PSI - Issue 34

Rhys Jones et al. / Procedia Structural Integrity 34 (2021) 39–44 Rhys Jones/ Structural Integrity Procedia 00 (2021) 000 – 000

40 2

Nomenclature

crack length

a

constant in the Hartman-Schijve equation rate of fatigue crack growth per cycle

A

da/dN

intercept in the Hartman-Schijve crack-growth equation maximum value of the applied stress in a fatigue cycle minimum value of the applied stress in a fatigue cycle

D

σ max σ min

FCG

fatigue crack growth

HS

An abbreviation for the Hartman-Schive crack growth equation.

the stress intensity factor

K

G co ∆ K

quasi-static value of the interlaminar fracture energy at the onset of crack growth maximum value of the stress intensity factor in the fatigue cycle minimum value of the stress intensity factor in the fatigue cycle range of the stress intensity factor in the fatigue cycle, as defined below

∆ = − ∆ K thr

the threshold value of the stress intensity factor used in the Hartman-Schive crack growth equation.

exponent in the Hartman-Schijve crack-growth equation

p

number of fatigue cycles stress ratio (= K min / K max ) coefficient of determination

N R

R 2

1. Introduction McMichael and Frazer explained that one of the drivers for AM is to rapidly build replacement parts, to both increase availability and alleviate logistics problems, and US Army Directive 2019-19 states that: i) Advanced manufacturing can be used to address the readiness challenges posed by parts obsolescence, diminishing sources of supply, and sustained operations in austere environments. ii) If employed to the maximum extent, advanced manufacturing could transform battlefield logistics through on demand fabrication of parts close to the point of need, thus reducing the large number of parts stored and transported around the world. In this context US Joint Services Structural Guidelines JSSG2006, MIL-STD-1530D, USAF Structures Bulletin EZ-19-01 and Gorelik (US FAA) highlight that the airworthiness certification of an AM part requires a durability and damage tolerance assessment (DADT). However, although aluminium alloys are widely used in current military and civil aircraft most of the work to date on the DADT assessment of AM parts has focused on other AM materials, viz: Ti-6Al-4V, 316L, 304L, 18Ni, Aermat100, etc. Unfortunately, if an AM part is used to replace an aluminium alloy part there is the potential that the difference in the Young’s modulus may result in a change in the load path, and hence compromise the airworthiness certification of the airframe. Consequently, the recent paper by Muhammad et al focused on assessing the mechanical properties of a range of additively manufactured (AM) aluminum alloys, viz: AlSi10Mg, Scalmalloy, and QuesTek Al. Of the various AM aluminium alloys studied it was found that AM Scalmalloy had a tensile strength, a Young ’ s modulus, a yield stress, and an elongation to failure that were similar to that of the aluminium alloy ’s AA7075-T7351 and AA7050-T7451, which are both widely used in legacy aircraft. As such AM Scalmalloy would appear to be an ideal candidate for use in legacy aircraft. As such the primary focus