Construction of a three-dimensional model for calculating multilayer orthotrophic plates

A three-dimensional mathematical model is suggested for layered orthotropic plates by introducing kinematic hypotheses for the distribution of displacements with respect to plate thickness. A feature of the hypotheses is the fact that they are written with respect to functions of displacements on the front surfaces of plates. Approximation of displacements is mutually independent. Equilibrium equations and boundary conditions are obtained on the basis of the Lagrange variation principle. The functions sought have similar operators not exceeding the second order which markedly simplifies their realization. A number of test problems point to the possibility of using this model even with ratios of elasticity moduli for the supporting layers and filler of one hundred with a ratio of four for plate length to height. Translated from Problemy Prochnosti, No. 12, pp. 57–61, December, 1994.     

Designing multilayer diamond like carbon coatings for improved mechanical properties

New multilayer coatings were produced by incorporating alternating soft and hard DLC layers enabled by varying the bias voltage during deposition process while maintaining a constant hard-to-soft layer thickness ratio.These coatings were deposited onto a Cr/Cr Cxgraded layer by closed field unbalanced magnetron sputtering(CFUBMS).The cross-sectional analysis of the coatings showed that the multilayer coatings possess sharp interfaces between the soft and hard layers with the hard to soft layer thickness ratio(1:1.33)constant in all the coatings.Raman analysis uncovered the increasing sp³character of the DLC coatings as a result of decreasing ID/IGratio and increasing full width at half maximum(FWHM)values of the G band peak induced supposedly by an increase in bias voltage during hard layer deposition.Nanoindentation tests showed an increase in hardness of the DLC coatings which can be correlated with the increase in the sp³content of the coatings as well as decreasing sp²-C cluster size,as calculated from the ID/IGratio.Furthermore,the coatings exhibited excellent plastic deformation resistance and adhesion strength upon microindentation and scratch testing,respectively.Although further investigations are required to assess coating durability,the multilayer design could offer the DLC coatings with a rare opportunity to combine the high hardness with damage resistance with a constant bilayer thickness and without the need to introduce complex multilayer system.     

A novel structure for carbon nanotube reinforced alumina composites with improved mechanical properties

Engineering ceramics have high stiffness, excellent thermostability, and relatively low density, but their brittleness impedes their use as structural materials. Incorporating carbon nanotubes (CNTs) into a brittle ceramic might be expected to provide CNT/ceramic composites with both high toughness and high temperature stability. Until now, however, materials fabrication difficulties have limited research on CNT/ceramic composites. The mechanical failure of CNT/ceramic composites reported previously is primarily attributed to poor CNT-matrix connectivity and severe phase segregation. Here we show that a novel processing approach based on the precursor method can diminish the phase segregation of multi-walled carbon nanotubes (MWCNTs), and render MWCNT/alumina composites highly homogeneous. The MWCNTs used in this study are modified with an acid treatment. Combined with a mechanical interlock induced by the chemically modified MWCNTs, this approach leads to improved mechanical properties. Mechanical measurements reveal that only 0.9?vol% acid-treated MWCNT addition results in?27% and?25% simultaneous increases in bending strength (689.6 ± 29.1?MPa) and fracture toughness (5.90 ± 0.27?MPa?m(1/2)), respectively.     

The mechanical properties of glass/polypropylene multilayer laminates

Multilayer laminates have been fabricated from thin sheets of glass and polypropylene. By the use of a special surface treatment applied to the glass surfaces, fully transcrystalline polypropylene layers could be formed. This facilitated the interpretation of the mechanical properties of the laminates in terms of the microstructure of the polymeric layers. It was found that the presence of transcrystalline layers leads to modest increases in flexural modulus and strength, and strain energy release rateG _c. These laminates can be valuable models for the mechanical properties of fibre-reinforced thermoplastics.     

