Table 2. Static Spring Constants for Compression aging

Aging time (h)	Static spring constant (kN/mm)
	Standard method			Modified method
	70°C	85°C	100°C	70°C	85°C	100°C
0	1.546	1.546	1.546		-
24	1.533	1.607	1.947	1.558	1.640	1.732
120	1.605	1.943	2.580	1.597	1.764	2.308
240	1.747	2.285	2.700	1.671	2.022	2.424
480	1.876	2.620	2.580	1.744	2.310	2.550
720	1.955	2.784	3.109	1.808	2.542	2.885
1,000	2.008	2.896	3.336	1.868	2.637	3.136
2,000	2.094	2.737	3.797	1.921	2.676	3.357