Deformation Limit
Strain capacity at the onset of plastic deformation establishes the physical limit before paper fibers experience irreversible inter-fibre bond failure under tension or compression. Exceeding the yield strain threshold permanently alters the dimensional stability and structural stiffness of paperboard packaging components during folding or scoring operations. Stress-strain curves derived from tensile testing identify this boundary where elastic recovery transitions into permanent deformation.
Mechanical Behaviour
Tensile stress applied beyond this elastic limit rearranges cellulose microfibrils within fiber walls, creating permanent elongation. When converted packaging exceeds its yield strain threshold during high-speed scoring or embossing, micro-cracks form along the score line, weakening corner post strength. Board moisture content significantly alters yield behavior, as absorbed water molecules lubricate inter-fibre bonds and shift the transition point toward higher strain percentages.
High-density linerboards exhibit distinct yield behavior compared to high-bulk recycled medium, requiring tailored forming parameters on carton erecting lines. Starch additions and fiber refining increase inter-fiber bonding, raising the force required to initiate plastic yield across the web.
Structural Boundary
Dynamic loading rates in drop testing subject containerboards to strain rates that exceed standard quasi-static laboratory tests. When high impact forces push packaging beyond the yield strain threshold, permanent creasing and structural buckling compromise box integrity. Designing within elastic limits prevents progressive carton sagging during long-term warehouse storage.
