FAQ about the imprinting process

Here you will find a summary of the most frequently asked questions

General questions

The result is a flow curve. From this flow curve

  • RIp0.2 Comparative yield strength to tensile test
  • RIm Comparative tensile strength to tensile test
determined.

It is a software algorithm which calculates material characteristics from the three-dimensional shape of a hardness impression using FEM simulations.

The test impression is created mechanically by a test piece, the evaluation is carried out optically by an interferometer and the calculation is carried out digitally by an algorithm. 

Both representations are possible in the user interface.

Currently, these statements can only be made qualitatively.

The transfer of results of a test point to the overall sample is basically the responsibility of the tester/user. In view of the large number of materials considered, this is generally an appropriate approach.

The following points must be observed:

  • If the sample exhibits a gradient in the material properties (e.g. due to surface hardening in the case of steel), the overall behaviour results from the totality of the local material properties.
  • Limitations exist with aluminium where brittle fractures of the material occur. An actual agreement in terms of tensile strength cannot be guaranteed in all cases. A transfer to a compressive strength, on the other hand, can. Here it depends on what actual load the component is subjected to
  • Texture/Anisotropy: Here an average value of the direction-dependent properties is determined
    •  

Questions about the procedure

The procedure is divided into these steps:

  • 3D measurement of the test impression
  • Solution by software algorithm with FEM simulation by an optimization algorithm
  • FEM simulations are adapted to the real test impression
  • The material characteristics and flow curves are taken from the simulation of the best match

No! - The special feature of the method lies in the calculation of the properties from the plastic deformation.

Yes! - Both the material throw-up and the depressed area are measured.

This depends on the load level and the material being tested. Typical penetration depths are between 10 and 300µm.

In the standard case, which also corresponds to the procedure of DIN SPEC 4684 (publication November 2019), we assume isotropic (direction-independent) material behavior and von-Mises plasticity. There are boundary conditions (specimen thickness, specimen storage) which are modified for special cases (e.g. thin specimens). In principle, however, the assumptions for the FEM simulation can be designed freely and adapted.

Measurement grids and cascades can be checked automatically. True stress-strain curves can be transferred to FEM simulations through CSV files (output of x-y coordinates of the grid are possible).

Questions about the company

Both and: We develop, produce and sell our testing machines ourselves and in cooperation. We carry out component testing, detailed analyses, damage analyses and contract measurements.

Please do not hesitate to contact us.

Questions about the machine

The test space depends on the selected model and can be adapted on request. This allows you to find the optimum size, regardless of whether you will be testing flat specimens or large castings.

Questions about the benefits and advantages

  • Fast and non-destructive quality assurance and optimization of products
  • Optimization of processes and heat treatments
  • In-process measurement to reduce scrap and adhesion

The procedure was specified within a DIN SPEC 4864 with the Federal Institute for Materials Testing (BAM Berlin), the Federal Physical-Technical Institute (PTB, Braunschweig), the Materials Testing Office NRW (MPA Dortmund), DIN and industrial partners.

Compared to the tensile test:

  • Fast
  • Low Destruction
  • Cheap
  • Local testing
  • Component testing, 100% testing and in-process testing with automated sample preparation possible

Compared to the hardness test

  • No revaluation necessary
  • More meaningful and robust (due to lower statistics and spread of results)

Compared to the tensile test, the internal test allows for

  • Time in the operational processes
  • Space and room requirements of conventional test technology
  • Audit costs
  • Staff

save.

Questions about testable materials and sample or sample preparation

  • In principle, all metallic materials can be tested with our imprinting method
  • For expected accuracies of individual materials and material groups, please refer to the section "Materials".

  • The ratio of penetration depth to specimen thickness shall be less than 0,1 for the standard boundary conditions
  • The component height should not be higher than approx. 350 mm.

  • Top and bottom sides must be plane-parallel
  • The inclination of both sides must not exceed 2% in order to guarantee optimum results.
  • The maximum roughness depends on the penetration depth

If flatness and roughness are not sufficient due to the process or the specimen, the following variants of specimen preparation are possible:

  • Grinding
  • Fine milling
  • Wire EDM
  • Wet cutting

Heating of the sample surface must be excluded.

This depends on the size of the measuring points and thus on the load level and the strength of the material. Usually 200-300µm minimum distance can be realized. If points can be measured in offset, smaller measuring point distances are possible.

Yes - but texture and anisotropy must be taken into account and have an influence on the results.

  • The distance to the edge must be 3x the indentation diameter
  • The distance between two indentations must be 2x the indentation diameter.
  • Smaller distances are possible, but have to be checked on the concrete example.

The lower the test load, the more local influences such as the grain size play a role. The scatter of the measured values typically increases. For forces from approx. 300N, however, these are negligible with a few exceptions.

Verification questions

Comparative measurements are carried out by us on tensile specimens. In this respect, the software is supplied with a material model optimized for the material
Verification work of new materials is carried out continuously.

Please do not hesitate to contact us on this subject.

The material cards serve to improve the comparability of the characteristic values Rp0.2 and Rm to the tensile test. Furthermore, a quantitative relationship to the elongation at break can often be established from the tensile test. To create the material cards we need results from tensile tests in the form of stress-strain curves. For an alloy of several strength levels this material card can be created.

Imprintec GmbH
Universitätsstraße 142 
44799 Bochum
T +49 (0) 234970414 00
F +49 (0) 234970414 09
info@imprintec.de