ACME Example

ACME manufacturing has implemented an accelerated life testing program for their new product design. A total of 40 units were tested at four different pressure levels. The operating stress level is 170 psi. The following table shows the data from the test. Determine the parameters of the inverse power law Weibull model and obtain the use level probability plot with 90% 2-sided confidence bounds on time.

Stress Level, psi	220 psi	230 psi	240 psi	250 psi
	165	93	72	26
	177	106	73	44
	238	156	99	63
	290	170	124	68
Times-to-failure, hr	320	185	134	69
	340	214	150	72
	341	220	182	77
	380	236	186	96
	449	252	190	131
	544	288	228	140

The parameters of the IPL-Weibull model are estimated to be:

The use level probability plot is shown next.

The probability plot at a use stress level.

In ALTA, the confidence bounds on time are the Type 1 bounds (Time Bounds).

The probability plot at a use stress level with 90% Type I confidence bounds.