Bài test uốn 3 điểm (3-Point Bending Test)

Introduction

If you have ever seen a video from CNC Kitchen or are interested in materials testing, you have probably heard of a 3-point bending test (see Wikipedia). 
It can be used to analyse the stiffness of materials. 

For this, a sample is placed between two points. If you now apply a force to the sample in the middle (i.e. at the third point), it deforms elastically. The goal is now to measure this bending as accurately as possible. For example: how far does a sample made of PETG bend with a force of 12 N?

With this design, the force can be applied to the specimen by attaching weights or pulling by hand. The deformation is measured by a precision dial indicator that can be adjusted in height on the 3030 T-Slot profile. 

Want to see it in action?
Check out one of my videos:

BOM

In the following list you will find everything that is additionally required in terms of screws and profiles. 

Parts

Quantity

Cap Head Screws

M3 x 16 mm 

2

M5 x 20 mm

3

M6 x 12 mm

3

M8 x 50 mm

2

(T-) Nuts

M3 self securing nut

2

M5 T-Nut for 2020 T-Slot

3

M6 T-Nut for 3030 T-Slot

3

M8 nut

2

Aluminium profiles

2020 T-Slot 250 mm (can also be longer)

1

3030 T-Slot 160 mm (min 100 mm)

1

Others

8 mm thick rod x 18 mm  

1

Optional

2020 Endcap

2

3030 Endcap

1

A precision dial indicator and weights are also needed. For the weights, a bucket and beverage cans, sand, etc. can be used. 

Assembly

1. Print the parts “base.stl”, “dial-Indicator-holder.stl” and “sample-hook.stl”
2. Slide the 2020 profile into the lower opening and the 3030 into the upper holder
3. Add matching T-nuts to the locations of the holes
4. Fasten the 2020 profile with three M5 x 20 mm screws
5. Fasten the 3030 profile with an M6 x 12 mm screw
6. Screw the two M8 x 50 mm screws into the base and secure them at the end with two M8 nuts
7. Slide the dial indicator into the holder and tighten it with the two M3 x 16 mm screws and self-locking nuts. Make sure that the gauge is firmly in place. Do not overtighten them! 
8. Slide the holder into the 3030 profile with two M6 x 12 mm screws and T-nuts and tighten the screws lightly
9. (Optional) Add end caps to the ends of the profiles
10. Press the 16 mm piece of the 8 mm shaft into the sample hook
11. Done!

Printing the samples

Use 15 Perimeters. 

Running a test

To be continued soon