Use of X-ray microtomography and full-field image correlation tools for the thermomechanical analysis of high temperature material behaviours

This research is geared toward exploring the physical mechanisms occurring during the deformation process of high temperature engineering materials, viz. the SLM AlSi10Mg alloy and the FV566 stainless steel. The thermomechanical behaviour of the SLM AlSi10Mg alloy and FV566 stainless steel was studied by conducting many experimental investigations. Conventional cyclic and creep-cyclic tests were performed on the SLM AlSi10Mg alloy specimens under high temperature conditions to study the mechanical response, microstructure evolution as well as the role of temperature and SLM defects on the high temperature cyclic behaviour of the SLM AlSi10Mg alloys. The effects of low cycle fatigue and creep, as well as their interactions during combined cycling, have been investigated further to improve the understanding of the mechanisms responsible for material degradation. In-situ high-stress ratio tensile-tensile low cycle fatigue tests at both room and elevated temperatures were also carried on the SLM AlSi10Mg alloy specimens through a time-lapse synchrotron radiation X-raycomputed microtomography to study fatigue damage accumulation arising from internal defects during tensile-tensile cycling. To follow the defect kinetics during the entire cyclic life, an in-situ high temperature cyclic test rig was designed to accommodate the synchrotron radiation beamline. Besides, high temperature tensile and short-term creep tests have been performed on the FV566 stainless steel specimens with different geometries to understand the governing deformation mechanisms and the real rate-controlling creep mechanisms. To track high temperature strain heterogeneities at both uniaxial and biaxial stress states, a homemade high temperature digital image correlation system was developed. The microstructure changes as well as deformation and damage mechanisms of both materials were investigated by several quantitative imaging techniques. These include optical microscopy, scanning electron microscopy, electron backscatter diffraction, energy dispersive spectrometer, X-Ray diffraction and Laboratory X-ray computed microtomography. These mapping tools have enabled to obtain information at the initial and ruptured states regarding changes of microstructure features including the crystallographic orientations, grain sizes, phases, local misorientation, the morphologies as well as defect sizes and locations

High temperature strain heterogeneities tracking within hole-specimens of fv566 turbine steel via digital image correlation

This paper presents experimental and numerical investigations to study spatial-temporal distributions of strain heterogeneities within a FV566 turbine rotor steel subjected to high temperature conditions. Strain field were determined during monotonic tensile tests performed on flat specimens containing a circular hole to give rise to heterogeneous strain fields. A home-made digital image correlation system with an image restoration module was developed and employed to record and analyse the deformation process till the macroscopic fracture of the investigated specimens. Noticeable in-plane strain concentration zones and effects of the sample design were highlighted and deeply examined. Experimental results combined with finite element analyses based on a classical Johnson-Cook model indicated that the hole shape was the important factor affecting the strength and the spatio-temporal distribution of the strain fields. Microstructural investigations were also conducted to characterize and assess the microscale damage features of the FV566 steel. The ruptured area for all the investigated temperature tests revealed ductile rupture behaviour. Changes on grain boundaries and misorientation near strain localized regions were also investigated. It was found that the propagation of cracks surrounding the hole in FV566 specimens was mainly affected by the nucleation and propagation of strain localization zones.AVIC (Chine), CSC (Chine

Use of X-ray microtomography and full-field image correlation tools for the thermomechanical analysis of high temperature material behaviours

