A Micromechanical Study of the Damage Mechanics of Acrylic Particulate Composites Under Thermomechanical Loading PDF Download

Author: Shihua Nie
Publisher:
ISBN:
Category : Composite materials
Languages : en
Pages : 744

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Book Description
"The main aim of this dissertation was to characterize the damage mechanism and fatigue behavior of the acrylic particulate composite. This dissertation also investigated how the failure mechanism is influenced by changes in certain parameters including the volume fraction of particle, the interfacial bonding strength, the stiffness and thickness of the interphase, and the CTE mismatch between the particle and the matrix. Monotonic uniaxial tensile and compressive testing under various temperatures and strain rates, isothermal low-cycle mechanical testing and thermal cycling of a plate with a cutout were performed. The influence of the interfacial bonding strength between the particle and the matrix on the failure mechanism of the ATH filled PMMA was investigated using in situ observations under uniaxial loading conditions. For composites with weak interfacial bonding, the debonding is the major damage mode. For composites with strong interfacial bonding, the breakage of the agglomerate of particles is the major damage mode. Experimental studies also demonstrated the significant influence of interfacial bonding strength on the fatigue life of the ATH filled PMMA. The damage was characterized in terms of the elastic modulus degradation, the load-drop parameter, the plastic strain range and the hysteresis dissipation. Identifying the internal state variables that quantify material degradation under thermomechanical loading is an active research field. In this dissertation, the entropy production, which is a measure of the irreversibility of the thermodynamic system, is used as the metric for damage. The close correlation between the damage measured in terms of elastic modulus degradation and that obtained from the finite element simulation results validates the entropy based damage evolution function. A micromechanical model for acrylic particulate composites with imperfect interfacial bonds was proposed. Acrylic particulate composites are treated as three-phase composites consisting of agglomerated particles, bulk matrix and an interfacial transition zone around the agglomerate. The influence of the interfacial bonding and the CTE mismatch between the matrix and the filler on the overall thermomechanical behavior of composites is studied analytically and experimentally. The comparison of analytical simulation with experimental data demonstrated the validity of the proposed micromechanical model for acrylic particulate composites with an imperfect interface. A damage-coupled viscoplastic constitutive model was also developed to predict the thermomechanical behavior and fatigue life of the acrylic particulate composites. The damage coupled constitutive model simulates the interaction between damage and response of the composite material under thermomechanical loading. The material parameters involved in the constitutive model have been experimentally determined and been implemented into the commercial general-purpose finite element package ABAQUS through user-defined subroutines. The finite element simulation results agree well with the test data from monotonic uniaxial tensile tests and fatique tests at various temperatures. It is shown that the proposed damage coupled viscoplastic constitutive model can be used to predict the fatique life of an acrylic particulate composite under thermomechanical fatigue loading"--Leaves xxvii-xxviii.