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Why monitor acoustic emissions during nanomechanical tests?
Čtvrtlík, Radim ; Václavek, L. ; Tomáštík, J.
Acoustic Emissions (AE) monitoring has been proved as an effective non-destructive technique at the macro scale. Nevertheless, it may also be employed at nano/micro scale during nanomechanical and nanotribological testing. Local mechanical properties of surfaces or micro object are routinely explored using nanoindentation, scratch test or dynamic impact tests that are evaluated based on analysis of depth-load-time records or microscopic observation of residual indents, scratch grooves or impact craters, respectively. Although these approaches have been proven to be sufficient in most cases for a variety of materials, there are many situations where they do not provide sufficient information for a complex understanding of the deformation response. On the other hand, analysis of AE signals generated during these tests may provide valuable complementary information and provide some insight into the dynamics of phenomena like cracking, phase transitions, plastic instabilities, etc.\n
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Evaluation of properties of pyrolysed resins
Halasová, M. ; Chlup, Zdeněk ; Strachota, Adam ; Černý, Martin ; Dlouhý, Ivo
The presented work describes mechanical properties of materials prepared by pyrolysis of polysiloxane resins. The polymeric precursors had different chemical composition. Materials under investigation are predetermined as a matrix for high temperature resistant long fibre composites. An instrumented hardness tester was employed for materials characterisation. The Vickers hardness, Martens hardness and indentation elastic modulus were the key parameters determined from the load-indentation depth curves. Influence of the mechanical properties on the ratio of T and D was established. Indents were observed by using confocal laser microscope.
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Modelling of nanoindentation of modern Nickel-based superalloys for turbofans
Hrubý, Zbyněk ; Plešek, Jiří ; Tin, S.
Stress and strain distribution underneath various types of indentors – spherical, conical, and Berkovich – can be provided by the finite element method. In the presented work, indentation of isotropic aluminium is introduced as a benchmark problem, in which plasticity and contact algorithms are tested. The knowledge obtained in this way passes on to the real-life indentation processes involving orthotropic materials such as FCC metals (Ni-based alloys) in the context of nonlinear continuum and finite strain elasto-plasticity, including homogenization approach on the material microscale.
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Modelling of micro and nano indentation of modern nickel-based superalloys for turbofans
Hrubý, Zbyněk ; Plešek, Jiří ; Tin, S.
Stress and strain distribution underneath various types of indentors – spherical, conical, and Berkovich – can be provided by the finite element method. In the presented work, indentation of isotropic aluminium is introduced as a benchmark problem, in which plasticity and contact algorithms are tested. The knowledge obtained in this way passes on to the real-life indentation processes involving orthotropic materials such as FCC metals (Ni-based alloys) in the context of nonlinear continuum and finite strain elasto-plasticity, including homogenization approach on the material microscale.
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Application of inverse FEM analysis for materials curve determination based on indentation test
Brumek, J. ; Strnadel, B. ; Dlouhý, Ivo
Study of instrumented indentation test is focused on prediction of the strain hardening behavior of the carbon steels. Indentation tests were applied on several steels samples. We proposed an improved technique to determine the plastic properties of material from the loaddisplacement curve from ball indentation test. The inverse finite element method was used for prediction of material properties. Results were found in good agreement with the data from conventional standard test. This non-destructive assessment of deformation behavior has good potential for the other materials.
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Instrumented indentation test used for mechanical properties determination
Brumek, J. ; Strnadel, B. ; Dlouhý, Ivo
Focusing on the materials with non-linear stress-strain behavior an instrumented indentation study is presented. Indentation tests were applied on steel R7T. The observed data were analyzed and mechanical properties, such as yield stress, strain hardening exponent and elastic modulus were assessed. Experimental results of load-depth (P-h) test were compared with FEM solution. FEM analysis was applied on two-dimensional model described by elastic-plastic elements. Presented method of prediction in mechanical characteristics is useful to judge deformations of steel and other materials under contact stressing. Experimental results of P-h relation and additional FEM analysis of indentation test provide very helpful information of mechanical behaviors in contact of two bodies.
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