This research is geared toward exploring the physical mechanisms occurring during the deformation process of high temperature engineering materials, viz. the SLM AlSi10Mg alloy and the FV566 stainless steel. The thermomechanical behaviour of the SLM AlSi10Mg alloy and FV566 stainless steel was studied by conducting many experimental investigations. Conventional cyclic and creep-cyclic tests were performed on the SLM AlSi10Mg alloy specimens under high temperature conditions to study the mechanical response, microstructure evolution as well as the role of temperature and SLM defects on the high temperature cyclic behaviour of the SLM AlSi10Mg alloys. The effects of low cycle fatigue and creep, as well as their interactions during combined cycling, have been investigated further to improve the understanding of the mechanisms responsible for material degradation. In-situ high-stress ratio tensile-tensile low cycle fatigue tests at both room and elevated temperatures were also carried on the SLM AlSi10Mg alloy specimens through a time-lapse synchrotron radiation X-raycomputed microtomography to study fatigue damage accumulation arising from internal defects during tensile-tensile cycling. To follow the defect kinetics during the entire cyclic life, an in-situ high temperature cyclic test rig was designed to accommodate the synchrotron radiation beamline. Besides, high temperature tensile and short-term creep tests have been performed on the FV566 stainless steel specimens with different geometries to understand the governing deformation mechanisms and the real rate-controlling creep mechanisms. To track high temperature strain heterogeneities at both uniaxial and biaxial stress states, a homemade high temperature digital image correlation system was developed. The microstructure changes as well as deformation and damage mechanisms of both materials were investigated by several quantitative imaging techniques. These include optical microscopy, scanning electron microscopy, electron backscatter diffraction, energy dispersive spectrometer, X-Ray diffraction and Laboratory X-ray computed microtomography. These mapping tools have enabled to obtain information at the initial and ruptured states regarding changes of microstructure features including the crystallographic orientations, grain sizes, phases, local misorientation, the morphologies as well as defect sizes and locations

Cloning and characterization of histone H3 and replacement histone H3.3 encoding genes of Manila clam (Ruditapes philippinarum)

456-464A full-length cDNA (rp-h3.3) encoding a replacement histone H3.3 had been identified in Manila clam (Ruditapes philippinarum). The cDNA consisted of 975 bp, including a ORF 411 bp in length, a 3′ untranslated regions 490 bp in length, a poly (A) tail and two polyadenylation signals. In addition, the cDNA encoded a peptide with the S.//.A.IG amino acid motif, which was identical to the replacement histone H3.3 variant. rpg-h3.3 and rp-h3s two sequences were obtained by amplifying the genomic DNA of R. philippinarum. The rpg-h3.3, which was the genomic DNA sequence of rp-h3.3, had one intron and the rp-h3s had no intron. It was predicted that h3s might be the h3l-like gene of R. philippinarum. Histone h3 (rp-h3) was also cloned from R. philippinarum genomic DNA. Therefore, the evolutionary origin between histone h3 and its replacement subtypes was analyzed. The study inclined to the viewpoint that h3l-like was the ancesteral gene of h3 and h3.3, which might be two different offsets from h3l-like. During histone evolution process, one copy of h3l-like genes became h3.3 by introns insertion and S-phase-coupled regulatory mechanisms lose, another copy became h3 by gene-duplication and accumulation of mutations in the S.//.A.IG motif

Defect evolution during high temperature tension-tension fatigue of SLM AISi10Mg alloy by synchrotron tomography

Lack of fusion defects and porosity are inevitable characteristics of additive manufacturing and these are expected to play a key role in determining fatigue life and fatigue failure when excluding the influence of inhomogeneous microstructures. This work followed damage accumulation under tension-tension cyclic loading at 250 °C in situ by time-lapse synchrotron radiation X-ray micro-computed tomography (SR-μCT) for AlSi10Mg test-pieces, produced by selective laser melting (SLM) over their complete fatigue lives (ranging from 180 to 38,000 cycles). These samples were found to accumulate widespread plastic strain each cycle in common with ultra-low cycle fatigue (UCLF) at low levels of triaxial constraint. The defects were found to elongate plastically at a rate approximately 10 times larger than their growth rate laterally. This elongation behaviour at room and elevated temperature fatigue is proportional to the accumulated longitudinal strain increment each cycle. Rotation under the influence of shear is also observed for those defects close to the surface of samples. Some defect coalescence was observed, but final failure was found to be associated with the nucleation of a high density of secondary microvoids (occurring at eutectic Si platelets) that form just prior to failure and link up by microvoid coalescence. These steps may take up approximate 90% of the fatigue life. The final stage of cyclic plasticity occurs when the longitudinal strain exceeds ∼0.9. Our results are in line with previous models of strain accumulation and defect growth under ULCF conditions

Evaluation of the field-aged performance of foamed warm mix asphalt: Comparisons with hot mix asphalt

