Yielding of engineering polymers at strain rates of up to 500 s-1

A method is described for measuring the mechanical properties of polymers in compression at strain rates in the range approximately 300-500 s-1. A gravity-driven pendulum is used to load a specimen on the end of an instrumented Hopkinson output bar and the results are processed by a microcomputer. Stress-strain curves up to high strains are presented for polycarbonate, polyethersulphone and high density polyethylene over a range of temperatures. The value of yield stress, for all three polymers, was found to vary linearly with log (strain rate) at strain rates up to 500 s-1. © 1985.

Distributed optical fiber strain sensing in a secant piled wall

An optical fiber strain sensing technique, based on Brillouin Optical Time Domain Reflectometry (BOTDR), was used to obtain the full deformation profile of a secant pile wall during construction of an adjacent basement in London. Details of the installation of sensors as well as data processing are described. By installing optical fiber down opposite sides of the pile, the distributed strain profiles obtained can be used to give both the axial and lateral movements along the pile. Measurements obtained from the BOTDR were found in good agreement with inclinometer data from the adjacent piles. The relative merits of the two different techniques are discussed. © 2007 ASCE.