Influence of the fibrous raw materials type on the evolution of local deformations in topliner board when tensile testing
The regularities of propagating the local tensile (longitudinal), compressive (transverse) and shear deformations in a topliner board samples from virgin and recycled fibrous raw materials have been established. To carry the research out the Method of quantitative estimating the distribution of local strains in a sample of pulp-and-paper material when uniaxial tensile testing was used. As the test samples the industrially manufactured white topliner board - virgin and recycled - were chosen. They had basis weight (125 and 130 g/m<sup>2</sup>), and different structure inhomogeneity (formation index was of 250 and 150) and anisotropy degree (TSIMD/CD was of 2.6 and 2.0). The regularities were established depending on the direction of their fiber orientation (it ranged from 0 to 90° to machine direction - MD). Experimental data were obtained while tensile testing and photo-fixing the samples with dimensions of 100 × 25 mm and a pre-applied dot-matrix with a step of 4 × 4 mm to their white top. The coordinates of the matrix dots and their displacement when testing were determined by means of using the special software. Data analysis and values calculation of local deformations were performed due to finite element method algorithms. It has been established that, increasing the cutout angle to MD of the samples of topliner board from different type of fibers led to as follows: local longitudinal deformations increased, transverse - decreased, and shear - had their maximum at 45° to MD. In addition, increasing the total deformation value caused a more pronounced character of dependencies. As it was established, the prevalence of compression deformations in the samples cut in MD (samples of 0°) was related to compressing, acted perpendicularly to the predominant axis of the fiber orientation in samples’ structure. A large amount of transverse deformations in recycled topliner board was associated with a lower degree of anisotropy and a smaller average length of fibers that increased the role of inter-fiber bonds. It was shown that, the heterogeneity of local strains increased along with their absolute value, and the trends of changes depended on the type of fibers and the direction of their orientation in the sample structure.