Layered Plates Research Articles

Numerical Simulation of the Influence of Interfacial Characteristics of Bulletproof Plates on Ballistic Protection Performance

The influence of three interfacial characteristics on the ballistic protection performance of double-layer steel plates is concluded through a numerical simulation of penetration of armor-piercing projectiles into double-layer steel plates with different interfacial characteristics. The research results show that the gap between double layers of steel plates has an adverse effect on the ballistic protection performance. The larger the gap is, the worse the ballistic protection performance is; appropriate interlaminar stress on double-layer steel plates can improve the ballistic protection of target plates; when the joint or fixed point of double-layer steel plates is too close to the impact point, the ballistic protection performance will demonstrate a downward trend.

ОПРЕДЕЛЕНИЕ ПОПЕРЕЧНЫХ РАЗМЕРОВ ДЕФЕКТОВ РАССЛОЕНИЯ БИМЕТАЛЛИЧЕСКОЙ ПЛАСТИНЫ ПРИ АКТИВНОМ ТЕПЛОВОМ НЕРАЗРУШАЮЩЕМ КОНТРОЛЕ

Various methods of nondestructive testing, including active infrared thermography, are used to detect latent subsurface defects in the contact of layers in multilayer products. One of the main difficulties using this method consists in processing and interpreting the thermal image data. The peculiarity of investigated defects of bimetal plate layers continuity violation is that the depth of defect location is known and the main task is to determine its size. Some methods are used for this purpose including analysis of spatial temperature profiles. Aim. To analyse the use of various approaches to determining the transverse dimensions of a delamination between metals in simulating active thermal non-destructive testing of steel-aluminium plates. Materials and methods. Mathematical and computer simulating methods, numerical differentiation are used. The delamination size is determined by projections of half the height of the amplitude signal and the extremum of the derivative of the temperature signal function. Calculations and graphical constructions are performed using the mathematical package GNU Octave. Results. Numerical simulation is carried out for different values of heat flow power, heating and cooling time. The temperature signal distribution over the surface of a multilayer bimetallic plate has been plotted. The values of the defect radius according to the projections of the characteristic points are determined. Conclusion. The results of simulation allow us to conclude that using the projection of the extremum of the temperature signal derivative function allows us to accurately estimate the defect size, while in the case of the point projection cor¬responding to half of the signal amplitude height, the result is underestimated. The obtained results can be used for further experimental studies of processes of active thermal non-destructive testing of products made of multilayer bimetallic materials.

Tensile Behavior of Titanium-Clad Bimetallic Steel Butt-Welded Joints

Because of the promising corrosion resistance and load-bearing capacity, titanium-clad (TC) bimetallic steel has gained increasing attention in ocean/coastal civil and structural engineering. Due to the double-layer nature of TC bimetallic steel, the characteristics of the structural member’s geometry and weld details are considerably different from that of conventional steel members. Even though previous studies have conducted systematical clarifications on parent material of TC bimetallic steels, the mechanical behaviors of weld joints are still vague. This paper firstly describes the manufacture features of TC bimetallic steel welded joints and welded members. Subsequently, the type II and type III butt-welded joints provided by GB/T 13149-2009 are selected to study the corresponding tensile mechanical behavior. Two butt-welded TC bimetallic steel plates were fabricated from hot-rolled bonding TA2 + Q355B TC bimetallic steel and welding wire of ER55-Ni1 and ERTA2ELI. Eight tensile coupons were then extracted from the two welded plates and loaded to failure monotonically. The failure mechanism, stress–strain curves and key mechanical properties are studied and compared with that of parent material. It is found that both types of welded joints possess two fracture points. The first one refers to the fracture of weld joint between the clad layer and titanium cover plate, whilst the second one is the eventual fracture of substrate metal. When the first fracture point is reached, the stress–strain relation exhibits a sharp drop in stress value. Thereafter, a strain-hardening behavior can still be observed prior to the ultimate strength point. The first fracture-induced stress drop of type II joint is less than that of type III joint, whilst the strain-hardening amount of type II joint is more outstanding than that of type III joint. The fracture elongations of type II joint and type III joint are respectively 37% and 57% that of the parent material, whilst the proportions between the ultimate strengths of welded joints and parent material are, respectively, 90% and 93%. In general, the two types of TC bimetallic steel weld joints investigated herein exhibit favorable load-bearing capacity but unfavorable ductility and deformability. Based upon the experimental results, the structural design methodology of welded TC bimetallic steel structure is discussed. The investigations conducted in this paper can provide reference for development of structural design theory of welded TC bimetallic steel structure.

