There are three main causes of failure for filament bulbs:
- Evaporation of the filament. The more voltage you put across the bulb, the more current will flow through the filament. The more current that flows through, the more heat and brightness in the bulb, causing the filament to evaporate faster and fail. (see chart)
- Heating/cooling cycles will also add mechanical stress on the filament. This can be done by turning the bulb on and off at some duty cycle to allow it to heat and cool.
- High current inrush can also make a bulb fail early. Inrush is when the bulb is switched on and the bulb driver produces a very abrupt voltage transition.
The above image (source) was in reference to halogen lamps, but the failure/brightness curves should be the about same shape as for filament bulbs in general.
Burning out the bulb
Overvolting the bulb seems like the most straightforward way to cause controlled yet random failures. By this method you can control the lifespan of the bulb from months to seconds, depending on the voltage you set. The further above the bulb's specified voltage rating, the quicker it will fail. With a variable trasformer, you can easily dial in the voltage and approximate lifespan of your bulbs. (image source)
Heat cycling can't give you this kind of control, and generating precise inrush current is needlessly complex for your application.
One of the things that makes it so hard to predict the lifespan of the filament is that very small imperfections or defects in filament can have a dramatic affect of lifespan:
Small variations in resistivity along the filament cause "hot spots"
to form at points of higher resistivity; a variation of diameter
of only 1% will cause a 25% reduction in service life. The hot
spots evaporate faster than the rest of the filament, increasing
resistance at that point—a positive feedback that ends in the familiar
tiny gap in an otherwise healthy-looking filament.