Application of laser speckle interferometry (LSI) to the determination of in-plane elastic constants of paper

With the use of a recently developed Laser Speckle Interferometry (LSI) technique, all the in-plane elastic constants of machine made paper have been measured successfully and efficiently, including in-plane shear modulus and in-plane Poisson ratios. These constants are sometimes difficult to measure.; An off-axis tension method and a modified off-axis tension method are introduced; these are incorporated together with the LSI technique, to measure the in-plane shear modulus of machine made paper materials. Especially, the in-plane shear modulus of a low basis weight paper can be measured with these techniques. An optimization process was developed to estimate the shear modulus of paper with ease by using experimental data for several Young's moduli and a Poisson ratio.; Tension buckling (or wrinkling in tension) has been studied experimentally and by simulation. A tension buckling theory is here developed to explain this behavior. The effect of tension buckling (or wrinkling) in the measurement of Poisson ratio is calculated and tabulated.; Several refinements of the LSI technique have been achieved, so that the method may be applied effectively in the paper physics field (e.g. sample geometry, sample preparation). The LSI technique is very efficient, especially in cases where small and extremely accurate two-dimensional measurements of displacements are needed. By systematic studies and the application of LSI techniques, a powerful tool for investigation of the micro and macro mechanical behavior of paper materials can be made available in the future.