Multilayer Composites Research Articles

Effect of SiC particle size and severe deformation on mechanical properties and thermal conductivity of Cu/Al/Ni/SiC composite fabricated by ARB process

SiC particles are among the most investigated types of reinforcing particles with high thermal conductivity in multilayered composites. This paper deals with the effect of the particle size and ARB rolled passes on tensile strength, elongation, and thermal conductivity of Cu/Al/Ni/SiC composite. Based upon the mechanical properties, the ultimate strength and the elongation of Cu/Al/Ni/SiC(2 μm) were more than that of Cu/Al/Ni/SiC(15 μm) at all passes, apart from the zero pass. This is because 2-μm particles not only tend to make smaller clusters than 15-μm particles but also are preferably trapped at the interfaces; however, 15-μm particles tend to be trapped in Al layers. Further, at each rolled pass, the values of thermal conductivity of Cu/Al/Ni/SiC (15 μm) were slightly higher compared to the other two composites. This is because of the larger cluster of 15-μm particles in the Al layers, providing better heat flux across the composite. In addition, the results of optical microscopy (OM) showed that applying more passes caused the discontinuity in all layers and also the non-uniform distribution of Ni and Al layers in the Cu matrix. Plus, due to the lower strength of Al layers in comparison to Cu and Ni layers, ceramic particles diffuse considerably in Al layers. The SEM images of the fracture surfaces indicated the ductile fracture with some uniaxial dimples for Al and Cu layers whereas for Ni layers both ductile and brittle cleavage fractures due to its higher work hardening exponent. • The fabrication of Cu/Al/Ni, Cu/Al/Ni/SiC(2 μm) and Cu/Al/Ni/SiC(15 μm) laminated composites was studied. • Effects of strain accumulation on all layers and the role of two sizes of SiC particles during four rolling passes of ARB process was investigated. • With increasing the strain accumulation, the ultimate strength of all three composites fluctuated due to the plastic instability of layers and the distribution of particles. • Reinforcing particles appeared in cluster shape at the interface of Al/Ni and Cu/Al because of being displaced by applied stress due to their small size and freedom of movement. Also, 15-μm particles were more trapped in Al layers than 2-μm trapped. • With increasing the strain accumulation, the elongations of composites decreased. • By increasing the number of ARB passes, thermal conductivity of composites dropped though at each pass Cu/Al/Ni/SiC(15 μm) had the highest values because of forming clusters at the interfaces.

Textured Tape Substrates of Ternary Copper–Nickel Alloys with Tantalum and Tungsten Additives for the Epitaxial Deposition of Multilayer Compositions

Textured Tape Substrates of Ternary Copper–Nickel Alloys with Tantalum and Tungsten Additives for the Epitaxial Deposition of Multilayer Compositions

Significantly improved high dielectric MWCNTs filled PVDF/PS/HDPE composites via constructing double bi-continuous structure

Multi-layer composites with vastly difference in electrical properties for each layer are a promising candidate to design high dielectric materials, showing a tremendous promise on dielectric applications. But fabrication of these dielectric materials is relatively complicated, and unsuitable for large-scale production. Herein, a novel dielectric poly (vinylidene fluoride)/polystyrene/high density polyethylene (PVDF/PS/HDPE) composite constructed via tri-continuous structure were designed. And via variation PS concentration to control the compatibilizer effect of PS phase, a smaller PS phase size has been obtained and this composite finally exhibits a double bi-continuous morphology structure. For this double bi-continuous PVDF/PS/HDPE composite, a better dispersion of MWCNT particles increases the density of interfacial charge enrichment, and the increase of the specific surface area of the interfacial layer increases the number of enriched charges, which make the interfacial polarization increase most significantly compared with the other composites. Thus, a high-performance dielectric PVDF/PS/HDPE composite with high ε′ and low tan δ have been realized.

