Study On Fatigue Performance Of Corrugated Paperboard

The fatigue properties of corrugated board were studied in this thesis.Three-point bending fatigue test was conducted to investigate the bending fatigue behavior of B-flute and C-flute corrugated paperboard under cycle loading.The S-N curves were obtained.The fatigue failure of corrugated paperboard may be described by both Basquin type and exponential type S-N curves,however the exponential type S-N curve is more appropriate.The stiffness is gradually degraded with almost same energy dissipation in most stress cycles,but it decreases abruptly with the enlarged energy dissipation when the testing cycle is very close to the ultimate cycles of fatigue failure.The corrugated board deforms constantly under the action of cycle loading,and no visible crack appears.The crushing of the flute generates near the front linerboard after a certain number of loading cycles,then spreads along the corrugated board thickness direction,and the fibers in the back linerboard are stretched to broken.The plastic deformation is accumulated continuously in the corrugated paperboard,and the ability to resist the fatigue load is gradually weakened until the ultimate bending fatigue failure takes place.The static mechanical properties and fatigue properties of corrugated board were also studied in the thesis.At 23 degrees Celsius,corrugated paperboard specimens were processed in constant humidity(relative humidity is 50%)environment and two cyclic humidity(relative humidity are 50%-70%-50% and 50%-90%-50%)environment and then the static mechanical properties and fatigue performance were studied experimentally.The edgewise crush resistance,adhesive strength,bending strength,elastic modulus,bending fatigue life and stiffness degradation of the specimens were obtained.Compared with the results corresponding to constant humidity environment,the edgewise crush resistance of the specimens decreased by 2.75% and 14.31%,respectively,corresponding to cyclic relative humidity of 50%-70%-50% and 50%-90%-50%,and the adhesive strength decreased by 3.72% and 1.15%,the bending strength decreased by 5.32% and 10.74%,the elastic modulus decreased by 6.0% and 12.8%,respectively,and the bending fatigue life decreased by 8.18% and 51.92%,respectively.According to the experimental results,the mechanical properties of corrugated board are irreversible and dropped to different extents in the process of humidity cycles compared with the results of specimens in constant humidity environment.Corrugated paperboard is more sensitive to cycles with relative humidity of 50%-90%-50% than relative humidity of 50%-70%-50% and its dynamic fatigue performance is more sensitive to cyclic humidity conditions than static properties do.The fatigue life data of corrugated paperboard and random load spectrum were used to evaluate the fatigue properties by finite element simulation method in this paper.From the simulation results,the failure mode of corrugated box is basically consistent with the actual test process.The rigidity of corrugated box kept decreasing during random vibration excitation and the wrinkling was first appeared in the corners of the corrugated box when the stiffness was reduced to a certain extent.And then the wrinkling was extended to the panels until the corrugated box was completely buckling.The finite element simulation also obtained the local fatigue life of corrugated box.The minimum fatigue life were 0min,52.82 min and 131.6min corresponding to the three vibration levels.The local fatigue life obtained were actually smaller than that in the real environment cause the failure of corrugated box is a cumulative process.