The 3D failure process in polymeric syntactic foams with different cenosphere volume fractions

The previous work (Huang and Li, Compos. Part B, 2015) proposed the failure mechanism in syntactic foams with low and high hollow microsphere volume fractions, based on the finite element simulation of localized stresses in the foam. In this work, in situ X‐ray microtomography of uniaxial compression tests was performed to provide the direct experimental evidence to the proposed mechanism by tracking the internal three‐dimensional failure process in epoxy syntactic foams with different cenosphere volume fractions (V). It was found that for both the low and high V, microcracks initiate in the matrix in the top and bottom of crushed cenospheres where the tensile stress concentrates, and then propagate longitudinally to become macrocracks. Increasing the cenosphere volume fraction also leads to the formation of matrix microcracks in the connection zone where the stress concentrates significantly; the matrix microcracks thus propagate diagonally and longitudinally in the high V foam

Motion response and energy harvesting of multi-module floating photovoltaics in seas

Floating Photovoltaic (FPV) systems are emerging as a new type of ocean renewable energy, offering advantages such as avoiding land use and promoting power generation efficiency. Providing significant cost-effectiveness for manufacturing, transportation, and installation, FPV systems with modular floating platforms exhibit the potential to replace the conventional large steel-frame one. However, the performance of such multi-floating body structures under wave conditions remain underexplored. In this paper, based on potential flow theory, the motion characteristics and power performance of the proposed FPV array connected by the articulated system are evaluated. The results indicate that the FPV arrays with shorter floating structures exhibit greater pitch motion, especially when the wave condition matches the pitch resonance. For multi-float cases, the articulated system, optimized with appropriate parameters, demonstrates efficacy as attenuators. Additionally, the proposed FPV array has great potential to serve as an infrastructure for integrating solar and wave energy. For a selected offshore site, potential wave energy output from motion attenuators between FPV floaters is assessed together with solar energy output. Overall, this study serves as a valuable reference for the design and optimization of the multi-modules FPV and advances the research on combined solar and wave energy utilization on floating structures.This work is supported by the National Natural Science Foundation of China National Outstanding Youth Science Fund Project (52222109), the National Natural Science Foundation of China (52071096 and 52201322), Project of State Key Laboratory of Subtropical Building and Urban Science (2023ZB14), Guangdong Basic and Applied Basic Research Foundation (2022B1515020036 and 2023A1515012144).Ocean Engineerin

Compressive properties of pristine and SiC-Te-added MgB 2 powders, green compacts and spark-plasma-sintered bulks

Pristine and (SiC+Te)-added MgB2 powders, green and spark plasma sintered (SPS) compacts were investigated from the viewpoint of quasi-static and dynamic (Split-Hopkinson Pressure Bar, SHPB) compressive mechanical properties The amount of the additive (SiC+Te) was selected to be the optimum one for maximization of the superconducting functional parameters. Pristine and added MgB2 show very similar compressive parameters (tan δ, fracture strength, Vickers hardness, others) and fragment size in the SHPB test. However, for the bulk SPSed samples the ratio of intergranular to transgranular fracturing changes, the first one being stronger in the added sample. This is reflected in the quasi-static KIC that is higher for the added sample. Despite this result, sintered samples are brittle and have roughly similar fragmentation behavior as for brittle engineering ceramics. In the fragmentation process, the composite nature of our samples should be considered with a special focus on MgB2 blocks (colonies) that show the major contribution to fracturing. The Glenn-Chudnovsky model of fracturing under dynamic load provides the closest values to our experimental fragment size data

