Formulation of Pre-Extension in a Practical Stress-Relaxation Measurement of the Plant Cell Wall

In practical measurement of stress-relaxation, a certain length of time is required to apply the initial stress to a specimen. We refer to this process as pre-extension. In the stress-relaxation analysis of the plant cell wall which we developed, a wall specimen is stretched at a constant rate in pre-extension. The condition of pre-extension, such as the length of the pre-extension period, affects the subsequent stress-relaxation process. Thus, the stress-relaxation time spectrum calculated directly from the stress-relaxation process is an approximation. In this study, the condition during pre-extension was formulated in a stress-relaxation function and the stress-relaxation time spectrum, H ( τ ) , was calculated as H ( τ ) = b · { exp ( − T 0 / τ ) − exp ( − T m / τ ) } / { r · τ · ( l − exp ( − T p / τ ) ) } where T 0 and T m are the minimum and maximum relaxation times, τ is the relaxation time, b is the relaxation rate, r is the extension rate in pre-extension and T p is the pre-extension time. The effect of the pre-extension condition on the spectrum is discussed.