Response of Viscoelastic Fluids in Dynamically Loaded Bearings

The dynamic response of polymer fluids to small sinusoidal shearing motions may be characterized by their relaxation spectra. Recent experiments show that great changes can be induced in the relaxation spectrum by steady shearing of the sample. This is the case of most relevance to bearing studies in, for example, a dynamically loaded journal bearing. It is shown that almost all relaxation processes longer than a small multiple of the (shear rate)⁻¹ are removed by steady shearing. This result implies that in a bearing undergoing dynamic loading with Fourier components which are low harmonics of the shaft speed a polymer fluid is expected to behave very like a quasi-Newtonian fluid with variable viscosity. The action of a sheared squeeze film is also considered and the implications for synovial joint lubrication are briefly mentioned.