Time-Dependent Strain Behavior of Wood in Tension Parallel to the Grain

Creep behavior at room temperature and 12 percent moisture content on 11 species of wood were studied by means of the type B tension specimen (ASTM D805-52). Specimens were conditioned and stored over a saturated sodium nitrite solution prior to test. All tests were conducted at temperature within the range of 75? to 86?F. Loads were applied by means of a hydraulic testing machine. Three different types of loading schedules were used: a single-cycle 30-minute creep test and a multiple-cycle test with and without a recovery period. The results indicated creep is proportional to log of time for only first 30 or 40 minutes. Creep occurs in all species at stress levels 15 percent of short-time strength or less. Set begins to occur at about the same initial extension region for all species. Creep-initial strain and creep-stress level show a two-stage relationship. Specific gravity and maximum tensile strain account for much difference in creep behavior below threshold of set.

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