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Testing

Tensile test

The principle of the test is to stretch a specimen by applying a tensile load. As a rule, the specimen is pulled until failure (breakage). This allows various mechanical property values to be determined. Unless otherwise specified, the test is performed at room temperature. It should also be mentioned that, due to a possible later heat treatment, the determined values do not remain constant except for the modulus of elasticity! In this case, a further tensile test must be carried out if required.

Sources:

DIN EN 10002-1 - Metallic materials - Tensile test - Part 1: Test method at room temperature
DIN 50125 - Testing of metallic materials - Tensile specimens

Torsion test

The purpose of the torsion test is to determine the breaking torque MB for bolts that can not be tested in tension.

Application

This procedure applies to bolts with the following technical specifications:

  • Screws with head stronger than the threaded part
  • Diameter of the threadless shank: dShank ≥ dThread
  • Thread length: b ≥ 1 x d + 2 x P
  • Thread: 1.6 mm ≤ d ≤ 10 mm
  • Strength classes: 4.6 to 12.9

Test method

The screw must be clamped in a test fixture over a thread length of at least 1 x d with a free thread length of at least 2 x P from the head to the thread run-out or from the thread-free shank to the thread run-out. The torque is applied continuously in an ascending manner.

In the event of a complaint, the following procedure generally applies:

  • Bolts that cannot be tested for tension ==> hardness value decisive for acceptance
  • For bolts that can be tested for tension ==> tensile strength decisive for acceptance

Sources:

DIN ISO 898-7 - Mechanical properties of fasteners; Part 7: Torsion test and minimum breaking torques for bolts M1 to M10

Vickers hardness test (HV)

The Vickers hardness test is performed using a diamond pyramid with a square base defined angle between the opposite faces. The pyramid is pressed into the material surface of the specimen. The diagonals d1 and d2 of the indentation made on the test surface after the test force is withdrawn are measured and the hardness value is determined from this. The results are displayed as follows:

600 - HV - 10 / 25

(Vickers hardness value - hardness designation - test force / exposure time of the test force in seconds)

The Vickers hardness testing method is universally applicable (also for small load or micro hardness testing) and is suitable for soft to very hard materials. Edge layers or structural parts can also be measured.

Sources:

DIN EN ISO 6507-1 - Metallic materials - Vickers hardness test - Part 1: Test method

Hardness test according to Brinell (HB)

The Brinell hardness test is performed with the aid of a carbide ball (formerly steel ball). In earlier standards, where a steel ball was used as an indenter, the designation for Brinell hardness was HB. The ball is pressed vertically into the surface of a specimen with a defined test force and the indentation diameter, on the specimen, is measured. The results are presented as follows:

280 - HB - 1 / 30 / 25

(Brinell hardness value - hardness designation - ball diameter / test force / duration of test force)

The Brinell hardness measurement method provides very accurate and reproducible results and is particularly suitable for soft and medium-hard materials (e.g. unalloyed steel, Al or Cu alloys).

Source:

DIN EN ISO 6506-1 - Metallic materials - Brinell hardness test - Part 1: Test method

Hardness test according to Rockwell (HRC)

The indenter of defined size, shape and material is pressed into the specimen in two stages under specified conditions. The permanent indentation depth h is measured after the test force has been removed. The Rockwell hardness measurement is usually performed with a cone or ball. The results are displayed as follows:

60 - HR - C - W

(Rockwell hardness value - hardness designation - scale designation (here scale C) - material of the indenter) (S=steel / W=hard metal)

The Rockwell test method has the advantage that the hardness values can be displayed directly without additional calculation. Depending on the selection of the suitable test specimen or the test load, soft to hard materials can be tested.

Source:

DIN EN ISO 6508-1 - Metallic materials - Rockwell hardness test - Part 1: Test method

Hardness comparison table

Tensile strength Vickers hardness Brinell hardness Rockwell hardness
MPa HV10 HB HRC
255 80 76,0 -
270 85 80,7 -
285 90 85,5 -
305 95 90,2 -
320 100 95,0 -
335 105 99,8 -
350 110 105 -
370 115 109 -
385 120 114 -
400 125 119 -
415 130 124 -
430 135 128 -
450 140 133 -
465 145 138 -
480 150 143 -
495 155 147 -
510 160 152 -
530 165 156 -
545 170 162 -
560 175 166 -
575 180 171 -
595 185 176 -
610 190 181 -
625 195 185 -
640 200 190 -
660 205 195 -
675 210 199 -
690 215 204 -
705 220 209 -
720 225 214 -
740 230 219 -
755 235 223 -
770 240 228 20,3
785 245 233 21,3
800 250 238 22,2
820 255 242 23,1
835 260 247 24,0
850 265 252 24,8
865 270 257 25,6
880 275 261 26,4
900 280 266 27,1
915 285 271 27,8
930 290 276 28,5
950 295 280 29,2
965 300 285 29,8
995 310 295 31,0
1030 320 304 32,2
1060 330 314 33,3
1095 340 323 34,4
1125 350 333 35,5
1155 360 342 36,6
1190 370 352 37,7
1220 380 361 38,8
1255 390 371 39,8
1290 400 380 40,8
1320 410 390 41,8
1350 420 399 42,7
1385 430 409 43,6
1420 440 418 44,5
1455 450 428 45,3
1485 460 437 46,1
Source:
DIN EN ISO 18265 - Metallic materials - Conversion of hardness values

Impact test

The purpose of the impact test is to test the resistance of the material of bolts to load at a specified temperature. Usually, the test is intended to prove the toughness of a material at very low temperatures. Thus, tests at room temperature down to -120 °C are common.

