Tensile failure observations in sintered steel foam struts revealed by sub-micron contrast-enhanced microtomography

Kaya, Ali Can; Zaslansky, Paul; Nikolaus, Anneke; Fleck, Claudia

doi:10.1016/j.matdes.2016.05.069

Cited by 26 publications

(27 citation statements)

References 34 publications

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“…The strains corrected by the images were significantly less than those directly measured in the INSTRON machine by a factor of ~2.7 in the elastic region (~1.9 in the plastic region). This implies that the slippage effect is still considerable between the specimen and the jaw faces regardless of the rough texture of the faces [8,25]. However, the use of high resolution images (the non-contact technique) can accurately record strains in the specimen despite the slippage effect.…”

Section: Dfmentioning

confidence: 99%

Characterisation and constitutive model of tensile properties of selective laser melted Ti-6Al-4V struts for microlattice structures

Wang

2018

Materials Science and Engineering: A

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Predicting the mechanical performance of selective laser melted (SLM) microlattice structures requires the constitutive data of the parent solid material in the struts. This work first characterised the cross-sectional features of individual SLM Ti-6Al-4V struts. The direct examination revealed the non-linear relation between the equivalent diameter and the Feret diameter of a strut, which was quantified by an empirical equation. The equation considering surface roughness effects allowed the non-destructive determination of the equivalent diameter using the directly measured Feret diameter prior to tension testing. Uniaxial tension experiments were then performed to accurately measure the constitutive behaviour of SLM Ti-6Al-4V struts, with the strain history tracked and recorded using high resolution imaging. It was found that the strut diameter ranging 300-1200 µm has a negligible effect on the stress-strain response. The strain hardening and fracture behaviour of the SLM Ti-6Al-4V can be quantitatively described using the Johnson-Cook models with damage. The constitutive models were finally validated by the 3D finite element model and experiments of uniaxial compression on an SLM microlattice structure.The methodology presented here can accurately characterise and formulate the constitutive behaviour of SLM metallic struts for microlattices.

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Section: Dfmentioning

confidence: 99%

Characterisation and constitutive model of tensile properties of selective laser melted Ti-6Al-4V struts for microlattice structures

Wang

2018

Materials Science and Engineering: A

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“…The mechanical properties of open‐cell foam struts generally differ from those of bulk metal specimens, due to a variety of reasons including differences in the testing methods, microstructures and geometry. The difficulties in testing the tiny struts have been addressed in several studies . Due to these challenges the results of the micro‐tensile tests scatter to a large extent.…”

Section: Discussionmentioning

confidence: 99%

“…Their yield strength was defined conventionally, as a 0.2% offset strain, and fracture strain was determined as the strain correlating to the point where an abrupt stress drop indicates fracture, as described in ref. .…”

Section: Methodsmentioning

confidence: 99%

“…Steel foam struts are much stronger than struts from Al‐ or Al‐alloy foams. Gluing is therefore not possible, and the complex geometry, curved shape and large testing force (60–70 N) hollow austenitic steel struts makes tensile testing of these struts very challenging …”

Section: Introductionmentioning

confidence: 99%

“…We previously reported the influence of imperfections such as micropores and edge defects on the failure behavior of powder metallurgical produced sintered austenitic steel struts . Imperfections and strut geometry lead to a non‐uniform stress distribution across the strut, resulting in premature fracture if stress raisers and tensile stresses from bending come together.…”

Section: Introductionmentioning

confidence: 99%

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Foams of Gray Cast Iron as Efficient Energy Absorption Structures: A Feasibility Study

et al. 2019

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Gray cast iron foams are produced using a reticulated polyurethane by using a modified investment casting process. To evaluate the attributes of the produced micro-geometries, foam segments and single struts are investigated by light and electron microscopy in 2D, and synchrotron micro-computed tomography in 3D. Mechanical properties are determined by macro/micromechanical testing and nanoindentation. In the microstructure of the gray cast iron struts, both flake-like coarse type A and locally fine undercooled type D graphite particles are observed. The distribution of the two graphite types is heterogeneous and is the likely cause for the large scatter of the mechanical properties of the single struts. The high graphite content and the resulting brittle behavior of the struts lead to strong serrations in the stressstrain curve of the foams with a negative effect on energy absorption. We found a relatively low energy absorption efficiency of below 50% as compared to 75% in 316L austenitic steel struts. The small specimen size results in scale effects which strongly influence the mechanical properties of the foams. Further improvement in the fabrication of gray cast iron foams is needed to tailor graphite distributions and optimize performance of cast iron-based foams.

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Micromechanical Characterization of Metal Foams

Jung¹,

Diebels²

2019

Adv Eng Mater

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Cellular materials such as foams, honeycombs, or auxetic structures are an interesting type of structural materials for lightweight constructions or dynamic energy absorbers. These microheterogeneous materials consist of a hierarchical structure. Foams can be separated into a macro scale, meso scale, and micro scale dealing with the entire specimen or component, individual pores, and individual struts, respectively. As a result, the macroscopic foam properties are strongly related to the mesoscopic and microscopic properties as a superposition of geometrical structural response and material properties. Whereas the geometry can be easily determined, e.g., by computer tomography measurements, the evaluation of real micro material properties of individual struts or cell walls is still a very challenging task. The material properties of these constituents of open‐cell or closed‐cell foams significantly differ from bulk material properties due to changes in boundary condition during production and different scaling effects, such as different surface‐to‐volume ratios of oxide layers or different cooling conditions due to less material in struts than in the bulk. However, the need for reliable micro material properties for the realistic forecast of macroscopic properties of components made of foam by numerical simulations makes the micromechanical characterization and testing of metal foams to an emerging field of research. The present contribution deals with the most relevant achievements in the field from the beginnings to the present day.

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Tensile failure observations in sintered steel foam struts revealed by sub-micron contrast-enhanced microtomography

Cited by 26 publications

References 34 publications

Characterisation and constitutive model of tensile properties of selective laser melted Ti-6Al-4V struts for microlattice structures

Characterisation and constitutive model of tensile properties of selective laser melted Ti-6Al-4V struts for microlattice structures

Foams of Gray Cast Iron as Efficient Energy Absorption Structures: A Feasibility Study

Micromechanical Characterization of Metal Foams

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