FAQ to the indentation method

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
  • RImComparative tensile strength to the tensile test

is determined.

It is a software algorithm that calculates material parameters 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 done optically by an interferometer and the calculation is done digitally by an algorithm.

Both displays are possible in the user interface.

Currently, these statements can only be made qualitatively.

The transfer of results of a test point to the whole sample is basically the responsibility of the inspector/user. Given the large number of materials under consideration, this is basically an appropriate consideration.

The following points must be observed:

  • If the sample shows a gradient in the material properties (e.g. due to surface hardening of steel), the overall behavior results from the totality of the local material properties
  • There are limitations with aluminum, where brittle fractures of the material occur. Actual conformance in terms of tensile strength cannot be guaranteed in all cases. However, a transfer to a compressive strength can be guaranteed. Here it depends on the actual load the component is subjected to
  • Texture/Anisotropy: A mean value of the directional properties is calculated here

Questions about the procedure

The procedure is divided into these steps:

  • 3D measurement of the inspection 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 is the calculation of the properties from the plastic deformation.

Both the material throw-up and the indented area are measured.

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

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 (sample thickness, storage of the sample), which are modified for special cases (e.g. thin samples). In principle, however, the assumptions for the FEM simulation can be freely and adapted.

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

Questions about the company

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

Please do not hesitate to contact us.

Questions about the machine

The test area 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 reject and liability

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:

  • Faster
  • Non-destructive
  • Cheaper
  • Local testing
  • Component testing
  • 100% testing and in-process testing with automated sample preparation possible

In comparison to hardness testing:

  • No revaluation necessary
  • More meaningful and robust (due to reduced statistics and scatter of results)

  • Time in operational processes
  • Space and room requirements of conventional test technology
  • Test costs
  • Personnel

Questions on testable material and on sample or samples preparation

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

  • The ratio of penetration depth to sample thickness must 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% to guarantee optimal results
  • The maximum roughness depends on the penetration depth

If flatness and roughness are not sufficient due to process or sample conditions, the following variants of sample 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 a minimum distance of 200-300µm can be realized. If points in offset can be measured, smaller measuring point distances are possible.

Ja! -  Textur und Anisotropie sind aber zu beachten und haben Einfluss auf die Ergebnisse.

  • Der Abstand zum Rand muss 3x dem Eindruckdurchmesser betragen
  • Der Abstand zweier Eindrücke zueinander muss 2x dem Eindruckdurchmesser betragen
  • Geringere Abstände sind möglich, aber am konkreten Beispiel zu überprüfen

Je geringer die Prüfkraft, desto eher spielen lokale Einflüsse wie die Korngröße eine Rolle. Die Streuung der Messwerte erhöht sich typischerweise. Für Kräfte ab ca. 300N sind diese jedoch bis auf wenige Ausnahmen zu vernachlässigen.

Verification questions

Vergleichsmessungen werden von uns an Zugproben durchgeführt. Die Software wird diesbezüglich mit einem werkstoffoptimierten Materialmodell geliefert
Verifikationsarbeiten neuer Werkstoffe werden fortlaufend durchgeführt.

Sprechen Sie uns gerne zu diesem Thema an.

Die Materialkarten dienen zur verbesserten Vergleichbarkeit der Kennwerte Rp0,2 und Rm zum Zugversuch. Weiterhin kann hierdurch oftmals auch eine quantitative Beziehung zur Bruchdehnung aus dem Zugversuch hergestellt werden. Zum Anlegen der Materialkarten benötigen wir Ergebnisse von Zugversuche in Form von Spannung Dehnung Kurven. Für eine Legierung mehrere Festigkeitsniveaus kann diese Materialkarte erstellt werden.

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