Third Point Loading

No. Three point test fixtures and four point test fixtures are used in all industry standard methods that relate to flexure and bend testing. Most standards specify one or the other and a few specify both. “Third point” refers to a special configuration of a bend test that employs four points. 

There are two types of four point loading configurations. ….

Because it is only the outermost fibers of the specimen that determine the parameters of the test, stress concentration at the loading points is of concern.

The four point, quarter point loading provide equal but the highest loading of the three methods. Four point, third point loading provides equal and lower loading.

The three point loading has the lowest loading at the two points. If the maximum force of the machine is a concern, note the Four point quarter point machine requires 2 times the applied load of the three point fixating.

Also because of the higher loads, four point fixtures need to be designed to handle the higher loads.

Three point testing the peak stress is at a maximum and tapers off to the ends so it tests a more localized spot on the specimen. This can be useful for component testing such a PC boards where you want to look at point where a component is installed.

Four point testing produces a wide area under uniform maximum stress exposing a greater surface area to failure from defects or stress concentrations.