The viscoelastic properties of an hydraulic oil determine the upper frequency limit for the mechanical movement of a constructional element using this oil.

Best regards

Wolfgang Jacobsen

Regarding drilling fluids, the viscoelastic properties are very important to evaluate gel structure, gel strength, barite sag, hydraulic modeling, and solid suspension.

Regards

Dear all, not all substances have such a feature. Viscoelasticity is more related to polymers and some other substances. If the oil in question has a high molecular weight may have such a feature. What is the physical state of the oil at ambiant conditions ? My Regards

These types of oils usually do not have noticeable viscoelastic properties, but can be shear thinning fluids.

"Viscoelasticity" is related to the time- and rate-dependend deformation properties of solid or solid-like materials. ATF-type oils are almost "watery" fluids, so it makes more sense to characterize the properties by the dynamic viscosity. It can be determined e.g. by ASTM D445: Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity).

The working conditions of ATF have a pretty wide temperature range, think of the use in an automatic transmission gearbox in a car: from -30°C (cold start, winter) up to +100°C under working conditions, the viscosity should meet certain specifications. Aging leads obviously to higher viscosity, at least it is my impression, when i change the ATF at my car (don't beliefe the "lifetime" filling promise of the manufactures...).

Eduardo, one research paper that you can refer to is by Maria Alejandra Rojas Luces titled " Viscoelastic properties of heavy oils" published in December 2009.

The viscous and elastic properties (which is dominating) of a liquid change with temperature and with the shear rate (speed of motion). Fundamental science is described as capillary rheology (rheometry), the Weissenberg and Deborah dimensionless numbers of a fluid (Wi and De). Dr. Luces concludes that the elastic component of a "heavy oil becomes very important for temperatures below 30°C, and for seismic to ultrasonic frequencies" (at high shear rates above 10,000/s (10 kHz)) - i.e. timescale of 0.1 ms and smaller). At higher temperatues and lower shear rates one can neglect the elasticity (more and more) and "pure" viscosity dominates (more and more).Is your oil a "heavy oil?" Heavy oils have viscosities (at shear rates 10-100/s) greater than 200cPs (1 centiPoise = 1 mPa*s) and densities less than 20 API degrees (i.e. paradoxically specific gravity higher than 940 kg/m3). By way of ILLUSTRATION: you are in that range if your fluid's DENSITY is around 1.0 like motor oil, milk or vinegar; your VISCOSITY is like car engine oil (SAE 10/30...) or between salad oil and honey (if you drip it from a spoon its flow looks less like water and more like salad oil or even honey). To directly see the extent of ELASTICITY of your oil, get a look and feel for the STRINGINESS: Put some of the fluid between thumb and index finger then pull them apart. Water will show no stringing, milk shows a little bit, yogurt or shampoo show quite a lot and syrup shows a lot. This stringiness (indication of high relaxation time value) is decreasing with higher temperature. A good reference might be to see how your oil compares to engine oil SAE 25W-50 which is considered mostly Newtonian, negligible elasticity in temperatures at and above room temperature.

Hi all.

I did some rheological measurements to determine the viscoelastic properties of a commercial ATF (attachments).

I see that the ATF is Newtonian up to a shear rate 10^3 s-1 (equipment limit), also, the values of the storage modulus are low.

The service conditions of an ATF are much more extreme, shear rate> 10^3 s-1 and the starting temperature can be between -30°C to 20°C and in service between 80°C to 120°C on average.

Is the limitation of measuring equipment the little interest in the viscoelastic properties of ATFs?

whow, interesting research! I think, from the perspective of the primary use of ATF in automatic transmission gearboxes (with torque converters), the stability of the dynamic viscosity over a wide temperature range is the determining functional parameter (apart from lubrification properties...). Can you test the viscosity over temperture?

Each fluid is viscoelastic. No matter if it is water, any oil or metal. The important here is the relationship between the relaxation time and the observation time, i.e. the value of the Deborah number. At T> 243 K, the viscoelastic properties of the oil mentioned in the question can be ignored, but not in Antarctica or Greenland outside.