Mechanical behavior and failure mechanisms in polymeric syntactic foams

Syntactic foams have been increasingly used in load bearing structures in the low to high speed applications due to their excellent specific properties. The aim of this research is thus to fully understand the overall mechanical properties and the associated failure mechanisms under different strain rates. The quasi-static (QS) compression tests and the finite element (FE) modeling of a representative elementary volume syntactic foam were first performed to investigate the elastic behavior and failure mechanism of the glass microballoon epoxy syntactic foams as well as the effect of glass microballoon volume fractions (V) and the radius ratio η. The elastic characteristics of the foam vary with both the V and η. The localized stresses concentrate in various zones within the foam. Dependent on the V, micro-cracks can propagate either in the preferred longitudinal or diagonal directions in the foam. To directly observe the internal microstructural change of the constituents during the failure process, the x-ray micro computed tomography (µXT) with interrupted uniaxial compression was conducted on cenosphere epoxy syntactic foams. Moreover, to further investigate the failure micromechanisms of the foam, FE modelling of the full scale foam specimen was developed and experimentally validated to predict the localized stress, fracture of cenospheres and deformation in the matrix. The FE predictions were related to the µXT observations to analyze the underlying mechanisms of internal 3D failure process in the plateau region of the foam. It was found that the internal compressive failure in microscopic scale consists of (1) the crushing of hollow spheres and (2) the plastic deformation and fracture of the matrix. The failure mechanisms in the two constituents are determined by the localized stress state and the stress transfer between the constituents, and govern the different strain stages of bulk stress–strain behavior of the foam. The failure mode of the individual hollow sphere was vertical splitting. Finally, to investigate the strain rate dependent failure mechanisms of syntactic foam, the QS compressive tests and Split-Hopkinson pressure bar tests were controlled to stop the deformation of the foams at various strains. It was found that the failure mechanism is significantly affected by strain rates. At dynamic rates, macro-cracks form earlier in the matrix and can split hollow spheres. An empirical constitutive equation was used to quantitatively relate the damage to the strain and strain rate.DOCTOR OF PHILOSOPHY (MAE

Elastic behaviour and failure mechanism in epoxy syntactic foams: the effect of glass microballoon volume fractions

A representative elementary volume (REV) in epoxy syntactic foams was generated to incorporate randomly distributed glass microballoons that followed a log-normal size distribution. Finite element modelling of the REV foam was developed and experimentally validated to investigate the elastic behaviour and failure mechanism in the foams with different microballoon volume fractions (V). The localised stresses concentrate in various zones within the foam, and can cause the vertical splitting fracture of microballoons and the micro-crack formation in the matrix. Dependent on the microballoon volume fraction, micro-cracks can propagate to join adjacent micro-cracks and voids left by fractured microballoons, and finally develop into a macro-crack either in the preferred longitudinal (for low V) or diagonal (for high V) directions. This is consistent with the macroscopic observations of the fracture process in the foam specimens. It was also found that elastic characteristics of the foam vary with microballoon volume fractions

On the Landscape Activity Measure Coupling Ecological Index and Public Vitality Index of UGI: The Case Study of Zhongshan, China

In the context of high-quality urban development and the increasingly important role of urban green infrastructure (UGI) in public life, landscape activity (LA) has gradually become a dominant indicator for improving UGI quality and efficiency, as well as optimizing its environmental friendliness and meeting the recreational needs of the public. Relevant studies have shown that the ecological index (EI) and the public vitality index (PVI) can characterize LA from the perspectives of greening quality and public activities, respectively, and their simultaneous analysis can provide professional judgment and quantitative technical approaches for the LA analysis of UGI. At the same time, with the support of remote sensing, big data, GIS, and other spatial information data, the LA model coupling EI and PVI of UGI needs to be developed. First, this article established a research framework for UGI landscape activity, and by combining environmental remote sensing and location-based services (LBS) technology, a technical LA measurement strategy suitable for the coupled analysis of EI and PVI was formed. Then, based on the MATLAB platform and the entropy-weighted TOPSIS model, this research developed a fusion analysis algorithm of EI and PVI to establish the LA model, taking the central urban area of Zhongshan as a case study. Finally, four-quadrant classification and quantitative grading of LA were developed based on the ArcGIS platform. Empirical research showed that the UGI area of the study area was about 176.43 km2, and 160 UGI units were identified. The minimum LA value is 0.06, and the maximum is 0.85. The LA of UGI in the study area can be divided into three grades: low (0–0.24), medium (0.24–0.46), and high (0.46–0.85). Among them, the top 5% of UGI units mainly correspond to urban parks and waterfront greenways, and the bottom 5% mainly correspond to islands and farmland. The quantitative distribution of UGI in the four quadrants of LA in the study area is relatively balanced: among them, the number of high-quality developing types is the largest, accounting for 29.4%, and that of high-quality mature types is the least, accounting for 20.0%. This article forms a concise model and technical process for the LA of UGI, which can be used for its quantitative analysis and evaluation. It is expected that the research result will be significant for the high-quality construction of UGI and the sustainable development of the urban landscape in terms of research and exploration

