Contact fatigue testing of camring steel

Abstract: The aim of the present thesis work was to establish a fatigue-test setup and
perform several tests to characterize different combinations of steels and
heat treatments. These materials should be suited for usage as cam ring
material in hydraulic drives. Carring out the tests in a short time was one
of the main features for the selection of the test-method.
For characterizing the materials the Standing Contact Fatigue method was
choosen. In this method, the sample is pressed against a hard ball in rapid
succession causing different types of cracks in the contact-zone.
The contact area was inspected after each test. Since a continuation of a
performed test is not possible, a following test was carried out with more
or less cylces, depending on the previous result (cracks found or no cracks
present). In addition, a strain-gauge set-up was established for testing an
insitu crack detection.
Mostly ring-cone cracks were found at the edge of the indentation but inside
the indent. The sectional view shows, that these crack grow underneath the
indentation. The tests, performed at 60 Hz and a load cycle between 500 N
and 15 kN, show a higher fatigue limit for the samples tempered at 240°C
than the samples at 180°C. The highest fatigue limit was tested for the
electro slag remelted steel tempered at 240°C.