When strength degenerates, reliability decreases with time more obviously, and the failure rate has the feature of a bathtub curve.

As the Stirling cryocoolers' reliability is at foreside of bathtub curve, the earlier failure problem of refrigerator, which results from manufacture and assembly process, should be solved.

The oil flow rate distribution curve mainly has an "S" shape, and the heat transfer rate shows a "bathtub" distribution.