QCP Calculations for Accelerated Life Testing

Calculates the probability that a new product will operate without failure for a given period of time at the stress level specified in the Stress field. Enter the time at which you wish to calculate the reliability in the Mission End Time field. The mission is assumed to start at time = 0.

For example, a reliability of 90% for a mission end time of 3 years means that if 100 identical units are fielded, then 90 of them will still be operating at the end of 3 years.

Calculates the probability that a new product will be failed in a given period of time at the stress level specified in the Stress field. Enter the time at which you wish to calculate the probability of failure in the Mission End Time field. The mission is assumed to start at time = 0.

Probability of failure is also known as unreliability, and it is the inverse of the reliability. For example, a probability of failure of 10% for a mission end time of 3 years is equivalent to a 90% reliability.

Calculates the probability that a product will successfully operate at a specific time interval given that it has operated successfully up to a specified time and at the stress level specified in the Stress field. Enter the start time of the interval in the Mission Start Time field and enter the duration of the interval in the Mission Additional Time field.

For example, a product may have a reliability of 90% for 3 years if it operates at a stress level of 10 volts. If the product has operated for 2 years without failure, the conditional reliability for an additional year (for a total of 3 years of operation) may be 95%.

Calculates the probability that a product will be failed at a specific time interval given that it has not failed up to a specified time and at the stress level specified in the Stress field. Enter the start time of the interval in the Mission Start Time field and enter the duration of the interval in the Mission Additional Time field.

For example, a product may have a 10% probability of failure for 3 years if it operates at a stress level of 10 volts. If the product has operated for 2 years without failure, the conditional probability of failure for an additional year (for a total of 3 years of operation) may be 5%.

Calculates the estimated time at which a specified reliability value will be achieved at the stress level specified in the Stress field. Enter the reliability goal in the Required Reliability field. For example, a goal of 90% reliability with a reliable life of 4 years means that if 100 identical units are fielded, then 90 of them will be still be operating at the end of 4 years.

Calculates the estimated time at which a specified probability of failure will be achieved at the stress level specified in the Stress field. Enter the probability of failure in the BX% Life At field. For example, a B10 life of 4 years means 10% of the fielded units are expected to be failed at the end of 4 years of operation (note that this is equivalent to a 90% reliability with a reliable life of 4 years).

Note: In the early days of reliability engineering, bearing manufacturers used the term "B10 life" to refer to the time by which 10% of the components would fail. Keeping with tradition, ReliaSoft retained this nomenclature but replaced "10" with "X%," since the software allows you to get this information at any percentage point and not just at 10% (e.g., B1 life, B5 life, etc.).

Calculates the average time at which a product is expected to operate before failure at the stress level specified in the Stress field. In the life-stress data folio, the mean life is the mean time to failure (MTTF) based on the fitted model.

Note: The term mean time to failure (MTTF) is used as a metric for the analysis of non-repairable components. In the Accelerated Life Testing life-stress data folio, all data are assumed to come from non-repairable components that are independent and identically distributed (i.i.d.). On the other hand, the term mean time between failures (MTBF) is used as a metric in repairable systems analysis, where the same system may fail and be repaired multiple times. Simple repairable system data can be analyzed in Weibull++ using the Recurrent Event Data Analysis (RDA) folio.

For more complex repairable system analyses, see ReliaSoft’s BlockSim.

Calculates the expected remaining life given that the product, component or system has survived to time t at the stress level specified in the Stress field. Enter the time at which you wish to calculate the mean remaining life in the Mission End Time field.

Calculates the instantaneous number of failures per unit time that can be expected at a certain time and at the stress level specified in the Stress field, given that a unit survives to that age. Enter the time at which you wish to calculate the failure rate in the Mission End Time field.

For example, a failure rate of 0.01 at 100 hours and at a stress level of 10 volts means that each unit that survives to 100 hours has approximately a 1% probability of failure in the next hour.

Calculates the ratio of the product's use level life to its life at an accelerated stress level. For example, if the product has a life of 100 hours at the use stress level, and it has a life of 50 hours at an accelerated level, then the acceleration factor at the specified stress levels would be 2. Click the arrow in the Stress field to enter the use level stress values for every stress that was used to calculate the data sheet. Click the arrow in the Accelerated Stress field to enter the accelerated stress values.

Calculates the specified bounds on the parameter estimates, allowing you to quantify the amount of uncertainty in those estimates. This option is available only when you have specified the type of confidence bounds to use from the Bounds drop-down list. When you click Calculate, the Results Window will open to display the estimated parameters and their bounds.