Graphene reinforced metal matrix composites (MMCs) have received extensive research interests as promising structural materials in developing lightweight structures. The mechanical performance of ...such composites, however, is considerably hindered by weak van der Waal (vdW) interaction between graphene and metal matrix. The present work shows that this challenging issue can be effectively alleviated by the use of chemically functionalized graphene fillers with mechanically induced wrinkles. Our extensive molecular dynamics (MD) simulations on graphene reinforced copper (Cu) composite manifest that the presence of shear-induced wrinkles and chemical modification of graphene using functional groups can significantly increase its surface roughness, enhance the vdW interaction and consequently lead to higher interfacial shear strength (IFSS) between graphene and Cu matrix. Compared with its counterpart functionalized with hydrogen, graphene functionalized with alkyl (methyl, ethyl, propyl, and butyl) offers better interfacial interactions with Cu matrix because these functional groups are longer than hydrogen functional group and can be embedded deeper into the matrix.
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Graphene has been widely used as new generation reinforcing nanofiller to achieve significantly improved mechanical properties in composites. However, its reinforcing effect has been considerably ...affected by the poor interfacial strength between graphene and the matrix. By using molecular dynamics simulations, the present work explores an effective route to improve the interfacial shear strength (ISS) of graphene sheets through the introduction of mechanically induced wrinkles that are formed by applying shear/compressive strains to graphene. The slide-out tests of a wrinkled graphene sliding over the graphene substrate show that the strain-induced wrinkles in graphene slider gives rise to larger surface roughness which leads to stronger interfacial interactions between graphene layers and consequently, significant improvement in ISS. Compared with compression induced wrinkles, shear induced wrinkles are found to be much more effective in enhancing ISS. Our results indicate that applying mechanical pre-strain, in particular, shear strain to graphene is a very useful strategy to improve its reinforcing effect in composites.
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•Wrinkles are designed by applying shear/compressive strain to graphene sheet.•The characteristics of wrinkles including amplitude/half-wavelength, roughness and ratio of interaction area are analyzed.•Shear/compressive strain-induced wrinkles effectively improve the interfacial shear strength between graphene sheets.•Shear-induced wrinkle is more effective in enhancing the interfacial shear strength than the compression-induced one.
One of the major causes of damage to column-supported concrete structures, such as bridges and highways, are collisions from moving vehicles, such as cars and ships. It is essential to quantify the ...collision damage of the column so that appropriate actions can be taken to prevent catastrophic events. A widely used method to assess structural damage is through the root-mean-square deviation (RMSD) damage index established by the collected data; however, the RMSD index does not truly provide quantitative information about the structure. Conversely, the damage volume ratio that can only be obtained via simulation provides better detail about the level of damage in a structure. Furthermore, as simulation can also provide the RMSD index relating to that particular damage volume ratio, the empirically obtained RMSD index can thus be related to the structural damage degree through comparison of the empirically obtained RMSD index to numerically-obtained RMSD. Thus, this paper presents a novel method in which the impact-induced damage to a structure is simulated in order to obtain the relationship between the damage volume ratio to the RMSD index, and the relationship can be used to predict the true damage degree by comparison to the empirical RMSD index. In this paper, the collision damage of a bridge column by moving vehicles was simulated by using a concrete beam model subjected to continuous impact loadings by a freefalling steel ball. The variation in admittance signals measured by the surface attached lead zirconate titanate (PZT) patches was used to establish the RMSD index. The results demonstrate that the RMSD index and the damage ratio of concrete have a linear relationship for the particular simulation model.