Negotiating Contemporary Indigeneity: Cultural Aesthetic and Communicative Practices among Contemporary! Xun and Khwe San Youth of Platfontein, South Africa

The San or Bushmen of South Africa have been represented in popular literature and media as hunter-gatherer primitives who live nomadic lives and whose history predates that of all later immigrants to the country. While the ubiquitous representation and myth provide incentives in the form of cultural/ecotourism and engenders much international interest, it has rarely translated into any form of sustainable socioeconomic benefit for the impoverished Bushmen. Rather, it obfuscates accounts of modern acculturation, hinders the process of self-determination and contributes to a systemic socio-political and economic exclusion, repression, and marginalisation of contemporary San in South Africa. The San youth who seem to have suffered the most as a result of this essentialised representation are appropriating modern popular cultures (such as hip-hop) to project self-identity, counter-narratives, and position themselves as a modernised people. Using ethnographic methods of participant observation and informal interviews from 2014 to 2018, this article examines the complex, multi-layered composition of contemporary!Xun and Khwe San identity, which places the youth at the nexus of competing expectations thrown up by imperatives of social change, global influence, dominant social paradigms, poverty, joblessness, and indigeneity. The analysis of their identities in the late-modern South Africa, provokes the question whether contemporary Indigenous people are “indigenizing modernity or modernizing indigeneity.”

A review of coextruded wood–plastic composites

AbstractWood–plastic composites (WPCs) are increasingly broadly applied composites that combine the merits of wood and plastics, such as the renewable, degradable, lightweight, and low‐cost characteristics of wood, and the thermoplasticity, hydrophobicity, and toughness of plastics. However, WPCs also display the disadvantages of the two main components including hydrophilicity and flammability of wood, and weathering degradability, flammability, and thermal expansion of plastics. Coextruded WPCs (Co‐WPCs) are multilayer composites in which regular WPCs are coated with a protective shell layer through coextrusion. The core–shell structure of Co‐WPCs provides a way to overcome the shortcomings of WPCs by modifications specific to the composite surfaces. This review summarizes the studies of Co‐WPCs in terms of their mechanical properties, moisture absorption, weathering, flame resistance, and dimensional stability. It also presents expectations for the further development of Co‐WPCs.

IMPACT OF THE HIGH-SPEED FLOW OF POWDER PARTICLES ON THE STRUCTURE OF POLYMER MATERIALS AND METAL-POLYMER COMPOSITES

The problem of protecting spacecraft from cosmic dust has recently come to the fore. There is still no enough data on the complex effect of short-term high-energy, dynamic loading on materials, including polymer materials and multilayer polymer-metal composites. The use of dynamic alloying in the super-deep penetration (SDP) mode by high-speed flows of powder particles allows assessing the effect on the material under dynamic action. Previous studies on steel and aluminum samples have shown a significant effect of high-speed flows of powder particles on the structure and properties of materials. As a result of a study of samples made of aliphatic polyurethane with steel reinforcement elements, it was found that there are traces of the penetration of high-speed particles into both metal and polymer layers. However, the number of flow elements detected in the polymeric part is significantly less than the number of elements in the metal reinforcing part. Thus, it is possible to assume that or the polymer material is a more effective barrier to the high-speed flow compared to the metal, or the “self-healing” effect is observed.

Strength prediction of multi-layered copper-based composites fabricated by accumulative roll bonding

This work aims to evaluate the feasibility of the fabrication of nanostructured Cu/Al/Ag multi-layered composites by accumulative roll bonding (ARB), and to analyze the tensile properties and electrical conductivity of the produced composites. A theoretical model using strengthening mechanisms and some structural parameters extracted from X-ray diffraction is also developed to predict the tensile strength of the composites. It was found that by progression of ARB, the experimental and calculated tensile strengths are enhanced, reach a maximum of about 450 and 510 MPa at the fifth cycle of ARB, respectively and then are reduced. The electrical conductivity decreased slightly by increasing the number of ARB cycles at initial ARB cycles, but the decrease was intensified at the final ARB cycles. In conclusion, the merit of ARB to fabricate this type of multi-layered nanocomposites and the accuracy of the developed model to predict tensile strength were realized.

