Modeling Acceleration for Failure Mode Control Variables

Base variables are independent of failure mode (i.e., they are a property of the Function or Action element). FMCVs, however, are specific to each of the element's failure modes. The FMCV for a particular failure mode is computed by applying a specified Initial Value and an Acceleration Factor to the base variable.

That is, these two parameters, along with the base variable (which is independent of the failure mode), are used to compute the FMCV, which is specifically applied for each particular failure mode:

FMCV(t) represents the value for the FMCV at time t. The sum is made over all the timesteps from the beginning of the realization (or the time the FMCV was reset) to time t.

Hence, the Acceleration Factor field is available for all FMCV-based failure modes.

The acceleration factor is a non-negative real number which multiplies the actual change in the base variable to arrive at the failure mode’s current "age". Setting this value to a number less than one means the component will age slower than normal (failure is decelerated), and setting it to a number greater than one will cause the component to age faster than normal (failure is accelerated).

For example, we might have a component which ages twice as fast when it operates in ambient temperatures of greater than 40 degrees Celsius.

To represent this, we would specify the following expression in the Acceleration Factor field:

The Acceleration Factor can also be used to predict how a system will perform in accelerated testing, or used along with accelerated failure data to predict the performance of a system in a regular duty cycle.

While the acceleration factor can be a function of time, it is important to note that the acceleration factor is only updated when the model is updated (model updates occur at timesteps and when certain events occur).

Acceleration factors will often be defined as functions of locally available properties such as operating time or total time. For example, you may want to accelerate failure after the component has been operating for 1 month. These variables are available as locally available properties within the Acceleration Factor input field.

Note: Although exponential failure modes are memoryless (i.e., they have a constant hazard function), they do support the use of acceleration. When used with an Exponential/Poisson failure mode, the specified failure rate is multiplied by the acceleration factor. So if an acceleration factor of 3 is specified, and a failure normally occurs 5 times per year, GoldSim will use a failure rate of 15 yr-1.