Dain S J
School of Optometry, University of New South Wales, Kensington, Australia.
Am J Optom Physiol Opt. 1988 Jul;65(7):585-90. doi: 10.1097/00006324-198807000-00009.
The procedure of applying pressure to a lens until fracture occurs and the use of the fracture pressure as a measure of lens strength has been proposed as a quantitative alternative to the drop ball test. The fracture pressure or pressure resistance of untempered, thermally tempered, and chemically tempered glass lenses and CR39 lenses were compared. The results for the glass lenses were consistent with workplace experience and previous studies using the drop ball test. The results for glass and CR39 lenses showed the reverse to what was expected. In order to investigate the basis of this difference, a second procedure was followed in which the annulus supporting the lens and the steel ball applying the pressure to the lens were systematically changed. Glass lenses showed a highly statistically significant change in fracture pressure with decreasing ball size and a small but statistically significant change with annulus size. CR39 lenses showed no statistically significant change in fracture pressure with changing ball size but a highly statistically significant increase in fracture pressure with increasing annulus size. The mechanism of fracture is known to differ in the glass and plastics materials and it is concluded that this method should not be used to compare the performance of different materials.
有人提出，对镜片施加压力直至其发生破裂，并将破裂压力用作镜片强度的一种度量，以此作为落球试验的一种定量替代方法。对未回火、热回火和化学回火的玻璃镜片以及CR39镜片的破裂压力或耐压性进行了比较。玻璃镜片的结果与工作场所经验以及先前使用落球试验的研究结果一致。玻璃镜片和CR39镜片的结果与预期相反。为了研究这种差异的原因，采用了第二种方法，其中系统地改变了支撑镜片的环形圈和对镜片施加压力的钢球。玻璃镜片的破裂压力随着球尺寸的减小呈现出高度统计学显著的变化，随着环形圈尺寸的变化呈现出小但统计学显著的变化。CR39镜片的破裂压力随着球尺寸的变化没有统计学显著变化，但随着环形圈尺寸的增加呈现出高度统计学显著的增加。已知玻璃和塑料材料的破裂机制不同，得出的结论是，这种方法不应被用于比较不同材料的性能。
