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Investigating the Fracture Behavior of Adhesive Joints at Different Strain Rates and Under Drop

Darvishi, Irana | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54792 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Nourani, Amir
  7. Abstract:
  8. Nowadays adhesives with the development of technology and the numerous benefits they have, are becoming a replacement for traditional joining methods in industries like electronics, automotive, aerospace, and naval. That’s why the need for studying the fracture behavior of adhesive joints becomes vital. So far, many engineers and designers are trying to investigate the behavior of adhesive joints in different conditions that these joints actually deal with. Also, finding solutions to predict the behavior of adhesive joints is the researchers’ other concern. The purpose of this research is to find the effect of factors that are less focused in the literature, on the fracture of adhesive joints. Therefore, this study investigated the mode I fracture behavior of epoxy adhesive joints with similar adherends on both sides (i.e., aluminum-aluminum or copper-copper) and dissimilar adherends (i.e., copper-aluminum) at different strain rates; i.e., quasi-static (~10-3 s-1), low (~7 s-1), intermediate (~14 s-1), and high (~1700 s-1) rates. Finally, it was tried to derive parameters to predict the fracture load of dissimilar adherends joints of copper-adhesive-aluminum using measured fracture load and a cohesive zone model (CZM). The effect of strain rate (before the high strain rate) on the fracture energy was not noticeable (p>0.05) excluding Al-adhesive-Al and Cu-adhesive-Al joints from quasi-static to low strain rates. It showed a high dependency of the behavior of joints to the glass transition temperature of the adhesive (Tg). The effect of stiffness (before the high strain rate) was more pronounced for Al-adhesive-Al joints that decreased (i.e., by ~62%, p=0.0013) with an increase in the applied strain rate from quasi-static to low values, consequently, for Cu-adhesive-Al joints that increased (i.e., by ~53%, p=0.0386) with an increase in the applied strain rate from quasi-static to low values. For drop test specimens, the results showed that the Al adherend with lower stiffness controls the fracture energy of Cu-adhesive-Al joints. A CZM was built and strain-rate dependent parameters of traction-separation (TS) law were obtained. These parameters were then used to predict the fracture of epoxy adhesive joints bonded with dissimilar substrates (i.e., copper-aluminum). Predicted fracture loads of the Cu-adhesive-Al cases obtained from the stain-rate dependent model were in reasonable agreement with measured forces (i.e., from ~0 to 24%) at a given strain rate. Therefore, once TS law parameters for Al-adhesive and Cu-adhesive interfaces were determined, the CZM could predict the fracture of the joint bonded with Al and Cu on its sides
  9. Keywords:
  10. Strain Rate ; Fracture Energy ; Drops ; Fracture ; Hardness ; Traction-Separation Model ; Adhesive Bonding

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