In the test, a specimen notched in the center (notch standardized), which is clamped on both sides, is penetrated with a single blow using a pendulum hammer. The impact energy consumed is measured in joules. This impact energy consumed is a measure of the resistance of the materials to impact stress.

The two most common notches are the V and U notches. They have received the name because of their shape.

Source:

DIN EN 10045-1 - Metallic materials; Charpy impact test; Part 1: Test method

Mix-up test (X-ray fluorescence analysis)

X-ray fluorescence analysis (XRF), also called X-ray fluorescence spectroscopy (RFS), is a method used in materials analysis.

XRF is one of the most commonly used methods for the qualitative and quantitative determination of the elemental composition of a sample, since the samples are not destroyed by the measurement and no digestion is required.

At Güldner, this method is used to check every raw material goods receipt for mix-ups by means of random sampling and to document the result in a traceable manner.

At the customer's request, this method is additionally used for testing the finished fasteners.

Crack testing

Crack testing of materials and finished components belongs to the so-called non-destructive testing (NDT). These tests are characterized by the fact that the workpiece is not affected by the test in its subsequent use. As a rule, the defects detected here cannot be detected by a normal visual inspection.

Magnetic particle testing (MT)

Magnetic particle testing (MT) is used to detect surface defects (cracks) in ferritic materials (mainly steel). The method has the advantage of a very high sensitivity for the detection of surface defects.

By using various magnetization techniques, a magnetic field is generated in the workpiece to be tested. Close to and in the surface of the workpiece, where the magnetic properties (relative permeability) of the material change significantly (e.g. cracks), the magnetic field emerges from the surface as stray magnetic flux. This effect can be visualized by colored (usually black or fluorescent) magnetizable particles (magnetic powder) applied to the test object during the test.

Compared to other non-destructive testing methods, magnetic particle testing can be used reliably even with complicated material geometry and unmachined surfaces.

Source:

DGZfP - German Society for Non-Destructive Testing (NDT) - http://www.dgzfp.de

Dye penetrant testing (PT)

Penetrant testing (PT) is a non-destructive testing method for the visual detection of material separations (e.g. pores and cracks) on a workpiece that are open towards the surface. The method is used for non-magnetizable steels (e.g. austenitic steels).

Due to chemical-physical properties (capillary effect), a liquid (penetrant) applied to the residue-free cleaned surface of the test object penetrates into the defective surface areas. After intermediate cleaning of the test surface, this penetrant is made visible by a so-called developer (usually white powder) as a contrast background. Red dye penetrants are often used, producing red indications on a white background ("red/white testing"). By using fluorescent penetrants in combination with UV radiation, the contrast of an indication can be significantly enhanced.

Source:

DGZfP - German Society for Non-Destructive Testing (NDT) - http://www.dgzfp.de

Ultrasonic testing (UT)

Ultrasonic testing (UT) can be used to detect inhomogeneities and flaws in the entire cross-sectional area of workpieces made of sound-conductive material. A probe attached by means of a coupling medium (gel, water or oil) emits or receives ultrasound from 0.5 to 25 MHz.

The method is based on the interaction between an ultrasonic pulse injected into the test specimen and its reflection, shadowing, refraction or attenuation when it strikes interfaces, discontinuities or the surface of another material. This influence can be measured using pulse-echo techniques, radiographic techniques, or resonance techniques, and is used to detect discontinuities and defects by location, shape, and size. Time-of-flight measurements also allow the determination of wall thicknesses and material properties.

Source:

DGZfP - German Society for Non-Destructive Testing (NDT) - http://www.dgzfp.de

Eddy current testing (ET)

Eddy current testing takes advantage of the effect that most impurities and damage in an electrically conductive material also have a different electrical conductivity or permeability than the actual base material.

If a coil to which an AC voltage is applied is brought close to a metallic or electrically conductive surface, circular symmetrical eddy currents are generated near the surface perpendicular to the magnetic field lines entering the workpiece. The eddy currents generate another secondary magnetic field that runs opposite to the original one and weakens it. A surface crack or material inhomogeneity forces the eddy currents to take a detour and weakens them. The damage- or material-specific feedback effect of the eddy currents on the generated secondary magnetic field can be measured by means of problem-adapted coil systems.

In addition to the detection of defects and material inhomogeneities on the surface and in the vicinity of the surface of electrically conductive materials, this measuring method is also used for the determination of mechano-technological material properties (e.g. hardness, strength, structural condition, residual stresses, etc.) as well as for mix-up testing.

Source:

DGZfP - German Society for Non-Destructive Testing (ZfP) http://www.dgzfp.de

X-ray testing (RT)

Radiographic testing (RT) requires high-energy radiation, such as X-rays and gamma rays, with the property of penetrating matter. Inhomogeneities and imperfections throughout the cross-section of workpieces made of materials of all kinds lead to varying degrees of attenuation of the penetrating radiation. The different degree of attenuation can be documented on a film lying behind the test object by special image converters as a difference in blackening.

In the projection image of the component, deviating material thickness, volumetric defects and also cracks can be detected as different blackening at a suitable irradiation angle. Contrast and defect resolution are functionally related to the thickness of the component, the emitter quality, the scattered radiation and the type of film.

Source:

DGZfP - German Society for Non-Destructive Testing (ZfP) http://www.dgzfp.de