Electromagnetic Interference Shielding Effectiveness of Direct-Grown-Carbon Nanotubes/Carbon and Glass Fiber-Reinforced Epoxy Matrix Composites.

In this study, carbon nanotubes (CNTs) were grown under the same conditions as those of carbon fibers and glass fibers, and a comparative analysis was performed to confirm the potential of glass fibers with grown CNTs as electromagnetic interference (EMI) shielding materials. The CNTs were grown directly on the two fiber surfaces by a chemical vapor deposition process, with the aid of Ni particles loaded on them via a Ni-P plating process followed by heat treatment. The morphology and structural characteristics of the carbon and glass fibers with grown CNTs were analyzed using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray photoelectron spectrometry (XPS), and the EMI shielding efficiency (EMI SE) of the directly grown CNT/carbon and glass fiber-reinforced epoxy matrix composites was determined using a vector-network analyzer. As the plating time increased, a plating layer serving as a catalyst formed on the fiber surface, confirming the growth of numerous nanowire-shaped CNTs. The average EMI SET values of the carbon fiber-reinforced plastic (CFRP) and glass fiber-reinforced plastic (GFRP) with grown CNTs maximized at approximately 81 and 40 dB, respectively. Carbon fibers with grown CNTs exhibited a significantly higher EMI SET value than the glass fiber-based sample, but the latter showed a higher EMI SET increase rate. This indicates that low-cost, high-quality EMI-shielding materials can be developed through the growth of CNTs on the surface of glass fibers.

The Emerging Layered Hydroxide Plates with Record Thickness for Enhanced High-Mass-Loading Energy Storage.

The past decade has witnessed the development of layered-hydroxide-based self-supporting electrodes, but the low active mass ratio impedes its all-around energy-storage applications. Herein, the intrinsic limit of layered hydroxides is broken by engineering F-substituted β-Ni(OH)2 (Ni-F-OH) plates with a sub-micrometer thickness (over 700nm), producing a superhigh mass loading of 29.8mg cm-2 on the carbon substrate. Theoretical calculation and X-ray absorption spectroscopy analysis demonstrate that Ni-F-OH shares the β-Ni(OH)2 -like structure with slightly tuned lattice parameters. More interestingly, the synergy modulation of NH4 + and F- is found to serve as the key enabler to tailor these sub-micrometer-thickness 2D plates thanks to the modification effects on the (001) plane surface energy and local OH- concentration. Guided by this mechanism, the superstructures of bimetallic hydroxides and their derivatives are further developed, revealing they are a versatile family with great promise. The tailored ultrathick phosphide superstructure achieves a superhigh specific capacity of 7144 mC cm-2 and a superior rate capability (79% at 50mA cm-2 ). This work highlights a multiscale understanding of how exceptional structure modulation happens in low-dimensional layered materials. The as-built unique methodology and mechanisms will boost the development of advanced materials to better meet future energy demands.

Finite Element Analysis on Inclusion Migration during Hot-Rolling Process of Ultralow Carbon Steel

Slivers on the surface of rolled plates, which are serious defects for interstitial-free (IF) steel, occur mainly as a result of inclusions in continuous casting (CC) slabs. It is, therefore, important to study inclusions in CC slabs in terms of their migration towards the surface during hot rolling. To investigate inclusion migration during the hot rolling of ultralow carbon steel, a 3D numerical model was constructed using the finite element method. The positions of the inclusions in the surface layer of an IF steel slab (50 mm) were tracked during hot rolling using a node-tracking method. Furthermore, the study analyzed the effects of scarfing on inclusion migration during hot rolling and inclusion distribution in a hot-rolled plate. During the hot-rolling process, inclusions in the wide faces of the intermediate slab gradually migrated to the surface of the intermediate slab. Owing to a thickness reduction, accumulation areas of inclusions were finally generated at the edge of the hot-rolled plate; these areas may lead to sliver defects. The scarfing of the slab did not affect the distribution of inclusions in the hot-rolled plate; however, it may have reduced the inclusion content in the outermost layers of the hot-rolled plate. The inclusions were mainly located within 1 mm underneath the hot-rolled plate. Moreover, the inclusions near the inner arc of the CC slab were concentrated within 1.5 mm of the upper plate surface. Using galvanostatic electrolysis, the number of large inclusions in samples prepared from a hot-rolled plate obtained from a plant was measured. The measurements agreed well with the numerical model predictions, which validated the FE model in the current work.

