Rate-dependent tensile properties of paperboard and its plies

Tensile properties of paperboard have been characterized, and it has been shown that paper tensile properties are dependent on the strain rate. Tensile testing was done using strain rates in the range 10(-4)-3 s(-1), which corresponds to crosshead movements ranging from 1 up to 24,000 mm/min, using an electro-mechanical testing machine. Two paperboards, and its free-laid top, middle and bottom plies were characterized in MD and CD. The testing was limited by the maximum crosshead speed of the testing machine. Initially 50 mm (grip to grip) long samples were tested, but to test even higher strain rates also short samples with length of 5 mm were tested. The results showed that ultimate strength increased by 9 % per decade increasing of testing rate, and Young's modulus increased by 7 %. This shows that the previously reported rule of thumb of 10 % increase of in-plane strength per decade increase of strain rate holds. The testing here shows that this is valid also at strain rates as high as 3 s(-1). Moreover, the strain at break in CD for long tensile specimens was observed to decrease when the strain rate exceeded 0.1 s(-1), which resulted in straighter crack paths.