As one of the studies of mechanical properties of paper for heavy duty paper sack, correlations between mechanical properties of paper and service strength of paper sack have been shown in other reports.
In this paper the distribution of dropping times at failures of sacks is required and changes of failure probability of sacks with dropping times are investigated.
And relationships between the failure probability of sacks and average dropping times at failures of sacks are studied.
As a result of this, it was found that failure probability of sacks μ (ν) increased proportionally with dropping times v based on fatigue phenimena except on sewn parts of sewn type paper sacks. It was expressed by the formula, μ (ν) =aν, provided that a is a constant depending on the strength of the paper and the conditions of drop test.
Furthermore at this time average dropping times ν at failures of sacks was expressed by the formula
ν=√π/2a
On the other hand several examples were investigated about failures on the sewn parts of sewn type heavy duty paper sacks.
But it was not able to decide whether failure probability of sacks increased proportionally with dropping times or it was constant independent on dropping times.
When failure probability, μ (ν) was a constant μ0, average dropping times ν at failures of sacks was expressed by the formula ν=1/μ0