Test method

摘要

A method of testing a shape memory alloy (SMA) actuated device includes cyclically operating the device. The method further includes determining a number of cycles in a functional life of the device based on observations of the device during the cyclical operation. The functional life is a range of consecutive cycles of operation of the device beginning with a first cycle during which the device performs within a specified limit. The functional life is immediately followed by a cycle during which the device performs outside of the specified limit. The method still further includes applying a progressive substitution sub-process to identify an opportunity to increase the number of cycles in the functional life of the device.

主权项

1. A method of testing a shape memory alloy (SMA) actuated device, the method comprising:
cyclically operating the device; determining a number of cycles in a functional life of the device based on observations of the device during the cyclical operation wherein the functional life is a range of consecutive cycles of operation of the device beginning with a first cycle during which the device performs within a specified limit, the functional life immediately followed by a cycle during which the device performs outside of the specified limit; and applying a progressive substitution sub-process to identify an opportunity to increase the number of cycles in the functional life of the device, wherein the progressive substitution sub-process includes:
modifying the device by substituting a modified SMA actuator for the unmodified SMA actuator to operate the modified device wherein:
the modified SMA actuator has a displacement from an unactuated state to a fully actuated state; andthe modified SMA actuator has a reduced length of SMA material relative to an original length of SMA material in the unmodified SMA actuator to cause a strain acceleration factor compared to the unmodified SMA actuator operating in the device;determining a predicted life by predicting a number of cycles to cause the modified device to perform outside of the specified limit based on the number of cycles in the functional life of the device and based on a predetermined relationship between strain and actuation cycles for the SMA material;cyclically operating the modified device;determining a test life wherein the test life is a range of consecutive cycles of operation of the modified device beginning with a first cycle during which the modified device performs within a specified limit immediately followed by a cycle during which the modified device performs outside of the specified limit;comparing the predicted life to the test life;if the predicted life is within a predetermined tolerance of the test life, concluding that the opportunity to increase the number of cycles in the functional life of the device is based on reducing a steady-state stress on the SMA actuator in the device;if the test life is within a second predetermined tolerance of the functional life:
concluding that a component other than the SMA actuator causes a stroke incompatibility;determining a solution for the stroke incompatibility by:
substituting progressively shorter lengths of the SMA material in a series of SMA actuators for cyclical operation in a series of the modified devices until determining a final length of SMA material in a final SMA actuator that first causes a final device to perform outside of the specified limit on a first cycle; andconcluding that a stroke is 4.5 percent of the final length; andidentifying the opportunity to increase the number of cycles in the functional life to a target life by determining a target stress based on the stroke and the original length of the SMA material based on the number of cycles in the target life of the device and based on a predetermined relationship between stress, strain and actuation cycles for the SMA material.