The recently completed Single-Tooth-Bending Fatigue (STBF) test program evaluated actual tooled toothed gears to establish the bending-fatigue response. While this method is preferred to evaluate as-formed PM tooled gear-tooth surfaces (not machined test specimens), the cost to manufacture these test gears was excessive. In order to accumulate a more extensive database for the bending-fatigue response of PM materials and processes, a lower-cost net-shape test specimen and test method is required. Since nearly all parts producers and powder manufacturers have a 3-point bend test fixture for transverse rupture testing, this approach was recommended for the test program. An expanded test matrix based on the STBF program will serve as the guide for this follow-on program. As in all past fatigue programs a wrought steel specimen will be prepared and tested as a baseline.

A second phase for this program will investigate the strain-controlled low-cycle-fatigue response of selected PM steels from a similar test matrix. This type of fatigue loading will require a machined test specimen. Due to limited program funds, the extent of this testing will be determined based on the materials/processing available from the overall matrix and the predicted response characteristics.   
 
Material Compositions
FC-0208, FD-0408, FLN2-4405, FL-4405, FN-0205, P/F-4620, FL-5208 and FL-5305

Density Levels
Medium and high density

Processing
Conventional, warm compaction, double press–double sinter, surface-densified, powder-forged, high-temperature sintering
Through harden, case carburize, and induction harden
Shot-peened

Testing
All test materials will be prepared by CPMT member companies. The bending-fatigue testing will be conducted by CPMT member companies. The strain-controlled, low-cycle-fatigue testing will be conducted by an accredited, contracted laboratory with experience in LCF specimen preparation and testing.

Status
The initial program plan was reviewed and approved at the spring 2004 CPMT meeting. Participants for the first phase were selected at the fall 2004 meeting with assignment for sample preparation and testing sites. The first test materials were received in the 1st Q 2005 with about two-thirds completed by 2nd quarter 2006 (20 different materials/processes). Bending fatigue qualification samples (carburized 8620 wrought steel) were prepared by one of the CPMT member companies and have been distributed to the volunteer fatigue test sites. Three sites have successfully completed the qualification testing and are now qualified to perform the actual bending fatigue tests.

Sixteen test sets are now out for test at these three laboratories. Results have been completed on nine materials.  Two new laboratories are now awaiting their qualification samples to demonstrate their ability as a successful fatigue test site. 

The second phase of the fatigue test program -- strain-controlled, low-cycle-fatigue portion was begun in 2006 in coordination with the MPIF Standards Committee.   Nine materials and processes were included in this initial segment of the LCF testing –
            FN-0205, as-sintered, 7.1 and 7.4 g/cc
            FN-0205, heat treated, 7.1 and 7.4 g/cc
            FN-0200 (0.2 carbon) carburized, 7.4 g/cc
            FC-0205, as-sintered, 6.9 and 7.3 g/cc
            FC-0205, heat treated, 6.9 and 7.3 g/cc      

Tests were conducted at Westmoreland Testing Lab.  The test results have been evaluated and compare favorably with cast irons and wrought plain carbon steels.  A follow-up program using high performance FLN2-4405 material is scheduled to begin in 2008.