Methods and systems to predict fatigue life in aluminum castings

An article of manufacture comprising a computer usable medium having computer readable program code embodied therein for predicting fatigue life in an aluminum casting, said computer readable program code in said article of manufacture comprising:

• computer readable program code portion for causing a computer to determine which of a casting flaw, second phase particle and persistent slip band predominates as a cause of fatigue failure;
• computer readable program code portion for causing the computer to calculate a predicted fatigue life based on extreme value statistics and a multiscale fatigue algorithm the latter of which is based on which of said predominant cause of fatigue failure is determined, wherein said multiscale fatigue life algorithm is configured such that in situations where fatigue behavior of the casting is dominated by said casting flaw, said multiscale fatigue life algorithm uses the equation
• N=Ni+Np=Np=C1σa−maeq−(m−2)/2
• in situations where a maximum flaw size in the casting is larger than a critical size, whereas in situations where said maximum flaw size is smaller than a critical size, said multiscale fatigue life algorithm uses the equation
• N=Ni+Np=Np=C2(εmaxσaσys−1)naeqq;
• wherein said multiscale fatigue life algorithm is configured such that in situations where fatigue behavior of the casting is dominated by at least one of said second phase particle and where a mean free path through an aluminum matrix associated with transgranular crack propagation is present and evidence of at least one of cracking and debonding of said second phase particle is present or anticipated, said multiscale fatigue life algorithm uses the equation
• N=Ni+Np=Np=C3(εmaxσaσys−1)ndeqq,
• whereas in situations where said mean free path through said aluminum matrix associated with intergranular crack propagation is present and evidence of at least one of cracking and debonding of said second phase particle is present or anticipated, said multiscale fatigue life algorithm uses the equation
• N=Ni+Np=C4(Δεeqp)−e(dg)f+C5σa−m(dg)−(m−2)/2;
• wherein said multiscale fatigue life algorithm is configured such that in situations where fatigue behavior of the casting is dominated by at least one said persistent slip band and where said persistent slip band size is constrained by a mean free path through said aluminum matrix that is smaller than a grain size is present and evidence of at least one of cracking and debonding of said second phase particle is neither present nor anticipated, said multiscale fatigue life algorithm uses the equation
• N=Ni+Np=C6(Δεeqp)−e(λeq)f+C7(εmaxσaσys−1)n(λeq)q,
• whereas in situations where said initiation site predominantly comprises said persistent slip band unconstrained by a mean free path through said aluminum matrix smaller than the grain size is present is present and evidence of at least one of cracking and debonding of said second phase particle is neither present nor anticipated, said multiscale fatigue life algorithm uses the equation
• N=Ni+Np=C8(Δεeqp)−e(dg)f+C9σa−m(dg)−(m−2)/2,
• wherein C1 through C9, m, n, e, f and q are constants, σa is a stress amplitude, σys is a yield strength, εmax is a maximum total strain during loading cycle, εmax is maximum total strain during loading cycle, aeq is an equivalent initial crack-like defect size, deq is an equivalent initial crack-like second phase particle size, λeq is an equivalent mean free path through said aluminum matrix, Δεeqp is a local equivalent plastic strain and dg is equivalent grain size;
• and
• computer readable program code portion configured to output results calculated by at least one of said equations to at least one of a machine-readable format and a human-readable format.

A machine for predicting fatigue life in aluminum castings, said machine comprising:

• a device configured to acquire at least one of measured or predicted sample defect information;
• and
• a computing member configured to accept fatigue property data gathered from said device and further configured to calculate fatigue properties of the casting in accordance to instructions provided by a computer-readable program, said program comprising:
• a code portion for causing said computing member to determine which of a casting flaw, second phase particle and persistent slip band predominates as a cause of fatigue failure;
• a code portion for causing said computing member to calculate a predicted fatigue life by using extreme value statistical methods to estimate an upper bound initiation site size expected to occur in the casting and multiscale fatigue equations where at least one of said multiscale fatigue equations is selected based upon which of said casting flaw, second phase particle and persistent slip band predominates,
• wherein situations where fatigue behavior of the casting is dominated by the casting flaw, said code portion uses the equation
• N=Ni+Np=Np=C1σa−maeq−(m−2)/2
• in situations where a maximum flaw size in the casting is larger than a critical size, whereas in situations where said maximum flaw size is smaller than a critical size, using the equation
• N=Ni+Np=Np=C2(εmaxσaσys−1)naeqq;
• wherein situations where fatigue behavior of the casting is dominated by at least one second phase particle and where a mean free path through an aluminum matrix associated with transgranular crack propagation is present and evidence of at least one of cracking and debonding of said second phase particle is present or anticipated, said code uses the equation
• N=Ni+Np=Np=C3(εmaxσaσys−1)ndeqq,
• whereas in situations where said mean free path through an aluminum matrix associated with intergranular crack propagation is present and evidence of at least one of cracking and debonding of said second phase particle is present or anticipated, by using the equation
• N=Ni+Np=C4(Δεeqp)−e(dg)f+C5σa−m(dg)−(m−2)/2;
• and
• wherein situations where fatigue behavior of the casting is dominated by persistent slip bands and where said persistent slip band size is constrained by a mean free path through said aluminum matrix that is smaller than a grain size is present and evidence of at least one of cracking and debonding of second phase particles is neither present nor anticipated, said code uses the equation
• N=Ni+Np=C6(Δεeqp)−e(λeq)f+C7(εmaxσaσys−1)n(λeq)q,
• whereas in situations where said initiation site predominantly comprises said persistent slip band unconstrained by a mean free path through said aluminum matrix that is smaller than a grain size is present and evidence of at least one of cracking and debonding of second phase particles is neither present nor anticipated, using the equation
• N=Ni+Np=C8(Δεeqp)−e(dg)f+C9σa−m(dg)−(m−2)/2,
• wherein C1 through C9, m, n, e, f and q are constants, σa is a stress amplitude, σys is a yield strength, εmax is a maximum total strain during loading cycle, εmax is maximum total strain during loading cycle, aeq is an equivalent initial crack-like defect size, deq is an equivalent initial crack-like second phase particle size, λeq is an equivalent mean free path through said aluminum matrix, Δεeqp is a local equivalent plastic strain and dg is equivalent grain size.