https://www.cavs.msstate.edu/publications/docs/2003/01/805Microstructure.pdf

Microstructure-based fatigue modeling of cast A356-T6 alloy

This review of multiscale modeling covers a brief history of various multiscale methodologies related to solid materials and the associated experimental influences, the various influence of multiscale modeling on different disciplines, and some examples of multiscale modeling in the design of structural components. Although computational multiscale modeling methodologies have been developed in the late twentieth century, the fundamental notions of multiscale modeling have been around since da Vinci studied different sizes of ropes. The recent rapid growth in multiscale modeling is the result of the confluence of parallel computing power, experimental capabilities to characterize structure-property relations down to the atomic level, and theories that admit multiple length scales. The ubiquitous research that focus on multiscale modeling has broached different disciplines (solid mechanics, fluid mechanics, materials science, physics, mathematics, biological, and chemistry), different regions of the world (most continents), and different length scales (from atoms to autos).

https://link.springer.com/content/pdf/10.1007%2F978-90-481-2687-3_4.pdf

Multiscale Modeling: A Review

https://www.cavs.msstate.edu/publications/docs/2004/01/749High%20cycle%20fatigue.pdf

High cycle fatigue of a die cast AZ91E-T4 magnesium alloy

The castability and properties of Al—Si based foundry alloys are affected by the inevitable introduction of impurity elements during melting and casting. Iron has consistently emerged as the most common impurity element that generally imparts negative influences on the soundness and mechanical properties of these alloys. It leads to the formation of iron-bearing intermetallics whose type, size, morphology and amount depend on the alloy composition, melt thermal history, cooling rate and post-casting heat treatments. These compounds, particularly their size and morphology, are the main culprits responsible for the significant influence of iron on the castability and mechanical properties. The most common of these compounds are β-Al5FeSi with a needle/platelet morphology, α-Al15Fe3Si2 with a Chinese script or polyhedron morphology and π-Al8Mg3FeSi6 also with a Chinese script morphology. The iron in the α phase can be substituted by Mn or Cr whereas the π phase forms when Mg is present. The β phase (the most...

Influence of iron on castability and properties of aluminium silicon alloys: literature review

https://www.cavs.msstate.edu/publications/docs/2003/01/754Cyclic%20plasticity.pdf

Cyclic plasticity at pores and inclusions in cast Al-Si alloys

r Mechanical fatigue tests were conducted on uniaxial specimens machined from a cast A356-T6 aluminium alloy plate at total strain amplitudes ranging from 0.1 to 0.8% (R = - 1). The cast alloy contains strontium-modified silicon particles (vol. fract. ∼6%) within an Al-Si eutectic, dispersed a intermetallic particles, Al 15 (Fe,Mn) 3 Si 2 (vol. fract. ∼1%), and an extremely low overall volume fraction of porosity (0.01%). During the initial stages of the fatigue process, we observed that a small semicircular fatigue crack propagated almost exclusively through the Al-1% Si dendrite cells. The small crack avoided the modified silicon particles in the Al-Si eutectic and only propagated along the a intermetallics if they were directly in line with the crack plane. These growth characteristics were observed up to a maximum stress intensity factor of ∼K tr max = 7.0 MPa m 1/2 (maximum plastic zone size of 96 μm). When the fatigue crack propagated with a maximum crack tip driving force above 7.0 MPa m 1/2 the larger fatigue crack tip process zone fractured an increased number of silicon particles and a intermetallics ahead of the crack tip, and the crack subsequently propagated preferentially through the damaged regions. As the crack tip driving force further increased, the area fraction of damaged a intermetallics and silicon particles on the fatigue fracture surfaces also increased. The final stage of failure (fast fracture) was observed to occur almost exclusively through the Al-Si eutectic regions and the a intermetallics.

The influence of modified intermetallics and Si particles on fatigue crack paths in a cast A356 Al alloy

Crack growth histories for creep-brittle aluminium alloy 2519-T87 are simulated by controlling the rate of release of finite element nodes along the crack growth path using a variable time-step, nodal release algorithm. While earlier experimental studies established little or no correlation between time-dependent fracture parameters and the crack growth rate, a˙, during creep-brittle fracture, the numerical results presented here indicate excellent correlation of the C t parameter with a˙ during the quasi-steady state crack growth regime. Differences in the experimental and numerical determination of time-dependent fracture parameters are likely to be due to difficulties in experimental determination of the creep component of the load line deflection rate, V c , during creep-brittle crack growth. A new quantity, K/r q∼c, is derived from time-dependent fracture parameters to predict crack growth for transient, quasi-steady state and steady state crack growth. However, C t and K/r q∼c should only be employed as parameters for predicting creep-brittle crack growth with an understanding of the couplings which exist between these parameters and the crack growth rate.

Crack tip parameters for creep-brittle crack growth

The C t parameter has proven very useful in correlations of creep crack growth behaviour under both transient and steady state creep conditions In this paper, we investigate the implications of adopting a different definition of the creep zone based on an absolute measure of creep strain rather than a measure that is relative to the elastic strain The analytical equations for small-scale creep and transition times from small-scale creep to extensive creep conditions are derived for the C t parameter using this alternative definition, considering both primary and secondary creep strain It is shown that this alternative definition gives a reasonable starting point for the theory, approximately in accordance with the transient evolution of the C t parameter based on the more conventional definition of the creep zone, and removes the somewhat artificial limit of applicability imparted by the classical creep zone definition used in creep fracture mechanics Accordingly, diffusional creep processes with a power law exponent n ≤ 3 are admitted in the C t description

McDowell

Papers

The influence of modified intermetallics and Si particles on fatigue crack paths in a cast A356 Al alloy

Crack tip parameters for creep-brittle crack growth

AN ALTERNATIVE ANALYTICAL APPROXIMATION OF THE Ct PARAMETER