Energy Criterion for Fatigue Strength of Wood Structural Members

This report describes a mathematical model for fatigue strength of cellulosic materials under sinusoidal loading. The model is based on the Reiner-Weissenberg thermodynamic theory of strength in conjunction with a nonlinear Eyring’s three-element model. This theory states that failure depends on a maximum value of the intrinsic free energy that can be stored elastically in a volume element of the material. The three-element mechanical model, which consists of a linear spring in series with a parallel array of another linear spring and an Eyring dashpot, provides a good description of rheological material properties. The strength model system was able to predict rupture occurrence of polymers and wood structural members under constant and ramp loading with satisfactory results. For sinusoidal loading, the present study shows that the strength model system can predict time at fracture as a function of applied mean stress, amplitude of cyclic stress, and stress frequency. Numerical examples with model parameters evaluated for small Douglas-fir beams are presented.

[1]  Lawrence A. Soltis,et al.  Load-Duration Effects in Structural Lumber: Strain Energy Approach , 1992 .

[2]  S. Teoh,et al.  Creep Rupture Modelling of Polymers , 1992 .

[3]  S. Teoh.  Computational aspects in creep rupture modelling of polypropylene using an energy failure criterion in conjunction with a mechanical model , 1990 .

[4]  B. Cherry,et al.  Energy criterion for modelling creep rupture of high-density polyethylene , 1983 .

[5]  B. W. Cherry,et al.  The role of recovery forces in the deformation of linear polyethylene , 1978 .

[6]  B. Cherry,et al.  Strain rate effects on the ratio of recoverable to non-recoverable strain in linear polyethylene , 1978 .

[7]  Lyman Wentsch Wood,et al.  Relation of strength of wood to duration of load , 1960 .

[8]  B. D. Coleman,et al.  The Interpretation of Creep Failure in Textile Fibers as a Rate Process , 1957 .

[9]  B. D. Coleman.  Application of the theory of absolute reaction rates to the creep failure of polymeric filaments , 1956 .

[10]  H. Eyring,et al.  Mechanical Properties of Textiles, X , 1946 .

[11]  Henry Eyring,et al.  Mechanical Properties of Polymeric Materials , 1943 .

[12]  E. L. Schaffer,et al.  Reaction Rate Model for the Fatigue Strength of Wood , 1994 .

[13]  S. Teoh,et al.  Bending creep rupture analysis using a non-linear energy criterion approach , 1990 .

[14]  S. N. Marsoem.  Mechanical responses of wood to repeated loading , 1987 .

[15]  S. Teoh,et al.  Creep rupture of a tropical wood polymer composite , 1987 .