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Metal Casting Technologies : March 2011
Trust your most complex cores to INCAST ®. The ideal combination of geometry, density and particle size distribution, INCAST improves critical core ma ing and casting properties including binder utilization, permeability and dimensional stability. igher strength cores, better surface finish and increased efficiency and yield are the INCAST advantages. These sands are engineered for the metalcaster. Optimize Core Performance For more information and availability: ContactUs@metalcaster.com CORE AND MOULDING SANDS ® INCAST is a trademar . All rights reserved. ©2011 ® at 90 degrees to the main tensile stress, step by step through the component reducing its effective load bearing cross section until complete failure occurs under a single tensile loading. Quite often more than one fatigue crack develops depending on the component design, its surface condition, distribution of defects and the environmental conditions and loading. The appearance of a fatigue fracture surface (Figure 1) is relatively smooth and may contain macroscopic "beach" marks which are formed when loading is intermittent or changed during service, or if there are changes in the environment at the crack tip. On the microscopic scale striations may also be seen on the fatigue fracture surface corresponding to the position of the fatigue crack after each stress cycle as shown in Figure 2 . Although the overall deformation under load is elastic, fatigue cracks develop in a ductile manner with plastic deformation occurring in the zone around the growing crack tip. Propagation may be transgranular or follow interphase or grain boundaries. Any crack will follow the easiest route in the microstructure so the presence of any elongated inclusions, clusters of inclusions, oxide films, coarse second phases and intermetallics, and gas or shrinkage pores will allow faster growth. For example (Figure 3) AlFeSi plates facilitate fatigue fracture in Al alloy cylinder heads . Second phases and intermetallics interact with freshly-formed oxide bifilms in Al alloys reducing tensile properties and fatigue resistance and limiting reliability . Figure 3. Fatigue crack formation follows coarse platelets of Al5FeSi in an Al alloy cast cylinder head .