10 research outputs found
Numerical investigation of fracture of polycrystalline ice under dynamic loading
Cohesive zone model is a promising technique for simulating fracture processes in brittle ice.
In this work it is applied to investigate the fracture behavior of polycrystalline cylindrical samples
under uniaxial loading conditions, four-point beam bending, and L-shaped beam bending.
In each case, the simulation results are compared with the corresponding experimental data
that was collected by other researchers. The model is based on the implicit finite element
method combined with Park-Paulino-Roesler formulation for cohesive potential and includes
an adaptive time stepping scheme, which takes into account the rate of damage and failure
of cohesive zones. The benefit of the implicit scheme is that it allows larger time steps than
explicit integration. Material properties and model parameters are calibrated using available
experimental data for freshwater ice and sea ice samples.
For polycrystalline ice, granular geometry is generated and cohesive zones are inserted between
grains. Simulations are performed for samples with different grain sizes, and the resulting
stress–strain and damage accumulation curves are recorded. Investigation of the dependency
between the grain size and fracture strength shows a strengthening effect that is
consistent with experimental results.
The proposed framework is also applied to simulate the dynamic fracture processes in Lshaped
beams of sea ice, in which case the cohesive zones are inserted between the elements
of the mesh. Evolution of the stress distribution on the surface of the beam is modeled for
the duration of the loading process, showing how it changes with progressive accumulation of
damage in the material, as well as the development of cracks. An analytical formula is derived
for estimating the breaking force based on the dimensions of the beam and the ice strength.
Experimental data obtained from the 2014-2016 tests are re-evaluated with the aid of this new
analysis.
The computation is implemented efficiently with GPU acceleration, allowing to handle geometries
with higher resolution than would be possible otherwise. Several technical contributions
are described in detail including GPU-accelerated FEM implementation, an efficient way of
creation of sparse matrix structure, and comparison of different unloading/reloading relations
when using an implicit integration scheme. A mechanism for collision response allows modeling
the interaction of fragmented material. To evaluate the collision forces, an algorithm for
computing first and second point-triangle distance derivatives was developed. The source code
is made available as open-source
The Gradient and the Hessian of the Distance between Point and Triangle in 3D
Computation of the distance between point and triangle in 3D is a common task in numerical analysis. The input values of the algorithm are coordinates of three points of the triangle and one point from which the distance is determined. An existing algorithm is extended to compute
the gradient and the Hessian of that distance with respect to coordinates of involved points. Derivation
of exact expressions for gradient and Hessian is presented, and numerical accuracy is evaluated for various cases. The algorithm has O(1) time and space complexity. The included open-source code may be used in applications where derivatives of point-triangle distance are required
Investigating Ice Loads on Subsea Pipelines with Cohesive Zone Model in Abaqus
Subsea pipelines and cables placed in ice-prone regions may be at risk of iceberg damage. In particular, pipes that are not buried may come in direct contact with iceberg keels. Knowing the range of interaction forces helps to assess the types and magnitudes of potential damage. Experimental studies provide the most valuable data about the interaction forces, while numerical modeling may give insight into configurations that are difficult to study experimentally. This work applies the cohesive zone model to investigate the fracture behavior of ice samples. Simulations are performed in 2D with Abaqus explicit solver. Modeled interaction forces from multiple simulations are recorded and compared to understand how the geometry of the samples affects the fracture. Repeat interactions with different grain configurations are conducted to investigate associated variance in fracture patterns and loads. t-tests show that the force application angle and the indenter’s position significantly affect the fracture force
New Unsymmetrically Substituted Benzothiadiazole-Based Luminophores: Synthesis, Optical, Electrochemical Studies, Charge Transport, and Electroluminescent Characteristics
Three new benzothiadiazole (BTD)-containing luminophores with different configurations of aryl linkers have been prepared via Pd-catalyzed cross-coupling Suzuki and Buchwald–Hartwig reactions. Photophysical and electroluminescent properties of the compounds were investigated to estimate their potential for optoelectronic applications. All synthesized structures have sufficiently high quantum yields in film. The BTD with aryl bridged carbazole unit demonstrated the highest electrons and holes mobility in a series. OLED with light-emitting layer (EML) based on this compound exhibited the highest brightness, as well as current and luminous efficiency. The synthesized compounds are not only luminophores with a high photoluminescence quantum yield, but also active transport centers for charge carriers in EML of OLED devices