Design of the Fatigue Testing Machine

The Fatigue Testing Machine Functionality

The goal of the machine is to conduct fatigue testing on an armchair by simulating as realistically as possible, a person sitting in the chair over a given number of cycles. Below is a image of the 3D model of the testing machine in SolidWorks.


*SolidWorks model of the chair testing machine setup*

The base of the testing machine is made of 40 mm hollow aluminum extrusion that surrounds the legs of the armchair. Two beams of extrusion are arranged in the shape of a "T" across the middle of the base to house the loading mechanism. The design of the loading mechanism is fairly straightforward. First, a load of up to 200 lbf is inputted into the system using a linear actuator. As this actuator extends, the load is converted from a roughly horizontal force into a vertical force through the rotation of the bell crank. This causes the linkage arm connected to the bell crank to move downwards, pulling along with it the aluminum extrusion sitting across the seat of the chair which serves as the load applicator.


*Load path of the chair testing system*

The Working Prototype

Here are images of a working prototype of the chair testing machine.


*Front view of the chair testing machine*


*Left view of the chair testing machine*


*Isometric view of the chair testing machine*

There are two actuators that we plan to use for the fatigue testing machine: a feedback and an optical actuator so that we can collect different data from the actuators for instrumentation and control. Both of these actuators will need to extend and retract automatically for a given number of cycles in order to do fatigue testing on the chair.


*A close-up of the load mechanism*

The first time we ran the machine we encountered a problem with the base of the machine lifting up when the actuator was fully extended. This happened because the base of machine is very light, and the seat of the chair is stiff enough to resist that load and experience very minimal deflection which is certainly not what was intended; here is a video of that:

The solution we devised to solve this problem was to add in three corner brackets along the inside perimeter of the base of the machine and have the leg of the chair sit on these. That way, when the base of the machine wants to lift upwards then the corner brackets will grip onto the bottom of the legs keeping it on the ground.

Corner brackets hook onto the leg of the chair

to prevent the machine from lifting up

This worked beautifully because the machine now behaves the way it was intended to, here's a video of the final working prototype.