Tribostand Castellón 21 January 2008 Concerning the experimental approach in tribology, the target results are in general the friction (friction force or friction coefficient), the wear amount and the investigation of the wear mechanisms. Tribological testPrimary tribology quantities  Friction force  Wear (mass loss, wear volume, transversal area…) Design-using parameters  Friction coefficient  Wear factors (k - specific wear rate…) Experimental approach in tribology

Tribostand Castellón 21 January 2008 Any tribotest include systematic errors A systematic error is a consistent and repeatable bias or offset in a measurement from the true value. This is typically the result of miscalibration of the test equipment, or problems with the experimental procedure. Error sources Friction Intrinsic reason - friction is not measured directly due to the nature of the friction force. In fact the friction force is a reaction force acting on the sliding interface, thus, can’t be measured itself. In most tribology testers the friction is measured as a force that equilibrates the system. Dynamic effects - An important aspect of friction is its interaction with the dynamics of the system of which it is a part. The mutual influence of friction and the dynamic response of a system on each other might take several forms. Non dynamic effects on normal load – O ffset of the normal load due to internal adhesion forces, unbalanced masses on the loading system, or even unbalance of the measurement system;

Tribostand Castellón 21 January 2008 Wear Nonequilibrium events – wear is strongly affected by instantaneous nonequilibrium events like galling points Measurement errors – Errors intrinsic to the evaluation of very small volumes. Examples of errors as a result of misinterpretation of friction and wear results (published papers) ?

Tribostand Castellón 21 January 2008 How to solve these problems? Using a data analysis procedure that allow to identify and correct the systematic errors. A data analysis approach that allows a stochastic form of the results should be investigated. Design engineers would have a mean to allow to establish the relationship between the tribology parameter values and their reliability. Normal load (N)K (mm 3 /Nm) x x x Average8.69 x K = x Using separately each one of the results of the 15 experiments Max= x Min= 7.27 x Average= 9.11 x 10 -7

Tribostand Castellón 21 January 2008 Scale effects in tribology Are there a scale tribological response of engineering materials? Is the scale response apparent because the relative error is proportional to (1/load and 1/stroke)? When we will have local models in tribology? Both friction and wear end use parameters are calculated by a global approach. However, the most precise tools are based I n local analysis (Finite element analysis, Dynamic molecular analysis, …). The global quantities can be used in local analysis? What is the magnitude of the error?

Tribostand Castellón 21 January 2008 FCTUC & IPN Validation of a suitable data analysis procedure for sliding tests in order to:  Correct the experimental systematic errors.  Allow a precise and easy way to establish a relationship between design-using tribological parameters (e.g. friction coefficient, specific wear rate, energetic wear rate…) and the reliability  Verify the robustness of the parameter values to allow their use in a wide range of contact conditions