• Finite Element Modeling Of Photoplastic Process In The Cold Drawing Of Polycarbonate Bars

      Choi, Dong Ju; Lee, Jonah H. (2001)
      The numerical simulation of the mechanical behavior and the photoplasticity method of polycarbonate have been studied by simulating an existing photoplastic experiment of a cold drawing process. This study will allow understanding the mechanical and optical behavior of polymers and also assessing of the adequacy of existing numerical models and the photoplastic experimental method such that both can be validated and improved in the future. We proposed several optical-mechanical relationships for the photoplasticiy method and also adopted two existing viscoplastic models for polymers. Among the studied optical-mechanical relationships, the Non-Gaussian optical-mechanical relationship for photoplasticity of large deformation of polycarbonate is found to agree well with existing photoplastic calibration tests. Two types of viscoplastic numerical models adopted in this study are the physically based constitutive model and the phenomenological constitutive model with J2 flow theory. The model with the physically based constitutive model and a non-Gaussian optical-mechanical relationship for the photoplastic method could simulate the cold drawing experiment better than the phenomenological viscoplastic model. This study included a parametric study of the physically based constitutive model with the imperfection geometry and several material property variances to understand the mechanical and optical behavior of polycarbonate.
    • Massive ice interactions with offshore structures

      Lu, Mingchi (1992)
      The interaction between a multiyear sea ice floe of variable thickness, and an offshore structure, has been examined using a 3-dimensional finite element method. Elastic response within the ice floe was assumed initially, and a uniform loading of the ice floe by the adjacent pack ice was used. As an example of the results for a frozen boundary condition at the ice/structure contact zone, with a central region of the ice floe having its thickness reduced to 50% as compared to the floe thickness at the structure ($\Delta$t/t = 0.5), tensile cracks first form at the top surface in the thinnest area of the floe. The total force on the structure was 108 MN, as compared with 1500 MN which would be present in the case of an ice floe of uniform thickness. Parameters varied were ice/structure contact zone (located in the centric or the eccentric region), the sliding boundary condition, two-dimensional ice thickness variation, variable ice elastic modulus as a function of depth, and viscoelastic ice behavior. Cases of rigid and of compliant structure and foundation were included. In a second part of the study, the ice island loads acting upon a cylindrical rigid structure were analyzed by this 3-dimensional finite element method. A force of 6600 MN was computed to be acting on the structure with a maximum penetration distance of 8.2 m. A different theoretical method based upon multiyear ice field data resulted in a force of 336 MN and a maximum penetration distance of 75 m. The ice forces on the structure are reduced by ice floe thickness variations, and also are affected by the geometries at the ice floe/structure and ice floe/pack ice boundaries. The reduced elastic modulus in the warmer. lower part of an ice sheet promotes ice bending failure and causes lower structure loads.