Material pair testing

Material pairings occur in all areas of daily life and are charac­terized by the fact that the materials are in direct contact with each other and exert a corre­sponding force on each other. If now they also exert a relative motion to each other by oscil­lation, vibration or displacement, a friction between them is created.

This effect belongs to the science of tribology. Friction depends on temper­ature, speed and pressure and also on material and surface properties. Thus, the basic condi­tions for stick-​​slip are also fulfilled, and this can lead to annoying noises and/​or malfunc­tions. In any case, these effects due to annoying noises reduce the subjective quality of a product.

Product devel­opers not only face the challenge of consid­ering practi­cality, ease of use, product safety and costs. Today, it is also very important to consider the subjec­tively perceived quality when manufac­turing products. It is influ­enced by the touch perception (haptics) and also by whether a product emits crackling noises, creaking noises or other annoying noises, caused by incom­patible material pairings. Here, it is important to either decouple materials that can poten­tially come into contact with each other and still have a high stick-​​slip risk or to eliminate the relative movement.

In numerous cases this is not possible. Therefore, it is important to select material pairings that are non-​​critical, i.e., do not show stick-​​slip under any condi­tions. For this purpose, we have developed a material database that enables devel­opers to select material pairings in advance that are non-​​critical to each other. The infor­mation in the database is based on measurement data collected with the ZIEGLER stick-​​slip test rig under real climatic and mechanical condi­tions. The database contains infor­mation on test temper­ature, humidity, contact force and relative speed as well as surface structure, surface coating and surface treatment. Since this repre­sents a prese­lection, to be sure, the materials should be subjected to a material pair testing for stick-​​slip behavior.

The occur­rence of stick-​​slip phenomena when using certain materials can be attributed either to contact points with incom­patible material combi­na­tions or to the influence of third-​​party substances. Our test institute can use its SSP-​​04 and H3P stick-​​slip test rigs to make predic­tions about possible stick-​​slip effects and the associated creaking problems.

The perfor­mance of stick-​​slip measure­ments provides indica­tions of critical material combi­na­tions and the influence of third-​​party materials that reduce the objective quality of the product due to abrasion and wear. Therefore, the durability test we have developed is of great impor­tance. It is a test, developed on the basis of real road profiles.

We are specialized in performing problem-​​oriented stick-​​slip tests as a service. Based on our 25 years of experience in the prevention and reduction of annoying noises, we can transfer real problems into the laboratory by individual test proce­dures and thus make them repro­ducible. These are the basic prereq­ui­sites for inves­ti­gating the core cause and subse­quently finding a solution.

On this basis, new findings about materials often emerge, which we then develop into new test methods. These in turn flow into the devel­opment of new testing technologies.

The objective of the above-​​mentioned KOREMA test rig, which is charac­terized by its extremely low operating noise, is noise testing of textiles. Under realistic motion profiles, we use highly sensitive measuring micro­phones to measure friction noise and evaluate it according to its degree of distur­bance.

Touch haptics means the perception caused by touching materials and surfaces. Deter­mined properties are surface texture, compliance, temper­ature, thermal conduc­tivity etc. of a surface.

Haptics refers to both the teaching of haptic percep­tions and the hapti­cally perceivable object properties, e.g. as an aspect of ergonomics.

We are focused on the touch-​​haptic perception of materials and surfaces.

Assuming that our sense of touch, i.e. haptics, signif­i­cantly influ­ences our purchasing decisions, our research has been geared towards making an objec­ti­fiable haptic finger­print measurable for many years. We succeeded in breaking down touch-​​haptic percep­tions to clearly defined physical properties.

These are:

• Macro-​​roughness (visible surface struc­tures)
• Micro-​​roughness (non-​​visible surface struc­tures)
• Touch temper­ature
• Hardness/​softness
• Jerk-​​slip (Stick-​​Slip)
• Slipper­iness

In order to unambigu­ously define each physical property in terms of language, we have keyworded them and named them with descriptors. Here we used the Senso-​​Tact scale, which rates each descriptor on a scale from 1 to 100. Each measured property was corre­lated to this scale for this purpose.

For touch temper­ature, for example, the scale for aluminium has a 100, since this element feels very cold to the touch. Styrofoam, on the other hand, was given a 1 because it feels very warm to the touch.

We offer the metro­logical acqui­sition of the touch haptic finger­print based on the above-​​mentioned physical properties of almost all solid materials. With the help of this haptic finger­print we are able to compare materials and surfaces with each other, e.g. with a reference.

In our physics laboratory we can objec­tively determine the touch haptic finger­print on almost all materials of daily life.

These are for example:

• Leather and imitation leather
• Packaging materials
• Plastics
• Softtouch coatings on plastics as well as leather and imitation leather
• Cooltouch coatings on plastics
• Paper
• Alcantara
• Metal sheets painted and unpainted