Advanced characterization of mechanical properties of multilayer ceramic capacitors

Characterization of the mechanical properties of small components is a significant issue. For the multilayer ceramic capacitor (MLCC), direct loading by conventional facilities is not suitable because of its small size. To date, the standard method used to determine MLCC’s mechanical properties is board flex test; i.e., mounting the capacitor onto a printed circuit board (PCB) and applying bending to the entire system. Failure is defined as cracking or capacitance loss of the MLCC when the mounted PCB is subjected to a specified deflection, and the measurements are usually performed after the test. In this case, characterization of the mechanical properties of MLCCs is qualitative. The purpose of the present study was to quantitatively characterize the mechanical properties of MLCCs. Specifically, the acoustic emission was used to detect cracking of MLCCs during the board flex test. To confirm cracking-induced acoustic emission, telemicroscope was used to perform the in situ observation of cracking. Finite element analyses were also performed to analyze the stress field resulting from the test to compare with the observed cracking path. In addition, nanoindentation was used to explore the mechanical properties of the constituents of MLCCs in the nanoscale. Our work not only allows identification and understanding of the fracture origin, but also provides guidelines in the material design.     

Measurement of mechanical properties of multilayer coatings by nanoindentation

Abstract

Multilayer protective coatings of alternate aluminium and titanium diboride TiB₂ layers have been tested by nanoindentation to measure both hardness and Young's modulus values. The initial results show that the values obtained depend upon the depth of indentation. An alternative view is presented to show that by considering the percentage of each coating in contact with the indenter a single relationship between either hardness or Young's modulus and the amount of aluminium layer penetrated can be produced. This technique allows the influence of the percentage ceramic on the results obtained to be identified. Comparison of the nanoindentation results with three point bending tests show how the coating structure influences the results obtained.     

A novel method for launching flyer plates

We describe a potential method for launching flat flyer plates by using explosives in complete cylindrical convergence. The basic problem we study in this computational analysis is how to turn the cylindrically convergent shock wave from the explosive into a flat front shock wave running parallel to the cylinder axis. We use a two-dimensional Lagrangian finite difference code to simulate the device. The code uses a free Lagrange method for dealing with mesh distortions.

The calculations predict that the method could launch relatively flat metal plates at velocities up to 14 km/s, but computational uncertainties make experimental verification mandatory.     

Hybrid stress reduced-Mindlin elements for thin multilayer plates

A hybrid-stress formulation of isoparametric elements for the analysis of thin multilayer laminated composite plates is presented. The element displacement behaviour is characterized by laminate reference surface inplane and transverse displacements and laminate non-normal cross-section rotations; as a result, simple C^o interpolation of displacement and rotation can be used, and the number of degrees-of-freedom is independent of the number of layers. All components of stress are included and are related to a set of laminate stress parameters, the number of which is independent of the number of layers. Attention is restricted here to thin laminates, for which it is shown that the contributions of transverse shear stress and transverse normal stress to the internal complementary energy can be neglected. As a result of this reduction, a modified stiffness-formation algorithm can be used which provides a significant improvement in computational efficiency. The formulation presented is used to develop an 8-node isoparametric thin multilayer plate element. The resulting element is naturally invariant, of correct rank, and non-locking in the thin plate limit.     

Geometry,mechanical properties and mounting of perforated plates for ballistic application

In this paper, the ballistic resistance of perforated plates made of different types of steel, mounting and geometry was investigated. Different types of steel in various heat treatment conditions were tested. Target mounting was also varied: rigid, oblique and hanging. Furthermore, four different perforated plate geometries were tested: two plate thicknesses and two hole diameters. Their behaviour was tested using impact from firing 12.7 mm M-8 API ammunition at eleven perforated plate samples. These samples were placed by means of a steel frame over a 13 mm RHA plate, at two distances. Damaged area on targets was correlated to ballistic resistance of the whole armour to find the optimal perforated plate. It was found that perforated plates, in optimized case offer a frequent fracture of the penetrating core in up to five parts. This debris is unable to penetrate the basic plate, offering mass effectiveness of the whole armour model of 1.76 and the mass effectiveness of the perforated plate of 5.91.     

