An 8th Grade Student Designed This Machine to Test the Tensile Strength of 3D-Printed Materials

When it comes to engineering and materials science, saying something is “strong” is pretty meaningless. That’s because there are many types of strength, and some materials and structures possess some of them and not others. Concrete, for example, is able to withstand huge compression forces and is difficult to crush. But it has very poor tensile strength, which is why it is often reinforced with material like steel rebar. Tensile strength refers to a material’s ability to withstand stretching. Instructables user Xieshi, who is now a 9th grade student from Arizona, built a machine specifically to test the tensile strength of 3D-printed objects.

This tensile testing machine was originally built by Xieshi (AKA “CrazyBlackStone”) and a friend for an 8th grade science fair project. Their goal was to test the strength of 3D-printed materials. The machine was originally designed in Tinkercad, but Xieshi has been redesigning it in Autodesk Fusion 360 and plans to make that design open source, too. This machine is capable of measuring tensile forces up to 500 newtons. For a homogenous material, it can be used to calculate the tensile strength by simply diving that by the cross sectional area of the material sample. The layers of 3D-printed material introduce inconsistencies that muddy the waters, but repeated testing can yield an average.

This machine was constructed from a combination of 3D-printed parts and aluminum extrusion. The material to be tested is clamped between a pair of two grips at one end of the machine. One of those grips is stationary and the other moves. The moving grip is attached to an actuator by a load cell. The actuator is a lead screw turned by a NEMA 17 stepper motor with a planetary gear (gear ratio between 51:1 and 100:1). That’s controlled by an Arduino Nano board through an A4988 stepper motor driver. The Arduino also monitors the load cell through a HX711 amplifier board. As the motor turns, it applies an increasing amount of force to the tested material. Eventually the material will break, and the user just needs to check the load cell readout to see what the highest value was. This is a very useful machine if you need to test tensile strength, and is even more impressive given Xieshi’s age.