A Chemical Kinetics Approach to The Duration-of-Load Problem in Wood

D. F. Caulfield

Abstract


The theory of absolute rates of chemical processes is presented as an appropriate conceptual framework for understanding the creep-rupture phenomena of duration of load (DOL) and rate of loading (ROL). The theory predicts the following experimentally observed phenomena:

(1) The logarithm of the time to failure under constant deadload stress increases linearly as the stress level is decreased.

(2) The rupture strength in a linear-ramp ROL experiment increases with the logarithm of the rate of stressing.

Moreover, the equations derived to describe these phenomena contain the same parameters. These parameters are denned physical quantities that describe the creep characteristics of the material. It is possible to predict how long a material will support a constant deadload stress (DOL behavior) from measurements of apparent rupture strength as a function of the rate of stressing in a linear-ramp loading experiment (ROL behavior).

Rupture of Douglas-fir in bending is selected as an example, and the experimental results from ROL-behavior experiments are used to predict DOL behavior. The theory adequately describes the experimentally observed results.


Keywords


Creep rupture;duration of load;rate of loading;bending rupture;Douglas-fir;absolute reaction rates;stress-strain behavior;tensile strength;modulus of rupture

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