while
impacted.
Thirdly, with slot or slots, simply add even more degree of stress
concentration factor to the bending stress.
Can you estimate the impact force?
Examples of daily impact scenarios
- knocking on the road with and without helmet
- Safety belt behavior
- Bumpers, shock up etc…
Our impact test is about high strength steels which have quite small
Plastic zone sizes at the onset of the notches of specimens.
Notch-free specimen
Where is the Max Bending Stress in tension?
Plane stress thin
Plane strain thick
As the plastic zone at the onset of the notch is stretched, the nearby
elastic material presses back in the equal magnitude but opposite
direction.
A shape of plastic zone can be found via Plain Stress approximation
on the top and under of specimen. Physically, you can see this
“Dimple” due to high strain in tension on the both surfaces.
As deep into the middle layer of the specimen, a shape of plastic
zone can be found via Plain Strain approximation, and its size is
clearly smaller than via Plain Stress.
Unexpected results (cracks not come from the middle slot) may
easily found if the specimens is not placed coorectly.
Now you could use the above explanation to explain the graphs.