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Finite Element Analysis of Bi-Metallic Structures with Adhesive Delamination

Cardanini, Alisha Ann

Abstract Details

2017, Master of Science, Ohio State University, Welding Engineering.
Bi-metal structures made of aluminum and steel are increasingly used for light-weighting applications. Replacing steel parts with aluminum in the body in white can reduce the weight of a vehicle up to 30%. The coefficient of thermal expansion (CTE) of aluminum is almost twice that of steel. Due to such large CTE mismatch, thermal buckling can become a concern when the bi-metal structure is exposed to elevated temperature. When adhesive is added between the aluminum and steel, its curing process can be affected due to buckling of the dissimilar metals. Moreover, stress in the structure developed at high temperature can be permanently locked in when the adhesive fully cures. This can lead to a higher residual gap between the aluminum and the steel than in structures without adhesive. The objective of this research is to quantitatively understand the stress and strain evolution in a bi-metallic Al / adhesive / steel structure exposed to a thermal cycle representative of that used in automotive paint bake process, including delamination of adhesive between the substrates. To achieve this objective, it is essential to first capture the behavior of the bi-metallic structure without adhesive and validating such models. Once validated, addition of cured adhesive and its delamination behavior is then incorporated. Delamination behavior relies on the fracture energy release rate of the adhesive material, which is determined through fracture toughness testing. Specially, the research consists of the following two main tasks. First, preliminary finite element models have been developed to capture the behavior of thermal induced buckling, including its deflection profile and stress close to the fasteners. These studies revealed that for a maximum paint bake temperature of 180°C residual stress is only found within the fastening region. This indicates that paint bake process itself does not produce enough heat to exceed elastic strain limits of the bulk structure. Several geometric factors are studied, including plate thickness, fastener pitch, and flange height. These factors reveal the effect of the geometry on the maximum deflection in buckling. Second, adhesive fracture toughness testing is conducted to measure the mode I fracture energy release rate. The fracture toughness is then incorporated in to both lap shear and thermal buckling model. Both use cohesive zone method incorporating linear traction-separation law for modeling the adhesive damage behavior. A hybrid continuum-cohesive element is created to incorporate both delamination effects as well as cured stress locking. The understanding established in this research is essential to optimize the design of bi-metallic structure to control distortion and residual stress in the structure, two important performance properties. Taken as a whole, the research results reported in this thesis represent a first step toward improving the quantitative understanding of adhesive deformation and failure behaviors in Al-steel bi-metallic structure. Future work includes (1) incorporation of non-linear traction-separation behavior in the cohesive elements, and (2) testing of adhesive fracture toughness as a function of temperature. Addressing the future work can further improve the accuracy of the computational model.
Wei Zhang (Advisor)
Avraham Benatar (Committee Member)
147 p.

Recommended Citations

Citations

  • Cardanini, A. A. (2017). Finite Element Analysis of Bi-Metallic Structures with Adhesive Delamination [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu150185598849201

    APA Style (7th edition)

  • Cardanini, Alisha. Finite Element Analysis of Bi-Metallic Structures with Adhesive Delamination. 2017. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu150185598849201.

    MLA Style (8th edition)

  • Cardanini, Alisha. "Finite Element Analysis of Bi-Metallic Structures with Adhesive Delamination." Master's thesis, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu150185598849201

    Chicago Manual of Style (17th edition)