Material microstructure and mechanical properties research

The properties of materials are based on the internal structure of the material, the microstructure, which can be studied using a microscope. Microstructure studies can look at things like the phases in the metal and their number, grain size, coating thicknesses, or cracks in the material. In order to study the microstructure of a material, a cross-section of the material must first be prepared. In the sanding process, the sample is removed from the material and cast into a “button” so that it can be sanded and polished to a mirror finish. Finally, the metal samples are etched to reveal the microstructure of the sample for microscopic examination.

The equipment available at HAMK Tech can be used to prepare metallographic cross-sectional slides of metallic materials for microstructural studies. The prepared sands can be examined with optical microscopes.

Sample preparation equipment:

• Metkon Micracut 202-AX
  • Precision cutter for the preparation of metallographic samples with XYZ control
• Struers CitoVac
  • Vacuum machine for the production of cold-cast fine-needle pins
• Struers Labopress-3
  • Hot stapling machine for the production of D 30 mm and D 50 mm fine grain pins
• Struers Labopol-30 + Laboforce-100
  • Grinding and polishing machine for fine metallographic samples
  • Semi-automatic preparation of 3-6 samples
• Struers LavaMin
  • Sample washer for sand preparation
• Sicco Auto-Star desiccators
  • Drying cabinet for protection of fine samples against humidity

Optical microscopes:

• Zeiss AxioSkop 2 MAT + AxioCam ERc5s camera
  • Optical measuring microscope and xy-measuring table
    • Lens 0.7 – 4.5 x
    • Determination of distances and angles from microscope image in xy-plane
    • Determination of distances on xy measuring stage

Keywords

microstructure, metallography, metallurgy, microscope, microscopy

The mechanical properties of materials, such as yield strength, fracture toughness, elastic modulus or elongation at break, are usually determined by various fracture test methods, such as tensile, compression and bending tests. These tests can be carried out using tensile testing equipment.

HAMK Tech’s tensile testing equipment can be used to load components or joints, or alternatively to perform standard tests (e.g. SFS-EN ISO 6892-1, A1-, A2- and B-method) using test rods made of the material to be tested. As a general rule, the tests are carried out at room temperature, but if necessary, tests can also be carried out in a heating cabinet (-30°C to +250°C).

The strain can be measured during the experiments using either a macro extensometer, strain gauges or optical strain measurement (Digital image correlation, DIC). Optical strain measurement allows a three-dimensional view of local deformations of the surface of the specimen under load. When the optically measured deformation is combined with the load data measured by the tensile equipment, the actual, local stresses in the part can be viewed. This allows, for example, the identification of stress concentration regions in the structure.

Test equipment:

• 250 kN mechanical hoist Zwick-Roell Z250
  • Accurate strain measurements with an extensometer from 10…100 mm initial gauge length
  • Maximum displacement speed 10 mm/s
• 50 kN mechanical drawbar Zwick-Roell Z050 + heating cabinet
  • low and elevated temperature tests -30…+250 °C
  • Accurate strain measurements with an extensometer from 10…100 mm initial gauge length
  • Maximum displacement rate 10 mm/s
• 5 kN mechanical tensile tester Zwick-Roell Z005
  • Accurate strain measurements with an extensometer from 10…1000 mm initial gauge length
  • Maximum displacement speed 10 mm/s
  • 20 N, 100 N and 500 N force sensors for accurate measurements at low load levels
• GOM Aramis 5M optical strain measurement system

Keywords

Tensile test, compression test, bending test, DIC, Aramis

Hardness describes the material’s ability to resist penetration, scratching, abrasion or cutting. There are several standardised methods of measuring hardness, and the method of measurement is typically chosen according to the material being tested.

Standard hardness measurements can be carried out in the HAMK Tech laboratory using methods such as Vickers (SFS-EN ISO 6507-1), Rockwell (SFS-EN ISO 6508-1), Knoop (SFS-EN ISO 4545-1) and Brinell (SFS-EN ISO 6506-1). The equipment also allows for automated hardness measurement profiles, for which several different measurement modules are available. Measurements can be made either from cross-sectional sand or as surface measurements. In the test pattern module, the pattern sets can be freely defined. In addition, an ISO 9015 standard measurement module for weld seams and a KiC crack detection module are available.