On the Landscape Activity Measure Coupling Ecological Index and Public Vitality Index of UGI: The Case Study of Zhongshan, China

In the context of high-quality urban development and the increasingly important role of urban green infrastructure (UGI) in public life, landscape activity (LA) has gradually become a dominant indicator for improving UGI quality and efficiency, as well as optimizing its environmental friendliness and meeting the recreational needs of the public. Relevant studies have shown that the ecological index (EI) and the public vitality index (PVI) can characterize LA from the perspectives of greening quality and public activities, respectively, and their simultaneous analysis can provide professional judgment and quantitative technical approaches for the LA analysis of UGI. At the same time, with the support of remote sensing, big data, GIS, and other spatial information data, the LA model coupling EI and PVI of UGI needs to be developed. First, this article established a research framework for UGI landscape activity, and by combining environmental remote sensing and location-based services (LBS) technology, a technical LA measurement strategy suitable for the coupled analysis of EI and PVI was formed. Then, based on the MATLAB platform and the entropy-weighted TOPSIS model, this research developed a fusion analysis algorithm of EI and PVI to establish the LA model, taking the central urban area of Zhongshan as a case study. Finally, four-quadrant classification and quantitative grading of LA were developed based on the ArcGIS platform. Empirical research showed that the UGI area of the study area was about 176.43 km2, and 160 UGI units were identified. The minimum LA value is 0.06, and the maximum is 0.85. The LA of UGI in the study area can be divided into three grades: low (0–0.24), medium (0.24–0.46), and high (0.46–0.85). Among them, the top 5% of UGI units mainly correspond to urban parks and waterfront greenways, and the bottom 5% mainly correspond to islands and farmland. The quantitative distribution of UGI in the four quadrants of LA in the study area is relatively balanced: among them, the number of high-quality developing types is the largest, accounting for 29.4%, and that of high-quality mature types is the least, accounting for 20.0%. This article forms a concise model and technical process for the LA of UGI, which can be used for its quantitative analysis and evaluation. It is expected that the research result will be significant for the high-quality construction of UGI and the sustainable development of the urban landscape in terms of research and exploration

Cone-beam CT reconstruction along any orientation of interest

We present a novel method which provides X-ray CT users the flexibility to reconstruct an object along any of its internal flat features. This internal feature, which is generally not parallel to the object's external surface, can be either an interface between two materials or one surface of an internal layer. This method is developed based on our existing CT differential reconstruction algorithm that is achieved by modifying the popular Feldkamp-Davis-Kress cone-beam reconstruction technique. The theory of this technology is described. One case-study demonstrates that this method is independent of the surface selection of several parallel features. Another case-study shows its capability to reconstruct any individual plate along the plate's own orientation with a three-plate object

X-ray microtomography and finite element modelling of compressive failure mechanism in cenosphere epoxy syntactic foams

The X-ray microtomography with interrupted uniaxial compression was performed on cenosphere epoxy syntactic foams to directly observe the internal microstructural change of the constituents during the failure process. Finite element modelling of the full scale foam specimen was developed and experimentally validated to predict the localised stress, fracture of cenospheres and deformation in the matrix. The finite element predictions were related to the X-ray microtomographic observations to analyse the underlying mechanisms of internal 3D failure process in the plateau region of the foam. The compressive failure process in microscopic scale consists of (1) the crushing of cenospheres and (2) the plastic deformation and fracture of the matrix. The failure mechanisms in the two constituents are determined by the localised stress state and the stress transfer between the constituents, and govern the different strain stages of bulk stress–strain behaviour of the foam. The maximum tensile stress concentration near the equator causes the earlier vertical splitting fracture of largest cenospheres. The localisation of stresses in the connection zone between adjacent cenospheres results in the formation of micro-cracks, which then propagate preferentially diagonally to form the macro-cracks by joining other micro-cracks and the voids left by crushed cenospheres