Bridging length scales in the analysis of transient tests for metallic materials
01 Jan 2019-Journal of Engineering Materials and Technology-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 141, Iss: 1, pp 014501
TL;DR: In this paper, the authors attempted to modify a recently proposed stress relaxation model with additional coefficients to accommodate the mechanical behavior at different length scales by using a tensile testing machine, whereas the micro- and nanoscale specimens were tested using indentation technique.
Abstract: The transient data obtained during stress relaxation test of polycrystalline materials has broader implications. The test is influenced by the material length scale. Efforts to mathematically bridge data at different length scales is scarce. In the present work, it is attempted to modify a recently proposed stress relaxation model with additional coefficients to accommodate the mechanical behavior at different length scales. The macroscale stress relaxation test was performed using a tensile testing machine, whereas the micro- and nanoscale specimens were tested using indentation technique. Assuming power law rate behavior, a scaling relation is derived initially to correlate the indentation pressure and flow stress.
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TL;DR: In this article, the authors review the current understanding of the mechanics governing elastic-plastic indentation as they pertain to load and depth-sensing indentation testing of monolithic materials and provide an update of how they now implement the method to make the most accurate mechanical property measurements.
Abstract: The method we introduced in 1992 for measuring hardness and elastic modulus by instrumented indentation techniques has widely been adopted and used in the characterization of small-scale mechanical behavior. Since its original development, the method has undergone numerous refinements and changes brought about by improvements to testing equipment and techniques as well as from advances in our understanding of the mechanics of elastic–plastic contact. Here, we review our current understanding of the mechanics governing elastic–plastic indentation as they pertain to load and depth-sensing indentation testing of monolithic materials and provide an update of how we now implement the method to make the most accurate mechanical property measurements. The limitations of the method are also discussed.
6,616 citations
Book•
29 Jun 2011
TL;DR: Experimental Charecterization of Dislocation Mechanisms, Interactions between Dislocations and Small-size Obstacles, Frictional Forces in Metals and Alloys, Experimental Studies of Peierls-Naborro-type Friction Forces in METALS and Alloy, The Peierl-Nabarro Mechanisms in Covalent Crystals.
Abstract: Experimental Charecterization of Dislocation Mechanisms, Interactions Between Dislocations and Small-size Obstacles, Frictional Forces in Metals, Dislocation Cross-slip, Experimental Studies of Peierls-Naborro-Type Friction Forces in Metals and Alloys, The Peierl-Nabarro Mechanisms in Covalent Crystals, Dislocations Climb, Dislocation Multiplication, Exhaustion and Work Hardening, Mechanical Behaviour of some ordered intermetallic
562 citations
TL;DR: In this article, the deformation of a creeping half-space with uniaxial stress-strain behavior is investigated, where the shape of the punch is described by most indenter profiles of practical importance.
Abstract: The aim of this paper is to establish a rigorous theoretical basis for interpreting the results of hardness tests on creeping specimens. We investigate the deformation of a creeping half-space with uniaxial stress-strain behaviour ⋵ = ⋵ 0 (σ/σ 0 ) m , which is indented by a rigid punch. Both axisymmetric and plane indenters are considered. The shape of the punch is described by a general expression which includes most indenter profiles of practical importance. Two methods are used to solve the problem. The main results are found using a transformation method suggested by R. Hill. It is shown that the creep indentation problem may be reduced to a form which is independent of the geometry of the punch, and depends only on the material properties through m . The reduced problem consists of a nonlinear elastic half-space, which is indented to a unit depth by a rigid flat punch of unit radius (in the axisymmetric case), or unit semi-width (in the plane case). Exact solutions are given for m = 1 and m = ∞. For m between these two limits, the reduced problem has been solved using the finite element method. The results enable the load on the indenter and the contact radius to be calculated in terms of the indentation depth and rate of penetration. The stress, strain and displacement fields in the half-space may also be deduced. The accuracy of the solution is demonstrated by comparing the results with full-field finite element calculations. The predictions of the theory are shown to be consistent with experimental observations of hardness tests on creeping materials reported in the literature.
308 citations
TL;DR: In this article, a unified elastic-viscoplastic constitutive model based on dislocation density considerations is proposed, which combines a combination of a kinetic equation, which describes the mechanical response of a material at a given microstructure in terms of dislocation glide, and evolution equations for internal variables characterising the micro-structure.
225 citations
148 citations