No abstract

A novel method for accurately measuring impact forces with small peak value and steep slope is proposed. In the method, a mass, which is levitated with a pneumatic linear bearing and hence encounters negligible friction, is made to collide with an object under test. The Doppler frequency shift of a laser beam reflecting from the mass is calculated by using an optical interferometer whose output signal waveform is recorded with a digitizer (i.e. a high-speed analogue-to-digital converter). The velocity, position, acceleration and inertial force of the mass are calculated from the measured varying frequency shift. The performance of the proposed method is demonstrated by evaluating the viscoelasticity of a small rubber block under an impact load with small peak value and steep slope.

An optical fibre based, speckle shearhg interferometer for out-of-plane time-averaged vibration analysis is described. The technique uses a h:ghly birefringent optical fibre to illuminate a test object with equal :ntens:ties of light guided by the orthogonal polarization eigenstates of the fibre. Phase modulation between the sheared images is read.ly achieved, w:thout mechanical movement of components, by sinusoidally strain modLlaling the relat.ve phase of the polarization states in the fibre. A Wollaston prism is used to obtain two sheared images with adjuslable shear.

An optical-fiber-based speckle shearing interferometer for an out-of-plane displacement derivative measurement is described. The technique uses a highly birefringent optical fiber to illuminate a test object with equal amounts of orthogonally polarized light, and the interferometer is readily phase stepped, without mechanical movement of components, by strain modulation of the relative phase of the polarization states in the fiber. A Wollaston prism is used to produce two sheared images with adjustable shear.