Partner: Paul Wood

University of Derby (GB)

Recent publications
1.Kopeć M., Dubey Ved P., Pawlik M., Wood P., Kowalewski Z.L., Experimental identification of yield surface for additively manufactured stainless steel 316L under tension–compression-torsion conditions considering its printing orientation, Manufacturing Letters, ISSN: 2213-8463, DOI: 10.1016/j.mfglet.2024.07.003, Vol.41, pp.28-32, 2024
Abstract:

Stainless steel 316L tubes and bars were additively manufactured (AM) by using the Laser Powder Bed Fusion Melting (LPBF-M) method in three orientations. As-built specimens were then machined and the initial yield surface was determined for three printing orientations based on the yield stress definition for 0.005 % plastic offset strain. The as-received, wrought material was additionally tested using the same tension–compression-torsion conditions to compare the mechanical behaviour of AM and wrought SS316L. The sizes of yield surfaces elaborated for LPBF-M specimens increased along the tensile and compressive directions and shrunk when torsion was applied, as compared to the as-received specimen.

Keywords:

Stainless steel ,Yield surface ,Additive manufacturing

Affiliations:
Kopeć M.-IPPT PAN
Dubey Ved P.-IPPT PAN
Pawlik M.-other affiliation
Wood P.-University of Derby (GB)
Kowalewski Z.L.-IPPT PAN
2.Kopeć M., Gunputh U., Williams G., Macek W., Kowalewski Z.L., Wood P., Fatigue Damage Evolution in SS316L Produced by Powder Bed Fusion in Different Orientations with Reused Powder Feedstock, EXPERIMENTAL MECHANICS, ISSN: 0014-4851, DOI: 10.1007/s11340-024-01118-1, pp.1-16, 2024
Abstract:

Background

Metal Laser Powder Bed Fusion Melting (LPBF-M) is considered economically viable and environmentally sustainable because of the possibility of reusing the residual powder feedstock leftover in the build chamber after a part build is completed. There is however limited information on the fatigue damage development of LPBF-M samples made from reused feedstock.
Objective

In this paper, the stainless steel 316 L (SS316L) powder feedstock was examined and characterised after 25 reuses, following which the fatigue damage development of material samples made from the reused powder was assessed.
Methods

The suitability of the powder to LPBF-M technology was evaluated by microstructural observations and measurements of Hall flow, apparent and tapped density as well as Carr’s Index and Hausner ratio. LPBF-M bar samples in three build orientations (Z – vertical, XY – horizontal, ZX – 45° from the build plate) were built for fatigue testing. They were then subjected to fatigue testing under load control using full tension and compression cyclic loading and stress asymmetry coefficient equal to -1 in the range of stress amplitude from ± 300 MPa to ± 500 MPa.
Results

Samples made from reused powder (25 times) in the LPBF-M process exhibited similar fatigue performance to fresh unused powder although a lower ductility for vertical samples was observed during tensile testing. Printing in horizontal (XY) and diagonal (ZX) directions, with reused powder, improved the service life of the SS316L alloy in comparison to the vertical (Z).
Conclusions

Over the 25 reuses of the powder feedstock there was no measurable difference in the flowability between the fresh (Hall Flow: 21.4 s/50 g) and reused powder (Hall Flow: 20.6 s/50 g). This confirms a uniform and stable powder feeding process during LPBF-M for both fresh and reused powder. The analysis of fatigue damage parameter, D, concluded cyclic plasticity and ratcheting to be the main mechanism of damage.

Keywords:

SS316L ,Stainless steel,Fatigue ,Additive manufacturing,Laser Powder Bed Fusion Melting (LPBF-M)

Affiliations:
Kopeć M.-IPPT PAN
Gunputh U.-other affiliation
Williams G.-University of Derby (GB)
Macek W.-other affiliation
Kowalewski Z.L.-IPPT PAN
Wood P.-University of Derby (GB)
3.Kopeć M., Gunputh U., Macek W., Kowalewski Z.L., Wood P., Orientation effects on the fracture behaviour of additively manufactured stainless steel 316L subjected to high cyclic fatigue, Theoretical and Applied Fracture Mechanics, ISSN: 0167-8442, DOI: 10.1016/j.tafmec.2024.104287, pp.1-20, 2024
Abstract:

In this paper, stainless steel 316L (SS316L) bars were additively manufactured (AM) in three orientations (Z – vertical, XY – horizontal, ZX45 – midway between vertical and horizontal) by using the Laser Powder Bed Fusion Melting (LPBF-M) method. The AM specimens were subjected to load control fatigue testing under full tension and compression (R = -1) at stress amplitudes ±350, ±400 and ±450 MPa. The XY and ZX45 printing orientations were found to significantly improve service life. Although similar strain response was found for each orientation when the same stress amplitude was applied, slightly different fracture mechanisms were identified during the post-mortem surface observations.

