Characterizing the fatigue damage in non-traditional laminates of carbon fiber composites using radiography
Rast, Joshua David
MetadataShow full item record
The goal of this academic project was to study the effects of different variables on the damage progression around a central hole in carbon fiber composite coupon specimens. The tracked variables included the type of layup, stress ratio, stress levels, and damage mechanisms observed in each specimen. In-situ x-ray of the individual laminates recorded the extent of damage, mostly longitudinal splitting, as a function of the cycle count. The following lay-ups were included in the experiment: [45/90/-45/02/45/02/-45/0]s, [±5/65/(±5)2/-65/±5]s, and [±5/65/(±5)2/-65/5/65]s. More specifically, the objective of this study was to determine the stress levels at which detectable damage started to develop. The researchers chose to apply 50,000 cycles at each stress level and once damage was detected, the stress level was typically raised by 34.5 MPa (5 KSI), and then cycled another 50,000 cycles until damage exceeding 1.27 cm (0.50") in length was observed. Once the damage exceeded 1.27 cm (0.50"), cycling was continued to 1,000,000 cycles. Upon completion of the fatigue cycling, each specimen's residual strength was determined. The damage length versus stress level was plotted as a way to compare damage onset stresses and growth as a function of lay-up and stress ratio.