A theoretical model for two‐way bending behavior of bilayer shape memory polymer plate

AbstractThis study proposes a simple theoretical model based on the principles of phase transition and strain energy balance theories (during the thermo‐mechanical cycle process) to predict the two‐way bending behavior of a bilayer plate composed of two types of shape memory polymers (SMPs) with different glass transition temperatures under axial strains from 5% to 20%. The two‐way bending behavior observed from the theoretical results was verified via comparison with the finite‐element method (FEM) simulation based on the Generalized Maxwell model, wherein good agreement was demonstrated. The maximum errors for the critical bending angle and deflection were 6.82% and 5.36%, respectively. In addition, the two‐way bending behavior of a bilayer plate, including SMP and elastic polymer layers, was also predicted by the theoretical model, where good agreement was observed. The maximum errors for the critical bending angle and deflection were 15.20% and 12.82%, respectively. The theoretical model can predict the thermo‐mechanical behavior of smart actuators and help design the geometry configuration based on bilayer SMP plates in the future, such as smart hands or grippers.

Size-dependent nonlinear vibration analysis of cracked graphene-platelets-reinforced-composites (GPLRC) plate under parametric excitation

The response of a size-dependent randomly distributed graphene-platelet-reinforced-composite (GPLRC) plates, with an inclined part-through surface crack, resting on viscoelastic foundation under the action of periodic parametric excitation with quadratic and cubic nonlinearities are studied in the present study. The crack is centrally located at the center of the plate while inclined at an angle β concerning the X-axis. The angled crack’s mathematical formulation is based on a line-spring model. Indeed, the assumption of the problem is considered as the crack remains a continuous straight line. Nonlinearity is considered based on Berger’s formulation and Von-Karman’s geometric relations. Using classical plate theory, Eringen’s theory, micromechanical models, and equilibrium equation, the governing equation of motion of the problem have been derived. Then the Galerkin method was applied to transform the partial differential equation into the ordinary one. Eventually, the solution procedure of the cubic–quadratic nonlinear equation was followed by the multiple-scale perturbation method. Steady-state response and nonlinear softening or hardening treatment of the problem have been presented. Significant results of the study can be emphasized as GPLs, crack’s dimension and inclination, nonlocal parameter, damping, and detuning parameter effects on nonlinear behavior and stability of the structure. Dispersing GPLs as reinforcement material in the plate layer caused improvement in structural behavior, as the amplitude response of the system with the presence of a crack is decreased, comparing to a similar system without any reinforcement and crack. In the end, current work will help in the development of nonlinear behavior, stability analysis and critical bifurcation points of size-dependent cracked GPLRC plate exposed to external parametric loading.

Flexural strengthening of damaged steel beams with prestressed CFRP plates using a novel prestressing system

This study developed a novel prestressing system of the carbon fiber reinforced polymer (CFRP) plate to strengthen damaged steel beams, which reduced the operation space at the tensioning end, thereby extending the application range of prestressing system. Flexural tests were conducted to verify this system and investigate the effects of the adhesive layer, prestressing level, and CFRP plate area on the strengthening efficiency, and subsequently, a parametric analysis was carried out using finite element modeling to obtain more influencing rules of the unbonded CFRP plate-strengthened steel beams. The results indicated that satisfactory strengthening efficiency could be achieved by the novel prestressing system. The adhesive layer significantly affected the strain distributions of the steel–CFRP composite section, whereas it had a very slight effect on the flexural behavior of the steel beams, and the bonded and unbonded CFRP plates had a similar strengthening efficiency. Nonprestressed CFRP plate exhibited limited improvement in the flexural capacity and stiffness of the damaged steel beams under the normal service state; in contrast, the prestressed CFRP significantly increased the flexural behavior of the beams in the elastic and elastic–plastic stages owing to the high strength utilization of the CFRP plate. In addition, as the prestressing level increased, strengthening efficiency increased. Solely increasing the area or elastic modulus of the CFRP plate improved the strengthening efficiency slightly, whereas applying a prestress simultaneously clearly increases the strengthening efficiency. The strengthening efficiency increases with artificial notch depth.

