Destructive materials testing
Hardness testing
Hardness testing is a static procedure.
Hardness is understood as the resistance of a material to the penetration of a test specimen.
The hardness value can be used to draw conclusions about the strength of the material.
The following hardness testing methods are presented in the materials science laboratory:
- Brinell (HB = Brinell hardness)
- Vickes (HV = Vickers hardness)
- Rockwell C (HRC = Rockwell Cone hardness)
- Rockwell B (HRB = Rockwell Ball hardness)
Tensile test
The tensile test is used to determine the behaviour of the material under a shock-free, steadily increasing external tensile load that is evenly distributed over the entire cross-section.
The test is used to determine characteristic values for strength calculations of materials:
- Yield strength ReH or Rp0.2
- Elongation at break A
- Tensile strength Rm
- Uniform elongation Ag
Notched bar impact test (Charpy test)
The notched bar impact test is a method for determining the toughness of materials as a function of temperature.
A pendulum hammer falls down and smashes a V notch impact specimen. Work is "consumed" in this process. The consumed impact energy KV [J] related to the specimen cross-section is called the notched impact strength αk [J/cm2].
Metallography
Preparation of mostly metallic samples to analyse the microstructure with the aid of suitable light microscopes.
Non-destructive testing (NDT)
Penetrant testing
Dye penetrant testing is a simple method for detecting surface defects. For this purpose, a penetrant (red paint) is applied to the surface of the workpiece. The penetrant penetrates any surface defects due to capillary action. The component is cleaned after a specified penetration time so that the penetrant is not washed out of the defects. Subsequently, a developer is applied, e.g. with the help of a swirl chamber. The developer draws out the penetrant remaining in the surface defects. The developer forms a clearly visible white/red contrast with the penetrant in the area of surface defects.
Magnetic particle test
Magnetic particle test (also called fluxing) is a method for detecting cracks in or near the surface of ferromagnetic materials.
The field lines created by magnetisation run parallel to the surface. Cracks and near-surface defects that lie transverse to the field lines generate a magnetic stray field. This stray field marks the defect and is detected with the help of iron powder.
Eddy current testing
When an electric current flows through an electrical conductor (e.g. a wire coil), a magnetic field is generated around the wire.
In electrically conductive materials, alternating current generates an alternating magnetic field. If a fault is located in the area of the eddy currents, the eddy current paths lengthen, the paths become longer.
This causes a local weakening of the secondary alternating magnetic field.
This weakening is indicated by the measuring device.
Ultrasonic testing
Testing principle: Sound waves propagate in metals or other materials as mechanical vibrations in a straight line at high speed. They are reflected at boundary surfaces (defects) so that the sound that continues to travel is weakened. The signal is displayed on an oscillograph.
Pulse-echo method: The probe contains receiver and transmitter combined in one component.
Thermography
An infrared camera is used to visualise the distribution and intensity of the infrared radiation emitted by an object surface. A temperature gradient induces a heat flow in the component. Defects, such as delaminations in a fibre composite component, impede this heat flow. The thermographic camera detects the associated change in the distribution of the infrared radiation intensity emitted by the respective component surface.