A finite element model for Mindlin plates

In the general framework of Reissner-Mindlin theory, a plate model based on certain potential functions is discussed, together with its mechanical interpretation. A finite element implementation is also described and numerical results are reported.     

Adsorbed multilayer effects on the mechanical properties in nanometer indentation depth

Nanoindentation is a powerful technique for determining the mechanical properties of a material at the nanometer scale. In this study, the changes induced in the mechanical properties of a thin film by the presence of adsorbed multilayers are examined by performing nanoindentation tests with ultra-low indentation depths. The current findings suggest that the results obtained for the mechanical properties of thin films under nanoindentation will be overestimated if the effects of the adsorbed multilayers on reducing elastic recovery between the indenter and the substrate are not taken into consideration.     

Sandwich-type composite multilayer films of strontium titanate and barium strontium titanate and their controllable dielectric properties

It is a challenge to reduce the dielectric loss and increase the tunability of pure barium strontium titanate(BST)films for microwave tunable application because these two properties change simultaneously.Herein,a novel composite of strontium titanate(ST)and potassium-doped BST(KBST)has been designed as ST/KBST/ST sandwich-type film with various ST and KBST layers.X-ray diffraction patterns show that the film exhibits cubic perovskite polycrystalline structure composed of BST and ST phase,mainly grow along(110)crystal plane with average grain size of less than 20 nm and decreasing BST phase/ST phase ratio with increasing film thickness.Scanning electron microscope shows that no interfacial layer can be observed,indicating that ST and KBST are fully compounded.Low dielectric loss and high tunability at-10-10V and stable and excellent dielectric properties at 1 GHz are achieved,meeting the needs of microwave tunable application at high frequency.The surface structures are also studied by other analysis methods,and ST/MgBST/ST sandwich-type film is compared.     

Raman spectroscopy and mechanical properties of multilayer tetrahedral amorphous carbon films

In order to take the tetrahedral amorphous carbon (ta-C) films as the high acoustic impedence layer in a Bragg reflector isolating acoustic wave from the substrate in solidly mounted resonator, the multilayer films consisting of sp2-rich layers and sp3-rich layers were deposited from a filtered cathodic vacuum arc by adjusting the substrate bias. The microstructure of the films was evaluated using a visible Raman spectroscopy. The stress was calculated according to the changed curvature of the coated and bare substrate. The hardness, modulus and scratching were measured using a nanoindenter. It has been shown that the multilayer structure maintaining high tetrahedral content, high hardness and high elastic modulus is still characterized with lower intrinsic stress and better adhesion.     

A hybrid finite element model for multilayered plates

We present a finite element model for multilayered plates, based on a primal-hybrid variational formulation. Namely, each layer is analyzed as it were a lonely structure, and the displacement continuity is imposed from one layer to the other by means of Lagrange multipliers. Then, a Mindlin-like displacement field is assumed for any layer; the resulting continuous problem is proven to be well-posed under rather general hypotheses. Finally, a finite element model is deduced, using a very simple scheme (piecewise linear approximation for the displacement components and piecewise constant Lagrange multipliers). The numerical results assess the good performance of the proposed model.     

A nonlocal model for plug formation in plates

By means of a nonlocal viscous fluid model, an investigation is carried out of the problem of penetration of a cylindrical projectile into a plate leading to a failure of the plate by a plug formation. The effect of impact is represented by a uniform initial velocity distribution over a circular region on the surface of the plate. The behavior of this plate material is assumed to be viscous and spatially nonlocal, and only the effects of vertical shearing stress are considered. The expression of stress, velocity and displacement are obtained and the calculated displacement profiles are compared with some existing experimental profiles.     

