Material Property Determination of Vibration Fatigued DMLS and Cold-Rolled Nickel Alloys

Abstract

An experimental procedure for qualifying material properties from cyclically worked parts was investigated in support of aging gas turbine engines and digital twin initiatives. For aging components, remanufacturing or repair efforts are necessary to sustain the life cycles of engines; and for digital twin, the virtual representation of a part requires accurate geometric and component material property measurement. Therefore, having an effective, non-destructive way to assess the material performance of parts is necessary. Since low cycle, low strain, mechanical testing is the ideal experimental approach for non-destructively assessing material properties, investigating the accuracy and trends of tensile properties of fatigue loaded parts was important. The fatigued parts used for this study were specimens tested according to the George Fatigue Method, and the materials observed were cold-rolled Inconel Alloys 625 and 718, and direct metal laser sintering (DMLS) Nickel Alloy 718. The tensile material properties were compared against pristine (non-fatigued) and published data. The comparison for the cold-rolled 625 and 718 results show an increase and a decrease, depending on rolling direction, of tensile strength due to the effects of fatigue cycles; however, the variation of the vibration affected tensile properties are all within one standard deviation of the pristine data. The comparisons of DMLS Nickel Alloys was conducted against two sets of alloys from different suppliers, and the results showed that the tensile properties are sensitive to DMLS manufacturing parameters and post-sintering processes. A digital twin related, nondestructive, material property determination technique is also discussed in this manuscript. The true alloy density was determined with the water displacement method, and elastic modulus is determined with an iterative Ritz method model. The modulus is under-predicted with this method, but suggestions for improving the model are discussed.

Bending fatigue life characterisation of direct metal laser sintering nickel alloy 718

“…all pristine H and V specimens combined) were used for overall comparisons to simulate unforeseen manufacturer uncertainties not present in the studied material stocks. Results show a 0.3-1% increase in strength properties due to vibration on 625 specimens in the V direction and a 0.4-0.7% decrease in strength 14 Results also show that the vibration affected strength properties of each individual specimen are within one standard deviation of the total pristine results in Table 2 and display no particular trends with respect to tensile specimen location along the span of vibrated plates. Results for the DMLS Ni Alloy 718 comparisons are shown in Table 3, where the final eight rows represent the vibration affected tensile properties.…”

“…In order to efficiently utilise available DMLS material and to correlate the strengths of specimens to respective fatigue lives, monotonic tensile data was acquired from dog bones cut out from fatigued plates . Four fatigue tested plates from each DMLS Vendor were analysed and six dog bone specimens with the geometry in Fig.…”

“…The 718 comparison shows the opposite results, where V specimens show roughly 1.5% decrease and H specimens show a 0.4–1.3% increase in strength properties because of the effects of vibration. These results do not indicate any trends based on cold‐rolling direction or accumulated cyclic damage . Results also show that the vibration affected strength properties of each individual specimen are within one standard deviation of the total pristine results in Table and display no particular trends with respect to tensile specimen location along the span of vibrated plates.…”

“…Vendor I plates were solution heat treated (968 o C for 1.5 h), aged (718 o C for 8 h to 612 o C for 8 h and then cooled below 150 o C), HIP (1177 o C at 103 MPa) and stress relieved (1065 o C for 1.5 h and then argon cooled). Vendor II plates were originally believed to have been stress relieved, but further inquiry on the manufacturing process shows no record of any post‐fusion treatment. The surface roughness for the finished products varied between Ra values of 5.08 and 12.7 µm; however, each plate was polished with a Merit fine‐grit buffing disc to Ra values between 1.27 and 5.08 µm.…”

Developing a Digital Twin and Digital Thread Framework for an ‘Industry 4.0’ Shipyard

“…Also, many of the physical phenomena involved in the manufacturing of several products such as aircraft, vehicles and machining tools are complex and hard to simulate, so these issues need more research to find better models. Additionally, the large amount of data that can be collected by a DTW introduces new challenges in data handling, processing and storage [13,14], and hence, a framework to build DTWs should address these challenges [8,[15][16][17][18][19][20].…”