This paper investigates the free vibration and compressive buckling characteristics of functionally graded graphene nanoplatelets reinforced composite (FG-GPLRC) beams containing open edge cracks by ...using the finite element method. The beam is a multilayer structure where the weight fraction of graphene nanoplatelets (GPLs) remains constant in each layer but varies along the thickness direction. The effective Young's modulus of each GPLRC layer is determined by the modified Halpin-Tsai micromechanics model while its Poisson's ratio and mass density are predicted according to the rule of mixture. The effects of GPLs distribution pattern, weight fraction, geometry, crack depth ratio (CDR), slenderness ratio as well as boundary conditions on the fundamental frequency and critical buckling load of the FG-GPLRC beam are studied in detail. It was found that distributing more GPLs on the top and bottom surfaces of the cracked FG-GPLRC beam provides the best reinforcing effect for improved vibrational and buckling performance. The fundamental frequency and critical buckling load are also considerably affected by the geometry and dimension of GPL nanofillers.
The concentrations of nitrite and thiocyanate in saliva can be used as the biomarkers of the progression of periodontitis disease and environmental tobacco smoke exposure, respectively. Therefore, it ...is particularly necessary to detect these two indicators in saliva. Herein, the three-dimensional single-layered paper-based microfluidic analytical devices (3D sl-μPADs) were, for the first time, fabricated by the spraying technique for the colorimetric detection of nitrite and thiocyanate at the same time. The conditions for 3D sl-μPADs fabrication were optimized in order to well control the penetration depth of the lacquer in a paper substrate. Then, the developed 3D sl-μPADs were utilized to simultaneously detect nitrite and thiocyanate and the limits of detection are 0.0096 and 0.074 mM, respectively. What is more, the μPADs exhibited good specificity, good repeatability, and acceptable recoveries in artificial saliva. Therefore, the developed 3D sl-μPADs show a great potential to determine nitrite and thiocyanate for the assessment of the human health.
We report recent developments on 980-nm single-transverse-mode ridge-waveguide (RW) lasers with high efficiency and low-vertical divergence. RW lasers fabricated with 7-μm-wide ridge and 3-mm-long ...cavity achieve 2-W optical power, 59% maximum power conversion efficiency, as well as a beam divergence of 7.2° in lateral and 10.3° in vertical under 1.5-A injection current. The lateral beam quality factors M 2 are below 1.7 up to 2-W output power.
Many subclasses of
H
-matrices have already been investigated in application areas of linear algebra. One of them is
SDD
1
matrices given in Peña (Adv Comput Math 35:357–373, 2011). In this paper, a ...new subclass of
H
-matrices, i.e., generalized
SDD
1
(
GSDD
1
) matrices, is considered. The relationship between
GSDD
1
matrices and other subclasses of
H
-matrices is analyzed. Infinity norm bounds for the inverse of a
GSDD
1
matrix
A
are given, using a scaling matrix that transforms
A
into a strictly diagonally dominant matrix. The given scaling matrix is also utilized to obtain error bounds for the linear complementarity problems when the related matrices are
GSDD
1
matrices. Numerical examples show that the obtained results can improve other existing bounds.
•The successful fabrication of FG-GPLRC is reported.•Micromechanics models to predict effective mechanical properties of GPLRC are reviewed.•A comprehensive review on the mechanical analyses of ...FG-GPLRC structures is presented.•Key technical challenges are identified and future research directions are discussed.
Owing to their superior mechanical properties, e.g. exceptionally high Young’s modulus, high strength, large specific surface area, and good thermal conductivity, graphene and its derivatives such as graphene platelets (GPLs) are excellent reinforcing nanofillers for composite materials. The most recently developed functionally graded graphene platelets reinforced composite (FG-GPLRC) where GPLs are non-uniformly dispersed with more GPLs in the area where they are most needed to achieve significantly improved mechanical performance has opened up a new avenue for the development of next generation structural forms with an excellent combination of high stiffness, light weight and multi-functionality. Research activities in this emerging area have been rapidly increasing since it was first proposed in 2017. The present paper (i) briefly reviews the mechanical properties of graphene and graphene composites; (ii) summarizes the characteristics of functionally graded materials (FGM) and reports the fabrication of FG-GPLRC; (iii) discusses the existing micromechanics models for the prediction of effective mechanical properties of GPLRC; (iv) presents a comprehensive review on the mechanical analyses of FG-GPLRC structures; and (v) discuss the key technical challenges and future research directions.
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