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Publication Number: FHWA-HRT-04-097
Date: August 2007

Measured Variability Of Southern Yellow Pine - Manual for LS-DYNA Wood Material Model 143

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3 EXAMPLES MANUAL

This section contains two sets of example problems that the user can review to become familiar with the use of the wood material model. The first set of problems are single-element simulations in tension and compression, both parallel and perpendicular to the grain. The second problem is a bogie impact into a wooden post.

3.1 SINGLE-ELEMENT SIMULATIONS

Wood material model input is given in figure 29 for default pine parameters, and in figure 30 for user-specified input parameters. A complete input file, with nodes and elements, is given in appendix G. This file is for tensile loading of a single element parallel to the grain. To convert to compressive loading, change the sign of the ordinate under *DEFINE_CURVE at the bottom of the file. To convert to loading perpendicular to the grain, change the orientation vectors to [A1, A2, A3] = [1, 0, 0] and [D1, D2, D3] = [0, 0, 1].

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Figure 29.

Example wood model input for selection of default input parameter (option MAT_WOOD_PINE).

Single-element stress-strain results are shown in figure 31 for saturated, room-temperature clear wood pine. These results can be achieved using either the default input shown in figure 29 or the user-specified input shown in figure 30. Note that the peak strengths attained match the input strength parameters listed in figure 30. These are XT = 85.2 MPa, XC = 21.2 MPa, YT = 2.05 MPa, and YC = 4.08 MPa. The results are plotted with LS-POST as cross-plots of element z stress versus node 8 displacement. As additional exercises, the user can vary the moisture content (MC), temperature (TEMP), grade (QT, QC, and IQUAL), units, hardening (GHARD), and rate effects (IRATE with rate of loading) to examine how the default behavior of pine varies with these quantities.

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Figure 30.

Example wood model input for user specification of input parameters (option MAT_WOOD).

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Figure 31.

Example single-element stress-strain results for clear wood pine.

3.2 BOGIE IMPACT SIMULATION

The wood model input is similar to that shown in figure 29, although units of GPa (UNITS = 0 with RO = 6.73-e07) and rate effects (IRATE = 1) are requested. In addition, the post is grade 1, rather than clear wood. The post is saturated along the entire length. The post is modeled with simplified boundary conditions to attain a fast run time.

Bogie-post output results are shown in figures 32 and 33. The post breaks just below ground level. Damage occurs in the impact regime and in the region of post breakage. The post displacement is linear with time. The post cross-sectional force (between the impact point and ground level) reaches a peak of approximately 47 MPa within the first 5 ms before decaying, in an oscillatory manner, back down to zero. The results are plotted with LS-POST.

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Figure 32.

Deformed configuration of post at 40 ms, including fringes of damage.

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Figure 33.

Post deflection and cross-sectional force histories.

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