3 Point Bend Test Fixture

Owned by Vansh Dhingra (Deactivated)
Last updated: Feb 06, 2021 by Min Qian Lu (Deactivated)
2 min read

FEB 6 MEETING UPDATE:

  • go with linear rail with measurements and set screw, we can stomach human error

  • consider the size of components, based on the force applied w/ SF 2-5

  • consider various loading “points” and shapes

  • tight tolerancing needed to ensure specimen parallelism etc.

  • Large surface area faces for datums to avoid wobble during assembly OR use flatness GD&T feature on fixture and rail

 

The 3 Point Bend Test provides values for the modulus of Elasticity, flexural stress, and flexural strain of a material. With the use of a universal testing machine, a load is applied to the middle of a specimen while two supports hold up the specimen. These two supporting pins are placed a set distance apart.

 

The goal of this project is to design a Support Test Fixture capable of being used to conduct 3 point bend testing of specimens using the Testing Machine in E3. The supports must be adjustable have a span that is accurate to 0.1mm. It also needs to be machined in house.

How will the supports move?

 

2 Options:

 

Spring and Screw

·      Spring joining two supports

·      Screws on either side apply torque and cause spring to compress which causes the support to move inwards

 

Rack and Pinion

·      Linear Gear and Circular Gear

·      Driving the pinion into rotation causes the support to move linearly

 

 

The circular gear is rotated by the knob in this example of a 3 point bend test fixture. The only caveat is that we need a way to lock the supports in place. Otherwise, the gears can rotate back into a neutral position, effectively making the positional accuracy of the support a function of the number of teeth on the gear.

 

NEXT STEPS:

  1. Develop ideas some more

  2. Pick one

  3. Do an initial design