Tj. Royston et R. Singh, EXPERIMENTAL-STUDY OF A MECHANICAL SYSTEM CONTAINING A LOCAL CONTINUOUS STIFFNESS NONLINEARITY UNDER PERIODIC EXCITATION AND A STATIC LOAD, Journal of sound and vibration, 198(3), 1996, pp. 279-298
Local stiffness non-linearities under dynamic (periodic) and static (t
ime-invariant) loads exist in many complex mechanical systems, oftenti
mes at the junctions of assembled components. Unlike in linear systems
, a static load may significantly alter the nature of the non-linearit
y and dynamic response, in terms of amplitude, frequency content and s
tability. To examine such phenomena, a controlled laboratory experimen
t with a local continuous stiffness non-linearity has been designed, f
abricated, instrumented and analyzed. It consists of a flexible suppor
t structure in the form of a simply supported beam and a rigid body mo
unted on the support structure by a multi-dimensional non-linear ''har
dening'' spring element. The non-linear elastic element is made of a v
ery thin beam clamped between tapered ends. Multi-harmonic, amplitude-
dependent, frequency-sweep-direction-dependent periodic responses to s
lowly swept harmonic excitation were measured by using order tracking
with a dynamic signal analyzer. It was found that the static load indu
ces the ''hardening'' stiffness element to behave like a ''softening''
spring under certain conditions. The cause of this is explained via t
heoretical studies of a simple single-degree-of-freedom non-linear osc
illator and a more complex model of the experimental system itself. Ex
perimental and theoretical studies of the multi-degree-of-freedom, mul
ti-dimensional test system also showed that the local non-linearity ha
s a broad spectral and spatial influence on the dynamic behavior of th
e overall system. For instance, it alters the characteristics of sever
al system resonances and modes. (C) 1996 Academic Press Limited