1,720,957 research outputs found
Microstructure and very high cycle fatigue characteristics of powder bed fused – laser beam (PBF-LB) scandium-free Al-Mg-Zr alloy
No full textMicrostructure, mechanical properties, and fatigue performance of a PBF-LB Al2139ZrTi alloy
Full text linkThis study investigates the microstructure, tensile, and fatigue behavior of post-aged powder bed fused-laser
beam (PBF-LB) Al2139ZrTi alloy, developed by EOS North America. The microstructure exhibits an equiaxed
grain structure with an average grain size of approximately 1.5 μm and lacks any strong crystallographic texture.
It also contains a dense dispersion of fine, uniformly distributed precipitates including: (i) Al3(Zr,Ti) dispersoids
with L12-type structure, acting as semi-coherent nucleation sites that contribute to grain refinement; (ii) a unique
Al3(Zr,Ti) plate-like phase, further confirming Zr–Ti-driven modification of precipitation pathways; (iii) Al
(CuFeMn) and Al(MnCu) intermetallics, notably Al7Cu2 (Fe,Mn) and Al20Cu2Mn3(T-phase), and (iv) Mg oxides,
pointing to minor oxidation during processing. Notably, Al2Cu-based θ′ and Ω phases are sparse, with only coarse
θ-phase particles (~0.5–1 μm) at grain boundaries and fine plate-like Ω-phase (~tens of nm thick) along the
[100] zone axis. Mechanical properties were evaluated via tensile testing, yielding ~ 470 MPa yield stress (YS),
~570 MPa ultimate tensile strength (UTS), and ~ 6.5 % elongation. Conventional (servo-hydraulic) and ultrasonic fatigue tests were performed to cover high cycle and very high cycle fatigue responses spanning up to 109
cycles. Fractographic analyses, including optical and electron microscopy techniques, were carried out to
quantify the crack initiation mechanisms in the mentioned regime
Fatigue behavior of powder bed Fused–Laser beam (PBF-LB) 70/30 Copper-Nickel (CuNi30)
Full text linkThe 70/30 Cu–Ni alloy (CuNi30) is widely employed in marine systems due to its excellent corrosion resistance
and mechanical reliability. Despite its industrial relevance, its behavior under additive manufacturing (AM),
particularly powder bed fusion–laser beam (PBF-LB) processing, has received limited attention in the context of
fatigue-critical applications. This study presents the first systematic assessment of the microstructure, defect
population, mechanical properties, and fatigue performance of PBF-LB 70/30 Cu–Ni in both the as-built and
heat-treated conditions, with specific attention to the role of build orientation using horizontally and vertically
fabricated specimens. The applied heat treatment increased mechanical strength and produced a marked
improvement in the stress–life (S–N) response of the alloy. Detailed microstructural characterization and postmortem fractography showed that fatigue cracks predominantly initiated from surface or subsurface crystallographic facets induced by local embrittlement in the matrix. The results provide essential guidance for designing
fatigue-resistant Cu–Ni components and support the broader adoption of PBF-LB 70/30 Cu–Ni in demanding
marine and naval environments. Furthermore, this work establishes a foundation for future investigations into
the corrosion-fatigue behavior of the alloy
Fatigue characteristics of a newly developed laser powder bed fused scandium-free Al-Mg-Zr-Mn alloy
No full textThis study investigates the fully reversed force-controlled fatigue response of a newly developed laser powder bed fused (LPBF) Al-Mg-Zr-Mn alloy (EOS Al5X1) in the post-aged condition. The fatigue behavior revealed a defect-driven response with a fatigue strength of approximately 140 MPa at 5 million cycles. Comprehensive microstructural analyses, including grain size, texture, and precipitate characterization, were performed using advanced microscopy techniques. Additionally, X-ray computed micro-tomography (XCT) was employed to assess defect size and distribution, yielding a relative density of 99.93 %. Fracture surfaces of all fatigue-failed specimens were examined using optical and scanning electron microscopy to determine the primary failure mechanisms, with a focus on distinguishing between defect-driven and microstructural causes. The results indicated that nearly all specimens, tested across seven stress levels, exhibited crack initiation from process-induced volumetric defects, such as pores and lack of fusion. At lower stress levels (up to 195 MPa), single crack initiation sites driven by defects were identified at either surface or subsurface locations. In contrast, at higher stress levels (234 to 351 MPa), multiple crack initiation sites were observed, also at the surface or subsurface
Homogenization and elastic-plastic transitions in random and FGM microstructures
Full text linkThe research presented here uses homogenization as a tool to estimate the effective properties of heterogeneous materials with varying microstructures. Separation of scales (Micro (d), Meso(δ), Macro (L)), in these microstructures leads to the problem of determination of the Representative Volume Element (RVE) that corresponds to the effective properties of materials. Microstructural randomness is inherent in these materials and hence we study the scaling from Statistical Volume Element (SVE) to RVE. Using Hill condition, the RVE is achieved when the material response becomes independent of the two boundary conditions (kinematic and static boundary condition) setup on the SVE. Elastic responses of 2d microstructures such as two-phase random checkerboard are considered, and RVE of the same is also identified. This technique is consistent with the Hill-Mandel macrohomogenity condition. We propose to homogenize the elastic response of FGM (functionally graded materials) type microstructure in 3d using the same technique. Since the Hill condition is independent