The development of composite materials for civil engineering applications is often a trial and error process, in which optimal use of raw materials is achieved only by chance or after extensive experimental work. A reliable analytical model can aid in this process, by identifying promising mixtures and arrangements of the constituents to guide physical experiments.; A micromechanical model for cement excelsior board is presented. The model simulates the three-dimensional network structure created by bonded wood strands in this wood-cement composite. Heterogeneity of strand geometric and mechanical properties, and disorder in their arrangement, are included. The model is implemented as a finite element computer program. Analysis consists of identifying the progression of failures within the network and the resulting accumulation of damage that determines stress-strain behavior of the composite and leads to its overall failure. Tests are conducted to determine properties of the constituents that are the input for the model, and to determine the mechanical properties of the composite for verification of the model.; Simulations of two types of cement excelsior board subjected to two loading conditions are compared to test results to verify the accuracy of the procedure. The model accurately predicts mean mechanical properties for groups of specimens. The model can also predict the variability in mechanical properties caused by irregularities in the microstructure; simpler models that ignore heterogeneity cannot do this.; Applications include parametric studies of the effect of fabrication variables on the composite properties. The wood-cement ratio to maximize the composite's strength-weight ratio is determined, and the effect of partial strand alignment is evaluated. A procedure to use the micromechanical model as a preliminary step in the analysis of heterogeneous panels is presented, and used to show the relationship between the spatial variation in composite properties and overall panel strength.
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