[Martens, 1900]
• The technical hardness is a mechanical quantity for describing a material or the state of a material.
• The hardness cannot be measured directly, it must be derived from primary measurement quantities (e.g. test load, indentation depth, indentation area).
o time consuming alignment of the test surface to achieve
symmetrical test indentations
Knoop – disadvantages
19
Zwick products for Knoop hardness testing
Zwick ZHV1m Zwick ZHV2m
Zwick ZHV10 A Zwick ZHV10 PC
Zwick ZHV20/Z2.5 Zwick ZHV30/Z2.5
Zwick ZHU250
Zwick ZHU2.5/Z2.5 Zwick ZHU0.2/Z2.5
Knoop – products, overview
hardness testing of metals
7
Hardness Testing according Rockwell (HR)
depth measurement, DIN EN ISO 6508-1
Rockwell - overview
8
Scale overview – Rockwell hardness
14
Tips for Vickers (HV…):
no shocks, vibration, strikes
contact diamond-specimen without shock use at least polished surfaces take an appropriate magnification minimise meas. errors
no displacement of specimen during testing proper specimen support, no burr no dirt (specimen, diamond) prevent diamond of damage regard correct „choice“ of scale regard minimum thickness (indentation depth 1/10 or 1/15) no imprint on support surface
Indenter Pre-Load [N] Total Load [N]
Scales - Rockwell
9
Application range
Hardness range in HV30 Hardness Min. Max. Indentation depth 1 Unit Max. Min. Calculation of Hardness
20
Hardness Testing according Brinell (HB)
optical indentation measurement, DIN EN ISO 6506-1
120°Diamond 1/16“– Ball 1/8“ – Ball 120°Diamond 1/16“– Ball
Anpplication range - Rockwell
10
Rockwell – application examples
11
Tips for Rockwell (HR…):
1 HR… - Unit means 2 or 1µm indentation depth
Zwick ZHU2.5/Z2.5 Zwick ZHU0.2/Z2.5
Vickers – products, overview
16
Hardness Testing according Knoop (HK)
optical indentation measurement, ISO 4545, DIN ISO 4516
4
basics – overview, methods
5
• Basics, Standards, Methods, related products
Introduction into hardness test methods, (dis-) advantages & applications 1.1 Definition of Hardness 1.2 Hardness Testing of Metals
agenda
6
• Mainly methods with static force application are used for metals. • The indentor (ball, cone, pyramid) made of steel, hard metal or diamond is pressed into the surface of the specimen which is placed on a hard and fixed base. • The test load is applied bumplessly with a defined application time and duration. The indentation is measured after load removal for many test methods.
1.3 Hardness Testing of Plastics and Rubber
Ball indentation, Shore, IRHD, Rockwell
2
• Terminology definition: “Hardness is the resistance that a body offers to indentation by another (hard) body”.
Knoop - overview
17
advantages: Knoop (HK)
suitable for small specimen owing to the high diagonal length
ratio of approx. 7:1
better than Vickers for thin specimen or layers as the indentation is
regard minimum distance (~ 5mm) no shocks, vibrations, strikes
Rockwell – tips
12
Zwick ZHR - Reihe
Zwick 3106
Zwick ZHU250 Zwick ZHU187,5
Zwick ZHU2.5/Z2.5 Zwick ZHU0.2/Z2.5
• Hardness values can only be compared if they have been determined via the same test method with identical test parameters.
3
• An explicit hardness value can only be characterised via the following criteria: • definition of the hardness value • indentor geometry and material, • size and indentation duration at test load, as well as the type of loading, • state and surface quality of the specimen. • The following is at the forefront for selection of a hardness test method: • economy, • time for specimen preparation, • availability of machines and devices.
Introduction into hardness test methods, (dis-) advantages & applications 1.1 Definition of Hardness 1.2 Hardness Testing of Metals
Rockwell, Vickers, Knoop, Brinell, Martens hardness (universal hardness testing)
horizontal specimen support, no dirt (specimen, diamond)
prevent diamond of damage take an appropriate load regard minimum thickness (indentation depth 1/10 or 1,5*d) regard minimum distance (~ 3*d) take care of load dependency of Vickers
shallow test indentations
Knoop – advantages
18
disadvantages: Knoop (HK)
o time consuming to achieve a sufficiently fine test area o sensitivity of the diamond indentor to damage