A compound Kinoform/Fresnel zone plate lens with 15 nm resolution and high efficiency in soft x-ray

X-ray microscope as an important nanoprobing tool plays a prevailing role in nano-inspections of materials. Despite the fast advances of high resolution focusing/imaging reported, the efficiency of existing high-resolution zone plates is mostly around 5% in soft x-ray and rapidly goes down to 1%–2% when the resolution approaches 10 nm. It is well known that the rectangular zone shape, beamstop, limited height/width ratios, material absorption of light and structural defects are likely responsible for the limited efficiency. Although zone plates with Kinoform profile are supposed to be efficient, progress for achieving both high resolution (<30 nm) and high efficiency (>5%) have hardly been addressed in soft x-ray. In this work, we propose a compound Kinoform/Fresnel zone plate (CKZP) by combing a dielectric Kinoform zone plate with a 15 nm resolution zone plate. Greyscale electron beam lithography was applied to form the 3D Kinoform zone plate and atomic layer deposition was carried out to form the binary zone plate. Optical characterizations demonstrated 15 nm resolution focusing/imaging with over 7.8% efficiency in soft x-ray. The origin of the efficiency improvement behind the proposed compound lens is theoretically analyzed and discussed.

Fatigue properties of RC beams reinforced with ECC layer and steel plate

Pasting steel plates on the tensile side of reinforced concrete (RC) beams to improve their flexural capacity is a standard strengthening method. However, the increase in the RC beam bearing ability is limited, and it is easy to induce “over-reinforced beam” failure. In this paper, therefore, the ECC layer and steel plate are employed for the flexural strengthening of RC beams and the static, and fatigue properties of RC beams are investigated through experiments. A total of seven test beams were made. The static failure test and fatigue performance test were conducted to measure the ultimate bearing ability, flexibility, strain of steel and concrete, mid-span deflection, and residual bearing ability of the three kinds of RC beams after specific fatigue times. The experimental results demonstrate that the flexural capacity of the RC beam with the ECC layer and steel plate is more than twice that of the non-reinforced beam, and its flexibility is 1.77 times that of the non-reinforced beam. The residual bearing ability is 96.2% of the static loading test after 200 thousand times of fatigue loading. Additionally, no apparent damage occurs after 2 million times of fatigue loading, and the residual bearing ability is 94.2% of the static loading test. The strain range of the tensile rebar and concrete of the beam reinforced with the ECC layer and steel plate significantly decrease. Thus, RC beams reinforced with the ECC layer and steel plate possess a good fatigue performance.

Inhomogeneous deformation substructure and its effect on the recrystallization behavior of yttria dispersion-strengthened tungsten plate

Tungsten materials have been chosen for use in critical parts (i.e., as the armor of plasma-facing material) in fusion reactors. Deformed tungsten will undergo recrystallization at a high-temperature service environment, and recrystallized tungsten exhibits brittleness, which reduces mechanical properties, thermal shock resistance and service lifetime. The deformation heterogeneity may result in an inhomogeneous microstructure, affecting its recrystallization behavior. The main aim of the present work is to qualitatively and quantitatively characterize the heterogeneity in the through-thickness deformed microstructure of an yttria dispersion-strengthened tungsten plate warm-rolled to 50 % thickness reduction ratio and study the effect of heterogeneous microstructure on recrystallization behavior. For this, topological maps of the surface, quarter and center region are measured on the deformed state and annealed state utilizing electron backscatter diffraction (EBSD). Distributions of grain size, geometrically necessary dislocations (GND) energy, potential nuclei density and texture have been analyzed in detail. The results revealed that the deformed microstructure of tungsten plate along full-thickness has no apparent heterogeneity gradient of grain size and texture, but the center layer has a larger subgrain size and more potential recrystallized nuclei compared to the surface layer. The larger subgrain is more conducive to static recrystallization nucleation, while the existing potential recrystallized nuclei can grow rapidly without incubation time during subsequent high-temperature annealing, thereby recrystallization preferentially undergoes in the center layer of the tungsten plate.

The effect of thickness of transverse and longitudinal layers on deformability and stress distribution in three-layer panels made of cross-laminated timber

