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Gamze S. Bas-Dissertation.pdf (32.44 MB)

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Predictive Modeling For Rate Dependent Toughened-Adhesive Behavior During Impact

Bas, Gamze S
http://orcid.org/0000-0003-3907-3189
http://rave.ohiolink.edu/etdc/view?acc_num=akron1499078572477787

Abstract Details

2017, Doctor of Philosophy, University of Akron, Polymer Engineering.
The use of structural adhesives has an increasing demand as a joining technique in the automotive industry due to the possibility of reduction in vehicle weight, fuel consumption and CO2 emission. By using load bearing structural adhesives, high-strength and tough structures can also be incorporated into automotive bodies to create impact resistant automobiles with improved crashworthiness. Consequently, it is important to understand mechanical response of adhesives subjected to crash loading in order to develop mechanical models with predictive capabilities. The focus of our study was to identify physical properties of different toughened structural adhesives and identify/develop an elastic-viscoelastic-plastic model as a function of loading rate by using Ludwik type equations to be able to predict adhesive behavior at higher loading rates and to make cars more crashworthy. We also measured and analyzed the fracture properties of toughened structural adhesives at different fracture modes to unveil their mechanical behavior more precisely as related to their crashworthiness. First, eight different commercial toughened epoxy structural adhesives were characterized to provide detailed information about the constituents of adhesives. The main crystalline inorganic ingredients were found as calcite and calcium oxide for all types of adhesives. The total amount of inorganic fillers was found to be different in each adhesive. Second, material parameters of four model adhesives were determined via tensile test and via Single Lap Joint (SLJ) test in shear. Stress-strain behavior of adhesives presented typical viscoelastic behavior in which linear–elastic behavior was observed first followed by viscoelastic behavior with strain rate sensitivity. The strain rate sensitivity was described by incorporating Ludwik type equations into our modelling process. Multiple elastic limit (yield) stresses and strains indicating bilinear-elastic behavior were identified for all adhesives except one. The Modified Bingham elastic-viscoelastic-plastic model altered to accommodate the bilinear-elastic region was used to predict the stress–strain behavior of adhesives with high statistical accuracy in tensile mode at different extension rates from 25 mm/min to 500 mm/min. Strain rate dependence of all material parameters were confirmed for all structural adhesives subjected both to tension and shear loadings. Failure criterion for the maximum stress of each adhesive at the onset of plastic flow was identified by considering the following failure criteria: Maximum shear stress failure criterion, Von-Mises failure criterion, and maximum normal stress failure criterion. Third, material parameters were determined via Split Hopkinson Pressure Bar (SHPB) test at high strain rates to unveil the high rate behavior of five model adhesives. Comparison of the elastic moduli results obtained from lower strain rate regime (tensile tests) and higher strain rate regime (SHPB tests) showed that strain rate sensitivities were of the similar order of magnitude between the regular tensile test results and the SHPB test results indicating the possibility of using regular tensile test results for predictive purposes. Lastly, critical strain energy release rates, GIc and GIIc, of five model adhesives were determined under different loading conditions: pure Mode I, pure Mode II and mixed mode (I/II) via Tapered Double Cantilever Beam (TDCB) specimens and Independently Loaded Mixed Mode (ILMM) specimens. Strain energy release rate results and fracture surfaces revealed that fracture behavior changes as the mode mixity is added for toughened epoxy adhesives. Moreover, it was found that all adhesives were more accurately governed by the “energy balance criterion” except for one, which was more accurately governed by the “principal stress criterion” indicating more brittle behavior.
Erol Sancaktar , Dr. (Advisor)
Xiong Gong, Dr. (Committee Chair)
Sadhan J. Jana, Dr. (Committee Member)
Darrell Reneker, Dr. (Committee Member)
Wieslaw K. Binienda, Dr. (Committee Member)
252 p.
Polymers
Structural adhesive, mechanical modeling, strain rate, tensile test, single lap joint test, fracture test, TDCB, ILMM, SHPB test

Recommended Citations

Citations

  • Bas, G. S. (2017). Predictive Modeling For Rate Dependent Toughened-Adhesive Behavior During Impact [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1499078572477787

    APA Style (7th edition)

  • Bas, Gamze . Predictive Modeling For Rate Dependent Toughened-Adhesive Behavior During Impact. 2017. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1499078572477787.

    MLA Style (8th edition)

  • Bas, Gamze . "Predictive Modeling For Rate Dependent Toughened-Adhesive Behavior During Impact." Doctoral dissertation, University of Akron, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1499078572477787

    Chicago Manual of Style (17th edition)

akron1499078572477787
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This open access ETD is published by University of Akron and OhioLINK.