A novel sheep vertebral bone defect model for injectable bioactive vertebral augmentation materials

New injectable bone substitutes have been developed that are, unlike polymethylmethacrylate, biologically active and have an osteogenic effect leading to osteogenesis and bone remodeling for vertebroplasty or kyphoplasty. In this study, we developed a sheep vertebral bone defect model to evaluate the new bioactive materials and assessed the feasibility of the model in vivo. Bone voids were experimentally created on lumbar vertebrae L2–L5 with L1 and L6 left intact as a normal control in mature sheep. The defect vertebrae L2–L5 in each sheep were randomized to receive augmentation with calcium phosphate cement (CPC) or sham. Vertebrae (L1–L6) were collected after 2 and 24 weeks of the cement augmentation and their strength and stiffness, as well as osseointegration activity and biodegradability, were evaluated. Finally, CPC significantly improved the strength and stiffness of vertebrae but did not yet restore it to the normal level at 24 weeks. Osteogenesis occurred at a substantially high level after 24 weeks of CPC augmentation or sham. Therefore, the sheep vertebral model with one void, 6.0 mm in diameter and 15.0 mm in depth, is replicable and can be used for evaluating the new injectable bioactive materials in vertebral augmentation or reconstruction.     

Effect of multilayer coating on mechanical properties of Nicalon-fibre-reinforced silicon carbide composites

Nicalon-fibre-reinforced SiC composites were fabricated by combining polymer solution infiltration (PSI) and chemical vapour infiltration (CVI). Effect of multilayer coating on mechanical properties of the composites was investigated. The coatings consisted of chemically vapour deposited (CVD) C and SiC and were designed to enhance fibre pull-out in the composites. It was found that the flexural strength and fracture toughness of the composites were increased with the number of coating layers and was a maximum for 7 coating layers which consisted of C/SiC/C/SiC/C/SiC/C. Typical flexural strength and fracture toughness of the composites were 300 MPa and 14.5 MPa m^1/2, respectively.     

Kinetic model for the mechanical properties of polymer glasses

The deformation behaviour and the mechanical properties of polymer glasses are studied with the help of a kinetic model introduced previously. The model, which is based on the Eyring chemical activation rate theory, takes into account the role of the strong attractive forces between macromolecular chains as well as chain slippage through entanglements. Application to poly(methyl methacrylate) has allowed us to calculate the yield stress, craze length and fracture toughness and their dependence on testing conditions. The model also clearly illustrates the transition from crazing to shear yielding in polymer glasses as the density of entanglements is increased.     

Geometry,mechanical and ballistic properties of ADI material perforated plates

In this paper, austempered ductile iron has been evaluated as an alternative to steel for perforated plates applied in the ballistic protection of military vehicles. The austempering was performed in lower and higher austempering ranges in order to obtain two types of austempered ductile iron: one with a higher strength, and the other with a higher ductility. Perforated plates having two different thicknesses of 7 and 9 mm were mounted in front of basic armour and 12.7 × 99 mm armour – piercing incendiary ammunition was fired from 100 m. It was shown that the austempered ductile iron material austempered at a lower temperature has superior ballistic resistance, providing a full (five out of five armour – piercing incendiary shots stopped) ballistic resistance if combined with 13 mm basic armour plate. The thicker austempered ductile iron perforated plate provides more significant penetrating core damage, and therefore, lower basic plate damage. On the other hand, the thinner austempered ductile iron material perforated plate can be considered optimal due to its lower weight and higher mass effectiveness. In austempered ductile iron material austempered at a higher temperature, besides a lower hardness, bulk retained low-carbon metastable austenite transforms into martensite through strain induced mechanism, causing a partial brittle fracture.     

Development of a novel magnesium-copper based composite with improved mechanical properties

Magnesium based composite with 17.95 wt.% of copper reinforcement was fabricated using an innovative DMD technique followed by hot extrusion. Microstructural characterization of the extruded composite samples showed fairly uniform reinforcement distribution, presence of Mg-Cu based intermetallics, good Cu_P-Mg interfacial integrity, and the presence of minimal porosity. Mechanical properties characterization revealed that the presence of copper as reinforcement lead to a significant increase in hardness, elastic modulus, 0.2% yield strength and UTS of pure magnesium while the ductility was adversely affected. An attempt is made in the present study to correlate the effect of copper as reinforcement with the microstructural and mechanical properties of magnesium.