Introduction. The key feature of timber and materials, made from it, is anisotropy, or a pronounced difference between mechanical properties manifested in different directions. The construction of a cross-laminated timber plate, or a CLT panel, ensures its high strength and rigidity due to the perpendicular arrangement of fibers in mutually perpendicular layers. The article examines the effect of thickness of transverse and longitudinal layers on deformability and stress distribution in three-layer CLT panels. The relevance of the work lies in the need to obtain computational data for analyzing changes in strength characteristics of panels to select the most effective panel configuration.&#x0D; &#x0D; Materials and methods. Due to the lack of a standardized testing methodology, SCAD+ software package was applied to conduct the studies using numerical methods. The design scheme is identified as a general system whose deformations and principal unknowns are represented by linear displacements of nodal points along the X, Y, Z axes and rotations around these axes. A three–layer plate was selected as the element to be analyzed, the outer layers of which are longitudinal, and the inner one is transverse. Its simplified design scheme is a hinged beam.&#x0D; &#x0D; Results. The results of the study and calculations made using SCAD+ were applied to make tables and graphs showing dependence of deflection, distribution of normal and shear stresses on thickness of transverse and longitudinal layers of timber.&#x0D; &#x0D; Conclusions. The data, obtained by the authors, allow evaluating the effect of thickness on deformability and stress distribution in three-layer CLT panels to select the effective design. A change in thickness does not always bring a large difference between mechanical properties, which allows optimizing the panel parameters. The significance of the research lies, among other things, in expanding the scientific and engineering knowledge of timber structures.

Aqueous Bubbles Stabilized with Millimeter-Sized Polymer Plates.

(Sub)millimeter-sized hexagonal polymer plates that were monodisperse in shape and size were utilized as stabilizers for aqueous bubbles, and the effects of the hydrophilic-hydrophobic property, size, and solid concentration of the plates on the formability, stability, and shape and structure of aqueous bubbles were investigated. The formability and stability of the bubbles were improved by increasing the hydrophobicity of the plate surface, decreasing the plate size, and increasing the solid concentration of the plates. For plates with suitable water wettability, three-dimensional bubbles with nearly spherical and polyhedral shapes were formed by the adsorption of plates to the bare air bubbles introduced into the continuous water phase by air-water mixing. On the contrary, two-dimensional bubbles with accordion-type structures consisting of alternating layers of plates and entrapped air bubbles were formed by the transfer of multiple plates with poor wettability from the air phase to the water phase by air-water mixing. Furthermore, a correlation was found between the bubble/stabilizer size ratio and bubble shape for plates with the suitable wettability: bubbles with nearly spherical shapes were formed when the bubble/plate size ratios were >2, bubbles with hexahedral, pentahedral, and tetrahedral shapes were formed when the size ratios were approximately 1, and bubbles with triangular and sandwich shapes were formed when the size ratios were <0.8. Additionally, bubbles with similar shapes were formed when the bubble/plate size ratios were close, even when the sizes of the plates and bubbles were different.

Light timber framed wall under fire: Effect of the load and cladding

Light Timber Frame Walls are made of solid timber elements and are usually protected by cladding materials (gypsum). This investigation finds the effect of different load levels and cladding systems on the fire resistance. The timber frame structure is made with three studs and two rails, and will be analysed with two different protection levels. The computational model includes the thermal analysis under standard fire and a sequential mechanical analysis with time increments. Both, thermal and thermo-mechanical models are validated against experimental results developed in the reduced scale and full scale. The timber frame structure is deemed to have failed when it is no longer supporting the test load. The results are also compared with the failure criteria used for the experimental tests. The timber frame is deformed and all simulated models attained the global bucking instability mode, with studs moving to the outside of the furnace, due to the effect of load and charred layer. The fire resistance of a double-layered light timber frame wall is higher than a single-layered, and both decrease with the load level. This ability is reduced by 46%, on average for all load levels, when using only one gypsum layer. A new formula is proposed to determine the fire resistance, based on the load level and cladding systems. The fire resistance of the specimens with two layers of gypsum plates decreases faster than the specimens with one layer of gypsum, with respect to the increase of the load level.

Interlayer Slidable Friction Structures on Soft-Substrate

Abstract In this paper, we consider the interlayer slidable friction structures on soft-substrate as the hardcover book-like-laminated-plates with internal friction on the Winkler foundation. For a quasi-static problem, a detailed analysis of the bending response and energy dissipation is carried out for a three-point-supported layered plate on the Winker foundation. Our numerical investigations show that the hardcover, friction, and substrate have a great influence on bending response, and in particular, the friction can cause a considerable amount of energy dissipation within per loading–unloading cycle. The study is not only to predict the mechanical interactions behavior in-between of geometry, friction, elasticity, and substrate but also as a representative case to help finding some clue on the universal behaviors of interlayer slidable friction structures on soft-substrate.

