Evaluation of SAE J840 Lining Shear Test Procedure

The SAE Brake Linings Committee launched an evaluation of the current SAE standard J840 “Test Procedures for Brake Shoe and Lining Bonds,” specifically the bond plane shear test. The aim of the study was to identify what settings in the shear test lead to the most repeatable results for a variety of linings. An initial four factor two-level design of experiments (DOE) was conducted, with 15 pads sheared for each condition. The DOE looked at pad material type (NAO and semi-metallic), backing plate attachment type (integrally molded and mechanical retention system), ram offset position (1.0 mm and 4.0 mm) and normal pressure (0 and 0.5 N/mm²). The test measured shear force and percentage material retention for each pad tested. The objective of the DOE was to guide revision of the SAE J840 shear test procedure. For example, the application of a normal force raises the nominal value of the shear force by 30-50%, and reduces the variability of the test results. Hence, the Committee will recommend incorporating normal force application for disc brake pads. This paper will present the results of the factorial DOE with resolution IV (8 trials, 4 two-level factors, 15 repetitions) and the proposed revisions to the standard.