It is seen from the table that tensile strength change after
50-h UV treatment is not evident. One may imagine that
short period of UV irradiation has no obvious influence
on the tensile property of the material.
Table 3 presents the statistic analysis results when data
of 0 and 170-h UV treatment are selected for the 2-layer
samples.
The analysis shows that after 170-h UV radiation, the
reduction of the tensile strength is evident. This is due in
great part to the reaction between the UV ray and the corresponding
molecular bonds of the material. Prolonged
irradiation weakens or breaks corresponding bonds. Calculation
for the 2-layer sample with 200-h treatment was also
conducted, the tensile strength reduction is also proved to
be significant, for simplicity, the data are not shown in
the paper.