Fatigue performance and optimal design of corrugated steel–concrete composite bridge deck

Orthotropic steel bridge deck (OSD) has been widely used in long and medium span bridges. However, traditional OSD with U-ribs is prone to fatigue cracking at the deck-to-rib welded joint. Corrugated steel–concrete composite bridge deck (CSCCBD) composed of corrugated steel plate, concrete layer and perforated plate shear connectors was proposed recently to improve the fatigue performance of the bridge deck. In this paper, comparing of the fatigue performance of OSD and CSCCBD was conducted through finite element (FE) analysis. The results showed that the stress amplitude of deck-to-rib welded joint of CSCCBD was reduced by more than 90 % compared with OSD. The fatigue problem of deck-to-rib welded joints can be solved fundamentally. It is further studied that distribution of fatigue vulnerability details of CSCCBD. The most unfavorable fatigue vulnerability details are located around the diaphragm-to-rib weld. The fatigue life of CSCCBD was evaluated based on the linear cumulative damage theory. Consequently, the effect of diaphragm cut-out on the fatigue performance of CSCCBD was studied. It was found that the diaphragm without cut-out can effectively reduce the stress amplitude caused by vehicles, and increase the earliest fatigue cracking life of details around the diaphragm-to-rib weld from 2.16 years to 43.4 years compared with OSD. Finally, the section form of CSCCBD without cut-out was optimized by response surface method (RSM). It was proved that RSM was adequate for the optimization design of CSCCBD.

Tunable broadband absorber based on a layered resonant structure with a Dirac semimetal.

With the development of science and technology, intermediate infrared technology has gained more and more attention in recent years. In the research described in this paper, a tunable broadband absorber based on a Dirac semimetal with a layered resonant structure was designed, which could achieve high absorption (more than 0.9) of about 8.7 THz in the frequency range of 18-28 THz. It was confirmed that the high absorption of the absorber comes from the strong resonance absorption between the layers, and the resonance of the localised surface plasmon. The absorber has a gold substrate, which is composed of three layers of Dirac semimetal and three layers of optical crystal plates. In addition, the resonance frequency of the absorber can be changed by adjusting the Fermi energy of the Dirac semimetal. The absorber also shows excellent characteristics such as tunability, absorption stability at different polarisation waves and incident angles, and has a high application value for use in radar countermeasures, biotechnology and other fields.

Comparative Evaluation of the Antimicrobial Activity of NeoPutty MTA and Modified NeoPutty MTA: An In Vitro Study.

Mineral trioxide aggregate (MTA) is a relatively new versatile dental material. MTA has many advantages as well as disadvantages. To reduce most of the drawbacks of MTA, a premixed bioceramic MTA, NeoPutty MTA, was introduced in 2020. In this study, we assessed the antimicrobial activity of the newer MTA, NeoPutty MTA. We modified NeoPutty MTA and compared both against Enterococcus faecalis, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. Using the agar diffusion method, NeoPutty MTA was tested for antibacterial activity against the above-mentioned microorganisms. A base layer of Petri plates was done using Muller-Hinton agar for S. aureus, E. coli, and P. aeruginosa and brain heart infusion agar for E. faecalis. A total of 32 plates were employed; the plates were divided randomly into four test groups having eight plates each, so microorganisms were tested eight times. Three cavities were made in agar and filled with freshly mixed materials after 24 h. A pour plate seeded the microorganisms. The plates were pre-incubated for 2 h at room temperature and incubated at 37°C for 24 h. An independent observer measured the inhibition zone diameters. NeoPutty MTA, when tested alone, did not show much antibacterial activity against E. faecalis, S. aureus, and E. coli but had significant antimicrobial activity against P. aeruginosa when used at different concentrations. Modified NeoPutty (NeoPutty with antibiotics added individually) showed significant antibacterial activity against these microorganisms, as seen by the zone of inhibition of these bacteria. Modified NeoPutty with antibiotics has a better antimicrobial effect than NeoPutty MTA.

Preliminary study on defect detection for sandwich composites using Impact-Echo method

The sandwich composites in this study are laminated structures with two outer thin glass fiber reinforced panels and one or more thick lightweight foam panels as the core material. Such sandwich composites are often used in wind turbine blade. The Impact-Echo method using a microphone as a receiver was used to test the sandwich composite panel specimens. The signals were analysed in the frequency domain and normalized by the Rayleigh wave amplitude. Preliminary results show that thicker plates generally have a lower maximum peak frequency (MPF) for specimens without defects, but MPFs are more unstable due to the higher number of layers of the inner foam plate. Internal defects generated by excavating the core material, with lateral dimensions as small as 20 mm, can be identified from lower MPF and higher maximum peak amplitude in the normalized amplitude spectrum.