Subsurface multilayer evolution of ZrB2–SiC ceramics in high-speed sliding and adhesion transfer conditions

High-speed continuous sliding experiments on ZrB2-20 vol% SiC ultra-high temperature ceramics have been carried out to elucidate specifics and details of tribooxidation under conditions of subsurface deformation and friction generated heating. Subsurface multilayer structure layer phase composition was obtained to testify on the intense mass transfer processes. Generation of thick boron-depleted and mechanically mixed layer (MML) composed of silicate glass, iron, high-temperature zirconia phases as well as silicon carbide insulated the underlying ZrB2 grains and served to generation of two transition layers composed of borosilicate glass, zirconia and iron oxyborides. This and sealing the voids and cracks by borosilicate glass had its effect on oxidation of silicon carbide grains, which might have caused intense formation of spherical particles even far below the worn surface. Mass transfer of iron and oxygen into ceramic composite grains has been discovered along with evaporation of boron anhydride from the MML.

Design and testing of polar-orthotropic multi-layered composites under rotational load

The growing requirements for efficient and reliable high-performance rotors have led to an increased application of advanced fiber-reinforced composites. For an efficient feasibility analysis, analytical calculation methods for composite structures can provide a first design draft of typical composite components without cumbersome finite element models to engineers having low experience with anisotropic materials. In these investigations, an analytical solution for polar-orthotropic multi-layered composite rotors under rotational load is presented by transferring the well-known formulation of the classical laminate theory given in Cartesian coordinates into a formulation given in a polar coordinate system taking into consideration of centrifugal loads. The analytical results are verified under different rotational speeds with standard finite element solutions and also with experimental results at selected positions from strain gauges and diffraction grating strain sensors. The results show the usefulness of analytical solutions for the design engineer and can be further expanded to take into consideration temperature and shrinkage effects.

Interlaminar fracture toughness of low curing temperature vinylester composites exposed to severe service conditions

The effects of high temperature environmental exposition and of soft curing treatment on the interlaminar shear strength for vinylester glass fibre multilayer composites have been studied. The degradation effects on the matrix and fibre–matrix interface are due to scissions of polymer chains, the oxidation process, the weakening of fibre–matrix bonding. Possibility of stabilization of Glassfiber – Vinylester-Bisphenol-A composite for prolonged high temperature service by low temperature curing is established.

Reinforcing carbonized polyacrylonitrile fibers with nanoscale graphitic interface-layers

Carbon fibers going through stabilization, carbonization, and graphitization heat-treatment stages will form continuous graphitic layers that are closely packed and preferentially aligned along the fiber axis, forming high mechanical stiffness or strength and electrical or thermal conductivity. The alignment of noncontinuous, powder-like graphene layers in polymers has been challenging due to the low bending modulus of a few- or even single-layered graphene, which causes aggregations or folding behaviors. This research demonstrates the leveraging of polymer-nanoparticle interactions to align graphene nanoplatelets (GNPs) in the polyacrylonitrile (PAN) matrix. An in-house designed spinning method produces a three-layered fiber that utilizes the interfacial interactions between each layer for graphene alignment between graphitic layers. This composite containing oriented GNPs significantly improves modulus (i.e., 42.3 to 74.6 GPa) and increases electrical conductivity for enhancing volatile organic compounds (VOCs) sensing behaviors. This research opens up a new scalable fabrication method for multilayered composites.

Diffusion behavior and bending fracture mechanism of W/Ti multilayer composites

Multilayer composites are effective to improve the toughness of Tungsten (W). To demonstrate the toughing mechanism, a series of W/Ti multilayer composites are prepared by diffusion bonding at different temperatures in a spark plasma sintering system. It shows that the mechanical properties of the composites vary with the change of bonding temperature, which is closely related with the microstructures developed at different bonding temperatures. The bending strength of the composites bonding at 1100 °C is highest, which reaches 1847 MPa. However, the composites bonding at 1200 °C has absorbed the highest fracture energy during three-point bending tests. The different microstructures developed at different bonding temperatures are mainly due to the different diffusion behaviors of W and Ti elements. The activation energy of W diffusion into Ti and Ti diffusion into W is 87.69 KJ/mol and 152.20 KJ/mol, respectively. And the diffusion coefficient of W into Ti is two orders of magnitude higher than that of Ti into W. Thus, β-Ti has formed in the Ti layer due to W diffusion into Ti. Although α-Ti is precipitated in the β-Ti, solid solution strengthening is the main strengthening mechanism in the Ti layer. The toughening mechanism of the W/Ti multilayer composites is mainly crack deflection, and the plastic deformation of the Ti layer. Meanwhile, the fracture modes of these composites are proposed.

