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Metal Casting Technologies : March 2006
Trust your most complex cores to INCAST ®. The ideal combination of geometry, density and particle size distribution, INCAST improves critical core making and casting properties including binder utilization, permeability and dimensional stability. Higher strength cores, better surface finish and increased efficiency and yield are the INCAST advantages. These sands are engineered for the metalcaster. Optimize Core Performance Unimin Australia Limited Tel.: +613 9586 5400 Fax: +613 9586 5411 E-mail: email@example.com Worldwide: www.metalcaster.com CORE AND MOULDING SANDS ® To allow for plastic deformation, the Griffith equation was revised by Irwin and other workers for non-brittle materials and written in simple form as: Where Gc =γs+γp In ductile materials γp is much greater than γs so Gc and hence the fracture stress needed to propagate a given flaw depend essentially on how much plastic deformation can occur in the material around the crack tip. Both the above forms of the equation relate to thin sheet material only. In this case (see Figure 2a), in response to the applied tensile loads (in direction y) tensile stresses, arising from the Poisson effect only develop across the width of the sheet (direction x). There is no such constraint through the thickness of the sheet (direction z) and a through the thickness stress is not developed. The stress system is biaxial (in y and x directions only), i.e. in the plane of the sheet, so this situation is called Plane Stress Figure 2. Difference between Plane Stress and Plane Strain (8). (a) In a thin specimen the Poisson contraction can take place in the z direction and a through the thickness stress σ z does not develop. The only constraint is across the sheet giving rise to σ x. Stress is only in the x and y (applied tensile) directions only and is termed Plane Stress. (b) In a thick specimen the material is not free to contract and constraint stresses develop in both x and z directions. This is the Plane Strain condition. a b ® INCAST is a registered trademark. All rights reserved. ©2003