Compressive strength of unidirectional fiber composites with matrix nonlinearity
Abstract
Compressive strength of the unidirectional fiber composite was studied in the form of fiber microbuckling. Fiber microbuckling was studied by including fiber misalignment and nonlinear behavior of the matrix. The matrix was assumed to be elastic-plastic following the von Mises $J\sb2$ flow rule. The buckling analysis was done in the form of bifurcation buckling by using the formulation of incremental deformation with initial stresses. The initial fiber misalignment constituted the combined axial and shear stress state in the matrix, and the state of stress just prior to the buckling was considered to be the initial state of the stress in this bifurcation analysis. The linear nature of the relationship between the incremental stress and the incremental buckled deformation warranted the use of the linear microbuckling solution. Beam-column analysis utilizing the Euler-Bernoulli approach produced the elastic microbuckling solution. This approach was extended to the multilayered composites when the two dimensionally idealized fiber plates were considered as beam-columns with supporting matrix between the fiber plates. The effects of the boundary conditions were included in the case of multi-layered composites. The critical microbuckling stress was found to be the same expression as that of elastic shear mode microbuckling stress except that the matrix elastic shear modulus was to be replaced by the matrix elastic-plastic shear modulus. Incremental theory of plasticity as well as the simpler deformation theory of plasticity were used to study the microbuckling problem and the results were compared. The analysis results showed reasonable correlation with available compressive test data for AS/3004, AS4/3501-6 graphite/epoxy composites and AS4/PEEK thermoplastic composites with 2$\sp\circ$ to 4$\sp\circ$ range of initial fiber misalignment.
Degree
Ph.D.
Advisors
Sun, Purdue University.
Subject Area
Aerospace materials|Mechanics
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