Obtaining Viscoelastic Properties from Instrumented Indentation
Instrumented indentation is a powerful tool for probing small-scale mechanical behaviors of “soft” materials, such as polymers, composites, and biomaterials [1-3]. Since many soft materials deform viscoelastically, it is important to develop robust analysis methods for obtaining viscoelastic properties from indentation measurements. Extending the early work by such pioneers as Lee , Radok , Lee and Radok , Hunter , Gramham , and Ting , a number of authors have recently proposed methods for determining viscoelastic properties from indentation measurements [10-33]. In this presentation, we will discuss our recent results on modeling instrumented indentation in linear viscoelastic solids [34-40]. We will first examine the relationships between initial unloading slope, contact depth, and viscoelastic properties for various loading conditions, including load- or displacement-control [35-37]. We will then discuss several commonly used methods, such as the "hold-at-peak-load" and "hold-at-the-maximum-depth" techniques . We will also evaluate methods for obtaining storage and loss modulus using dynamic indentation using either spherical or pyramidal indenters . Furthermore, we will discuss a set of newly proposed methods for measuring shear relaxation modulus and creep compliance using axisymmetric indenters of power-law profiles . Results on indentation in viscoplastic solids will also be presented. These investigations may help improve instrumented indentation techniques for measuring mechanical properties of soft materials.
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