37. mode-ii dynamic fracture behavior of carbon fiber/epoxy

Department: Structural Engineering
Research Institute Affiliation: Center for Extreme Events Research
Faculty Advisor(s): Veronica Eliasson

Primary Student
Name: Rodrigo Enrique Chavez Morales
Email: rchavezm@ucsd.edu
Phone: 785-979-7102
Grad Year: 2020

In recent years fiber reinforced polymers have become popular materials in the construction of naval and aerospace vessels. As a result, there is a need to understand and predict their failure behavior. Currently, there is a lack of knowledge on the dynamic fracture behavior of these materials, especially when coupled to different environmental conditions. Thus, a study on the impact of water content on the dynamic fracture behavior of composite materials is being conducted. An experiment has been designed to asses the dynamic fracture behavior of carbon-fiber/epoxy under different environmental conditions. Edge-on impact experiments were performed on rectangular carbon/epoxy notched samples by using a projectile launched from a gas gun. The impact generated a stress pulse that initiates mode-II and mixed mode fracture. The specimens were divided in two sets that are conditioned in two different environments. The first set was left dry and simulated ideal laboratory conditions. The second set has been submerged in water for prolonged amounts of time. The water absorption rate of the second set is constantly monitored to quantify the amount of water absorbed. Digital image correlation (DIC) was used in conjunction with ultra high-speed photography to obtain the stress intensity factor along with other relevant fracture parameters. A strain gage was bonded to the specimens, to send a signal once a stress wave was detected and trigger an ultra high-speed camera. The event was captured using a Shimadzu HPV X-2 camera, that allows recording speeds of up to 10 million frames per second with a resolution of 50,000 pixels. A speckle pattern was applied to every sample, so that the displacement field around the crack tip could be obtained using VIC-2D DIC software. From the displacement field, a nonlinear least-square method was used to obtain the dynamic stress intensity factor of the material. Previous research performed with carbon fiber/vinyl ester under mode-I dynamic loading showed that this material did experience a decrease in fracture toughness when submerged in water for prolonged periods of time. The decrease in fracture toughness was attributed to water having a negative effect on the matrix-fiber bond. This study will confirm if a similar trend is present in mode-II loading.

Industry Application Area(s)
Aerospace, Defense, Security | Materials | Naval

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