Problem of Acceptability of Internal Porosity in Semi-Finished Cast Product as New Trend "Tolerance of Damage" Present in Modern Design Office

Abstract

Discontinuities in cast products, obtained from a liquid state of an alloy, are the result of phenomena occurring during multiphase system crystallization. On the one hand, compacted defects as a shrinkage pipe are relatively easy to eliminate. On the other hand, it is known that presence of fine shrinkage and gas porosity is unavoidable. Detectability of these dispersed discontinuities depends on type of inspection method applied. Structure, including intensity and location of porosity zones, is dependent on the type of the alloy, casting configuration and conception of technological solution, related with control of velocity of the heat extraction to the mould. Thus, mechanical properties in the volume of a casting are not homogenous and are strongly reduced only in the zones of porosity. However, in strength calculations of cast products, this obvious fact is not taken into consideration. The rule of material homogeneity is applied instead, along with drastic increase of factor of safety. The paper indicates benefits of precise determination of limits of porosity zones located in the casting, using the NTD methods (for example, Phased Array ultrasonic tomography). Coordinates of porosity zones in 3D, introduced into CAD geometry and assigned with different properties allow to estimate the actual state of stress and strain of real object using FEM methods (systems like Ansys, Comsol). Load justified by operating conditions and application of tolerance of damage rule, with simultaneous reference to the limited state of stress according to LOV (Loss of Volume) and LEFM (Linear Elastic Fracture Mechanics) methods should find their place in design procedures of cast products, which will allow for better use of material and reduction of weight of the casting. This approach, named Tolerance of damage concerning the castings is the motto of this paper.

Contribution to the Identification of Porosity Type in AlSiCu High-Pressure-Die-Castings by Experimental and Virtual Way

“…The presence of discontinuities in the material structure may have different effect on the deterioration of mechanical properties. Discontinuities, regardless of the origin and nature of porosity (shrinkage, gas and gas-shrinkage, delamination in solid-liquid state (hot tears)), causing a reduction in the active cross-section (LOV -Loss of Volume) [7]. It can also be a site of initiation of cracking and its further propagation, resulting in irreversible degradation of the casting product during exploitation.…”

“…The method complementary to the LOV known as LEFM (Linear Elastic Fracture Mechanics) refers to the stresses intensity factor (SIF) [7] and assumes that the material fulfils the assumption of linear elasticity. For the case of tensile stress:…”

The Conditions for Application of Foundry Simulation Codes to Predict Casting Quality

“…The problem of missing or unreliable coefficients in databases, essential for modeling processes, concerns not only the hard models (based on differential equations of elementary processes such as fluid and heat flows, diffusion, mechanical impact -stress), but also occurs in the case of the use of soft models (empirical equations including modeling of nucleation and grain growth, supply and the formation of shrinkage defects, local structures and their mechanical properties, expansion movements) [6,[22][23][24][25].…”

Ultrasonic signal processing techniques for Pipeline: A review

“…Trapped gas in weld bead commonly happen and called porosity. During welding in joining the two pipeline, the torch being applied and the gas in the molten metal released and trapped on solidification [16]. It could be wide in gas dispersion throughout the welds.…”