A modified laser occlusive extensometer technique was developed to measure the specimen strain with reasonably high and tunable resolutions in Kolsky tension bar experiments. This new technique used a novel concept where a laser beam was split into two independent sections to track the displacement histories of the incident and transmission bar ends, respectively, with independent resolutions. This technique ensures highly precise small strain measurements without sacrificing the capacity for large strain measurement. The uncertainty caused by rigid body motion of the specimen during dynamic strain measurement, which is induced by slight variation of laser intensity along the gage length, was also minimized in this technique. The validation test on Vascomax Ò maraging C250 alloy demonstrated that the new technique was capable of making both small and large strain measurements in Kolsky tension bar experiments, which is also applicable to Kolsky compression bar experiments.

This paper presents the experimental measurements of a highly magnetoelastic material (Galfenol) under impact loading. A Split-Hopkinson Pressure Bar was used to generate compressive stress up to 275 MPa at strain rates of either 20/s or 33/s while measuring the stress-strain response and change in magnetic flux density due to magnetoelastic coupling. The average Young's modulus (44.85 GPa) was invariant to strain rate, with instantaneous stiffness ranging from 25 to 55 GPa. A lumped parameters model simulated the measured pickup coil voltages in response to an applied stress pulse. Fitting the model to the experimental data provided the average piezomagnetic coefficient and relative permeability as functions of field strength. The model suggests magnetoelastic coupling is primarily insensitive to strain rates as high as 33/s. Additionally, the lumped parameters model was used to investigate magnetoelastic transducers as potential pulsed power sources. Results show that Galfenol can generate large quantities of instantaneous power (80 MW=m 3 ), comparable to explosively driven ferromagnetic pulse generators (500 MW=m 3 ). However, this process is much more efficient and can be cyclically carried out in the linear elastic range of the material, in stark contrast with explosively driven pulsed power generators. V C 2015 AIP Publishing LLC. [http://dx.

No abstract

No abstract

For many years there have been controversial opinions on the value of dynamic tensile data obtained through the Kolsky bar spall tension technique. This is primarily due to the experimental conditions (i.e., specimen stress state and strain rate) not being well defined for these types of tests, thus making data interpretation and comparisons difficult. In this paper, a new spall theory is presented that ensures constant strain rate deformation while maintaining a uniform tensile stress within a large portion of the specimen. In light of this theoretical framework, pulse shaping was carefully designed to experimentally obtain this solution in Kolsky bar experiments. The incident wave generated under the guideline of the new theory has shown promising results for better refined Kolsky bar spall tension experiments on brittle materials.