The Ring Test for P/M Materials

Abstract

The application of the ring test to assess die-workpiece interface friction during forging of powder metallurgical materials has been investigated. As for fully dense materials, the change in internal diameter as a function of height reduction was used to quantify friction. To this end, calibration curves were generated by conducting finite element method (FEM) simulations of ring forging with different friction factors. The method was validated by conducting isothermal, hot compression tests on rings of an alpha-two titanium aluminide alloy with starting densities of 75, 85, or 100 percent of full theoretical density. Comparison of the test data to the calibration curves revealed somewhat higher friction factors for the porous materials (as compared to the fully dense material) for both lubricated and unlubricated interface conditions. Furthermore, the accuracy of the FEM simulations of the ring test was confirmed by good agreement between measured and predicted density distributions and load-stroke curves for tests on the porous titanium aluminide material.

Quasi-static axially symmetric viscoplastic flows near very rough walls

“…Velocity gradients are very high in these layers. Conventional numerical methods fail to predict both high velocity gradients and the evolution of material properties in the vicinity of interfaces between tool and workpiece with high friction [21,26,27]. A possible reason for that is that solutions may be singular [1][2][3].…”

“…Meanwhile, the singular solutions near maximum friction surfaces can play a significant role in the development of methods for predicting the evolution of material properties in a narrow layer near surfaces with high friction in metal forming processes [20]. Such layers often appear in special experiments and real processes [21][22][23][24][25]. Velocity gradients are very high in these layers.…”

Plastic flow of porous materials in friction contact area

“…Therefore, the asymptotic behavior of the equivalent strain rate near the friction surface r = a is completely determined by the behavior of the shear strain rate ξ rθ . In particular, (2) and (27) …”

“…The properties in this layer substantially differ from those of the main material [1][2][3]. In particular, the paper [2] describes the densification of a powder material.…”

“…The properties in this layer substantially differ from those of the main material [1][2][3]. In particular, the paper [2] describes the densification of a powder material. Methods of predicting the distribution of some material properties were proposed in [4][5][6][7].…”