Thesis (M.S.)--Rochester Institute of Technology, 1990. / Typescript. Includes bibliographical references.

No description available.

Thesis (M.S. in Econ.)--School of Economics, Georgia Institute of Technology, 2004. Directed by Haizheng Li. / Includes bibliographical references (leaves 55-56).

Master's thesis. / Format: PDF. Bibl.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1944. / Includes bibliographical references (leaves 141-145).

Abstract The primary objective of this work is to study and model the fracture process and durability of paperboard cores in cyclic loading. The results are utilized in creating analytic model to estimate the life time of cores in printing industry. The life time means here the maximum number of winding-unwinding cycles before the core delaminates. This study serves also as an example of use of board as a constructional engineering material. Board is an example of complicated, fibrous, porous, hydroscopic, time dependent and statistic material. Different core board grades are typically made of recycled fibers. The material model in this work is linear-elastic, homogeneous and orthotropic. The material characteristics, elastic and strength properties are studied first. Then the material is studied from the points of view of fracture and fatigue mechanics. Some of the analysis and test methods are originally developed for fiber composites but have been applied successfully here also for laminated board specimen. An interesting finding is that Scott Bond correlates well with the sum of mode I and mode II critical strain energy release rates. It was also possible to apply Paris' law and Miner's cumulative damage theory in the studied example situations. The creation of the life time model starts by FEM-analysis of cracked and non cracked cores in a typical loading situation. The elastic-linear material model is used here. The calculated stresses are utilized in analytic J-integral model. The agreement between analytic and numerical J-integral estimations is good. The analytic life time model utilizes the analytic J-integral model, Miner's cumulative damage theory and analytically formulated Wöhler-curves which were constructed by applying the Paris' law. The Wöhler-curves were constructed also by testing cores to validate the theoretical results. The testing conditions are validated by FEM-analysis. The cores heat up when tested or used with non expanding chucks and a temperature correction was needed in the life time model to consider this. Also, single or multi crack model was used depending on the studied case. The calculated and tested durability prediction curves show good correspondence. The results are finally reduced to correspond to certain confidence level.

Paperboard combined with polymer and aluminium films are widely used in food packages. Paperboard is used for the bulk of the package material, and provides the stiffness. Paperboard is a highly anisotropic material, which is affected by how the fibers are orientated. Most fibers are aligned in the machine direction (MD), which is the stiffest direction, perpendicular is the cross-machine direction (CD) where fewer fibers are aligned, and the thickness direction (ZD) which is considerably weaker than in the MD and CD directions. Continuum models are used to describe the material properties to aid the design of package manufacturing processes. In continuum models there are no inherent length scale effects, and the material behaviour is the same regardless of the geometry. For paperboard there have been experimentally observed effects of the gauge length and width of tensile tests. To calibrate and develop these models it is important to observe which effect is a material property, if there is an inherent length scale, and which properties are from the boundary conditions of the experimental setup. Creasing is a process where the length scale is considerably smaller than at the standard tensile test, where the material deforms plastically to create creasing lines to easier fold the paperboard. The failure properties from standard tensile tests are not a good predictor of failure in creasing, where the length scale is considerably smaller. To investigate if there is an effect of the length scale, as the length gets smaller, tensile tests have been performed at different gauge lengths. The tensile tests were performed with a width of 15mm and the gauge length was varied in the range 3-100mm in MD and CD. The results from the tensile tests were, the failure strain and failure stress increased as the gauge length of the tests specimens decreased, both in MD and in CD. Initial stiffness decreased as the gauge length decrease (more notable in MD), and there was an increase in hardening at large strains with decreasing gauge length (more notable in CD). An analytical calculation of the reduction in measured stiffness as the gauge length get smaller was performed, where the decrease in stiffness deemed to be strongly related to the out-of-plane shear modulus. By fitting the analytical solution the experimental data the shear modulus was approximated to 60MPa. The shear modulus has been measured for the same paperboard to 70±23MPa. Simulations of the tensile tests at 5mm did fit the experimental data when the material model was calibrated from the tensile test at 100mm, except the increase in hardening at large strains in CD. It was noted that it was important to use the shear modulus that was inversely calculated by the analytical calculations to get the right initial slope of the simulations of the 5mm tensile tests. Creasing simulations were performed of a test setup of the creasing procedure. The male die was lowered 0.3mm to perform the creasing, which in the tests setup do not result in failure in the material. From the simulations the stress at the bottom of the paperboard during creasing exceeded the failure stress from the tensile test performed at 100mm. The stress during creasing was biaxial, it has stresses both in MD and CD, with is different compared to the uniaxial tensile tests at 100mm. The stress from the creasing simulation in CD was at a maximum of 40MPa where the 3mm tensile tests in CD resulted in a failure stress at 39MPa. The maximum stress in the MD creasing simulation was 96MPa, where the 3mm tensile test resulted in a failure stress at 69MPa. The properties from a long span tensile test are not good predictors of failure in creasing, where both stress state and length scale are very different. The failure stress at 3mm tensile tests in CD is close to the maximum stress from creasing simulations, and may be a good indication of failure. The 3mm tensile test in MD resulted in a considerably lower failure stress than the maximum stress in the creasing simulations, which indicates that the 3mm long tensile test is not a good predictor of failure in MD for creasing, where the length scale is even smaller.

The growth and survival of the psychrotroph Penicillium spinulosum in paperboard was studied along with the wicking characteristics of ultra-pasteurized milk to understand sporadic fungal contamination of ultra-pasteurized, extended shelf life milk products. Previous research has indicated paperboard packaging as a potential source for the fungal contamination. Migration from paperboard to ultra-pasteurized skim milk during a 60-day shelf life, was investigated by inoculating condia (spores) into sterilized paperboard squares (57.2 by 57.2 mm) made from ultra-pasteurized milk cartons. Test-squares were sealed on three sides and inoculated at 3.2, 6.4, 9.5 and 12.7 mm from the uncoated (unskived) edge. The surrounding milk was tested for the presence of the fungus. Penicillium spinulosum was detected in 84% of samples at 3.2, 72% at 6.4, 50% at 9.5, and 28% at 12.7 mm from the uncoated edge. Survival in paperboard was investigated in sealed paperboard test-squares incubated in ultra-pasteurized skim milk at 7°C every 10 days up to 60 days. Penicillium spinulosum survived in the interior of paperboard for the entire incubation period. Survival was also measured on all test-squares for which P. spinulosum was not detected in the surrounding milk in the migration study. Penicillium spinulosum was detected in 94.4% of all negative samples. The wicking characteristics of ultra-pasteurized skim and whole milk were measured in four boards from gable-top cartons for ultra-pasteurized milk products. Test-squares were sealed on 3 sides and incubated in ultra-pasteurized skim or whole milk at 7°C. Wicking distances were measured every 10 days up to 60 days. A significant interaction was seen between the types of paperboard and milk. It is most likely that P. spinulosum at all inoculation distances had access to milk as a source of nutrition by day 40 in the migration study. / Master of Science

No description available.

Thesis (M.S. in P.S. & E)--School of Chemical Engineering, Georgia Institute of Technology, 2004. Directed by Howard (Jeff) Empie. / Includes bibliographical references (leaves 80-82).