| 1. |
- Auenhammer, Robert, 1991, et al.
(författare)
-
Fibre orientation distribution function mapping for short fibre polymer composite components from low resolution/large volume X-ray computed tomography
- 2024
-
Ingår i: Composites Part B: Engineering. - 1359-8368. ; 275
-
Tidskriftsartikel (refereegranskat)abstract
- Short glass fibre injection moulded composites, used in interior and exterior automotive parts, are exposed to complex stress states, for example during a crash. As the fibre scale dominates the composite’s material properties, numerical models need to account for the local fibre orientation. In recent years, mould flow simulation results have been exploited to predict the fibre orientations for finite element models, albeit with limited accuracy. Alternatively, X-ray computed tomography can be used to directly image and analyse fibre orientations. Traditionally, achieving the necessary resolution to image individual fibres restricts the imaging to small regions of the component. However, this study takes advantage of recent advancements in imaging and image analysis to overcome this limitation. As a result, it introduces, for the first time, a reliable, fast, and automated fibre orientation mapping for a full component based on image analysis at the individual fibre level; even for cases where the pixel size is significantly larger than the fibre diameter. By scanning at lower resolutions, a drastically larger volume of interest can be achieved. The resulting fibre orientation analysis and mapping algorithm, based on X-ray computed tomography, is well matched to the level of information required for automotive crash modelling with a standard element-size of a few millimetres. The entire process, encompassing image acquisition, image analysis and fibre orientation mapping, can be directly integrated into an industrial full component application in a matter of hours.
|
|
| 2. |
- Borgh, Ida, et al.
(författare)
-
On the three-dimensional structure of WC grains in cemented carbides
- 2013
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 61:13, s. 4726-4733
-
Tidskriftsartikel (refereegranskat)abstract
- In the present work, the size distribution and shape of WC grains in cemented carbides (WC-Co), with different Co contents, have been investigated in three dimensions. Direct three-dimensional (3-D) measurements, using focused ion beam serial sectioning and electron backscattered diffraction (EBSD), were performed and a 3-D microstructure was reconstructed. These measurements were supplemented by two-dimensional (2-D) EBSD and scanning electron microscopy on extracted WC grains. The data from 2-D EBSD collected on planar sections were transformed to three dimensions using a recently developed statistical method based on an iterative inverse Saltykov procedure. This stereological analysis revealed that the assumed spherical shape of WC grains during the Saltykov method is reasonable and the estimated 3-D size distribution is qualitatively in good agreement with the actual distribution measured from 3-D EBSD. Although the spherical assumption is generally fair, the WC grains have both faceted and rounded surfaces. This is a consequence of the relatively low amount of liquid phase during sintering, which makes impingements significant. Furthermore, the observed terraced surface structure of some WC grains suggests that 2-D nucleation is the chief coarsening mechanism to consider.
|
|
| 3. |
- Hedström, Peter, et al.
(författare)
-
On the Three-Dimensional Microstructure of Martensite in Carbon Steels
- 2012
-
Ingår i: Proceedings Of The 1st International Conference On 3D Materials Science. - Hoboken, NJ, USA : John Wiley & Sons. - 9781118470398 - 9781627489331 ; , s. 19-24
-
Konferensbidrag (refereegranskat)abstract
- The mechanical properties of high-performance steels are often reliant on the hard martensitic structure. It can either be the sole constituent e. g. in tool steels, or it can be part of a multi-phase structure as e. g. in dual-phase steels. It is well-known that the morphology of martensite changes from lath to plate martensite with increasing carbon content. The transition from lath to plate is however less known and in particular the three-dimensional (3D) aspects in the mixed lath and plate region require more work. Here the current view of the 3D microstructure of martensite in carbon steels is briefly reviewed and complemented by serial sectioning experiments using a focused ion beam scanning electron microscope (FIB-SEM). The large martensite units in the Fe-1.2 mass% C steel investigated here are found to have one dominant growth direction, less transverse growth and very limited thickening. There is also evident transformation twinning parallel to the transverse direction. It is concluded that more 3D analysis is required to understand the 3D microstructure of martensite in the mixed lath and plate region and to verify the recently proposed 3D phase field models of martensite in steels.
|
|
| 4. |
- Lu, Xuekun, et al.
(författare)
-
Anisotropic crack propagation and deformation in dentin observed by four-dimensional X-ray nano-computed tomography.
