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Abstract
The fracture behavior of eramic/polymer laminates has been investigated to
improve fracture behavior of ceramic by reinforcing with ductile polymer layers.
Epoxy is used to toughen ceramic laminates (partially stabilized Zirconia (PSZ)
or Alumina). It is assumed that interface bonding between laminates takes place.
The ductile polymer layers are assumed ductile and cause bridging stress.
A virtual model based on FEM is developed to calculate the J-integral of ceramic/polymer laminated composite. The fracture toughness is studied by
applying 3-point bend test on laminates. The J-integral is calculated numerically as a mathematical expression for fracture toughness. A parametric study of variables affecting J-integral is conducted.
The virtual model is based on the following assumptions: Bonding between
ceramic and polymer layers is represented by an interface element. A cohesive one element with exponential traction-separation relationship is used.
Constrained stress (J (u) is used to represent the polymer bridging effect on the crack growth and fracture toughness of laminates.
In order to validate the results of the applied virtual model a verification of the finite element model has been performed by a comparison with previous research results which has been experimentally conducted. There is a definite coincidence of theoretical results and the results of the experimental model of lK.Spelt. A
reasonable indication of the proposed virtual model precision has been approved.
The effect of laminates geometry on fracture toughness is studied. It can be concluded that increasing polymer layer thickness (by increasing thickness ratio)
improves the fracture toughness behavior or laminates. Also the variation of polymer and ceramic modulus of elasticity and interface between ceramic and polymer layers and constrained polymer have been examined to check their effect on fracture toughness of the materials. Polymer bridging constraints are varied by changing the peak values of stress and strain values. The results show
that it is preferable to use bridging layers with higher strength and less plasticity properties.
Crack growth behavior can be either single or multiple dominant cracking which determines the amount of absorbed energy before fracture, and consequently
laminates toughness properties. A fracture map has been developed by finite element modeling (which is used to characterise the non-deterministic strength of the ceramic layer) to the parameters controlling the transition from single to multiple cracking and a study of ceramic and polymer mechanical properties show a significant effect on transition from single to multiple cracking.
Since different design parameters interact to affect the final fracture behavior of the laminate, an optimization study is carried. out to obtain the optimum combination of laminate parameters for maximum toughness/weight of the
laminate. Three techniques are used (first order, random iteration and
subproblem approximation methods). Best results are obtained using the first
order technique. Moreover it is time consuming. Subproblem and random
iteration optimum design methods are more time saving and yield results close to each other but lower than the results obtained by first order method. The results show that the optimum design parameters for maximum toughness/weight correspond to laminates with the same polymer and ceramic layer thickness ratio.