The foamed warm mix asphalt (FWMA) has been widely used as a sustainable construction technique in pavement engineering, yet has not yet been fully studied for its aging performance or durability. Here we aim to examine and evaluate the performance variation characteristic of FWMA compared with conventional hot mix asphalt (HMA) under long-term service conditions. The performance evolution of FWMA core samples drilled from four highways was compared to that of ordinary HMA, which was simultaneously constructed. Fourier transform infrared (FTIR), dynamic shear rheology (DSR), and bending beam rheometer (BBR) tests were respectively performed to evaluate the aging degree, high-temperature, and low-temperature rheological characteristics. The results demonstrated that the aging resistance of foamed WMA was slightly diminished under construction conditions with no temperature reduction. With increased service time, the rheological characteristics of FWMA were enhanced at high temperatures, while deteriorated at low temperatures. The foaming water and service time were primary determinants of the aging as well as high and low-temperature rheological properties of FWMA without temperature construction reduction. Additionally, the aging degree of FWMA under short-term and long-term service was smaller than HMA when the construction temperature decreased. The rheological characteristics of FWMA were inferior to those of HMA during both short-term and long-term service stages. Under conditions of temperature reduction, foaming water and mixing temperature exhibited a considerable influence on the aging and rheological properties of FWMA at high and low temperatures. Therefore, the amount of water used for foaming and the temperature of production should be strictly control in the foamed warm mix asphalt technology

Graphene-Supported Sc2O3/TiO2 for Superior Catalysis on Hydrogen Sorption Kinetics of MgH2

Complex metal oxide catalysts greatly accelerate the hydrogen sorption rates in the magnesium hydride system. In this study, the graphene-supported Sc2O3/TiO2 catalyst is synthesized by means of a simple method, and a surprisingly synergetic effect of the Sc2O3-TiO2 cocatalyst on the hydrogen storage performance of MgH2 is observed. The MgH2-Sc2O3/TiO2@Gn composite starts to release hydrogen at 140 °C and reaches the peak dehydrogenation temperature at 239.9 °C. It absorbs 6.55 wt% of H2 in 1 min and desorbs 5.71 wt% of H2 in 10 min at 300 °C, showing excellent hydrogen absorption and desorption performance. Furthermore, with the decrease of the grain size and changes in the structure, the activity of the catalyst is greatly improved. The low-valent titanium and scandium and oxygen vacancies formed in the process of dehydrogenation facilitate hydrogen diffusion and electron transfer, and further improve the kinetic performance of the Mg/MgH2-Sc2O3/TiO2@Gn system. This study aims to provide insights into studying complex metal oxides as catalysts to improve hydrogen storage performance, and shed light on other catalysis-related research

Hot dwell-fatigue behaviour of additively manufactured AlSi10Mg alloy: Relaxation, cyclic softening and fracture mechanisms

This paper presents the results of high temperature strain-range controlled low cycle fatigue tests of a laser powder bead fused AlSi10Mg alloy. Following stress relief (2hrs at 300 ℃), two cyclic loading waveforms (standard triangular and dwell-type trapezoidal waveforms) and three temperatures (100 ℃, 250 ℃ and 400 ℃) were applied to investigate both the mechanical response and the related microstructural changes of this additively manufactured (AM) aluminium alloy. The bulk mechanical responses were found to exhibit a continuous cyclic softening, decreasing stress relaxation and decreased energy dissipated per cycle. The stress relaxation is strongly affected by the test temperature rising to almost complete relaxation at 400 ℃. At lower temperatures (100 ℃ and 250 ℃), the higher the temperature the more subgrains are developed during cyclic loading. Up to 250 ℃, the subgrain size increases with temperature and laser powder bead fused defects pref­erentially act as the fatigue crack initiation sites. While at 400 ℃, coarse Si particles precipitate during cyclic deformation and a high density of microvoids are nucleated from these coarse Si precipitates, which grow and link up to cause failure, resulting in a dimple dominated ductile fracture.Jianguang Bao, Professor Adil Benaarbia and Professor Wei Sun would like to acknowledge the China Scholarship Council for the sponsorship of the PhD project for Jianguang Bao. Financial support through the Joint Fund of Large-scale Scientific Facility of National Natural Science Foundation of China (U2032121) is gratefully acknowledged. Sincere thanks are also due to Professor Yanan Fu from the SSRF for her technical assistance on performing the SR- μ CT exper­imental setup, and to Mr Shane Maskill at the University of Nottingham for his support during LCF tests. The Manchester (Henry Moseley) X-ray Imaging Facility was funded in part by the EPSRC (grants EP/F007906/1, EP/F001452/1 and EP/M010619/1)