Low-frequency resonance curves associated with non-linear internal friction

Computer-controlled electronic instrumentation to scan the amplitude/frequency and phase angle/frequency curves for a sample in a low-frequency pendulum is described. Examples are presented of both 'hard' and 'soft' resonant frequency curves associated with amplitude-dependent internal friction and dynamic elastic modulus changes. Using the data from much faster, simpler, free-decay experiments, it is shown that both the amplitude/frequency and phase angle/frequency curves can be calculated with good accuracy, despite the non-linearities involved