of the microstructure, hence it is counter-intuitive that FGM microstructure can- not be easily homogenized using the same approach. The inelastic response of FGM microstructures in 2d and 3d are also studied here. The elastic-plastic transition in multiphase materials is smooth (not sudden), suggesting fractal nature of the evolving plasticity in the material. An attempt is made to calculate the fractal dimension of these evolving plastic grains in the 2d and 3d FGM microstructure. In 3d, this results in massive simulations performed in parallel using commercially available FEM package called ABAQUS. The simulations were carried out using the computational resources available at the National Center for Supercomputing Applications (NCSA). This opens up the possibility of assessing plastic damage in material through fractals. Preliminary experimental study using viscoelastic materials for FGM microstructure is also presented here. Furthermore, we also present the scaling effect under finite mesoscale size quantified in the form of normalized scaling function. We propose to study the effect of this scaling function for the two-phase correlated microstructures of Gaussian type, formulation of which is also presented here. Comparison with existing experimental data shows our numerical model is well in agreement with the experimental data for various volume fractions of the constituent phases.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2017-05-01The student, Ankit Saharan, accepted the attached license on 2015-04-22 at 10:05.The student, Ankit Saharan, submitted this Dissertation for approval on 2015-04-22 at 10:16.This Dissertation was approved for publication on 2015-04-23 at 07:34.DSpace SAF Submission Ingestion Package generated from Vireo submission #8012 on 2015-07-22 at 14:26:06Made available in DSpace on 2015-07-22T22:45:57Z (GMT). No. of bitstreams: 4
SAHARAN-DISSERTATION-2015.pdf: 19031769 bytes, checksum: 9b2129b44635cb0875851f838b604db6 (MD5)
C12_50_movie.avi: 26952192 bytes, checksum: 29dda7a0e1acced85e8a0992f055e9e7 (MD5)
S12_50_movie.avi: 29626368 bytes, checksum: 5fb163e3f340eb95b41d8dc9982bed6c (MD5)
LICENSE.txt: 4210 bytes, checksum: 18d7c4092d1219a03f5a9f765e086a4e (MD5)
Previous issue date: 2015-04-23Embargo set by: Seth Robbins for item 80013
Lift date: 2017-07-22T22:46:21Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 80013 on 2017-07-23T09:15:24Z
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Characterization of functionally graded materials through fractal geometry
No full textFunctionally Graded Materials are the material systems whose properties vary spatially through the solid. These material systems are fairly new and though expensive to fabricate; they serve as excellent engineering materials for various applications. The material system we consider in this work is a metal- ceramic system, which can easily substitute for heat shielding tiles on the reentry space vehicles replacing the conventional ceramic tiles. This system while providing a structurally and thermally excellent heat shielding also reduces the weight penalty by introducing metal in the system without compromising on the strength. In this thesis we study the behavior and characteristics of the FGM in terms of fractals. There has been no prior literature on linking FGM and fractals. We characterize the interfaces between the two- phase FGM using fractals and estimate an interfacial fractal dimension for varying degrees of coarseness. Also, the variation in local fractal dimension as we move lengthwise (left to right) in the domain is characterized by a Fourier fit, and a simpler relation using a Beta function. Assuming an isotropic nature of both Titanium and Titanium Monoboride (TiB), pure shear tests are simulated using ABAQUS for coarseness level of 50, 100 and 200 under the Uniform Kinematic Boundary Condition (UKBC) and the Uniform Static Boundary Condition (USBC). The material response observed under both these BC’s shows a high sensitivity of these systems to loading conditions. Furthermore, plastic evolution of Titanium grains assuming isotropic plastic hardening shows fractal plane filling behavior. Fractal dimensions of sets of plastic grains are calculated using the box counting method, and it validates our mechanical results, thus again showing high sensitivity of this material system to loading conditions.Item withdrawn by Mark Zulauf ([email protected]) on 2010-07-23T18:10:51Z
Item was in collections:
University of Illinois Theses & Dissertations (ID: 1)
No. of bitstreams: 1
Saharan_Ankit.pdf: 4799036 bytes, checksum: 6bc09a162adc7ccba6b8f320e5012b3f (MD5)Made available in DSpace on 2010-08-31T20:30:44Z (GMT). No. of bitstreams: 3
Saharan_Ankit.pdf: 4799036 bytes, checksum: 6bc09a162adc7ccba6b8f320e5012b3f (MD5)
1_Saharan_Ankit.pdf: 4799610 bytes, checksum: 018ebaf8ae5ab454d9ebf47a53810ccd (MD5)
license.txt: 4063 bytes, checksum: 8dca3cf3e493b275e6e8a416e25ebc34 (MD5)Item marked as restricted to the 'Administrator' Group (id=1) by William Ingram ([email protected]) on 2010-08-31T20:32:55Z
Item is restricted until 2012-08-31T20:32:49ZItem reinstated by Sarah Shreeves ([email protected]) on 2012-09-07T16:43:39Z
Item was in collections:
University of Illinois Dissertations and Theses (ID: 204)
Dissertations and Theses - Mechanical Science and Engineering (ID: 675)
No. of bitstreams: 4
Saharan_Ankit.pdf: 4799036 bytes, checksum: 6bc09a162adc7ccba6b8f320e5012b3f (MD5)
1_Saharan_Ankit.pdf: 4799610 bytes, checksum: 018ebaf8ae5ab454d9ebf47a53810ccd (MD5)
license.txt: 4063 bytes, checksum: 8dca3cf3e493b275e6e8a416e25ebc34 (MD5)
1_Saharan_Ankit.pdf.txt: 43705 bytes, checksum: a5c12327259569c64e02b642c60a7058 (MD5)Item released from any restrictions by Sarah Shreeves ([email protected]) on 2012-09-07T16:43:39
- …