Thermal Properties and Structural Features of Multilayer Films Based on Chitosan and Anionic Polysaccharides.

This study investigates the thermal and structural properties of multilayer composites based on chitosan (CS) and polyanions with different functionalities, including sodium sulfoethyl cellulose (SEC), sodium alginate (ALG), and sodium hyaluronate (HA). Unlike polyelectrolyte complexes (PECs) obtained by polymer mixing, the formation of a PEC layer by a process of layer-by-layer deposition of oppositely charged polymers is accompanied by the transformation of the CS polymorphic state, and this affects the relaxation and thermal properties of the resulting multilayer composite. X-ray diffraction analysis showed that the formation of the PEC layer in the CS/SEC multilayer film is accompanied by crystallization of the CS chains and the formation of a predominantly anhydrous CS modification. Thermogravimetric analysis of the CS/SEC film registers a high-temperature peak associated with the thermal decomposition of crystalline CS in the PEC composition. According to the dynamic mechanical analysis, the CS/SEC composite was characterized by a single glass transition temperature, indicating a strong interaction between the layers when using SEC (a strong acid salt) as the counterion to CS. For multilayer composites with weak polyacid salts (ALG and HA), the crystallization of CS in the PEC layer is weaker, as reflected in the thermal degradation of these films. A high-temperature peak is recorded in the thermal decomposition of CS/HA and is absent in the case of CS/ALG. Dynamic mechanical analysis of the CS/ALG composite showed two glass transition temperatures close to those of the original polymers, indicating weak PEC formation. The CS/HA composite showed an intermediate response. Thus, the effect of the PEC layer on the properties of the poly-layer composites decreases in the order CS/SEC > CS/HA > CS/ALG.

Effect of Interface on the Deep Drawability of Ti/Al Multilayered Composites

Ti/Al multilayered composites (LMCs) with different layers were prepared by hot-pressing and hot-rolling. The effects of interface on the deep drawability of LMCs were explored. The results indicate that LMCs with more layers have a higher limit-drawing ratio (LDR) and exhibit an excellent deep drawability. The texture strength of the Ti layer gradually weakens with the increase of layers, which leads to the smaller yield ratio (σs/σb), the plastic strain ratio (r), and the larger strain hardening index (n), thus the deep drawability of LMCs with more layers is enhanced effectively. The Ti/Al interfaces in three, five, and seven layers of LMCs exhibit straight, small wave-like interlocking, and dense serrated structures at the corner of the cylindrical parts, respectively. The component metals become thinner with the increase of layers, and the increased interfacial pressure promotes the formation of an increasingly firm overlapped interfacial structure. The load transfer via the interfaces makes the stress distribution between layers more uniform with the increase of layers, which helps to coordinate deformation. Deflection and tearing occur when the cracks propagate to the interface due to the complex stress state, which hinders and delays the crack penetration, thereby improving the deep drawability of LMCs with more layers.

Electromechanical properties of multilayer structured composites of ferroelectric ceramics - polymer system

A method for fabrication of piezomaterials based on the ferroelectric ceramics - polymer composites in the form of multilayer structures was developed. Samples of these materials were obtained and their electromechanical properties, as well as the dependences of these properties on the number of layers in multilayer structures, were studied.

Stochastic Thermal Properties of Laminates Filled with Long Fibers.

In this paper, the stochastic parameters of the effective thermal conductivity of multilayer composites are considered. The examined specimens of composites were built with a different number of layers and each had a different saturation density of a composite matrix with fibers. For each case of laminate built with a prescribed number of layers and assumed saturation density, 10,000 tests of its effective thermal conductivity were carried out using numerical experiments. It was assumed that the fibers located in each layer were rectilinear, had a circular cross-section and that they could take random positions in their repeatable volume elements (RVEs). In view of the mentioned assumptions, the heat flux passing throughout a cross-section of a composite sample, perpendicular to the fibers’ direction, was considered. The probability density functions were fitted to the obtained data and then the chosen stochastic parameters of the effective thermal conductivity coefficients were determined.

