4-Point Bend Testing of Carbon Fiber

Carbon fiber is an extremely strong material. Depending on the manufacturing process, this textile can have typical modulus values of about 138 Gpa and ultimate tensile strengths of about 3.5 Gpa. Industry professionals can find themselves seeking to replace traditional steel components with lighter carbon fiber counterparts to achieve a much higher stiffness to weight ratio. To determine the appropriate thickness for the corresponding carbon component, one must undergo some experimental validation.

4 Point Bend

In a recent test, an ElectroPuls E3000 was fitted with a 5kN Dynacell™ load cell and a 4-point bend fixture. Once aligned, the upper and lower spans of the 4-point bend fixture were set to 30mm and 100mm respectively. For this sample, a cyclic load-controlled test was conducted with a mean load of 110N of compression and an R value of 0.1 (equivalent to a 90N amplitude). The cyclic loading was carried out at 10Hz for 2 million cycles, which was expected to last around 55 hours. The maximum deflection of the carbon fiber specimen was collected for every 1000 cycles with WaveMatrix™ software.

All ElectroPuls systems are fitted with an optical encoder for precise extension control. This allows for accurate displacement measurement readings of the carbon fiber specimen of up to one micron of a millimeter over the course of the entire 2 million cycles. The resultant displacement of the carbon fiber specimen is acquired by the 8800 controller at a rate of up to 5kHz. WaveMatrix™ software conveniently allows users to specify exactly which data is saved and at what frequency. For this test, a higher data acquisition rate was used during the first few hundred cycles. Thereafter, every 1000 cycles was recorded and exported in the form of an easy to read Microsoft Excel file. From this, researchers can then determine the overall changes in displacement of the carbon fiber over the entire 2 million cycles, and whether or not the material properties of the specimen suit a particular application.

Originally posted on March 25, 2014 , Updated On August 28, 2023