Abstract
A key limitation of current moderate and high strain rate test methods is the need for external force measurement. For high loading rate hydraulic machines, ringing in the load cell corrupts the force measurement. Similarly, the analysis of split-Hopkinson bar tests requires the assumption that the specimen is in a state of quasi-static equilibrium. Recently, image-based inertial test methods have shown that external force measurement is not required if full-field measurements are available and inertial effects are significant enough. In this case the load information is provided by the acceleration fields which are derived from full-field displacement measurements. This article describes a new image-based inertial test method that can be used for simultaneous quasi-static and high strain rate stiffness identification on the same test sample. An experimental validation of the new test method is provided using PMMA samples. A major advantage of this new test method is that it utilises a standard tensile test machine and the only specialist equipment that is required is an ultra-high speed camera.
Highlights
In many engineering applications materials are subjected to dynamic loads
A similar problem occurs for brittle materials which can fail before the inertial effects have damped out corrupting the force measurement
There is a need for new test methods that can be used to investigate the elastic response of materials at high strain rates
Summary
For cases where materials are subjected to dynamic loads it is necessary to account for any strain rate dependent properties in the design. When using fast hydraulic or drop tower machines ringing from wave reverberation in the load cell corrupts the force measurement. For low wave speed materials a significant amount time is taken for multiple wave reverberations to occur eventually causing inertial effects to damp out. This means the usable portion of the test occurs after the specimen has already undergone significant elastic deformation making it difficult to accurately measure the stiffness of the material [1]. There is a need for new test methods that can be used to investigate the elastic response of materials at high strain rates
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