Hirpa G. Lemu

Prof. Hirpa G. Lemu

Faculty of Science and Technology, University of Stavanger, N-4036 Stavanger, Norway
orcid

Research Focus & Metrics

Academic Career Length

17Years (2010-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

View All Publications
27 March 2018 in Materials
Verified
Journal Article
Open access
PDF file
AGAboma Wagari Gebisa
Aboma Wagari Gebisa
HLHirpa G. Lemu
Hirpa G. Lemu
Fused-deposition modeling (FDM), one of the additive manufacturing (AM) technologies, is an advanced digital manufacturing technique that produces parts by heating, extruding and depositing filaments of thermoplastic polymers. The properties of FDM-produced parts apparently depend on the processing parameters. These processing parameters have conflicting advantages that need to be investigated. This article focuses on an investigation into the effect of these parameters on the flexural properties of FDM-produced parts. The investigation is carried out on high-performance ULTEM 9085 material, as this material is relatively new and has potential application in the aerospace, military and automotive industries. Five parameters: air gap, raster width, raster angle, contour number, and contour width, with a full factorial design of the experiment, are considered for the investigation. From the investigation, it is revealed that raster angle and raster width have the greatest effect on the flexural properties of the material. The optimal levels of the process parameters achieved are: air gap of 0.000 mm, raster width of 0.7814 mm, raster angle of 0°, contour number of 5, and contour width of 0.7814 mm, leading to a flexural strength of 127 MPa, a flexural modulus of 2400 MPa, and 0.081 flexural strain.

18 February 2023 in Metals
Verified
Journal Article
Open access
PDF file
Naol Dessalegn DejeneNaol Dessalegn Dejene
Naol Dessalegn Dejene
HLHirpa G. Lemu
Hirpa G. Lemu
Powder bed fusion (PBF) is recognized as one of the most common additive manufacturing technologies because of its attractive capability of fabricating complex geometries using many possible materials. However, the quality and reliability of parts produced by this technology are observed to be crucial aspects. In addition, the challenges of PBF-produced parts are hot issues among stakeholders because parts are still insufficient to meet the strict requirements of high-tech industries. This paper discusses the present state of the art in PBF and technological challenges, with a focus on selective laser melting (SLM). The review work focuses mainly on articles that emphasize the status and challenges of PBF metal-based AM, and the study is primarily limited to open-access sources, with special attention given to the process parameters and flaws as a determining factor for printed part quality and reliability. Moreover, the common defects due to an unstrained process parameter of SLM and those needed to monitor and sustain the quality and reliability of components are encompassed. From this review work, it has been observed that there are several factors, such as laser parameters, powder characteristics, material properties of powder and the printing chamber environments, that affect the SLM printing process and the mechanical properties of printed parts. It is also concluded that the SLM process is not only expensive and slow compared with conventional manufacturing processes, but it also suffers from key drawbacks, such as its reliability and quality in terms of dimensional accuracy, mechanical strength and surface roughness.

13 August 2021 in Journal of Composites Science
Verified
Journal Article
Open access
PDF file
Tomasz TrzepiecińskiTomasz Trzepieciński
Tomasz Trzepieciński
Sherwan Mohammed NajmSherwan Mohammed Najm
Sherwan Mohammed Najm
Manel SbaytiManel Sbayti
Manel Sbayti
HBHedi Belhadjsalah
Hedi Belhadjsalah
Marcin SzpunarMarcin Szpunar
Marcin Szpunar
HLHirpa G. Lemu
Hirpa G. Lemu
Fibre metal laminates, hybrid composite materials built up from interlaced layers of thin metals and fibre reinforced adhesives, are future-proof materials used in the production of passenger aircraft, yachts, sailplanes, racing cars, and sports equipment. The most commercially available fibre–metal laminates are carbon reinforced aluminium laminates, aramid reinforced aluminium laminates, and glass reinforced aluminium laminates. This review emphasises the developing technologies for forming hybrid metal–polymer composites (HMPC). New advances and future possibilities in the forming technology for this group of materials is discussed. A brief classification of the currently available types of FMLs and details of their methods of fabrication are also presented. Particular emphasis was placed on the methods of shaping FMLs using plastic working techniques, i.e., incremental sheet forming, shot peening forming, press brake bending, electro-magnetic forming, hydroforming, and stamping. Current progress and the future directions of research on HMPCs are summarised and presented.

1 January 2021 in Materials Today: Proceedings
Verified
Journal Article
Open access
RHRobin H. Helle
Robin H. Helle
HLHirpa G. Lemu
Hirpa G. Lemu

1 December 2018 in Polymer Testing
Verified
Journal Article
Closed access
KBKate Iren Byberg
Kate Iren Byberg
AGAboma Wagari Gebisa
Aboma Wagari Gebisa
HLHirpa G. Lemu
Hirpa G. Lemu

1 February 2022 in Polymer Testing
Verified
Journal Article
Open access
ABAbera E. Bekele
Abera E. Bekele
HLHirpa G. Lemu
Hirpa G. Lemu
MJMoera G. Jiru
Moera G. Jiru