Method for friction estimation in reciprocating wear tests

► Coefficients of friction were determined for conditions similar to total knee arthroplasty. ► Spherical Co-Cr indenters linearly reciprocated on flat UHMWPE samples with 20 MPa contact stress. ► Periodic variations in the coefficient of friction were related to the reversal of direction. ► 30 estimates for μ about the midpoint between reversals were averaged over 3 repeated test cycles. ► The coefficient of friction could reliably be estimated with a standard deviation of 0.005.