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Numerical modeling of timber with knots

The progressively damaged lattice approach vs. the equivalent damaged continuum
: Guindos, P.


Holzforschung 68 (2014), Nr.5, S.599-613
ISSN: 0018-3830
ISSN: 1437-434X
Fraunhofer WKI ()
heterogeneous continuum; knot; lattice; material model; multiscalar modeling; plasticity; progressive damage

Two new numerical models for simulating structural timber with knots are presented. The first one, the lattice model (LM), was built from an arrangement of linear truss elements, meanwhile, the second one, the continuum model (CM), was constructed of nonquadratic quadrilateral elements. Both models shared similar characteristics, which allows for an objective comparison between the two approaches. Common characteristics are as follows: they (1) possess identical geometry and node locations, (2) consider the fiber deviation of wood based on the flow-grain theory, (3) account for the longitudinal and transverse plasticity, and (4) permit tensile damage. Experimental four-point bending tests were performed to compare failure prediction, failure location, deflection, and qualitative failure pattern. Considerable construction and calibration work were required for the LM approach in comparison with the CM approach. However, the LM acceptably predicted the behavior of wood at the macroscale, and previous research documented satisfactory predictions for small scales. This suggests the lattice paradigm to be a valid approach for multiscalar simulations of wood. Moreover, complex mechanical principles (e.g., plasticity and damage) were found to be easier to incorporate into lattice elements. This can lead to deeper material understanding and innovation, as limitations for multiscale modeling may be more computational than theoretically constrained.