Keywords:

SS316L,stainless steel,fatigue,additive manufacturing,Laser Powder Bed Fusion Melting (LPBF-M)

Affiliations:
Kopeć M.-IPPT PAN
Gunputh U.-other affiliation
Macek W.-other affiliation
Kowalewski Z.L.-IPPT PAN
Wood P.-University of Derby (GB)
4.Wood P., Libura T., Kowalewski Z.L., Williams G., Serjouei A., Influences of horizontal and vertical build orientations and post-fabrication processes on the fatigue behavior of stainless steel 316L produced by selective laser melting, Materials, ISSN: 1996-1944, DOI: 10.3390/ma12244203, Vol.12, No.24, pp.4203-1-19, 2019
Abstract:

In this paper, the influences of build orientation and post-fabrication processes, including stress-relief, machining, and shot-peening, on the fatigue behavior of stainless steel (SS) 316L manufactured using selective laser melting (SLM) are studied. It was found that horizontally-built (XY) and machined (M) test pieces, which had not been previously studied in the literature, in both stress-relieved (SR) or non-stress-relieved (NSR) conditions show superior fatigue behavior compared to vertically-built (ZX) and conventionally-manufactured SS 316L. The XY, M, and SR (XY-M-SR) test pieces displayed fatigue behavior similar to the XY-M-NSR test pieces, implying that SR does not have a considerable effect on the fatigue behavior of XY and M test pieces. ZX-M-SR test pieces, due to their considerably lower ductility, exhibited significantly larger scatter and a lower fatigue strength compared to ZX-M-NSR samples. Shot-peening (SP) displayed a positive effect on improving the fatigue behavior of the ZX-NSR test pieces due to a compressive stress of 58 MPa induced on the surface of the test pieces. Fractography of the tensile and fatigue test pieces revealed a deeper understanding of the relationships between the process parameters, microstructure, and mechanical properties for SS 316L produced by laser systems. For example, fish-eye fracture pattern or spherical stair features were not previously observed or explained for cyclically-loaded SLM-printed parts in the literature. This study provides comprehensive insight into the anisotropy of the static and fatigue properties of SLM-printed parts, as well as the pre- and post-fabrication parameters that can be employed to improve the fatigue behavior of steel alloys manufactured using laser systems.

Keywords:

selective laser melting, stainless steel 316L, fatigue, defect, fracture

Affiliations:
Wood P.-University of Derby (GB)
Libura T.-IPPT PAN
Kowalewski Z.L.-IPPT PAN
Williams G.-University of Derby (GB)
Serjouei A.-University of Derby (GB)

Conference abstracts
1.Dubey V.P., Kopeć M., Pawlik M., Wood P., Kowalewski Z.L., Effect of Build Orientation on the Yield Surface of Stainless Steel 316L Fabricated by Laser Powder Bed Fusion Melting (LPBF-M), BSSM, 18th International Conference on Advances in Experimental Mechanics, 2024-09-03/09-05, Liverpool (GB), pp.1-2, 2024
Abstract:

The Laser Powder Bed Fusion Melting (LPBF-M) method was used to additively manufacture stainless steel 316L tubes in three different orientations. The yield surface approach was implemented to assess the variation of mechanical properties within the as-built specimens. Yield surfaces were determined for each build orientation based on the definition of yield stress for 0.005% plastic offset strain. The initial yield surfaces obtained for the as-built material exhibit anisotropic behaviour, possibly resulting from the preferred grain orientation developed during LPBF-M processing.

Affiliations:
Dubey V.P.-IPPT PAN
Kopeć M.-IPPT PAN
Pawlik M.-other affiliation
Wood P.-University of Derby (GB)
Kowalewski Z.L.-IPPT PAN
2.Libura T., Sienkiewicz J., Nowak Z., Kowalewski Z.L., Rusinek A., Voyiadjis G.Z., Gunputh U., Wood P., CHARACTERISATION OF THE COLLAPSE BEHAVIOUR IN 3D PRINTED IN718 ALLOY UNDER A RANGE OF STRESS STATES AND STRAIN RATES, DAS 2024, 40th DANUBIA-ADRIA SYMPOSIUM on Advances in Experimental Mechanics, 2024-09-24/09-27, Gdańsk (PL), pp.1-2, 2024
3.Dubey V.P., Kopeć M., Pawlik M., Wood P., Kowalewski Z.L., Yield surface identification of additively manufactured stainless steel 316L considering its printing orientation, KonDokPAN 2024, The 8th edition of the Conference of Doctoral Students of the PAS, 2024-10-11/10-13, Warszawa (PL), pp.38-38, 2024
4.Wood P., Gunputh U., Williams G., Carter W., Boud F., Bahi S., Rusinek A., Kowalewski Z.L., Nowak Z., Libura T., Vojiadjis G.Z., Diaz-Alvare J., Miguelez M.H., SELECTIVE LASER MELTING OF A HIGH PRECISION TURBOMACHINERY APPLICATION IN IN718 ALLOY, ICEM, 19th International Conference on Experimental Mechanics, 2022-07-17/07-21, Kraków (PL), pp.34-35, 2022