Comparative study of ultrasonic techniques for reconstructing the multilayer structure of composites

The multilayer structure of fiber-reinforced polymers may be extracted by ultrasonic pulse-echo inspection. Depending on the employed ultrasonic frequency and subsequent processing methodology, different depth resolution and dynamic depth range can be achieved. This study compares the performance of different ultrasonic pulse-echo approaches for extracting the ply-by-ply structure of multilayered composites. The following methodologies are studied: Method 1: 50 MHz, 15 MHz, and 5 MHz ultrasound with low-pass filtering using analysis of the instantaneous amplitude, Method 2: 15 MHz ultrasound with Wiener deconvolution (and autoregressive spectral extrapolation) using analysis of the instantaneous amplitude, and Method 3: 5 MHz ultrasound with low-pass or log-Gabor filtering using analysis of the instantaneous phase. In the simulation study, the performance of the various techniques is investigated on synthetic data representative for a 24-ply carbon fiber reinforced polymer. The robustness of the techniques is evaluated for different signal-to-noise ratios. The various techniques are further investigated on experimental data of a 24-ply cross-ply carbon fiber reinforced polymer. The ply-by-ply structure is extracted and presented in the form of both B-scan and C-scan images. The thickness of each ply is estimated for quantitative analysis. The obtained results indicate that the 5 MHz ultrasound coupled to analytic-signal analysis with log-Gabor filter shows the best performance for reconstructing the multilayer structure of the studied composites.

Two-Stage Production of Multilayer Composites Containing a Heat-Resistant Superalloy and an Oxide Ceramic

Two-Stage Production of Multilayer Composites Containing a Heat-Resistant Superalloy and an Oxide Ceramic

Comparative study of the tensile properties of 2D and UD over-braided multilayer composites

In over-braided multilayer composites, the braid angle gradually increases from the first layer (the innermost layer) to the last one (the outermost layer). A two-dimensional (2D) braided structure is the most commonly used architecture for over-braiding. A unidirectional (UD) braided structure was developed to decrease the out-of-plane crimp in the 2D braided structure. To broaden the application of the 2D over-braided multilayer composite (2DMLC) and UD over-braided multilayer composite (UDMLC), their tensile properties and failure mechanisms must be studied. This research revealed that a slight range variation (2°–7°) in the braid angle has a significant effect on the tensile properties of these two composites, and the modulus and strength of the UDMLC were 8.63% and 10.90% higher than those of the 2DMLC, respectively. During tensile failure, the generation and propagation of matrix cracks were affected by the braided structure. As the braid angle gradually increased from the first to the last layer, the damage decreased. Moreover, after the tensile test, both the 2DMLC and UDMLC were concave toward the first layer in the transverse direction of the samples, and only the 2DMLC bent to the last layer in the longitudinal direction of the sample.

Magneto-optical properties of two – layer film systems based on Fe and Pt

The paper shows the experimental results of the study of magneto - optical properties and phase composition of thin films and multilayers based on Fe and Pt. Samples were obtained in a high-vacuum chamber (10–8 Pa) by layer-by-layer deposition from pots at room temperature. It has been shown that FCC solid solution of FePt is formed already in the process of deposition on the substrate (sital plates). Depending on the concentration of the atoms of the components in the unannealed samples, three phases can be formed: (i) s.s. Fe(Pt); (ii) Fe3Pt; (iii) FePt. The first sign of the beginning of ordering in the FCC phase of FePt should be considered the appearance of superreflections in the form of lines (001) and (002) during heat treatment. Depending on the total thickness of the multilayer or individual layers, the annealing temperature at which extrareflexes appear can vary in the range of 300–570 K. All the samples obtained have a low coercivity (0.25 - 0.4 mT). Magneto-optical studies have shown that an increase in the content of the non-magnetic component decreases the main magnetic characteristics. However, In [Fe(3)/Pt(3)]n/S multilayers with the number of repeatable elements from 2 to 8 an increase in the main magnetic parameters is observed compared with bilayer films at the same effective thickness.