- 2019
-
Ingår i: Acta Biomaterialia. - : Elsevier BV. - 1742-7061 .- 1878-7568. ; 96, s. 400-411
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding the cracking behaviour of biological composite materials is of practical importance. This paper presents the first study to track the interplay between crack initiation, microfracture and plastic deformation in three dimensions (3D) as a function of tubule and collagen fibril arrangement in elephant dentin using in situ X-ray nano-computed tomography (nano-CT). A nano-indenter with a conical tip has been used to incrementally indent three test-pieces oriented at 0°, 45° and 70° to the long axis of the tubules (i.e. radial to the tusk). For the 0° sample two significant cracks formed, one of which linked up with microcracks in the axial-radial plane of the tusk originating from the tubules and the other one occurred as a consequence of shear deformation at the tubules. The 70° test-piece was able to bear the greatest loads despite many small cracks forming around the indenter. These were diverted by the microstructure and did not propagate significantly. The 45° test-piece showed intermediate behaviour. In all cases strains obtained by digital volume correlation were well in excess of the yield strain (0.9%), indeed some plastic deformation could even be seen through bending of the tubules. The hoop strains around the conical indenter were anisotropic with the smallest strains correlating with the primary collagen orientation (axial to the tusk) and the largest strains aligned with the hoop direction of the tusk. STATEMENT OF SIGNIFICANCE: This paper presents the first comprehensive study of the anisotropic nature of microfracture, crack propagation and deformation in elephant dentin using time-lapse X-ray nano-computed tomography. To unravel the interplay of collagen fibrils and local deformation, digital volume correlation (DVC) has been applied to map the local strain field while the crack initiation and propagation is tracked in real time. Our results highlight the intrinsic and extrinsic shielding mechanisms and correlate the crack growth behavior in nature to the service requirement of dentin to resist catastrophic fracture. This is of wide interest not just in terms of understanding dentin fracture but also can extend beyond dentin to other anisotropic structural composite biomaterials such as bone, antler and chitin.
|
|
| 5. |
- Moverare, Johan, 1973-
(författare)
-
Microstresses and anisotropic mechanical behaviour of duplex stainless steels
- 2001
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The evolution of deformation during monotonic and cyclic loading of a two-phase material like duplex stainless steel is more complex than in a single-phase material. One reason for this is the microstresses formed due to differences in thermal and mechanical properties between the two phases. Another factor contributing to a complex load partitioning between the two phases is that hot and cold rolled duplex stainless steel exhibits anisotropic material properties. The aim of this thesis has therefore been to investigate the influence of microstresses and an isotropy on the mechanical properties of duplex stainless steels.The effect of microstresses was clearly revealed when X-ray diffraction was used to study the evolution of microstresses during cyclic loading. Even if the hardness and yield strength were found to be higher in the austenitic phase compared to the ferritic phase more plastic deformation occurs in austenite during cyclic tensile loading. This was also confirmed by transmission electron microscopy investigations of the dislocation structure in both phases. The main reason for the higher degree of plastic deformation in the austenitic phase is that the microstresses are tensile in this phase and compressive in the ferritic phase.Measurements of the crystallographic texture were used as input to theoretical predictions of both elastic and plastic anisotropy. The predicted anisotropic material properties were then used in finite element simulations to study the flow behavior and the load partitioning between phases during deformation in different loading directions. The experiments and the simulations show that the microstresses and the anisotropy make the load partitioning between the two phases dependent on the loading direction. For loading in the rolling direction, both phases deform plastically to the same degree, while more plastic deformation occurs in the austenitic phase during loading in the transverse direction. For loading in the 45°-direction more plastic deformation occurs in the ferritic phase.The anisotropic flow behaviour of the as-received material can be predicted from the crystallographic texture. However, it was found that prestraining introduces a transient work hardening behaviour during the second stage deformation, whjch causes an anisotropic flow behaviour immediately after yielding that cannot be described by the crystallographic texture. Instead the an isotropy can be associated with the rearrangement of the dislocation structure that occurs during changes in the loading path. Prestraining also alters the microstresses from being higher in the transverse direction to being higher in the rolling direction. At the same time the fatigue limit is changed from being higher in the rolling direction to being higher in the transverse direction. This study shows that microstresses have a significant influence on fatigue crack initiation and the fatigue limit of duplex stainless steels.
|
|
| 6. |
|
|
| 7. |
- Rawson, Shelley D., et al.
