Linearity and non-linearity in mechano-sorptive creep of softwood in compression and bending

Summary

Non-linearity of softwood in axial mechano-sorptive creep during moisture cycling can be characterised as departure from linear behaviour. Linear behaviour is shown by experimental measurement to be a gradual approach to a creep limit with exponentially decreasing increments of compliance, J_i, per moisture cycle, when tested under a constant stress. On the other hand, when the stress is progressively increased by a small increment Δσ after each moisture cycle, the compliance increments will progressively increase, having a value of $\Delta \sigma \sum\limits_1^n {{\text{J}}_{\text{i}} }$, where n is the cycle number. By subtracting one compliance increment from the succeeding one, the value of Δσ J_i can be obtained. Analysis of experimental results in bending tension and compression showed that the compression test pieces departed from linearity at total strains around 0.14% to 0.15%, the bending test pieces showed slight evidence of non-linearity at about the same strain, whilst the tensile pieces were approximately linear up to 0.18% strain.