Hardness measuring equipment:

• Innovatest Nemesis 5102
  • Test loads: 0.010 – 250 kgf
  • Methods: Vickers, Brinell, Knoop, Rockwell, Rockwell surface hardness.

Keywords

Hardness, hardness measurement, Vickers, Rockwell, hardness profile

If the material is subjected to impact loads in the operating environment, it is essential to investigate the mechanical properties of the material at high deformation rates. In this case, impact tests can be carried out, where a test rod prepared for the test is struck with an impact hammer.

HAMK Tech can perform Charpy impact tests on metals according to SFS-EN ISO 148. Typically, the tests are carried out at room temperature, but in order to determine the possible cold embrittlement of the material, tests can also be carried out at low temperatures (min. -40°C). The test probe can be inserted manually or, if the number of samples to be tested is large, testing can be accelerated by automatic insertion of test probes.

Impact resistance equipment:

• MTS Exceed E22, 450 J

Keywords

Impact resistance, Charpy

The limits of formability of thin sheet under different types of forming conditions can be illustrated and comprehensively defined by means of a Forming Limit Diagram (FLD). A Forming Limit Curve (FLC), specific to each sheet material, is drawn on the diagram to distinguish between successful and failure forming. The curve is used to assess the manufacturability of the sheet product and as a reference for numerical calculation results.

The limiting ductility curve is determined using a Nakajima-based tool on specimens moulded with a strain gauge in accordance with EN 12004-2. 5-6 different sub-geometries provide a comprehensive description of the ductility limits of the material on both the deep and tensile sides. The strain magnitudes are calculated on the basis of a pattern on the surface of the test piece, either during forming or on the finished piece.

Formability testing equipment:

• Stenhøj twin-cylinder FPS 200/100M press
  • Maximum force 2000 kN
  • Maximum holding force 1000 kN
  • Working area size 650 mm x 500 mm
  • Speed 1,5 mm/s…10 mm/s
• Limit Formability Nakajima-based tools for plate thicknesses t = 0.2…5 mm
• Stretch measuring equipment: ASAME, Argus and Aramis based on real-time measurement

Keywords

Formability test, sheet metal, interfacial ductility, Nakajima

Scanning a physical object into a digital form allows the shape of the object to be studied and used in CAD design, 3D printing, manufacturing and quality control. 3D scanned digital models can be measured, studied and used for years to come, even if the original scanned object is no longer available.

HAMK’s accurate 3D scanning measurement equipment can scan existing pieces, turning them into digital, malleable models. This means that no drawings or other documentation of the piece is needed, just the existing piece. 3D scanning is therefore a natural part of reverse engineering.

3D scanning equipment:

• 3D scanner ATOS 5 Compact scan
  • 3 sets of optics for a wider range of scan sizes
  • largely geometry independent
  • measurement accuracy of around 0.015-0.04 mm (depending on conditions)
  • GOM inspect analysis software (including measurement)
  • Studio foot mounting
• 3D handheld scanner SCANTECH AXE B11
  • Volumetric accuracy 0,02mm+0,035mm
  • Scan screen volume 550 x 600 mm
  • Operating temperature -10..+40 degrees Celsius
  • Compatibility with GOM inspect analysis software (including measurement)
  • Silver reference set for easy scanning

Keywords

3D scanning, reverse engineering, digital twin

The surface roughness meter can be used to determine the surface roughness, waviness or shape profile of a piece in a linear manner.

Surface roughness measuring equipment:

• Mitutoyo SJ-210
  • Linear measurements with a diamond tip along the sample surface
  • Maximum single profile length 16 mm
  • Standards: EN ISO, VDA, JIS, ANSI

Keywords

Surface roughness, waviness, Ra, Rq