Investigation of simultaneous effects of loading rate and temperature on delamination in FMLs in tensile, ballistic and three-point bending tests

نوع: Type: Thesis

مقطع: Segment: PHD

عنوان: Title: Investigation of simultaneous effects of loading rate and temperature on delamination in FMLs in tensile, ballistic and three-point bending tests

ارائه دهنده: Provider: Ali Shirafkan

اساتید راهنما: Supervisors: Dr. Gholam Hossein Majzoobi

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr. alavinia,Dr khalili, Dr. feli

زمان و تاریخ ارائه: Time and date of presentation: 2025

مکان ارائه: Place of presentation: مجازی

چکیده: Abstract: Abstract: Fiber Metal Laminates (FMLs) have attracted attention in the aerospace and automotive industries in recent years due to their favorable mechanical properties. These sheets are composed of thin metal layers and a fiber-reinforced epoxy layer and are considered composite structures. In this study, the effect of temperature and strain rate on the mechanical behavior and failure mechanisms of these materials was investigated experimentally and numerically based on the finite element method. The fiber metal laminates used in this thesis are composed of 2024 aluminum and titanium metal sheets and glass and carbon fibers in epoxy resin. The results of three-point bending tests on these materials showed that with increasing temperature, their bending strength decreases, and conversely, increasing the strain rate increases the bending strength. By examining the SEM images of the FML samples in the bending test, it was found that at a constant loading rate and with increasing temperature, delamination occurred more intensely between the metal and composite layers. Also, at a constant temperature with increasing loading rate, in addition to delamination, there was also fiber-pull out. In ballistic tests, it was found that with increasing target temperature and projectile speed, the projectile exited at a faster rate. Additionally, for all samples, increasing the target temperature was accompanied by a decrease in the energy return coefficient. Digital Image Correlation (DIC) images show that at higher temperatures, the connection between the layers weakens, which leads to delamination or separation of the layers during impact. Since the simulation is based on ideal models and assumptions, they do not fully reflect the real-world effects. The error of the simulation results compared to the experimental results increased with increasing temperature. In all simulated GLARE 1/2 specimens, more than 50% of the kinetic energy was absorbed by the aluminum layer at the back of the impact. In the Hopkinson tensile test of FML specimens at temperatures above 0°C, it was observed that the yield strength of the specimen increased with increasing strain rate at a constant temperature. At temperatures below 0°C, the materials constituting the FML layers tended to become more brittle. This brittleness reduced the yield strength because the ability of the material to deform decreased, resulting in a lower yield point. By examining the images from DIC, it was observed that with increasing tensile rate, delamination of the metal layers and composite material became more obvious and pronounced. In the Hopkinson tensile test, with increasing temperature in the FML, the time to failure decreased. Also, at subzero temperatures, increasing the strain rate reduced the time to failure, and further decreasing the temperature also reduced the time to failure.