The shape of the wave for the control signal versus time must be kept constant during all the process. (exception: when we want to know the influence of this parameter). The standards say that if there is no specific requirement about the wave shape, it is better to use a triangular one because the strain rate is constant.
While the test is being performed, it is necessary to control at least one variable (stress, strain, load, displacement or other suitable parameter). To define the test, it is necessary to indicate the parameter control and its characteristics.
The standard says that for the low cycle tests, the parameter control must be the axial strain amplitude, although it is also possible to use the axial plastic strain.