Abstract
Dynamic behavior of materials is investigated using different devices. Each of the devices has some restrictions. For instance, the stress-strain curve of the materials can be captured at high strain rates only with Hopkinson bar. However, by using a new approach some of the other techniques could be used to obtain the constants of material models such as Johnson-Cook model too. In this work, the restrictions of some devices such as drop hammer, Taylor test, Flying wedge, Shot impact test, dynamic tensile extrusion and Hopkinson bars which are used to characterize the material properties at high strain rates are described. The level of strain and strain rate and their restrictions are very important in examining the efficiency of each of the devices. For instance, necking or bulging in tensile and compressive Hopkinson bars, fragmentation in dynamic tensile extrusion and petaling in Taylor test are restricting issues in the level of strain rate attainable in the devices.
Highlights
In dynamic tensile extrusion (DTE) proposed by Gray et al [19] several years ago, a spherical projectile is shot through an open conical die in which the exit diameter of the die is smaller than the sphere diameter, the projectile undergoes severe dynamic tension at high strain rates
Dynamic Tensile Extrusion (DTE) is mostly used for studying the fracture mechanism for determining the ductile to fracture transition in materials especially in polymers, it has been used by Bonora et al and a few others for adjusting some material models
A few techniques can be used for investigating fragmentation but dynamic tensile extrusion method is the best choice for this purpose
Summary
A wide variety of dynamic materials testing machines with different capabilities have been developed across the world. One of the earliest types of dynamic mechanical testing machines was built by Nadia and Manjoine [3]. In this machine, the flywheel rotates at a constant angular velocity. At the time of impact, a hammer which is supported by a spring is suddenly released and is engaged with the base of the specimen Another testing machine which is capable of producing a uniform strain rate is the cam plastometer [4]. An alternative dynamic tensile testing facility, known as the Flying Wedge, which is capable of generating strain rates from 102 s−1 up to in excess of 104 s−1, has been developed and used at Leeds University for several decades [8]
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