(författare)
-
Tailoring the Microstructure of Lamellar Ti3C2Tx MXene Aerogel by Compressive Straining
- 2022
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 16:2, s. 1896-1908
-
Tidskriftsartikel (refereegranskat)abstract
- Aerogels are attracting increasing interest due to their functional properties, such as lightweight and high porosity, which make them promising materials for energy storage and advanced composites. Compressive deformation allows the nano- and microstructure of lamellar freeze-cast aerogels to be tailored toward the aforementioned applications, where a 3D nanostructure of closely spaced, aligned sheets is desired. Quantitatively characterizing their microstructural evolution during compression is needed to allow optimization of manufacturing, understand in-service structural changes, and determine how aerogel structure relates to functional properties. Herein we have developed methods to quantitatively analyze lamellar aerogel domains, sheet spacing, and sheet orientation in 3D and to track their evolution as a function of increasing compression through synchrotron phase contrast X-ray microcomputed tomography (μCT). The as-cast domains are predominantly aligned with the freezing direction with random orientation in the orthogonal plane. Generally the sheets rotate toward flat and their spacing narrows progressively with increasing compression with negligible lateral strain (zero Poisson’s ratio). This is with the exception of sheets close to parallel with the loading direction (Z), which maintain their orientation and sheet spacing until ∼60% compression, beyond which they exhibit buckling. These data suggest that a single-domain, fully aligned as-cast aerogel is not necessary to produce a post-compression aligned lamellar structure and indicate how the spacing can be tailored as a function of compressive strain. The analysis methods presented herein are applicable to optimizing freeze-casting process and quantifying lamellar microdomain structures generally.
|
|
| 8. |
- Zhang, Xun, et al.
(författare)
-
Determination of local residual stress in an air plasma spray thermal barrier coating (APS-TBC) by microscale ring coring using a picosecond laser
- 2019
-
Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 167, s. 126-130
-
Tidskriftsartikel (refereegranskat)abstract
- A picosecond laser for incremental annular trench cutting is combined with digital image correlation (DIC) to extend the incremental ring-core method to the profiling of residual stress in thick (>100 μm) coatings. In this case the local residual stress in a TBC is depth profiled after exposure to 1150 °C for 190 h. The topcoat was found to be in compression with an average compressive stress of −94 ± 8 MPa which is representative of the stresses that would be generated elastically on cooling from a stress-free temperature of ~970 °C. The stress profile measurements have been validated by high-energy synchrotron X-ray diffraction measurements. © 2019
|
|
| 9. |
- Örnek, Cem, et al.
(författare)
-
Time-dependent in situ measurement of atmospheric corrosion rates of duplex stainless steel wires
- 2018
-
Ingår i: NPJ MATERIALS DEGRADATION. - : Springer Nature. - 2397-2106. ; 2:1
-
Tidskriftsartikel (refereegranskat)abstract
- Corrosion rates of strained grade UNS S32202 (2202) and UNS S32205 (2205) duplex stainless steel wires have been measured, in situ, using time-lapse X-ray computed tomography. Exposures to chloride-containing (MgCl2) atmospheric environments at 50 degrees C (12-15 M Cl(-)and pH similar to 5) with different mechanical elastic and elastic/plastic loads were carried out over a period of 21 months. The corrosion rates for grade 2202 increased over time, showing selective dissolution with shallow corrosion sites, coalescing along the surface of the wire. Corrosion rates of grade 2205 decreased over time, showing both selective and pitting corrosion with more localised attack, growing preferentially in depth. The nucleation of stress corrosion cracking was observed in both wires. Stainless steel: Comprehending corrosion The corrosion of two grades of stainless steel has been studied, in situ, under atmospheric exposure conditions. Grade '2205' duplex stainless steel (DSS) has been suggested as a possible container material for the storage of intermediate-level radioactive nuclear waste in the UK because of its high resistance to corrosion and stress corrosion cracking (SCC). Now a team led by D. Engelberg from The University of Manchester, United Kingdom, have used time-lapse X-ray computed tomography to determine the corrosion rates of strained grade '2202' and '2205' DSS wires-over the course of 21 months-that had been exposed to a chloride-containing thin-film electrolyte. They saw that although the corrosion rate of grade 2202 DSS wires increased with time, the corrosion rate for grade 2205 decreased, confirming its superior corrosion resistance. They also observed the nucleation of SCC cracks in both grades of wire and demonstrated that duplex stainless steels can suffer from low-temperature SCC.
|
|
